Introduction to Nondestructive Testing A Training Guide (1)

HIGH-PERFORMANCE THERMAL IMAGER 431

Figure 10.8 ThermoView Ti30 thermal imager. Courtesy of Raytek Corporation.

• Multilanguage training materials (CDROM)
• Carrying pouch
• Quick Reference Card

10.13.1 Predictive Maintenance Program

The goal of both preventive and predictive maintenance (PPM) programs is
to minimize repair and labor costs, reduce parts inventory, determine product
variation, and minimize production losses. The ThermoView Ti30 thermal
imager displays clear, clean thermal images while automatically recording
radiometric readings for establishing complete maintenance records. The
built-in laser functions as a sighting air to help pinpoint target details. A cross-
hatched indication at the center of the image display is used to locate and
identify high-temperature spots for recording purposes. The captured radio-
metric readings and related thermal images shown on the LCD screen can be
used for future quantitative or qualitative reporting.

For record purposes, unique names and locations are assigned to equipment
when making the initial inspection. Thermal images and data are then down-
loaded using InsideIR software to establish an initial equipment database and

432 THERMAL/INFRARED TESTING METHOD

Figure 10.9 Rear view of ThermoView Ti30 thermal imager showing display area.
Courtesy of Raytek Corporation.

inspection report. Operating temperatures can be compared to maximum
recommended operating temperatures if known. Subsequent thermal imaging
records can then be downloaded for comparison with previous records and
established guidelines. When maximum operating temperatures are exceeded,
corrective action can be taken.
10.13.2 Specifications
10.13.2.1 Thermal

Measurement range: 0 to 250°C (32 to 482°F)
Accuracy: ±2% or ±2°C, whichever is greater at calibration geometry and

25°C
Repeatability: ±1% or ±1°C, whichever is greater
Noise equivalent temperature difference (NETD): 250 mK
Temperature indication resolution: 0.1 (°F or °C)
Optical/IR
Spectral range: 7 to 14 microns

HIGH-PERFORMANCE RADIOMETRIC IR SYSTEMS 433

Target sighting: single laser dot (meets IEC Class 2 and FDA Class II
requirements)

Optical resolution: 90 : 1
Minimum diameter of measurement spot: 7 mm (0.27≤) at 60 cm (24≤)
Image frame rate: 20 Hz
Field of view (FOV): 17° horizontal ¥ 12.8° vertical
Instantaneous field of view (IFOV): 1.9 mrad

10.13.2.2 Controls
Focus: focusable from 61cm (24≤) to infinity
Temperature scale: °C or °F—selectable
Palettes: gray, ironbow, or rainbow—selectable
Measurement modes: automatic, semiautomatic, or manual—selectable
Laser on/off, gain, and level controls: same as above
LCD backlight: bright, dim, or off—selectable

10.13.2.3 Optional Features
Emissivity, adjustable: 0.10 to 1.00 in 0.01 steps (contact Raytek for details)
Liquid crystal display: thin film transistor (TFT) technology—optimized for
indoor and outdoor use
Reflected background temperature: -50 to 460°C (58 to 860°F)
Ambient operating temperature: 0 to 50°C (32 to 122°F)
Relative humidity: 10 to 90% noncondensing
Storage temperature: -25 to 70°C (-13 to 158°F) (without batteries)
Stage capacity: 100 images
Laser on, low-battery, palette, and measurement mode icons: available
Thermal analysis software: InsideIR (included)
PC software operating systems: Microsoft®, Windows® 98/2000/XP

10.13.2.4 Other
Weight (including batteries): 1 kg (2.2 lb)

10.14 HIGH-PERFORMANCE RADIOMETRIC IR SYSTEMS

10.14.1 Introduction

High-performance, real-time digital thermal video imaging systems are being
applied in new applications almost daily. With the proper lens, applications
range from microscopic to telescopic in nature. Typical applications include
circuit design and testing, microcircuit analysis, arterial restriction research,

434 THERMAL/INFRARED TESTING METHOD

engine design and development, detection of minute thermal changes, gas
detection, ignition process development, HVAC control analysis and record-
ing of rapidly changing thermal events, nondestructive testing (NDT) of
composites and other advanced aerospace materials, and numerous military
applications.

10.14.2 Applications

Examples of NDT using such powerful and sensitive InSb (indium anti-
monide) cooled midwave IR detection as embodied in the TVS-8500 are seen
in aerospace applications ranging from imaging subsurface delamination of
cracks in multilayer aerospace composites to detecting disbonded or corroded
rivets along an airplane skin.

Some automotive applications are seen in developing more effective safety
systems such as the thermal pattern on an air bag after inflation, or the extreme
temperature variations across the surface of a brake rotor after multiple panic-
stop testing.

In the process and manufacturing industries, applications include monitor-
ing multicavity injection-molded temperature differences due to plugged
cooling channels and imaging of bonded surface junctions for consistency.
Thermal imaging can also determine the existence of excess moisture created
in a process, which is especially useful when out-of-control processes result in
excessive final drying operations and thousands of dollars being wasted.

Note: In a paper mill process, the first section or wet end of the process is
pressed out by the second section rollers. If enough water is not pressed out
in the roller section, then thousands of dollars in excess energy are wasted in
the drying process to counteract the excess moisture left going into the dryers
at the third section of the process.

Finally, in the research-and-development areas, the system provides
unequalled performance when it comes to designing more effective cooling
for laptop computers, comparing product design performance during envi-
ronmental testing, and noncontacting thermal evaluation of component items
within the whole design.

With regard to arterial research, the system is so sensitive that a thermal
image of a bare arm is able to differentiate the blood coming from the heart
via arteries (warmer) versus the blood returning to the heart via veins (cooler).
The high-performance CMC Electronics Cincinnati TVS-8500 can even see
changes in individual sweat pore temperature of the fingertips as they cool the
human body by convection.

10.14.3 Theory of Operation

The heart of CMC Electronics Cincinnati’s Model TVS-8500 thermal video
system (TVS), Figure 10.10, starts with the closed-system Sterling-cycle cooled

HIGH-PERFORMANCE RADIOMETRIC IR SYSTEMS 435

Figure 10.10 CMC Electronics TVS-8500 thermal video system. Courtesy of CMC
Electronics.

indium antimonide (InSb) photodiode focal plane array (FPA). The photodi-
ode detector provides over 60,000 noncontacting individual IR detectors or
pixels on a single silicon wafer, which corresponds to individual pixels viewed
on the integral video screen or external display. Add one of four top-quality
lenses to this thermal imaging system, and you have a combination that’s hard
to beat. Finally, user-friendly PE Professional thermographic analysis and
reporting software tops off a great system.

The InSb focal plane array provides the highest level of performance avail-
able today in the midwave infrared (MWIR) range of 3–5 micrometers (mm).
CMC Electronics Cincinnati utilizes a patented process focal plane array con-
struction method that yields superior discrimination and far less cross talk than
competitive systems. Photons from the object being inspected are detected by
the individual photocells on the focal plane array to provide real-time full-
view thermal images up to 120 hertz. The performance of the focal plane array
drops off rapidly if the cryogenic temperature is not properly maintained.
While liquid nitrogen is the most cost-effective way to cool these detectors, it
is not practical for small, highly portable equipment.

The Sterling-cycle cooling engine provides a practical, if somewhat expen-
sive, alternative. The Sterling cooler keeps the detector at 77°K; the tempera-
ture of liquid helium, where the semiconductor array is nonconductive. At this
temperature, each photon that strikes the detector produces a measurable
output. Costs are expected to come down as applications and sales increase.
As listed below, the minimum temperature resolution for an individual pho-
todiode is 0.020°C taken at 30°C, NEDT blackbody. However, an absolute
change of this order of magnitude cannot be detected due to the unknown

436 THERMAL/INFRARED TESTING METHOD

variance in emissivity of the object being inspected. Therefore, the accuracy
range of ±2°C or ±2%, whichever is greater, defines the accuracy of the
system.

As inspection surface temperature increases, the number of photons strik-
ing each detector increases, producing digital counts. As temperature goes up,
digital counts increase. For each of the six available temperature ranges up to
900°C (2000°C option), 256 colors are possible for each detector, resulting in
a full-view display of more than 16,000 levels (14 bits) of color possibilities.

Additional flexibility of the system is obtained with four precise lenses as
described in Figure 10.11. The lenses are identified as the standard lens, wide-
angle lens, closeup lens, and microscope lens. The focus distance for these focus
lenses are 30 cm to infinity, 30 cm to infinity, approximately 77 mm, and approx-
imately 27 mm, respectively. The field of view is 14.6°H ¥ 13.5°V, 44.0°H ¥
40.5°V, 25.6 mm (H) ¥ 23.6 mm (V), and 2.56 mm (H) ¥ 2.36 mm (V), respec-
tively. The TVS-8500 camera recognizes the lens being used and provides auto-
matic calibration for the lenses via built-in look-up tables. When pointed at an
object to be inspected, the camera automatically can be set to select the best
temperature range for the detector based on the range of temperatures within
the FOV. Figure 10.12, not to scale, shows the FOV as a function of distance
for the standard lens. The individual photocell spatial resolution or pixel IFOV
within the FOV is represented by the square in the center. Therefore, at the
distance of 1.0 meter, the camera images an area 25.4 cm wide by 24 cm high.
Each photocell in the focal plane array averages the temperatures contained
within the IFOV, in this case a 1 mm square.

10.14.4 Operating Technique

This high-tech thermal imaging camera is about as automatic as it can be,
thereby placing the burden of satisfactory operation on the nondestructive
inspection (NDI) technician. It would be just as foolish to point the camera at
a stationary airplane reflecting bright sunlight as it would be to point the
camera at the sun and saturate the detector. Simple radiant heat from the
ground or concrete on hot days may cause irrelevant moving bands of color
and heat. The NDI technician must place the camera in the correct position,
at the correct distance, to observe the expected defects of interest.

In most cases, the best procedure is to place the imager at a distance where
the maximum desired IFOV size is small enough to detect the anticipated size
of the defect. The defect could be a subsurface delamination within a com-
posite; a crack under the surface finish of a fiberglass material, or voids within
injection molded parts. Different lenses are available to achieve imaging of
the object so that it fills the field of view and still achieves satisfactory imaging
with good spatial resolution. The simple heating of the surface by a halogen
lamp for a short period, or warm air for a longer period, will produce a thermal
differential where such cracks, bubbles, or voids within the subsurface will
appear.

HIGH-PERFORMANCE RADIOMETRIC IR SYSTEMS

Figure 10.11 Lens options for CMC TVS-8500 thermal video system. Courtesy of CMC Electronics.

437

438 THERMAL/INFRARED TESTING METHOD

Figure 10.12 Field of view vs. distance with TVL-8530A standard lens. Courtesy of
CMC Electronics Cincinnati.

10.14.5 Typical Specifications
The following list itemizes the TVS-8500 system specifications:

• Detector: InSb focal plane array (FPA), 256 ¥ 256 pixels.
• Detector cooling method: Sterling-cycle cooling engine.
• Temperature measurement range: -40°C to 900°C (2000°C optional).
• Minimum temperature resolution: 0.020°C or less (30°C blackbody).
• Accuracy: ±2°C or ±2%, whichever is greater. Greatest variance is know-

ing the object’s emissivity.
• Scanning speed: up to 1/120 fps image acquisition.
• Measuring wavelength: 3.4 to 4.1 mm and 4.5 mm to 5.1 mm (broad-band

2.5 mm to 5.0 mm available first Q 2003).
• FOV: 14.6 (H) ¥ 13.5 (V) when used with standard lens.
• Measured distance: 30 cm to infinity.
• A/D conversion: 14 bit.
• Correction function: emissivity/reflectivity correction, auto-room-

temperature correction.
• Display: 5-inch-high gain color matrix liquid crystal display (LCD).
• Functions: Multipoint temperature measurement, memory, zoom, and

isotherm. Highest temperature display, display color selection, averaging,
a scope. Auto/manual temperature range sensing and switching.
• Fourteen-bit thermographic recording/play back: real-time recording at
120, 30, 10, 5, 2, or 1 frame per second. Compact flash card 100 frames
using the supplied 16 MB card, 300 frames with a 48 MB card.

MIKRON INSTRUMENT COMPANY, INC. 439

• Image output: National Television System Committee (NTSC), phase
alternating line (PAL).

• External interface: RS-232C, specialized Institute of Electrical and Elec-
tronics Engineers (IEEE) 1394 Firewire® PC interface, remote trigger and
synch terminals via 4 integral strip terminals with TTL inputs.

• Input power: 120 VAC/240 VAC, 50/60 Hz.

• Dimensions: 200 mm wide ¥ 250 mm deep ¥ 120 mm high (excluding
protrusions).

• Weight: approximately 5.0 kg.

10.15 MIKRON INSTRUMENT COMPANY, INC.

The Mikron Instrument Company manufactures a complete line of IR imaging
and temperature-measuring instruments. Included in their product line are
lightweight, hand-held IR and VIS/IR cameras, fixed-mount IR thermal
imagers, a single spot radiometric IR camera, High-Speed IR-line cameras, and
software for managing images, analyzing images, and generating reports. The
Mikron TJ-200 IR Man is a data storage and display system capable of pro-
ducing a matrix of temperature distribution with 64 distinct areas superim-
posed on a visible image. The company makes blackbody radiation calibration
sources covering the range from -20°C to 3000°C, traceable to NIST.

One unique product is the SpyGlass lens for the MikroScan 7200/7515
IR cameras. Figure 10.13 shows the camera/lens system. The SpyGlass lens
permits thermal inspection of electrical switchgear without opening the
enclosure door or disconnecting circuits. The camera can view the field of
interest through a 5/8-in.-diameter hole in the cabinet. Other products include
advanced portable IR thermometers with through-the-lens sighting, an IR
thermometer with precision laser sighting, and process control instruments

Figure 10.13 Mikron IR camera with SpyGlass lens. Courtesy of Mikron Instruments.

440 THERMAL/INFRARED TESTING METHOD

such as IR temperature sensors with TC or linear voltage output and IR tem-
perature transmitters with 2-wire linear 4–20-mA outputs. One model of this
transmitter has a laser sighting for pinpoint aiming accuracy.

Process instruments include a fiber-optic IR temperature transmitter for
inaccessible or severe environmental applications, a 2-color Infraducer with
4–20-mA linear output that is independent of emissivity and unaffected by
dust and other contaminants. Other process control instruments include a
high-accuracy, high-resolution IR thermometer with exceptional software
capabilities, miniature IR temperature sensors, and an IR thermocouple. Addi-
tional process control instruments are a smart IR fiber-optic temperature
transmitter with wide temperature span and focusing optics, and a multi-
channel fiber-optic Infraducer with wide temperature range and absolute accu-
racy of 0.2% of reading.

10.16 MIKRON 7200V THERMAL IMAGER AND
VISIBLE LIGHT CAMERA

10.16.1 General Features

This camera is designed for comfortable one-hand point-and-shoot operation
and combines on-board digital voice recording with 14-bit thermal and digital
visual imaging. The camera is housed in a self-contained splash-proof metal
case and is battery operated. Images and other data can be stored on PCMCIA
cards. Images can also be viewed in real-time via the video output or through
an optional built-in IEEE 1394 Firewire®. Figure 10.14 shows the MikroScan
7200V thermal imager/visible light camera.

10.16.2 Technical Data

10.16.2.1 Performance
• Temperature ranges: -40 to 120°C, 0°C to 500°C, and 200 to 2000°C
• Measurement accuracy: ±2% or 2°C of reading
• Field of view: 29°(H) ¥ 22°(V)
• Focus range: 50 cm to infinity
• IFOV/spatial resolution: 320 ¥ 240 uncooled focal plane array (UFPA)
vanadium oxide (VOX) microbolometer
• Spectral band: 8.0 to 14.0 mm
• Atmospheric transmission correction: input correction by outside tem-
perature, humidity, and measuring distance
• Emissivity setting: automatic based on operator input
• Alarm: upper or lower
• Image freeze: provided

MIKRON 7200V THERMAL IMAGER AND VISIBLE LIGHT CAMERA 441

Figure 10.14 MicroScan 7200V thermal imager/visible light camera. Courtesy of
Mikron Instruments.

10.16.2.2 Presentation
• File format: 14 bit
• Digital visual recording: on-board
• Digital voice recording: on-board
• B&W/color: several palettes available
• Automatic gain control (AGC): automatic level, gain and focus
• Viewfinder: standard (color LCD optional)
• Video output: NTSC/PAL, S-video
• Image zoom: 2 : 1 (4 : 1 with spatial filtering)

10.16.2.3 Measurement
• NUC: flag correction by specifying the interval time. (Manual/auto selec-
table. Interval time setting available at auto.)
• DT Display: display temperature difference between points A and B
• Region-of-interest setting: display max/min temperature in operator-
defined box
• Peak temperature hold: keep max/min temperature in an operator-
defined box

442 THERMAL/INFRARED TESTING METHOD

• Isotherm: variable bandwidth. Multicolor for regions available
• Temperature span: automatic
• Temperature range setting: auto and manual
• Multispot temperature measurement: 10-point max with EMISS setting

10.16.2.4 Interface
• Communication: RS-232/C (computer control available)
• Memory card: provided—PCMCIA 16 mb
• Remote control operation: GPIB, RS-232C or LCD remote panel, IEEE
1394 Firewall® interface (optional)

Note: The MikroScan 7302 fixed-installation thermal imager and MikroScan
7515 single spot IR camera with thermal imaging software have image update
rates of 30 frames/sec or 60 frames/sec.

10.17 HIGH-SPEED IR LINE CAMERAS

10.17.1 General Information—MikroLine Series 2128

These cameras are housed in rugged industrial housings and have air purges
for lenses and water-cooling. They can be operated independently or with a
PC and feature fiber-optic data transmission. There are no optomechanical
scanners. These cameras feature uncooled IR linear arrays and 16-bit A/D con-
version. There are 128 data points per line and a measuring rate of 128 lines
per second. These units have a large dynamic range and provide for triggered
inputs and alarmed outputs. Data recording and application-specific hardware
and software are provided. There are seven models available in this series,
which are well suited for fast noncontacting temperature measurements of
production line processes.

10.17.2 High-Speed Temperature Measurement of Tires

The MikroLine 2250 is specially designed for the high-speed temperature mea-
surement of tires. The camera has a rugged industrial housing, air purge for its
lens system, and no operating elements. Data transfer is by fiber optics. The
unit provides parallel measurement of 160 measuring points, using lead
selenide (PbSe) sensors, and a measuring frequency of 18,000 lines/s.

The triggered measurement provides exact geometrical assignment of the
individual measuring points and efficient online software controls thresholds
and processes. Rapid temperature changes can be accumulated as a film,
providing a 360° temperature image of a tire traveling at 100 mph. Figure
10.15 shows a line diagram of the temperature measurement and recording
system.

HIGH-SPEED IR LINE CAMERAS 443

Figure 10.15 MicroLine 2250 camera for tire temperature measurements. Courtesy
of Mikron Instruments.

10.17.2.1 Camera Specifications
• Spectral range: 3 to 5 mm
• Temperature range: 50 to 180°C
• Sensor: PbSe-160 element sensor with CMOS multiplexer
• Opening angle: 30° ¥ 0.13°
• Measuring distance: 10 cm to infinity
• Spatial resolution: 3.3 mrad (50% modulation)

444 THERMAL/INFRARED TESTING METHOD

• Temperature resolution: 0.5 K at 50°C
• Temperature accuracy: ±2 K ±2% from measurement (°C)
• Line scan frequency: 2000 Hz up to 18 kHz
• Response time: approximately 1 second
• Warmup time: <30 minutes
• Interface: fiber-optic/PCI-PC card
• Camera housing: protective housing IP-65
• Operating temperature-camera: 0 to 40°C
• Storage temperature: -20 to 70°C

10.18 OTHER THERMAL TESTING METHODS

10.18.1 Fourier Transform Infrared Spectrometer

Design Features. The Shimadzu Prestige-21 Fourier transform infrared (FTIR)
spectrophotometer features high sensitivity and accuracy with improved
operability and expandability. This highly optimized instrument features a
high-throughput optical system with gold-coated mirrors and temperature
stabilized deuterated L-alamine triglycine sulfate (DLATGS) detector that
results in a signal-to-noise (S/N) ratio of 40,000 to 1. The instrument can
operate in the near-IR, mid-IR, and far-IR ranges with simple exchanges of
the light source, beam splitter, and detector.

Other features include a patented precision control and stabilization of
the optical bench that ensures reliable, reproducible results. Powerful IR
Solution Software also provides a Windows®-based 32-bit control to enable
operation to be performed quickly and easily using dedicated analysis
screens.

Key Specifications. The Shimadzu Prestige 21 Fourier transform infrared
spectrophotometer is shown in Figure 10.16. An IR spectrum is seen on the
computer display. Some key specifications are shown below:

• Interferometer—30° incident angle Michelson interferometer, built-in
advanced dynamic alignment (ADA) function, sealed with autodryer

• Optical system—single-beam optics
• Beam splitter—Ge-coated KBr (moisture-proof) for mid-IR (standard),

Ge coated Csl (moisture-proof) for mid/far-IR (optional), Si coated CaF2
for near-IR (optional)
• Light source—air-cooled high-intensity ceramic light source for mid/far-
IR (standard), tungsten-iodine lamp for near-IR (optional)
• Detector—temperature-controlled DLATGS detector for mid/far-IR
(standard), liquid-nitrogen-cooled mercury cadmium telluride (MCT)
detector for mid-IR (optional), InGaAs detector for near-IR (optional)

OTHER THERMAL TESTING METHODS 445

Figure 10.16 Modern IR spectrophotometer. Courtesy of Shimadzu Scientific Instru-
ments, Inc.

• S/N—above 40,000 : 1 (4 cm-1 resolution, 1 minute accumulation, around
2100 cm-1, P-P)

• Wave number range—7800 to 350 cm-1 for near- and far-IR ranges
(standard)

• Resolution—0.5, 1, 2, 4, 8, 16 cm-1
• Mirror speed—3 steps: 2.8 mm/s, 5 mm/s, 9 mm/s
• Data processing functions—arithmetic calculation, peakpick, spectrum

subtraction, smoothing, baseline correction, data cut, data correction,
normalization, Kubelka-Munk conversion, Kramers-Kronig analysis,
ATR correction, Fourier transform, derivatives, transmittance/absorbance
conversion, peak area integration, peak ratio calculation, emission cor-
rection, deconvolution, quantitation, multilinear regression quantitation,
spectrum search, JCAMP conversion, ASCII conversion, logarithmic con-
version, wavelength/wave number conversion, shift along X-axis, and
optional programs
• Validation program—provided as standard (validation program con-
forming to the Japanese Pharmacopoeia/European Pharmacopoeia/
ASTM), optional items for the Japanese/European Pharmacopoeia vali-
dation program
• Operating temperature—15 to 30°C

Note: JCAMP conversion refers to the JCAMP standard of spectroscopic data
transfer. Existing JCAMP standards represent the first nonbinary approach,
which is vendor independent (not owned by anyone), features printable char-

446 THERMAL/INFRARED TESTING METHOD
acters only, and has reasonable compression rates. It is extendable and its open
definitions provide for future improvements.

Horizontal ATR Operation. Thin film sampling techniques frequently use
single reflection or attenuated total reflection (ATR) of the IR signal. With this
technique, the sample can be in direct contact with a diamond prism bonded
into a tungsten carbide support disc or germanium prism bonded into stain-
less-steel support disc version of a single reflection top plate. The sample
is held in place with a quick-release bridge and self-leveling pressure anvil
arrangement having a sapphire insert. The single reflection horizontal ATR
system, shown in Figure 10.17, is well suited for the measurement of corrosive
solutions, strongly absorbing polymers and rubbers, powders, thin films on
semiconductors, macro and micro sample volumes, and forensic science
samples, many of which are difficult to handle in a vertical cell.

Schematic Figure 10.18 shows how the FTIR beam is reflected by mirrors
and passes through a beam-condensing lens into the ATR element fixed in the
top plate where the sample is held in place. Beam-condensing optics is ZnSe
or KRS-5, depending on application. The signal is reflected back from the
sample through another condensing lens, mirrors, then on to the input of the
FTIR spectrometer. Total reflection takes advantage of the refractive index of

Figure 10.17 Golden Gate single reflection diamond ATR System. Courtesy of Specac
Limited.

OTHER THERMAL TESTING METHODS 447

Figure 10.18 Internal view of Golden Gate single reflection ATR system. Courtesy of
Specac Limited.

the prism to assure that all light entering the prism is reflected back, thereby
providing 100% reflectance at the prism/sample surface. The ratio of total light
reflected, when there is and is not a sample, provides a transmission-like ATR
spectrum. With the ATR cell, flat samples can be placed on or painted on the
top surface of the prism for measurement. Cameras may also be used with
some ATR systems.

10.18.1.1 DLATGS Pyroelectric Detectors The main features of deuter-
ated l-alamine triglycine sulfate detectors include high detectivity, from 1 Hz
to 4 kHz, and wide spectral range, from 0.1 to over 1000 microns. Applications
for these detectors include gas analysis, radiometric measurements, high-speed
spectroscopy (FTIR), laser modulation studies, and interferometry.

Window materials typically used with these detectors include:

• Sapphire (Al2O3)—0.15 to 6.0 microns
• Calcium fluoride, polycrystalline (CaF2)—0.2 to 11.0 microns
• Coated germanium (Ge)—1.8 to 17.0 microns
• Potassium bromide (KBr)—0.25 to 25 microns
• Thallium bromide iodide (KRS-5)—0.55 to 40 microns
• Cesium iodide (CsI)—0.25 to 50 microns

10.18.1.2 FTIR Evaluation of Hard Disk Fluororesin Coating A fluo-
roresin coating is applied to the surfaces of computer hard disks as a lubri-
cant. Reflectance absorbance spectroscopy (RAS) is an effective means of

448 THERMAL/INFRARED TESTING METHOD

measuring the thickness of fluororesin film coatings. A reflection IR device
with a large angle of incidence is used to measure thin films on a metal plate.
An RAS device with an angle of incidence of at least 70° is able to measure
film thickness of 1.0 mm or less. Thinner films several nanometers thick can
be measured using a combination RAS device with polarizer to measure the
polarized component only.

A combination RAS device with polarizer was used to measure film coating
thickness of 11.8, 25.4, 41.0, and 48.8 Å using the measurement conditions
listed below:

• Resolution—8.0 cm-1
• Accumulation—300 times
• Detector—DLATGS
• Mode—reflection

At a peak area near 1300 cm-1, a linear calibration curve was obtained for the
wavelength range of 1200 to 1350 cm-1 for a film coating thickness range of

10.0 to 50.0 Å.

10.18.1.3 Measurement of Film Thickness on a Silicon Wafer Film thick-
ness can be calculated from the interference fringe spectrum obtained by
FTIR using Eq. 10.9:

d = Dm 2÷(n2 - sin2 q)◊1 (1 v1 - 1 v2 ) (10.9)

where n = the refractive index
q = the angle of incidence to the sample
Dm = the number of peaks or troughs in the calculated wavenumber region
v1 and v2 = are the maximum and minimum values of the wavenumber region

FTIR software calculates the equation in the quantitative analysis mode, dis-
plays the IR spectrum, and identifies wavelength range numbers with a verti-
cal cursor. This FTIR nondestructive evaluation method provides a rapid and
simple way to evaluate semiconductor materials.

10.18.2 Advanced Mercury Analyzer

10.18.2.1 Introduction While not a nondestructive test in the traditional
sense of the word, LECO’s AMA254 advanced mercury analyzer is a unique
identification of materials (IM) thermal testing method (TTM). What makes it
unique is its high-speed, high-accuracy determination of mercury in nominal
sample sizes of 100 mg for solids and 100 ml for liquids without sample pre-
treatment for solids or preconcentration for liquids.

OTHER THERMAL TESTING METHODS 449

LECO’s AMA254 advanced mercury analyzer (Figure 10.19) complies with
EPA Method 7343 dealing with the measurement of mercury in solids and
solutions by thermal decomposition, amalgamation, and atomic absorption
spectrometry. It also complies with recently approved ASTM Method D-6722
as it pertains to efficient, automatic determination of total mercury in coal and
combustion residues. Because it has been estimated that 60% of the total
mercury deposited in the U.S. environment comes from airborne emissions,
the EPA has proposed that coal-fired power plant emissions of mercury be
released by 2003 and adopted as final rules by 2004. When fully implemented,
the new regulations should reduce airborne mercury emissions by 50%
compared with 1990. In the future, even more restrictive regulations are
anticipated.

Mercury from power plants eventually makes its way into both fresh- and
saltwater systems where it is converted by biological processes into methyl
mercury. This highly toxic compound is readily absorbed by fish and eventu-
ally by human tissue when the fish are eaten. People who eat moderate or
large amounts of fish and women of childbearing age are most at risk because
mercury ingestion can cause both neurological and developmental damage.

The concentration of mercury in coal is very low, in the order of 0.1 part
per million by weight (ppmw), but mercury is extremely volatile when coal is
combusted. And after years of combusting millions of tons of coal, dangerous
levels of mercury compounds have accumulated in some fish populations in
the United States and elsewhere. Health officials frequently quarantine cont-
aminated bodies of water, but the problem needs to be solved, not contained.

10.18.2.2 Theory of Operation Designed with a front-end combustion
tube that is ideal for the decomposition of difficult matrices like coal, com-
bustion residues, soils, and fish, the instrument’s operation may be separated
into three distinct phases for a given analysis.

Figure 10.19 LECO AMA254 advance mercury analyzer. Courtesy of LECO Corp.

450 THERMAL/INFRARED TESTING METHOD

The first phase is the decomposition phase. During this phase, a sample con-
tainer with a nominal amount of material is placed inside a prepacked com-
bustion tube. The combustion tube is heated to 750°C through an external coil
that provides the necessary decomposition of the sample into a gaseous form.
The evolved gases are then transported via oxygen carrier gas to the other side
of the combustion tube. This portion of the tube, which is prepacked with spe-
cific catalytic compounds represents the area in the instrument where all inter-
fering impurities, such as ash, moisture, halogens, and minerals, are removed
from the evolved gases.

Following decomposition, the cleaned, evolved gas is transported to the
amalgamator for the collection phase of the system. The amalgamator, a small
glass tube containing gold-plated ceramics, collects all the mercury in the
vapor. With a strong affinity for mercury and a significantly lower tempera-
ture than the decomposition phase, the amalgamator traps all of the mercury
for subsequent detection. When all the mercury has been collected from the
evolved gases, the amalgamator is heated to 900°C, releasing the mercury
vapor to the detection system.

The released mercury is transported to the final phase of analysis, the detec-
tion phase. During the detection phase, all vapor passes through two sections
of an apparatus known as a curvette. The curvette is positioned in the path
length of a standard atomic absorption spectrometer. This spectrometer uses
an element-specific lamp that emits light at a wavelength of 253.7 nm, and a
silicon UV diode detector for mercury quantification. The dual-path length of
the curvette expands the dynamic range of the mercury from the subpart per
billion (ppb) levels to the upper part per million (ppm) levels.

The advanced mercury analyzer houses an autoloader, which is a rotating
carousel that holds up to 45 nickel-sample boats. The sample boats are auto-
matically inserted in the combustion/catalyst tube. Each nickel sample boat
can contain up to 500 milligrams (mg) of various samples.

10.18.2.3 Software Highly effective Windows-based operating software,
known as Quicksilver, maximizes mercury analysis results, while streamlining
the process. This user-friendly software provides easy-to-use icons, spreadsheet
formats, and on-board manuals for improved user–machine interaction. The
instrument and its standard were compared to cold-vapor atomic absorption
spectroscopy (CVAAS). Results obtained with the advanced mercury analyzer
were more accurate and precise than those obtained with the CVAAS. In addi-
tion to the improved performance, the AMA254 reduced total analysis time
to less than six minutes.

10.18.3 Identification of Materials

10.18.3.1 Thermoelectric Alloy Sorting Introduction. C. S. Taylor and J. S.
Edwards appear to be the first Americans to report information on thermo-
electric testing of aluminum-manganese and other alloys in the Transactions

OTHER THERMAL TESTING METHODS 451

of the American Electrochemical Society in 1930. Thirty years later, E. H.
Greenberg developed and patented an improved instrument operating on the
Seebeck effect.

Thermoelectric alloy sorting using the Seebeck effect has been popular for
a long time, probably due to its low cost-to-benefit ratio. Applications for these
systems are somewhat limited, but in applications where they work, they work
very well. The Industrial Instruments, Inc. thermoelectric alloy sorter, known
as the Identomet G-II, complies with ASTM Standard Practice E977-84.

Alloy sorting is of concern for many industries because improper alloy iden-
tification can result in pipe and equipment failures, plant shutdowns, and pos-
sibly injury or death to personnel. For example, pipe corrosion can be rapidly
accelerated, causing sudden pipe failure and worse when the wrong alloy is
used in the wrong service. Correct identification of materials is of prime impor-
tance in refineries, salvage yards, material storage areas, process areas, and
manufacturing. In some cases, a plant shutdown can cost thousands of dollars
a day.

Theory of Operation. Basically, a thermoelectric sorter consists of a power
supply, sensitive voltmeter, temperature-controlled hot probe, and cold probe
as shown schematically in Figure 10.20. Both the hot probe and cold probe are
combined in one probe assembly. Probe tips can be made of copper, nickel, or
gold, depending on application. Gold has the highest thermal and electrical
conductivity. The difference in thermocouple voltage between the hot and cold
probe junctions is a function of the thermoelectric properties of the alloy,
which vary with alloy composition, but are independent of the size and shape
of the test specimen. Automatic temperature compensation can be provided

Figure 10.20 Thermoelectric alloy sorter. Courtesy of Industrial Instruments, Inc.

452 THERMAL/INFRARED TESTING METHOD
when test specimen temperatures vary. Instrument sensitivity is in the range
of 50 to 100 mV. When utilizing the Seebeck effect, voltage readings may be
positive or negative, depending on alloy composition.

Operation. A photograph of the Identomet G-II is shown in Figure 10.21.
Instrument operation is straightforward as outlined in the following steps:

1. Inspect the probe assembly. The two fine wires brazed to the tip of one
side identify the hot probe, which is the most vulnerable part of the
instrument.

2. An internal heavy-duty 6 V rechargeable battery powers the Identomet.
The power switch is on the left side of the front panel. Turn the instru-
ment on and note the three dots or decimals that appear on the display
with a reading of zero.

Figure 10.21 Identomet G-II instrument. Courtesy of Industrial Instruments, Inc.

OTHER THERMAL TESTING METHODS 453

3. Allow about 2 minutes for probe warmup. When the hot side of the probe
is at operating temperature, the dots on the display will disappear and
the green AT TEMP light on the right side of the display will turn on.

4. Hold the probe handle the same way you would hold a dinner knife, palm
down and index finger extended. Always apply the cold side to the spec-
imen before applying the hot side. Allow the cold tip to make contact
first. Then make contact with the hot tip while keeping contact with the
cold tip. Hold the probe assembly at an angle of about 30 degrees with
the plane of a flat specimen.

5. Watch the display closely. It will go up quickly, settle down, and lock on
a reading. At this point, note the reading, then remove the probe and
allow the probe to reheat before reading the next specimen. The probe
takes longer to recover when samples have high thermal conductivity.

Calibration. The Identomet G-II is calibrated before it leaves the shop, but
recalibration is simple. Remove the top cover by unscrewing four bolts and
locate the slide switch on the left front circuit board. Slide the switch to its
other position. Connect the probe to the instrument and turn the power switch
on. Allow the probe to reach operating temperature. When the AT TEMP light
turns on, turning the trim pot, R9, near the center of the circuit board until
the display reads 404 sets the probe temperature. After the probe tempera-
ture has been calibrated, return the slide switch to its original position and
reinstall the cover.

10.18.3.2 Applications Successful applications include the thermoelectric
sorting of refinery alloys, expensive alloys, electronic industry alloys, and tool
steel saw blade alloys.

Refinery Alloy Comments

• 5 chrome springs out and produces a positive identification reading of
-85 +3 for easy identification.

• Monel also springs out and provides rapid and easy identification.
• Carbon steels usually produce signals less than -51. Therefore, the Iden-

tomet G-II can be used to make sure there are no carbon streaks where
specs call for 2–14 , 5, or 9 chrome.
• With nickel probes signals from 2–14 and 9 chrome can be separated.

Steels that nominally contain 1–14 % chrome may actually contain as little as 1%
chrome and will produce somewhat lower chart readings.

Expensive Alloys. Within certain limitations, alloys such as hastelloy, inconel
800 and 825, monel, and copper-nickel can easily be sorted. Typical Identomet
G-II values are shown in Figure 10.22.

Identification of Saw Blade Materials. Electric jigsaw and circular saw blades
are fabricated by welding a wire of tool steel to a carbon steel base. The assem-

454 THERMAL/INFRARED TESTING METHOD

Figure 10.22 Identification of nickel alloys. Courtesy of Industrial Instruments, Inc.

bly is then notched, formed, and heat-treated to the proper hardness. The
resulting blade has the flexibility and toughness of carbon steel with teeth
having the hardness of tool steel. Figure 10.23 shows the Seebeck voltage chart
for the saw blade application. Other charts for other applications are available
from the manufacturer.

Many types of tool steel are used for different saw blades in large manu-
facturing plants. The welding, notching, and heat-treating operations obliter-
ate alloy identification marks and products can easily get mixed up. Therefore,
a rapid nondestructive method is needed for identification of tool steel teeth.
In seconds, the thermoelectric sorter is able to identify M2, M42, and D6 tool
steels. In this application the thermoelectric sorter is more feasible than most
other methods because it does not depend on the size and shape of the spec-
imen. It is also very cost effective in cases where a relatively small number of
well-defined choices exist.

Note: Consult the manufacturer for additional application data.

10.18.4 Advantages and Disadvantages
10.18.4.1 Advantages

• Instrument operation and calibration is simple. Readings settle down and
lock in as described in the operating section.

• The test is not sensitive to surface size or shape—it can measure fine wires
or large girders.

• Portability and high-speed response—alloy identification can be made in
minutes.

• For known alloys of 4340 and 17-4PH, the instrument reading may be
helpful in determining the degree of heat treatment.

• The alloy composition of thick plating or cladding materials can be
determined.

• The Identomet G-II instrument readily identifies alloys used for saw
blade teeth.

• Diagnostic analysis is fast, predictable, and reproducible.

OTHER THERMAL TESTING METHODS

Figure 10.23 Thermoelectric sorting of saw blades. Courtesy of Industrial Instruments, Inc.

455

456 THERMAL/INFRARED TESTING METHOD

10.18.4.2 Disadvantages
• The probe assembly is somewhat position sensitive.
• The cold side of the probe assembly must be applied to specimen first to
minimize cooling of the hot side.
• One tip of the probe assembly is hot, capable of reaching a maximum
temperature of 450°F.
• The probe assembly should be shielded from air currents, which can limit
its use.
• The test is sensitive to the heat treatment of some alloys as well as alloy
composition.
• Good readings are difficult to obtain on thinly plated alloys.
• The instrument cannot tell the difference between 304 and 316 stainless
steel.

11

ULTRASONIC TESTING

11.1 INTRODUCTION
Modern ultrasonic transducers are used for the nondestructive analysis of
solids, liquids, and gases. Recent improvements include super-high-sensitivity,
high-frequency, high-resolution, high-power, dry coupling, and noncontacting
transducers for a host of applications.

The advantages of ultrasonic testing include:
• It can be used to determine mechanical properties and microstructure.
• It can be used for imaging and microscopy.
• It is portable and cost effective.
• It can be used with all states of matter except plasma and vacuum.
• It is not affected by optical density.
Ultrasonic transducers can be used in the time, attenuation, frequency, and
image domains. Time domain transducers measure the time of flight and the
velocity of longitudinal, shear, and surface waves. Time domain transducers
measure density and thickness, detect and locate defects, and measure elastic
and mechanical properties of materials. These transducers are also used for
interface and dimensional analysis, proximity detection, remote sensing, and
robotics.

Introduction to Nondestructive Testing: A Training Guide, Second Edition, by Paul E. Mix
Copyright © 2005 John Wiley & Sons, Inc.

457

458 ULTRASONIC TESTING

Attenuation domain transducers measure fluctuations of transmitted and
reflected signals at a given frequency and beam size. These transducers are
used for defect characterization and determining surface and internal micro-
structures. They also can be used for interface analysis.

Frequency domain transducers measure the frequency dependence of ultra-
sonic attenuation, thereby providing ultrasonic spectroscopy. These transduc-
ers are especially used for microstructure analysis, grain boundary studies,
determining porosity and surface characterization, and phase analysis.

Image domain transducers measure the time of flight and are used for atten-
uation mapping as function of discrete point analysis by raster C-scanning
or synthetic aperture techniques. These transducers can provide surface and
internal imaging of defects, microstructure, density, velocity, or mechanical
properties. True 2D or 3D imaging can be provided.

11.2 DEFINITION OF ACOUSTIC PARAMETERS
OF A TRANSDUCER

Nominal frequency (F)—nominal operating frequency of the transducer
(usually stamped on housing)

Peak frequency (PF)—the highest frequency response measured from the
frequency spectrum

Bandwidth center frequency (BCF)—the average of the lowest and highest
points at a -6 dB level of the frequency spectrum

Bandwidth (BW)—the difference between the highest and lowest frequen-
cies at the -6 dB level of the frequency spectrum; also % of BCF or of
PF

Pulse width (PW)—the time duration of the time domain envelope that is
20 dB above the rising and decaying cycles of a transducer response

11.3 NONCONTACTING ULTRASONIC TESTING

One of the most significant advances in recent years has been the develop-
ment of noncontacting ultrasonic transducers with perfect air/gas impedance
(Z) matching. Non-Contacting Ultrasound, NCUTM, was made possible by the
development of high-transduction piezoelectric transducers in 1997 (U.S. and
international patents) and the creation of a dedicated noncontacting ultrasonic
analyzer in 1998 to 2003. As a result of this work the Ultran Group formed
Second Wave Systems.

One of the greatest advantages of NCU is its total freedom from touch and
contamination, which is of great importance to many high-tech manufactur-
ing, food, pharmaceutical, and biotechnical industries. NCU provides a cost-
effective alternative to X-ray, g-ray, neutron, infrared, laser, and nuclear
magnetic resonance (NMR) methods in many applications.

NONCONTACTING ULTRASONIC TESTING 459

Conventional ultrasonic testing (UT) methods currently extend well beyond
traditional flaw detection and material thickness measurements into material
characterization and 2D and 3D imaging surface and internal applications
where flaws, composition, homogeneity, structure, texture, and material prop-
erties can also be determined. These applications are of prime importance for:

• Manufacturers of electronic materials and components
• Manufacturers of plastics and composites
• Aircraft and aerospace industries
• Chemical and petrochemical industries
• Food and pharmaceutical industries

For medical diagnosis, UT can replace harmful X-rays for fetus visualiza-
tion, cornea measurement, tissue characterization, imaging of plaque in the
arteries, and gum disease. Other medical uses for UT include measurement of
brain waves, detection of skin and breast cancer, and blood-flow monitoring.
In general, the UT method is also portable and cost effective. See Figure 11.1.

The primary limitations of conventional UT (200 kHz to 5 MHz) include its
high attenuation in air and its need for a physical coupling agent such as water

Figure 11.1 Problems that need to be overcome for Noncontacting ultrasound.
Courtesy of Ultran Labs.

460 ULTRASONIC TESTING

or grease between the transducer and test medium. Because of these limita-
tions, NCU was once considered an impossible dream because of the acoustic
impedance mismatch, which can be as high as six orders of magnitude for prop-
agation from air to hard alloys and dense ceramics. For NCU to work, this
acoustic barrier had to be broken.

The development of dry coupling for longitudinal and shear wave trans-
ducers operating at frequencies up to 25 MHz was the NCU transducer pre-
cursor. Since 1983, these transducers have been used to characterize thickness,
velocity, elastic, and mechanical properties of green, porous, and dense mate-
rials. This research was followed by the development of planar and focused
air/gas propagation transducers, which utilized a less than 1 Mrayl acoustic
impedance matching layer of a nonrubber material on the piezoelectric mate-
rial. These 250 kHz to 5 MHz air-coupled (AC) transducers with polymer
acoustic impedance matched layers depended on high-energy or tone burst
excitation, and high signal amplification, and were somewhat application and
range limited.

In 1997, Mahesh C. Bhardwaj* produced and evaluated transducers with
compressed fiber as the final acoustic impedance matching layer. These trans-
ducers produced unprecedented and phenomenal transduction in air. This
work was instrumental in the development of current noncontacting trans-
ducers with perfect air acoustic impedance matching. As a result, current non-
contacting transducers, covering the range of ª 50 kHz to >5 MHz, can now be
propagated though practically any medium including very-high-acoustic-
impedance materials such as steel, cermets, and dense ceramics.

Note: NCUTM, NCTTM, NCITM, GMPTM, iPassTM, iMoveTM, and iStandTM are
trademarks of Ultran Labs/Second Wave Systems.

11.3.1 NCU Transducers
NCUTM transducer signal-to-noise ratio (SNR) is determined by Eq. 11.1:

SNR = 20 log Vx Vn [dB] (11.1)

where Vx is the received signal in volts
Vn is noise voltage

The SNR is determined without signal processing and includes the noise
associated with measuring instruments, cables, etc.

NCU transducer sensitivity (S) is determined by Eq. 11.2:

S = 20 log Vx V0 [dB] (11.2)

* Mahesh C. Bhardwaj, “Non-Destructive Evaluation: Introduction of Non-Contact Ultrasound,”
in Encyclopedia of Smart Materials, Editor Mel Schwartz, John Wiley & Sons, New York (2002).

NONCONTACTING ULTRASONIC TESTING 461

where Vx is the received signal in volts
V0 is the excitation voltage

Figure 11.2 shows a group of NCU transducers having a frequency range
of ª 50 kHz to 10 MHz with active dimensions ranging from <1 mm to >75 mm.
Since the invention of a gas matrix piezoelectric composite transducer by
Mahesh C. Bardwaj (U.S. and international patents pending), transduction
efficiency has been further improved, including the possibility of producing
extremely large transducers with dimensions up to 1 ¥ 1 m. Optimum trans-
ducer performance is a function of the piezoelectric material characteristics
and its frequency constants. As an example, optimum dimensions for a 200 kHz
GMP (gas matrix piezo) transducer are about 50 ¥ 50 cm. To date Ultran Labs
has successfully produced transducers as large as 25 ¥ 25 cm between ª 50 kHz
and 200 kHz.

Figure 11.3 shows the setup for determining the transmission characteris-
tics of both AC and NC transducers. Frequency, bandwidth, and signal-to-noise
ratio can be directly read from the oscilloscope.

NCU transducers generate immense acoustic pressure in air over their
frequency range, making it possible to provide transmission in 25 mm of steel
(6 orders of magnitude Z mismatch) using 2 MHz transmission with only one
16 Vpp burst and 64 dB amplification. Figure 11.4 shows acoustic pressure
as a function of transducer-to–reflecting target distance in air (mm) for
50 mm transducers operating at frequencies between 100 KHz and 1 MHz.
Note the significant spread in the first 50 mm of distance.

Figure 11.2 Selection of noncontacting transducers. Courtesy of Ultran Labs.

462 ULTRASONIC TESTING

Figure 11.3 Theory of operation diagram for noncontacting transducers. Courtesy of
Ultran Labs.

Figure 11.4 Acoustic pressure vs. target distance. Courtesy of Ultran Labs.

NONCONTACTING ULTRASONIC TESTING 463

Figure 11.5 Ultran focused transducer. Courtesy of Ultran Labs.

NCU transducers can be compensated for velocity fluctuations in air caused
by thermal currents, humidity variations, and turbulent air flow. Compensation
is typically recommended for high-accuracy thickness, velocity, transmittance,
reflectance, and density measurements.

NCU transducers may be cylindrically (line) or point focused. Figure 11.5
shows a focused transducer along with the equation for calculating relative
aperture (RA). Active transducer diameters range from 6.3 to 50 mm, focal
lengths in air range from 25 to 300 mm, and focal points in air range from about
0.28 to 10 mm, depending on transducer frequency and diameter. In special
cases, transducers with an RA of 1.0 have been made.

11.3.2 Instant Picture Analysis System

iPassTM is a Microsoft Windows-based industrial pulser/receiver system
designed for noncontacting transducers for analytical and imaging applica-
tions. It features square wave pulsed ultrasound and true 76 dB gain amplifi-
cation for high resolution through complex high-attenuation materials. The
system has a pulse repetition rate of greater than 1 kHz for extremely fast
reading rates and sampling speeds. iPass measures defects, attenuation, time
of flight, and velocity. Two transducers are used for the direct transmission or
transmit-receive (T-R) pitch-catch reflection mode (Figure 11.6).

464 ULTRASONIC TESTING

Figure 11.6 Ultran noncontacting pitch-catch mode. Courtesy of Ultran Labs.

iPass measures data in two modes. The first mode is a continuously rolling
trend line that acquires data across the sample in one or two dimensions. The
x-axis of the trend plot is the distance traveled by the transducer in one or
both directions. The y-axis represents the transmittance value in dB through
the material. Scanning directions are established using an iMoveTM translation
device. The ultrasonic picture created by iPass is analogous to an X-ray. iPass
can provide A- and C-scans.

The iMove translation device provides standard travel speeds of
0.0125 mm/s to 510 mm/s. Custom travel speeds greater than 2.5 m/s can be
provided. Resolution of the scanning device is 0.0125 mm and maximum
thrust force is 91 kg or 200 lb. iMove devices are available in a multitude of
sizes and degrees of freedom depending on customer application and needs.

AirTech 4000 is a Microsoft® Windows-based burst ultrasonic pulser/
receiver system exclusively designed for non-contact (air/gas coupled) Ultra-
sound (NCUTM) analytical and imaging applications. Again, rectangular pulses
are used for measurement of materials with very high acoustic impedance.

Specifications for the transmitter/excitation section, preamplifier, and
receiver/amplifier are the same as for the iPass system described above. The
only exception is that in the ADC and software section of the specifications,
iPassTM for windows is used for A- and C-scans for the iPass system and Hillgus
for Windows® NT® is used for A- and C-scans for the AirTech 4000 system.
Both systems use industrial computers suitable for operation in demanding
environments. This equipment has been successfully applied to imaging and
analysis of materials in all stages of formation. Ultrasound now can be applied
to all critical process control functions, saving material, energy, and time costs
while providing excellent quality control.

Materials successfully tested using the AirTech 4000 system and NCU
transducers include:

• Uncured and cured polymers
• Prepregs

NONCONTACTING ULTRASONIC TESTING 465

• Multilayered structures
• Green and sintered ceramics
• Powder metals
• Porous material
• Food and pharmaceutical products
• Tissue and bone
• Rubber and tire
• Automotive and aircraft components
• Wood and lumber
• Concrete and other construction materials

11.3.3 Limitations

• A single NCU transducer cannot be used in pulse-echo testing techniques
at the present time.

• Similar to conventional ultrasound, NCU is limited by the complexity of
material shape and size.

• Extremely high-acoustic-impedance materials have special requirements
for successful NCU testing.

• It is nearly impossible, without special considerations, to transmit ultra-
sound through materials at or above 250°C.

Figure 11.7 shows degradation of hybrid rocket motor insulation. The light-
est circles show about 67% of original insulation value, gray areas within the
lighter areas show about 40% of original insulation value, and dark areas
within the gray show about 10 to 20% of original insulation value.

Figure 11.7 Light areas show nonbonding for 50 mm hybrid rocket motor insulation.
Courtesy of Ultran Labs.

466 ULTRASONIC TESTING

11.3.4 Bioterrorism

One timely and interesting original article by Kelli Hoover, Mahesh
Bhardwaj, Nancy Ostiguy, and Owen Thompson, titled, “Destruction of
Bacterial Spores by Phenomenally High Efficiency Non-Contact Ultrasonic
Transducers,” was published in Materials Research Innovation (volume 6,
Springer-Verlag 2002). This article deals with the destruction of disease-
causing microorganisms that are highly resistant to killing and exhibit high
toxicity in low numbers, making it difficult to control human exposure through
air-delivery systems. This problem was brought to the forefront by the recent
contamination of government offices and postal inspection facilities through
the anonymous mailing of anthrax spores. The contamination resulted in
extraordinary confinement and destruction costs, and worst of all, the
irreplaceable loss of human life.

Freeze-dried spores of Bt were used as a model for evaluating the destruc-
tion of anthrax spores because they are very closely related and are safe to
work with outside of a biocontainment facility. The Bt spores were irradiated
with 50 mm NCU planar transducers in the pulsed mode with a 50 dB power
amplifier, generating about 10 MPa of acoustic pressure in ambient air. A fre-
quency range of 70 kHz to 200 kHz was used and exposure times were varied
from 10 to 180 seconds. Pulse repetition rate was kept at 50 ms for all tests.

As a result of these tests, 98.12% to 99.99% of the spores were destroyed
at 161 and 93 kHz respectively. Exposure of 93 kHz destroyed 99.99% of the
spores, representing a reduction in spore loads of 4900-fold and 6500-fold
following 30 and 60 seconds of exposure, respectively. Treatments for longer
than 60 seconds did not improve the destruction efficiency.

While 60 seconds seems like a long time for exposing a relatively small area,
future NCU scanning arrays and advancements could conceivably keep pace
with post office processing rates. Other opportunities for NCU sterilization
can be easily visualized for the medical services and food processing indus-
tries (U.S. patent pending).

In light of significant implications of germicidal applications of noncontact
ultrasonic transducers, a new company, SONIPURE, has been formed by the
Ultran Group and the Penn State Research Foundation of Pennsylvania State
University.

11.4 ULTRASONIC PULSERS/RECEIVERS

JSR Ultrasonics, a division of Imagilent, provides UT instruments, systems,
and system components for NDT applications and research projects. The com-
pany makes a PRC35 pulser/receiver card for PCs, a DPR300 pulser/receiver,
DPR500 dual pulser/receiver, and remote pulsers for use with the DPR500
unit. They also make the mP501 PELT® multi-layer ultrasonic thickness gauge
and Robotic PELT automated coating thickness measurement system for
rapid measurement of up to five coating layers of automotive finishes.

ULTRASONIC PULSERS/RECEIVERS 467

Remote pulsers and pulser/preamps provide improved performance and
increased system reliability in cases where transducers must be located at rel-
atively long distances from the receiver or when a transducer has a center fre-
quency greater than 50 MHz. Figure 11.8 shows remote pulsers and preamps.
Remote pulsers are selected based on their performance characteristics,
namely fall time, pulse amplitude, and pulse width or energy, based on the
specific application. Significant improvements in performance may result
when cable lengths between the pulser and the transducer can be minimized.

The PRC35 pulser/receiver card is a 35 MHz computer-controlled ultra-
sonic pulser/receiver on a 2/3 length ISA card. Instrument controls include
receiver gain, pulse repetition rate, pulse energy, pulse-echo or through-
transmission mode select, pulse trigger source select, high- and low-pass filter
cut-off frequency select, selection is correct and damping adjustment. A
standby mode can be selected to reduce power consumption for use in power-
sensitive applications.

The PRC35 card (Figure 11.9) is fully shielded from electromagnetic noise
and interference while inside the PC to ensure a high signal-to-noise ratio. The
fast recovery amplifier provides rapid recovery from the initial excitation pulse
and large interference echoes.

A turnkey software front panel control program provides an unlimited
number of instrument setups to be stored and retrieved through named setup
files. The instrument base I/O port address is selectable allowing multiple cards
to be installed in the same host computer. Windows® 95/98, NT and LabVIEW

Figure 11.8 Remote pulsers and preamplifiers. Courtesy of JSR Ultrasonics.

468 ULTRASONIC TESTING

Figure 11.9 PRC35 computer-controlled pulser/receiver card. Courtesy of JSR
Ultrasonics.

drivers and C-language source code are provided to enable rapid development
of custom software.

Applications include:

• Computer-controlled imaging and measurement systems
• Materials analysis and inspection
• Transducer evaluation
• Portable NDE systems

The DPR500 pulser/receiver is a dual channel, modular instrument consisting
of two complete pulsers/receivers integrated into one unit. Standard receiver
modules are available in 500 MHz, 300 MHz and 50 MHz bandwidths. The unit
can be configured as a single channel unit using any of the available modules.
The DPR500 is shown in Figure 11.10.

Remote pulsers can be located in close proximity to UT transducers.
The elimination of long cable lengths between the pulsers and transducers
minimizes undesirable UT reflections and ringing. Interchangeable remote
pulsers accommodate a wide range of transducer frequencies and energy
requirements.

Instrument functions include adjustable damping, gain, pulse amplitude,
pulse energy, pulse repetition rate, high-pass filters, low-pass filters, echo or
through mode selectable operation (based on pulser selection), and pulser
trigger source selection.

The receiver can be configured for one or two of the following frequen-
cies—500 MHz, 300 MHz, or 50 MHz. Phase is 0° (noninverting). Input referred
noise, bandwidth, and high- and low-pass filter frequencies are operating fre-

ULTRASONIC PULSERS/RECEIVERS 469

Figure 11.10 Dual pulser/receiver. Courtesy of JSR Ultrasonics.

quency dependent. Output impedance is 50 W in all cases and maximum output
power is 5.5 to 5.2 dBm (approx. 0.58 to 0.60 V into 50 W, depending on
frequency).

Applications include:

• Acoustic microscopy
• Thin material or coating thickness gauging
• Computer-controlled imaging and measurement systems
• Material analysis and characterization
• Transducer evaluations

The DPR300 is a computer-controlled ultrasonic pulser/receiver with an
extremely low-noise receiver. Instrument controls include receiver gain, high-
and low-pass filter cut-off frequency selection, pulse energy, pulse amplitude,
pulser impedance, damping level, pulse-echo or through transmission mode
select, pulse repetition rate, and pulser trigger source select. The DPR300 is
shown in Figure 11.11.

The rapid recovery receiver is fully shielded from electromagnetic noise
and interference to ensure a high signal-to-noise ratio. Pulser impedance, pulse
energy, and pulse amplitude may be individually adjusted to optimize the
excitation pulse for a specific application or transducer. A Windows-based
software program is included for immediate usage in customer applications.
Multiple DPR300’s can be controlled from one computer using a hardware
daisy-chain interconnection scheme. Windows® 98/95 NT and LabVIEW
drivers are provided to enable rapid development of custom software.

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Figure 11.11 DPR 300 pulser/receiver. Courtesy of JSR Ultrasonics.

Areas of application include:
• Computer-controlled imaging and measurement systems
• NDE systems
• Research and development
• Materials analysis and inspection
• Transducer evaluation
• Exacting low-noise measurement systems

11.5 MULTILAYER ULTRASONIC THICKNESS GAUGE
The mP501 PELT® (Pulse Echo Layer Thickness) gauge, shown in Figure 11.12,
is a high-resolution multilayer thickness gauge that provides accurate and
repeatable measurements on many types of coatings from ceramics to spe-
cialized elastomers. Up to five coating layers may be simultaneously measured
on many different substrates. Individual layer thickness as thin as 8 microns
(0.3 mil) may be measured regardless of how the coatings are applied, includ-
ing “wet on wet.”

The mP501 generates and displays an A-scan waveform for each measure-
ment taken. Waveform analysis can be performed directly on the gauge and
the resulting individual layer as well as total layer thickness is displayed.
Larger data files can be transferred to a host PC for automated analysis. Figure
11.13 shows PELT Explorer (with Autogauge) host PC software.

CONVENTIONAL ULTRASOUND 471

Figure 11.12 Multilayer ultrasonic thickness gauge. Courtesy of JSR Ultrasonics.

Instrument features include:

• Simultaneous measurement of up to five layers
• Unparalleled gauge repeatability and reproducibility
• Measurements can be made on virtually any substrate from polymer

matrix composites to steel, plastic, wood, and glass
• Measurement accuracy is unaffected by varying thickness or composition

of substrate
• Autogauge software provides easy data analysis
• Up to 8-hours of continuous operation on a single removable and

rechargeable battery

11.6 CONVENTIONAL ULTRASOUND

Ultrasonic testing (UT) is widely used by industry for quality control and
equipment integrity studies. Major uses include flaw detection and wall thick-

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Figure 11.13 Explorer (with Autogauge) host PC software. Courtesy of JSR
Ultrasonics.

ness measurements. Using ultrasonic techniques, it is possible to detect flaws
and determine their size, shape, and location. It is also possible to measure the
thickness of process pipes and vessels with ultrasonic transducers. Wall thick-
ness measurements are especially important in corrosion studies where cor-
rosion can cause a uniform reduction in wall thickness over a period of time.

Process pipes and vessels are designed to have a specific corrosion
allowance or added amount of metal wall thickness based on design pressure,
acceptable corrosion rates, and the expected life of the equipment. If unex-
pectedly high corrosion rates are encountered, wall thinning can occur at
accelerated rates, resulting in dangerous conditions with regard to pipe and
pressure vessel ratings. If pipes and vessels become too thin, they can burst,
causing extensive plant damage as well as endangering the lives of workers.
For these reasons, many chemical and petrochemical plants have active
corrosion-monitoring programs where periodic wall thickness measurements
are made on all process pipes and vessels.

Ultrasonics can also be used to determine differences in material structure
and physical properties. Heat treatment, material grain size, and the modulus
of elasticity or Young’s modulus can affect the attenuation of ultrasound.
Young’s modulus is the ratio of stress to strain in a material within its elastic
limit.

CONVENTIONAL ULTRASOUND 473

11.6.1 Flaw Detection

When a piezoelectric crystal is driven by high-voltage electrical pulses, the
crystal “rings” at its resonant frequency and produces short bursts of high-
frequency vibrations. These “sound wave trains” generated by the ultrasonic
transducer or “search unit” are transmitted into the material being tested.
When the search unit is in direct contact with the test material, the technique
is known as “contact” testing.

If flaws or discontinuities are present, an acoustic mismatch occurs and
some or all of the ultrasonic energy is reflected back to the search unit. The
piezoelectric crystal in the search unit converts the reflected sound wave
or “echo” back into electric pulses whose amplitudes are related to flaw
characteristics and whose time of travel or time of flight through the material
are proportional to the distance of the flaw from the entrance surface.
Ultrasonic pulses are also reflected from the back surface of the material and
this signal represents the total distance traveled. The pulse received from the
back surface can also represent the width, length, or thickness of the material
depending on its orientation. Ultrasonic thickness testing measures the wall
thicknesses of pipes and vessels by measuring the total distance traveled
by the ultrasonic pulses, which is represented by the distance from the initial
pulse or front surface to the back reflection from the back surface. Ultrasonic
flaw and thickness indications are frequently displayed on an instrument or
computer display screen. Figure 11.14 illustrates the pulse-echo contact tech-
nique and shows the initial pulse, flaw indication, and back surface reflection
display.

Figure 11.14 Pulse-echo contract testing technique.

474 ULTRASONIC TESTING

Figure 11.15 Pulse-echo immersion testing technique.

Immersion testing is another popular technique used for ultrasonic flaw
detection. In immersion testing, both the ultrasonic search unit and the test
piece are immersed in a liquid, usually water. The advantage of this technique
is that the water excludes air and acts as a “couplant” or coupling agent
for the transmission of ultrasonic energy. A couplant is used to couple (or
complete the ultrasonic path) between the search unit and test surface.
Figure 11.15 illustrates the immersion testing technique and shows a typical
screen presentation.

11.6.2 Frequency
In theory, any frequency about 20,000 cycles per second (cps) (20 kHz) can be
thought of as an ultrasonic frequency or frequency above the normal sound
range. In practice, ultrasonic transducers and equipment operate in the
frequency range of <50 kHz to 200 MHz. This frequency range extends well
beyond the audio sound wave frequency range of 20 Hz to 20 kHz, but ultra-
sonic waves are still propagated as waves of particle vibrations. These waves
travel with ease in uniform solids and low-viscosity liquids; voids or gases such
as air quickly attenuate them.

Some important characteristics of ultrasonic vibrations are:

• They travel long distances in solid materials.
• They travel in well-defined sonic beams.
• Their velocity is constant in homogeneous materials.
• Circuitry is designed so that the energy from the first wave train is

dissipated before the next wave train is introduced.
• Vibrational waves are reflected at interfaces where elastic and physical

properties change; they are also refracted when elastic properties change.

CONVENTIONAL ULTRASOUND 475

• Vibrational waves may change their mode of vibration or be subject to
mode conversion at material interfaces.

Ultrasonic pulses can be generated by radio frequency (RF) wave trains
driving a crystal at a controlled frequency and precise time or they can be
generated by a shock pulse that permits the crystal to resonate at its natural
frequency thus establishing the vibrational frequency. For maximum sensitiv-
ity, the piezoelectric crystal should be driven at its fundamental resonant
frequency.

In ultrasonic testing, a search unit may be thought of as an ultrasonic probe
or transducer containing one or more piezoelectric crystals. The search unit is
driven for 1 to 3 ms, producing a short burst of ultrasonic waves. The ultrasonic
waves are transmitted through the material where it is reflected by the back
surface. After this initial burst of pulses is transmitted, the transducer acts as
a receiver, waiting to receive the reflected wave train or echo pulse. This trans-
mitting–receiving cycle is repeated 60 to 1000 times or more based on trans-
ducer design and application requirements. To avoid confusion, sufficient time
must be allowed to elapse between transmitted pulses to permit return of the
echo pulse and provide for the decay of the initial pulse. Figure 11.16 shows
UT pulse generation.

The relationship among frequency, wavelength, and velocity is given by Eqs.
(11.3)–(11.5):

V=l¥f (11.3)
l=V f (11.4)
f=V l (11.5)

Figure 11.16 Ultrasonic pulse generator.

476 ULTRASONIC TESTING

where V = velocity in cm/s
l = wavelength in cm
and f = frequency in Hz

From these equations it can be seen that velocity varies directly with wave-
length and frequency, but wavelength and frequency vary inversely with each
other. Velocity is the speed at which ultrasonic vibrations pass through various
materials; it is dependent on the elastic properties of the material and the
mode of vibration. The elasticity and density of the material determines its
sound velocity.

In practice, the test frequency selected depends on the sensitivity and sound
penetration required. In general, high-frequency crystals are more sensitive to
discontinuities and lower-frequency crystals provide greater depth penetra-
tion. All frequencies work equally well with fine-grained materials or in
immersion testing. High frequencies usually are not used with coarse-grained
materials because the material tends to scatter the energy. Also, frequencies
above 10 MHz are seldom used with contact-type search units because of the
fragile nature of the high-frequency crystals.

11.6.3 Ultrasonic Wave Propagation

The four fundamental modes of ultrasonic wave propagation are:

1. Longitudinal or compression waves
2. Shear or transverse waves
3. Surface or Rayleigh waves
4. Plate or Lamb waves

Longitudinal waves are similar to audible sound waves in that they are also
compressional in nature. The alternate expansion and contraction of a piezo-
electric crystal generates longitudinal waves. Particle displacement is in the
direction of wave propagation as shown in Figure 11.17. Only longitudinal
waves can travel through a liquid.

With shear waves, particle vibration is transverse (at a right angle) to the
direction of wave propagation. Passing the ultrasonic beam through the mate-
rial at an angle generates shear waves. Plastic wedges with angles of about
27.5° (1st critical angle) to 57° (2nd critical angle) are used with transducers
to generate shear waves in steel at 33 to 90°. At 90° the transverse wave
propagates along the surface of the object, becoming a surface wave. Figure
11.18 illustrates the shear wave relationship between the direction of particle
vibration and direction of wave propagation.

Surface waves (Figure 11.19) travel with little attenuation in the direction
of wave propagation. However, their energy decreases rapidly as the wave
penetrates below the surface of the material. Surface waves do not exist in

CONVENTIONAL ULTRASOUND 477

Figure 11.17 Particle motion and wave propagation with longitudinal waves.

Figure 11.18 Particle motion and wave propagation with shear waves.

Figure 11.19 Particle motion and wave propagation with surface waves.

immersion testing. Particle displacement of the wave follows an elliptical
orbit.

When ultrasonic energy is introduced into relatively thin plates, it is prop-
agated by Lamb waves. Lamb waves have multiple or varying wave velocities.
Lamb wave velocity is dependent on the thickness of the material and fre-
quency. With Lamb waves, a number of modes of particle vibration are pos-
sible, but the two most common modes of vibrational motion are symmetrical
and asymmetrical as shown in Figure 11.20. The complex particle motion is
somewhat similar to the elliptical orbits of surface waves.

11.6.4 Acoustic Impedance

The characteristic impedance (Z) of a material is defined as the product of
density (d) and longitudinal wave density (v). The equation for acoustic
impedance is shown in Eq. (11.6):

( )Z(g cm2 ◊ s) = d g cm3 ¥ v(cm s) (11.6)

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Figure 11.20 Particle motion and wave propagation with Lamb waves.

The acoustic impedance of a material determines its reflection and trans-
mission characteristics. As the impedance ratio of two dissimilar metals
increases, the amount of sound coupled through their interface decreases.
Acoustic impedance values for some common materials are listed in Table
11.1.

11.6.5 Reflection and Refraction
Ultrasonic vibrations are reflected at the interface of two different materials
when a mismatch occurs in acoustic impedance. Acoustic mismatches are
likely to occur at the water–metal interface, metal–flaw surface interface,
or metal–metal interface where the material properties are quite different.
One important property of the reflected wave is that the angle of reflection
is always equal to the angle of incidence. Figure 11.21 shows the angular rela-
tionship of the incident, reflected, and refracted waves.

When the ultrasonic beam passes at an angle from one material to another,
refraction and mode conversion can occur. Refraction occurs when the ultra-
sonic wave changes direction and velocity as it crosses a boundary between
different materials. Both reflection and refraction are analogous to what can
be observed with light beams. The reflection of light beams with mirrors is
similar to the reflection of sound waves when an acoustic mismatch occurs.
The refraction of the sound wave is similar to viewing a stick half in and half
out of the water. The stick appears to be broken or disjointed at the surface
of the water or air–water interface and its direction appears to change. In
contact testing, the search unit utilizes a plastic wedge with the ultrasonic
crystal to introduce the ultrasonic beam at an angle to produce shear waves.
In immersion testing a transducer manipulator is used to angulate (vary the
angle of) the transducer to produce shear waves. Mode conversion occurs
when the longitudinal waves in plastic or water are converted into shear waves
in the material. The refraction angle of waves passing from water into metals,

CONVENTIONAL ULTRASOUND 479

TABLE 11.1. Acoustic Impedance of Various Materials

Material Longitudinal Velocity Density Acoustic Impedance
(cm/s)a (g/cm3) (g/cm2 · s)a

Acrylic 2.67 1.18 3.15
Air 0.33 0.0001 0.00033
Aluminum 250 6.35 2.71 17.2
Aluminum 17ST 6.25 2.80 17.5
Beryllium 12.80 1.82 23.3
Brass 4.43 8.10 35.9
Bronze 3.53 8.86 31.3
Cadmium 2.80 8.57 24.0
Copper 4.66 8.90 41.5
Glass, crown 5.30 3.56 18.9
Glycerin 1.90 1.26 2.4
Gold 3.20 19.56 62.6
Ice 4.00 0.88 3.5
Inconel 7.82 8.25 64.5
Iron 5.90 7.69 45.4
Iron, cast 4.60 7.22 33.2
Lead 2.16 11.40 24.6
Magnesium 5.79 1.74 10.1
Mercury 1.40 14.00 19.6
Molybdenum 6.30 10.19 64.2
Monel 6.02 8.33 53.2
Neoprene 1.60 1.31 2.1
Nickel 5.63 8.80 49.5
Nylon, 66 2.60 1.11 2.9
Oil, SAE 30 1.70 0.88 1.5
Platinum 3.30 21.15 69.8
Plexiglass 2.70 1.15 3.1
Polyethylene 1.90 0.89 1.7
Polystyrene 2.40 1.04 2.5
Polyurethane 1.90 1.00 1.9
Quartz 5.80 2.62 15.2
Rubber, butyl 1.80 1.11 2.0
Silver 3.60 5.99 21.6
Stainless 302 5.66 8.03 45.4
Stainless 410 7.39 7.67 56.7
Steel 5.85 7.80 45.6
Teflon 1.40 2.14 3.0
Tin 3.30 7.33 24.2
Titanium 6.10 4.47 27.3
Tungsten 5.20 19.42 101.0
Uranium 3.40 18.53 63.0
Water 1.49 1.00 1.49
Zinc 4.20 7.05 29.6

a Times 100,000.

Source: Based on information supplied by the courtesy of Automation/Sperry, a unit of Qualcorp,
and Krautkramer Branson, Incorporated, Manufacturers of Ultrasonic Nondestructive Testing
Equipment.

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Figure 11.21 The relationship among the angle of incidence, angle of reflection, and
angle of refraction.

Figure 11.22 Angle beam construction and mode conversion.

at angles other than normal, varies as a function of the relative velocities of
sound in water and metal. Figure 11.22 shows angle beam construction, refrac-
tion of the ultrasonic beam, and resulting particle motion. Snell’s law, Eq.
(11.7), defines both the angle of reflection and refraction as:

sin q1 V1 = sin q2 V2 (11.7)