Review of Ultrasound Performance From 5 to 20 MHz 

on an Aluminum Standard 

by Raymond E. Brennan and James M. Sands 

ARL-TR-4662 December 2008 

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Army Research Laboratory 

Aberdeen Proving Ground, MD 21005-5069 

ARL-TR-4662 December 2008 

Review of Ultrasound Performance From 5 to 20 MHz 

on an Aluminum Standard 

Raymond E. Brennan and James M. Sands 

Weapons and Materials Research Directorate, ARL 

Approved for public release; distribution is unlimited. 
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Review of Ultrasound Performance From 5 to 20 MHz 

on an Aluminum Standard 

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Raymond E. Brennan and James M. Sands 

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13. SUPPLEMENTARY NOTES 

14. ABSTRACT 

An ultrasound system has been set up for nondestructive evaluation of armor tiles and composite systems. Critical system 

components including an internal pulser-receiver and digitizer board, a stepper motor indexer board, a four-axis scanning 

frame, an additional two-axis controller, a central processing unit with integrated software package, an immersion tank, and a 

series of ultrasonic transducers are described in detail. Characteristics and parameters of the various transducers are 

summarized. Operation of the equipment and utilization of various software tools are detailed to provide a basic method for 

conducting ultrasound C-scan imaging and analysis. This method is applied to experimental characterization of a standard, 

which is important for verifying system and transducer parameters as well as exploring system capabilities and limitations. A 

full system evaluation citing these specific capabilities and limitations is discussed. 

15. SUBJECT TERMS

ultrasound, transducer, nondestructive evaluation, standard 

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Raymond E. Brennan 

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iii

Contents 

List of Figures iv

List of Tables iv

1. Introduction 1

2. Equipment Description 1

3. Ultrasound System Procedure and Parameters 4

4. Ultrasound System Capabilities and Limitations 10

5. Summary and Future Considerations 17

Distribution List 19 
iv

List of Figures 

Figure 1. Ultrasound system equipment. ........................................................................................2 

Figure 2. Schematics of X, Y, Z, T, G, and S axes. ........................................................................3 

Figure 3. A-scan of 20-mm-thick AD-995 alumina ceramic. .........................................................6 

Figure 4. Screenshots of typical A/D, gate, and scanner parameters. .............................................7 

Figure 5. Aluminum standard sample featuring steps and drilled holes. ......................................11 

Figure 6. A-scan evaluation of aluminum standard at various positions. .....................................12 

Figure 7. TOF B-scan and C-scan evaluations of aluminum standard. ........................................14 

Figure 8. AMP B-scan and C-scan evaluations of aluminum standard. .......................................14 

Figure 9. AMP 3D construction of aluminum standard. ...............................................................15 

Figure 10. Transducer TOF frequency comparison of aluminum standard at 10, 15, 

and 20 MHz..............................................................................................................................16 

Figure 11. Transducer AMP frequency comparison of aluminum standard at 10, 15, 

and 20 MHz..............................................................................................................................16 

List of Tables 

Table 1. Ultrasound transducers and parameters. ...........................................................................5 

Table 2. General hardware configuration and scanner parameters for ultrasound system. ............6 
1

1. Introduction 

A comprehensive ultrasound system has been set up in Laboratory L1088 of the U.S. Army 

Research Laboratory (ARL) for nondestructive evaluation (NDE) and characterization of various 

armor tiles and armor systems. The unit will serve as a critical NDE component to complement 

the x-ray computed tomography (XCT) capabilities that are currently in place. This report 

outlines the abilities and limitations of the ultrasound system, provides details of key parameters 

involved in the system setup, and summarizes a procedure for operation of the equipment. 

2. Equipment Description 

The ultrasound system consists of eight major components including an internal pulser-receiver 

and digitizer board, a stepper motor indexer board, a 4-axis scanning frame, an additional 2-axis 

controller, an immersion tank, various ultrasonic transducers, and a central processing unit 

(CPU) with an ultrasound software package for integrating and controlling the unit (figure 1). 

The ultrasonic transducer is the central component of the system while the rest of the equipment 

is used to perform functions that relate directly to its operation. Some of these tasks include 

supplying initial energy to the transducer, collecting and amplifying signals detected by the 

transducer, providing mechanical positioning and manipulation of the transducer, and displaying 

and converting the collected signals into a usable format for interpretation. While a transducer, 

in general, is a device that converts one form of energy into another, an ultrasonic transducer 

specifically uses a piezoelectric component to convert electrical energy in the form of an initial 

pulse into mechanical energy in the form of vibrations. This results in the generation of an 

acoustic wave at a specified frequency which interacts with the material under analysis. The 

acoustic impedance differences between the immersing medium and the sample or between the 

sample and any material inhomogeneities result in reflection of the acoustic waves at these 

boundaries. The reflected signals are collected by the transducer and re-converted from 

mechanical waves into electrical signals that are interpreted for nondestructive evaluation of the 

test material. In order to improve the acoustic impedance match between the transducer and 

enhance the amount of ultrasound energy that is transmitted into the test material, an acoustic 

medium of water is often utilized. For this purpose, a large immersion tank capable of handling 

materials as large as 20 × 20 in and as thick as 20 in is set up to contain the water. 

The roles of the pulser-receiver, digitizer, motion controllers, CPU, and software are described in 

relation to operation of the ultrasonic transducer and collection of acoustic signals. The 

combined pulser-receiver/digitizer board is an external analog-to-digital internal pulser-receiver 

12-bit unit (AD-IPR-1210) that is connected to one of the peripheral component interconnect 
2

X,Y,Z Axis

Controller

Full Scale

Immersion Tank

Immersion

Transducer

T-Axis

Controller

CPU with Internal

Pulser-Receiver

Digitizer

Stepper Motor Board

G, S Axis

Controller

Scanning

Arm

Small Scale

Immersion Container

Top View

of System

Figure 1. Ultrasound system equipment. 

(PCI) slots of the CPU. The pulser-receiver component of the board is used to send the initial 

electrical pulse to the transducer which generates the ultrasound waves. This unit also collects 

and amplifies the reflected ultrasound signals in the form of analog data. The digitizer 

component of the board is used to convert the raw analog signal data from the pulser-receiver 

into a digital format that can be directly interpreted by the software. Some of the specific 

features of the AD-IPR-1210 card include high-voltage negative spike pulsing of 300 V standard 

and 400 V optional, adjustable pulse width from 100 ns to 10 s, pulse-repetition rates from 

0.1 to 10,000 pulses per second, 0.5–30 MHz bandwidth, a gain range of –20 to +80 dB, and a 

100-MSample/second sampling rate. These parameters make the system ideal for handling 

ultrasonic transducers with frequencies up to 20 MHz. 

Up to this point, only ultrasound signal related issues have been discussed. Another key 

component for performing ultrasound imaging is the mechanical manipulation of the transducer 

to control positioning and motion. A 4-axis scanning frame is fitted to the immersion tank for 

control of the x, y, z, and t (translation) axes (figure 2). The ultrasonic transducer is attached to a 

mechanical arm that is translated in the x, y, and z directions while the bottom of the immersion 

tank contains a rotating circular table through which translation can be controlled. In addition, 

the mechanical arm is fitted with a counter-rotating pulley system for manipulation of the tilt and 

rotation of the transducer. The tilt is controlled by the g, or gimbal axis, while the rotation is 

controlled by the s, or swivel axis, making a total of 6 axes that control the x, y, z, t, g, and s 

directions (figure 2). The g and s axes are controlled by a 2-axis external box, the x, y, z, and t 
3

Immersion

Transducer

Z-axis

Y-axis

X-axis

Immersion

Transducer

G-axis

Immersion

Transducer

Z-axis

S-axis

Figure 2. Schematics of X, Y, Z, T, G, and S axes. 

axes are controlled by the 4-axis scanning frame, and both of these units are input to a stepper 

motor indexer board (SMC8-PCI) that is connected to one of the PCI slots of the CPU. While 

the SMC8-PCI board is capable of driving up to eight independent channels, only six are used in 

this case, one for each axis. 

With the ultrasound signal and 6-axis control capabilities integrated into the CPU, the next major 

component is a suitable software package that enables the system to generate useful ultrasound 

data. The software that is used for this purpose is a program called UltraWin* Version 2.83. 

Some of the software capabilities include multiple pulser/receiver and analog-to-digital converter 

support through the AD-IPR-1210 board, 6-axis motion control support through the SMC8-PCI 

board, real time display and acquisition of A-, B-, and C-scans, up to two gate settings, RF 

waveform storage and replay, cluster analysis, and three-dimensional (3-D) C-scan imaging. 

The aforementioned A-, B-, and C-scans are different methods for displaying ultrasound signal 

information. The first and most common is the A-scan, or amplitude scan, which displays the 

intensity of the received ultrasound signals as a function of time. This type of data can be 

collected by conducting point analysis of a specimen at any given position. The B-scan is a 

cross-sectional profile view of the test specimen. In this scan mode, the A-scan results are 

collected over either the x or the y dimension of the sample, and ultrasonic data representative of 

the cross-section of the selected area is displayed. In the final type of ultrasound display, the 

transducer moves in raster-like fashion so both x and y coordinates are collected in addition to 

 *

UltraWin is a registered trademark of NDT Automation, Princeton Junction, NJ. 
4

the reflected signals. A time gate is set to consider only signals within the chosen range, and this 

produces a two-dimensional top view of defect response, referred to as a C-scan. The C-scan is 

another name for the ultrasound image map, and is used to locate flaws and defects within a 

specimen based on acoustic differences. 

The following section will describe the procedure for utilizing the ultrasound system to perform 

analysis on a test sample and include a description of the important parameters used to extract 

valuable ultrasound data. 

3. Ultrasound System Procedure and Parameters 

There are two components of the procedure that will be described for analysis of an armor 

ceramic plate test sample including a description of the physical setup of the sample and a 

description of the UltraWin test parameters and scan execution. In terms of the physical setup, 

the immersion tank is filled, preferably with higher purity deionized or distilled water as the 

acoustic medium to minimize the presence of particulates that could potentially interfere with the 

integrity of the data collection. The tank is filled to a suitable level to account for the thickness 

of the test specimen and the desired water path between the transducer and the specimen. Next, 

the armor ceramic test plate is immersed in the tank. After immersion, air bubbles that form on 

any sample surfaces are removed to avoid interference with the relevant sample data collection. 

In general, it may also be advantageous to use small parallel plates or slides of the same 

thickness to prop the test specimen above the bottom floor of the tank. This can often provide a 

greater acoustic impedance mismatch between the sample and its contacting medium which may 

enhance the strength of the bottom surface reflected signals. Some characteristics of an ideal 

specimen for ultrasound testing include two flat, parallel top and bottom surfaces and minimal 

surface roughness. While these are not requirements for performing ultrasound characterization, 

they provide ideal conditions for analysis.

In addition to sample setup, the transducer must also be selected and attached to the end of the 

scanning arm. There are many types of transducers in-house, but the ones that will be briefly 

described are the newest set from the most recent purchase from Olympus NDT (table 1). The 

majority of these transducers are focused longitudinal immersion transducers with standard 

active ultrahigh frequency (UHF) top-mounted connections for attachment to the scanning arm. 

The transducers that are compatible with the current ultrasound system setup have frequencies of 

0.5, 1, 2.25, 3.5, 5, 10, 15, and 20 MHz. While higher frequency transducers were also 

purchased at frequencies of 25, 50, and 100 MHz, these could not be used due to the AD-IPR1210 limitations. For these focused transducers, the element sizes range from 0.25 to 1 in while 

the focal lengths range from 1.65 to 8.5 in. There are also two main types of transducers 

including Accuscan, or narrowband, and Videoscan, or broadband, transducers. Once the 

desired transducer is selected, the active UHF connection is screwed into the bottom of the 
5

Table 1. Ultrasound transducers and parameters. 

Transducer Type Frequency 

(MHz) 

Focal Length 

(in) 

Element Size 

(in) 

A301S A 0.5 1.65 1.0 

V301 V 0.5 1.65 1.0 

A302S A 1.0 3.35 1.0 

V302 V 1.0 3.35 1.0 

A304S A 2.25 7.00 1.0 

V304 V 2.25 7.00 1.0 

A380S A 3.5 8.50 1.0 

V380 V 3.5 8.50 1.0 

A307S A 5.0 8.50 1.0 

V307 A 5.0 8.50 1.0 

A315S A 10.0 6.45 0.75 

V315 V 10.0 6.45 0.75 

A319S A 15.0 6.45 0.50 

V319 V 15.0 6.45 0.50 

V317 V 20.0 4.20 0.25 

V324 V 25.0 5.25 0.25 

V358 V 50.0 Unfocused 0.25 

V30007 V 100.0 0.75 0.25 

scanning arm. After completing the physical setup, the UltraWin parameters are set up for 

conducting ultrasound analysis. 

The first set of critical parameters is the hardware configuration which ensures that the AD-IPR1210 and SMC8-PCI boards are communicating properly with the UltraWin software. The 

general hardware configuration including motor type, encoder ratio, acceleration rate, and jog 

speed for each of the six axes is shown in table 2. The board configuration for Channel 1 is set 

to IPR-90 for the pulser-receiver, AD-IPR-1210 for the digitizer, and SMC-PCI for the stepper 

motor board. For compatibility with the motion controllers, the scanner parameters including 

pitch, steps per revolution, and gear ratio for each of the six axes is shown in table 2. The 

advanced settings are set at encoders unused, linear acceleration/deceleration, acceleration 

/deceleration jog stop mode, 5-s step clock pulse width, limit switch unused, 0.10% start speed, 

and 30.0 maximum speed limit for all axes. After setting up all of the hardware parameters, the 

A-scan parameters specific to the test specimen and transducer conditions are determined. 

The amplitude scan (A-scan) displays a series of reflected ultrasound signals from the test 

sample and is plotted on a graph of voltage in mV along the y-axis and time in s along the 

x-axis. Figure 3 shows an A-scan for a typical alumina (Al2O3) AD-995 ceramic plate. The 

position of the transducer is set by using the jog function to control the x, y, z, t, g, and s 

positions of the transducer. The transducer is immersed in the water by controlling the z-axis to 

place it at the desired focal distance from the test sample. Just as it was mentioned for sample 
6

Table 2. General hardware configuration and scanner parameters for ultrasound system. 

Axis 

Motor 

Type 

Encoder 

Ratio 

Acceleration 

Rate Jog Speed 

(in/s) 

Pitch 

(in/s) 

Steps Per 

Revolution 

Gear 

Ratio 

X Internal 1.0 15 2.0 0.2 500 1.00 

Y Internal 1.0 15 2.0 0.5 1000 1.00 

Z Internal 4.0 10 1.0 6.0 500 0.05 

T Internal 1.0 50 30.0 62.5 1000 0.20 

G Internal 4.0 60 20.0 360.0 80,000 2.78 

S Internal 4.0 60 20.0 360.0 80,000 2.78 

immersion, it is important to remove any air bubbles that may have formed on the face of the 

transducer. The x and y positions are jogged until the transducer is placed over the desired 

sample area. The g and s parameters are fine-tuned to ensure that the transducer is perpendicular 

to the top surface of the sample in order to maximize the ultrasound signal intensity. The jog 

function is also used to program the starting position in x, y, z, t, g, and s before performing an 

ultrasound scan. 

Figure 3. A-scan of 20-mm-thick AD-995 alumina ceramic. 

To locate the reflected ultrasound signals from the test specimen at the current position, the 

analog-to-digital (A/D) function is selected (figure 4). The delay is set to 0.0 s and the width 

expanded to 50.0 s to locate the reflected signals. When the ultrasound signals from the sample 

are found, the delay and width are adjusted to hone in on the desired signals, most likely the top 

surface and bottom surface reflected signals as shown in figure 3. Other parameters in the A/D 
7

Figure 4. Screenshots of typical A/D, gate, and scanner parameters. 

function are typically set as RF to display the full signal, P/R for pulser-receiver mode, a 

sampling rate of 100 MHz, a pulser voltage of 390 V, damping of 545 ohms, and an energy level 

of 820 J. Some of the parameters that are often varied are the voltage scale between 0.125 and 

0.500 V, wave average between 1 and 20, and gain between 20 and 40 dB, depending on the 

amount of noise. For a combined transducer and sample interaction with minimal noise, the 

voltage is set as 0.500 V with an average of 1 and a gain between 20 and 30 dB. If there is a 

high degree of noise, this might be changed to 0.125 with an average between 5 and 10 and a 

gain between 30 and 40 dB. This must be optimized on a case-by-case basis depending on the 

signal-to-noise ratio. The gain control is highlighted in figure 4 under the AD-IPR setup 

window. Another option in the A/D function is to obtain a fast fourier transform (FFT) of the 

selected signals. As opposed to the standard method of subtracting the distance between 

reflected signals to measure the time-of-flight (TOF), or travel time of the ultrasound signal 

through the sample, the FFT analysis can be performed as a cross-correlational measurement of 

TOF. However, the FFT method may result in large variations due to its sensitive nature, so both 

methods should be employed to accurately measure TOF. 

Two more critical A-scan functions that must be established before performing ultrasound 

imaging include gates and scan parameters. Under gates, the gated regions are set up to define 
8

the positions of the desired reflected ultrasound signals (figure 4). A common practice is to set 

gate 1 to account for the top surface reflected signal and gate 2 to account for the bottom surface 

reflected signal. Gate 2 can also be set for the region between the top and bottom surface 

reflected signals for a bulk scan that is used to detect small peaks directly from material 

inhomogeneities within the sample, but these are often difficult to conduct unless the features are 

of a significantly large size. For each gate, the detection threshold is set as a horizontal line 

below which the signal data will not be collected. This is designed to reduce the effect of noise 

in a scanned image, and is compatible with the max and peak detection strategies for collecting 

data from the maximum peak over the desired gate. The detection threshold is often chosen as 

1% if it is desirable to detect peaks from small inhomogeneities close to the noise floor, 3% for 

an intermediate range, or 5% if the goal is to capture high intensity signals while eliminating the 

effect of noise from electrical signal interference. While 1% is ideal for comprehensive sample 

evaluation, it is more likely that noise from signal interference will be included in the data since 

the threshold is set so close to the noise floor. The detection threshold is highlighted in the Gate 

Setup module in figure 4. It is often desirable to run scans under different gating conditions to 

account for every possibility. The start and width of the gate are used to set the position and 

range for each gate, while the normal option is used to collect data from a single gate and the 

difference option is used to collect data which is measured as the difference between gate 1 and 

gate 2. For a TOF evaluation, the Difference option is most useful as TOF2 – TOF1 determines 

the TOF difference at each point. The difference option is also used to describe the amplitude 

(AMP) of gate 1 divided by the AMP of gate 2. Again, it is useful to collect both normal and 

difference data in most cases. While setting the gates, it is important to use the jog function to 

look for any peak shifting that may occur due to thickness variations, nonparallel surfaces, or 

improperly calibrated positioning of the immersion tank or transducer that may cause unwanted 

tilt. If shifting does occur, the gates need to be widened so that the signal remains within its 

confines and all of the data can be collected over the entire sample area. 

The scan function is important for choosing the scan area and the desired resolution (figure 4). 

The scan axis is defined as the axis over which the majority of motion is occurring, in most cases 

the x-axis, while the index axis is defined as the axis over which there is minimal motion, in 

most cases the y-axis. These are the two axes that are in use to define the scan and should be set 

accordingly. The length in inches of the scan in each of these directions is set. For a 4- × 4-in 

armor ceramic test plate, typical settings are 4.5 inches in each direction so that the entire sample 

area can be covered. The speed is set, typically at around 4.0 in the scan axis direction and 1.0 in 

the index axis direction in which there is minimal motion. The resolution is often chosen as the 

Automatic Maximum Resolution over the scan area, as set by the software according to the scan 

area. The length, resolution, and speed of the scan axis, in this case the x-axis, are highlighted in 

the Scanner Setup module in figure 4. For a setting of 4.5 in of scanning length and width, this 

results in an automated maximum resolution of 0.0098, which translates to a pixel size of 

~249 m. While it is often desirable to increase this resolution, especially at higher frequencies, 

the automatic maximum resolution setting is dictated by the size of the scan area. Manual 
9

reduction of the resolution settings below the automated value results in glitches and processing 

errors in the resulting scan including offset lines and erroneous scan data. Due to these 

automated settings, smaller samples benefit with much higher resolution capabilities compared to 

larger samples. 

Once the A-scan parameters are set, the C-scan function is selected to construct the ultrasound 

image. As opposed to an A-scan evaluation for a single point, a C-scan is a collection of data 

points, typically based on changes in reflected signal amplitude or TOF values. The gated 

regions confine the top and bottom surface reflected peaks, and the values from these gates are 

measured in terms of reflected signal intensity for AMP in mV and time difference in s for 

TOF. The AMP values can also be directly converted into attenuation, , or signal loss, using 

the equation  = 20 log AMP. After setting these parameters, each individual A-scan generates a 

single value of TOF or AMP and the C-scan image maps these data at each x and y position. A 

color scale is used to display the different values over the maximum range so that high and low 

AMP and TOF features and regions can be identified. After selecting the C-scan function, the 

acquire tab is used to set the map options. C-scan TOF and C-scan AMP data can be saved while 

scanning, the map can be magnified, the display options can be set for gate 1 TOF, gate 1 AMP, 

gate 2 TOF, or gate 2 AMP while running the scan, and the ranges for TOF in s and attenuation 

in dB can be set. The radio frequency (RF) mode can also be selected before running the scan. 

This option allows not only the C-scan image data to be saved, but also saves each corresponding 

A-scan at each point over which the data was collected. Once the parameters are finalized, the 

go button initializes the scan. The scanning arm translates the ultrasonic transducer to the 

starting point and begins rastering over the sample at the desired speed and positions until the 

entire area is covered. The result is a C-scan image that can be qualitatively analyzed before 

performing post-processing. 

The post-processing menu is opened by selecting the Replay function, which displays the 

selected C-Scan image. Under the Process tab, the image is selected for gate 1 TOF, gate 1 

AMP, gate 2 TOF, or gate 2 AMP, and only one of these images can be viewed at a time. The 

scale and rulers are also displayed. Options for zooming in on specific sample areas are also 

displayed. However, the s scale values for TOF images and the dB scale values for AMP 

images cannot be changed. The Image Filter tab fills in any missing data points by averaging the 

values of its nearest neighbors. The 3-D view provides a unique three-dimensional display of the 

AMP or TOF data that can be re-scaled and rotated in the x, y, and z directions. This is not only 

a good visual tool, especially for test samples with pronounced inhomogeneities, but can prove 

useful for observing variations from angles that were previously difficult to access. Another 

display option is B-scan imaging, which is also very useful for viewing a cross-sectional slice 

through the C-scan image. This serves as a collection of A-scan data over a selected horizontal 

or vertical line across the C-scan image, and is good for observing a side view by digitally slicing 

through the sample and looking for TOF and AMP variations. The horizontal and vertical lines 

can be positioned over the C-scan image to evaluate the desired regions. 
10

The cluster tab includes the quantitative analysis options for the C-scan image. Analysis is 

conducted by choosing the lower and upper threshold percentage of data for evaluation, selecting 

the minimum pixel size of the clustered area, and selecting the minimum number of pixels 

contained in each cluster. When the analysis is performed, the cluster data are displayed in terms 

of number of pixels, total cluster area, percent area, cluster position, and peak amplitude of the 

cluster region. The numbered clusters can also be overlaid directly onto the C-scan image map. 

This is the extent of direct quantitative analysis that is available. While there is an option to 

convert some of the raw scan data into XLS format for use with Microsoft Excel,* this is 

extremely limited to a maximum number of 254 data points, which is miniscule in comparison to 

the tens and hundreds of thousands of data points that are collected for typical C-scan images. 

The number of collected data points increase as the resolution is increased, which is vital for 

high frequency scans and detection of features and inhomogeneities, and also increase with 

sample size. The limit of 254 is based on the column limit of data in Excel, and the small value 

renders the conversion of data to be relatively useless. The raw data is also encoded by the 

software and there is no apparent way to access the C-scan data which is vital for proper 

quantitative analysis. With access to the raw data, the values could at least be evaluated using a 

different software package such as SigmaPlot† or Origin,‡ but the UltraWin software does not 

allow for this access and this serves as one of its most severe limitations.

4. Ultrasound System Capabilities and Limitations 

The ultrasound system is fully operational and is being used for evaluation of both undamaged 

and damaged armor ceramic plates and armor systems. By working with the system extensively, 

many of the capabilities and limitations have been identified. On the positive side, the system 

works well as a fully integrated unit, with the boards communicating well with the software. The 

ability to have full control over six axes is phenomenal, in that most ultrasound systems are 

limited to control of only the x and y axes and possibly the z axis. The parameter settings 

provide a great deal of flexibility for conducting a variety of scans that enable comprehensive 

study of the test samples. For example, common parameters that are altered to provide unique 

scans on the same test sample include detection threshold percentage, waveform averaging, 

Normal and Difference gating options, an extensive gain setting range, and a multitude of pulser 

settings including pulse width which dictates the axial resolution. In terms of post-processing, 

the B-scan and 3-D view display methods are extremely useful from a qualitative standpoint, 

giving several options for observing the C-scan image data. The FFT tool is a solid option that 

can be useful for generating TOF values through cross-correlation. The RF waveform storage 

and replay is also very important for changing gates and other settings on the full set of A-scan 

 *

Excel is a registered trademark of Microsoft Corp., Redmond, WA. 

†

SigmaPlot is a registered trademark of Systat, Inc., San Jose, CA. 

‡

Origin is a registered trademark of OriginLab Corporation, Northamption, MA. 
11

data without physically re-running a scan. This is valuable for observing the A-scan data 

associated with the C-scan image map at a selected point for direct comparison. 

The system capabilities are demonstrated with a 15-MHz ultrasound evaluation of an aluminum 

standard containing steps and drilled holes of different sizes and depths (figure 5). As shown in 

the image in the upper left corner of figure 5, the drilled holes in the first column increase in 

diameter and depth from top to bottom while the drilled holes in the second column decrease 

diameter and depth from top to bottom. This standard is useful for testing detectability limits of 

ultrasonic transducers with varying frequencies. A series of A-scans is exhibited over various 

regions of the sample to show the different reflected signals that can occur during point analysis 

evaluation (figure 6). The image to the right of each A-scan shows the transducer position over 

which the A-scan was collected. In figure 6a, a bulk region of the standard is selected to show 

top and bottom surface signals and their reflections. In contrast, the region in figure 6b is chosen 

to show signal changes during evaluation of one of the drilled holes. In this case, there are 

characteristic reflections from the holes and a corresponding reduction in amplitude of the 

bottom surface reflected signal. A-scan evaluations of the steps are shown in figures 6c, 6d, and 

6e. In these A-scans, there is a TOF shift representing the change in distance from the transducer 

to the standard. The top and bottom surface reflected signals become closer together, exhibiting 

smaller TOF differences due to a shorter travel distance of the acoustic waves through the steps. 

In figure 7, B-scan and C-scan TOF images of the aluminum standard are shown. In the C-scan 

image, the TOF differences of the three steps vary in TOF compared to the upper platform. On 

the upper platform, four of the eight drilled holes are resolved, showing increased TOF values as 

the depths of the detected holes increase. The four drilled holes with the smallest diameters are 

5 mm

5 mm

5 mm

5 mm

Figure 5. Aluminum standard sample featuring steps and drilled holes. 
12

 (a) 

 (b) 

 (c)

(a)

Top Surface Signal

Bottom Surface Signal

Top Surface 1st Reflected Signal

Bottom Surface 1st Reflected Signal

Top Surface 2nd Reflected Signal

Top Surface Signal

Bottom Surface Signal

Top Surface 1st Reflected Signal

Bottom Surface 1st Reflected Signal

Top Surface 2nd Reflected Signal

Top Surface Signal

Bottom Surface Signal

Hole Signal Reflection

Top Surface 1st Reflected Signal

Bottom Surface 1st Reflected Signal

Additional Hole Signal Reflections

Top Surface Signal

Bottom Surface Signal

Hole Signal Reflection

Top Surface 1st Reflected Signal

Bottom Surface 1st Reflected Signal

Additional Hole Signal Reflections

Top Surface Signal

Bottom Surface Signal

Top Surface 1st Reflected Signal

Bottom Surface 1st Reflected Signal

Top Surface 2nd Reflected Signal

Top Surface Signal

Bottom Surface Signal

Top Surface 1st Reflected Signal

Bottom Surface 1st Reflected Signal

Top Surface 2nd Reflected Signal

Figure 6. A-scan evaluation of aluminum standard at various positions. 
13

 (d) 

 (e) 

Top Surface Signal

Bottom Surface Signal

Top 1st Reflected Signal

Bottom 1st Reflected Signal

Top 2nd Reflected Signal

Top Surface Signal

Bottom Surface Signal

Top 1st Reflected Signal

Bottom 1st Reflected Signal

Top 2nd Reflected Signal

Top Surface Signal

Bottom Surface Signal

Top 1st Reflected

Bottom 1st Reflected

Top 2nd Reflected

Bottom 2nd Reflected

Top Surface Signal

Bottom Surface Signal

Top 1st Reflected

Bottom 1st Reflected

Top 2nd Reflected

Bottom 2nd Reflected

Figure 6. A-scan evaluation of aluminum standard at various positions (continued). 

not resolved by TOF C-scan imaging at 15 MHz. In addition to the drilled holes, there are also 

four circular regions of complete signal loss due to the presence of four rubber feet in the corners 

of the upper platform. The B-scan images show cross-sectional representations through 

horizontal and vertical lines selected from the C-scan image. The horizontal line intersects the 

steps, which increase in TOF from left to right as the transducer moves further away from the 

sample. This line also intersects the deepest drilled hole, which again corresponds to a high TOF 

value. The vertical line intersects two of the drilled holes, contrasting their depth and TOF 

values. 

Figure 8 shows B-scan and C-scan AMP images. While the TOF images only detect four of the 

drilled holes, the AMP images are able to detect all eight, though the smaller diameter holes are 

more difficult to resolve at 15 MHz. The acoustic wave scattering that dictates the degree of 

attenuation is more sensitive to material inhomogeneties. A higher degree of attenuation 
14

Figure 7. TOF B-scan and C-scan evaluations of aluminum standard. 

Figure 8. AMP B-scan and C-scan evaluations of aluminum standard. 
15

corresponds to a lower bottom surface signal amplitude and these lower amplitude values are 

evident in the areas where the drilled holes are present (figure 8). However, unlike the 

TOF C-scan images, the AMP C-scan images are unable to provide the same amount of depth 

information for either the drilled holes or the steps in the standard. Some depth information is 

evident in the B-scan AMP images in which the depths of the holes and relative heights of the 

steps are observed through the cross-sections of the C-scan image. The horizontal line shows 

slight reductions in amplitude of the steps from left to right. The vertical line successfully 

demonstrates the trend of larger diameter and increasing depth from the top to the bottom of the 

sample. In figure 9, the culmination of the B-scan and C-scan images is utilized to construct a 

three-dimensional representation of the aluminum standard using the aforementioned 3-D postprocessing function. 

Figure 9. AMP 3D construction of aluminum standard. 

In an additional test, the sample is flipped over to an orientation represented by the bottom left 

image in figure 5. However, instead of performing an evaluation at a single frequency, three 

different transducers with frequencies of 10, 15, and 20 MHz are used to contrast detectability. 

Figure 10 shows TOF scans and figure 11 shows AMP scans of the aluminum standard. In the 

TOF scans, as the frequency is increased, the drilled holes become more apparent. At 20 MHz, 

the size, shape, and depth are accurately represented in the C-scan image, while at lower 

frequencies the smaller diameter features are either undetected or only partially detected. For the 

AMP scans, the contrast between the bulk of the sample and the drilled holes increases with 

increasing frequency. At 20 MHz, all eight drilled holes are represented accurately in terms of 

diameter due to an improved detectability at the highest frequency. For evaluation of the 
16

10 MHz 15 MHz 20 MHz

Figure 10. Transducer TOF frequency comparison of aluminum standard at 10, 15, and 20 MHz. 

10 MHz 15 MHz 20 MHz

Figure 11. Transducer AMP frequency comparison of aluminum standard at 10, 15, and 20 MHz. 

aluminum standard sample, the 20 MHz TOF and AMP scans provide the most detailed and 

accurate ultrasound analysis. Figures 6–11 give an example of some of the standard A-scan, 

B-scan, and C-scan ultrasound data that can be collected for evaluation of various test specimens. 

While there are several positive features of the current ultrasound C-Scan imaging setup, there 

are also severe limitations. The first is the inability of the system to utilize transducers with 

frequencies higher than 20 MHz. Many of the new transducers acquired, as well as several of 

the older transducers, have frequencies much higher than 20 MHz, up to 100 MHz, and these 

cannot be utilized due to the current AD-IPR-1210 card. A severe limitation is the scan 

resolution capability of the software. The automatic maximum resolution option is the best 

choice for running any scan because it sets the optimum pixel size for a given area. By basing 

the maximum resolution on the size of the scan region, a larger sample can only be scanned at 

low resolution. However, when the resolution is manually set to a higher resolution than the 

automatic maximum resolution value, the resulting scan produces major processing errors and 

the image cannot be rendered properly. Without these glitches, this would not be an issue since 

manually setting a high resolution should increase the scan time due to collection of more data 

points but should not affect the integrity of the scan itself. It is the inability to use a resolution 
17

below the automatic maximum resolution without experiencing errors that is the underlying 

problem. Another severe limitation is the inability to access the raw A-scan, B-scan, and C-scan 

image data, which prevents sufficient quantitative analysis. While qualitative analysis can be 

conducted by viewing the C-scan images, this option is limited to the range of TOF and AMP 

values set before the scan is run and cannot be altered to target specific values of interest. If the 

internal quantitative analysis package was strong or the raw data could be extracted, this would 

not be an issue. However, internal quantitative analysis is limited to cluster analysis, and the 

inability to extract raw data prevents transfer of x-position, y-position, AMP, and TOF data to a 

separate software package such as SigmaPlot or Origin, which are capable of performing 

extensive quantitative analysis. Since these issues are not only minor inconveniences but major 

limitations, there is a need for an additional system that can address these critical needs. At the 

minimum, an ideal system will have the capability of handling high frequency transducers, 

selecting a high resolution value without sacrificing the scan integrity, and collecting the raw 

C-scan data for proper quantitative analysis. This being said, the current system is sufficient for 

providing C-scan images, A-scan and B-scan data, flexible hardware options, and good 

qualitative capabilities with several unique features, but another system is necessary for full 

comprehensive ultrasound evaluation and quantitative analysis in order to conduct top level 

research. 

5. Summary and Future Considerations 

The current ultrasound system is an important tool for basic nondestructive evaluation. For more 

advanced evaluation and quantitative analysis, upgrading to a system with higher frequency, 

flexible resolution, and data extraction capabilities is necessary. While this paper is limited to 

describing standard systems for utilizing single element transducers and immersion scanning, 

comparatively newer technologies such as phased array and non-contact ultrasound are 

emerging. Non-contact, or air coupled, transducers have traditionally suffered from an inability 

to efficiently transmit acoustic waves through a medium of air. Air creates a large acoustic 

impedance mismatch with a majority of materials, causing a high degree of attenuation that is 

difficult to overcome. However, specialized transducers and signal processing methods are 

under development for providing increased sensitivity to reflected ultrasound signals. Noncontact ultrasound can eliminate the need for immersion of samples, especially those that are 

sensitive to water infiltration such as green ceramics. 

Another technique is linear or phased array ultrasound. By increasing the number and reducing 

the size of transducer elements, a linear array or phased array transducer can be assembled. 

These smaller individual elements can be driven independently so that parameters such as array 

firing order, element selection, and pulse delay can be controlled. By pulsing elements 

simultaneously, depth of focus can be controlled for evaluating the test specimen at different 
18

depths without changing the mechanical position of the transducer. Dynamic ultrasound beam 

control and steering can also be achieved by pulsing individual elements at slightly different 

times to control beam angle, focal distance, and focal spot size. Dynamic beam control is 

advantageous for inspecting components with complex shapes and for detecting defects of 

irregular shapes or multiple features along the perpendicular beam axis that would be difficult to 

detect using single element transduction. Electronic scanning can also be achieved using linear 

and phased array transducers by controlling the firing order of individual elements or groups of 

adjacent elements. This not only leads to faster inspection times, but also reduces the amount of 

mechanical transducer manipulation required for evaluating a large part. However, there are also 

disadvantages to utilizing phased array ultrasound. Since it is more difficult to fabricate the 

smaller elements that make up the linear and phased arrays, the cost is much higher than a single 

element transducer. With a large number of elements, there is a greater risk that the dimensions 

of the elements will vary slightly, increasing the degree of error involved since the frequencies 

and other parameters may change for different elements. Current linear and phased array 

transducers are incapable of achieving frequencies higher than 20–25 MHz, which limits the 

detection of defects. As the fabrication methods improve for producing specialized linear and 

phased array transducers, it is believed that the transducer frequencies will increase and the costs 

will be reduced. If this is achieved in the future, these transducers will be ideal due to their 

advantages of faster inspection times of complex parts at multiple angles and depths. These 

techniques will continue to be explored and implemented as technological advances are made. It 

is in this way that state-of-the-art ultrasound research can be achieved for successful 

nondestructive evaluation and quantitative analysis. 
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