Ultrasonic radio frequency tone-bursts are launched into a sample of material tested. The amplitude of the tone-bursts and the slope of the resulting static displacement pulses are measured. These measurements are used to calculate the nonlinearities of the materials

Cantrell, John H., Jr.

Yost, William T.

English

NASA Technical Reports Server

United States Patent [19] [11] Patent Number: 4,649,750 
Cantrell, Jr. et al. [45] Date of Patent: Mar. 17, 1987 
ACOUSTIC RADIATION STRESS 
MEASUREMENT 
Inventors: John H. Cantrell, Jr.; William T. 
Yost, both of Newport News, Va. 
Assignee: The United States of America as 
represented by the Administrator of 
the National Aeronautics and Space 
Administration, Washington, D.C. 
Appl. No.: 775,989 
Filed: Sep. 13,1985 
Int. (3.4 ............................................. GOlN 29/00 
U.S. Cl. ..................................... 73/59; 73/1 DV 
Field of Search .............. 73/597, 599, 1 DV, 602 
References Cited 
U.S. PATENT DOCUMENTS 
4,312,228 1/1982 Wohltjen .............................. 73/597 
4,399,702 8/1983 Suzuki ................................... 73/597 
RECTIFIER 
SAMPLE/ 
FILTER 
VOLTMETER 
4,452,082 6/1984 Miwa .................................... 73/599 
4,471,657 9/1984 Voris et al. ........................... 73/597 
4,522,071 6/1985 Thompson ............................ 73/597 
OTHER PUBLICATIONS 
R. T. Smith, “Stress-Induced Anisotropy in Solids the 
Acousto-Elastic Effect”, Ultrasonics, pp. 135-147, Jul- 
.-Sep. 1963. 
Primary Examiner-Stephen A. Kreitman 
Attorney, Agent, or Firm-George F. Helfrich; John R. 
Manning; Robert D. Marchant 
1571 ABSTRACT 
Ultrasonic radio frequency toneburst are launched into 
a sample of material tested. The amplitude of the tone- 
bursts and the slope of the resulting static displacement 
pulses are measured. These measurement are used to 
calculate the nonlinearities of the material. 
10 Claims, 1 Drawing Figure 
7 
https://ntrs.nasa.gov/search.jsp?R=19870012220 2020-03-23T15:28:23+00:00Z
U.S. Patent Mar. 17,1987 4,649,750 
1 
4,649,750 
2 
BRIEF DESCRIPTION OF THE DRAWING 
The sole FIGURE is a drawing of the apparatus used 
to measure the amplitude of the toneburst and the slope 
5 of the static displacement pulse. 
DETAILED DESCRIPTION OF THE 
INVENTION 
ACOUSTIC RADIATION STRESS MEASUREMENT 
ORIGIN OF THE INVENTION 
The invention herein was made by employees of the 
United States Government and may be manufactured 
and used by or for the Government for governmental 
purposes without the p a p e n t  of any royalties thereon Turning now to the drawing of the apparatus for 
or therefor. 10 illustrating the invention, the number 11 designates a 
sample of the material whose nonlinear parameters are 
to be measured. A 30-MHz rf signal from a continuous- BACKGROUND OF THE INVENTION 
The invention relates generally to acouStiC radiation wave oscillator 12 is combined in a mixer 13 with a 
stress measurements and more specifically concerns a gating pulse from a logic and timing generator 14. The 
method and apparatus for quantitatively characterizing 15 logic and timing generator 14 counts down from the 
those properties of fluids and solids related to material oscillator 12 reference to time the generation of the 
nonlinearity. gating pulse to the mixer 13. The length of the gating 
Each material has a unique set of nonlinearity param- pulse is set such that the resulting gated rf signal from 
eters that characterizes that material and which are mixer 13 is composed Of an integral number of 30-MHz 
related to the thermodynamic state of that material. The 2o CYCla .  such an arrangement assures Phase coherence of 
thermodynamic state is here generalized to include the each rf pulse. The gated rf pulse is fed through a 8.5- 
degree of residual or applied stress, the atomic or mo- high pass filter l5 to remove any leakage Of the 
lecular composition of the material, defect structures, gating pulse the mixer 13* The rf pulse is amp1i- 
and the state of material order or disorder. The no&- 25 fied by a broadband linear rf amplifier l6 and is used to drive a 30-MHz narrow-based lithium niobate 
transducer 17 bonded to one end of sample 11. The earity parameter thus serves as an important and distinct measure of the material state that is both complemen- transducer 17 generates a gated 30-MHz ultrasonic 
ple 11. The toneburst is received by a broadband air-gap tic attenuation measurements. 
ble for acoustic waveform distortion leading to acoustic 
harmonic generation (the harmonics of the fundamental The capacitive transducer 18 is a parallel plate ar- 
driving frequency) and acoustic radiation-induced Static rangement in which the end surface 19 functions 
strains in the material. The acoustic radiation induced as the ground plate. The other plate 20 is an optically 
static strains are a manifestation of the acoustic radia- 35 flat electrode which is recessed approximately 7 pm 
tion stress in the material. The previous art has been to from the sample surface. A dc bias 21 of 50 V is applied 
measure the nonlinearity parameters by means of a har- through a 1-M ohm resistor 22 to plate 20. It is known 
monic generation method. The harmonic generation that the measurement of the output voltage from such a 
method, however, is sensitive to phase cancellation capacitive arrangement may be converted to a displace- 
&facts in the transducer and cannot & r e  unambiguous ment measurement Of the sample Surface UShg the rela- 
values for the sign of the nonlinearity parameters with- tion 
out the addition of a phase detection system which must 
be calibrated to a standard sample. 
method and apparatus for measuring the 'Onlinear pa- 
rameters of a material that characterize that material. 
Another object Qf this invention is to provide a 
method and apparatus for quantitatively characterizing 
those properties of fluids and solids related to material 50 
nonlinearity without the addition of a phase detection 
system. 
Other objects and advantages of this invention will 
become apparent hereinafter in the specification and 
drawing. 
SUMMARY OF THE INVENTION 
tarY and supplemenw to and acous- signal or toneburst which propagates through the sam- 
Operationally, the nonlinearity Parameter is reswnsi- 30 capacitive transducer 18 at the opposite end of the sam- 
(1) vd= v&U/S) 
It is the Primary Object Of this invention to provide a 45 Where Vd is the output voltage, Vb is the dc volt- 
age, u is the displacement of the sample surface, and s is 
the gap spacing beween the capacitor plates 19 and u). 
The capacitive transducer 18 is capable of m F e g  
&placement amplitude of the order of 10-4 A. 
The theory on which this invention is b& is found 
in Physical Review B, Volume 30, Number 6, Sept. 15, 
1984, pages 3221-3227. This theory predicts that an 
acoustic toneburst propagating through a solid gener- 
ates a radiation-induced static pulse having the shape of 
55 a right-angled triangle. The slope of the triangular pulse 
is dependent upon the frequency and amplitude of the 
toneburst as well as the acoustic nonlinearity parameter 
of the solid. The theory can be stated mathematically as ultrasonic radio frequency Q tonebursts are 
launched into a sample of the material tested. These 6o 
tonebursts generate low frequency static displacement 
pulses having the shape of a right angled triangle. The 
amplitude of the tonebursts and the slope of the right were B~ is the is the slope of 
angled triangle are measured and these n ~ a s ~ e m e n t s  the radiation-induced static pulse, Pi is the amplitude of 
are used to calculate the acoustic nonlinear parameter 65 the toneburst, Co is the small-amplitude sound wave 
of the material. The polarization of the toneburst can be velocity and k is the propagation number which is equal 
varied to give a different acoustic nonlinear parameter to w/C, where w is the frequency of oscillator 12 as 
for each polarization. indicated by a counter 23. The subscript j = 1,2,3 is the 
Bj= [-4m/(kz(~)zCo)] (2) 
4,649,750 
3 
index of polarization of the acoustic wave correspond- 
ing to one quasilongitudinal and two quasitransverse 
modes. The polarization is introduced by transducer 17 
as is well known in the art. The value for Pj in equation 
(2) can be determined by measuring the amplitude Vdof 
the rf output at plate 20 and solving equation (1) for u 
which corresponds to Pj. The remaining circuitry in the 
drawing is for measurhg Vdand the slope of the radia- 
tion hduced static pulse. 
The displacement amplitude of the rf tomeburst is 
obtained by placing switches 24,25, and 26 in the posi- 
tions shown. Consequently, the output form transducer 
18 is fed through a capacitor 27 into a 30 MHz amplifier 
28. The output from the amplifier 28 is sent into a recti- 
fier and filter assembly 29 which converts the 30-MHz 
toneburst into a detected signal. The rectifier and filter 
assembly also contains a sample and hold circuit which, 
when strobed, holds the voltage of the detected signal. 
The strobe signal is set by the logic and timing circuit 14 
and is adjusted to coincide with the center of the first 
toneburst through the sample 11 following the electrical 
drive pulse to the transducer (Le. the first ultrasonic 
echo). The output of the sample and hold is measured 
by a voltmeter 30 and recorded. 
The capacitive transducer 18 is now switched out and 
a Thevenin equivalent network 31 is switched into the 
circuit by means of switch 24. The parameters of the 
Thevenin equivalent network 31 are set to match the 
appropriate values of the capacitive transducer 18. The 
resistor 22 is removed from the bias source 21 and that 
end grounded by means of switch 25 to prevent electri- 
cal surges through the circuits which may damage the 
instruments. A substitutional 30-MHz calibration signal 
32 is now switched, by means of a switch 33, into the 
Thevenin equivalent network 31 and adjusted in ampli- 
tude until the Voltmeter 30 reads the same value as that 
of the ultrasonic toneburst measurement. Since the am- 
plitude of the 30-MHz calibration signal 32 is measured 
at the input to the Thevenin equivalent network 31, the 
measured value is equal to the signal voltage produced 
by the capacitive transducer 18. 
In order to display the acoustic-radiation-iYlduced 
static displacememt pulse the output of the capacitive 
tramsducer 18 is connected throngh switch 24 to a 
Princeton Applied Research Model-113 low frequency 
(3-300 kHz) amplifier 34 by switch 26 and a short, low 
capacitance lead 35. The narrow band width is neces- 
sary to reduce electrical noise in the measurement of the 
small static displacement signal. The output of the am- 
plifier 34 is sent to an oscilloscope 36 where the static 
displacement signal is displayed. A template (not 
shown) is placed over the screen to record the static 
pulse shape. 
The measurement of the slope of the static displace- 
ment pulse is performed by grounding resistor 22 by 
means of switch 25 and switching to the Thevenin 
equivalent network 31 by means of switch 24. A static 
displacement calibration signal 37 (Hewlett-Packard 
3614% function generator) havimg the shape of a right- 
angled triamgle is connected to the Thevenin equivalent 
network 31 by means of switch 33. The amplitude and 
width (reciprocal frequency) of the calibration signal is 
adjusted until the slope is identical to that of the acous- 
tic-radiation-induced static displacement pulse. The 
slope of the static displacement pulse is readily obtained 
from the measured calibration signal and is expressed in 
units of displacement per unit of time using equation (1). 
Switch 38 is for connecting rectifier filter 29 to the 
4 
oscilloscope 36 while the amplitude of the toneburst is 
being measured. 
The advantage of this invention is that is can be used 
to characterize material nonlinearity in solids and liq- 
5 uids and uncover material properties not previously 
known. The invention is expected to become an impor- 
tant research tool in the understanding of material prop- 
erties. With appropriate refinements the invention may 
serve as a field moonitor for the EdBE of material proper- 
In a stress free isotropic solid the shear wave modin- 
earity parameter is zero. When the isotropic solid has 
applied or residual stresses the shear wave nonlinearity 
parameter becomes non-zero because of stress induced 
15 anisotropy. In such a case the value of the nonlinearity 
parameter becomes a measure of the stress field in a 
solid when compared to the stress free isotropic solid. 
Alternative embodiments of the invention pertain 
primarily to the specific methods for detection of the 
20 acoustic signals. For example, rather than using a 
broadband capacitance transducer as was used in the 
prototype model, a calibrated point contact transducer 
having an appropriately large bandwidth extending to 
low frequencies may be employed or an optical trans- 
25 ducer employing a phase Retrodyning scheme may be 
used. 
For tramsparent media the Raman-Nath diffraction 
technique using coherent light hpimging at right angles 
to the acoustic propagation direction may be employed. 
30 The essential feature of the detection system is that it 
must be capable of measuring absolute amplitudes of the 
acoustic signals for absolute measurement of the nonlin- 
earity parameter. For applications such as acoustic im- 
aging where only relative values of the nodinearity 
35 parameters are of interest the absolute amplitude re- 
quirement may be relaxed. 
10 ties related to strength and residual/applied stresses. 
What is claimed is: 
1. A method for measuring the nonlinear characteriz- 
providing a material to be analyzed; 
applying a gated rf ultrasonic signal to a m p l e  of 
said material at several different polarka~ows; 
measuring the amplitude of said gated rf dtrasonaic 
sign4 
measuring the dope of the static displacememt pulse 
generated by said gated rf ultrasonic signal; and 
calculating the nonlinear characterizing parameter by 
using said measured amplitude and slope in the 
following equation: 
ing parameters of a material comprising the steps of: 
4 
45 
50 
@j= [-4m/(k*(qYCo1 
where B is the nonlinear characterizing parameter; 
the j index represents the polarization of said gated 
rf ultrasonic signa k=w/C, where w is the fre- 
quency of the gated rf ultrasonic signal; Co is the 
small-amplitude sound wave velocity; Pj is the am- 
plitude of the gated rfultrasonie signal; and m is the 
slope of the static displacement pulse generated by 
said gated rf ultrasomic signal. 
2. A method according to claim 1 wherein the step of 
measuring the amplitude of said rf ultrasonic signal 
comprises the steps of changing the rf ultrasonic signal 
to an rf electrical signal, rectifying the rf electrical sig- 
65 nal, measuring the amplitude of the rectified signal, 
rectifying and measuring an rf calibration signal and 
changing the amplitude of the rf calibration signal until 
the two rectified signals are equal. 
55 
60 
5 
4,649,750 
6 
3. A method according to claim 1 wherein the step of 
measuring the slope of the static displacement pulse 
comprises the steps of producing a picture of the slope 
of the static displacement pulse, producing a picture of 
a static displacement calibration signal and varying the 
slope of the static displacement calibration signal until 
the two pictures coincide. 
4. A method according to claim 1 including the fur- 
placement pulse generated by said gated rf ultrasonic 
signal. 
6. Apparatus according to claim 5 wherein said sec- 
ond transducer is a broadband air-gap capacitive trans- 
7. Apparatus according to claim 6 wherein said means 
for measuring the rf amplitude of said output signal 
comprises an rf calibration signal that is adjustable in 
5 ducer. 
ther step of comparing the amplitude and slope mea- amplitude connected to a Thevenin equivalent network, 
surements of the material with a stress free isotropic 10 a switch means for selecting the output from said sec- 
solid whose shear wave nonlinearity parameter is zero ond transducer or the output from said Thevenin equiv- 
to measure the stress field in the solid being tested. alent network and means for measuring the rfamplitude 
5. Apparatus for measuring the nonlinear charactek- at the output of said switch means whereby the rf ampli- 
ing parameters of a material comprising: tude of said output signal can be measured by compar- 
means for generating a gated rf signal; 
first transducer means for applying said gated rf sig- 8. Apparatus according to claim 7 wherein said means 
nal to a sample of said material at several different for measuring the rf amplitude at the output of said 
polarizations to produce gated rf ultrasonic sign& switch means includes an rf amplifier, a rectifier fdter 
in said sample; and a voltmeter. 
second transducer means for receiving said gated rf 20 9. Apparatus according to Chim 6 wherein said means 
ultrasonic signal and converting it to an output for measuring the low frequency slope Of said output 
signal; signal comprises a right angled function generator with 
means for measuring the amplitude Qf said output its output applied to a Thevenin equivalent network, 
signal; switch means for selecting the output from said second 
means for measuring the slope of A d  output signal; 25 transducer or the output from said Thevenin equivalent 
means for calculating said nonlinear characterizing network and means for measuring the low frequency 
slope at the output of said switch means whereby the 
low frequency slope at the output of said second trans- 
ducer can be measured by comparing it with the known 
30 slope of the output of the right angled function genera- 
tor. 
10. Apparatus according to claim 9 wherein said 
means for measuring the low frequency slope at the 
output of said switch means includes a low frequency 
15 ing it with the rf calibration signal. 
parameter by using the following equation: 
Bj= [-4m/(k*(qyCo)l 
where B is the nonlinear characterizing parameter; the j 
index represents the polarization of said gated rf ultra- 
sonic signal; k=w/Co, where w is the frequency of the 
gated rf ultrasonic signal; C, is the small-amplitude 
sound wave velocity; Pjis the amplitude of the gated rf 35 amplifier and an oscilloscope. 
ultrasonic signal; and m is the slope of the static dis- * * * * *  
45 
50 
\ 
55 
65 


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