# US 10,309,934 B2 · Method and system of deducing sound velocity using time-of-flight of surface wave

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- Number: US 10,309,934 B2
- Document ID: US10309934B2
- Status: Granted
- Kind: B2
- Application number: 15/472,449
- Filed: 2017-03-29
- Published: 2018-10-04
- Granted: 2019-06-04
- Earliest claimed: 2017-03-29
- Assignees: Olympus Scientific Solutions Americas Inc.
- Applicants: Cécile Brütt; Guillaume Painchaud-April; Chi-Hang Kwan; Benoit Lepage
- Inventors: Cécile Brütt; Guillaume Painchaud-April; Chi-Hang Kwan; Benoit Lepage
- Web page: https://patentgrep.com/patent/US10309934B2

## CPC

- G01N 29/07: by measuring propagation velocity or propagation time of acoustic waves
- G01N 29/0645: {Display representation or displayed parameters, e.g. A-, B- or C-Scan}
- G01N 29/262: {by electronic orientation or focusing, e.g. with phased arrays (phased arrays per se G10K11/34)}
- G01N 29/30: Arrangements for calibrating or comparing, e.g. with standard objects
- G01N 2291/011: Velocity or travel time
- G01N 2291/0423: Surface waves, e.g. Rayleigh waves, Love waves
- G01N 2291/102: one emitter, one receiver
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)

## Abstract

Disclosed is an ultrasonic non-destructive testing and inspection system and method for determining acoustic velocities in a test object. Beams of acoustic energy from firing an element of an emitting probe propagate in a first wedge, and a beam incident at the critical angle generates a surface wave in the test object. The surface wave propagates to a second wedge and signals are received at receiving elements of a receiving probe array. When a set of appropriate delays is applied to the receiving elements, the acoustic time-of-flight is the same to all receiving elements. Determination of the appropriate delays and the times-of-flight for P-type surface waves and Rayleigh surface waves enables computation of the P- and S-wave acoustic velocities in the test object. The time-of-flight measurement also enables computation of the separation between the first and second wedges.

## Claims

### Claim 1

A method of determining ultrasonic velocity in a test object using an ultrasonic measurement system, the system having an emitting probe operable with an emitting wedge and a receiving probe operable with a receiving wedge, the wedges configured to be in contact with a test surface of the test object, wherein the receiving probe is an array probe having a number N of receiving elements, the receiving elements designated element (n) for n=1 to N, the method comprising the steps of:
obtaining known parameters for the probes and the wedges;
firing at least one emitting element of the emitting probe, thereby causing the at least one emitting element to emit beams of ultrasonic energy into the emitting wedge, including a critical beam at a critical angle which generates a surface wave of ultrasonic energy propagating near the test surface in the test object towards the receiving wedge;
receiving corresponding A-scans from each element (n) of the receiving probe, the A-scans comprising amplitudes of received echo signals as a function of arrival times at each element (n); and,
determining at least one surface wave velocity of the surface wave, and,
wherein the known parameters comprise the number N of the receiving elements, a pitch p, wherein p is the distance between adjacent receiving elements, an emitting wedge angle θw′ of the emitting wedge, a receiving wedge angle θw of the receiving wedge, and a wedge velocity Vw, wherein Vw is the velocity of longitudinal waves in the receiving wedge.

### Claim 2 (depends on 1)

The method of claim 1 wherein the at least one surface wave velocity is a longitudinal wave (P-wave) velocity VP of a P-type surface wave.

### Claim 3 (depends on 1)

The method of claim 1 wherein the at least one surface wave velocity is a longitudinal wave (P-wave) velocity VP of a P-type surface wave and a Rayleigh wave velocity VR of a Rayleigh surface wave.

### Claim 4 (depends on 3)

The method of claim 3 further comprising the step of calculating a shear wave (S-wave) velocity VS in the test object based on the P-wave velocity and the Rayleigh wave velocity.

### Claim 5 (depends on 4)

The method of claim 4 wherein the step of calculating the S-wave velocity further comprises the step of calculating the S-wave velocity VS in accordance with the following equation
(
2
-
v
R
2
v
S
2
)
2
-
4
*
(
1
-
v
R
2
v
P
2
)
1
2
*
(
1
-
v
R
2
v
S
2
)
1
2
=
0.

### Claim 6 (depends on 3)

The method of claim 3 wherein the receiving wedge angle is zero, and wherein the calculated P-wave velocity VP and the calculated Raleigh wave velocity VR are independent of the wedge velocity VW.

### Claim 7 (depends on 3)

The method of claim 3 further including the steps of:
defining a P-wave region of interest in each of the A-scans, the P-wave region of interest corresponding to approximate P-wave arrival times of P-wave signals generated by the P-type surface wave and being based on at least one nominal P-wave mode property;
finding a set of P-wave reception delays to be applied to each element (n), wherein, after application of the P-wave reception delays, P-wave time-of-flight measurements from the at least one emitting element of the emitting probe to each element (n) of the receiving probe are equal to a constant P-wave time-of-flight τP for all n from 1 to N; and,
calculating the P-wave velocity from the set of P-wave reception delays and the known parameters.

### Claim 8 (depends on 7)

The method of claim 7 wherein the at least one nominal P-wave mode property is that the P-type surface wave has a high acoustic velocity and comprises earliest received echo signals in the A-scans.

### Claim 9 (depends on 7)

The method of claim 7 wherein the set of P-wave reception delays comprises P-wave reception delays which vary linearly as a function of n, and a nth P-wave reception delay is equal to εP*n wherein εP is a constant, and wherein the step of calculating the P-wave velocity comprises calculating the P-wave velocity VP in accordance with the following equation
ɛ
P
=
p
v
w
*
(
sin
⁢
⁢
θ
w
*
1
-
(
v
w
v
P
)
2
-
(
v
w
v
P
)
*
cos
⁢
⁢
θ
w
)
.

### Claim 10 (depends on 7)

The method of claim 7 further comprising the step of measuring a separation distance S between a first surface of the emitting wedge and a second surface of the receiving wedge, the measurement being based on the constant P-wave time-of-flight τP and the P-wave velocity VP.

### Claim 11 (depends on 10)

The method of claim 10 wherein the first surface and the second surface are perpendicular to the test surface and wherein the step of determining the separation distance S comprises the steps of:
performing a reference acquisition to measure a reference propagation delay τ0; and,
calculating the separation distance S according to the following equation
S=vP*(τP−τ0).

### Claim 12 (depends on 11)

The method of claim 11 wherein the step of performing a reference acquisition further comprises the steps of:
placing the emitting wedge and the receiving wedge at a zero separation distance wherein the first surface is in contact with the second surface;
firing the at least one emitting element of the emitting probe;
receiving corresponding A-scans from each element (n) of the receiving probe;
defining a P-wave region of interest in each of the A-scans;
finding a set of reference reception delays to be applied to each element (n), wherein after application of the reference reception delays a measured reference P-wave time-of-flight from the at least one emitting element of the emitting probe to each element (n) of the receiving probe is a constant reference time-of-flight for all n from 1 to N;
setting the reference propagation delay τ0 equal to the constant reference time-of-flight; and,
placing the emitting wedge and the receiving wedge at the separation distance S, wherein the emitting wedge and the receiving wedge are at locations on the test surface convenient for NDT/NDI of the test object.

### Claim 13 (depends on 3)

The method of claim 3 wherein the step of calculating the Rayleigh wave velocity further includes the steps of:
defining a Rayleigh wave region of interest in each of the A-scans, the Rayleigh wave region of interest corresponding to approximate Rayleigh wave arrival times of Rayleigh wave signals generated by the Rayleigh surface wave and being based on at least one nominal Rayleigh wave mode property;
finding a set of Rayleigh reception delays to be applied to each element (n), wherein, after application of the Rayleigh reception delays, a measured Rayleigh wave time-of-flight from the at least one emitting element of the emitting probe to each element (n) of the receiving probe is a constant Rayleigh wave time-of-flight τR for all n from 1 to N; and,
calculating the Rayleigh wave velocity from the set of Rayleigh reception delays and the known parameters.

### Claim 14 (depends on 13)

The method of claim 13 wherein the at least one nominal Rayleigh wave mode property is that the Rayleigh surface wave has a lower acoustic velocity than the P-type surface wave and that there is an approximately known velocity ratio of the Rayleigh wave velocity to the P-wave velocity, enabling the approximate Rayleigh wave arrival times to be calculated.

### Claim 15 (depends on 13)

The method of claim 13 wherein the set of Rayleigh reception delays comprises Rayleigh reception delays which vary linearly as a function of n, and a nth Rayleigh reception delay is equal to εR*n wherein εR is a constant, and wherein the step of calculating the Rayleigh wave velocity comprises calculating the Rayleigh wave velocity VR in accordance with the following equation
ɛ
R
=
p
v
w
*
(
sin
⁢
⁢
θ
w
*
1
-
(
v
w
v
R
)
2
-
(
v
w
v
R
)
*
cos
⁢
⁢
θ
w
)
.

### Claim 16 (depends on 1)

The method of claim 1 wherein the ultrasonic measurement system is an ultrasonic non-destructive testing and inspection (NDT/NDI) system, and the method is activated during a NDT/NDI operation.

### Claim 17 (depends on 1)

The method of claim 1 wherein the emitting probe is a single element probe.

### Claim 18 (depends on 1)

The method of claim 1 wherein the emitting probe is an array probe.

### Claim 19 (depends on 18)

The method of claim 18 wherein the steps of the method are performed twice, a first time with a first probe configured as the emitting probe and a second probe configured as the receiving probe, and a second time with the second probe configured as the emitting probe and the first probe configured as the receiving probe.

### Claim 20 (depends on 1)

The method of claim 1 wherein the emitting wedge angle is equal to the receiving wedge angle.

### Claim 21

An ultrasonic measurement system for measuring ultrasonic velocity, the system comprising:
an emitting probe operable with an emitting wedge and a receiving probe operable with a receiving wedge, wherein the receiving probe is an array probe having a number N of receiving elements, the receiving elements designated element (n) for n=1 to N, and wherein the wedges are configured to be in contact with a test surface of a test object;
a known parameter unit for storing known parameters for the probes and the wedges;
an acquisition unit configured to fire at least one emitting element of the emitting probe, thereby causing the at least one emitting element to emit beams of ultrasonic energy into the emitting wedge, including a critical beam at a critical angle which generates a surface wave propagating near the test surface in the test object towards the receiving wedge, the acquisition unit further configured to receive corresponding A-scans from each element (n) of the receiving probe, the A-scans comprising amplitudes of received echo signals as function of arrival times at each element (n); and,
at least one velocity unit configured to determine at least one surface wave velocity of the surface wave, and,
wherein the known parameters comprise the number N of the receiving elements, a pitch p, wherein p is the distance between adjacent receiving elements, an emitting wedge angle θw′ of the emitting wedge, a receiving wedge angle θw of the receiving wedge, and a wedge velocity Vw, wherein Vw is the velocity of longitudinal waves in the receiving wedge.

### Claim 22 (depends on 21)

The system of claim 21 wherein the at least one velocity unit is a P-wave velocity unit and the at least one surface wave velocity is a longitudinal wave (P-wave) velocity VP of a P-type surface wave.

### Claim 23 (depends on 21)

The system of claim 21 wherein the at least one velocity unit is a P-wave velocity unit and a Rayleigh wave velocity unit and the at least one surface wave velocity is a longitudinal wave (P-wave) velocity VP of a P-type surface wave and a Rayleigh wave velocity VR of a Rayleigh surface wave.

### Claim 24 (depends on 23)

The system of claim 23 further comprising a shear wave (S-wave) velocity calculator configured to calculate an S-wave velocity VS in the test object based on the P-wave velocity and the Rayleigh wave velocity.

### Claim 25 (depends on 24)

The system of claim 24 wherein the S-wave velocity calculator is further configured to calculate the S-wave velocity VS in accordance with the following equation
(
2
-
v
R
2
v
S
2
)
2
-
4
*
(
1
-
v
R
2
v
P
2
)
1
2
*
(
1
-
v
R
2
v
S
2
)
1
2
=
0.

### Claim 26 (depends on 23)

The system of claim 23 wherein the receiving wedge angle is zero, and wherein the calculated P-wave velocity VP and the calculated Raleigh wave velocity VR are independent of the wedge velocity VW.

### Claim 27 (depends on 23)

The system of claim 23 wherein the P-wave velocity unit further comprises:
a P-wave region of interest estimator configured to define a P-wave region of interest in each of the A-scans, the P-wave region of interest corresponding to approximate P-wave arrival times of P-wave signals generated by the P-type surface wave and being based on at least one nominal P-wave mode property;
a P-wave delay finding unit configured to find a set of P-wave reception delays to be applied to each element (n), wherein after application of the P-wave reception delays a measured P-wave time-of-flight from the at least one emitting element of the emitting probe to each element (n) of the receiving probe is a constant P-wave time-of-flight τP for all n from 1 to N; and,
a P-wave velocity calculator configured to calculate the P-wave velocity from the set of P-wave reception delays and the known parameters.

### Claim 28 (depends on 27)

The system of claim 27 wherein the at least one nominal P-wave mode property is that the P-type surface wave has a high acoustic velocity and comprises earliest received echo signals in the A-scans.

### Claim 29 (depends on 27)

The system of claim 27 wherein the set of P-wave reception delays comprises P-wave reception delays which vary linearly as a function of n, and a nth P-wave reception delay is equal to εP*n wherein εP is a constant, and wherein the step of calculating the P-wave velocity comprises calculating the P-wave velocity VP in accordance with the following equation
ɛ
P
=
p
v
w
*
(
sin
⁢
⁢
θ
w
*
1
-
(
v
w
v
P
)
2
-
(
v
w
v
P
)
*
cos
⁢
⁢
θ
w
)
.

### Claim 30 (depends on 27)

The system of claim 27 further comprising a probe separation calculator configured to measure a separation distance S between a first surface of the emitting wedge and a second surface of the receiving wedge, wherein the first surface and the second surface are perpendicular to the test surface, and wherein the measurement of the separation distance S is based on the constant P-wave time-of-flight τP and the P-wave velocity VP.

### Claim 31 (depends on 30)

The system of claim 30 further comprising a reference acquisition unit configured to determine a reference propagation delay τ0, wherein the reference acquisition unit comprises:
a zero separation A-scan acquisition unit configured to fire the at least one emitting element of the emitting probe an
d to receive corresponding A-scans from each element (n) of the receiving probe;
a reference region of interest estimator configured to define a P-wave region of interest in each of the A-scans;
a reference delay finding unit configured to find a set of reference reception delays to be applied to each element (n), wherein, after application of the reference reception delays, measured reference times of flight from the at least one emitting element of the emitting probe to each element (n) of the receiving probe are a constant reference time-of-flight for all n from 1 to N, and wherein the reference propagation delay τ0 is equal to the constant reference time-of-flight.

### Claim 32 (depends on 31)

The system of claim 31 wherein the probe separation calculator calculates the separation distance S according to the following equation
S=vP*(τP−τ0).

### Claim 33 (depends on 23)

The system of claim 23 wherein the Rayleigh velocity unit further comprises:
a Rayleigh region of interest estimator configured to define a Rayleigh wave region of interest in each of the A-scans, the Rayleigh wave region of interest corresponding to approximate Rayleigh wave arrival times of Rayleigh wave signals generated by the Rayleigh surface wave and being based on at least one nominal Rayleigh wave mode property;
a Rayleigh delay finding unit configured to find a set of Rayleigh reception delays to be applied to each element (n), wherein after application of the Rayleigh reception delays a measured Rayleigh wave time-of-flight from the at least one emitting element of the emitting probe to each element (n) of the receiving probe is a constant Rayleigh time-of-flight τR for all n from 1 to N;
a Rayleigh velocity calculator configured to calculate the Rayleigh wave velocity from the set of Rayleigh reception delays and the known parameters.

### Claim 34 (depends on 33)

The system of claim 33 wherein the at least one nominal Rayleigh wave mode property is that the Rayleigh surface wave has a lower acoustic velocity than the P-type surface wave and that there is an approximately known velocity ratio of the Rayleigh wave velocity to the P-wave velocity, enabling the approximate Rayleigh wave arrival times to be calculated.

### Claim 35 (depends on 33)

The system of claim 33 wherein the set of Rayleigh reception delays comprises Rayleigh reception delays which vary linearly as a function of n, and a nth Rayleigh reception delay is equal to εR*n wherein εR is a constant, and wherein the step of calculating the Rayleigh wave velocity comprises calculating the Rayleigh wave velocity VR in accordance with the following equation
ɛ
R
=
p
v
w
*
(
sin
⁢
⁢
θ
w
*
1
-
(
v
w
v
R
)
2
-
(
v
w
v
R
)
*
cos
⁢
⁢
θ
w
)
.

### Claim 36 (depends on 21)

The system of claim 21 wherein the ultrasonic measurement system is an ultrasonic non-destructive testing and inspection (NDT/NDI) system, and the method is activated during a NDT/NDI operation.

### Claim 37 (depends on 21)

The system of claim 21 wherein the emitting probe is a single element probe.

### Claim 38 (depends on 21)

The system of claim 21 wherein the emitting probe is an array probe.

### Claim 39 (depends on 38)

The system of claim 38 wherein the acquisition unit is further configured to acquire A-scans a first time with a first probe configured as the emitting probe and a second probe configured as the receiving probe, and a second time with the second probe configured as the emitting probe and the first probe configured as the receiving probe.

### Claim 40 (depends on 21)

The system of claim 21 wherein the emitting wedge angle is equal to the receiving wedge angle.