Apparatus and method for evaluating the physical properties of a sample using ultrasonics
First Claim
1. A method of evaluating the physical properties of a sample, comprising:
- generating an ultrasound field in a local region of the sample with non-contact source such that the generated ultrasound diffuses away from said local region;
waiting until the generated ultrasound field has reached a diffusion regime wherein the ultrasound field has locally populated all ultrasonic modes with substantially equal probability;
monitoring the evolution of the resulting ultrasound field with a non-contact detector while said ultrasound field is in the diffusion regime; and
adjusting parameters in a mathematical model describing the predicted behavior of the ultrasound field in the diffusion regime to fit the detected behavior of the ultrasound field to the mathematical model and thereby derive at least one parameter dependent on the physical properties of the sample.
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Abstract
A method is disclosed for evaluating the physical properties of a sample, for example, the grain size in a polycrystalline material. An ultrasound field is generated in a local region of the sample with a non-contact source, such as a pulsed laser, such that the generated ultrasound diffuses away from said local region. After waiting until the generated ultrasound field has reached a diffusion regime, the resulting ultrasound field is measured with a non-contact detector. Parameters are adjusted in a mathematical model describing the predicted behaviour of the ultrasound field in the diffusion regime to fit the detected ultrasound field to the mathematical model. In this way, parameters dependent on the physical properties of the sample, such as the diffusion coefficient and absorption coefficient, can be derived. The grain size, for example, can be estimated from these parameters preferably by calibrating the diffusion coefficient to grain size.
47 Citations
33 Claims
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1. A method of evaluating the physical properties of a sample, comprising:
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generating an ultrasound field in a local region of the sample with non-contact source such that the generated ultrasound diffuses away from said local region;
waiting until the generated ultrasound field has reached a diffusion regime wherein the ultrasound field has locally populated all ultrasonic modes with substantially equal probability;
monitoring the evolution of the resulting ultrasound field with a non-contact detector while said ultrasound field is in the diffusion regime; and
adjusting parameters in a mathematical model describing the predicted behavior of the ultrasound field in the diffusion regime to fit the detected behavior of the ultrasound field to the mathematical model and thereby derive at least one parameter dependent on the physical properties of the sample. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
wherein U({right arrow over (r)},t0,ω
) represents the spectral energy density in the sample at time t and D(ω
) and α
(ω
) are respectively the diffusion coefficient and the absorption coefficient for the spectral component of frequency ω
.
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12. A method as claimed in claim 11, wherein a time-frequency analysis is performed on the detected ultrasound field to fit it to the mathematical model.
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13. A method as claimed in claim 1, wherein the ultrasound field contains a range of frequencies in which there is sufficient scattering to permit a local equipartition of energy before the ultrasound energy is completely carried away or completely absorbed.
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14. A method as claimed in claim 1, wherein the ultrasound detector is wideband.
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15. A method as claimed in claim 1, wherein the ultrasound detector senses a point-like location on the sample.
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16. A method as claimed in claim 1, wherein said sample contains a polycrystalline aggregate and the grain size of said aggregate is determined from said derived at least one parameter.
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17. A method of determining grain size in a target sample of material, comprising the steps of:
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building a calibration of kd vs Dk/c, based on the measurement of D at one or several values of k on several calibration samples which are similar to the target sample but which differ with respect to their grain size, where D is the diffusion coefficient, k is the wavenumber of the ultrasound, d is the grain size and c is the velocity of sound;
measuring the diffusion coefficient D at one or more values of k in the target sample; and
determining the grain size in the target sample from the measured diffusion coefficient using said calibration.
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18. A method of evaluating the physical properties of a sample, comprising:
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generating an ultrasound field in a local region of the sample with a pulsed laser such that the generated ultrasound diffuses away from said local region;
waiting until the generated ultrasound field has reached a diffusion regime wherein the ultrasound has locally populated all ultrasonic modes with substantially equal probability;
monitoring the evolution of the resulting ultrasound field with a non-contact, point-like detector; and
adjusting parameters in a diffusion equation describing the predicted behavior of the ultrasound field in the diffusion regime to fit the detected behavior of the ultrasound field to the diffusion equation and thereby derive at least one sample parameter selected from the group consisting of the absorption coefficient and the diffusion coefficient. - View Dependent Claims (19)
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20. An apparatus for evaluating the physical properties of a sample, comprising:
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a time-varying source of radiation for generating an ultrasound field in a local region of the sample such that the generated ultrasound diffuses away from said local region;
a non-contact detector for monitoring the evolution of the resulting ultrasound field while in a diffusion regime wherein the ultrasound has locally populated all ultrasonic modes with substantially equal probability; and
an analyzer for analyzing the portion of said resulting ultrasound field that is in a diffusion regime and adjusting parameters in a mathematical model describing the predicted behavior of the ultrasound field in said diffusion regime to fit the detected behavior of the ultrasound field and thereby derive at least one parameter dependent on the physical properties of the sample. - View Dependent Claims (21, 22, 23, 24, 25, 29, 30)
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- 26. An apparatus as claimed in 25, wherein said mathematical model describing the predicted behavior of the ultrasound field in the diffusion regime is stored in said computer.
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31. An apparatus for determining grain size in a target sample of material, comprising:
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a computer programmed to store a calibration of kd vs Dk/c, based on the measurement of D at one or several values of k on several calibration samples which are similar to the target sample but which differ with respect to their grain size, where D is the diffusion coefficient, k is the wavenumber of the ultrasound, d is the grain size and c is the velocity of sound; and
an ultrasonic measuring system for measuring the diffusion coefficient D at one or more values of k in the target sample; and
said computer being programmed to determine the grain size in the target sample from the measured diffusion coefficient using said calibration.
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32. An apparatus for evaluating the physical properties of a sample, comprising:
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a pulsed laser for generating an ultrasound field in a local region of the sample such that the generated ultrasound diffuses away from said local region;
a non-contact, point-like ultrasound detector for monitoring the evolution of the resulting ultrasound field with a with a delay such that the generated ultrasound field has reached a diffusion regime wherein the ultrasound has locally populated all ultrasonic modes with substantially equal probability; and
an analyzer for adjusting parameters in a diffusion equation describing the predicted behavior of the ultrasound field in the diffusion regime to fit the detected behavior of the ultrasound field and thereby derive at least one sample parameter selected from the group consisting of the absorption coefficient and the diffusion coefficient. - View Dependent Claims (33)
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Specification