Ultrasonic non-destructive evaluation of thin specimens

• US 5,305,239 A
• Filed: 10/04/1989
• Issued: 04/19/1994
• Est. Priority Date: 10/04/1989
• Status: Expired due to Fees

• Current Assignee: Texas A&M University System
• Original Assignee: Texas A&M University System
• Inventors: Kinra, Vikram K.
• Primary Examiner(s): Cosimano, Edward R.
• Application Number:
  US07/416,889
• Time in Patent Office: 1,658 Days
• Field of Search: 73/602, 364/507, 364/563, 367/13
• US Class Current: 702/39
• CPC Class Codes: G01H 5/00 Measuring propagation velocity of ultrasonic, sonic or infrasonic waves , e.g. of pressure waves
• CPC Class Codes: G01N 2291/0289 Internal structure, e.g. defects, grain size, texture
• CPC Class Codes: G01N 29/075 by measuring or comparing phase angle measuring frequencies or phase angles per se G01R23/00, G01R25/00
• CPC Class Codes: G01N 29/348 with frequency characteristics, e.g. single frequency signals, chirp signals measuring frequency of mechanical vibrations or acoustic waves in general G01H1/06, G01H3/04; measuring frequency or analysing frequency spectra G01R23/00
• CPC Class Codes: G01N 29/42 by frequency filtering or by tuning to resonant frequency
• CPC Class Codes: G01N 29/46 by spectral analysis, e.g. Fourier analysis or wavelet analysis spectral signal processing per se G06F17/14

Abstract

In the field of non-destructive evaluation of materials, conventional ultrasonic measurement techniques are limited to materials having a thickness which is relatively large compared to the wavelength of the ultrasonic signal used. The present technique enables the accurate ultrasonic non-destructive measurement of materials which are relatively small compared to the wavelength of the ultrasonic signal used. Ultrasonic signals received from a thin material are processed in the frequency-domain either directly or by use of a Fast Fourier Transform. Specifically, the frequency response of the ultrasonic transducers used in the measurement is removed from the frequency response of the signal received when measuring the material. This yields a frequency response which is indicative of the material alone. Then, the measured frequency response of the material is evaluated to determine unknown parameters of the material. For instance, the phase of the measured signal is determined over a predetermined frequency range (usually the bandwidth of the transducers), and the phase is used to determine the speed of ultrasonic waves travelling in the material for frequencies within the predetermined range. Likewise, the magnitude of the measured signal is determined over the predetermined frequency range, and the magnitude is used to determine the attenuation of ultrasonic waves travelling in the material for frequencies within the predetermined range.

Claims

1. A method for non-destructively evaluating a material, comprising the steps of:

transmitting an ultrasonic wave having a frequency within a predetermined frequency range into said material;

receiving said ultrasonic wave from said material;

measuring a frequency response of said material at frequencies within said predetermined frequency range from said received ultrasonic wave; and

determining a frequency-dependent normalized wavenumber in said material from said frequency response.

2. The method, as set forth in claim 1, wherein said wavenumber is a complex mathematical quantity having a real portion and an imaginary portion.

3. The method, as set forth in claim 2, wherein said real portion is correlative to a speed of said ultrasonic wave within said material.

4. The method, as set forth in claim 3, wherein the speed of said ultrasonic wave in said material is dependent upon the frequency of said ultrasonic wave.

5. The method, as set forth in claim 2, wherein said imaginary portion is correlative to an amount of attenuation of said ultrasonic wave produced by said material.

6. The method, as set forth in claim 5, wherein the attenuation of said ultrasonic wave in said material is dependent upon the frequency of said ultrasonic wave.

7. A method for non-destructively evaluating a material, comprising the steps of:

transmitting an ultrasonic wave having a frequency within a preselected frequency range into said material;

receiving said ultrasonic wave from said material;

measuring a frequency response of said material at frequencies within said preselected frequency range from said received ultrasonic wave; and

equating said measured frequency response to a preselected frequency-dependent function of said material to determine an unknown parameter of said material.

8. The method, as set forth in claim 7, wherein said step of measuring comprises:

calculating the Fourier Transform of said received ultrasonic wave; and

dividing the Fourier Transform of said received ultrasonic wave by a predetermined frequency response to yield the frequency response of said material.

9. The method, as set forth in claim 7, wherein said step of equating comprises:

calculating said frequency-dependent function of said material using a predetermined number of known parameters of said material, said frequency-dependent function having an unknown variable which is correlative to said unknown parameter of said material;

equating said frequency-dependent function to said measured frequency response; and

calculating said unknown variable.

10. An apparatus for evaluating a specimen, comprising:

a generator being adapted to deliver an electrical pulse having a predetermined duration;

a transducer being adapted to receive said electrical pulse, convert said electrical pulse into an ultrasonic acoustical wave correlative thereto, direct said ultrasonic acoustical wave toward said specimen, detect ultrasonic acoustical waves reflected from said specimen, and convert said reflected acoustical waves into an electronic signal correlative thereto;

a computer being adapted to receive said electronic signal, determine a frequency response of said specimen in response to said electronic signal, and determine a frequency-dependent wavenumber in said specimen from said frequency response.

11. The apparatus, as set forth in claim 10, wherein said computer:

stores a predetermined number of known parameters of said specimen, said known parameters being known variables in a given equation and said wavenumber being an unknown variable; and

uses said equation to calculate said wavenumber from the determined frequency response of said specimen.

12. An apparatus for evaluating a material, comprising:

a generator being adapted to deliver an electrical pulse having a predetermined duration;

a transducer being operably connected to said generator to receive said electrical pulse, said transducer converting said electrical pulse into an ultrasonic acoustical wave correlative to said electrical pulse;

said transducer being positioned to direct said ultrasonic acoustical wave toward said material and to detect ultrasonic acoustical waves reflected from said material, and said transducer converting said reflected acoustical waves into an electronic signal correlative to said reflected acoustical waves; and

a computer being operably connected to said transducer to receive said electronic signal, said computer being programmed to determine a frequency response of said material in response to said electronic signal, and to determine a frequency-dependent normalized wavenumber in said material from said frequency response.

13. A method for evaluating a material having a known thickness, comprising the steps of:

imparting an ultrasonic wave into said material;

receiving the ultrasonic wave from said material;

determining the frequency response of said material within a predetermined frequency range from said received ultrasonic wave;

calculating the attenuation of said material for ultrasonic waves having a frequency within said predetermined frequency range; and

calculating the speed with which ultrasonic waves having a frequency within said predetermined frequency range propagate through said material.

14. A method for evaluating a material having a known attenuation and through which speed of an ultrasonic wave is known, comprising the steps of:

imparting an ultrasonic wave into said material;

receiving the ultrasonic wave from said material;

determining the frequency response of said material within a predetermined frequency range from said received ultrasonic wave; and

calculating the thickness of said material in response to said determined frequency response.

15. The method, as set forth in claim 14, wherein said step of determining comprises:

calculating the Fourier Transform of said received ultrasonic wave; and

dividing the Fourier Transform of said received ultrasonic wave by a predetermined frequency response to yield the frequency response of said material.

16. The method, as set forth in claim 14, wherein said step of calculating comprises:

relating an unknown thickness to an equation determined by said known speed and said known attenuation, said equation having the frequency response of said material as an unknown variable; and

replacing said unknown variable with the frequency response of said material; and

solving said equation for said unknown thickness.

17. A method for non-destructively evaluating a material using at least one transducer being adapted to emit ultrasonic waves, comprising the steps of:

determining the frequency response of said transducer;

transmitting an ultrasonic wave having a frequency within a predetermined frequency range into said material;

receiving said ultrasonic wave from said material;

determining the frequency response of said received ultrasonic wave;

dividing the frequency response of said received ultrasonic wave by the frequency response of said transducer, said division producing the frequency response of said material; and

determining phase and magnitude of the frequency response of said material, phase velocity of said ultrasonic wave within said material being correlative to the phase and attenuation of said material being correlative to the magnitude.

18. A method for non-destructively evaluating a thin material, comprising the steps of:

delivering a first ultrasonic signal from a first transducer;

receiving said first ultrasonic signal by a second transducer;

calculating the Fourier Transform of said received first ultrasonic signal;

acoustically coupling said thin material between said first transducer and said second transducer;

delivering a second ultrasonic signal from said first transducer to said thin material;

receiving a portion of said second ultrasonic signal transmitted through said thin material by said second transducer;

calculating the Fourier Transform of said received portion;

dividing the Fourier Transform of said received portion by the Fourier Transform of said received first ultrasonic signal, said division producing a measured transfer function;

equating said measured transfer function to a preselected transfer function corresponding to said thin material, said preselected transfer function having at least one unknown variable, said unknown variable being related to said thin material; and

solving for said unknown variable.

19. A method for non-destructively determining the unknown thickness of a thin material, comprising the steps of:

delivering a first ultrasonic signal from a first transducer;

receiving said first ultrasonic signal by a second transducer;

calculating the Fourier Transform of said received first ultrasonic signal;

acoustically coupling said thin material between said first transducer and said second transducer;

delivering a second ultrasonic signal from said first transducer to said thin material;

receiving a portion of said second ultrasonic signal transmitted through said thin material by said second transducer;

calculating the Fourier Transform of said received portion;

dividing the Fourier Transform of said received portion by the Fourier Transform of said received first ultrasonic signal, said division producing a measured transfer function;

equating said measured transfer function to a preselected transfer function corresponding to said thin material, said preselected transfer function including the unknown thickness of said thin material; and

solving said equation for the unknown thickness.

20. A method for non-destructively determining speed and attenuation of an ultrasonic wave in a material of known thickness, comprising the steps of:

delivering a first ultrasonic wave from a first transducer;

receiving said first ultrasonic wave by a second transducer;

calculating the Fourier Transform of said received first ultrasonic wave;

acoustically coupling said material between said first transducer and said second transducer;

delivering a second ultrasonic wave from said first transducer to said material;

receiving a portion of said second ultrasonic wave transmitted through said material by said second transducer;

calculating the Fourier Transform of said received portion;

dividing the Fourier Transform of said received portion by the Fourier Transform of said received first ultrasonic wave, said division producing a measured transfer function; and

determining phase and magnitude of said measured transfer function, the speed of said ultrasonic wave within said material being correlative to the phase and the attenuation of said material being correlative to the magnitude.

21. A method for non-destructively evaluating a thin material, comprising the steps of:

acoustically coupling an ultrasonic transducer to a reference material;

delivering a first ultrasonic signal from said transducer to said reference material, said transducer receiving a portion of said first ultrasonic signal reflected from said reference material;

calculating the Fourier Transform of said received first ultrasonic signal;

acoustically coupling said thin material to said transducer;

delivering a second ultrasonic signal from said transducer to said thin material;

receiving a portion of said second ultrasonic signal reflected from said thin material by said transducer;

calculating the Fourier Transform of said received second ultrasonic signal;

dividing the Fourier Transform of said received second ultrasonic signal by the Fourier Transform of said received first ultrasonic signal, said division producing a measured transfer function;

equating said measured transfer function to a preselected transfer function having known parameters of said thin material, said preselected transfer function having at least one unknown parameter, said unknown parameter being related to said thin material; and

solving for said unknown parameter.