Method and apparatus for acoustic wave measurement

• US 5,955,669 A
• Filed: 07/18/1997
• Issued: 09/21/1999
• Est. Priority Date: 03/06/1997
• Status: Expired due to Fees

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Egami, Noritaka
• Primary Examiner(s): CHAPMAN JR, JOHN E
• Application Number:
  US08/896,850
• Time in Patent Office: 795 Days
• Field of Search: 73/579, 73/594, 73/597, 73/602, 73/615, 73/616, 73/628, 73/630
• US Class Current: 73/579
• CPC Class Codes: G01N 2291/02854 Length, thickness
• CPC Class Codes: G01N 2291/0423 Surface waves, e.g. Rayleigh waves, Love waves
• CPC Class Codes: G01N 2291/044 Internal reflections (echoes), e.g. on walls or defects
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 29/11 by measuring attenuation of acoustic waves
• CPC Class Codes: G01N 29/2412 using the magnetostrictive properties of the material to be examined, e.g. electromagnetic acoustic transducers [EMAT]; investigating the presence of flaws using eddy currents G01N27/90, magnetostrictive transducers B06B1/08, measuring magnetostrictive properties G01R33/18
• 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

An apparatus and a method for acoustic wave measurement according to the present invention are characterized by oscillating a magnetostrictive vibrator with a frequency to emit an acoustic wave to an object to be measured, calculating the amplitude of a signal received by a wave receiver, and repeating the previous steps throughout a range of different frequencies to detect the resonance frequency. The amplitude of the received signal is calculated from values of the signal sampled at an interval of 1/4 of one cycle of the emitted frequency. This reduces the time of the measurement of a thickness a presence of flaws, a presence of impurities and minimizes noises during the measurement.

Claims

1. A method for acoustic wave measurement comprising:

a first step of placing a magnetostrictive vibrator and a narrow band wave receiver which receives a narrow bandwidth of acoustic waves on one surface of an object to be measured;

a second step of oscillating the magnetostrictive vibrator with a predetermined frequency to emit an acoustic wave toward the interior of the object;

a third step of receiving by the narrow band wave receiver the acoustic wave reflected to an interior location of the object and calculating the amplitude of the received wave corresponding to the predetermined frequency;

a fourth step of repeating the process of the second and the third steps a plurality of times, where the magnetostrictive vibrator produces a frequency which is different from the predetermined frequency as well as different each time it is produced in a sequence of times;

a fifth step of identifying the frequency corresponding to the maximum of received amplitudes calculated repeatedly at the fourth step; and

a sixth step of calculating the distance from the surface to the interior location of the object or the acoustic velocity through the interior of the object on the basis of the frequency identified at the fifth step.

2. A method for acoustic wave measurement comprising:

a first step of placing a magnetostrictive vibrator and a wave receiver on one surface of an object to be measured;

a second step of oscillating the magnetostrictive vibrator with a predetermined frequency to emit an acoustic wave toward the interior of the object;

a third step of receiving by the wave receiver the acoustic wave reflected to an interior location of the object and calculating the amplitude of the received wave corresponding to the predetermined frequency, wherein the third step includes a step of calculating a first crest value and a second crest values of each signal received by the wave receiver at an interval equal to 1/4 of one cycle of the predetermined frequency, and a step of determining the amplitude of the received wave corresponding to the predetermined frequency on the basis of the first and the second crest values;

a fourth step of repeating the process of the second and the third steps a plurality of times, where the magnetostrictive vibrator produces a frequency which is different from the predetermined frequency as well as different each time it is produced in a sequence of times;

a fifth step of identifying the frequency corresponding to the maximum of received amplitudes calculated repeatedly at the fourth step; and

a sixth step of calculating the distance from the surface to the interior location of the object or the acoustic velocity through the interior of the object on the basis of the frequency identified at the fifth step.

3. An acoustic wave measurement apparatus comprising:

a magnetostrictive vibrator placed on one surface of an object to be measured for emitting an acoustic wave upon oscillation with a predetermined frequency;

a sine-wave variable frequency oscillator for oscillating the magnetostrictive vibrator at the predetermined frequency;

a wave receiver placed on the surface of the object for receiving a reflected acoustic wave;

a variable frequency band-pass filter for extracting a signal of a directed predetermined frequency from the signal received by the wave receiver;

a controller for producing a train of different frequencies in a predetermined order, and directing each of the same frequencies of the train to the sine-wave variable frequency oscillator and the variable frequency band-pass filter at predetermined intervals of time in order;

a first amplitude detecting means for detecting a first crest value on the basis of the output signal of the variable frequency band-pass filter, during the period in which the variable frequency band-pass filter is supplied with one of the frequencies;

a second amplitude detecting means for detecting a second crest value on the basis of the output signal of the variable frequency band-pass filter at an interval of 1/4 of one cycle of the frequency after the output signal of the variable frequency band-pass filter is received by the first amplitude detecting means; and

a calculating means for calculating the amplitude of the received wave corresponding to the frequency on the basis of the first and the second crest values.

4. The acoustic wave measurement apparatus according to claim 3, further comprising a second calculating means for calculating a resonance frequency from a plurality of frequencies and the corresponding amplitudes of the received wave to determine the distance from the surface to an interior location of the object where the reflection is made or the acoustic velocity through the interior of the object.

5. An acoustic wave measurement apparatus comprising:

a magnetostrictive vibrator placed on one surface of an object to be measured for emitting an acoustic wave upon oscillation with a predetermined frequency;

a sine-wave variable frequency oscillator for oscillating the magnetostrictive vibrator at the directed predetermined frequency;

a wave receiver placed on the surface of the object for receiving a reflected acoustic wave;

a variable frequency band-pass filter for extracting a signal of a directed predetermined frequency from the signal received by the wave receiver;

a controller for producing a train of different frequencies by a predetermined order, and directing each of the same frequencies of the train in sequence to the sine-wave variable frequency oscillator and the variable frequency band-pass filter at regular intervals of time;

a timing signal generating means for generating, a first and a second timing signals at an interval of 1/4 of one cycle of a frequency during the period in which the frequency is supplied to both the sine-wave variable frequency oscillator and the variable frequency band-pass filter;

an amplitude detecting means for detecting a first crest value on the basis of the output signal of the variable frequency band-pass filter when receiving the first timing signal as well as for detecting a second crest value on the basis of the output signal of the variable frequency band-pass filter when receiving the second timing signal; and

a calculating means for calculating the amplitude of the received wave corresponding to the frequency on the basis of the first and the second crest values.

6. The acoustic wave measurement apparatus according to claim 5, further comprising a second calculating means for calculating a resonance frequency from a plurality of frequencies and the corresponding amplitudes of the received wave to determine the distance from the surface to an interior location of the object where the reflection is made or the acoustic velocity through the interior of the object.

7. The acoustic wave measurement apparatus according to claim 5, further comprising a first oscillation correcting amplifier for controlling the amplification of an output signal of the sine-wave frequency variable oscillator in accordance with the frequency characteristic of the magnetostrictive vibrator.

8. The acoustic wave measurement apparatus according to claim 5, further comprising a second oscillation correcting amplifier for controlling the amplification of an output signal of the wave receiver in accordance with the frequency characteristic of the magnetostrictive vibrator.

9. The acoustic wave measurement apparatus according to claim 5, further comprising:

a first oscillation correcting amplifier for controlling the amplification of an output signal of the sine-wave frequency variable oscillator in accordance with the frequency characteristic of the magnetostrictive vibrator; and

a second oscillation correcting amplifier for controlling the amplification of an output signal of the wave receiver in accordance with the frequency characteristic of the magnetostrictive vibrator.

10. The acoustic wave measurement apparatus according to claim 7, wherein the first oscillation correcting amplifier corrects the output signal of the sine-wave variable frequency oscillator so that the amplitude of the output from the magnetostrictive vibrator generates a constant level throughout the frequencies.

11. The acoustic wave measurement apparatus according to claim 8, wherein the second oscillation correcting amplifier is corrected the output signal of the wave receiver so that variations of the amplitude of the output from the magnetostrictive vibrator dependent on the frequencies is eased.

12. The acoustic wave measurement apparatus according to claim 9, wherein the first oscillation correcting amplifier corrects the output signal of the sine-wave variable frequency oscillator so that the amplitude from the output from the magnetostrictive vibrator generates a constant level throughout the frequencies, and the second oscillation correcting amplifier is corrected the output signal of the wave receiver so that variations of the amplitude of the output from the magnetostrictive vibrator dependent on the frequencies is eased.