Cepstral Method for the Measurement of Ultrasonic Pulse Transmission Time Variations

A precise method for determining relative changes or small differences in ultra-sonic pulse transmission times has been developed. The method uses multiple-echo signals obtained by injecting a pulsed, plane ultrasonic wave of the compressional mode into a sample with free, parallel surfaces. The ult...

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Bibliographic Details
Main Author: Gericke, Otto R
Format: Report
Language:English
Subjects:
Acoustic Detection and Detectors
ACOUSTIC PULSES
ACOUSTIC SIGNALS
ACOUSTIC VELOCITY
CALIBRATION
CEPSTRUM TECHNIQUE
COORDINATES
DATA PROCESSING
FOURIER TRANSFORMATION
NONDESTRUCTIVE TESTING
PARALLEL ORIENTATION
PE6310SD
PLANE WAVES
PRECISION
PROPAGATION
PULSES
SOUND TRANSMISSION
SURFACES
Test Facilities, Equipment and Methods
TIME
TRANSDUCERS
TRANSMITTANCE
ULTRASONICS
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Summary:A precise method for determining relative changes or small differences in ultra-sonic pulse transmission times has been developed. The method uses multiple-echo signals obtained by injecting a pulsed, plane ultrasonic wave of the compressional mode into a sample with free, parallel surfaces. The ultrasonic transducer employed for this purpose acts as both transmitter and receiver. The received ultrasonic signals are subjected to two consecutive Fourier transformations to produce a cepstrum. The cepstral function derived from the multiple-echo signal exhibits characteristic maxima whose positions on the frequency abscissa, after calibration in units of time, represent multiples of the ultrasonic transmission time. Since minute variations of this time can be determined from a shift in the position of a cepstral maximum, the detection of very small changes or differences in sample thickness or ultrasonic propagation velocity becomes feasible. Keywords: Nondestructive testing, Ultrasonics, Data processing, Cepstrum technique, Thickness, Velocity.