Ultrasonic Inspection System Employing Spectral and Time Domain Processing of Ultrasonic Signal

Abstract

A method performed by an ultrasonic inspection system includes delivering to a multilayer structure an ultrasonic pulse that sweeps through a chirp bandwidth, and receiving from the multilayer structure ultrasonic energy including a series of time-overlapping reflections of the pulse delivered to the multilayer structure from layers of the multilayer structure. The method also includes performing frequency domain processing on the ultrasonic energy to produce frequency resonance peaks respectively indicative of distinct layers of the multilayer structure, and performing time domain processing on the ultrasonic energy to compress the time-overlapping reflections into respective time-separated reflection time peaks. The method also includes displaying the frequency resonance peaks on a frequency domain plot, and displaying the reflection time peaks on a time domain plot.

What is claimed is: 
     
         1 . A method comprising:
 delivering to a structure under inspection, via an ultrasonic transmit transducer, an ultrasonic chirp pulse having a swept frequency that sweeps through a chirp bandwidth;   receiving, via an ultrasonic receive transducer, ultrasonic energy including time-overlapping chirp pulse reflections of the ultrasonic chirp pulse from structural features of the structure, wherein the ultrasonic transmit transducer and the ultrasonic receive transducer are both arranged on a same side of the structure;   performing one or more Fourier transforms on the ultrasonic energy, to produce frequency resonance peaks respectively indicative of distinct features of the structure;   performing pulse compression on the ultrasonic energy to compress the time-overlapping chirp pulse reflections into respective time-separated reflection time peaks;   displaying the frequency resonance peaks on a frequency domain plot; and   displaying the respective time-separated reflection time peaks on a time domain plot.   
     
     
         2 . The method of  claim 1 , wherein the ultrasonic transmit transducer and the ultrasonic receive transducer are both arranged on the same side of the structure such that the receiving includes receiving the time-overlapping chirp pulse reflections of the ultrasonic chirp pulse instead of receiving through transmissions of the ultrasonic chirp pulse. 
     
     
         3 . The method of  claim 1 , wherein the structure includes a planar side and the ultrasonic transmit transducer and the ultrasonic receive transducer are both arranged on the planar side. 
     
     
         4 . The method of  claim 1 , wherein the structure is a multilayer structure and the respective time-separated reflection time peaks are indicative of responses of individual layers of the multilayer structure. 
     
     
         5 . The method of  claim 1 , further comprising concurrently performing the one or more Fourier transforms and the pulse compression, to produce the frequency resonance peaks and the respective time-separated reflection time peaks, concurrently. 
     
     
         6 . The method of  claim 5 , further comprising using a frequency domain processor and a time domain processor to perform the one or more Fourier transforms and the pulse compression, respectively. 
     
     
         7 . The method of  claim 5 , further comprising:
 digitizing the ultrasonic energy to produce a digitized ultrasonic signal; and   concurrently performing the one or more Fourier transforms and the pulse compression on the digitized ultrasonic signal.   
     
     
         8 . The method of  claim 1 , wherein performing the one or more Fourier transforms includes:
 performing a first Fourier transform on the ultrasonic energy to produce a first frequency spectrum; and   performing a second Fourier transform on the first frequency spectrum to produce a second frequency spectrum that includes the frequency resonance peaks.   
     
     
         9 . The method of  claim 1 , wherein performing the pulse compression includes filtering the time-overlapping chirp pulse reflections using a filter response matched to the swept frequency of the ultrasonic chirp pulse delivered to the structure. 
     
     
         10 . The method of  claim 1 , further comprising concurrently displaying the frequency resonance peaks on the frequency domain plot and the respective time-separated reflection time peaks on the time domain plot. 
     
     
         11 . An apparatus comprising:
 an ultrasonic transmitter to deliver to a structure under inspection, via an ultrasonic transmit transducer, an ultrasonic chirp pulse having a swept frequency that sweeps through a chirp bandwidth;   an ultrasonic receive transducer to receive from the structure ultrasonic energy that includes time-overlapping chirp pulse reflections of the ultrasonic chirp pulse from structural features of the structure, wherein the ultrasonic transmit transducer and the ultrasonic receive transducer are both arranged on a same side of the structure;   a frequency domain analyzer to perform one or more Fourier transforms on the ultrasonic energy, to produce frequency resonance peaks respectively indicative of distinct features of the structure;   a time domain analyzer to perform pulse compression on the ultrasonic energy to compress the time-overlapping chirp pulse reflections into respective time-separated reflection time peaks; and   a display to display the frequency resonance peaks on a frequency domain plot, and the respective time-separated reflection time peaks on a time domain plot.   
     
     
         12 . The apparatus of  claim 11 , wherein the ultrasonic transmit transducer and the ultrasonic receive transducer are both arranged on the same side of the structure such that the ultrasonic receive transducer is configured to receive the time-overlapping chirp pulse reflections of the ultrasonic chirp pulse instead of through transmissions of the ultrasonic chirp pulse. 
     
     
         13 . The apparatus of  claim 11 , wherein the structure includes a planar side and the ultrasonic transmit transducer and the ultrasonic receive transducer are both arranged on the planar side. 
     
     
         14 . The apparatus of  claim 11 , wherein the structure is a multilayer structure and the respective time-separated reflection time peaks are indicative of responses of individual layers of the multilayer structure. 
     
     
         15 . The apparatus of  claim 11 , wherein the frequency domain analyzer and the time domain analyzer are configured to concurrently perform the one or more Fourier transforms and the pulse compression, respectively, to concurrently produce the frequency resonance peaks and the respective time-separated reflection time peaks, respectively. 
     
     
         16 . The apparatus of  claim 11 , wherein the frequency domain analyzer is configured to perform the one or more Fourier transforms by:
 performing a first Fourier transform on the ultrasonic energy to produce a first frequency spectrum; and   performing a second Fourier transform on the first frequency spectrum to produce a second frequency spectrum that includes the frequency resonance peaks.   
     
     
         17 . The apparatus of  claim 11 , wherein the display is configured to concurrently display the frequency resonance peaks on the frequency domain plot and the respective time-separated reflection time peaks on the time domain plot.