A Non-Phase Sensitive Transducer for Ultrasonics

I would like to describe some of our programs at NASA, Langley Research Center, Hampton, VA, on the development and use of a new type of phase insensitive transducer we call an Acoustoelectric Converter, or an AEC. In the very short time I have here, I shall indicate why the AEC is significant and show some ultrasonic transmission results obtained from modified isometric attentuation scans of conventional NDE resolution test plates containing simple flaws. Disciplines Materials Science and Engineering This 8. advances in electromagnetic transducers is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ cnde_yellowjackets_1976/31 A NON-PHASE SENSITIVE TRANSDUCER FOR ULTRASONICS J. Heyman NASA-Langley Research Center Hampton, Virginia 23665 I would like to describe some of our programs at NASA, Langley Research Center, Hampton, VA, on the development ~nd use of a new type of phase insensitive transducer we call an Acoustoelectric Converter, or an AEC. In the very short time I have here, I shall i~dicate why the AEC is significant and show some ultrasonic transmission results obtained from modified isometric attentuation scans of conventional ~DE resolution test plates containing simple flaws. In general ultrasonic NDE, an acoustic wave incident on a transducer is composed of many phase fronts and frequency components which are all added in a complicated \vay with conventional phase sensitive transducers. For example, consider the simplest use of just two phase fronts at the same frequency entering a piezoelectric transducer from the left, as shown in Fig. l. To the right of the transducer, the electrical signal thus produced is shown. IN PHASE PIEZOELECTRIC DETECTOR Figure 1. This fiqure shows two incident ultrasonic waves entering from the left and im-. pinging on a conventional piezoelectric transducer in the center of the figure. To the right is shown the resulting electrical signal obtained from the transducer for waves of the sar,le frequency and phase. If the two incident waves are slightly out of rhase, the resulting electrical signal is reduced as shown in Fig. 2. This occurs because a conventional transducer is phase sensitive and averages the piezoelectric voltaqes. OUT OF PHASE PIEZOELECTRIC DETECTOR Figure 2. Same as Fig. l, but with a phase shift between the two incident waves. Note the decreased amplitude of the electrical output as compared to Fig. l. If the acoustic waves are composed of two different frequencies entering the piezoelectric transducer, then severe phase modulation occurs as shown in Fig. 3. In other words, the use of piezoelectric transducers suffers, if you will, from too much information in some instances; i.e., their output is modulated due to the phase of the acoustic wave front. t~l FRE[;IUENCY SHIFT PIEZOELECTRIC DETECTOR Figure 3. Same as Fig. 1, but with a frequency shift between the two incident waves. In this case note the severe modulated electrical output.