Pitch-catch method

In the pitch catch method, two ultrasound transducers are used, one as a transmitter and one as a recaver. However, unlike the TTU method, the pitch catch transducers may be on the same side of the part or oriaited in a number of ways for the ultrasound to progress from one transducer to the otha". The intapretalion is usually based on changes in detected signal strength or frequency and calibrated against a known test sample. 

Acousto-ultrasonics [49] is a guided-wave pitch-catch method. The acousto part in the name reminds one of the reception of guided waves generated by the AE process at a propagating crack. The term ultrasonics infers that this is an active technique in which ultrasonic waves are generated by the transmitter thus this technique is different from the AE technique in that is just a passive technique. 

Figure 16.24 Impact damage identification in a composite panel with the embedded pitch-catch method, (a) Real damage detected by X-rays superposed with the estimated damage computed Irom the data the location of the four PZT is also shown (b) comparison between estimation and real damage size is described by an ellipse with parameters a, b, 0 [19].

Dm JB, Chang EK. Pitch-catch active sensing methods in structural health monitoring for aircraft structures. Struct Health Monit Int J 2008 7(1) 5—19. http //dx.doi.org/ 10.1177/1475921707081979. 

The pitch and catch technique is a test with a transmitter and a receiver transducers where the path of the ultrasonic beam is not straight line but follows a complex path (the beam is reflected one or more times before reaching the receiver). Different configurations can be distinguished direct pitch and catch, in which the receiver is placed where the reflected ultrasonic beam is expected if there is no discontinuity indirect pitch and catch, in which the receiver is placed where the ultrasonic beam is expected to be if reflected by a discontinuity (Figure 12.8). Tandem method is a typical example of direct pitch and catch test. Delta testing is an example of an indirect pitch and catch test. 

---