The following reference works are cited in this example problem:
Yan, T. H., Wang, W., Chen, X. D., Li, Q., & Xu, C. (2009). Design of a smart ultrasonic transducer for interconnecting machine applications. Sensors. 9.6: 4986-5000.
Or, S.W., Chan, H. L. W., Lo, V. C., & Yuen, C. W. (1998). Performance study of an ultrasonic transducer used for wire bonding. Electron Devices Meeting.
Berlincourt, D., Krueger, H. H. A., Near, R. C. Properties of Morgan electro ceramic ceramics. Properties of Piezoelectricity Ceramics. Technical Publication TP-226.