21. Magnetostrictive transducers were pursued after WW2 as an alternative to piezoelectric ones. 22. The acoustic impedance of piezoelectric materials facilitated their use as underwater transducers. 23. A sound wave is typically produced by a piezoelectric MHz. 24. Ferroelectric, dielectric ( paraelectric ) and piezoelectric materials have electric polarisation. 25. All ferroelectric materials are pyroelectric and piezoelectric , but not the converse. 26. Ferroelectrets display strong piezoelectricity, comparable to ceramic piezoelectric materials. 27. Other works use a piezoelectric system to generate and control the vibrations. 28. Acoustic guitars, upright basses and fiddles often use a piezoelectric pickup. 29. A less frequently used combination is a piezoelectric and a magnetic pickup. 30. The related piezoelectric effect occurs only in a particular class of dielectrics.
