Acoustic generation in piezoelectric materials by microwave excitation

As an application of ultrasound generation by microwave excitation, a study of piezoelectric material behavior is presented. Piezoelectric bars excited electrically or by microwave irradiation give different resonance frequencies. Piezoelectric materials are subject to a stiffening phenomenon (variation of the apparent Young’s modulus) when the electrical boundary conditions change and, as a result, when the material is dynamically excited, a modification of the natural resonance frequencies occurs. A one-dimensional model, to predict the acoustic waves generated in piezoelectric materials by an unspecified excitation source, is presented and compared to experimental results. This model is used as a nondestructive evaluation method to characterize piezoelectric samples and to highlight the thermoelastic origin of the acoustic generation when the piezoelectric materials are excited by pulsed microwaves.