Piezoelectric materials have the unique ability to transform mechanical energy into electrical energy, and vice versa. If an electric charge is applied to a piezoelectric material, it will deform. The magnitude and orientation of the deformation is determined by the polarity, magnitude, and orientation of the charge relative to the polarization direction. If an alternating charge is applied, the material will deform cyclically. At the appropriate frequency, an audible sound (< 20 kHz) or ultrasound (> 20 kHz) can be generated. Harnessed effectively through transducer or sensor design, this unique property makes piezoelectric materials ideal for medical, defense and industrial applications.