The capacitance transducer as a standard ultrasonic source in solids

An air-gap capacitance transducer with a guard ring has been used as a standard source of wideband ultrasound in solid material. Theoretical and experimental displacement waveforms have been compared, indicating that this capacitance source is characterized by a simple transduction mechanism. The bandwidth can be altered from a sharp transient to a steplike response, while the polarity can be reversed, all through simple changes in the excitation voltage and without damage to the sample. An example of the transducer acting as a source in a dielectric material is also presented.