With the development of silicon micromachining technology, Micro Electro Mechanical Systems (MEMS) is widely applied in silicon acoustics devices, such as micro-microphone, micro-transducer and so on. Owing to the characteristics of small size, light quality, low power consumption and being prone to batch production, micro-machined ultrasonic transducers and transducer array are becoming important MEMS devices.

There are two kinds of micro-machined ultrasonic transducer. One is capacitive micro-machined ultrasonic transducer (CMUT); the other is piezoelectric micro-machined ultrasonic transducer (PUMT). To the latter one, its vibration property is influenced by elastic force of material and residual force formed in MEMS processing. In order to have a clear idea about the resonant frequency and amplitude distribution caused by these two kinds of force, researchers of Institute of Acoustics, Chinese Academy of Sciences conducted a series of studies.

They made a PUMT by themselves and carried out theoretical and experimental investigation based on it. For the case that the thickness of the diaphragm is much smaller than its length, the experimental results and theoretical analysis prove that the residual stress in diaphragm effects on its resonant frequency strongly. The results from the classical theory for thin plate show big discrepancies with the experimental results if its residual stress is omitted. With the residual stress in the diaphragm is considered, the analysis results could explain the resonant prosperities of PMUT well. They also obtain the equivalent circuit of the transducers form the measured admittance results. The resonant frequency of the PMUT is about 71 kHz and the membrane width is 1mm. Some preliminary experiments were also done to demonstrate PMUT as a transmitter or a receiver of acoustic waves. The measured receiving sensitivity is -201.6 dB (ref 1 V/uPa) and the acoustic pressure output is about 137 dB (ref 1 uPa·m / V) at 71 kHz.