ABSTRACT
This chapter describes research on wideband piezoelectric transducers and microelectromechanical system (MEMS) sensors for ultrasonic in-air applications. The transducers and sensors described are compact, low-cost, and have low power consumption. The chapter also describes the application of the transducers and sensors in a prototype local positioning systems (LPS). The LPS achieves submillimeter-range accuracy and high-accuracy angle of arrival estimation using a seven-mm diameter uniform circular array of sensors. There are four main categories of ultrasonic in-air transducer—piezoelectric, polyvinylidene fluoride (PVDF), electromechanical film (EMFi), and capacitive MEMS ultrasonic transducer. Piezoelectric ultrasonic transducers are typically zirconate titanate polymer or composite materials. The maximum range that transducers, based on PVDF, can achieve is comparable to the range provided by the piezoelectric transducers, having a typical mean sound pressure level of 110 dB. EMFi is a low-cost thin film of microporous polypropylene foam with high resistivity and permanent charge due to being polarized by the corona method.
