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Many measurement tasks in industrial automation, e.g. non-contact distance measurement, room surveillance, object identification and gas flow measurement can be accomplished by sensors using airborne ultrasound. Their performance is determined by the properties of the ultrasonic transducers. The authors compare electrostatic and piezoelectric transducers. Piezoceramic transducers combine a high efficiency factor and ruggedness. Composite transducers consisting of piezoceramic and polymer materials show a wider relative bandwidth of about 30% at the expense of efficiency. Ultrasonic transducers based on piezopolymer foils offer a variety of acoustic properties at low expenditure. Their bandwidth corresponds to that of composite transducers. Composite, as well as piezopolymer, foil transducers are suited to the design of phased arrays. Foil transducers have the additional advantage of very small crosstalk between neighbouring transducer elements. By electronically controlled deflection of the sound beam, lateral details and consequently the spatial structure of objects can also be detected.
Manthey et al. (Sun,) studied this question.