Capacitive ultrasonic transducers fabricated using microstereolithography

Abstract

Air-coupled thin-membrane capacitive ultrasonic transducers have been developed that use microstereolithography fabrication with architectures comprised entirely of partially metalised photopolymer. These devices derive considerable advantages from rapid prototyping technology, in that they are cheap to produce, and benefit from the design-to-product lead times inherent in the production of components using stereolithography. To date membranes have been produced with thicknesses ranging from 30 to 90 μm with aspect ratios in the range of 100 - 1000. These devices have been shown to operate both as transmitters and as receivers of ultrasound, and have a bandwidth approaching 100% with a centre frequency of 100 kHz. The method of fabricating these devices allows for easy modification for various applications including structural health monitoring and immersion, as well as affording the possibility of integrated focussing or wave-guiding architecture and packaging that can be incorporated into a single build. Fundamental or subtle changes to a given transducer design may be achieved incurring little additional cost or time. This novel approach to transducer fabrication enables the bespoke manufacture of specific transducer architectures from a computer aided design package using polymers that exhibit different material properties to materials used in silicon micromachining, but at the same time allow for fabrication on a scale that is approaching that of microfabrication. The versatility of 3-D rapid prototyping allows the realisation of more complicated structures than was possible previously. This work examines these transducers in terms of their characterisation and their operation in conjunction with other transduction architecture, such as focussing parabolic mirrors that were also produced using the same manufacturing technology. In addition, their operation in contacting acoustics and the reception of surface acoustic waves has been demonstrated. Immersion studies using these devices have found that that they hold promise for operation in a variety of different media. These transducers are seen as an important prototype development tool in the field of capacitive ultrasonic transduction and microphone-speaker design