Design and fabrication of ultrasonic transducers with nanoscale dimensions

The development of nanometre sized ultrasonic transducers is important in both biological and industrial applications. The small size can be important in its own right or necessary in order to generate acoustic waves with nanometric wavelengths. Potential applications of nanotransducers range from embedded sensors through to sub optical wavelength acoustic imaging. In this paper, we show the generation and detection of ultra high frequency acoustic waves using nanometre scaled optical ultrasonic transducers. The optical and mechanical properties of these devices have been modelled using finite element modelling (FEM) and analytical techniques. The models allow the fine tuning of the design parameters to enhance both the acoustic and optical performance of the transducers. The devices were fabricated by evaporating the required metal and transparent layers onto a substrate, and then surface patterning of the device was created by laser machining or photolithography, thus allowing close comparison between model and experiment. We discuss the transducer design process and the effect of the coating parameters and how these affect the operating frequency and efficiency of the devices. We discuss the possibility of using molecular self assembly to produce even smaller devices.