Gas coupled polymeric capacitive transducers via pad printing

Micropatterning of polymer substrates has been shown to be effective methodology for the manufacture of capacitive transducers. The method involves creating a positive mask of sessile liquid droplets on a polymer substrate. The droplets define the cavity dimensions and spatial distribution, a subsequent processing stage independently defines the cavity depth. Droplets can be defined in a variety of ways - this paper explores the patterning the droplets, and hence cavities, on the polymer substrate via a pad-printing technique. The printing pad is manufactured using 3D printing technique, an example pad is illustrated in Figure 1 - essentially the pad comprises an array of styli. The lateral dimensions and spatial distribution of the styli are replicated via the pattern of deposited droplets on the polymer substrate. The morphology of the styli tips has been explored - planar tips were found to droplet patterns with the highest fidelity. Single element air coupled devices operating with a nominal centre frequency of 500kHz have been constructed and evaluated experimentally. Transducer bandwidths in excess of 100% were observed with two-way insertion loss of 60dB being typical.