Investigation into the effects of modification of the passive phase for improved manufacture of 1-3 connectivity piezocomposite transducers

The 1-3 connectivity composite transducers comprise active piezoceramic pil lars within a passive polymer matrix. The first stage in manufacturing the 1-3 material is to produce a bristle block (comprising a solid stock of act ive material with protruding pillars) by injection moulding or by dicing a piece of ceramic using precision sawing equipment. The bristle block is fil led with a reactive polymer liquid that produces the passive polymer phase, and the filled block is machined to the desired dimensions. For optimum pe rformance, the polymer phase should have complementary interaction with the ceramic phase as well as imparting dimensional stability. Epoxy-based poly mers are the most usual passive materials because of their low viscosity in the uncured state and solvent resistance, coupled with their excellent adh esive, mechanical, and electrical properties. However, the curing of epoxy resins results in shrinkage of the polymer matrix and internal stress withi n the passive phase. This can lead to prestressing of the active ceramic ma terial, distortion of pillars, reduction in the parallelism between the sid es of pillars, and, in certain circumstances, warpage of transducers. This is particularly evident when the solid stock in the bristle block is relati vely thin. This paper reports the in situ modification of epoxy in the bris tle block by UV-based low temperature polymerization of acrylate monomers w ithin the epoxy matrix prior to polymerization of the epoxy resin. Internal stress measurements are presented to quantify the influence of this modifi cation via a reduction of internal stress within the polymer matrix. Result s from finite element analysis emphasise the conclusions of the experimenta l work, and examples of manufactured devices are presented. Composite trans ducer performance is assessed by laser measurement of surface displacement profiles, and a 50% improvement in surface displacement magnitude was obser ved for the modified devices.