Bharat Rawal

Comparison of piezoelectric and electrostrictive actuator stacks

Piezoelectrics have been around for decades as acoustic or sensing components. In the last few years, however, they have seen increasing use as means to provide motion and control in the micron realm, well below the resolution level of mechanical or electromechanical devices. Their high hysteresis (15 - 20%), however, was a problem in some systems, and this led to the development of electrostrictive materials, which reduced that hysteresis by an order of magnitude, but at a cost of other parameters. The purpose of this paper is to compare the properties of each of them, without favoring one or the other.

An electrically-excited acoustic emission test technique for screening multilayer ceramic capacitors

An AC-voltage-induced acoustic emission test technique for screening physical flaws, particularly delaminations, in various Z5U and X7R/BX ceramic capacitors was extensively evaluated. The test results showed that the severity of delaminations strongly coincided with the corresponding degree of severity in the acoustic signal. This led to a ten-times-higher rejection rate against the ceramic capacitors with delaminations in most of the screening tests. The source of acoustic waves was attributed to the partial discharge in delaminations, cracks, and pores due to the field intensification by the high-K dielectric materials. Almost identical patterns of behavior were found for acoustic emission and partial discharge with respect to the application of voltage and the chance of dielectric material.<<ETX>>

Multilayer electroactive ceramic actuators

A type of electrical component which produces slight (micron level) mechanical movements is introduced. Made from electroactive ceramics and using MLC (multilayer ceramic) fabrication techniques, it offers a new domain of movements with a high degree of precision and absence of magnetic fields. The construction, properties and some potential applications are provided.<<ETX>>