Investigation into the effectiveness of different highpower ultrasonic transducers on cavitation yield and field control for consumer devices

Interest into consumer applications of high power ultrasound is growing and investigation into the development of transducers for this application is necessary. This paper conducts a primary evaluation on alternative small-scale transducer designs for potential application as cavitation generators in portable ultrasonic devices for cleaning applications. Simulation of the pressure field produced by concave cymbal, convex cymbal and uni-ring-morph transducers are compared with disc and ring only transducers. The potential to increase the active cavitation area through alternative transducer drive signals is also investigated. High power ultrasound production from a piezoelectric disc with simultaneous dual frequency drive has been investigated through simulation and experimentation. Implementation of the Rayleigh-Sommerfeld integral is used to estimate the pressure fields from the disc transducer with both dual and single frequency sonication. Experimentation has been carried out using acoustic emission measurements and aluminium foil erosion experiments to evaluate the cavitation behaviour when dual frequency ultrasound is applied. The results indicate an increase in the number and size range of cavitation bubbles as well as improved foil erosion when dual frequency drive signals containing specially selected frequencies are used.

I. Introduction

The design of the household washing machine has largely remained the same for many years. With advances in technology, many household products are now smaller and require less mechanical parts. However, this effect has not yet been observed in washing machines. In industry, ultrasonic cleaning of textiles has been used since the 1950’s [1], advantages include the ability to wash textiles at low temperatures and the ability to remove foreign particles without the need for mechanical agitation. There is therefore great scope to use ultrasonic technology to provide all of these advantages in the home environment, while minimising the design footprint to allow portability in a consumer washing device.