Microheaters based on ultrasonic actuation of piezoceramic elements

Abstract

This paper describes the use of micromachined lead zirconate titanate (PZT) piezoceramic elements for heat generation by ultrasonic energy dissipated within the elements and surrounding media. Simulations based on three-dimensional finite-element models suggest that circular disk-shaped elements provide superior steady-state temperature rise for a given cross-sectional area, volume of the PZT element and drive voltage. Experimental validation is performed using PZT-5A heaters of 3.2 mm diameter and 0.191 mm thickness. Single-element heaters and dual-element stacks are evaluated. Although the steady-state temperature generated by these heaters reaches the maximum value at the frequency of maximum electromechanical conductance, the heating effectiveness is maximized at the frequency of maximum electromechanical impedance. Stacked PZT heaters provide 3.5 times the temperature rise and 3 times greater heating effectiveness than single elements. Furthermore, the heaters attain the maximum heating effectiveness when bonded to highly damping and non-conducting substrates. A maximum temperature of 120 • C is achieved at 160 mW input power. Experiments are performed using porcine tissue samples to show the feasibility of using PZT heaters in tissue cauterization. A PZT heater probe brands a porcine tissue in 2-3 s with 10 V RMS drive voltage. The interface temperature is ≈150 • C.

Dispersion of Switching Processes in Ferroelectric Ceramics

“…Due to favourable combination of piezoelectric properties and coefficients of electromechanical coupling, the ferroelectric ceramics of lead zirconate titanate family (PZT) is the main functional material for the production of microelectromechanical systems (MEMS) [1][2][3]. Nevertheless piezoceramic elements for MEMS suffer from a number of disadvantages becoming apparent at high power regimes of working in high electric field strengths.…”

“…In piezoceramic materials the losses of the first kind dominate over other ones. They are related to the motion of domain walls including dielectric, elastic, and electromechanical hysteresis losses [3]. As a result of the losses significant undesirable selfheating comes into existence [9,14,15].…”

Power Dissipation during Dielectric Loop Evolution in PZT Ceramics

“…On the other hand, there are examples of direct utilization of the heating losses, such as in microheaters, which are widely used in various branches of microsystem technology [6] and in medicine, e.g. for needle tract cauterization during needle aspiration biopsy [7].…”