Microheaters based on ultrasonic actuation of piezoceramic elements

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.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90803/1/0960-1317_21_8_085030.pd

Locomotion response of airborne, ambulatory and aquatic insects to thermal stimulation using piezoceramic microheaters

This paper reports the locomotion response of airborne, ambulatory and aquatic insects to thermal stimulation. A finite element model has been developed to predict the variation of insect–stimulator interface temperature with input power. Piezothermal stimulators have been fabricated from lead zirconate titanate (PZT) using a batch mode micro ultrasonic machining process. Typical sizes range from 200 µm to 3.2 mm. For PZT stimulators, the temperature and thermal efficiency reach the maximum value around the resonance frequency which is typically in the range of 650 kHz to 47 MHz. Experiments have been conducted on green June beetles (GJBs), Madagascar hissing roaches and green diving beetles (GDBs) in order to show the versatility of the proposed technique. The stimulators have been implanted near the antennae of the GJBs and on either side of the thorax of the Madagascar hissing roaches and GDBs, respectively. In all cases, the insects move away from the direction of the actuated stimulator. The left and right turns are statistically similar. Thermal stimulation achieves an overall success rate of 78.7%, 92.8% and 61.6% in GJBs, roaches and GDBs, respectively. On average, thermal stimulation results in an angle turn of about 13.7°–16.2° on GJBs, 30°–45° on the roaches and 30°–50° on GDBs. The corresponding average input power is 360, 330 and 100 mW for GJBs, roach and GDBs, respectively. Scaling limits of the PZT stimulators for operating these stimulators are also discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90797/1/0960-1317_21_12_125002.pd

Bulk Micromachined Piezoelectric Transducers for Ultrasonic Heating of Biological Tissues.

This work explores the use of bulk micromachined piezoelectric transducers for ultrasonic heat generation. The work includes basic studies of the phenomenon, the development of simulation models, the design and fabrication of practical devices and interface circuits. The technology is demonstrated in two application contexts: cauterization with a biopsy needle, and stimulation of insect locomotion. Simulations based on three-dimensional finite element models, indicate that circular disc-shaped elements provide superior steady-state temperature rise for a given cross-sectional area, volume of the PZT element, and drive voltage. The heating is greatest at the frequency of maximum electromechanical conductance. The thermal efficiency is maximized at frequency of maximum electromechanical impedance. Stacked PZT heaters provide 3.5x the temperature rise and 3x greater efficiency than single elements. A biopsy needle with an embedded array of four piezoceramic microheaters of 200µm diameter and 70-80µm thickness has been fabricated. The PZT-5A heaters generate the target temperature rise of 33˚C at the tissue-needle interface for an input power of <325mW and a drive voltage of <17VRMS when inserted into porcine tissue. The extent of tissue cauterization is <1.25mm beyond the perimeter of the needle. Cauterization of porcine tissue sample results in a decrease of 600kHz in the resonance frequency and 900ohms in the peak impedance magnitude, allowing the extent of cauterization to be monitored easily. Interface circuits for measurement of resonance frequency shift due to cauterization and for actuation of PZT heaters are also described. Experiments have been conducted using piezothermal stimulators implanted near antennae of green June beetles (GJB), and on either side of the thorax of Madagascar hissing roaches and green diving beetles (GDB) to show the feasibility of locomotion control using microthermal stimulation. Thermal stimulation causes the insects to move away from the direction of the actuated stimulator. Thermal stimulation achieves an overall success rate of 80%, 93.5% and 68% in GJB, roaches and GDB, respectively. On average, thermal stimulation results in an angle turn of about 15˚-18˚ on GJB, 30˚-45˚ on the roaches and 15˚-60˚ on GDB. The corresponding average input power is 360mW, 330mW and 100mW for GJB, roach, and GDB, respectively.Ph.D.Mechanical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/86544/1/vkarthik_3.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/86544/2/vkarthik_2.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/86544/3/vkarthik_1.pd