David T. Markus

Phenomenon of skipping-sparks in discharges on a dielectric surface

Gliding sparks are associated with channel breakdown in air near a corona precharged dielectric layer backed by ground. Characterized by high-current, their bright channels usually end in sudden branching/dimming. Infrequently, a subclass occurs in which channel brightness is interrupted, with no evident local branching but a new leader continuing on propagating after momentary delay. This skipping-spark phenomenon has been studied in an experimental system intended for taking Kirlian photographs. Operated in a Lichtenberg figure mode, the method yields evidence in some detail. The authors report on observations of spark-channel touchdown and subsequent rebounding. A model based on nonuniform surface charging is proposed for explanation. Simulation tests are performed and shown to support the hypothesis. >

Precision micromotor for surgery

A silicon-based piezoelectric linear stepper motor has been designed and fabricated. The motor is based on an inertial drive concept derived from sequential electrostatic clamping and unclamping of a piezoelectric bar measuring 38.1/spl times/6.36/spl times/0.787 mm. The piezoelectric micromotor has been constructed and tested for precision surgical applications. The measured performance is dependent on the operating conditions selected. Representative performance is a speed of 1.2 mm/s against a 3.0 N load. The motor is limited in its travel by approximately the diameter of the silicon wafer used to fabricated it. The resolution of the motor is less than 100 nm in its most precise actuation mode.

Integration of a CMOS Preamplifier with a Lead Zirconate Titanate Resonant Frequency Microsensor

We report in this paper on the fabrication of a two-stage, folded-cascode complementary metal oxide semiconductor (CMOS) amplifier and a resonant frequency microsensor. The fabrication of a CMOS amplifier was performed in the microtechnology laboratory at the University of Minnesota for applications in microelectromechanical (MEM)-based sensors. The fabrication of a CMOS amplifier employs the University of Minnesota 3 μm CMOS process. Results from circuit measurements show the 3 dB frequency of 600 kHz, the unity-gain frequency of 3.78 MHz, and the dc gain of 14 dB. The phase margin is around 83°. For the fabrication of a resonant frequency microsensor, Pb(Zr 0.53 Ti 0.47 )O 3 (lead zirconate titanate, PZT) thin film was used. PZT is a promising piezoelectric material for fabricating MEMs-based sensors and actuators on a silicon substrate. The resonant frequency microsensor reaches a maximum in amplitude at 133 kHz. The sensor was connected to the fabricated CMOS amplifier. Then a 10 mV p-p sine wave of 1.5 MHz was driven to the sensor. The output of 5 mV p-p at 1.5 MHz was obtained from the output of the CMOS amplifier.

Bridge structure PZT thin film microtransducer with mass loading

We report on a bridge structure PZT [Pb(ZrxTi1- x)O3] thin film microtransducer with proof mass that has been fabricated successfully at the Microtechnology Laboratory (MTL) of the University of Minnesota. The bridge microtransducer is made on silicon wafer using bulk micromachining of microelectromechanical systems (MEMS) and special techniques for deposition of a PZT thin film. The bridge is 300 micrometers wide, 1000 micrometers long, and a few micrometers thick. A proof mass made from the silicon wafer is loaded under the bridge at the central region, its area is 300 X 300 square micrometers and its thickness is 475 micrometers (same as the wafer). Used as an accelerometer, the microtransducer is calibrated using a Vibration Test Systems (VTS), which is a commercial accelerometer calibration instrument. The sensitivity of the microtransducer is constant over the range of frequencies from zero to 10 kHz, 240(mu) V/g at 0.5g with a dc bias voltage of 0.2 volts and a deviation of 5%. The Brownian thermal noise equivalent acceleration is 9.072(mu) g/(root)Hz. Design of a bridge structure with mass loading is modeled using ANSYS. Simulation analysis shows that the fundamental natural frequency of the microtransducer is 11.352 kHz, which is close to the measured resonant frequency of 12.28 kHz.

A method of direct corona imaging on a dielectric transparency

The standard scheme of Kirlian photography is modified to have water on top of a thin mylar dielectric layer, underneath which the object is placed. Water serves both as an electrode and as a constant-temperature heat reservoir. HV is applied between object and water to create sustained corona discharges. Experiments showed that, under an AC or pulsating-current excitation over a duration of minutes, a permanent optical image becomes retained on the mylar surface, which is then usable for projection or for direct viewing with slanted lighting. Direct current approaches were found inefficient to produce the same results. A thermo-plastic theory is hypothesized to account for the observations.<<ETX>>