Innovative 'voltage dependent resistor' developed at Texas State

By Mariah Medina
University News Service
April 28, 2015

Two engineering professors from Texas State University’s Ingram School of Engineering have created an innovative new magnetic field sensor.

Kumar Pandey and William Stapleton said they believe their non-conventional approach will allow the device to have applications ranging from the exploration of energy sources to the study of the magnetic properties of rocks.

“Instead of using the magnetic properties of materials--which is the conventional way--to build our sensor, we exploit the magnetic response of a device called varistor,” Pandey said.

Pandey explained varistors as two devices used to protect an electronic circuit from sudden surges in voltage. The aspect of the devices Pandey and Stapleton exploited is their resistance properties relative to voltage.

Using this property to their advantage, the duo created a device called a “voltage dependent resistor,” abbreviated as VDR. The VDR allowed the operation of the magnetic sensor under conditions most sensors would not be able to function in efficiently.

“(The sensor) might find its applications in hazardous environments, such as at high temperatures or in the harsh radiation of space,” Pandey said. “Unlike many other sensors commercially available, our sensor would be most suitable for high temperature operations. This makes it possible for our sensors to be useful for automotive electronics where large magnetic fields are generated by its solenoid valve.”

The idea for the VDR magnetic field sensor came during the group’s investigation into a new type of hybrid transistor. Pandey and Stapleton, along with two now-graduated electric engineering students Ivan Sutanto and Amanda Scantlin, had already discovered a new class of electronic device—the varistor-transistor hybrid device.

“During the course of that research I realized that varistors based on iron titanate ceramic substrates responded well to a magnetic field,” Pandey said. “My hunch paid off. Instead of varistor we found that a 'voltage dependent resistor (VDR)' could be manipulated to sense magnetic fields.”

Both discoveries have been featured in notable physics journals.

“Inspiration and determination are two key virtues that a scientist must have to invent and discover,” Pandey said. “I am inspired when I see a challenge. I look at a problem and then begin thinking for unconventional ways to solve it. But my ways are not like wandering senselessly in wilderness rather they are based on solid scientific logic and common sense.”