CENTENNIAL HONORS COLLEGE
Western Illinois University
Undergraduate Research Day 2015
Poster Presentation
Measuring Material Properties with Parts-Per-Billion Sensitivity by Utilizing a Tunnel
Diode Resonator Circuit
Justin Gonzales
Faculty Mentor: Ryan Gordon
Physics
My research utilizes a tunnel diode resonator (TDR) circuit to measure material properties with
extreme precision and at low temperatures. The TDR circuit is a specialized LC oscillator powered by a
tunnel diode with a resonance frequency near 10 MHz. The key advantage of this experimental technique
is its sensitivity, where frequency changes of the TDR can be measured with parts-per-billion resolution.
This circuit has been used to measure magnetic properties of materials in the past by using the inductor of
the TDR circuit. The main goal of this project is to use the capacitor of the TDR circuit to measure
dielectric properties of samples by placing them between the conductors of the TDR capacitor. Utilizing
the capacitor of the TDR to measure material properties is the first systematic study for this sense element
in the experiment. My research will focus on the basic design for this TDR circuit and how it will be
interfaced with the cooling stage of the closed-cycle helium cryostat in our laboratory. Once the design
and construction of this circuit are finished, the plan is to study the dielectric properties of single crystals
of VO2, which shows a transition from a state where it is a very good conductor to a state where it is a
very poor conductor, also known as a metal-insulator transition.