Andrew J. Dupree
University: University of Maryland, College Park
Major: Computer Engineering
Gradation Date: May, 2011
Hometown: Bowie, MD
New Designs for High-Resistance Hamon Transfer Standards
About my project: To understand my project, one should first grasp the fundamentals of the field of resistance metrology. For your textbook definition, resistance metrology is the precise measurement and calibration of resistors. This definition subsumes four subgoals. First, the scientists in this field strive to create increasingly accurate methods of defining the value of a resistance. Since 1990 this has been done with the Quantum Hall Resistance, a value composed of fundamental constants. Second, they build highly accurate and stable resistors (called standards) which serve as storage mechanisms for a resistance. Additionally, resistance metrologists accurately calibrate other resistors to these standards, and, finally, seek to improve dissemination of resistance to commercial calibration labs. In particular, my project was part of a sub-field of resistance metrology, high resistance metrology. This branch is concerned with accomplishing the aforementioned tasks with resistors in the range of 10 MΩ to 100 TΩ.
The main problem we have sought to solve is that current designs for high-valued standard resistors have reached a plateau in accuracy. Lengthy settling times have made direct scaling from the Quantum Hall Resistance challenging, and leakage current due to insufficient implementations of guard circuitry and resistor connections has been a source of error. To circumvent these obstacles, we have implemented several new design features in the construction of a new set of 100MΩ standard resistors and Hamon transfer standards – special standards whose value can be changed depending on how you connect the device. First, film type resistors are being used instead of the traditional wire-wound variety, due to the improved stability of modern films and lack of inductive properties. Second, an internal guard network has been carefully measured and simulated for maximum reduction of leakage current between the main resistor circuit and ground. Also, to decrease leakage current at resistor terminals, new glass-to-metal seals have replaced older metal-PTFE connectors. These new seals do not suffer from charge accumulation to the same extent as did their predecessors.
A complete battery of tests and measurements are necessary before reaching a firm conclusion, but initial calibrations with NIST’s Dual Source Bridge and Cryogenic Current Comparator show promising results. These new standards show no settling time, and the resistors hold quite stable across multiple measurements. If our results continue to be positive, we will apply these same techniques to resistors in giga and teraohm range.
About Me: I remember my father bringing home our first computer – a Gateway machine running Windows 95 – when I was 5 years old. It captivated me then, and my interest in science and technology has been a constant ever since. When I was accepted into the University of Maryland and it came time to choose a major, the choice was clear. I decided on Computer Engineering because I knew that I wanted to be involved in building the next generation of technology, in creating new and exciting things.
It is that wish – to do new things – that lead me to NIST. When looking for a summer job I focused solely on finding research opportunities. And when a national laboratory whose entire purpose is innovating new technology offered me a research fellowship, I surely could not say no. Working in the Electronics and Electrical Engineering Laboratory at NIST has been an incredibly rewarding experience. I have gained a real understanding of what the research world is like, and where I might be able to find a place for myself in it.
To be honest though, one cannot talk about SURF and only mention the research aspect. Equally rewarding has been getting to know the other SURF students from all over the country. Cook-outs and ultimate Frisbee, DC trips and midnight movie outings, all of these experiences and more have made for a truly special summer.