University: The University of San Diego
Major: Electrical Engineering
Gradation Date: Spring 2011
Hometown: Boulder, Colorado
Project: The kilogram is currently defined by the mass of the International Prototype Kilogram (IPK), making it the only SI unit derived from a physical artifact instead of fundamental properties of nature. We now believe that the mass of the IPK is drifting slowly over time. Because of this inconsistency, scientists are scrambling to find a new definition for the kilogram that will not change over time. The electronic kilogram experiment hopes to redefine the mass standard based on Planck’s constant (h), an unchanging fundamental constant. If we were to fix Plank’s constant to an exact value, the kilogram would be tied to the second through this number and other constants. The electronic kilogram at NIST currently has the best measurement of Planck’s constant in the world (6.62606889 * 10-34 J s) with an uncertainty of only 36 x 10-9, making our approach the leading candidate for the redefinition.
The electronic kilogram is a complicated system that compares electrical power (UI) to mechanical power (mgv). To do this, we use a two step procedure. First, an induction coil is suspended in a magnetic field which produces an electromagnetic force exactly opposed to the gravitational force of the mass (mg=ILB). The coil is then moved through the magnetic field, inducing a voltage (U=BLv). We can combine these two equations to get our final formula (mgv=UI). By using our knowledge of the Josephson effect and the Quantum Hall effect, we are able to find a value for Planck’s constant. Precise values for voltage, resistance, mass, time, length, and the gravitational constant are needed for this experiment. These quantities are found using a Josephson array voltage standard, a quantum hall calibrated standard resistor, a calibrated artifact mass, a laser interferometer, a GPS, and both an absolute and a relative gravity meter.
Over the course of the summer I worked on three concurrent projects. 1) The computer program for our Josephson Voltage standard was many years old and needed to be replaced. I integrated a new program based on LabVIEW that runs more efficiently and is better coupled with our main program. 2) I also wrote a LabVIEW program that drives high precision piezo motors to control the tilt of the induction coil. When the coil is tilted, a cosine term is introduced into the equation, leading to possible errors and making our calculations more difficult. With the use of these motors, we can greatly reduce this potential source of error. 3) We also needed to synchronize many of our instruments to a standard frequency. I built a transmitter/receiver circuit that brought a 10 MHz signal from our GPS standard to our instruments in another room upstairs. With these improvements and further progress, we hope to reduce our uncertainty for Planck’s constant, and ultimately form the basis of a new kilogram standard.
About me: I grew up in Boulder, Colorado. In high school I really started to become interested in science. I was particularly interested in Physics and its practical applications in the world. For this reason I decided to study electrical engineering at the University of San Diego. Last year, I participated in the SURF program where I gained many skills that helped me both inside and outside of school. I had a great experience so I decided to return to NIST this summer. I am enjoying my project and have learned a lot during my time here. I plan on attending graduate school in electrical engineering, and will ultimately pursue a career in research.