To measure, it means to compare the properties of an object of interest to an etalon or a fixed standard. The science of precise measurements is called metrology and national laboratories are tasked to produce and maintain the standards necessary for both commerce, industry and advances in sciences. The field of electrical metrology includes standards of: voltage, current, power, impedance, etc. As a master’s degree student in Serbia I build and calibrated a device to compare voltage and current signals while measuring electric power [j29]. This comparator had the measurement uncertainty of parts per million and it was part of the regional power etalon used for calibration at the University of Novi Sad standards laboratory.
My first project in US was the NASA Zeno experiment which focused on determining the critical point of the inert gas Zenon. The objective of the research was to determine increased viscosity of Zenon in microgravity, at precisely specified volume, pressure and temperature [j21, j22]. The utility of this research, beyond the basic science, is the possibility to use Zenon as a breaking fluid. In the Zeno experiment the pressure and the volume were kept constant and the temperature was controlled with the resolution of micro Kelvin in order to keep Zenon to stay between its gaseous and liquid states. As a PhD student at the University of Maryland, I developed a measurement system to calibrate the temperature measurements obtained by Zeno bridge. Balancing a bridge involves zeroing the current through electrical components in order to precisely determine relationship between the standard and the device under the test. I constructed binary inductive dividers with the resolution on the order of parts per billion and successfully defined the accuracy of the Zeno bridge [j20]. This work continued and the national standard for calibrating voltage ratio measurements at NIST, was developed [j17, j18].
Mastering the bridge measurements facilitates the impedance evaluation procedures. In the end, the users bring resistors, inductors and capacitors to calibrate at a national lab. Air capacitors are critical components because they exhibit relatively stable performance over time in a reasonably controlled environments. While at the Academy my research focused on the capacitance evaluation [j15]. The culmination was the development of the measurement procedure to calibrate capacitors ranging from 100 pico Farad to 10 micro Farad [j16]. This process is presently used at NIST. Its significance is in the fact that this is a unique comprehensive analysis based on using reference measurement to identify the parameters of a capacitor model and estimate its performance at high frequencies. Even though performed in 2000, high frequency impedance calibration work remains to be relevant, being cited as recent as last month.
Displacement sensors based on the change in capacitance are comparatively simple devices and as such they are attractive in various applications. In particular, planar sensors are often used as noninvasive motion detectors. Macro scale planar sensors I built and analyzed [j14] are important because they exhibit stability at the order of 30 parts per million, allowing them to be used in simple automated industrial measurement systems. This research is also currently internationally popular.
To implement nano scale positioners in autonomous nano robots, displacement measurements at the order of nanometers at the distances of micrometers are required. Planar capacitive sensor are critical in this case, because of their sensitivity, simplicity and most importantly they do not load the nano devices they measure. The sensors I developed use the nano device itself as changing dielectric above the planar charged plates [j12]. NIST facilitated the fabrication of my nano scale sensors and provided test bed for the evaluations. This research has been ongoing for number of years and our latest publications [j13, j11] summarize a novel sensor structure that, at distances of approximately 0.5μm and 30μm, demonstrates resolution at the order of tens of nanometers.
The details of my scientific contributions discussed in this overview, are given in cited journal papers labeled [j xx]. More nuanced deliberations on my research are in the 64 technical conference proceedings and the 29 journal papers.
- National Institute of Standards and Technology (NIST) NIST Laboratory publications
- I collaborate with scientists in The Quantum Electrical Metrology Division
- AC-DC Difference Standards and Measurement Techniques
- Farad and Impedance Metrology
Most interesting projects
- Capacitance Scaling system used presently at NIST for world-wide customer capacitor calibrations
- Hard Disk Interface used in Computer Forensic Science in NIST Aroma project
- Inductive Voltage Divider calibration system for NASA Zeno experiment that flew in space in 1994 and 1996
- Capacitance sensors Making a very sensitive capacitance probe
- Intelligent system Precision Meso/Micro Systems for Nano-manufacturing