From NIST Tech Beat, 10/07/2014
Researchers at the National Institute of Standards and Technology (NIST) and the University of Michigan have demonstrated a technique based on the quantum properties of atoms that directly links measurements of electric field strength to the International System of Units (SI).
The new method could improve the sensitivity, precision and ease of tests and calibrations of antennas, sensors, and biomedical and nano-electronic systems and facilitate the design of novel devices.
Conventional electric field probes have limited frequency range and sensitivity, often disturb the field being measured, and require laboratory calibrations that are inherently imprecise (because the reference field depends on the geometry of the source). Furthermore, linking these measurements to SI units, the highest level of calibration, is a complex process.
NIST’s new electric-field probe spans enormous ranges. It can measure the strength of fields from 1 to 500 gigahertz, including the radio, microwave, millimeter-wave and sub-terahertz bands. It can measure fields up to 100 times weaker than conventional methods can (as weak as 0.8millivolts per meter, the SI unit of measure). Researchers used the new method to measure field strengths for a wide range of frequencies, and the results agreed with both numerical simulations and calculations.
Importantly, the new method can calibrate itself, as well as other instruments, because it is based on predictable quantum properties: vibrations in atoms as they switch between energy levels. This self-calibration feature improves measurement precision and may make traceable calibrations possible in the millimeter and sub-terahertz bands of the spectrum for the first time.