RF field strength is typically measured using a calibrated antenna. Researchers at the National Institute of Standards and Technology (NIST) and the University of Michigan have come up with a technique based on the quantum properties of atoms that directly links measurements of electric field strength to the International System of Units (SI).
A major advantage of this new method is that it does not disturb the field being measured and does not require laboratory calibrations that are inherently imprecise because the reference field depends on the geometry of the source. Because the method is based on predictable quantum properties of vibrations in atoms as the switch between energy levels, it can calibrate itself.
NIST project leader Chris Holloway said, “The exciting aspect of this approach is that an atom is rich in the number of transitions that can be excited. This results in a broadband measurement probe covering a frequency range of 1 to 500 gigahertz and possibly up to 1 terahertz.”
To measure field strength, researchers use a red and a blue laser to propel atoms contained in a cylinder to high-energy (“Rydberg”) states, which have properties such as extreme sensitivity and reactivity to electromagnetic fields. An electric field generated by and antenna or other source affects the spectrum of light absorbed by the atoms. Researchers can calculate the field strength by measuring this effect. Different atoms can be used, depending on the frequency spectrum being measured. NIST uses rubidium or cesium.
Potential applications include measuring and optimizing densely packed electronics, including radar and wireless communications and control links and integration into endoscope probes with medical applications such as investigating implants in the body. The NIST instrument is currently tabletop-sized, researchers are working on miniaturizing it using photonic structures. A smaller version could become part of a future “NIST on a chip” offering multiple measurement methods and standards in a portable form. The technique is the first to enable calibrated measurements at frequencies above 100 GHz.
For references and more on the NIST research, see the NASA Tech Beat article NIST Quantum Probe Enhances Electric Field Measurements.
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