Executive Summary : | Objective: The very core of all electromagnetic measurements (i.e., antenna characterization, propagation measurements, and channel modelling and measurements) is having accurate calibrated probes and antennas. Calibrating an electric field probe and/or measuring an E-field probe can be challenging, and is somewhat of a chicken-or-egg dilemma. In that to calibrate a probe, one must place the probe (sensor) in a “known” field. However, to know the field we need a calibrated probe. The E-field probes for RF E-field measurement currently in use across the world are of several types, and these do have the limitations. They are not very sensitive, may perturb the field during the measurements, may be relatively large, and require a calibration. The calibration procedure relies on a field value that is known to within only 5%. One promising approach to remedy these problems is by using an E-field probe based on room-temperature Rydberg atoms. In addition, there are probes based on nonlinear materials (e.g., lithium niobate crystals), where the phase of an optical signal propagating through this material changes when exposed to an E-field. These types of probes can gain about one order of magnitude in sensitivity but they still require calibration and will perturb the field being measured.
In the field of electromagnetic measurements, the accuracy in the measurement of E-field amplitude plays a crucial role in the determination of many other parameters such as Specific Absorption Rate (SAR) in biomedical application, EMI/EMC testing of RF and electronic devices, non-invasive RF based detection and diagnostic medical devices, etc. With the rise in the need for precise and accurate measurement of E-field amplitude, arises the need for the new technique to realize the amplitude flawlessly. The lack of traceability in the RF E-field strength measurements has been a major source of errors throughout the years and limits the growth of research works requiring impeccable measurements. Moreover, till now we don’t have the E-field sensors which work in the Infrared region clearly showing the measurable gap in the electromagnetic spectrum. Atom-based metrology standards have been widely accepted in the recent past for a number of measurements namely length, time, and frequency. This approach facilitates the stated goal of direct SI traceability in the measurements. The present calibration process of the E-field probes poses indirect and complex traceability path thus making it a very challenging task to perform. To calibrate them one need a known field in the testing room and to ensure the field in the roomone again need a probe to read it. To overcome this dilemma during the calibration process, research work is going on to realize the RF E-field strength measurement through the atomic transitions based approach. |