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An infrared (IR) measurement technique is described which can be used to detect microwave fields, both continuous wave (CW) and pulsed. The technique involves placing a thin lossy detection screen material in the region over which the electromagnetic (EM) field is to be mapped. The fields are detected through the Joule heating that occurs when EM energy is absorbed by the screen material. When the surface temperature of the screen rises to 0.1 K or higher above the ambient temperature, the induced temperature distribution at the surface of the screen (which corresponds to the EM field intensities in the screen) can be detected by an IR scanning system via emitted thermal radiation. CW measurements by an IR measurement technique have been demonstrated and reported over the past several years. While the technique requires a minimum energy deposition for sufficient heating, the electrical parameters of the detection screen can be selected, such that the thermal mass of the screen is reduced, allowing a faster response. IR data acquisition to a high-speed memory has also been developed to store approximately 500,000 pixels of a two-dimensional IR image in less than three seconds. 5 This corresponds to thirty 128 x 128 frames of data with each pixel element represented as an 8-bit word, which correlates to the electric or magnetic field intensity at that location. As a diagnostic tool, this technique can be used to measure radiated fields and to support tests and evaluations of electronic systems in the presence of EM radiation, e.g., to determine the free-field environments around microwave sources, to determine the energy coupled into electronic circuits through partially shielded enclosures, and to verify hardening techniques. The near, far, and internal fields generated by a microwave horn can be mapped using a thin lossy screen. Apertures in enclosures can be identified by placing a resistive coating on the surface of the metal in the area suspected of containing an aperture. Examples of energy coupled into an electronic circuit and analysis of radiation from antennas are presented. The applications, advantages, and disadvantages of this new infrared technology are also discussed.
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