Electromagnetic Field Intensity Imaging by Thermofluorescence in the Visible Range

International audience; Methods to measure the electromagnetic field intensity on a large scale should be improved to meet the growing demand in civil and military applications. The recent development and an application of a microwave electromagnetic field imaging method using a thermofluorescent device and detection in the visible-light range are described. The sensor is a flexible film sensitive to either an electric field (slightly conductive film) or a magnetic field (insulating film with ferromagnetic particles) coated with a polymer doped with fluorescent molecules displaying temperature-dependent emission. We use a lock-in thermog-raphy protocol consisting of modulation of the field at low frequency, which allows us to suppress the noise due to heat-transfer phenomena and the part of the signal not directly related to field absorption. Two applications of the method are presented: (i) imaging the microwave magnetic field emitted by a resonator antenna and (ii) the local probe measurement of the electric field inside a multibeam antenna. The process to develop the sensitive film, its detailed characterization, and the thermofluorescence-image demodula-tion postprocessing are presented in detail. This approach is much cheaper than one based on infrared thermometry and could permit democratization of microwave-and radio-frequency electromagnetic field imaging.