Radio-frequency identification systems used for the remote diagnostics of diseases and contactless monitoring and assessment of human health are reviewed. The propagation of electromagnetic waves inside a biological medium and along interfaces between different media, as well as the problem of telemetry data acquisition from implanted systems or system on the human body surface using wireless sensors, is considered. Emphasis is on radio-frequency identification systems that use far-field electromagnetic radiation, since they are necessary in emergency situations to find injured people in hard-to-reach places and assess the state of emergency response workers.
An original structure of tiled transmitarray is presented, comprising a number of topologically similar unit cells arranged in arbitrary pattern within a planar array frame. Each unit cell represents a passive receiver-transmitter structure with integrated phase-shifter, fabricated in commercial 5-layer printed circuit board process, which can take either of two coding states corresponding to 0° or 180° phase shift imparted to the signal transmitting through the device. The unit cell design supports two orthogonal linear polarizations. An example of a 10x10 element 1-bit beam steering transmitarray operated in C-band is demonstrated by simulations and measurements. The proposed structure represents a cost-efficient solution for scalable transmitarrays and also for proof-of-concept experiments in research and education.
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