Abstract
Objectives: To fabricate planar models of antennas with resonance frequencies in the ultrahigh frequency band that allow short-range detection of respiration and heartbeat by a simple continuous wave Doppler radar system. Methods: Models of antennas were created in CST Studio software and the main parameters were computed. Then, antennas were fabricated at a PCB prototyping machine and were experimentally characterized in an anechoic chamber. Total efficiency and radiation patterns indicated the best working frequencies of 2.12 GHz and 8.82 GHz respectively, to test the human vital signs detection with a continuous-wave Doppler radar technique in direct visibility conditions. Findings: The patch antenna at 2.12 GHz had a maximum gain of 3.15 dBi and total efficiency of 43% while the Sierpinski antenna at 8.82 GHz had a maximum gain of 5.5 dBi and total efficiency of 65%. At incident power densities on the human subject’s chest of 4.5 x 10-4 mW/m2 and of 2.6 x 10-2 mW/m2 respectively, the Doppler radar system based on these antennas offered precise responses. Practically, it was possible to extract both the heartbeat rate and the respiration rate, by simply applying the classical FFT algorithm on a time-series phase data of the transmission coefficient recorded during 30 seconds, when the set-up was composed of just the antennas and a vector network analyzer. Novelty: Increased detection accuracy was obtained due to careful characterization of the antennas parameters with no need of special processing algorithms. Keywords: Sierpinski Antenna; Patch Antenna; CW Doppler Radar; Respiration Rate; Heartbeat Rate
Highlights
The development of antennas for various applications is a branch of continuous development
The present approach aimed at a comprehensive characterization of two in-house fabricated antennas using the printed circuit board (PCB) technique, to establish their proper use for vital signs detection based on continuous wave (CW) Doppler radar principle
Two narrow resonance frequency bands and a larger one are identified on the standing wave ratio (SWR) graph of the patch antenna, while multiple resonance narrow bands and an ultra-wideband one are observed at the Sierpinski antenna
Summary
The development of antennas for various applications is a branch of continuous development. The present approach aimed at a comprehensive characterization of two in-house fabricated antennas using the printed circuit board (PCB) technique, to establish their proper use for vital signs detection based on continuous wave (CW) Doppler radar principle. Microstrip patch antennas are consisting of a pair of good conducting layers separated by a dielectric substrate. The upper conducting layer is the radiating/active part of the antenna, while the bottom layer is the ground plane. One needs to connect the active surface with the ground plane. Having lots of advantages supplemented by the possible reconfigurability, patch antennas are present today in laptops (for Wi-Fi, GPS, Bluetooth connections, etc.), mobile phones, WiMax networks, MIMO systems, cognitive radios, satellite communications, and in radars and body-centric communications [3,4]
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