Microstrip patch and Sierpinski fractal antennas: simulations and experimental characterization for vital signs detection with Doppler radar technique

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/m 2 and of 2.6 x 10 -2 mW/m 2 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.

Microwaves propagation through a small fire curtain at 3.55 GHz and 6.26 GHz and the impact on vital signs detection by using a four-element patch antenna array

“…The human pulse frequency values detected with the couple of array antennas at 3.55 GHz in the present session of tests were a bit striking at first site, mainly because they were spread due to the noisy recorded signal. If compared to some of our previous results reported in [21], when a single patch antenna was used, the present antenna solution seems worse. At a deepen analysis we identified the possible cause, which seems to be the mutual coupling between the patches of the array.…”