Abstract
This paper explores antenna's polarization for Radio-Frequency Identification (RFID) based non-contact human activity detection. For the first time, a cross circular polarization configuration between reader antenna and tag antenna is proposed to increase the sensing range and spatial sensitivity. Compared to conventional RFID configurations - linearly polarized (LP) tag and circularly polarized (CP) reader, a cross CP configuration can improve the signal-to-noise ratio (SNR) which leads to 230% increase in the detection area over traditional approach in our experiment. As the result of the improvement of spatial sensitivity, the proposed approach can detect subtle and small body movements at almost 4.5m from the reader, such as head movements or even respiration, which enables a low-cost, easy-to-use, non-contact and non-intrusive monitoring of the elderly and disabled peoples in places like hospitals and assisted living homes.
Highlights
Human activity monitoring grants an important role in making lives easier for everyone
It is expected that the RSSI variation with the presence of metal sheet is larger than human body because the reflection loss from a perfect conductor is negligible. These experiments verify that left-hand circular polarized waves (LHCP)-right-hand circular polarized (RHCP) configuration in Radio-Frequency Identification (RFID) system can effectively suppress the LOS signal strength while enabling the reception of the reflected signal. This result shows that the circularly polarized (CP) tags are much more sensitive to human presence, given their large variations in RSSI compared to the linearly polarized (LP) tags, which suggests that the cross circular polarization configuration can enable the small and subtle body movement detection that is barely possible for LP tags
DESIGN AND SETUP The proposed RFID based non-contact human activity detection system consists of one regluar RFID reader and a circular polarized RFID tag
Summary
Human activity monitoring grants an important role in making lives easier for everyone. These experiments verify that LHCP-RHCP configuration in RFID system can effectively suppress the LOS signal strength while enabling the reception of the reflected signal This result shows that the CP tags are much more sensitive to human presence, given their large variations in RSSI compared to the LP tags, which suggests that the cross circular polarization configuration can enable the small and subtle body movement detection that is barely possible for LP tags. Using this data preprocessing method for calibrating the RSSI and phase allows the activities to be clearly and accurately detected
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