Reduction of Proximity Effects on UHF Passive RFID Systems by Using Tags With Polarization Diversity
A new technique that enables passive ultra high frequency (UHF) radio frequency identification (RFID) tags to be read when they are placed in close proximity in an array is presented. This paper demonstrates that, in a linear tag array with a tag separation of 1 cm, the interaction between the backscattered waves and incident wave causes a significant degradation in tag sensitivity. It is found that the use of tags that have polarization diversity can improve the read performance when they are placed in close proximity to one another compared with conventional linear tags. Two ways of achieving polarization diversity are studied in this paper, namely: 1) using a circularly polarized tag and 2) using a cross-polarized tag pair. Both methods show an improvement in close proximity read performance and it is experimentally demonstrated that by using cross-polarized tag pairs in an array, one achieves on average a 2.6-dB increase in read power margin for a 57-tag array with 1 cm separation compared with using conventional linearly polarized tags.
CRH: A Contactless Respiration and Heartbeat Monitoring System with COTS RFID Tags
Monitoring respiration and heartbeat contributes to disease prediction, sub-health diagnosis, exercise and sleep quality analysis, fatigue warning, and even emotion estimation. There is a compelling need for contactless, easy-to-deploy and long-term respiration and heartbeat monitoring. In this paper, we present CRH, an RFID-based contactless respiration and heartbeat monitoring system. The key insight is that the RFID signal fluctuation induced by the chest motion is synchronous with respiration and heartbeat. Therefore, CRH collects the temporal phase information from the tag array near or on body to extract respiration and heartbeat signals using a sequence of signal processing techniques. We propose a signal separation method based on multi-tag empirical mode decomposition (EMD) to obtain respiration rate and heart rate after preprocessing. Furthermore, CRH can also detect intense motions and abnormal respiration. We implement and evaluate CRH using Commercial Off-The-Shelf (COTS) RFID devices. Extensive experimental results in different scenarios show that CRH can achieve high accuracy for monitoring multi-user respiration and heart rates, validating its wide applicability and high reliability for contactless fine-grained respiration and heartbeat monitoring.
An image converter-intensifier detector for high-resolution astronomical spectroscopy in the balloon ultraviolet
A rugged and compact image converter-intensifier camera has been developed for a balloon-borne spectrograph used in a programme of UV astronomical interference spectroscopy. Details are given of the construction of this new detector and of relevant performance characteristics in comparison with direct photography.