A portable wireless monitoring system for sleep apnoea diagnosis based on active RFID technology

A novel portable wireless monitoring system for sleep apnoea diagnosis is presented in this paper. The presented system is composed of two main parts. The first is an on-body sensor system; the second is a reader and base station. In order to minimize the physical size of the on-body sensors and to avoid interference with 2.4 GHz wireless applications, the system is designed to operate in the 5.8 GHz ISM band. Each on-body sensor system consists of a physiological signal detection circuit, an analogue-to-digital convertor (ADC), a microcontroller (MCU), a transceiver, a channel selection bandpass filter (BPF) and a narrow band antenna. The reader uses 6 narrow band antennas, 6 channel selection BPFs, a transceiver and a MCU. Instead of dealing with channel selection at baseband, multiple passive BPFs at the RF front-end are adopted to select the desired signals, in order to minimize the power consumption and cost of the overall system. Moreover, a 5.8 GHz circular patch antenna is simulated and measured. Both the simulated return loss of 21 dB and the measured one of 26 dB have a 10 dB bandwidth of 140 MHz which satisfies the requirements for the reader system. The measured antenna gain from 5.725 GHz to 5.875 GHz is more than 7.5 dBi. Furthermore, the 3 dB beam-width is about 60° and the front to back ratio is 14 dB.