Sistema RFID para monitoramento das frequências respiratória e cardíaca.

Abstract

In this work, an RFID system for monitoring respiratory rate was developed and a circuit for monitoring heart rate was designed. A metamaterial structure was used in the passive RFID tags to improve its performance by increasing its maximum gain value. The monitoring of the respiratory rate was based on the variations of the Received Signal Strength Indicator (RSSI) by the reader due to respiratory movements. In some breath measurement configurations, the maximum read range was greater than 1 m, which is the distance considered in the measurements setups described in some scientific papers. The RSSI data, obtained by reading the RFID tag, were processed using the Daubechies wavelet of order 3 (db3) and considering three levels of signal decomposition. Less noisy breathing signals were obtained in measurements with the participant seated, at rest, and considering the RFID tag with two CSRR cells in positions 1 and 3 and the RFID tag with eight CSRR cells and the 11 mm polyethylene foam in position 2 on the abdomen. The respiratory rates acquired from the variations of the RSSI parameter, considering the participant at rest, were validated by comparison with the results obtained using a vital signals monitor. For heart rate monitoring, a heart rate detection circuit was developed, consisting of an ECG acquisition circuit, which provides the amplified and filtered ECG signal, and a timer, which is fed by the output signal of this ECG signal acquisition circuit and changes its output to a high level after a heartbeat is detected. The output signals of these circuits were visualized on an oscilloscope, checking the detection of the ECG signal peaks by the timer. In addition, from the output signal of the ECG signal acquisition circuit, it was possible to obtain the heart rate value considering the time interval between two successive R waves. However, it was not possible to communicate between the timer and the RFID tag chip, which would allow obtaining that frequency from the time interval between successive RFID transmission interruptions.