Fully-passive wireless and disposable bodysensors are promising for unobtrusive monitoring of physiological signals at natural settings. We present a new type of wireless analog passive sensor (WAPS) based on resistive damping, which can be used for biopotential sensing. The resistive WAPS operates by modulating the amplitudes of the incident RF signal, and composes of a loop antenna, a tuning capacitor, and a MOSFET (an additional biasing resistance is used in one variation). The scanner transmits carrier RF signal at 13.34MHz and the load modulated signal is captured with the signal analyzer. The envelope of the modulated signal correlates with the biopotential being sensed. Both enhancement and depletion MOSFETs are demonstrated, where the earlier demonstrated superior performance. The sensitivity can be as low as 10 mV, suitable for ECG and EMG physiological signal capture. The transmission power were 0 dBm while the co-axial separation between antennas were 21.5 mm. The results show that the proposed WAPS can be used to develop disposable biopotential sensor suitable for body-worn physiological signal monitoring system.
Dry electrodes for impedimetric sensing of physiological parameters (such as ECG, EEG, and GSR) promise the ability for long duration monitoring. This paper describes the feasibility of a novel dry electrode interfacing using Patterned Vertical Carbon Nanotube (pvCNT) for physiological parameter sensing. The electrodes were fabricated on circular discs (φ = 10 mm) stainless steel substrate. Multiwalled electrically conductive carbon nanotubes were grown in pattered pillar formation of 100 µm squared with 50, 100, 200 and 500µm spacing. The heights of the pillars were between 1 to 1.5 mm. A comparative test with commercial ECG electrodes shows that pvCNT has lower electrical impedance, stable impedance over very long time, and comparable signal capture in vitro. Long duration study shows minimal degradation of impedance over 2 days period. The results demonstrate the feasibility of using pvCNT dry electrodes for physiological parameter sensing.
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