Body-worn fully-passive wireless analog sensors for biopotential measurement through load modulation

Abstract

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.

Inkjet Printed Fully-Passive Body-Worn Wireless Sensors for Smart and Connected Community (SCC)

“…However, for body-worn sensors, inductive loading is a more appropriate solution due to non-ionizing radiation and proximity of the portable scanner to body-worn sensors [36]. For the simple WRAP sensor system [37,38], the effective impedance from the scanner side correlates to load resistance (RL) of a RLC parallel circuit, and is given by:…”

“…For instance, R L can be simply transducer resistance [37], or the resistance across a transistor [38,39] used to probe bioelectric or impedimetric signals. The carrier signal amplitude is modulated due to change of R L , and the modulated signals at the scanner correlate to the changes of R L .…”

“…The carrier signal amplitude is modulated due to change of R L , and the modulated signals at the scanner correlate to the changes of R L . We have previously describes WRAP sensors based on this technique for physiological signal collection and bio-potential signal capture [37][38][39].…”

“…This paper focuses on the development and application of a system for collecting physiological data using this novel type of low-cost disposable IJP electronic WRAP sensor. While prototyping of the sensors for measuring ECG, heart rate, respiration rate, and temperature is underway or have been reported elsewhere [37][38][39], this paper focuses on the development of our recent complete system framework development efforts for SCC with an illustrative example of the WRAP temperature sensor. This new technology aims to empower community members to self-monitor personal health, and to generate temporal and spatial knowledge that might improve the overall SCC health condition.…”

“…A major drawback of capacitive sensing is that the sensed signal is limited to voltage only. In contrast, we have developed fully-passive wireless sensors based on a resistive approach, "Wireless Resistive Analog Passiv" (WRAP) sensors, that can sense bioelectric potential (voltage signal) as well as other physical stimuli (e.g., pressure, temperature, light) [37][38][39]. The advantages of WRAP sensors are low cost, high sampling rate, low power, and the possibility of prototyping on flexible substrates using inkjet printing (IJP) technique as discussed below.…”