Wireless Analog Passive Sensors for Small Bioelectric Signal Measurement Through Load Modulation

David Arellano has been working in the Embedded Systems lab in the Electrical Engineering Department since Spring 2014 and plans on attending graduate school after receiving a bachelors degree. He also plans to stay involved with the research community after graduation. With a passion for travel, he hopes to see as much of the world as possible. Free time is spent studying theology, philosophy, and enjoying movies, music, art and nature. Family, friends, and religion have all been incredible influences in his life, and he owes all of his success to these blessings and the continuing support of loved ones. Abstract Fully-passive wireless body-sensors open the possibility for unobtrusive physiological signal capture and monitoring in natural settings. While ca-pacitive analog passive wireless sensors have been developed, we present an alternative solution for signal capture based on load modulation using resistive transducers. The passive sensor is composed of a loop antenna, a tuning capacitor, and a resistive transducer suitable for the type of physiological signals to be measured. The interrogator transmits a carrier RF signal at 11.776MHz whose amplitude is modulated based on the resistive loading by the transducer. In this study, in place of a resistive transducer , an N-Channel Enhancement MOSFET is used to modulate the carrier signal with an applied small signal voltage. In previous studies, the sensor was characterized for various resistive loads of 1.2? to 82K? with an interrogator of low quality factor (Q F). We demonstrate the effect of raising the QF of the interrogator, which increases sensitivity and allows for small signal voltage sensing at very low power levels (0dBm to +5dBm). The results demonstrate the viability of developing body-worn fully-passive sensors for small bioelectrical signal capture.