A Circuit Model For Passive RF Autonomous Devices With Protocol Considerations

Abstract

This paper focuses on a lumped circuit model for autonomous untethered wireless devices powered by remote radio frequency (RF ) sources including radio frequency identification (RFID) tags. The technology presents major challenges for these passive (no on-board power) devices, including the ability to provide maximum power for data transmission and data rates under powering constraints due primarily to governmental regulations. This paper presents the electronic circuit model of a remote temperature-sensing device less than 0.5 cubic inches in volume. The RF energy is first converted to a DC voltage that is then used to power circuitry to measure temperature and transmit the reading to a remote receiver. These devices are typically deployed in large groups functioning as sensors or RFID tags that communicate with a single receiver. The typical rate at which energy can be harvested, converted, and used to power circuitry and transmitter is about 0.025% of the rate at which the power is used. Thus, careful consideration must be given to the circuit model, including parameters and communication protocols. Included in the paper are a logically derived circuit topology and the methodology by which the parameters can be determined. The protocol can then be analyzed with respect to power using the resulting circuit model.