There is a growing interest in wireless and batteryless implants for
long-term sensing of organ movements, core pressure, glucose
levels, or other biometrics [1]. Most research on such implants has
focused on ultrasonic [2] and nearfield inductive [3-4] methods for
power and communication, which require direct contact or close
proximity (<1-5cm) to the human body. Recently, RF backscatter has
emerged as a promising alternative due to its ability to communicate
with far-field (> 10cm) wireless devices at ultra-low-power [5]. While
multiple proposals have demonstrated far-field RF backscatter in
deep tissues, these proposals have been limited to tag identification
and could neither perform biometric sensing nor secure the wireless
communication links, which is critical for ensuring the confidentiality
of the sensed biometrics and for responding to commands only from
authorized users [6]. Moreover, such far-field RF implants are
susceptible to tissue variations which impact their resonance and
hence their efficiency in RF backscatter and energy harvesting.
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Receiver Selectivity Limits on Bistatic Backscatter Range
Backscatter communication has been a popular choice in low-power/battery-free sensor nodes development. However, the effect of RF source to receiver distance on the operating range of this communication system has not been modeled accurately. In this paper, we propose a model for a bistatic backscatter system coverage map based on the receiver selectivity, receiver sensitivity, and geometric placement of the receiver, RF source, and the tag. To verify our proposed model and simulations, we perform an experiment using a low-cost commercial BLE receiver and a custom-designed BLE backscatter tag. We also show that the receiver selectivity might depend on the interference level, and present measurement results to signify how this dependence relates the system bit error rate to the RF excitation power.
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- Award ID(s):
- 1823148
- NSF-PAR ID:
- 10205333
- Date Published:
- Journal Name:
- 2020 IEEE International Conference on RFID (RFID)
- Page Range / eLocation ID:
- 1 to 8
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The food and drug industry is facing the need to monitor the quality and safety of their products. This has made them turn to low-cost solutions that can enable smart sensing and tracking without adding much overhead. One such popular low-power solution is backscatter-based sensing and communication system. While it offers the promise of battery-less tags, it does so at the cost of a reduced communication range. In this work, we propose PACT - a scalable communication system that leverages the knowledge asymmetry in the network to improve the communication range of the tags. Borrowing from the backscatter principles, we design custom PACT Tags that are battery-less but use an active radio to extend the communication range beyond standard passive tags. They operate using the energy harvested from the PACT Source. A wide-band Reader is used to receive multiple Tag responses concurrently and upload them to a cloud server, enabling real-time monitoring and tracking at a longer range. We identify and address the challenges in the practical design of battery-less PACT Tags using an active radio and prototype them using off-the-shelf components. We show experimentally that our Tag consumes only 23μJ energy, which is harvested from an excitation Source that is up to 24 meters away from the Tag. We show that in outdoor deployments, the responses from an estimated 520 Tags can be received by a Reader concurrently while being 400 meters away from the Tags.
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Large scale networks of intelligent sensors that can function without any batteries will have enormous implications in applications that range from smart spaces to structural and environmental monitoring. RF tags present an amenable platform for sensor integration as the backscatter communication offers low energy cost of communication. Current RF tags either use extremely low-power sensors or perform tasks of tag localization and identification based on the strength of the backscatter signal. We present a technique for estimation of amplitude and phase of the tag-to-tag channel that can be performed with very limited computational and energy resources. This enables monitoring of the interactions between tagged objects and activities around tags, as well as assessment of a variety of engineering structures. Experimental results demonstrate high resolution in the amplitude and phase channel measurement at a distances ranging from 22 cm to 1.34 m.more » « less
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/RFID49298.2020.9244826
