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1. RTSense: passive RFID based temperature sensing

   https://doi.org/https://doi.org/10.1145/3384419.3430729  

   Swadhin Pradhan, Lili Qiu (November 2020, ACM SenSys)

   null (Ed.)

   Passive radio-frequency identification (RFID) tags are attractive because they are low cost, battery-free, and easy to deploy. This technology is traditionally being used to identify tags attached to the objects. In this paper, we explore the feasibility of turning passive RFID tags into battery-free temperature sensors. The impedance of the RFID tag changes with the temperature and this change will be manifested in the reflected signal from the tag. This opens up an opportunity to realize battery-free temperature sensing using a passive RFID tag with already deployed Commercial Off-the-Shelf (COTS) RFID reader-antenna infrastructure in supply chain management or inventory tracking. However, it is challenging to achieve high accuracy and robustness against the changes in the environment. To address these challenges, we first develop a detailed analytical model to capture the impact of temperature change on the tag impedance and the resulting phase of the reflected signal. We then build a system that uses a pair of tags, which respond differently to the temperature change to cancel out other environmental impacts. Using extensive evaluation, we show our model is accurate and our system can estimate the temperature within a 2.9 degree centigrade median error and support a normal read range of 3.5 m in an environment-independent manner. 

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2. Wireless Identification and Sensing Platform Version 6.0

   https://doi.org/10.1145/3560905.3568109  

   Menon, Rohan; Gujarathi, Rohit; Saffari, Ali; Smith, Joshua R. (November 2022, SenSys '22: Proceedings of the 20th ACM Conference on Embedded Networked Sensor Systems)

   Connected devices are becoming more ubiquitous, but powering them remains a challenge. The Wireless Identification and Sensing Platform (WISP) is a fully programmable device capable of energy harvesting and backscatter communication. It can accommodate a variety of sensing modalities and operate without batteries or a wired power supply, making it a suitable device for ubiquitous computing. A new version of WISP is presented. WISP-6.0 is designed to be lowpower, modular, and enable dual energy harvesting from sources like a solar panel. Additionally, an upgraded cross-platform host application is built using the latest web technologies. Compared to its predecessor, WISP-5.1, WISP-6.0 consumes 13.62% and 6.29% less power in active accelerometer and active acknowledgment modes respectively. Furthermore, WISP-6.0 is better able to harvest RF energy collected from its antenna, with the greatest improvements at higher input powers. 

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3. Communication by means of modulated Johnson noise

   https://doi.org/10.1073/pnas.2201337119  

   Kapetanovic, Zerina; Morales, Miguel; Smith, Joshua R. (December 2022, Proceedings of the National Academy of Sciences)

   We present the design of a passive wireless communication method that does not rely on ambient or generated RF sources. Instead, the method modulates the Johnson (thermal) noise of a resistor to transmit information bits wirelessly. By selectively connecting or disconnecting a matched resistor to an antenna, the system can achieve data rates of up to 26 bps and distances of up to 7.3 m. This communication method operates at very low power, similar to that of an RFID tag, with the advantage of not requiring a preexisting RF signal to reflect. 

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4. Towards scalable soft e-skin: Flexible event-based tactile-sensors using wireless sensor elements embedded in soft elastomer

   https://doi.org/10.1109/BioRob49111.2020.9224353  

   Slepyan, Ariel; Thakor, Nitish (November 2020, IEEE BIOROB Conference)

   null (Ed.)

   Scalable, high-density electronic skins (e-skins) are a desirable goal of tactile sensing. However, a realization of this goal has been elusive due to the trade-off between spatial and temporal resolution that current tactile sensors suffer from. Additionally, as tactile sensing grids become large, wiring becomes unmanageable, and there is a need for a wireless approach. In this work, a scalable, event-based, passive tactilesensing system is proposed that is based on radio-frequency identification (RFID) technology. An RFID-based tactile sensing hand is developed with 19 pressure sensing taxels. The taxels are read wirelessly using a single ‘hand-shaped’ RFID antenna. Each RFID tag is transformed into a pressure sensor by disconnecting the RFID chip from its antenna and embedding the chip and antenna into soft elastomer with an air gap introduced between the RFID chip and its antenna. When a pressure event occurs, the RFID chip contacts its antenna and receives power and communicates with the RFID reader. Thus, the sensor is transformed into a biomimetic event-based sensor, whose response is activated only when used. Further, this work demonstrates the feasibility of constructing event-based, passive sensing grids that can be read wirelessly. Future tactile sensing e-skins can utilize this approach to become scalable and dense, while retaining high temporal resolution. Moreover, this approach can be applied beyond tactile sensing, for the development of scalable and high-density sensors of any modality. 

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5. Antenna System Optimization for Active Metamaterial-enhanced Magnetic Induction Communications

   Li, Zhangyu; Sun, Zhi (March 2019, European Conference on Antenna and Propagation)

   Magnetic induction (MI) communication are widely used in applications in extreme environments, including environment surveillance, past disaster rescue, and resource detection since it does not su↵er from high material absorption in lossy media. However, existing MI systems rely on high transmitting power and large antenna to reach practical communication range. Recently, metamaterial enhanced MI (M2I) communication was proposed, which can increase the signal strength of the original MI system to 30 dB in theory. However the latest practical implementation of M2I system only achieves an 8 dB gain due to the metamaterial loss. In this paper, the active metamaterial unit is introduced to the current M2I communication system to close the performance gap between theoretical and practical results. The antenna system is optimized based on the rigorously model of circuit, coil array structure and channel. Through analytical deduction and COMSOL simulations, the proposed active M2I antenna system shows significant power gain and improvement in communication range compared with the passive M2I system and the original MI system. 

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