Human external biofluid (e.g., sweat, urine) contains vast health data that is readily harvestable. Currently, wearable sweat sensors require an electrochemical-based approach that is used in single use, creating environmental pollution as people track their exercise in the wild. Moreover, such solution relies on a battery-powered design, which brings battery health and thermal related issues. We present MetaBioLiq, a 3D printed wireless-readable sweat sensing system that offers continuous monitoring, featuring completely passive, environmentally friendly, and easily accessible. MetaBioLiq is developed upon sweat liquid's resonance upon high frequency RF interaction, with different sweat content driving RF resonance characteristics. To activate such resonance, we design 3D PolyLactic Acid (PLA) structures that capture e-field energy from the air, and tunneling it to the sweat. Once the resonance effect occurs, we analyze return signal from a wireless RF receiver to decouple the sweat's resonance. Lastly, we evaluate MetaBioLiq's performance with 24 artificial sweat samples containing different levels of glucose, electrolytes, and fat. MetaBioLiq proves its effectiveness with 95% liquid level detection performance, and 96% sweat liquid identification performance. We further investigate MetaBioLiq's robustness and reliability, as well as limitations. Overall, MetaBioLiq shows promising results to expand the realm of mobile continuous sensing to microscopic realm untangible in the past.

Soil moisture level sensing is essential for enabling smart irrigation, which is crucial for our food security and sustainable agriculture. Existing soil moisture sensing systems face limitations such as single-layer sensing, limited depth, power supply reliance, and complex calibration. In addition, costly and cumbersome sensor unit design hinders mass and dense deployment of passive intelligence. This paper introduces MetaSoil, a soil moisture sensing system that is calibration-free, continuous, and multi-layered, leveraging a passive 3D printable mmWave metamaterial. When soil moisture level changes, our hydrogel patched polylactic acid (PLA) metamaterial alters resonant frequency in the impinging mmWave signals due to impedance match offset. Our system eliminates in-soil power supply dependencies by utilizing the RF resonance of 3D-printed metamaterial, allowing for deeper placement, and simultaneous multi-layer sensing. We then integrate a commercial-off-the-shelf (COTS) mmWave radar to query the metamaterial sensor. With MetaSoil's fully passive metamaterial pole, RF signal from far is redirected towards the sensor unit, bypassing soil's heavy attenuation effect. Through our extensive evaluation, MetaSoil achieves 98.9 % accuracy with ±10% moisture level precision in single-layered sensing, at depth of 1m meter. It achieves 98.8 % accuracy with ±10% in double layered sensing at same depth with 10cm sensor spacing. We further examine the robustness of our system with real-world requirements. Overall, MetaSoil represents a low-cost, durable, and easily deployable solution that supports remote and continuous soil moisture monitoring, advancing the scalability and effectiveness of smart agricultural practices.

Reliable cross medium (e.g., air-water) communication using radio frequency (RF) has remained an open-problem for decades. Currently, underwater devices cannot communicate directly with land-based or airborne devices. Typical solutions are inadequate when communicating through the boundary due to cross-medium boundary reflection/refraction/attenuation effects. We present MetaLink, an RF wireless communication system that enables underwater radios to communicate with airborne ones using novel underwater antenna design and 3D printed bianisotropic metasurface. MetaLink leverages bianisotropic structures that can correct for the severe boundary reflections/refractions between the air/water mediums, opening up the air/water medium as a viable communication channel without the need for multiple types of signals. We further exploit the electromagnetic properties of water to drastically scale down MetaLink's meta-atom size, and improve communication range. To examine real world communications performance from water to air, we prototype MetaLink and measure in a 14 ft deep swimming pool. Moreover, we push the robustness, reliability, and performance of MetaLink to its limit under various real-world circumstances. Our experiments demonstrate that MetaLink can communicate through the water/air boundary with SNR improvements of more than 35dB using WiFi modulation at distances of 14 ft and reach a simulated maximum of 95 ft within water using commercially available equipment and measured data.

Modern autonomous vehicles are commonly instrumented with radars for all-weather perception. Yet the radar functionality is limited to identifying the positions of reflectors in the environment. In this paper, we investigate the feasibility of smartening transportation infrastructure for the purpose of conveying richer information to automotive radars. We propose RoS, a passive PCB-fabricated smart surface which can be reconfigured to embed digital bits, and inform the radar much like visual road signs do to cameras. We design the RoS signage to act as a retrodirective reflector which can reflect signals back to the radar from wide viewing angles. We further introduce a spatial encoding scheme, which piggybacks information in the reflected analog signals based on the geometrical layout of the retroreflective elements. Our prototype fabrication and experimentation verifies the effectiveness of RoS as an RF ''barcode'' which is readable by radar in practical transportation environment.

Abstract Unit disk graphs form a natural model for cellular radio channel assignment problems under the assumption of equally powerful, omnidirectional transmitters located on a uniform, flat plane. Here, we introduce and give motivation for an extension of this model, namely, sectorization at transmitter sites. We define and analyze properties of one case of sectorization, bisectored unit disk graphs, in particular, investigating properties concerning their chromatic number. Finally, we provide some experimental evidence to draw comparisons between graphs of this model and other classes of graphs. © 2004 Wiley Periodicals, Inc.