Battery-free Radio Frequency Research Articles

Digitally-defined ultrathin transparent wireless sensor network for room-scale imperceptible ambient intelligence

Wireless and battery-free radio-frequency (RF) sensors can be used to create physical spaces that ambiently sense and respond to human activities. Making such sensors ultra-flexible and transparent is important to preserve the aesthetics of living environments, accommodate daily activities, and functionally integrate with objects. However, existing RF sensors are unable to simultaneously achieve high transparency, flexibility, and the electrical conductivity required for remote room-scale operation. Here, we report 4.5 µm RF tag sensors achieving transparency exceeding 90% that provide capabilities in room-scale ambient wireless sensing. We develop a laser-assisted water-based adhesion-reversion process to digitally realize computer-aided RF design at scale. By individually tagging multiple objects and regions of the human body, we demonstrate multiplexed wireless tracking of human-environment interactions and physiological signals at a range of up to 8 m. These radio-frequency identification sensors open opportunities for non-intrusive wireless sensing of daily living spaces for applications in health monitoring and elderly care.

A Breathable, Reusable, and Zero-Power Smart Face Mask for Wireless Cough and Mask-Wearing Monitoring.

We herein introduce a lightweight and zero-power smart face mask, capable of wirelessly monitoring coughs in real time and identifying proper mask wearing in public places during a pandemic. The smart face mask relies on the compact, battery-free radio frequency (RF) harmonic transponder, which is attached to the inner layer of the mask for detecting its separation from the face. Specifically, the RF transponder composed of miniature antennas and passive frequency multiplier is made of spray-printed silver nanowires (AgNWs) coated with a poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) passivation layer and the recently discovered multiscale porous polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) substrate. Unlike conventional on-chip or on-board wireless sensors, the SEBS-AgNWs/PEDOT:PSS-based RF transponder is lightweight, stretchable, breathable, and comfortable. In addition, this wireless device has excellent resilience and robustness in long-term and repeated usages (i.e., repeated placement and removal of the soft transponder on the mask). We foresee that this wireless smart face mask, providing simultaneous cough and mask-wearing monitoring, may mitigate virus-transmissive events by tracking the potential contagious person and identifying mask-wearing conditions. Moreover, the ability to wirelessly assess cough frequencies may improve diagnosis accuracy for dealing with several diseases, such as chronic obstructive pulmonary disease.

Battery-free radio frequency wireless sensor for bacteria based on their degradation of gelatin-fatty acid composite films

Continuous and automated bacteria detection is pivotal for a myriad of biomedical, food safety and environmental applications. This work presents the fabrication of a prototype of a passive (battery-free) radio frequency sensor for wireless detection of bacteria. The sensing mechanism is based on the bacterial-induced (proteases and peptidases) degradation of glutaraldehyde (GTA) cross-linked gelatin-caprylic acid (CA) composite film. Proteolytic degradation of the film resulted in a decrease of its resistivity, a quantity that could be wirelessly monitored by coupling the film to a radio-frequency antenna (an inductor-capacitor resonator) and monitoring the frequency for which the transferred power between this antenna and another antenna connected to a Vector Network Analyzer (VNA) was maximized. We experimentally proved this concept by monitoring E.coli bacteria in aqueous medium and detected at 18.0 ± 2.8 h, 23.5 ± 0.7 h, 27.0 ± 2.8 h, 40.5 ± 3.5 h, 45.5 ± 0.7 h for the initial E.coli concentration of 3.2 × 108, 6.8 × 107, 2.3 × 106, 4.3 × 105, and 3.6 × 104 CFU/mL, respectively. Further, the E.coli induced degradation of the composite film was investigated by evaluating the thickness of the film by optical microscopy as well as morphology by scanning electron microscopy techniques.

A fully autonomous platform for power measurement of environmental RF sources based on a time domain readout

Abstract The introduction of Internet of Things (IoT) technologies, connected and synchronized devices, and smart solutions have brought tremendous technological advancements in global communication. The increasing demand for innovative measurement systems, smart sensing nodes and battery-less instruments is challenging instrumentation and measurement industries to improve communication, power budget and the efficiency in Wireless Sensor Nodes (WSN). In this context, this paper aims to contribute to the state of the art with an energy autonomous platform for power measurement in RF environments. The architecture is a self-sustained, battery-free Radio Frequency (RF) measurement system with a time domain record that it can transmit to receiving stations through appropriate IoT channels. This paper discusses the viability of a battery-free measuring device capable of initiating measurement activity only when ambient RF power levels rise above set thresholds. The paper presents the working principles through modeling, simulation and experimental characterization in order to demonstrate the validity of the proposed method.

Soft Wireless Battery-Free UHF RFID Stretchable Sensor Based on Microfluidic Technology

Stretchable microfluidic sensors have recently been developed and employed in many sensing applications. However, they are still in their early stage of development and facing considerable challenges, such as practical system integration due to the limitation of costs, wired connections, and sensitivity. In this paper, we present a compact soft wireless battery-free radio frequency identification (RFID) stretchable sensor based on microfluidic technology. The proposed RFID sensor has high sensitivity and is able to be stretched to 160% of its original size. Moreover, the sensor is completely wireless powered and battery-free. It can be fully embedded into sensor carriers, such as robots to eliminate wires, reduce the weight, and increase the agility. Difference to known received signal strength indicator (RSSI) techniques for RFID sensing monitoring, resonance frequency shift is used in this paper, significantly increasing the measurement accuracy, usefulness, and reliability for many practical applications.

Wireless Passive Stimulation of Engineered Cardiac Tissues.

We present a battery-free radio frequency (RF) microwave activated wireless stimulator, 25 × 42 × 1.6 mm3 on a flexible substrate, featuring high current delivery, up to 60 mA, to stimulate engineered cardiac tissues. An external antenna shines 2.4 GHz microwave, which is modulated by an inverted pulse to directly control the stimulating waveform, to the wireless passive stimulator. The stimulator is equipped with an on-board antenna, multistage diode multipliers, and a control transistor. Rat cardiomyocytes, seeded on electrically conductive gelatin-based hydrogels, demonstrate synchronous contractions and Ca2+ transients immediately upon stimulation. Notably, the stimulator output voltage and current profiles match the tissue contraction frequency within 0.5-2 Hz. Overall, our results indicate the promising potential of the proposed wireless passive stimulator for cardiac stimulation and therapy by induction of precisely controlled and synchronous contractions.

Battery-free Radio Frequency Identification (RFID) Sensors for Food Quality and Safety

Market demands for new sensors for food quality and safety stimulate the development of new sensing technologies that can provide an unobtrusive sensor form, battery-free operation, and minimal sensor cost. Intelligent labeling of food products to indicate and report their freshness and other conditions is one important possible application of such new sensors. This study applied passive (battery-free) radio frequency identification (RFID) sensors for the highly sensitive and selective detection of food freshness and bacterial growth. In these sensors, the electric field generated in the RFID sensor antenna extends from the plane of the RFID sensor and is affected by the ambient environment, providing the opportunity for sensing. This environment may be in the form of a food sample within the electric field of the sensing region or a sensing film deposited onto the sensor antenna. Examples of applications include monitoring of milk freshness, fish freshness, and bacterial growth in a solution. Unlike other food freshness monitoring approaches that require a thin film battery for operation of an RFID sensor and fabrication of custom-made sensors, the passive RFID sensing approach developed here combines the advantages of both battery-free and cost-effective sensor design and offers response selectivity that is impossible to achieve with other individual sensors.

Multivariable passive RFID vapor sensors: roll-to-roll fabrication on a flexible substrate

We demonstrate roll-to-roll (R2R) fabrication of highly selective, battery-free radio frequency identification (RFID) sensors on a flexible polyethylene terephthalate (PET) polymeric substrate. Selectivity of our developed RFID sensors is provided by measurements of their resonance impedance spectra, followed by the multivariate analysis of spectral features, and correlation of these spectral features to the concentrations of vapors of interest. The multivariate analysis of spectral features also provides the ability for the rejection of ambient interferences. As a demonstration of our R2R fabrication process, we employed polyetherurethane (PEUT) as a "classic" sensing material, extruded this sensing material as 25, 75, and 125-μm thick films, and thermally laminated the films onto RFID inlays, rapidly producing approximately 5000 vapor sensors. We further tested these RFID vapor sensors for their response selectivity toward several model vapors such as toluene, acetone, and ethanol as well as water vapor as an abundant interferent. Our RFID sensing concept features 16-bit resolution provided by the sensor reader, granting a highly desired independence from costly proprietary RFID memory chips with a low-resolution analog input. Future steps are being planned for field-testing of these sensors in numerous conditions.