Phase-separated porous nanocomposite with ultralow percolation threshold for wireless bioelectronics.

Realizing the full potential of stretchable bioelectronics in wearables, biomedical implants and soft robotics necessitates conductive elastic composites that are intrinsically soft, highly conductive and strain resilient. However, existing composites usually compromise electrical durability and performance due to disrupted conductive paths under strain and rely heavily on a high content of conductive filler. Here we present an in situ phase-separation method that facilitates microscale silver nanowire assembly and creates self-organized percolation networks on pore surfaces. The resultant nanocomposites are highly conductive, strain insensitive and fatigue tolerant, while minimizing filler usage. Their resilience is rooted in multiscale porous polymer matrices that dissipate stress and rigid conductive fillers adapting to strain-induced geometry changes. Notably, the presence of porous microstructures reduces the percolation threshold (Vc = 0.00062) by 48-fold and suppresses electrical degradation even under strains exceeding 600%. Theoretical calculations yield results that are quantitatively consistent with experimental findings. By pairing these nanocomposites with near-field communication technologies, we have demonstrated stretchable wireless power and data transmission solutions that are ideal for both skin-interfaced and implanted bioelectronics. The systems enable battery-free wireless powering and sensing of a range of sweat biomarkers-with less than 10% performance variation even at 50% strain. Ultimately, our strategy offers expansive material options for diverse applications.

Multimodal Wireless Wound Sensors via Higher-Order Parity-Time Symmetry.

Chronic wounds have emerged as a significant healthcare burden, affecting millions of patients worldwide and presenting a substantial challenge to healthcare systems. The diagnosis and management of chronic wounds are notably intricate, with inappropriate management contributing significantly to the amputation of limbs. In this work, we propose a compact, wireless, battery-free, and multimodal wound monitoring system to facilitate timely and effective wound treatment. The design of this monitoring system draws on the principles of higher-order parity-time symmetry, which incorporates spatially balanced gain, neutral, and loss, embodied by an active -RLC reader, an LC intermediator, and a passive RLC sensor, respectively. Our experimental results demonstrate that this wireless wound sensor can detect temperature (T), relative humidity (RH), pressure (P), and pH with exceptional sensitivity and robustness, which are critical biomarkers for assessing wound healing status. Our in vitro experiments further validate the reliable sensing performance of the wound sensor on human skin and fish. This multifunctional monitoring system may provide a promising solution for the development of futuristic wearable sensors and integrated biomedical microsystems.

Microwave bone fracture diagnosis using deep neural network.

This paper studies the feasibility of a deep neural network (DNN) approach for bone fracture diagnosis based on the non-invasive propagation of radio frequency waves. In contrast to previous "semi-automated" techniques, where X-ray images were used as the network input, in this work, we use S-parameters profiles for DNN training to avoid labeling and data collection problems. Our designed network can simultaneously classify different complex fracture types (normal, transverse, oblique, and comminuted) and estimate the length of the cracks. The proposed system can be used as a portable device in ambulances, retirement houses, and low-income settings for fast preliminary diagnosis in emergency locations when expert radiologists are not available. Using accurate modeling of the human body as well as changing tissue diameters to emulate various anatomical regions, we have created our datasets. Our numerical results show that our design DNN is successfully trained without overfitting. Finally, for the validation of the numerical results, different sets of experiments have been done on the sheep femur bones covered by the liquid phantom. Experimental results demonstrate that fracture types can be correctly classified without using potentially harmful and ionizing X-rays.

Electromagnetically unclonable functions generated by non-Hermitian absorber-emitter.

Physically unclonable functions (PUFs) are a class of hardware-specific security primitives based on secret keys extracted from integrated circuits, which can protect important information against cyberattacks and reverse engineering. Here, we put forward an emerging type of PUF in the electromagnetic domain by virtue of the self-dual absorber-emitter singularity that uniquely exists in the non-Hermitian parity-time (PT)-symmetric structures. At this self-dual singular point, the reconfigurable emissive and absorptive properties with order-of-magnitude differences in scattered power can respond sensitively to admittance or phase perturbations caused by, for example, manufacturing imperfectness. Consequently, the entropy sourced from inevitable manufacturing variations can be amplified, yielding excellent PUF security metrics in terms of randomness and uniqueness. We show that this electromagnetic PUF can be robust against machine learning-assisted attacks based on the Fourier regression and generative adversarial network. Moreover, the proposed PUF concept is wavelength-scalable in radio frequency, terahertz, infrared, and optical systems, paving a promising avenue toward applications of cryptography and encryption.

Emulating the Deutsch-Josza algorithm with an inverse-designed terahertz gradient-index lens.

An all-dielectric photonic metastructure is investigated for application as a quantum algorithm emulator (QAE) in the terahertz frequency regime; specifically, we show implementation of the Deustsh-Josza algorithm. The design for the QAE consists of a gradient-index (GRIN) lens as the Fourier transform subblock and patterned silicon as the oracle subblock. First, we detail optimization of the GRIN lens through numerical analysis. Then, we employed inverse design through a machine learning approach to further optimize the structural geometry. Through this optimization, we enhance the interaction of the incident light with the metamaterial via spectral improvements of the outgoing wave.

Review on Recent Advances and Applications of Passive Harmonic RFID Systems.

Radio frequency identification (RFID) has gained significant attention because it provides a highly versatile platform for identifying, tracking, and monitoring objects. An emerging trend in this technology is the use of nonlinear RFID, such as passive harmonic tags, which have been demonstrated to be effective against clutters, echoes, crosstalk, and other electromagnetic interferences. This article presents a comprehensive review of recent advances and applications of passive harmonic RFIDs and integrated systems. A passive harmonic RFID exploits the frequency orthogonality of the transmitted (fundamental tone) and received (harmonics) radio-frequency (RF) signals to enable robust interrogation in noisy and cluttered environments, not possible with traditional passive linear RFIDs. This review article evaluates passive harmonic RFID systems in comparison to traditional systems and highlights their pros and cons. Several state-of-the-art chipless and chip-based harmonic RFIDs are presented, and their novel applications in identification, tracking, sensing, and biotelemetry are discussed. The review summarizes the key successes and challenges of passive harmonic RFID systems and provides insights into their future development, implementation, and optimization.

Recent Advances in Nanomaterials Used for Wearable Electronics.

In recent decades, thriving Internet of Things (IoT) technology has had a profound impact on people's lifestyles through extensive information interaction between humans and intelligent devices. One promising application of IoT is the continuous, real-time monitoring and analysis of body or environmental information by devices worn on or implanted inside the body. This research area, commonly referred to as wearable electronics or wearables, represents a new and rapidly expanding interdisciplinary field. Wearable electronics are devices with specific electronic functions that must be flexible and stretchable. Various novel materials have been proposed in recent years to meet the technical challenges posed by this field, which exhibit significant potential for use in different wearable applications. This article reviews recent progress in the development of emerging nanomaterial-based wearable electronics, with a specific focus on their flexible substrates, conductors, and transducers. Additionally, we discuss the current state-of-the-art applications of nanomaterial-based wearable electronics and provide an outlook on future research directions in this field.

Spectral sensitivity near exceptional points as a resource for hardware encryption.

The spectral sensitivity near exceptional points (EPs) has been recently explored as an avenue for building sensors with enhanced sensitivity. However, to date, it is not clear whether this class of sensors does indeed outperform traditional sensors in terms of signal-to-noise ratio. In this work, we investigate the spectral sensitivity associated with EPs under a different lens and propose to utilize it as a resource for hardware security. In particular, we introduce a physically unclonable function (PUF) based on analogue electronic circuits that benefit from the drastic eigenvalues bifurcation near a divergent exceptional point to enhance the stochastic entropy caused by inherent parameter fluctuations in electronic components. This in turn results in a perfect entropy source for the generation of encryption keys encoded in analog electrical signals. This lightweight and robust analog-PUF structure may lead to a variety of unforeseen securities and anti-counterfeiting applications in radio-frequency fingerprinting and wireless communications.

Materials, Designs, and Implementations of Wearable Antennas and Circuits for Biomedical Applications: A Review.

The intersection of biomedicine and radio frequency (RF) engineering has fundamentally transformed self-health monitoring by leveraging soft and wearable electronic devices. This paradigm shift presents a critical challenge, requiring these devices and systems to possess exceptional flexibility, biocompatibility, and functionality. To meet these requirements, traditional electronic systems, such as sensors and antennas made from rigid and bulky materials, must be adapted through material science and schematic design. Notably, in recent years, extensive research efforts have focused on this field, and this review article will concentrate on recent advancements. We will explore the traditional/emerging materials for highly flexible and electrically efficient wearable electronics, followed by systematic designs for improved functionality and performance. Additionally, we will briefly overview several remarkable applications of wearable electronics in biomedical sensing. Finally, we provide an outlook on potential future directions in this developing area.

Reconfigurable beam-steerable leaky-wave antenna loaded with metamaterial apertures using liquid crystal-based delay lines.

An original liquid crystal (LC)-based substrate integrated waveguide (SIW) leaky-wave antenna is proposed. Inside the SIW, there is an embedded stripline sandwiched between an LC pool and another dielectric slab. The antenna couples the guided quasi-TEM mode into free space through a periodic set of complementary electric inductive-capacitive (cELC) resonators. Simulation results show that the antenna performs fixed-frequency continuous beam steering of 52° from backward -28° to forward 24° at 25.85 GHz. This relatively wide beam scan angle is achieved by tuning the LC permittivity through an applied quasi-DC bias voltage to the stripline. Simulation results show that the antenna has high realized gain through the entire scanning range (less than 1 dB degradation), relatively wide bandwidth, and good tolerance to frequency drift and fabrication errors.

Laser-scribed conductive, photoactive transition metal oxide on soft elastomers for Janus on-skin electronics and soft actuators.

Laser-assisted fabrication of conductive materials on flexible substrates has attracted intense interests because of its simplicity, easy customization, and broad applications. However, it remains challenging to achieve laser scribing of conductive materials on tissue-like soft elastomers, which can serve as the basis to construct bioelectronics and soft actuators. Here, we report laser scribing of metallic conductive, photoactive transition metal oxide (molybdenum dioxide) on soft elastomers, coated with molybdenum chloride precursors, under ambient conditions. Laser-scribed molybdenum dioxide (LSM) exhibits high electrical conductivity, biocompatibility, chemical stability, and compatibility with magnetic resonance imaging. In addition, LSM can be made on various substrates (polyimide, glass, and hair), showing high generality. Furthermore, LSM-based Janus on-skin electronics are developed to record information from human skin, human breath, and environments. Taking advantage of its outstanding photothermal effect, LSM-based soft actuators are developed to build light-driven reconfigurable three-dimensional architectures, reshapable airflow sensors, and smart robotic worms with bioelectronic sensors.

In-Vitro Demonstration of Ultra-Reliable, Wireless and Batteryless Implanted Intracranial Sensors Operated on Loci of Exceptional Points.

Vital signal monitoring, such as pulse, respiration rate, intra-organ and intra-vascular pressure, can provide important information for determination of clinic diagnosis, treatments, and surgical protocols. Nowadays, micromachined bioimplants, equipped with antennas for converting bio-signals to modulated radio transmissions, may allow remote continuous monitoring of patients' vital signs. Yet, current passive biotelemetry techniques usually suffer from poor signal reproducibility and robustness in light of inevitable misalignment between transmitting and receiving antennas. Here, we seek to address this long-existing challenge and to robustly acquire information from a passive wireless intracranial pressure (or brain pressure) sensor by introducing a novel, high-performance biotelemetry system. In spite of variable inductive links, this biotelemetry system may have absolute accuracy by leveraging the uniqueness of loci of exceptional points (EPs) in non-Hermitian radio-frequency (RF) electronic systems with parity-time (PT) symmetry. Our in-vitro experimental demonstration shows that the proposed intracranial (ICP) monitoring system can provide a sub-mmHg resolution in the ICP range of 0-20 mmHg and ultra-robust wireless data acquisition against the misalignment-induced weakening of inductive link. Our results could provide a practical pathway toward reliable, real-time wireless monitoring of ICP, and other vital signals generated by bio-implants and wearables.

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.

A Passive Smart Face Mask for Wireless Cough Monitoring: A Harmonic Detection Scheme With Clutter Rejection.

Cough detection has aroused great interest because the assessment of cough frequency may improve diagnosis accuracy for dealing with several diseases, such as chronic obstructive pulmonary disease (COPD) and the recent COVID-19 global pandemic crisis. Here, we propose and experimentally demonstrate a wireless smart face mask based on a passive harmonic tag for real-time cough monitoring and alert. Our results show that the cough events can be successfully monitored through non-contact track of the received signal strength indicator (RSSI) at the harmonic frequency. Owing to the frequency orthogonality between the launched and backscattered radio-frequency (RF) signals, the harmonic tag-based smart mask can well suppress the electromagnetic interferences, such as clutters and crosstalks in noisy environments. We envision that this zero-power and lightweight wireless wearable device may be beneficial for cough monitoring and the public health condition in terms of tracking potential contagious person and virus-transmissive events.

Degeneracy of light scattering and absorption by a single nanowire.

We theoretically and numerically prove that under an electromagnetic plane wave with linear polarization incident normally to a single nanowire, there exists a power diagram that could indicate scattering properties for any system configurations, material parameters, and operating wavelength. We demonstrate the distinct power distribution boundary in absorption, scattering, and extinction for a generalized nanowire with any partial wave modes dominant. In the boundary, each dominant scattering coefficients remain constant, and its energy performance would display superabsorbers or superscatterers. Interestingly, for a system with larger partial wave modes dominant, the occupied domain in the power diagram could completely cover that with lower ones. Hence, a system with different levels of partial wave modes can display the same power results, reflecting the degeneracy. This degenerate property could release more degrees of freedom in design of energy harvesting devices and sensors. We demonstrate several systems based on realistic materials to support our findings.

Superdirective leaky radiation from a PT-synthetic metachannel.

Spectral singularities appearing in parity-time (PT)-symmetric non-Hermitian optical systems have aroused a growing interest due to their new exhilarating applications, such as bifurcation effects at exceptional points and the coexistence of coherent perfect absorber and laser (so-called CPAL point). We introduce here how the concept of CPAL action provoked in PT-symmetric metasurfaces can be translated into practical implementation of a low-loss zero/low-index open channel supporting a nearly undamped fast-wave propagation. Such a PT-synthetic metachannel shows the capability to produce a high-directivity leaky radiation, with a tunable beam angle that depends on the gain-loss parameter. The proposed structure may enable new kinds of super-directivity antennas, as well as many applications that demand extreme dielectric properties, such as epsilon-near-zero (ENZ).

PTX-symmetric metasurfaces for sensing applications.

In this paper, we introduce an ultra-sensitive optical sensing platform based on the parity-time-reciprocal scaling (PTX)-symmetric non-Hermitian metasurfaces, which leverage exotic singularities, such as the exceptional point (EP) and the coherent perfect absorber-laser (CPAL) point, to significantly enhance the sensitivity and detectability of photonic sensors. We theoretically studied scattering properties and physical limitations of the PTX-symmetric metasurface sensing systems with an asymmetric, unbalanced gain-loss profile. The PTX-symmetric metasurfaces can exhibit similar scattering properties as their PT-symmetric counterparts at singular points, while achieving a higher sensitivity and a larger modulation depth, possible with the reciprocal-scaling factor (i.e., X transformation). Specifically, with the optimal reciprocal-scaling factor or near-zero phase offset, the proposed PTX-symmetric metasurface sensors operating around the EP or CPAL point may achieve an over 100 dB modulation depth, thus paving a promising route toward the detection of small-scale perturbations caused by, for example, molecular, gaseous, and biochemical surface adsorbates.

Pencil-paper on-skin electronics.

Pencils and papers are ubiquitous in our society and have been widely used for writing and drawing, because they are easy to use, low-cost, widely accessible, and disposable. However, their applications in emerging skin-interfaced health monitoring and interventions are still not well explored. Herein, we report a variety of pencil-paper-based on-skin electronic devices, including biophysical (temperature, biopotential) sensors, sweat biochemical (pH, uric acid, glucose) sensors, thermal stimulators, and humidity energy harvesters. Among these devices, pencil-drawn graphite patterns (or combined with other compounds) serve as conductive traces and sensing electrodes, and office-copy papers work as flexible supporting substrates. The enabled devices can perform real-time, continuous, and high-fidelity monitoring of a range of vital biophysical and biochemical signals from human bodies, including skin temperatures, electrocardiograms, electromyograms, alpha, beta, and theta rhythms, instantaneous heart rates, respiratory rates, and sweat pH, uric acid, and glucose, as well as deliver programmed thermal stimulations. Notably, the qualities of recorded signals are comparable to those measured with conventional methods. Moreover, humidity energy harvesters are prepared by creating a gradient distribution of oxygen-containing groups on office-copy papers between pencil-drawn electrodes. One single-unit device (0.87 cm2) can generate a sustained voltage of up to 480 mV for over 2 h from ambient humidity. Furthermore, a self-powered on-skin iontophoretic transdermal drug-delivery system is developed as an on-skin chemical intervention example. In addition, pencil-paper-based antennas, two-dimensional (2D) and three-dimensional (3D) circuits with light-emitting diodes (LEDs) and batteries, reconfigurable assembly and biodegradable electronics (based on water-soluble papers) are explored.

Improved Contacts and Device Performance in MoS2 Transistors Using a 2D Semiconductor Interlayer.

We report a contact engineering method to minimize the Schottky barrier height (SBH) and contact resistivity of MoS2 field-effect transistors (FETs) by using ultrathin 2D semiconductors as contact interlayers. We demonstrate that the addition of a few-layer MoSe2 between the MoS2 channel and Ti electrodes effectively reduces the SBH at the contacts from ∼100 to ∼25 meV, contact resistivity from ∼6 × 10-5 to ∼1 × 10-6 Ω cm2, and current transfer length from ∼425 to ∼60 nm. The drastic reduction of SBH can be attributed to the synergy of Fermi-level pinning close to the conduction band edge of the MoSe2 interlayer and favorable conduction-band offset between the MoSe2 interlayer and MoS2 channel. As a result of the improved contacts, MoS2 FETs with Ti/MoSe2 contacts also demonstrate higher two-terminal mobility.

Enhancing THz generation in photomixers using a metamaterial approach.

Photomixers at THz frequencies offer an attractive solution to fill the THz gap; however, conventional photomixer designs result in low output powers, on the order of microwatts, before thermal failure. We propose an alternative photomixer design capable of orders of magnitude enhancement of continuous-wave THz generation using a metamaterial approach. By forming a metal-semiconductor-metal (MSM) cavity through layering an ultrafast semiconductor material between subwavelength metal-dielectric gratings, tailored resonance can achieve ultrathin absorbing regions and efficient heat sinking. When mounted to a tunable E-patch antenna, gratings also act as vertically biased electrodes, further enhancing photoconductive gain by reducing the carrier path length to nanoscales. Thus, through these multiplicative enhancements, the metamaterial-enhanced photomixer is projected to generate THz powers in the milliwatt range and exceed the Manley-Rowe limit for frequencies less than 2 THz.