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With favorable properties of stretchability, stitchability, and potential to be woven into a fabric, thread-based sensors have gained considerable interest for wearable devices for smart and connected health applications. To facilitate wearable applications, an easy and reliable way to fabricate these thread-based sensors with good performance and consistency is the key while manufacturing these smart threads. In this paper, we propose an automated thread-coating system that can fabricate thread-based strain sensors with controlled parameters. The platform uses integrated sensors for controlled manufacturing of the threads in a highly compact structure that consists of an innovative tension sensor and a closed-loop thermal management system. Using this new system, a sample thread with a gauge factor of 1.47 and tension sensitivity of 32.64 K Ω /N is prepared. Compared with hand-coated thread, the machine-fabricated thread shows much better sensitivity and consistency. The prepared strain sensor is made into a respiration sensor patch and a limb motion patch to demonstrate its application. [ABSTRACT FROM AUTHOR]

Animal‐borne biologging technology allows researchers to understand the physiological responses of wild animals, especially songbirds, to environmental changes. Songbirds are of interest in studying these responses because of their visibility and relatively small body size yet high energetic demand of their various life‐history stages (e.g., molt, migration, breeding). Previous methods for monitoring responses, such as heart rate activity, have relied on surgical implantation of electrodes connected to bulky electronic devices which affect the well‐being of birds, indirectly influence bird behavior and create stress artifacts. A non‐invasive, lightweight solution is needed. This study introduces eutectogels, a long‐lasting gel made from deep eutectic solvents, combined with conductive threads and a wireless device to monitor the heart rate of house sparrows noninvasively through skin contact. In this work, heart rate and respiration rate measurements are validated on birds under anesthesia. These tests are repeated on birds that are awake but restrained. The eutectogel outperforms commercial electrodes and gels, yielding high signal‐to‐noise ratio measurements on restrained birds. The respiration rate is extracted and processed electronically from motion artifacts in the recorded signals without the need for a separate dedicated sensor. The system shows promise for future field studies on free‐living species. [ABSTRACT FROM AUTHOR]

This study introduces the development of a photothermal-based microfluidic paper analytical device (PT-µPAD) integrated with near-field communication (NFC) technology and smartphone readout for enzyme-free glucose quantification in human samples. With the properties of gold nanoparticles (AuNPs) both as a nanozyme and as a photothermal substrate, there is no need for costly reagents like enzymes or a readout instrumentation for the selective and sensitive detection of glucose. In PT-µPADs, AuNPs are etched by hydrogen peroxide (H2O2) generated from glucose catalysis. Photothermal detection from the plasmonic heating of these AuNPs when illuminated by a 533nm LED light source is achieved by inserting the PT-µPAD sensor into a portable NFC platform suitable for smartphone readout. Temperature variation is directly proportional to the glucose concentration. After optimization, we acquired a linear range between 5.0 and 20.0 µmol L−1 (R2 = 0.9967) and a limit of detection (LOD) of 25.0 nmol L−1 for glucose. Additionally, while our sensor does not utilize any enzyme, it is remarkably selective to glucose with no effects from interferences. Recovery studies in various human control samples indicated a range of 99.73–102.66% with the highest RSD of 3.53%, making it highly accurate and precise. Moreover, our method is more sensitive than other methods relying on conventional µPADs for glucose sensing. By integrating the potential benefits of microfluidics, nanomaterials as nanozymes, and NFC technology for wireless readout, our sensor demonstrates great promise as an accessible, affordable, and shelf-stable device for glucose quantification. Moreover, this concept can be extended to detect other molecules of interest as a point-of-care (POC) diagnostics device. [ABSTRACT FROM AUTHOR]

This article presents the development of a distance-based thread analytical device (dTAD) integrated with an ion-imprinted polymer (IIP) for quantitative monitoring of zinc ions (Zn2+) in human urine samples. The IIP was easily chemically modified onto the thread channel using dithizone (DTZ) as a ligand to bind to Zn2+ with methacrylic acid (MAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as well as 2,2-azobisisobutyronitrile (AIBN) as cross-linking agents to enhance the selectivity for Zn2+ detection. The imprinted polymer was characterized using Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDS). Under optimization, the linear detection range was from 1.0 to 20.0 mg L-1 (R2 = 0.9992) with a limit of detection (LOD) of 1.0 mg L-1. Other potentially interfering metal ions and molecules did not interfere with this approach, leading to high selectivity. Furthermore, our technique exhibits a remarkable recovery ranging from 100.48% to 103.16%, with the highest relative standard deviation (% RSD) of 5.44% for monitoring Zn2+ in human control urine samples, indicating high accuracy and precision. Similarly, there is no significant statistical difference between the results obtained using our method and standards on zinc supplement sample labels. The proposed method offers several advantages in detecting trace Zn2+ for point-of-care (POC) medical diagnostics and environmental sample analysis, such as ease of use, instrument-free readout, and cost efficiency. Overall, our developed dTADbased IIP method holds potential for simple, affordable, and rapid detection of Zn2+ levels and can be applied to other metal ions' analysis. [ABSTRACT FROM AUTHOR]

Modern strategies to deliver drugs efficiently via less toxic non-aqueous carriers like deep eutectic solvents (DES) has grown tremendously. Herein, we develop several synthetic and natural DES to improve solubility of poorly soluble drug, docetaxel (DTX). Menthol:thymol-based natural DES showed 1500-folds higher solubility for DTX than that in water. FTIR-spectroscopy confirmed reduced crystallinity and stable encapsulation of DTX in DES through formation of hydrogen-bond. DTX-DES was developed further into self-emulsified formulation that upon dilution formed nanostructured globules (< 200 nm) and released 20-folds higher DTX than pure drug thereby highlighting the potential of DES for designing formulations of poorly soluble drugs. [ABSTRACT FROM AUTHOR]

Selectivity and enhanced response remain an issue in gaseous acetone sensing. This report demonstrates MoS2 on MXene (Ti3C2Tx) contact based on a low-cost flexible sensor for selective detection of acetone using principle component analysis and binary logistic regression. The piezotronic effect enhances the response of the sensor. The fabricated acetone sensor exhibited an excellent response of ∼5.84% at lower concentrations of acetone ranging from 5 to 30 ppm at room temperature (25 °C). The sensor's response values with (5%) and without applied external strain were calculated to be approximately 5.84 and 7.21%, respectively. This suggested an increment in the sensing performance under the applied external strain with an improved response time (448 s). A detailed study is presented in terms of comparative performance of MoS2 and MXene/MoS2 under strained and unstrained conditions. Principle component analysis and binary logistic regression techniques were used to successfully selectively detect acetone among other eight VOC (volatile organic compound) (toluene, benzene, isopropyl alcohol, formaldehyde, hydrogen sulfide, dimethyl sulfide, ethanol, and methanol) gases. A real-time breath analyzer is presented wherein an artificial breath consisting of different humidities and acetone was created, and acetone was sensed using the fabricated sensor. Finally, a proof of concept for the flexible bracelet is presented for the on-site detection of acetone levels in human breath to monitor diabetes at the point-of-care setting. This successful demonstration of the acetone sensor presents future possible avenues for healthcare, food, and industrial research. [ABSTRACT FROM AUTHOR]

This article introduces distance-based paper analytical devices (dPADs) integrated with molecularly imprinted polymers (MIPs) and carbon dots (CDs) for simultaneous quantification of cytokine biomarkers, namely C-reactive protein (CRP), tumor necrosis factor-alpha (TNF-a), and interleukin-6 (IL-6) in human biological samples for diagnosis of cytokine syndrome. Using fluorescent CDs and MIP technology, the dPAD exhibits high selectivity and sensitivity. Detection is based on fluorescence quenching of CDs achieved through the interaction of the target analytes with the MIP layer on the paper substrate. Quantitative analysis is easily accomplished by measuring the distance length of quenched fluorescence with a traditional ruler and naked eye readout enabling rapid diagnosis of cytokine syndrome and the underlying infection. Our sensor demonstrated linear ranges of 2.50-24.0 pg mL-1 (R2 = 0.9974), 0.25-3.20 pg mL-1 (R2 = 0.9985), and 1.50-16.0 pg mL-1 (R2 = 0.9966) with detection limits (LODs) of 2.50, 0.25, and 1.50 pg mL-1 for CRP, TNF-a, and IL-6, respectively. This sensor also demonstrated remarkable selectivity compared to a sensor employing a non-imprinted polymer (NIP), and precision with the highest relative standard deviation (RSD) of 5.14%. The sensor is more accessible compared to prior methods relying on expensive reagents and instruments and complex fabrication methods. Furthermore, the assay provided notable accuracy for monitoring these biomarkers in various human samples with recovery percentages ranging between 99.22% and 103.58%. By integrating microfluidic systems, nanosensing, and MIPs technology, our developed dPADs hold significant potential as a cost-effective and user-friendly analytical method for point-of-care diagnostics (POC) of cytokine-related disorders. This concept can be further extended to developing diagnostic devices for other biomarkers. [ABSTRACT FROM AUTHOR]

A natural stress response induces elevated cortisol levels in biological fluids, such as saliva. While current sensor technologies can detect cortisol in real time, their sensitivity and reliability for human subjects have not been assured. This is due to relatively low concentrations of salivary cortisol, which fluctuate throughout the day and vary significantly between individuals. To address these challenges, we present an improved electrochemical biosensor leveraging graphene's exceptional conductivity and physicochemical properties. A 1-pyrenebutyric acid N-hydroxysuccinimide ester (PBASE-NHS)–modified commercial graphene foam (GF) electrode is presented to realize an ultra-sensitive biosensor for cortisol detection directly in human saliva. The biosensor fabrication process entails the attachment of anti-cortisol monoclonal antibodies (mAb-cort) onto a PBASE-NHS/GF electrode through noncovalent immobilization on the vertically stratified graphene foam electrode surface. This unique immobilization strategy preserves graphene's structural integrity and electrical conductivity while facilitating antibody immobilization. The binding of cortisol to immobilized mAb-cort is read out via differential pulse voltammetry using ferri/ferro redox reactions. The immunosensor demonstrates an exceptional dynamic range of 1.0 fg mL−1 to 10,000 pg mL−1 (R2 = 0.9914) with a detection limit of 0.24 fg mL−1 (n = 3) for cortisol. Furthermore, we have established the reliability of cortisol sensors in monitoring human saliva. We have also performed multiple modes of validation, one against the established enzyme-linked immunosorbent assay (ELISA) and a second by a third-party service Salimetric on 16 student volunteers exposed to different stress levels, showing excellent correlation (r = 0.9961). These findings suggest the potential for using mAb-cort/PBASE-NHS/GF-based cortisol electrodes for monitoring salivary cortisol in the general population. [ABSTRACT FROM AUTHOR]

There is a need for flexible chemical sensors for the ecological and physiological research of avian species such as house sparrows (Passer domesticus). Current methods in this field are invasive and require multiple physical interactions with the birds. Emerging research in flexible bioelectronics can enable realization of implantable devices that are mechanically compliant with the underlying tissues for continuous real-time sensing in situ. However, challenges still remain in forming an intimate flexible interface. One of the promising flexible bioelectronic platforms for tissue-embedded sensing is based on functionalizing surgical sutures or threads. Threads have three-dimensional flexibility, high surface-area-to-volume ratio, inherent wicking properties, and are easily functionalizable using reel-to-reel dip coating. Threads are ideal as they are lightweight, therefore, would not interfere with flight motion and would only require minimal interaction with the bird. However, the challenge remains in achieving a highly conductive yet flexible electrode for electrochemical sensing using materials such as gold. In this study, we address this issue through novel gold deposition directly on thread substrate followed by enzyme immobilization to realize flexible electrochemical glucose biosensors on medical-grade sutures. These sensors were calibrated and tested in a range that is wide enough to include the expected range of glucose concentration in house sparrows (0–8.55 mM). Glucose monitoring in house sparrows will provide insights into energy metabolism and regulation during stress responses. In addition, the stability, repeatability, and selectivity of the sensor were tested with final validation in a real bird. Our innovative gold-coated, thread-based flexible electrochemical glucose sensor can also be used in other small and large animals. This can also be extended to monitoring other metabolites in future. [ABSTRACT FROM AUTHOR]

There exists a strong correlation between the pH levels of the gastrointestinal (GI) tract and GI diseases such as inflammatory bowel disease (IBS), ulcerative colitis, and pancreatis. Existing methods for diagnosing many GI diseases predominantly rely on invasive, expensive, and time-consuming techniques such as colonoscopy and endoscopy. In this study, an autonomous ingestible smart biosensing system in a pill format with integrated pH sensors is reported. The smart sensing pills will measure the pH profile as they transit through the GI tract. The data is then downloaded from the pills after they are collected from the feces. The sensor is based on electrodeposited PANI on carbon-coated conductive threads providing high pH sensitivity. Engineering innovations allowed integration of thread-based sensors on 3D-printed pill surfaces with front-end readout electronics, memory, and microcontroller assembled on mm-size circular printed circuit boards. The entire smart sensing pill possesses an overall length of 22.1 mm and an outer diameter of 9 mm. The modular biosensing system allows integration of thread-based biosensors to monitor other biomarkers in GI tract that mitigates the complex sensor fabrication process as well as overall pill assembly. [ABSTRACT FROM AUTHOR]

There is a need to develop low-cost and compact frequency reconfigurable antennas with continuous frequency tuning capability. Existing approaches rely on dedicated electrical, mechanical, or MEMS-based approaches to reconfigure the antenna, which requires extra components and fabrication steps. In this paper, we propose a physics-based approach to realize tunable helical antennas based on a shape memory alloy (SMA). By utilizing the temperature-induced irreversible mechanical deformation of the SMA, the temperature-controlled antenna can continuously change its resonant frequency and lock the state when the desired frequency response is achieved. The height of the helical antenna changes in response to applied temperatures. No additional circuitry or mechanical modules are required for the reconfiguration of the antenna geometry. The fabricated helical antenna can shift resonant frequency between 150 and 195 MHz with a tuning sensitivity of 284 kHz/°C. [ABSTRACT FROM AUTHOR]

There is a need to develop cost-effective and compact solutions for Smart Home monitoring. Existing monitoring systems depend on continuous power sources to support the operation of sensors and electronics modules used therein. In this article, we present three simple battery-free, Radio-Frequency Identification (RFID)-based solutions for real-time monitoring of the orientation of an object using a tilt sensor based on a metallic bead, an entry detection system utilizing a reed switch-based proximity sensor, and a temperature crossing event detection using a thermistor. All sensors are integrated with individual passive RFID tags. The proposed sensing mechanisms were also combined to achieve multi-modal logic sensing operation. Active events (change in position, motion, and temperature) would alter the state of the corresponding flexible RFID sensors to transmit warning signals wirelessly to an RFID reader, realizing a simple RFID-based Smart Home network. The proposed platform has been validated through extensive simulation and actual measurements. [ABSTRACT FROM AUTHOR]

Microneedles offer a convenient transdermal delivery route with potential for long term sustained release of drugs. However current microneedle technologies may not have the mechanical properties for reliable and stable penetration (e.g. hydrogel microneedles). Moreover, it is also challenging to realize microneedle arrays with large size and high flexibility. There is also an inherent upper limit to the amount and kind of drugs that can be loaded in the microneedles. In this paper, we present a new class of polymeric porous microneedles made from biocompatible and photo-curable resin that address these challenges. The microneedles are unique in their ability to load solid drug formulation in concentrated form. We demonstrate the loading and release of solid formulation of anesthetic and non-steroidal anti-inflammatory drugs, namely Lidocaine and Ibuprofen. Paper also demonstrates realization of large area (6 × 20 cm2) flexible and stretchable microneedle patches capable of drug delivery on any body part. Penetration studies were performed in an ex vivo porcine model supplemented through rigorous compression tests to ensure the robustness and rigidity of the microneedles. Detailed release profiles of the microneedle patches were shown in an in vitro skin model. Results show promise for large area transdermal delivery of solid drug formulations using these porous microneedles. [ABSTRACT FROM AUTHOR]

Devices that can morph their functions on demand provide a rich yet unexplored paradigm for the next generation of electronic devices and sensors. For example, an antenna that can morph its shape can be used to adapt communication to different wireless standards or improve wireless signal reception. We utilize temperature-sensitive shape memory alloys (SMA) to realize a shape morphing antenna (ShMoA). In the designed architecture, multiple conjoined shape memory alloy sections form the antenna. The shape morphing of this antenna is achieved through temperature control. Different temperature threshold levels are used for programming the shape. Besides its conventional use for RF applications, ShMoA can serve as a multi-level temperature sensor, analogous to thermoreceptors in an insect antenna. ShMoA essentially combines the function of temperature sensing, embedded computing for detection of threshold crossings, and radio frequency readout, all in the single construct of a shape-morphing antenna (ShMoA) without the need for any battery or peripheral electronics. The ShMoA can be employed as bio-inspired wireless temperature sensing antennae on mobile robotic flies, insects, drones and other robots. It can also be deployed as programmable antennas for multi-standard wireless communication. [ABSTRACT FROM AUTHOR]

Wearables have garnered significant attention in recent years not only as consumer electronics for entertainment, communications, and commerce but also for real-time continuous health monitoring. This has been spurred by advances in flexible sensors, transistors, energy storage, and harvesting devices to replace the traditional, bulky, and rigid electronic devices. However, engineering smart wearables that can seamlessly integrate with the human body is a daunting task. Some of the key material attributes that are challenging to meet are skin conformability, breathability, and biocompatibility while providing tunability of its mechanical, electrical, and chemical properties. Electrospinning has emerged as a versatile platform that can potentially address these challenges by fabricating nanofibers with tunable properties from a polymer base. In this article, we review advances in wearable electronic devices and systems that are developed using electrospinning. We cover various applications in multiple fields including healthcare, biomedicine, and energy. We review the ability to tune the electrical, physiochemical, and mechanical properties of the nanofibers underlying these applications and illustrate strategies that enable integration of these nanofibers with human skin. [ABSTRACT FROM AUTHOR]

Microneedles offer a convenient transdermal delivery route with potential for long term sustained release of drugs. However current microneedle technologies may not have the mechanical properties for reliable and stable penetration (e.g. hydrogel microneedles). Moreover, it is also challenging to realize microneedle arrays with large size and high flexibility. There is also an inherent upper limit to the amount and kind of drugs that can be loaded in the microneedles. In this paper, we present a new class of polymeric porous microneedles made from biocompatible and photo-curable resin that address these challenges. The microneedles are unique in their ability to load solid drug formulation in concentrated form. We demonstrate the loading and release of solid formulation of anesthetic and non-steroidal anti-inflammatory drugs, namely Lidocaine and Ibuprofen. Paper also demonstrates realization of large area (6 × 20 cm2) flexible and stretchable microneedle patches capable of drug delivery on any body part. Penetration studies were performed in an ex vivo porcine model supplemented through rigorous compression tests to ensure the robustness and rigidity of the microneedles. Detailed release profiles of the microneedle patches were shown in an in vitro skin model. Results show promise for large area transdermal delivery of solid drug formulations using these porous microneedles. [ABSTRACT FROM AUTHOR]

This work presents the development of a robotic hand using 3D printing technology for robotic and prosthetic applications. The 3D printed hand presented herein is very cost-effective and involves elementary fabrication steps paving the way for rapid manufacturing at low cost. Fused deposition modeling (FDM) printers using polymer composites are used to print with optimized manufacturing settings to achieve a truly low-cost solution through minimal waste, minimal material requirement while achieving the required durability. Further, the 3D printed hand is embedded with pressure and strain sensors for tactile feedback required for human-like dexterity. A piezoresistive polymer-based flexible pressure sensor and an in-house carbon-coated elastic thread-based strain sensor are employed to realize the cost-effective 3D printed hand with tactile feedback. The sensors employed need a highly linear readout circuit for the effective implementation of the tactile feedback. Owing to this, a highly linear null detection-based Wheatstone bridge is proposed for the readout. Detailed analysis and their effect on the readout's linearity are presented for the non-idealities involved in the design. A prototype is fabricated and tested to evaluate the performance of the circuit. Experimental results show that the circuit was able to reduce the nonlinearity error from 52% (in case of single-element Wheatstone bridge followed by a difference amplifier) to 0.14% for a wide resistance range from 1 kΩ to 1 MΩ. The circuit was further used as an analog readout for the sensors embedded in the 3D printed robotic hand. The complete system was finally evaluated under laboratory conditions verifying the design of the truly cost-effective and simple 3D printed robotic hand with tactile feedback. [ABSTRACT FROM AUTHOR]

This work presents high resolution and adaptable frequency measurement techniques for relaxation oscillator based capacitive sensors. The techniques rely on extremely simple hardware such as a 1-bit coarse voltage quantizer to generate a 1-bit data stream and subsequently determine frequencies with resolutions greater than 20 bits from the 1-bit data stream. The proposed readouts are based on two types of 1-bit hardware approaches with Nyquist sampling in one approach and oversampling in the other. The first approach employs a Nyquist rate sampled 1-bit comparator while the second approach relies on an oversampled 1-bit quantizer based delta-sigma modulator (DSM) as a hardware to generate the bit stream. High resolution frequency is estimated from the 1-bit data stream using parametric, non-parametric and compressed sensing approaches. We provide detailed study and measurement results comparing the performance of the proposed techniques for test inputs with different frequencies and amplitudes and multiple signal shapes including sine, square, triangular and sawtooth. We show that the 1-bit comparator along with the CS approach provides the best performance across all input amplitude, frequency and shapes. A capacitive water level sensor was implemented in a PCB and embedded in a conventional square wave relaxation oscillator to verify the proposed technique. Measurement results show that incremental SNRs can be achieved only by increasing the 1-bit data stream length without any change in the hardware thereby demonstrating the adaptability of the technique based on an application requirement. [ABSTRACT FROM AUTHOR]

This brief proposes a novel current output resistor string DAC architecture implemented for a 10-bit resolution. The DAC consists of a 6-bit coarse resistor string DAC followed by a 4-bit multi-input interpolation amplifier, and a voltage to current conversion stage. Use of a multi-input interpolation amplifier with shared resistive load provides accurate fine conversion with reduced resistor count. The current output DAC has high output impedance from the regulated current source architecture. The prototype was fabricated in a 0.18 μm CMOS process technology. The measured integral non-linearity (INL) and differential non-linearity are 0.5 LSB and 0.4 LSB, respectively. The chip consumes static power 0.54 mW at 1.8 V supply and occupies 0.042 mm2 area. [ABSTRACT FROM AUTHOR]

Oxygen plays a key role in human physiology and is abnormally modulated in various disease pathologies making its in situ monitoring quite important. Most oxygen sensors are not able to measure oxygen levels deep inside the tissue or have mismatched electrode–tissue interfaces. In this study we developed a flexible thread-based oxygen sensor that combines the unique advantages of minimal invasiveness and superior flexibility offering the possibility for tissue integration. The sensor is featured by a simple and low-cost fabrication approach which allows for measuring the overall oxygen concentration either over a large surface area or locally at any spot in any three-dimensional environment with high spatial accuracy and high sensitivity. The sensor can sensitively detect dissolved oxygen levels within the physiological range of tissue oxygenation. The sensor's performance is insensitive to pH variation from 5.8 to 8.0. The sensor shows good repeatability and stability over a period of one week in phosphate buffered saline. In addition, the signal variation is less than 10% after hundreds of cycles of physical bending. Using a hydrogel-based tissue model the sensor has been shown to probe dissolved oxygen levels at different spatial locations inside a tissue-like environment. [ABSTRACT FROM AUTHOR]

Economical sensing and recording of temperature are important in the transportation and management of fragile goods such as medicine, fish/poultry, and other temperature-sensitive items. Existing approaches measure the entire temperature profile using electronic devices running on a continuous power source. This letter presents a simple, intelligent, and battery-free solution for capturing interesting temperature events using the natural thermo-mechanical state of a shape memory alloy (SMA). Our approach utilizes the temperature variation induced irreversible configuration of SMA, which provides a natural ability to capture the temperature history without the need for electronic data logging. In this letter, SMA is used to record the threshold temperature violation event. A prototype antenna is shown to monitor the temperature at 30  $^\circ$ C with a $\pm$ 1  $^\circ$ C error. A difference of 17 dB in frequency response was observed with and without temperature violation. Detailed design and experimental studies have been performed to validate the proposed approach. [ABSTRACT FROM AUTHOR]

Human machine interfaces that can track head motion will result in advances in physical rehabilitation, improved augmented reality/virtual reality systems, and aid in the study of human behavior. This paper presents a head position monitoring and classification system using thin flexible strain sensing threads placed on the neck of an individual. A wireless circuit module consisting of impedance readout circuitry and a Bluetooth module records and transmits strain information to a computer. A data processing algorithm for motion recognition provides near real-time quantification of head position. Incoming data is filtered, normalized and divided into data segments. A set of features is extracted from each data segment and employed as input to nine classifiers including Support Vector Machine, Naive Bayes and KNN for position prediction. A testing accuracy of around 92% was achieved for a set of nine head orientations. Results indicate that this human machine interface platform is accurate, flexible, easy to use, and cost effective. [ABSTRACT FROM AUTHOR]

Ionic liquid/ionogel gate dielectrics can provide significant advantages for transistor architectures that utilize high surface area semiconductors and/or nonplanar substrates because of their cleanroom-free, liquid-based processability and their inherently large electrostatic double layer capacitance. These attributes of ionogels have already enabled the facile fabrication of several up-and-coming transistor devices geometries for which a highly conformal interface between the electrolyte gate dielectric and the semiconductor is readily achievable, and remote gating with a nonaligned gate electrode is possible. Further, ionogel gating can improve device performance to maximize current densities at low operating voltages. This Perspective highlights three classes of emerging transistor architectures, namely, vertical transistors, surround gate transistors, and thread/fiber-based transistors, and provides several key examples of instances where ionogel gating has either already enabled or still stands to improve device fabrication and performance. [ABSTRACT FROM AUTHOR]

Sensor platforms that exploit the fibrous textile threads as substrates offer great promise since they can be directly sewn, woven or stitched on to any clothing. They can also be placed directly in intimate contact with the skin. In this work, we present a thread-based sensing platform in the form of a multiplexed sensing patch for continuous simultaneous on-skin monitoring of sweat. The patch performs real-time, on-body measurements of important biomarkers present in sweat such as electrolytes (sodium and ammonium ions), metabolites (lactate) and acidity (pH). Flexible threads coated with conductive inks were used as sensing electrodes. Selective potentiometric detection of electrolytes and pH was made possible through ion-selective membrane deposition and pH-sensitive polyaniline coating on threads, respectively. An amperometric enzymatic sensing scheme with lactate oxidase was used for the detection of lactate. An array of the thread sensors is integrated onto a patch with connectivity to a miniaturized circuit module containing a potentiostat, microprocessor and wireless circuitry for wireless smartphone readout. Extensive in vitro validation and an in vivo human pilot study involving a maximal exertion test show the promise of this platform for real-time physiological monitoring of human performance/fitness under stress, as well as diagnostic monitoring through sweat analysis. [ABSTRACT FROM AUTHOR]

There is a need for economical monitoring of fragile goods that are sensitive to temperature, tilt or vibrations during transit. The mishandling of these goods could permanently alter or damage them. Existing methods rely on electronic devices that need a continuous power source for sensing and data logging. This article introduces a simple battery-free economical solution for recording a singular event of temperature crossing or a tilt activity using liquid metal, namely eutectic gallium indium (EGaIn) coupled to a Radio-Frequency Identification (RFID) tag. The crossing of a threshold of either temperature or tilting angle results in EGaIn flow, which activates or deactivates the RFID tag permanently. This change is irreversible; thus, the sensor memorizes the specific temperature or tilt event. This built-in memory function and wireless communication of the RFID sensor enables economical monitoring of temperature and motion-sensitive goods during transport without the need for a battery. In this paper, we have further reduced cost by fabricating these temperature and tilt sensors on paper substrates. [ABSTRACT FROM AUTHOR]

In this article, we present a magnetically–tunable quad–band filter with high tunability in the frequency range of 2.1–3.9 GHz. A multi–band filter with four stop–bands comprises of a microstrip line coupled to four frequency–selective split–ring resonators (SRRs). We achieve tuning of individual frequency bands using magnetic reed switches connected in between the capacitive gaps of each split–ring resonator. Application of magnetic field tunes this capacitance affecting its resonance frequency. The measured reflection spectrum of the proposed device matches well with the simulation results. The results show more than 25% tunability for each of the four bands with bandwidth values in the range of 30–70 MHz with over 100% overall tunability in the 2.1–3.9 GHz frequency spectrum. [ABSTRACT FROM AUTHOR]

There is a growing demand for devices that exhibit human skin-like sensory capabilities due to their broad applications in soft robotics and healthcare. Ionically conductive hydrogels have long been studied for wearable, flexible sensor applications; however, the volatility of water inevitably leads to dehydration issues that can limit the long-term use of hydrogel-based devices. In this report, highly stretchable, gelatin biopolymer-supported deep eutectic solvent (DES) gel electrolytes are presented as a promising nonvolatile alternative to hydrogels for ionic skin applications. The DES gel containing 22 wt% gelatin exhibited high stretchability (fracture strain > 300%) and a room temperature ionic conductivity of 2.5 mS cm−1. Capacitive-type pressure and strain sensors fabricated using gelatin-supported DES gel electrolytes provided linear responses over a wide range; an applied pressure as low as 1 kPa could be detected using a 1 V bias. A 3 × 3 sensor array was also constructed, which exhibited excellent performance for identifying the (multi)touch location(s) of applied pressure. These characteristics not only demonstrate the suitability of gelatin-supported DES gels for ionic skin applications, but also present a new class of materials for developing future nonvolatile sensors. [ABSTRACT FROM AUTHOR]

We present washable smart sensing threads for creation of smart wearable fabrics. More specifically, we report the fabrication of a facile stretchable and washable thread-based strain/force sensor, which can be sewn into wearable textiles and is capable of measuring human physiological motion. We use polybutylene terephthalate (PBT) puffy threads as our substrate which is made strain-sensitive using a simple reel-to-reel coating process. While PBT in itself is not very stretchable, threads made from them have coiled helical filaments. Stretching such threads uncoils these filaments imparting them stretchability. To convert them into strain sensor, we coat these PBT threads with resistive carbon ink. The straightening (uncoiling) of the helical filaments changes its resistance. There is a negligible change in resistance after repeated washing steps. Such washable immunity is achieved by coating thin layer of PDMS on them. The sensor exhibits a constant gauge factor of ~2.5 within its working range (50% strain) and exhibits a linear response to applied strain up to 50% of its initial length. Such strain sensing threads can form the basis of smart fabrics that can track human motion and for use in real-time physiological monitoring. We present promising results on the detection of the human form (seated versus standing) and human motion (running versus walking) using these threads sewn onto trousers. [ABSTRACT FROM AUTHOR]

This paper presents a novel ${\text{32}}\times {\text{64}}$ CMOS image sensor for luminescence imaging with direct lifetime-dependent digital pulse frequency modulated output. Recently reported parasitic insensitive multicycle charge modulation scheme is applied to accumulate photon-generated charges in discrete programmable time windows over multiple exposures. An autoreset pulse serving as the digital output is generated by comparing the multicycle charge integrated output with a reference threshold. The detected luminescence's lifetime is extracted by monitoring the frequency in this digital pulse. To compensate for the background photocurrent generated by ambient light and built-in offset, a charge pump based calibration circuitry is also proposed. Driven by a 10-KHz clock signal with 20-μs pulse width as the integration time window, the proposed circuitry can achieve $\text{93 Hz/}(\mu \text{W/cm}^{2})$ responsivity and ${\text{19 nW/cm}}^{2}$ resolution at 575 nm wavelength. It has lifetime resolution of 8 ns. The proposed sensor chip was applied for lifetime measurement of a Ru(dpp)3(PF6)2 fluorescent sample whose lifetime was estimated to be 4.2 μs. A two-dimensional luminescence intensity and lifetime images of a single white LED have also been obtained to further validate its functionality. [ABSTRACT FROM AUTHOR]

This paper presents a novel ${\text{32}}\times {\text{64}}$ CMOS image sensor for luminescence imaging with direct lifetime-dependent digital pulse frequency modulated output. Recently reported parasitic insensitive multicycle charge modulation scheme is applied to accumulate photon-generated charges in discrete programmable time windows over multiple exposures. An autoreset pulse serving as the digital output is generated by comparing the multicycle charge integrated output with a reference threshold. The detected luminescence's lifetime is extracted by monitoring the frequency in this digital pulse. To compensate for the background photocurrent generated by ambient light and built-in offset, a charge pump based calibration circuitry is also proposed. Driven by a 10-KHz clock signal with 20-μs pulse width as the integration time window, the proposed circuitry can achieve $\text{93 Hz/}(\mu \text{W/cm}^{2})$ responsivity and ${\text{19 nW/cm}}^{2}$ resolution at 575 nm wavelength. It has lifetime resolution of 8 ns. The proposed sensor chip was applied for lifetime measurement of a Ru(dpp)3(PF6)2 fluorescent sample whose lifetime was estimated to be 4.2 μs. A two-dimensional luminescence intensity and lifetime images of a single white LED have also been obtained to further validate its functionality. [ABSTRACT FROM AUTHOR]

Computer vision algorithms are often limited in their application by the large amount of data that must be processed. Mammalian vision systems mitigate this high bandwidth requirement by prioritizing certain regions of the visual field with neural circuits that select the most salient regions. This work introduces a novel and computationally efficient visual saliency algorithm for performing this neuromorphic attention-based data reduction. The proposed algorithm has the added advantage that it is compatible with an analog CMOS design while still achieving comparable performance to existing state-of-the-art saliency algorithms. This compatibility allows for direct integration with the analog-to-digital conversion circuitry present in CMOS image sensors. This integration leads to power savings in the converter by quantizing only the salient pixels. Further system-level power savings are gained by reducing the amount of data that must be transmitted and processed in the digital domain. The analog CMOS compatible formulation relies on a pulse width (i.e., time mode) encoding of the pixel data that is compatible with pulse-mode imagers and slope based converters often used in imager designs. This letter begins by discussing this time-mode encoding for implementing neuromorphic architectures. Next, the proposed algorithm is derived. Hardware-oriented optimizations and modifications to this algorithm are proposed and discussed. Next, a metric for quantifying saliency accuracy is proposed, and simulation results of this metric are presented. Finally, an analog synthesis approach for a time-mode architecture is outlined, and postsynthesis transistor-level simulations that demonstrate functionality of an implementation in a modern CMOS process are discussed. [ABSTRACT FROM AUTHOR]