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This paper presents a bio-inspired adaptive micro-lens with electrically tunable focus made of non-ionic high-molecular-weight polyvinyl chloride (PVC) gel. The optical device mimics the design of the crystalline lens and ciliary muscle of the human eye. It consists of a plano-convex PVC gel micro-lens on Indium Tin Oxide (ITO) glass, confined with an annular electrode operating as an artificial ciliary muscle. Upon electrical activation, the electroactive adhesive force of the PVC gel is exerted on the annular anode electrode, which reduces the sagittal height of the plano-convex PVC gel lens, resulting in focal length variation of the micro-lens. The focal length increases from 3.8 mm to 22.3 mm as the applied field is varied from 200 V/mm to 800 V/mm, comparable to that of the human lens. The device combines excellent optical characteristics with structural simplicity, fast response speed, silent operation, and low power consumption. The results show the PVC gel micro-lens is expected to open up new perspectives on practical tunable optics.

This paper presents a passive wireless sensor for simultaneously and remotely measuring pressure and temperature under harsh environments. The sensor consists of a dual $LC$ (inductor and capacitor) resonant circuit, one without a cavity and the other with a cavity capacitor for temperature and pressure sensing, respectively. The low-temperature co-fired ceramic technology is used to fabricate the sensor, making it suitable for high-temperature harsh environment operations. Experimental results show the prototype sensor has temperature sensitivity of 8.15 kHz/°C and pressure sensitivity of 1.96 MHz/Bar up to 400°C. [2016-0157]

In a nanowire dispersed in liquid droplets, the interplay between the surface tension of the liquid and the elasticity of the nanowire determines the final morphology of the bent or buckled nanowire. Here, we investigate the fabrication of a silver nanowire ring generated as the nanowire encapsulated inside of fine droplets. We used a hybrid aerodynamic and electrostatic atomization method to ensure the generation of droplets with scalable size in the necessary regime for ring formation. We analytically calculate the compressive force of the droplet driven by surface tension as the key mechanism for the self-assembly of ring structures. Thus, for potential large-scale manufacturing, the droplet size provides a convenient parameter to control the realization of ring structures from nanowires.

Piezoelectricity in macromolecule polymers has been gaining immense attention, particularly for applications in biocompatible, implantable, and flexible electronic devices. This paper introduces core–shell-structured piezoelectric polyvinylidene fluoride (PVDF) nanofibers chemically wrapped by graphene oxide (GO) lamellae (PVDF/GO nanofibers), in which the polar β-phase nanocrystals are formed and uniaxially self-oriented by the synergistic effect of mechanical stretching, high-voltage alignment, and chemical interactions. The β-phase orientation of the PVDF/GO nanofibers along their axes is observed at atomic scale through high resolution transmission electron microscopy, and the β-phase content is found to be 88.5%. The piezoelectric properties of the PVDF/GO nanofibers are investigated in terms of piezoresponse mapping, local hysteresis loops, and polarization reversal by advanced piezoresponse force microscopy. The PVDF/GO nanofibers show a desirable out-of-plane piezoelectric constant (d33) of −93.75...

Composite membranes have been fabricated made of ultrafine PVDF fibers via a tip-induced electrospinning (TIE) process and Al2O3 nanoparticles via a dip-coating process. These membranes exhibit good thermal stability and electrochemical properties as the separators for applications in lithium ion batteries (LIBs). Experimental results show that the as-fabricated separators may mechanically contract less than 2% when kept at a high temperature of 140 °C for an hour showing good thermal stability as compared with commercial polypropylene separators and electrospun PVDF membranes. The membrane has a measured porosity of 55.8% and ionic conductivity of 2.23 mS cm−1, achieving a low battery discharge capacity loss of 1.8% after 100 cycles in the 1.0C-rate tests, and a retention rate of 92.9% in the 4C-rate tests. These results show the great potential of PVDF/Al2O3 separators in LIB applications under high temperature and high current/power operations.

Poly(vinylidene fluoride) (PVDF) has been widely utilized in scientific research and the manufacturing industry for its unique piezoelectric properties. In the past few decades, the vibrational spectra of PVDF polymorphic polymers via FTIR (Fourier transform infrared spectroscopy) have been extensively investigated and documented. However, reports on the analysis of α, β and γ phases often have conflicting views based on measured data. In this work, we analyze the FTIR vibrational bands of PVDF materials fabricated by different processes with detailed XRD (X-ray diffraction) characterization to identify the structural α, β and γ phases. By examining the results in this work and extensively reviewing published research reports in the literature, a universal phase identification procedure using only the FTIR results is proposed and validated. Specifically, this procedure can differentiate the three phases by checking the bands around 763 and/or 614, 1275, and 1234 cm−1 for the α, β and γ phases, respectively. The rule for assignment of the 840* and 510* cm−1 bands is provided for the first time and an integrated quantification methodology for individual β and γ phase in mixed systems is also demonstrated.

Although multichip light-emitting diode (LED) modules are becoming popular in high-power lighting applications, better light extraction efficiency is always desirable in the industry. In this paper, V-grooves fabricated by the low-cost dicing process have been utilized on the top face of the multichip LED module to enhance the output power. An analytical model including the consideration of surface has been established by using a fractal theory. The combined finite difference time domain and ray tracing method has been used to simulate the light extraction enhancement considering the surface roughness scattering effects. The results show 12% enhancements in the experiments when the measured surface roughness of the V-groove has RMS roughness of $0.25~\mu \text{m}$ , which is in good agreement with the simulation result of 13.7%. The multichip LED models have been applied in indoor downlight systems and it is found that the luminous efficiency has been enhanced by 9.6% under a current of 350 mA (5.8 W) when compared with multichip LED modules without V-grooves.

Herein, we demonstrated direct-write flexible micro-supercapacitors prepared by the near-field electrospinning of polypyrrole (PPy) nanofibers on a patterned metal electrode deposited on a flexible polymer substrate. The continuous porous nanofiber network with a pseudocapacitance effect greatly increases the capacitance and facilitates ion transport in the electrodes. The prototype based on the lab-synthesized PPy nanofibers shows a high capacitance of 0.48 mF cm−2 when the total area of both electrodes and electrolyte is considered, and the performance is not affected when it is bent to different extents. The micro-supercapacitors were experimentally proved to be highly flexible with excellent electrochemical performance and cycling stability. Our approach is simple, versatile, and compatible with different substrates for the direct integration of energy storage devices in flexible microsystems.

This work demonstrates the fabrication of micro carbon fibers with hierarchical nanostructures of nickel-carbon nanotubes by electroless plating and chemical vapor deposition. Characterizations show that the micro coaxial fibers have 1400 times larger surface area, and 100 times larger electrochemical capacitance than pristine carbon fibers, while their mechanical strength has only 8% degradation. These outstanding properties make the micro coaxial fibers promising for applications in flexible or wearable supercapacitor electrodes.

Accumulative ultraviolet (UV) radiation from sunlight could be harmful to human skin and a reliable detection scheme is desirable as part of the protection strategy. This article reports the fabrication of an all passive, battery-free, irreversible, wireless smart UV patch for recording the amount of UV energy accumulation by resistance change. An ultrahigh sensitivity, with 5 orders of magnitude in resistance drop within 2 hours of exposure to sunlight, has been successfully demonstrated. The photo-induced protonation of a conductive polymer is assisted by carbon nanotube (CNT) composites for improved detection sensitivity. More importantly, the whole sensor has been successfully fabricated and optimized on a patterned flexible substrate using a laser printing technique for the electrodes and a subsequent dip-coating method has been utilized to deposit the sensing composite. As such, this novel UV accumulation sensor along with its proposed sensing scheme could be further developed for potential commercial applications.

Environmental sensing is an important task in the development of infrastructures for the applications of the Internet of things. In this work, we introduce a flexible humidity sensor based on electrochemically polymerized polypyrrole to absorb or desorb water vapors to detect relative humidity (RH). A test platform was built to mix the different amounts of dry and wet air for the relative humidity ranging from 15% to 95%. Experimental results show that the response time from 20% to 90% RH of the sensor was 505 seconds and the recovery time from 90% to 20% RH was 328 seconds with good repeatability during three cycles. The wide dynamic range, excellent repeatability and reasonable response time make the sensor applicable for home monitoring applications. Furthermore, the flexible sensor is suitable for embedding into wallpaper or decorations for promising future systems to map the environmental status of buildings and homes.

Respiration is an important physiological function in which air is moved into and out of the lungs. This paper designed a flexible patch for continuous detections of respiration, especially for evaluating nasal symmetry. The monitoring system comprises an integrated hot-film and two time-of-flight flow sensors on a flexible polyimide (PI) substrate. The 5 μm-thick polyimide substrate is flexible to construct wearable devices while the hot-wire flow sensor can monitor the respiration conditions and states, such as different breathing patterns of mouth or nose modes, normal or deep forms, and happy or nervous signs. Moreover, the power consumption of the system is low for possible long-term monitoring applications of sleep and medical diagnosis. The two time-of-flight sensors are aligned symmetrically on different sides of the hot-film heating element for differential signal readings, which used asymmetrical thermal distribution to reveal breathing state differences of two nostrils and they don’t require additional energy since they are located near the heating element. The system serves as a noninvasive wearable device to monitor respiratory airflow while avoiding uncomfortable nasal cannula. Various testing results show the feasibility and effectiveness of the proposed system.

Electrochemical sensors can provide numerous health information while analyzing ions in bio-fluids. Ion selective electrodes (ISEs) have become ideal sensing devices for measuring cation and anion concentrations in aqueous samples. In the scenario for human bio-fluidics detection, substrate should be flexible in comply with body and hydrophilic to enrich fluidics in natural perspiration analysis in a possible way. Here graphite paper ISE combined with paper microfluidic is presented to meet both requirements. The ion-to-electron transducer of the ISE electrodes was achieved by subjecting PEDOT: PSS and carbon nanotubes solutions on the top of conducting layer (Ag, Graphite paper) accordingly, through which potential drift can be minimized. A no-mask process including paper-cutting, wax-printing and cast-dropping, has also been introduced to realize the easy fabrication for lab experiments and future development.

Mobility and robustness are two important features for practical applications of robots. Soft robots made of polymeric materials have the potential to achieve both attributes simultaneously. Inspired by nature, this research presents soft robots based on a curved unimorph piezoelectric structure whose relative speed of 20 body lengths per second is the fastest measured among published artificial insect-scale robots. The soft robot uses several principles of animal locomotion, can carry loads, climb slopes, and has the sturdiness of cockroaches. After withstanding the weight of an adult footstep, which is about 1 million times heavier than that of the robot, the system survived and continued to move afterward. The relatively fast locomotion and robustness are attributed to the curved unimorph piezoelectric structure with large amplitude vibration, which advances beyond other methods. The design principle, driving mechanism, and operating characteristics can be further optimized and extended for improved performances, as well as used for other flexible devices.

This work presents the first demonstration of a fully transparent, piezoelectric ultrasonic transducer with a 3D printed substrate. All layers of the transducers were fabricated using optically transparent materials namely: polyvinylidene difluoride (PVDF) for active piezoelectric material, polydimethylsiloxane (PDMS) for a supporting elastic layer, indium tin oxide (ITO) for the conductive electrode, and polymethil methacylate (PMMA) as the substrate. The prototype transducer is 500μm in radius, 100μm in thickness with the active piezoelectric layer, and 20μm in thickness for the inactive layer. The fabricated devices were used to record acoustic signals generated by a commercial ultrasonic transducer driven by 16V peak-to-peak (Vpp) amplitude 3cm away in air medium. The amplitude of the recorded acoustic pressure by the fabricated devices were 70mVpp. We concluded that fabricated devices demonstrate entirely transparent ultrasonic transducers. These results indicate that the approach has the potential for displays applications such as gesture recognitions, and finger print sensing.

This study presents a novel 3D printed bio-sensing chip to characterize the antibiotic-resistant reaction profile of bacteria in real time for the first time. The chip adapts the dead-end filling method to achieve the sample solution transfer process. The experimental results demonstrate several accomplishments: (1) fabrication of the disposable and real-time bacteria detection system by 3D-printing; (2) alleviation of the typical leakage problems associated with 3D-printed structures during the transfer process for the sample solutions; and (3) demonstration of the detection of E. coli-antibiotic tests using a smart phone with the RGB pixel analysis app with the color identification to achieve the bacteria antibiotic-resistant profile. As such, this work could open up a new class of disposable bio-sensing characterization systems based on the combination of 3D-printing and wireless data transmission technologies.

We use a desktop-size vinyl cutter as the fabrication platform for stretchable micro- supercapacitor patches with interdigital patterns. Compared with similar works, our method can greatly reduce the cost (by ~70%) and time (by ~70%) in fabrication process, because no photolithography -based procedures were required. Instead, electrode patterns, interconnects and patch outlines were defined by automated cutting blades at sufficient resolution (smallest feature ~100μm). This fabrication method is compatible with both spray- and electro-deposited active materials, and yields comparable capacitor performances to previously reported devices. Our stretchable micro-supercapacitor patches can sustain considerable mechanical deformation with no performance degradation, and be applied as convenient power-supply modules for temperature sensors and commercial LEDs.

In this work, we proposed a fiber-based wearable piezoresistive sensor that had high sensing performance and well flexibility. The sensor can detect a force as low as 1.5 mN, and showed excellent properties of fast response, quick recovery, good repeatability and stability. Here, the potential of using the sensitive fiber materials to achieve flexible and knitted structures for tactile application was explored. Taking advantage of the weaving feature, these fibers can be easily knitted into fabric to form sensor array to achieve multiple sites measurement. For another, knitted fibers are structural flexibility and could be integrated into various configurations, which demonstrates the potential in wearable tactile perception.

We present a new class of soft robots inspired by the bone-and-flesh construct in human body for fast, deterministic actuation. Two distinctive advancements have been achieved: (1) untethered robots with external magnetic power, boasting high normalized power density of ~2*10-2/s (40-6,000,000× higher than most reports); (2) ultrafast and deterministic-shape actuation in ~0.1 seconds (100x faster than the state-of-the-art). Inspired by the natural human architecture, our soft robots with different elastomer ("flesh") structures and magnet ("bone") placements can complete various tasks quickly and precisely (e.g., planar contraction, out-of-plane gesture transitions, breaking lock-in states, and manipulating small objects). We envision that our design and operation principles can be potentially extended to even more complex applications.

This work demonstrates, for the first time, conformal coating of conductive polymer electrodes onto PolyJet 3D printed structures to enable the fabrication of in-channel 3D electrodes for sensing applications. The reagent (3-Glycidoxypropyl) trimethoxysilane (GOPS) is used as the chemical material to crosslink carbon nanotube-doped poly(3,4ethyelenedioxythiophene) polystyrene sulfonate (CNT-PEDOT:PSS) to a variety of 3D printing materials. The conformally-coated electrodes are functionalized via electropolymerization of polyaniline (PANI), an ethanol sensitive material, to demonstrate a 3D printed ethanol sensor with a measured detection limit of ~0.19 %v/v. As such, this work opens up a new class of 3D printed sensing systems based on the conformal coating of conductive sensing material.

This work uses a real-time evaluation method on graphene field effect transistors (FETs) to characterize the scattering strength of chemical vapors at room temperature. Compared with state-of-art technologies, three distinctive advancements have been achieved: (1) an electrical measurement scheme on graphene FETs to evaluate the scattering strength of chemical vapors by the real-time estimation of carrier concentration and mobility; (2) the demonstration of quantitative test results for three chemical vapors (water, methanol, and ethanol) with different concentrations; and (3) the illustrations of the sensing selectivity in the binary mixture scenarios by the differentiable characteristics of scattering strength. As such, the proposed method of real-time scattering strength evaluation can offer a potential alternative approach for selective gas sensing.

This paper shows vacuum powered pneumatic actuators designed for wearable robots using the Kirigami of polymeric thin films for the first time. Distinctive advancements have been achieved, including (1) lightweight and the flexible thin sheet of polymeric materials made by Kirigami designs to allow either bending or twisting movements; (2) capable of shape-transforming to the surrounding such as the attachments to the surface of the cloth. The design concept, material/fabrication process, and driving mechanism described in this paper can be potentially extended to a variety of flexible devices and soft robots.

This work introduces a metal cathodic protection scheme based on a self-powered flexible electret generator which harvests energy from the environment vibration energy. The key innovations in this work include: (1) a 2×2 cm2 flexible electret generator producing peak output power of 450 μW with good stability; (2) power generation demo by lightening up 28 blue LEDs; (3) the measured reduction of metal corrosion rate by 245% with the proposed protection mechanism. As such, this low-cost, power supply-free, and environmentally friendly scheme could be applicable for the protection of metal surface from corrosions by utilizing surrounding mechanical vibration energy, including ships.

We report for the first time that stretchable electronics systems with complex geometric constructs and multiple layers of patterns can be fabricated rapidly without the need of photolithography steps. Instead, a desktop-size vinyl cutter and a CO2 laser cutter are used as patterning tools in our proposed process. To demonstrate the capacity of our method, we fabricate within 50 minutes per device a waterproof, omnidirectionally stretchable micro-supercapacitor patch with four stacked constituent layers, each with a different pattern. This soft, compliant patch can maintain full electrochemical performances after >16 hours of immersion in water, and/or various types of extreme folding and stretching deformations.

This work presents three dimensional laminar flow chaotic fluidic mixing via novel intra-channel microscale 3D structures - only made possible using high resolution 3D printing - fabricated into an entirely-3D printed modular microfluidic mixing device. These 3D micromixer (μ-mixer) structures generate passive chaotic advection in three dimensions to enhance mixing quality per-unit microchannel (μ-channel) length as compared to other state-of-the-art additive manufacturing-based 3D μ-mixer designs. Additionally, these 3D μ-mixers can be easily incorporated into any arbitrary 3D printable microfluidic device design, being fabricated along the μ-channel where efficient mixing is desired.

This paper presents a new class of supercapacitor with high mass-loading and high mechanical strength using reduced graphene oxide/carbon fiber (RGO/CF) composite electrodes for practical applications such as wearable and flexible energy storage systems. Key innovative claims include: 1) interconnected CF structures as the framework for enhanced mechanical strength, (2) high surface area RGO nanosheets for increased energy storage capability; 3) a complex 3D hierarchical structure to maintain highly efficient ion transports for high mass-loading independent of the thickness of the electrode up to 4 mg cm-2. As such, these high mass-loading electrodes could potentially find real-world applications such as wearable devices.

Please be advised that the name of one of the coauthors in the original article [1] has been incorrectly spelled: ‘Ranish M. Ramachandran’ should be ‘Ranjith K. Ramachandran’.

In this paper, a special decision surface for the weakly-supervised sound event detection (SED) and a disentangled feature (DF) for the multi-label problem in polyphonic SED are proposed. We approach SED as a multiple instance learning (MIL) problem and utilize a neural network framework with a pooling module to solve it. General MIL approaches include two kinds: the instance-level approaches and embedding-level approaches. We present a method of generating instance-level probabilities for the embedding level approaches which tend to perform better than the instance-level approaches in terms of bag-level classification but can not provide instance-level probabilities in current approaches. Moreover, we further propose a specialized decision surface (SDS) for the embedding-level attention pooling. We analyze and explained why an embedding-level attention module with SDS is better than other typical pooling modules from the perspective of the high-level feature space. As for the problem of the unbalanced dataset and the co-occurrence of multiple categories in the polyphonic event detection task, we propose a DF to reduce interference among categories, which optimizes the high-level feature space by disentangling it based on class-wise identifiable information and obtaining multiple different subspaces. Experiments on the dataset of DCASE 2018 Task 4 show that the proposed SDS and DF significantly improve the detection performance of the embedding-level MIL approach with an attention pooling module and outperform the first place system in the challenge by 6.6 percentage points., Accept by TASLP

Wafer-scale, conformal, two-dimensional (2D) TiO2-Ga2O3 n-p heterostructures with a thickness of less than 10 nm were fabricated on the Si/SiO2 substrates by the atomic layer deposition (ALD) technique for the first time with subsequent post-deposition annealing at a temperature of 250 °C. The best deposition parameters were established. The structure and morphology of 2D TiO2-Ga2O3 n-p heterostructures were characterized by the scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), electrochemical impedance spectroscopy (EIS), etc. 2D TiO2-Ga2O3 n-p heterostructures demonstrated efficient photocatalytic activity towards methyl orange (MO) degradation at the UV light (λ = 254 nm) irradiation. The improvement of TiO2-Ga2O3 n-p heterostructure capabilities is due to the development of the defects on Ga2O3-TiO2 interface, which were able to trap electrons faster. Graphical Abstract

Conductive polymer composite (CPC) based strain sensor due to its lightweight, tunable electrical conductivity, and easy processing has promising application in wearable electronics. However, it is still challenging to develop the CPC strain sensors with excellent stretchability, sensitivity, durability, anticorrosion, and deicing performance. Herein, a facile method is proposed to prepare fluorine-free superhydrophobic and highly conductive rubber composite. Ag nanoparticles (AgNPs) are first decorated on the RB (rubber band) surface, forming a conductive shell. Then, the RB/AgNPs experiences PDMS (polydimethylsiloxane) modification, which could not only endow the composite with superhydrophobicity and hence excellent corrosion resistance but also improve the interfacial adhesion between the AgNPs. The RB composite possesses a good self-cleaning performance and remains superhydrophobic even after experiencing cyclic abrasion or stretching-releasing test. Also, the high conductivity and superhydrophobicity endow the RB composite with excellent Joule heating performance and water repellence, broadening its application in deicing and water removal. Moreover, the obtained RB composite exhibits both large stretchability with a break elongation larger than 900% and high sensitivity with a response intensity as high as 3.6 × 108 at a strain of 60%. In addition, the RB composite strain sensor can be used to detect full-range human motions including large and subtle body movement. The flexible, durable, and anticorrosive RB composite has potential applications in flexible electronic, health monitoring, physical therapy, and so on.

Two kinds of flexible ozone (O3) sensors were obtained by placing pristine ZnO nanorods and gold-modified ZnO nanorods (NRs) on a bi-axially oriented poly(ethylene terephthalate) substrate. The chemiresistive sensor is operated at typically 1 V at room temperature under the UV-light illumination. The ZnO nanorods were prepared via a hydrothermal route and have a highly crystalline wurtzite structure, with diameters ranging between 70 and 300 nm and a length varying from 1 to 3 μm. The ZnO NRs were then coated with a ca. 10 nm gold layer whose presence was confirmed with microscopy analysis. This sensor is found to be superior to detect ozone at a room temperature. Typical figures of merit include (a) a sensor response of 108 at 30 ppb ozone for gold-modified ZnO NRs, and (b) a linear range that extends from 30 to 570 ppb. The sensor is stable, reproducible and selective for O3 compared to other oxidizing and reducing gases. The enhanced performance induced by the modification of ZnO nanorods with thin layer of gold is attributed to the increased reaction kinetics compared to pristine ZnO NRs. The sensing mechanism is assumed to be based on the formation of a nano-Schottky type barrier junction at the interface between gold and ZnO.

Intracardiac echocardiography (ICE) is an ultrasound sonogram that visualizes the anatomical structure of the heart in real time, with a mm-scale catheter inserted through the intracardiac vessels, and guides surgical intervention for atrial septal defect (ASD) closure. To achieve high-quality medical imaging, an ICE system must meet stringent power consumption requirements with low-noise operation. Since an ASIC and ultrasound transducers are tightly bonded through flip-chip or direct integration, an ultrasound unit TRX channel must be pitch-matched to each transducer channel [1], [2]. A piezoelectric Micro-machined Ultrasound Transducer (pMUT) is a suitable ultrasound transducer for implantable sensor applications, since it does not need high $(\sim 200\mathrm {V})$ bias that is a must in capacitive MUTs (cMUT) [3]. However, pMUT devices suffer from process variation, which leads to low image quality, and to date, no work addresses this issue for both TX/RX in real time. To meet all these requirements at once, we present a $6 \times 6$ TRX pitch-matched pMUT ASIC with a standard CMOS-compatible 13.2V HV pulser, on-chip per-pixel calibration scheme, and a Dynamic Bit-Shared (DBS) ADC for portable ICE applications.

This work presents a novel handheld, manually-actuated microfluidic prototype designed for on-site colorimetric detection of infectious pathogens in drinking water. We have also developed a custom drop-casting protocol we use to pre-load the entirely 3D printed device, fabricated via ultra-high resolution additive manufacturing technology, with colorimetric enzymatic reagents and bacteria-specific nutrients, which we use to experimentally detect Escherichia coli (E. coli) bacteria in model drinking water, as well as to determine a limit of detection of 1e6 cfu/mL of E. coli in 6 hours. Our proposed microfluidic platform will enable entirely on-site water quality testing, eliminating the need for off-site, lab-based water sample analysis, thus significantly increasing analytical throughput. Furthermore, we have developed a design methodology for engineers to customize the number of desired on-chip pathogen detection chambers, enabling multiplexed detection of multiple pathogens.

This work marks the first use of an AC sensing technique on a graphene transistor to realize label-free gas sensing of 100 ppb-level formaldehyde in the air at room temperature. Compared with the state-of-art technology, three distinctive advances have been achieved: (1) extraordinary sensitivity of trace amount of formaldehyde using an AC phase detection method on a single graphene transistor made of the monolayer graphene from the chemical vapor deposition (CVD) process without adding functional materials; (2) high signal stability on devices with or without artificial defects; (3) fast response time of 10 seconds and recovery time of 60 seconds with minimal baseline drifts. As such, the proposed AC sensing method can achieve fast detection of the low concentration formaldehyde in air with reproducible performances on CVD graphene with different defect densities.

This work reports a piezoelectric micromachined ultrasonic transducer (pMUT) with a pinned boundary for enhanced vibrational deformation and emission pressure. In contrast to the state-of-art large-scale piezoelectric ultrasonic transducers, pMUTs have limited output ranges/amplitudes due to their physical sizes which constrains their various potential applications. Using the pinned boundary design instead of the traditionally clamped structure, we demonstrate drastic performance enhancements without any added fabrication complexity. Experimental results show that the operational mode shape matches with simulations and produces a measured 2.5× improvement in displacement and an estimated 3.3× higher pressure output per volt at resonance.

This work marks the first use of a quasi-static electrical measurement method on graphene field effect transistors (FET) to characterize sub-ppm level of toxic gases in air at room temperature. Compared with the state-of-art technology, three distinctive advances have been achieved: (1) a quasi-static electrical measurement scheme on graphene FETs without sweeping a large range gate voltage to avoid the dipole flipping or charge trapping problem; (2) the real-time estimation of the charge neutral point $(\mathrm{V}_{\mathrm{CNP}})$ and carrier mobility $(\mu)$ of graphene during the exposure to sub-ppm toxic gases in air; and (3) the demonstration of differentiable characteristics of NO 2 and formaldehyde by the extractions of their intrinsic charge transfer and Coulomb scattering characteristics. As such, the proposed quasi-static monitoring method can be used to sense and differentiate sub-ppm level toxic gases on graphene FETs without using an array of devices with different surface functionalization materials.

We present a fast-moving micro crawling robot driven directly by electromagnetically induced resonance for the first time. The forelegs of the crawling robot are glued to the resonating beams and can achieve periodical raise and recover motions to realize forward movement. Under an applied AC voltage of 4 V, the crawling robot with a total mass of 137 mg can achieve a maximum crawling speed of 232 mm/s (18.9 body lengths per second). As such, this work presents a new efficient direct driving scheme for the legged micro crawling robots.

This paper reports the control and manipulation of the moving trajectories of insect-scale soft robots by the applied driving electrical voltage frequency utilizing the asymmetric structural design of the actuating mechanism. Three distinctive advancements have been achieved: (1) a simple asymmetric structural design to create uneven responses on the legs of artificial insects to realize motion controls; (2) the capability of moving forward, leftward and rightward by adjusting the applied driving frequency; and (3) a demonstration of recording the ethanol concentration map around an area in real time by carrying a gas sensor on top of the robot on a controlled path bypassing the existing obstacles. As such, this work can advance the state-of-art technologies on wirelessly controlled, unmanned robots for various potential applications.

A paper-based, disposable strain sensor by means of a direct laser printing process with high sensitivity has been developed and demonstrated. Commercially-available printing papers are first soaked with the gelatin-Mo5+ ink and ablated by a CO 2 laser to convert molybdenum ions into conductive MoC and graphene nanocomposite flakes for disposable paper electronics. The strain sensor made of continuous MoC flakes has the capability of detecting and distinguishing both tensile and compressive strain. It is found that the stability of the sensor is preserved when there are defects in the device as well as in environments with heavy humidity for potential applications in wearable devices.

We present a new way for the fabrication of stretchable electronics systems without photolithography procedures by exploiting the through-cut, tunnel-cut, and blind-cut modes of a commercial desktop-size vinyl cutter. Compared to previous studies involving photolithography, our method produces a batch of representative devices in significantly reduced time (by ∼69%) and cost (by ∼73%) with similar feature sizes $(100-1000\mu \mathrm{m})$ . Our inclusion of blind-cut and tunnel-cut modes facilitates the fabrication of complex stretchable electronics systems, rather than only electrodes and interconnects. Finally, we demonstrate the capacities of our photolithography-free fabrication via a stretchable temperature-mapping patch and flexible functional electronic components.

In this paper, we describe in detail the system we submitted to DCASE2019 task 4: sound event detection (SED) in domestic environments. We employ a convolutional neural network (CNN) with an embedding-level attention pooling module to solve it. By considering the interference caused by the co-occurrence of multiple events in the unbalanced dataset, we utilize the disentangled feature to raise the performance of the model. To take advantage of the unlabeled data, we adopt Guided Learning for semi-supervised learning. A group of median filters with adaptive window sizes is utilized in the post-processing of output probabilities of the model. We also analyze the effect of the synthetic data on the performance of the model and finally achieve an event-based F-measure of 45.43% on the validation set and an event-based F-measure of 42.7% on the test set. The system we submitted to the challenge achieves the best performance compared to those of other participates., Comment: Accept by DCASE2019 Workshop

We have successfully demonstrated a stretchable gas sensor with enhanced sensitivity to hydrogen based on crumpled graphene structures. Compared with the state-of-art technologies, three distinctive advancements have been achieved: (1) enhanced sensitivity to hydrogen based on the crumpled graphene at room temperature; (2) a model on the enhanced sensing mechanism on the crumpled graphene surface; and (3) stretchable gas sensor utilizing crumpled graphene with up to 200% stretchability. As such, the proposed sensing scheme and results could open up a new class of graphene-based, stretchable gas sensing systems for environmental and biological monitoring.

This work reports the first use of polymeric piezoelectret films for direct water splitting using ultrasonication as the driving mechanism. Piezoelectret devices are analogous to piezoelectret ceramic materials which produce electrical charges in response to mechanical stimulus. Water splitting has gained increasing attention as an alternative for producing renewable hydrogen energy. Hydrogen energy has high energy conversion efficiency and does not contribute to the harmful greenhouse gas effect that is responsible for various environmental hazards such as climate change, acid rain, and smog. The piezoelectret device is made of a polymer with charged microscopic dipoles that is bounded by metal electrodes. Ultrasonication is used to produce mechanical stimulus on the device which then generate a voltage on the surface of the metal electrode layers. This voltage catalyzes the water splitting reaction to produce hydrogen from water. Our process achieves water splitting without complicated thermal annealing (in contrast to previous work using piezoelectric ceramics) and does not use complicated transformer circuits. We show voltage measurements from mechanical stimulus to demonstrate that the device voltage can surpass the 1.23 V required to catalyze the water splitting reaction. Additionally, hydrogen quantification is conducted using Gas Chromatography (GC). Based on the analysis, the device has potential for passive energy harvesting of vibrational motion in liquid media such as tidal motions in the ocean.

Photocatalytic water splitting represents an emerging technology well positioned to satisfy the growing need for low-energy, low CO2, economically viable hydrogen gas production. As such, stable, high-surface-area electrodes are increasingly being investigated as electrodes for the photochemical conversion of solar energy into hydrogen fuel. We present a titanium dioxide (TiO2)/zinc oxide (ZnO) nanowire array using a hybrid hydrothermal/atomic layer deposition (ALD) for use as a solar-powered photoelectrochemical device. The nanowire array consists of single crystalline, wurtzite ZnO nanowires with a 40 nm ALD TiO2 coating. By using a TiO2 nanocoating on the high surface area-ZnO array, three advancements have been accomplished in this work: (1) high aspect ratio nanowires with TiO2 for water splitting (over 8 μm), (2) improved stability over bare ZnO nanowires during photocatalysis, and (3) excellent onset voltage. As such, this process opens up new class of the micro/nanofabrication process for making efficient photocatalytic gas harvesting systems.

This work reports distinctive gas sensing patterns for water vapor and methanol using graphene FET (Field Effect Transistors) functionalized with atomic layer deposition (ALD) RuO 2 . Compared with the state-of-art, three distinctive advancements have been achieved: (1) enhanced sensitivity using the scheme of electron mobility characterizations by a hybrid structure of graphene and ALD-RuO 2 base layer; (2) first demonstration of gas sensing by means of the 4-dimentional (4D) physical properties vectors of graphene FETs; (3) using the 16-dimensional (16D) characteristic gas sensing pattern to distinguish water vapor and methanol. As such, the device structure and the multi-dimensional physical properties vectors could offer robust gas classification schemes for gas sensing applications.

Ammonia gas sensors are very essential in many industries and everyday life. However, their complicated fabrication process, severe environmental fabrication requirements and desorption of residual ammonia molecules result in high cost and hinder their market acceptance. Here, laser direct writing is used to fabricate three parallel porous 3D graphene lines on a polyimide (PI) tape to simply construct an ammonia gas sensor. The middle one works as an ammonia sensing element and the other two on both sides work as heaters to improve the desorption performance of the sensing element to ammonia gas molecules. The graphene lines were characterized by scanning electron microscopy and Raman spectroscopy. The response and recovery time of the sensor without heating are 214 s and 222 s with a sensitivity of 0.087% ppm&minus, 1 for sensing 75 ppm ammonia gas, respectively. The experimental results prove that under the optimized heating temperature of about 70 &deg, C the heaters successfully help implement complete desorption of residual NH3 showing a good sensitivity and cyclic stability.

Recent years have seen the wide application of Location-Based Services (LBSs) in our daily life. Although users can enjoy many conveniences from the LBSs, they may lose their trajectory privacy when their location data are collected. Therefore, it is urgent to protect the user’s trajectory privacy while providing high quality services. Trajectory k-anonymity is one of the most important technologies to protect the user’s trajectory privacy. However, the user’s attributes are rarely considered when constructing the k-anonymity set. It results in that the user’s trajectories are especially vulnerable. To solve the problem, in this paper, a Spatiotemporal Mobility (SM) measurement is defined for calculating the relationship between the user’s attributes and the anonymity set. Furthermore, a trajectory graph is designed to model the relationship between trajectories. Based on the user’s attributes and the trajectory graph, the SM based trajectory privacy-preserving algorithm (MTPPA) is proposed. The optimal k-anonymity set is obtained by the simulated annealing algorithm. The experimental results show that the privacy disclosure probability of the anonymity set obtained by MTPPA is about 40% lower than those obtained by the existing algorithms while the same quality of services can be provided.

Smart textile devices have now received increasing attention for potential application in wearable human motion monitoring, healthcare and personal thermal management. MXene (Ti3C2Tx), which is a new two-dimensional material with remarkable properties, has been widely applied in wearable electronics. However, it remains a challenge to prepare MXene based smart textile that possesses multifunctional wearable sensing applications and can also keep MXene from oxidizing. Here, we fabricated a waterproof and breathable smart textile by construction of a multiple core–shell structure, i.e., MXene decoration onto the polydopamine (PDA) modified elastic textile followed by polydimethylsiloxane (PDMS) coating. MXene wrapping the fibers formed the conductive network, while PDMS could not only protect the MXene from oxidation but also endow the textile with superhydrophobicity and thus corrosion resistance. The smart textile possessed outstanding and durable photo-thermal and electro-thermal conversion performance. More importantly, the textile electronic exhibited sensitive and stable strain sensing performance and temperature sensing capacity with a high thermal coefficient of resistance. Evidently, such smart textile device is highly promising for application in next generation all-in-one wearable electronics.

High-performance multifunctional sensors that are powered wirelessly could find applications in athlete training, health monitoring, and human-machine interactions. In this paper, a humidity sensor based on a reduced graphene oxide (RGO) and tungsten disulfide (WS2) heterojunction is proposed. The sensor exhibits high performance in regard to humidity sensing. The wireless humidity sensor has a fast response time (0.56 s) and recovery time (2.26 s), which can be attributed to the heterojunction and the synergistic effect. The sensor also has a wide working range between 5%RH to 95 %RH. The flexible humidity sensor can be used to monitor the skin humidity and evaluate the metabolism of the human body. Moreover, in situ Raman spectrum was used to prove the electron transfer between the water molecule and RGO-WS2 (RGWS) at different humidity. Thus, this work could have broad applications in various fields such as personal health, physical training, and psychological state monitoring.