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Chaotic communication requires the knowledge of corresponding phase relationship between the primary phase of Duffing oscillator's internal driving force and the primary phase of the undetected signal. Currently, there is no method of noncoherent demodulation for DPSK (Differential Phase Shift Keying) signal and mobile communication signal by Duffing oscillator. To solve this problem, this study presents a noncoherent demodulation method based on the Duffing oscillators array and Duffing oscillator optimization. We first present the model of Duffing oscillator and its sensitivity to undetected signal primary phase. Then the zone partition is proposed to identify the Duffing oscillator's phase trajectory, and subsequently, the mathematical model and implementation method of the Duffing oscillators array are outlined. Thirdly, the Duffing oscillator optimization and its adaptive strobe technique are proposed, also their application to DPSK signal noncoherent demodulation are discussed. Finally, the design of new concept DPSK chaotic digital receiver based on the Duffing oscillators array is presented, together with its simulation results obtained by using SystemView simulation platform. The simulation results suggest that the new concept receiver based on the Duffing oscillator optimization of Duffing oscillators array owns better SNR (signal-to-noise ratio) threshold property than typical existing receivers (chaotic or nonchaotic) in the AWGN (additive white Gaussian noise) channel and multipath Rayleigh fading channel. In addition, the new concept receiver may detect mobile communication signal. [ABSTRACT FROM AUTHOR]

In wireless communication an orthogonal frequency division multiplexing (OFDM) system is efficiently used in recent years. The OFDM method in wireless channels can create deep fades, as a result of multipath dispersive spreading. Thus, a channel state information is essential when coherent detection is involved in OFDM system. Therefore, in many coherent communication systems, a good channel estimation method is necessary for OFDM receiver design. And semi-blind channel estimation is one of these good channel estimation methods. Conventionally, a semi-blind channel estimation uses least square (LS) technique. In our paper, we applied the scaled least square (SLS) to enhance the performance of the semi-blind channel estimator. The SLS requires less knowledge of the channel second-order statistics and has improved performance than the LS technique. Simulation results show that the proposed SLS semi-blind channel estimation method enhances the performance reasonably than conventional semi-blind channel estimation. [ABSTRACT FROM AUTHOR]

Microelectrode-based electrochemical detection methods have been extensively applied in microfluidic sensors, but there are significant challenges for achieving fast and efficient contact between analytes and the microarray electrodes and, thus, enhancing the sensing performance. In this paper, we develop a technique using asymmetrically aligned focused surface acoustic waves (FSAWs) to enhance sensitivity of microarray electrodes detection. Effects of various focusing angles of the FSAW devices on the values and distributions of acoustic wave amplitudes were analyzed using finite element simulations, and torques, which determine the acoustic streaming velocity, were calculated as a function of values and distributions of amplitude. Based on simulation results, the FSAW device with a focusing angle of 30° was used to investigate sensitivity of microarray electrochemical sensors. The maximum value of instantaneous current was increased up to 11 times, researching a current value of 4.3 μA with the applied FSAWs. This developed electrochemical sensing platform shows great potentials for highly sensitive food quality control and biochemical detections. [ABSTRACT FROM AUTHOR]

The paper presents a new method to estimate the two-dimensional (2D) direction of arrival (DOA) (the azimuth angle and the elevation angle) of electromagnetic signal emitted from a single communication station. This method is passive and accurate in the case of low signal-noise ratio (SNR) based on the virtual time reversal (VTR) theory. In order to illustrate its principle, the theoretical formulas of VTR direction finding with uniform circular array (UCA) are derived firstly. Based on these formulas, the implementation scheme for estimating azimuth angle and elevation angle passively is then provided. In the derivation, the strict mathematical proof for compressing planar search area to a curve line is proposed, reducing the complexity of VTR algorithm greatly. Finally, the simulation experiments are performed to validate the performance of VTR algorithm. The results show that the VTR method is effective and it delivers accurate DOA estimation in the case of low SNR. [ABSTRACT FROM AUTHOR]

An optimization approach for black-and-white and hinge-removal topology designs is studied. To achieve this motive, an optimal topology allowing grey boundaries is found firstly. When a suitable design has been obtained, this solution is then used as a starting point for the follow-up optimization with the goal to free unfavorable intermediate elements. For this purpose, an updated optimality criterion in which a threshold factor is introduced to gradually suppress elements with low density is proposed. The typical optimality method and new technique proposed are applied to the design procedure sequentially. Besides, to circumvent the one-point hinge connection problem producing in the process of freeing intermediate elements, a hinge-removal strategy is also proposed. During the optimization, the binary constraints on design variables are relaxed based on the scheme of solid isotropic material with penalization. Meanwhile, the mesh-independency filter is employed to ensure the existence of a solution and remove well-known checkerboards. In this way, a solution that has few intermediate elements and is free of one-point hinge connections is obtained. Finally, different numerical examples including the compliance minimization, compliant mechanisms and vibration problems demonstrate the validity of the proposed approach. [ABSTRACT FROM AUTHOR]

Abstract: TiNi films were prepared by co-sputtering TiNi and Ti targets. X-ray photoelectron spectroscopy (XPS) was employed to study surface chemistry of the films and interfacial structure of Si/TiNi system. Exposure of the TiNi film to the ambient atmosphere (23°C and 80% relatively humidity) facilitated quick adsorption of oxygen and carbon on the surface. With time, carbon and oxygen content increased drastically at the surface, while oxygen diffused further into the layer. After a year, carbon content at the surface became as high as 65.57% and Ni dropped below the detection limit of XPS. Depth profiling revealed that significant inter-diffusion occurred between TiNi film and Si substrate with a layer of 90–100nm. The detailed bond changes of different elements with depth were obtained using XPS and the formation of titanium silicides at the interface were identified. [Copyright &y& Elsevier]

Abstract: TiNi-based films sputtered at room temperature are amorphous; thus, postsputtering annealing is a must because shape memory effect only occurs in their crystalline form. It is suggested that the lowest possible annealing temperature be used in a bid to conserve thermal processing budgets, and to minimize thermal stresses and possible interfacial reactions between film and its substrate. In this paper, Ti49.5Ni47.5Cu3 (at.%) films with a thickness of 3.5 μm were deposited on Si substrate by cosputtering of TiNi and Cu targets at room temperature, then annealed at different temperatures from 430 to 650 °C. Phase transformation behaviors, crystalline structure, residual stress and stress evolution of the films were systematically studied. At the gas pressure of 0.8 mTorr, the residual stress in the as-deposited films was 260 MPa, compressive. A minimum annealing temperature (450 °C) was necessary for film crystallization; thus, large thermal stress could be released significantly due to martensitic transformation. With increase of annealing temperature, crystallite and martensite plate sizes in the film increased; thus, both recovery stress and stress-increase rate increased, while the transformation temperatures shifted to higher values. The surface roughness increased drastically with increase of annealing temperature in correlation to martensitic transformation. [Copyright &y& Elsevier]

Abstract: TiNi films with different Ti/Ni ratios were deposited on Si substrates with and without silicon nitride interlayer. Near-equiatomic TiNi films were found to have the lowest residual stress and the highest recovery stress regardless of the existence of silicon nitride interlayer. The addition of silicon nitride interlayer between film and Si substrate did not cause much change in phase transformation behavior as well as adhesion properties. X-ray photoelectron spectroscopy (XPS) analysis revealed that there is significant interdiffusion of elements and formation of Ti–N and Si–Si bonds at TiNi film/silicon nitride interface. Scratch test results showed that adhesion between the TiNi film and substrate was slightly improved with the increase of Ti content in TiNi films. [Copyright &y& Elsevier]

TiNi thin films have attracted much attention in recent years as intelligent and functional materials because of their unique properties. TiNi thin film based micro-actuators will become the actuator of choice in many aspects in the rapidly growing field of micro-electro-mechanical systems (MEMSs). In this review paper, some critical issues and problems in the development of TiNi thin films are discussed, including preparation and characterization considerations, residual stress and adhesion, frequency improvement, fatigue and stability, modeling of behavior as well as functionally graded or composite thin films. Comparison is made of TiNi SMA micro-actuation with other micro-actuation methods. Different types of TiNi thin film based microdevices, such as microgrippers, microswitches, microvalves and pumps, microsensors, etc. are also described and discussed. [Copyright &y& Elsevier]

Nanocrystalline TiNi powder, prepared by the electro-explosion of wire method, was characterized in this work. Analysis using differential scanning calorimetry (DSC) clearly indicated the shape memory effect for this material. An activation energy of 113 ± 10% kJ/mol for sintering was obtained using DSC with variable heating rates. [Copyright &y& Elsevier]

TiNiCu films with different Cu contents (up to 15 at.%) were prepared by co-sputtering of TiNi and Cu targets using a magnetron sputtering system. Film crystalline structure, phase transformation and shape memory behaviors were characterized by X-ray diffraction, differential scanning calorimeters (DSCs) and curvature method. The substitution of Ni by Cu in TiNi based films resulted in a dramatic change in martensite structure, film orientation and phase transformation behavior. With the increase of Cu content in the films, both the transformation temperatures and hysteresis decreased significantly. From DSC and curvature measurement results, the specific heat and the maximum recovery stress (corresponding to actuation force) generated during martensite transformation decreased with Cu contents, indicating the weak performance of phase transformation, especially at high Cu contents above 9 at.%. There was a maximum value for the stress increase rate (corresponding to actuation speed) at a Cu content of 9 at.%. [Copyright &y& Elsevier]

Shape memory alloy TiNi films were prepared on Si and Si/SiO2 by co-sputtering of TiNi target (Ti 50 at.% and Ni 50 at.%) and Ti target (99.999 at.%). When comparing Si/TiNi with Si/SiO2/TiNi, the addition of SiO2 sandwich layer did not result in significant change in the crystalline structures and shape memory properties. The SiO2 sandwich layer served as an effective diffusion barrier in preventing formation of interfacial titanium silicide at the expense of film adhesion. As revealed by X-ray photoelectron spectroscopy, under the same conditions, the interfacial diffusion zone in Si/TiNi system was approximately 120 nm while in Si/SiO2/TiNi system the diffusion zone was only approximately 30 nm—a four-fold reduction in inter diffusion. Meanwhile, the scratch adhesion testing registered a sharp drop in adhesion of the film from 170 mN in Si/TiNi system to 60 mN in Si/SiO2/TiNi system. [Copyright &y& Elsevier]

The presence of an adherent and hard TiN layer (200 nm) on TiNi-based shape memory alloy (SMA) film (3.5 μm) formed a passivation layer, improved hardness and tribological properties, without sacrificing the phase transformation and shape memory effect of the TiNi film. [Copyright &y& Elsevier]

TiNi films were prepared by co-sputtering a Ti50Ni50 target and a Ti target under different process parameters. Stress in TiNi film on silicon substrate were evaluated using curvature method. A wide range of residual stress levels (either tensile or compressive) were found in the deposited films, depending significantly on Ti/Ni ratio, gas pressure, deposition temperature and/or annealing conditions. Stress evolution for as-deposited amorphous films during annealing process were systematically studied with the consideration of residual stress in as-deposited films; thermal stress; tensile stress due to densification crystallization; stress relaxation due to martensite transformation, etc. Upon heating, the crystallized TiNi films generated large tensile stresses when transforming from martensite to austenite, whereas during cooling, the stress relaxed significantly when austenite transformed back to the ductile martensite. The stress generation and relaxation behavior was significantly affected by film composition, deposition temperature and/or annealing temperature. [Copyright &y& Elsevier]

TiNi based shape memory alloy (SMA) thin films have been widely used in biomedical and microelectromechanical systems. However, there are still some concerns for their wide applications because of their unsatisfactory mechanical and tribological performances, chemical resistance and biological reliability. This paper explored the deposition and effects of TiN protective layer on TiNi thin films to improve their surface properties while retaining the shape memory effects. Results indicated that the presence of an adherent and hard TiN layer (300 nm) on TiNi based SMA film (3.5 μm) formed a passivation layer, improved hardness and tribological properties, without sacrificing the phase transformation and shape memory effect of the TiNi film. [Copyright &y& Elsevier]

TiNi films with different Ni/Ti ratios were prepared by co-sputtering of a Ti50Ni50 (at.%) target with a separated Ti target at a temperature of 723 K. The stress values in the deposited films changed significantly with Ti contents and post-annealing temperatures due to the differences in phase transformation behaviors and intrinsic stress. For the film with Ti content of 51.3%, a two-step transformation was observed among martensite, R-phase and austenite, and residual stress was quite low at room temperature. After post-annealing the above film at 923 K, only one-stage transformation was observed. For the films with Ti contents of 47.3 and 53%, residual stress was quite high due to the high intrinsic stress and partial relaxation of stress caused by the R-phase transformation. When the films with Ti contents of 47.3 and 53% were annealed at 923 K, residual stress in films decreased significantly, because post-annealing could probably modify the film structure, reduce the intrinsic stress, increase the transformation temperatures, and cause martensite transformation above room temperature. For all the three types of films annealed at 1023 K for 1 h, the high thermal stress in the thin films could cause non-recoverable deformation during phase transformation, damage the shape memory effect, and result in the peeling-off of film from Si substrate. [Copyright &y& Elsevier]

The interfacial structures of diamond coatings deposited on pure titanium substrate were analyzed using scanning electron microscopy and grazing incidence X-ray diffraction. Results showed that beneath the diamond coating, there was one titanium carbide and hydride interlayer, followed by a heat-affected and carbon/hydrogen diffused Ti layer. Residual stress in the diamond coating and TiC interlayer under different process parameters were measured using Raman and X-ray diffraction (XRD) methods. Diamond coatings showed large compressive stress on the order of a few giga Pascal. XRD analysis also showed the presence of compressive stress in the TiC interlayer and tensile stress in the Ti substrate. With increasing deposition duration, or decreasing plasma power and concentration of CH4 in gas mixture, the compressive residual stress in the diamond coating decreased. The large residual stress in the diamond coating resulted in poor adhesion of the coatings to substrate, but adhesion was also related to other factors, such as the thickness and nature of the TiC interlayer, etc. A graded interlayer design was proposed to lower the thermal stress, modify the interfacial structure and improve the adhesion strength. [Copyright &y& Elsevier]

In this paper, diamond microstructures were patterned over silicon/silicon dioxide substrate using the processes combined with bulk or surface micromachining, selective growth of diamond and plasma etching technique. Polycrystalline diamond films were prepared using microwave plasma enhanced chemical vapour deposition (MW-PECVD) and a gas mixture of hydrogen and methane. Two types of techniques for precise patterning of diamond microstructures were investigated in this paper. The first one was to selectively grow diamond films in the desired region by pre-depositing a Pt interlayer on silicon dioxide layer. The second one was to selectively etch the deposited diamond film in oxygen/argon plasma under an Al mask. Different microstructures, e.g., microgear, microrotor, comb drive structure, etc. were successfully fabricated. [Copyright &y& Elsevier]

Shape memory alloys (SMAs) offer a unique combination of novel properties, such as shape memory effect, super-elasticity, biocompatibility and high damping capacity, and thin film SMAs have the potential to become a primary actuating mechanism for micro-actuators. In this study, TiNiCu films were successfully prepared by mix sputtering of a Ti55Ni45 target with a separated Cu target. Crystalline structure, residual stress and phase transformation properties of the TiNiCu films were investigated using X-ray diffraction (XRD), differential scanning calorimeter (DSC), and curvature measurement methods. Effects of the processing parameters on the film composition, phase transformation and shape-memory effects were analyzed. Results showed that films prepared at a high Ar gas pressure exhibited a columnar structure, while films deposited at a low Ar gas pressure showed smooth and featureless structure. Chemical composition of TiNiCu thin films was dependent on the DC power of copper target. DSC, XRD and curvature measurement revealed clearly the martensitic transformation of the deposited TiNiCu films. When the free-standing film was heated and cooled, a ‘two-way’ shape-memory effect can be clearly observed. [Copyright &y& Elsevier]

Superhard nanocrystalline (Ti, Cr)CN/DLC coatings were prepared through co-sputtering of Ti, Cr and graphite targets in an argon/nitrogen atmosphere. Results from both transmission electron microscopy (TEM) and grazing incident X-ray diffraction (GIXRD) indicated that the grain size of (TiCr)CxNy crystals was approximately 10–20 nm. X-ray photoelectron spectroscopic studies confirmed that an increase in the sputtering power at the Ti target not only increased the Ti composition in the film but also brought about an increase in sp3 bonding in DLC matrix, in agreement with the raising hardness with Ti sputtering power. Film hardness and elastic modulus were measured with a nano-indenter, and film hardness reached 40 GPa. Tribological behaviors of the films were evaluated using a ball-on-disk tribometer, and the films demonstrated properties of low-friction and good wear resistance. [Copyright &y& Elsevier]

Microwave plasma enhanced chemical vapor deposition (MW-PECVD) is considered as one of the most successful growth techniques in recent diamond and crystalline carbon nitride investigations. In this study, we tried to synthesize crystalline carbon nitride film using MW-PECVD by gradually increasing the content of nitrogen into H2/CH4 gas mixture. Well-faceted crystalline diamond films could be synthesized with a H2/CH4 gas ratio of 198:2. With the gradual increase of nitrogen content up to 3% in the gas mixture diamond film quality deteriorates seriously, and the morphological crystal size and growth rate of diamond coatings decreased significantly. With the nitrogen gas content increased to approximately 6–22%, a lot of separated round diamond or diamond-like carbon particles formed on the surface rather than a continuous film. Only with the nitrogen content increased above 72%, could some tiny crystals with a type of hexagonal facet form on the silicon surface, together with many large, round diamond particles. With the further increase of nitrogen gas content above 90%, many large, well-faceted hexagonal crystals formed on Si surface. However, XRD, energy dispersive X-ray spectrometry, X-ray photoelectron spectroscopy and nano-indentation analysis indicated that these crystals were actually silicon carbonitride (Si–C–N) with a crystalline structure of Si3N4 modified with the introduction of carbon atoms, rather than carbonitride as expected and regarded. [Copyright &y& Elsevier]

Residual stress, relaxation and recovery of stress during martensite transformation of the sputtering-deposited TiNi films were studied in this paper. Results showed that a wide range of residual stress levels (both tensile and compressive) were obtained with the change of Ti contents in the deposited films. After film deposition, the thermal and intrinsic stress in the film could be very large, but due to the differences in phase transformation stress and transformation temperatures, the real stress values under room temperature, and stress evolution with temperature during phase transformation were quite different. For the film with a Ti content of 50.2%, due to the significant relaxation of stress caused by the perfect martensite transformation, the residual stress under room temperature was very low (−20 MPa) and recovery stress during heating was as high as 750 MPa. With both decrease and increase in Ti content in the deposited films, the tensile residual stress increased significantly. For the films with a Ti content of 51.3%, a two-step transformation was observed among martensite, R-phase and austenite. The recovery stress and average increase rate of stress during both heating and cooling were lower than those of film with 50.2% Ti. For the films with a Ti content of 47.3 and 53%, only partial relaxation of stress occurred due to the existence of R-phase transformation at room temperature. Also, because of non-equilibrium contents of Ni and Ti in these films, shape memory effect and the recovery of stress due to the phase transformation was not so significant. High residual stress in the thin films could cause non-recoverable deformation during phase transformation. [Copyright &y& Elsevier]

Supercapacitors (SCs) are attractive as promising energy storage devices because of their distinctive attributes, such as high power density, good current charge/discharge ability, excellent cyclic stability, reasonable safety, and low cost. Electrode materials play key roles in achieving excellent performance of these SCs. Among them, binary transition metal sulfides (BTMSs) have received significant attention, attributed to their high conductivity, abundant active sites, and excellent electrochemical properties. This topic review aims to summarize recent advances in principles, design, and evaluation of the electrochemical performance for nanostructured BTMSs (including nickel–cobalt sulfides, zinc–cobalt sulfides, and copper–cobalt sulfides.) and their nanocomposites (including those carbon nanomaterials, transition metal oxides, binary transition metal oxides, transition metal sulfides, and polymers). Nanostructuring of these BTMSs and nanocomposites as well as their effects on the performance were discussed, including nanoparticles, nanospheres, nanosheets, nanowires, nanorods, nanotubes, nanoarrays, and hierarchitectured nanostructures. Their electrochemical performance has further been reviewed including specific capacitance, conductivity, rate capability, and cycling stability. In addition, the performance of hybrid supercapacitors (HSCs) assembled using the nanostructured BTMSs as the cathodes also have been summarized and compared. Finally, challenges and further prospects in the HSCs-based BTMS electrodes are presented. [ABSTRACT FROM AUTHOR]

Catalysts based on Pt single atom (SA) on metal oxides have shown tremendous potentials for alkaline hydrogen evolution reaction (HER), but they are severely limited by insufficient electron interactions of Pt sites and supports. Herein, a new methodology is developed to precisely locate Pt SAs and Pt clusters into NiCo layered double oxide (LDO) nanosheets, achieved using a dual‐ion etching process with subsequent phase transformation method. Uniquely, the Pt SAs are inserted into LDO layers to form Pt─Co bonds by occupying partial Ni positions, significantly strengthening electron interactions with NiCo LDO and promoting activity of HER. Results from density functional theory calculations indicate that the H* species are preferentially absorbed onto O sites on top of these Pt SAs, which are coupled with their adjacent Pt clusters to accelerate water dissociation in the Volmer step. As‐obtained Pt─NiCo LDO exhibits a low overpotential of 92 mV at 10 mA cm−2 and a Tafel slope of 73 mV dec−1, an excellent stability over 105 hours at 60 mA cm−2, and its mass activity is 6 times higher than commercial 20% Pt/C. This study highlights essential functions of coupling interactions between Pt SAs/clusters and LDOs to boost HER for hydrogen energy production. [ABSTRACT FROM AUTHOR]

Diabetes is one of the common chronic diseases in worldwide and increasing among young children. Testing glycated hemoglobin levels as well as blood glucose levels is a method for detecting diabetes. In this article, with multivariate statistical analysis was used to monitor the blood glucose levels by the Fourier Transform Raman spectroscopy. Principal component regression with direct orthogonal signal correction is developed and applied to analyze the glucose concentration with the blood Raman spectroscopy. The root means square error of calibration is 3.0824 mg/dL (0.1712 mmol/L), the root means square error of prediction is 3.2688 mg/dL (0.1816 mmol/L), the correlation coefficients (R2) is.9946 and ratio of performance to deviation is 6.4789 and, respectively. The results show that this method can be used as a strong potential diagnostic tool for diabetes mellitus. [ABSTRACT FROM AUTHOR]

Conductive hydrogels are compelling materials for the development of soft electronics; however, their essential attributes such as high sensitivity, excellent stretchability, and environmental stability have rarely been achieved simultaneously in one hydrogel. Herein, a Kirigami‐inspired strategy is proposed to improve organohydrogel sensitivity without sacrificing their mechanical stretchability and environmental stability. The organohydrogels with multiple interpenetrating networks are synthesized by introducing sodium alginate nanofibrils and conductive MXene nanoflakes into polymer double networks infiltrated with glycerol–water mixtures, featuring remarkable stretchability (>5000%), good sensitivity, and water retention (>30 days). The Kirigami structures are further applied to enhance strain sensitivity, achieving a gauge factor of 29.1, which is ≈5.5 times that of an unstructured organohydrogel. Using the Kirigami‐inspired sensors, a durable glove is developed for grabbing underwater objects through operating a robotic arm, demonstrating a subaqueous interactive human–machine interfacing.Meanwhile, by integrating the wearable sensor with a machine learning algorithm, a wearable Morse code intelligent recognition system is demonstrated, enabling real‐time conversion of Morse code signs into speech with superior recognition accuracy (>99%) and fast response time (≈17 ms). This work offers a new route to synthesize highly sensitive, stretchable, and extremely tolerant organohydrogels, providing a promising platform for next‐generation soft electronics. [ABSTRACT FROM AUTHOR]

Due to the sluggish kinetics of oxygen evolution reaction (OER), electrocatalysts are urgently needed to simultaneously achieve increased activity, enhanced stability, and reduced cost. Herein, CoFePS quaternary alloy sub‐nanometric sheet is synthesized via synchronously phosphor‐sulfurizing CoFe‐bimetallene. Heteroatomization results in increasing conductivity, enhancing interactions with electrolyte, and improving chemical structural stability to exhibit a current density of 10 mA cm−2 at 211 mV and a large current of 1053 mA cm−2 at 570 mV. Density functional theory calculations reveal that the adjustment of Fermi levels of adjacent metal atoms reduces reaction energy barrier and accelerates electron transfer, resulting in a Tafel slope of 14 mV dec−1. In situ Raman monitors the formation of phosphor‐sulfate shell oxidized surface as active sites improved the OER stability of CoFePS, with a retention rate of 99.7% at 10 mA cm−2 for 78 h. This study provides a promising strategy for the synthesis of multicomponent alloy sub‐nanometric sheet as good electrocatalyst candidates for OER. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW)-based acoustofluidics shows broad applications in biomedicine and chemistry. Conventional manufacturing process for SAW devices uses photolithography and metal deposition, thus requires accessing cleanroom facilities. This study presents an efficient and versatile technique based on a flexible printed circuit board (FPCB) for developing SAW acoustofluidic devices. By mechanically clamping interdigital electrodes (IDEs) made on the FPCB onto a piezoelectric substrate, SAWs can be effectively generated with an additional matching network. The SAW amplitudes were measured by a laser vibrometer, which increases with the applied input voltage. The FPCB-SAW device has been applied to actuate 10-μm microspheres to form strong streaming vortices inside a droplet, and to drive a sessile droplet for transportation on the substrate surface. The use of the FPCB rather than a rigid printed circuit board (PCB) can help cut down on the overall footprint of the device and save space. The low requirement in assembling the FPCB-SAW device can facilitate versatile acoustofluidic applications by providing fast prototyping devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • Controlled growth of CeO 2 nanoparticles (NPs) on reduced graphene oxide (rGO) layers was designed and synthesized via heterogeneous reactions of Ce3+ ions and oxygen-containing functional groups. • The growth process of CeO 2 NPs was studied using the in-situ TEM analysis. • We identified the key formation mechanisms of in-situ grown CeO 2 NPs on rGO layers and reported good adsorption-photocatalytic activities of the as-synthesized CeO 2 @rGO. • Degradation rate of rhodamine B using the composite reached 94.7% within 120 min, and after five cycles, the degradation rate was still maintained at 87.2%. Nanostructured composites of metal oxides and graphene often exhibit synergistic physicochemical properties, which can be explored for applications in photocatalysis and water treatment. However, there are key issues about effective structure controls such as distributions and sizes of nanoparticles inside these composite materials. Herein, we report a green approach using hydrothermal calcination processes to in-situ grow CeO 2 nanoparticles (with their ultrafine crystalline sizes, homogeneous dispersion and controlled oxygen-vacancy) directly onto surfaces of reduced graphene oxides (rGOs). The growth process of CeO 2 NPs was characterized by in-situ TEM analysis. During the calcination process, oxygen-containing functional groups such as –OH and C O on the rGOs were transformed into H 2 O and CO 2 , which acted as oxidizing agents to react with cerium ions and produce CeO 2 nanoparticles directly onto surfaces of rGOs. Integration of ultrafine crystalline oxygen deficient CeO 2 and electrically conducting rGOs facilitated fast adsorption of reactant molecules and provided numerous active sites, which effectively achieved superior photocatalytic performance and enhanced adsorption capability for colored organic dyes of rhodamine B and methyl orange. Degradation rate of rhodamine B using the composite reached 94.7% within 120 min, and after five cycles, the degradation rate was still maintained at 87.2%, showing good stability and reusability. [ABSTRACT FROM AUTHOR]

Strain sensors are crucial for development of smart systems, providing valuable feedback on the conditions of structures and mechanical components. However, there is a huge challenge for highly accurate detection of both strain intensity and direction (i.e., omnidirectional strain) using one single strain sensor, mainly because only one signal feature is commonly obtained from a single device. To overcome this limitation, we proposed a strategy to achieve omnidirectional strain detection by applying a single flexible surface acoustic wave (SAW) strain sensor, empowered by a machine learning algorithm to analyze multiple signals derived from the same device, simultaneously. Using AlN/flexible glass based SAW devices, we performed omnidirectional strain predictions using eight different machine learning models, and the data were compared with the experimental measurement results. The results showed that the extreme gradient boosting (XGBoost) model showed the highest prediction ability and the best accuracy (i.e., with its coefficient of determination larger than 0.98 and root mean square error less than 0.1) for both strain intensity and direction. This work provides an effective solution for omnidirectional strain sensing using a single device. [ABSTRACT FROM AUTHOR]

Flexible and wearable acoustic wave technology has recently attracted tremendous attention due to their wide-range applications in wearable electronics, sensing, acoustofluidics, and lab-on-a-chip, attributed to its advantages such as low power consumption, small size, easy fabrication, and passive/wireless capabilities. Great effort has recently been made in technology development, fabrication, and characterization of rationally designed structures for next-generation acoustic wave based flexible electronics. Herein, advances in fundamental principles, design, fabrication, and applications of flexible and wearable acoustic wave devices are reviewed. Challenges in material selections (including both flexible substrate and piezoelectric film) and structural designs for high-performance flexible and wearable acoustic wave devices are discussed. Recent advances in fabrication strategies, wave mode theory, working mechanisms, bending behavior, and performance/evaluation are reviewed. Key applications in wearable and flexible sensors and acoustofluidics, as well as lab-on-a-chip systems, are discussed. Finally, major challenges and future perspectives in this field are highlighted. [ABSTRACT FROM AUTHOR]

Acoustofluidics offers contact-free manipulation of particles and fluids, enabling their uses in various life sciences, such as for biological and medical applications. Recently, there have been extensive studies on acoustic streaming-based acoustofluidics, which are formed inside a liquid agitated by leaky surface acoustic waves (SAWs) through applying radio frequency signals to interdigital transducers (IDTs) on a piezoelectric substrate. This paper aims to describe acoustic streaming-based acoustofluidics and provide readers with an unbiased perspective to determine which IDT structural designs and techniques are most suitable for their research. This review, first, qualitatively and quantitatively introduces underlying physics of acoustic streaming. Then, it comprehensively discusses the fundamental designs of IDT technology for generating various types of acoustic streaming phenomena. Acoustic streaming-related methodologies and the corresponding biomedical applications are highlighted and discussed, according to either standing surface acoustic waves or traveling surface acoustic waves generated, and also sessile droplets or continuous fluids used. Traveling SAW-based acoustofluidics generate various physical phenomena including mixing, concentration, rotation, pumping, jetting, nebulization/atomization, and droplet generation, as well as mixing and concentration of liquid in a channel/chamber. Standing SAWs induce streaming for digital and continuous acoustofluidics, which can be used for mixing, sorting, and trapping in a channel/chamber. Key challenges, future developments, and directions for acoustic streaming-based acoustofluidics are finally discussed. [ABSTRACT FROM AUTHOR]

Chaotic communication has aroused general interests in recent years, but its communication effect is not ideal with the restriction of chaos synchronization. In this paper a new chaos M-ary digital modulation and demodulation method is proposed. By using region controllable characteristics of spatiotemporal chaos Hamilton map in phase plane and chaos unique characteristic, which is sensitive to initial value, zone mapping method is proposed. It establishes the map relationship between M-ary digital information and the region of Hamilton map phase plane, thus the M-ary information chaos modulation is realized. In addition, zone partition demodulation method is proposed based on the structure characteristic of Hamilton modulated information, which separates M-ary information from phase trajectory of chaotic Hamilton map, and the theory analysis of zone partition demodulator's boundary range is given. Finally, the communication system based on the two methods is constructed on the personal computer. The simulation shows that in high speed transmission communications and with no chaos synchronization circumstance, the proposed chaotic M-ary modulation and demodulation method has outperformed some conventional M-ary modulation methods, such as quadrature phase shift keying and M-ary pulse amplitude modulation in bit error rate. Besides, it has performance improvement in bandwidth efficiency, transmission efficiency and anti-noise performance, and the system complexity is low and chaos signal is easy to generate. [ABSTRACT FROM AUTHOR]

A heat transfer model of polymer composite reinforced by buckypaper was established in this study to analyze how the shapes, heating power and thermal conductivity of polymer matrix affect the temperature distribution and heating uniformity. Thermal responses of the polymer composites reinforced by flat and pulse bending buckypaper were systematically studied, and the heating mechanisms of multiple-field coupling were investigated. The shapes and dimensions of the buckypaper are crucial in the optimization of such the polymer composites for heat generation. Results showed that the polymer composites reinforced by the flat buckypaper had relatively higher maximum and average temperatures in a steady heated state compared with those by the pulse bending ones, whereas the minimum temperature of the composites reinforced by the flat buckypaper was relatively lower, so the temperature distribution in those flat ones was more non-uniform. The overall heating temperature of the polymer composites reinforced by both the flat and pulse bending buckypaper was increased linearly with the applied power. The larger the thermal conductivity of the polymer is, the lower the maximum and average temperatures are. [ABSTRACT FROM AUTHOR]

Flexible and wearable sensors are highly desired for health monitoring, agriculture, sport, and indoor positioning systems applications. However, the currently developed wireless wearable sensors, which are communicated through radio signals, can only provide limited positioning accuracy and are often ineffective in underwater conditions. In this paper, a wireless platform based on flexible piezoelectric acoustics is developed with multiple functions of sensing, communication, and positioning. Under a high frequency (≈13 MHz) stimulation, Lamb waves are generated for respiratory monitoring. Whereas under low‐frequency stimulation (≈20 kHz), this device is agitated as a vibrating membrane, which can be implemented for communication and positioning applications. Indoor communication is demonstrated within 2.8 m at 200 bps or 4.2 m at 25 bps. In combination with the sensing function, real‐time respiratory monitoring and wireless communication are achieved simultaneously. The distance measurement is achieved based on the phase differences of transmitted and received acoustic signals within a range of 100 cm, with a maximum error of 3 cm. This study offers new insights into the communication and positioning applications using flexible acoustic wave devices, which are promising for wireless and wearable sensor networks. [ABSTRACT FROM AUTHOR]

Thin film-based surface acoustic wave (SAW) technology has been extensively explored for physical, chemical, and biological sensors. However, these sensors often show inferior performance for a specific sensing in complex environments, as they are affected by multiple influencing parameters and their coupling interferences. To solve these critical issues, we propose a methodology to extract critical information from the scattering parameter and combine the machine learning method to achieve multi-parameter decoupling. We used the AlScN film-based SAW device as an example in which the highly c-axis orientated and low stress AlScN film was deposited on silicon substrate. The AlScN/Si SAW device showed a Bode quality factor value of 228 and an electromechanical coupling coefficient of ∼2.3%. Two sensing parameters (i.e., ultraviolet or UV and temperature) were chosen for demonstration, and the proposed machine learning method was used to distinguish their influences. Highly precision UV sensing and temperature sensing were independently achieved without their mutual interferences. This work provides an effective solution for decoupling of multi-parameter influences and achieving anti-interference effects in thin film-based SAW sensing. [ABSTRACT FROM AUTHOR]

2D materials, with their extraordinary physical and chemical properties, have gained extensive interest for physical, chemical and biological sensing applications. However, 2D material‐based devices, such as field effect transistors (FETs) often show high contact resistance and low output signals, which severely affect their sensing performance. In this study, a new strategy is developed to combine metallic and semiconducting polymorphs of transition‐metal dichalcogenides (TMDCs) to solve this critical issue. Such a phase engineering methodology to integrate large‐scale and spatially assembled multilayers of 2H MoTe2 FETs with coplanar metallic 1T′ MoTe2 contacts is applied. Such in‐plane heterophase‐based FETs exhibit an ohmic contact behavior with an extremely low contact resistance due to the coplanar and seamless connections between 2H and 1T′ phases of MoTe2. These 1T′/2H/1T′ based FETs are successfully demonstrated for detecting NH3 with high current outputs increased up to microamp levels without using any conventional interdigital electrodes, which is compatible with the current CMOS circuits for practical applications. Furthermore, the as‐fabricated sensors can detect NH3 gas concentrations down to 5 ppm at room temperature. This study demonstrates a new strategy of applying the heterophase MoTe2‐based nanoelectronics for high‐performance sensing applications. [ABSTRACT FROM AUTHOR]

Co-doping AlN film with various elements of rare earth or transition metals has been considered as a good method to significantly improve its piezoelectric responses of surface acoustic wave (SAW) devices. In this paper, we investigated the influences of different Er/Sc atomic percentage ratio on the piezoelectric and acoustic wave properties of the Er and Sc co-doped AlN films prepared by RF magnetron sputtering. Results show that c/a-axis ratio of the AlN films decreases after doped with Sc, whereas those of the AlN films co-doped with Er and Sc increase as the Er/Sc ratio increases. The reasons can be explained from the competitions of Sc and Er elements for occupying the Al atoms sites, and the larger ion radius of the Er compared that of Sc, which causes significant increase of c/a. Resonant frequency and Rayleigh wave velocity of the SAW resonators fabricated using these co-doped AlN films decrease as the Er/Sc ratio increases. Electromechanical coupling coefficient (k2eff) of the SAW devices increases after the AlN film is single doped with either Sc or Er element, but decreases after co-doping with both Er and Sc. [ABSTRACT FROM AUTHOR]

In this study, polyacrylic acid (PAA) films were deposited onto a quartz surface acoustic wave (SAW) resonator using a spin-coating technique for ammonia sensing operated at room temperature, and the sensing mechanisms and performance were systematically studied. The oxygen-containing functional groups on the surfaces of the PAA film make it sensitive and selective to ammonia molecules, even when tested at room temperature. The ammonia molecules adsorbed by the oxygen-containing functional groups of PAA (e.g., hydroxyl and epoxy groups) increase the membrane's stiffness, which was identified as the primary mechanism leading to the positive frequency shifts. However, mass loading due to adsorption of ammonia molecules is not a major reason as it will result in a negative frequency shifts. When the PAA coated SAW sensor was exposed to ammonia with a low concentration of 500 ppb, it showed a positive frequency shift of 225 Hz, with both good repeatability and stability, as well as a good selectivity to ammonia compared with those to C2H5OH, H2, HCl, H2S, CO, NO2, NO, and CH3COCH3. [ABSTRACT FROM AUTHOR]

• Direct ink writing combined with acoustofluidics enhances material control. • Organizing microparticles in flowing multiphase bioink. • Creating patterned and interconnected porous microstructures in 3D scaffolds. • Fibroblasts exhibit patterned distribution following the scaffold's microstructure. Vascular scaffolds with well-organized pore characteristics are crucial for promoting infiltration, adhesion, growth, tissue-specific arrangement, and substance-exchanges of biological cells. However, their controllable fabrication is extremely challenging, especially for those with specially designed three-dimensional (3D) tubular and porous microstructures. In this paper, a new methodology based on acoustofluidics-assisted direct ink writing (DIW) technique is developed to fabricate vascular scaffolds with controlled porosity distributions and well-defined porous microstructures. Calcium carbonate (CaCO 3) particles and alginate are uniformly mixed as the printing ink, which is printed along a rotating rod to form a vessel-like structure. Distributions of these CaCO 3 particles in the printed structure are precisely controlled using bulk acoustic waves. The particles within the vessel-like structure are dissolved in situ using hydrochloric acid, resulting in the formation of 3D vascular scaffolds with intrinsically patterned porous microstructures. The scaffolds printed by the acoustofluidics-assisted DIW method exhibit a 69% improvement in pore connectivity compared to conventional 3D-printed scaffolds. Fibroblast cells are successfully seeded onto these scaffolds, achieving distinctive distributions along the patterned porous microstructures. This innovative methodology, with its excellent microfabrication capabilities, holds great promise for applications in tissue engineering, drug release, composite formation, microfluidic chips, and biosensors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Hybrid materials integrated with Zn 0.76 Co 0.24 S nanoparticles and Co(OH) 2 nanosheets (ZCS@CH) can have a good synergistic effect. • Hierarchically nanostructured hybrid of ZCS@CH was prepared using a simple but effective two-step hydrothermal method. • ZCS@CH electrode achieves a large specific capacity of 1152 C g−1 at 0.5 A g−1. • Hybrid supercapacitor of ZCS@CH//AC obtains an excellent energy density of 62.5 Wh kg−1 at a power density of 425.0 W kg−1. • ZCS@CH//AC shows an excellent long-term stability. It is a great challenge to achieve both high specific capacity and high energy density of supercapacitors by designing and constructing hybrid electrode materials through a simple but effective process. In this paper, we proposed a hierarchically nanostructured hybrid material combining Zn 0.76 Co 0.24 S (ZCS) nanoparticles and Co(OH) 2 (CH) nanosheets using a two-step hydrothermal synthesis strategy. Synergistic effects between ZCS nanoparticles and CH nanosheets result in efficient ion transports during the charge-discharge process, thus achieving a good electrochemical performance of the supercapacitor. The synthesized ZCS@CH hybrid exhibits a high specific capacity of 1152.0 C g-1 at a current density of 0.5 A g-1 in 2 M KOH electrolyte. Its capacity retention rate is maintained at ∼ 70.0% when the current density is changed from 1 A g-1 to 10 A g-1. A hybrid supercapacitor (HSC) assembled from ZCS@CH as the cathode and active carbon (AC) as the anode displays a capacitance of 155.7 F g-1 at 0.5 A g-1, with a remarkable cycling stability of 91.3% after 12,000cycles. Meanwhile, this HSC shows a high energy density of 62.5 Wh kg-1 at a power density of 425.0 W kg-1, proving that the developed ZCS@CH is a promising electrode material for energy storage applications. [ABSTRACT FROM AUTHOR]

The key challenge for a lab-on-chip (LOC) device is the seamless integration of key elements of biosensing and actuation (e.g., biosampling or microfluidics), which are conventionally realised using different technologies. In this paper, we report a convenient and efficient LOC platform fabricated using an electrode patterned flexible printed circuit board (FPCB) pressed onto a piezoelectric film coated substrate, which can implement multiple functions of both acoustofluidics using surface acoustic waves (SAWs) and sensing functions using electromagnetic metamaterials, based on the same electrode on the FPCB. We explored the actuation capability of the integrated structure by pumping a sessile droplet using SAWs in the radio frequency range. We then investigated the hybrid sensing capability (including both physical and chemical ones) of the structure employing the concept of electromagnetic split-ring resonators (SRRs) in the microwave frequency range. The originality of this sensing work is based on the premise that the proposed structure contains three completely decoupled resonant frequencies for sensing applications and each resonance has been used as a separate physical or a chemical sensor. This feature compliments the acoustofluidic capability and is well-aligned with the goals set for a successful LOC device. [ABSTRACT FROM AUTHOR]

Medical image segmentation is a crucial step in diagnosis and analysis of diseases for clinical applications. Deep convolutional neural network methods such as DeepLabv3+ have successfully been applied for medical image segmentation, but multi-level features are seldom integrated seamlessly into different attention mechanisms, and few studies have fully explored the interactions between medical image segmentation and classification tasks. Herein, we propose a feature-compression-pyramid network (FCP-Net) guided by game-theoretic interactions with a hybrid loss function (HLF) for the medical image segmentation. The proposed approach consists of segmentation branch, classification branch and interaction branch. In the encoding stage, a new strategy is developed for the segmentation branch by applying three modules, e.g., embedded feature ensemble, dilated spatial mapping and channel attention (DSMCA), and branch layer fusion. These modules allow effective extraction of spatial information, efficient identification of spatial correlation among various features, and fully integration of multi-receptive field features from different branches. In the decoding stage, a DSMCA module and a multi-scale feature fusion module are used to establish multiple skip connections for enhancing fusion features. Classification and interaction branches are introduced to explore the potential benefits of the classification information task to the segmentation task. We further explore the interactions of segmentation and classification branches from a game theoretic view, and design an HLF. Based on this HLF, the segmentation, classification and interaction branches can collaboratively learn and teach each other throughout the training process, thus applying the conjoint information between the segmentation and classification tasks and improving the generalization performance. The proposed model has been evaluated using several datasets, including ISIC2017, ISIC2018, REFUGE, Kvasir-SEG, BUSI, and PH2, and the results prove its competitiveness compared with other state-of-the-art techniques. [ABSTRACT FROM AUTHOR]

• Surface acoustic wave (SAW) technology is proposed to exfoliate large quantities and uniform layers of two-dimensional (2D) metal-organic framework (MOF) Zn 2 (bim) 4 nanosheets. • The thickness of MOF sheet can be controlled by adjusting the exposure time of surface acoustic wave. • Electric field generated by surface acoustic waves plays an important role in the stripping process. Monolayer nanosheets can only be obtained under the simultaneous action of sound field and electric field. Two-dimensional (2D) metal–organic framework (MOF) nanosheets have recently received extensive attention due to their ultra-thin thickness, large specific surface area, chemical and functional designability. In this study, an unconventional method using surface acoustic wave (SAW) technology is proposed to exfoliate large quantities and uniform layers of 2D MOF-Zn 2 (bim) 4 nanosheets in a microfluidic system. We successfully demonstrated that the thickness of 2D MOF is effectively and accurately controlled by optimizing the SAW parameters. The mechanisms for the efficient exfoliation of 2D MOF nanosheets is attributed to both the electric and acoustic fields generated by the SAWs in the liquid. The electric field ionizes the methanol to produce H+ ions, which intercalate Zn 2 (bim) 4 sheets and weaken the interlayer bonding, and the strong shear force generated by SAWs separates the MOF sheets. A yield of 66% for monolayer MOFs with a maximum size of 3.5 μm is achieved under the combined effect of electric and acoustic fields. This fast, low-energy exfoliation platform has the potential to provide a simple and scalable microfluidic exfoliation method for production of large-area and quantities of 2D MOFs. [ABSTRACT FROM AUTHOR]

[Display omitted] MnCo 2 O 4 is regarded as a good electrode material for supercapacitor due to its high specific capacity and good structural stability. However, its poor electrical conductivity limits its wide-range applications. To solve this issue, we integrated the MnCo 2 O 4 with Ni 3 S 4 , which has a good electrical conductivity, and synthesized a MnCo 2 O 4 /Ni 3 S 4 nanocomposite using a two-step hydrothermal process. Comparing with individual MnCo 2 O 4 and Ni 3 S 4 , the MnCo 2 O 4 /Ni 3 S 4 nanocomposite showed a higher specific capacity and a better cycling stability as the electrode for the supercapacitor. The specific capacity value of the MnCo 2 O 4 /Ni 3 S 4 electrode was 904.7 C g−1 at 1 A g−1 with a potential window of 0–0.55 V. A hybrid supercapacitor (HSC), assembled using MnCo 2 O 4 /Ni 3 S 4 and active carbon as the cathode and anode, respectively, showed a capacitance of 116.4 F g−1 at 1 A g−1, and a high energy density of 50.7 Wh kg−1 at 405.8 W kg−1. Long-term electrochemical stability tests showed an obvious increase of the HSC's capacitance after 5500 charge/discharge cycles, reached a maximum value of ∼162.7% of its initial value after 25,000 cycles, and then remained a stable value up to 64,000 cycles. Simultaneously, its energy density was increased to 54.2 Wh kg−1 at 380.3 W kg−1 after 64,000 cycles. [ABSTRACT FROM AUTHOR]

Rapid advances in wearable electronics and mechno‐sensational human–machine interfaces impose great challenges in developing flexible and deformable tactile sensors with high efficiency, ultra‐sensitivity, environment‐tolerance, and self‐sustainability. Herein, a tactile hydrogel sensor (THS) based on micro‐pyramid‐patterned double‐network (DN) ionic organohydrogels to detect subtle pressure changes by measuring the variations of triboelectric output signal without an external power supply is reported. By the first time of pyramidal‐patterned hydrogel fabrication method and laminated polydimethylsiloxane (PDMS) encapsulation process, the self‐powered THS shows the advantages of remarkable flexibility, good transparency (≈85%), and excellent sensing performance, including extraordinary sensitivity (45.97 mV Pa−1), fast response (≈20 ms), very low limit of detection (50 Pa) as well as good stability (36 000 cycles). Moreover, with the LiBr immersion treatment method, the THS possesses excellent long‐term hyper anti‐freezing and anti‐dehydrating properties, broad environmental tolerance (−20 to 60 °C), and instantaneous peak power density of 20 µW cm−2, providing reliable contact outputs with different materials and detecting very slight human motions. By integrating the signal acquisition/process circuit, the THS with excellent self‐power sensing ability is utilized as a switching button to control electric appliances and robotic hands by simulating human finger gestures, offering its great potentials for wearable and multi‐functional electronic applications. [ABSTRACT FROM AUTHOR]

An ultra-sensitive temperature sensor was proposed and demonstrated by inserting polarization maintaing fibers (PMFs) into cascading Sagnac fiber loops. Effect of the length of PMFs in an individual Sagnac loop on the temperature sensitivity of the sensor was firstly studied. As the PMF length reduces, the sensitivity increases. In the PMFs cascade Sagnac loops, the closer the lengths of the two sections of PMFs embedded in the Sagnac loops, the wider the free spectral range, resulting stronger Vernier effect and thus higher sensitivity. The temperature sensitivity of the cascade Sagnac loops is ∼ -44.28 nm/°C, a 27-fold increase than that of an individual Sagnac loop (∼-1.64 nm/°C). This newly developed temperature sensor has the merits of simple structure, high sensitivity and easy operation, and good competitiveness in the sensing field. • The sensitivity of the sensor is as high as 44.28 nm/°C. • The sensing structure is easy to realize. • The sensitivity is enhanced 27 times by Vernier effect. [ABSTRACT FROM AUTHOR]

• A self-powered wireless sensing system based on TENG is developed. • The system utilizes negative resistance resonator as transmitter. • The system demonstrates excellent stability and sensing precision. • Practicability for monitoring gas pressure is validated. Triboelectric nanogenerators (TENG) based self-powered instantaneous wireless sensing systems have attracted much attention for applications. However, such sensing systems typically use passive inductor capacitor (LC) resonators with low-quality factor, Q , as the transmitter, and have very low sensing precision and accuracy due to the tremendously short sensing signals duration of 10–50 μs and very short sensing distance. Here, we proposed a TENG-based self-powered wireless sensing system with extremely high precision and signal stability by using a negative resistance LC resonator. The introduction of negative resistance greatly increased the system's Q -factor from 102 to 2.6 × 105, and significantly extended the signal duration of up to 1 ms. These allowed the sensor system to achieve a frequency precision and accuracy down to 50 Hz with a fluctuation of less than 0.05 % for a sensing distance of 50 cm, both of them are 40 times better than those of conventional ones (2 kHz, 2 %). A self-powered wireless gas pressure sensing system was developed, showing a high theoretical sensing precision of 2.4 Pa, demonstrated its great application prospects. [ABSTRACT FROM AUTHOR]

Surface Acoustic Wave (SAW) technology has been widely applied in the fields such as communication and sensing. The performance of SAW devices is significantly influenced by designs of their key component, Interdigital Transducers (IDTs), and thus Coupling of Modes (COM) theory has been used as one of the most employed design tools for SAW devices due to its fast computational speed. Accuracy of this model is primarily dependent upon the COM parameters, but the traditional approach to obtain these parameters is heavily relied on accuracy of the input material properties, which has become a key issue for successful applications of this model. This paper proposed a new strategy to utilize the results obtained from the COM model as a dataset and then employ five different machine learning models for performing regression analysis and accurately extracting the COM parameters. To validate the accuracy of this approach, experimental verifications were performed using a 128°Y-X LiNbO 3 based SAW resonator as an example. The machine learning model with the best predictive performance, i.e., Extreme Gradient Boosting, was used to predict the COM parameters corresponding to experimental results, which were subsequently used in conjunction with the COM model for further calculations and comparisons with the experimental results. Results showed that the calculated results exhibit the same trend of resonance Q-values as the experimental results, demonstrating its effective solution for accurately extracting COM parameters. [Display omitted] • Different machine learning regression algorithms were used to build models, and the most suitable model was determined. • This work presents a novel and effective solution for the accurate extraction of COM parameters. • A Novel Strategy of Machine Learning Assisted Design for Surface Acoustic Wave Resonators. [ABSTRACT FROM AUTHOR]

• Innovative GO-MoS 2 /SnO 2 composite utilized as sensitive layer for NO 2 detection. • Novel activation strategy of the sensing nanomaterial by ultraviolet (UV) irradiation. • Faster response/recovery speed (t res /t rec = 16.4 s/19.1 s) of SAW-based NO 2 sensor. • Wider linear detection range (1 ppm to 50 ppm) for NO 2 sensing at room temperature (25°C). • New sensing mechanisms to UV-activated GO-MoS 2 /SnO 2 ternary nanocomposite. There is a great concern for nitrogen oxide (NO 2) due to its hazardous effects on environment and human health, therefore, many types of NO 2 sensors have been proposed. Among them, surface acoustic wave (SAW) NO 2 sensors show intrinsic advantages such as wireless monitoring, but their combined sensitivities, responses, and limits of detection operated at room temperature remain huge challenges. In this study, we proposed an integration strategy in which graphene oxide-molybdenum disulfide/tin dioxide (GO-MoS 2 /SnO 2) ternary composite film was rationally designed on a SAW resonator for detection of low concentrations of NO 2 at room temperature (25°C), and its response speed are enhanced with ultraviolet (UV) light irradiation. Characterization results revealed that MoS 2 and SnO 2 formed the MoS 2 /SnO 2 heterojunctions through interfacial chemical bonds of S-Sn-O, and the GO-MoS 2 /SnO 2 ternary composite showed a hierarchical structure with the heterojunctions exposed and covered by the flake-structure GO. It achieved a large specific surface area of 111.6 m2/g, abundant functional groups, and numerous surface defects, providing plentiful adsorption and reaction sites of NO 2. The developed NO 2 sensor showed a low limit of detection of 1 ppm, a high sensitivity of ∼164.77 Hz/ppm, and fast response/recovery time of 16.4 s/19.1 s, as well as excellent repeatability, selectivity, and long-term stability. The key sensing mechanisms were identified as the large surface areas of the stacked composite leading to the increased adsorption and reaction sites, enhanced conductivity through the MoS 2 /SnO 2 heterojunctions, and numerous photogenerated charge carriers produced by UV activation. [ABSTRACT FROM AUTHOR]