[en] The feasibility of laboratory-synthesized polyurethane-based shape-memory polymer (SMPU) actuators has been investigated for possible application in medical pressure bandages where gradient pressure is required between the ankle and the knee for treatment of leg ulcers. In this study, using heat as the stimulant, SMPU strip actuators have been subjected to gradual and cyclic stresses; their recovery force, reproducibility and reusability have been monitored with respect to changes in temperature and circumference of a model leg, and the stress relaxation at various temperatures has been investigated. The findings suggest that SMPU actuators can be used for the development of the next generation of pressure bandages.

[en] The increased public concerns on healthcare, the environment and sustainable development inspired the development of biodegradable and biocompatible electronics that could be used as degradable electronics in implants. In this work, a fully biodegradable and flexible resistance random access memory (RRAM) was developed with low-cost biomaterial gelatin as the dielectric layer and the biodegradable polymer poly(lactide-coglycolide) acid (PLGA) as the substrate. PLGA can be synthesized by a simple solution process, and the PLGA substrate can be peeled off the handling substrate for operation once the devices are fabricated. The fabricated memory devices exhibited reliable nonvolatile resistive switching characteristics with a long retention time over 10⁴ s and a near-constant on/off resistance ratio of 10² even after 200 bending cycles, showing the promising potential for application in flexible electronics. Degradation of the devices in deionized water and in phosphate buffered saline (PBS) solution showed that the whole devices can be completely degraded in water. The dissolution time of the metals and the gelatin layer was a few days, while that for PLGA is about 6 months, and can be modified by changing the synthesis conditions of the film, thus allowing the development of biodegradable electronics with designed dissolution time. (paper)

[en] Highlights: • Transparent TEGs based on commercial glasses have been developed. • The outputs of the TEGs increase with contact force, frequency and distance, and with decreasing glass thickness. • An improved model has been proposed for the TEG with excellent agreement with experiments. • The TEGs have excellent stability without deterioration after tens of thousands contacts. Glasses are widely used in modern society, mostly for achieving brightness for buildings, transportations etc. Here a transparent triboelectric generator (TEG) based on commercially available glasses and polydimethylsiloxane (PDMS) plates is proposed and fabricated to harvest mechanical energy. Using flat glass and PDMS plates, an open voltage, short-circuit current and power up to 850 V, 20.6 μA and 3.13 mW are achieved for devices with 5 cm×5 cm dimension, whereas the transparency of glass and PDMS structures exceeds 81% and 89%, respectively. The TEGs show excellent mechanical stability and reliability upon cyclical contact for 10,000 times. The voltage and power outputs of the glass based TEGs improve with increasing contact force, frequency and distance, and with decreasing glass thickness and humidity level. Our results demonstrate the feasibility to utilize abundant glass windows to fabricate transparent TEGs for energy harvesting, which could make a great contribution to the sustainable development.

[en] We propose an on-chip film bulk acoustic resonator (FBAR) device based pressure sensor with a simple cavity structure. By sealing the back trench cavity of the FBAR device, the FBAR device become sensitive to the outside environmental pressure. The pressure sensor possesses two resonant peaks with high quality factors and coupling coefficients, which exhibit different temperature coefficients of frequency, and could be used as on-chip temperature compensation. The results show that mode 1 resonant peak of the FBAR pressure sensor has a pressure sensitivity of 1.642 ppm kPa⁻¹, while that of mode 2 resonant peak is 0.1764 ppm kPa⁻¹. Both of the two resonant peaks have high pressure response linearity above 0.999 in the pressure ranges of 17 kPa to 101 kPa and 101 kPa to 400 kPa. A method for temperature calibration is provided. The pressure sensor is simple in package and small in dimension, and the output data is frequency, which can easily be transmitted wirelessly, demonstrating great potential for applications such as the tire pressure monitor system. (paper)

[en] Flexible surface acoustic wave (SAW) strain sensors made on ZnO/ultrathin glass (100 μm) substrates have been developed. The sensitivity of the SAW strain sensors under different strain angles and annealing temperatures, as well as the mechanical stability, are investigated. It was shown that the thickness of ZnO has a strong effect on the sensitivity of the strain sensors, and thicker ZnO makes sensors with better performance. Thermal annealing at a temperature up to 200 °C also improves the sensitivity of the strain sensor significantly. The temperature coefficient of frequency remains unchanged under different strains, showing good thermal stability. A cyclic bending test with the strain varied between zero and 2000 με exhibits good mechanical stability and reliability of SAW strain sensors. All the results demonstrate the great potential of flexible SAW strain sensors for flexible electronic applications. (paper)

[en] A film bulk acoustic wave resonator (FBAR) is a type of resonator with high frequency and small dimensions, particularly suitable for use as a sensor for physical and biochemical sensing with high sensitivity. FBAR-based sensors have been extensively studied, however they commonly use discrete devices and network analyzers for evaluation, and therefore are far from being able to be used in practical applications. This paper reports the design and analysis of an FBAR-based Pierce oscillator and a field-programmable gate array (FPGA)-based frequency counter, and the use of the oscillator as a humidity sensor with the frequency counter as the measuring circuit. Graphene oxide (GO) is used as the sensitive film to improve the sensitivity. The resonant frequency of the oscillator with a GO film shows a linear decrease with an increase in relative humidity, with a sensitivity of ca . 5 kHz per %RH (relative humidity) in the range of 3%RH to 70%RH, and a higher frequency shift is induced above 70%RH. The FBAR oscillator sensor shows excellent stability and repeatability, demonstrating the feasibility and potential sensing application using the integrated FBAR chip and simple frequency counter, particularly suitable for portable electronics. (paper)

[en] Highlights: • A rotational charge pump and integrated microswitch enhanced TENG is designed for self-powered real-time wireless sensing. • The self-powered system uses a coil to perform real-time tin vertical height and horizontal position recognition. • The self-powered wireless sensing system can transmit optical signal up to 2 m without severe performance deterioration. Harvesting high entropy energy using triboelectric nanogenerator (TENG) has attracted more and more attentions. For normal self-powered wireless sensing applications, a significant portion of harvested energy will be consumed by the subsequent power management and wireless communication units, leading to the incapability of real-time wireless sensing. In this paper, we proposed a pumping switched TENG (PSW-TENG) for real-time wireless sensing. An inductor magnetic sensor coil integrated with the TENG forms a LC resonant circuit, converts the pulsed output of TENG into resonant signal with the encoded sensing informationwhich is significantly boosted using an integrated microswitch and a charge pump, and then transmitted via a laser diode up to 2 m. The sensor system has been utilized to detect metallic components passing through. The self-powered metal component monitoring system has a height recognition sensitivity of 11.7 kHz/mm and a horizontal position recognition sensitivity of 5.6 kHz/mm with the largest error of 8.5 kHz, showing good sensitivity and stability. Based on the sensing system, the types and passing number of tins on a conveyor can be simultaneously identified and counted. All the results have demonstrated the great potential of the real-time self-powered wireless sensing system for production line management.

[en] Highlights: • A facile and efficient method is proposed to develop translucent, porous P(VDF-TrFE) composites. • The inhomogeneous interface effects have been clarified by the direct structure mapping. • A 3 × 2 pixel tactile sensor array is integrated to work as self-powered coded lock. Piezoelectric polyvinylidene fluoride (PVDF) and its copolymer based piezoelectric nanogenerators (PENGs) have attracted extensive attention, which can hopefully be applied in the fields of wearable electric devices and sensing systems. However, one great challenge that limits their large-scale application is to achieve PVDF based composites with high piezoelectric performance. Herein, a facile and efficient method is proposed to develop translucent, porous composites with high β phase content and abundant micropores. Enhanced β phase formation is attributed to the electrostatic bonding between fillers (ZnO nanoparticles and Ag nanowires) and -CH₂ and -CF₂ chains, yet, local conformational disorder at the ZnO-matrix interface region caused by strong interface effect results in local stabilization of β phase. Coupling of high β phase content and microporous structure is believed to be essential for achieving considerable piezoelectric outputs (7.1 μW/cm²) and excellent force sensitivity (1.155 V/kPa). In practical applications, the composites based PENGs can efficiently harvest mechanical energy from human motions and detect weak physiological signals. Furthermore, a 3 × 2 pixel tactile sensor array is integrated successfully to work as self-powered flexible coded lock without power supply. Our work offers a simple approach to high-performance piezoelectric composites and moves a step toward sensing application.

[en] Ultrathin dielectric materials prepared by atomic-layer-deposition (ALD) technology are commonly used in graphene electronics. Using the first-principles density functional theory calculations with van der Waals (vdW) interactions included, we demonstrate that single-side fluorinated graphene (SFG) and hexagonal boron nitride (h-BN) exhibit large physical adsorption energy and strong electrostatic interactions with H₂O-based ALD precursors, indicating their potential as the ALD seed layer for dielectric growth on graphene. In graphene-SFG vdW heterostructures, graphene is n-doped after ALD precursor adsorption on the SFG surface caused by vertical intrinsic polarization of SFG. However, graphene-h-BN vdW heterostructures help preserving the intrinsic characteristics of the underlying graphene due to in-plane intrinsic polarization of h-BN. By choosing SFG or BN as the ALD seed layer on the basis of actual device design needs, the graphene vdW heterostructures may find applications in low-dimensional electronics. (paper)

[en] This work presents the development of flexible dual-mode surface acoustic wave (SAW) sensor based on single crystalline thin film lithium niobate (TF-LN). Numerical modeling is conducted to investigate the SAW propagation and the effects on strain sensitivity. The dependence of strain sensitivity on angles between the applied strain and SAW propagation direction is analyzed numerically and experimentally, showing that the maximum strain sensitivity is at 45° rather than longitudinal direction. 128° Y-cut TF-LN (∼50 µm), obtained by micromachining technique, is utilized as the piezoelectric substrate to fabricate the SAW strain sensors with dual-mode, namely Rayleigh mode and thickness shear mode. The sensor has excellent flexibility and demonstrates remarkable capability for an ultra-wide range strain measurement up to  ±3000 . Temperature effects on resonant frequency and strain sensitivity are investigated in the range of 25 °C–100 °C, and similar temperature characteristics are observed for the dual modes. A method of beat frequency between the dual modes is introduced which is able to eliminate the temperature effect on strain sensing, an on-chip temperature influence removing capability. All the results clearly show that this sensor exhibits great potential for applications in flexible electronics and microsystems. (paper)