[en] Highlights: • Transparent SETEG based on commercial glass has been developed. • The glass based SETEG shows high electric performance and stability. • An automatic measure and real-time display system is developed to track the motion of the stylus. A glass-based single electrode triboelectric generator (SETEG) is developed with polydimethylsiloxane (PDMS) as the negative material. Its performance under different contact forces, frequencies and spacers is investigated in detail. The SETEGs have higher electric output under higher contact force, frequency and larger spacer, and show better performance with a thinner glass layer at lower humidity condition. An open circuit voltage, short circuit current and power up to 318 V, 8.3 μA and 427 μW are obtained for a SETEG of 5×5 cm² size. Based on the study, a tracking sensor array consisting of nine 5×5 mm² SETEGs is proposed and developed. A LabVIEW-based automatic measurement system is also developed to record, process and display the real-time output voltages of the sensing array. Results show that an output voltage up to 4 V can be easily generated when a PDMS-covered stylus touches/slides the sensor array, and the output voltages from different sensors are independent from each other. This work demonstrates the great application potential of the SETEGs sensor array for self-powered detection, tracking or monitoring motion or a touch of a stylus or some objects, thus would be very useful for touch screen display, handheld tracking device, domestic security, traffic monitoring etc.

[en] In thiswork, dynamic thermodynamic analyzer (DMA) was used to determine the stress-temperature relationship of polyurethane fibers to research the thermodynamic properties under small strains. The results show that the stress of polyurethane fibers increases with the increase of temperature. The study of the energy conversion during the heating processof polyurethane fibers demonstrates that the entropy change decreases with the increase of the strain while the enthalpy change has the contrary tendency. The entropy change is the key reason for the stress of polyurethane fibers. (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] 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] Highlights: • Contact-mode TEGs prepared using phase-inversion PVDF-ZnSnO₃ & PA6 membranes. • At 490 N/3 Hz, PVDF-ZnSnO₃ TEG provides 520 V/2.7 mA m⁻² vs. 300 V/0.9 mA m⁻² for PVDF/PA6 TEG. • For PVDF-ZnSnO₃ d₃₃ of −65 pm V⁻¹ provides higher charge-density & piezo-potential. • Phase-inversion with high polarisation material eliminates prior charge injection need. Vertical contact-separation mode triboelectric generator (TEG) based on lead-free perovskite, zinc stannate (ZnSnO₃)-polyvinylidene fluoride (PVDF) composite and polyamide-6 (PA6) membrane is demonstrated. For the 5 wt% PVDF-ZnSnO₃ nanocomposites, the facile phase-inversion method provides a simple route to achieve high crystallinity and β-phase with a piezoelectric coefficient d₃₃ of −65 pm V⁻¹, as compared to −44 pm V⁻¹ for pristine PVDF membranes. Consequently, at a cyclic excitation impact of 490 N/3 Hz, the PVDF-ZnSnO₃/PA6 based TEGs provide a significantly higher voltage of 520 V and a current density of 2.7 mA m⁻² (corresponding charge density of 62.0 µC m⁻²), as compared to the pristine PVDF-PA6 TEG which provides up to 300 V with a current density of 0.91 mA m⁻² (corresponding to a charge density of 55.0 µC m⁻²). This increase in the electrical output can be attributed to not only the enhanced polarisation of PVDF by ZnSnO₃ leading to an increase in the β-phase content, but also to the surface charge density increase by stress induced polarisation of ZnSnO₃, leading to the generation of stronger piezoelectric potential. The work thus introduces a novel method of enhancing the surface charge density via the addition of suitable high polarisation piezoelectric materials thus eliminating the need for prior charge injection for fluoropolymer membranes.

[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 TENG-based self-powered instantaneous wireless humidity sensor system is developed with the passive components only. • A precise analytical model is developed for the capacitive sensor systems, shows excellent agreement with experiments. • A high performance TENG is developed using PA66 and FEP films with an peak power density of 4.8 W/m². • The sensor system has a high sensitivity of 1.26 kHz/%RH and high linearity. Self-powered wireless sensor systems are highly sought for the forthcoming Internet of Things era. However, most of the technologies take the route of energy harvesting, storage, and power regulation to power wireless sensor systems, which has a limited operation duration due to the low energy utilization efficiency of the multiple energy conversions involved. Here, we propose a triboelectric nanogenerator (TENG) based fully self-powered, instantaneous wireless sensor system which yet does not contain electronic devices and chips, but the passive components only. By integrating a capacitive sensor and an inductor coil with TENG, the pulse voltage output of the TENG is converted into a sinusoidal signal containing the sensing information with a resonant frequency and is transmitted to the receiver in distance wirelessly and continuously. A precise analytical model is developed for the capacitive sensor system with general implication; the oscillating signal generated by the model shows excellent agreement with experimental results. A capacitive humidity sensor is then utilized for sensing demonstration, showing that the maximum transmission distance of the sensor system is 50 and 90 cm for a 1 cm diameter magnetic-core coil pair and 20 cm diameter air-core coil pair, respectively. The wireless humidity sensor exhibits a sensitivity of 1.26 kHz/%RH, fast response speed, and excellent linearity, demonstrating its great application potential of the self-powered technology.

[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)

[en] Highlights: • Conductive carbon tapes with coarse surface and high electric affinity have been utilized as the electrodes to enhance TENG performance. • Carbon-PDMS/PA6 TENG demonstrates ultrahigh triboelectric performance and stability. • Interaction between PDMS film and coarse carbon electrode dramatically enhances the charge density of the Carbon-PDMS/PA6 TENG. -- Abstract: As a promising nanoenergy technology to harvest mechanical energy from environment, triboelectric nanogenerator (TENG) has attracted much attention and various strategies focused on optimization of triboelectric materials have been proposed to further improve its output power density. This work focuses on the electrode material for improvement of TENGs. A commercial double-sided conductive carbon tape composed of carbon powder is proposed as the electrodes for TENGs, based on which a superior performance TENG comprised of spin-coated flat polydimethylsiloxane (PDMS) and polyamide-6 (PA6) films is fabricated. Owing to the strong additional interaction between carbon electrode and tribo-layer, a 20 × 20 mm² carbon-PDMS/PA6 TENG demonstrates a peak output voltage of ~ 1760 V, a short-circuit current density of ~ 240 mA m⁻², and a maximum power density of ~ 120 W m⁻², much higher than those of aluminum electrode-based Al-PDMS/PA6 TENGs. Detailed investigations reveal that the dramatically enhanced performance originates from the additional interaction in the pores between coarse carbon electrode and PDMS film, and from the enhanced electric negative polarity of PDMS films with the peeling and transferring treatment. This study provides a promising simple and low-cost strategy of selecting and preparing electrode materials with special micro/nanostructures to interact with triboelectric layers to generate additional triboelectric charges for high performance TENGs.

[en] Bendable surface acoustic wave (SAW) devices were fabricated using high quality c-axis orientation ZnO films deposited on flexible polyethylene terephthalate substrates at 120 °C. Dual resonance modes, namely, the zero order pseudo asymmetric (A₀) and symmetric (S₀) Lamb wave modes, have been obtained from the SAW devices. The SAW devices perform well even after repeated flexion up to 2500 με for 100 times, demonstrating its suitability for flexible electronics application. The SAW devices are also highly sensitive to compressive and tensile strains, exhibiting excellent anti-strain deterioration property, thus, they are particularly suitable for sensing large strains.