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Flexible sensors have been widely studied for use in motion monitoring, human‒machine interactions (HMIs), personalized medicine, and soft intelligent robots. However, their practical application is limited by their low output performance, narrow measuring range, and unidirectional force detection. Here, to achieve flexibility and high performance simultaneously, we developed a flexible wide-range multidimensional force sensor (FWMFS) similar to bones embedded in muscle structures. The adjustable magnetic field endows the FWMFS with multidimensional perception for detecting forces in different directions. The multilayer stacked coils significantly improved the output from the μV to the mV level while ensuring FWMFS miniaturization. The optimized FWMFS exhibited a high voltage sensitivity of 0.227 mV/N (0.5–8.4 N) and 0.047 mV/N (8.4–60 N) in response to normal forces ranging from 0.5 N to 60 N and could detect lateral forces ranging from 0.2–1.1 N and voltage sensitivities of 1.039 mV/N (0.2–0.5 N) and 0.194 mV/N (0.5–1.1 N). In terms of normal force measurements, the FWMFS can monitor finger pressure and sliding trajectories in response to finger taps, as well as measure plantar pressure for assessing human movement. The plantar pressure signals of five human movements collected by the FWMFS were analyzed using the k-nearest neighbors classification algorithm, which achieved a recognition accuracy of 92%. Additionally, an artificial intelligence biometric authentication system is being developed that classifies and recognizes user passwords. Based on the lateral force measurement ability of the FWMFS, the direction of ball movement can be distinguished, and communication systems such as Morse Code can be expanded. This research has significant potential in intelligent sensing and personalized spatial recognition. [ABSTRACT FROM AUTHOR]

In our daily lives, low-frequency kinetic energy primarily manifests as vibrations. However, effective harnessing of low-frequency kinetic energy remains a formidable challenge. This paper proposes a rope-driven rotor that rotates around an axis and consists of an ultra-high-molecular-weight polyethylene (UHMWPE) wire wrapped around a metal shaft. The rotor can convert ultra-low frequency vibration/linear motion into rapid rotation by pressing the top at low frequencies and driving the rope for a quick release. The harvester can generate up to 36.25 mW power using a 0.1-mm-diameter UHMWPE wire as the rotor when periodically pressed down to 20 mm at a frequency of 1 Hz. A simple power generation floor is assembled, generating 28.58-mW power with a matching load at a frequency of 1.5 Hz. Moreover, the harvester can increase the charging voltage of a 0.47-F supercapacitor from 0 to 6.8 V within 10 min. In addition, the harvester can harvest energy through a light finger press motion, and the energy obtained can also support the continuous operation of multiple electronic devices concurrently. This study introduces an effective method for harvesting ultra-low frequency energy and has great prospects in the field of power generation floor and human movement energy harvesting. [ABSTRACT FROM AUTHOR]

Electromagnetic vibration energy harvesters are promising for the power supply of wireless sensor nodes, small electronic devices, and wearable electronics. Conventional electromagnetic harvesters usually increase output by increasing the size of coils and magnets, limiting the improvement of energy conversion efficiency and power density. In this study, multilayer microelectromechanical system (MEMS) coils were prepared using flexible electronics, and their high integration performance in arbitrary space was utilized to greatly improve the utilization of the space magnetic field by the electromagnetic harvester. The core magnet of the generator was magnetically balanced to achieve levitation, which improved the sensitivity and reduced fatigue damage compared with traditional spring structures. The wound coils on the top and bottom of the magnet and the flexible coils on the sides worked together to improve the energy efficiency and output of the devices. The output performance of the device with different number distributions was simulated using mathematical models to obtain the optimal structural parameters. The results show that by introducing flexible multilayer MEMS coils on the side surface of the energy harvester, the open-circuit voltage of the energy generators increased from 7 to 10 V by more than 43%. Flexible multilayer MEMS coils can enhance energy conversion rates and possess compact dimensions, making them suitable for integration onto complex surfaces. After the vibration energy harvesting system testing, the maximum peak power of the harvester was 7.1 mW at an acceleration of 1 g and a resonant frequency of 11 Hz with a resistor of 3.5 internal resistance. Moreover, a 470 µF capacitor can be charged to 3.5 V within 10 s to drive a hygrothermograph to work for more than 80 s and can supply a light bulb continuously. This strategy shows the great potential of vibration-energy-driven electromagnetic generators for powering small electronics in limited spaces. [ABSTRACT FROM AUTHOR]

The application of standing surface acoustic wave (SSAW) tweezers based on backpropagation superposition to achieve precise behavior manipulation of microscale cells and even nanoscale bacteria has been widely studied and industrialized. However, the structure requires multiple transducer components or full channel resonance. It is very challenging to design a simple structure for nano-control by complex acoustic field. In this study, a reflector-interdigital transducer (R-IDT) acoustofluidic device based on unilateral coherence enhancement is proposed to achieve SSAW definition features of periodic particle capture positions. The SAW device based on a unilateral transducer can not only generate leaky-SAW in water-filled microchannel, but also have a contribution of spherical waves in the vibration area of the substrate-liquid interface due to the Huygens-Fresnel diffractive principle. Both of them form a robust time-averaged spatial periodicity in the pressure potential gradient, accurately predicting the lateral spacing of these positions through acoustic patterning methods. Furthermore, a reflector based on Bragg-reflection is used to suppress backward transmitted SAW and enhance forward conducted SAW beams. By using a finite element model, R-IDT structure's amplitude enhances 60.78% compared to single IDT structure. The particle manipulation range of the diffractive acoustic field greatly improves, verified by experimental polystyrene microspheres. Besides, biocompatibility is conformed through red blood cells and Bacillus subtilis. We investigate the overall shift of periodic pressure field that can still occur when the phase changes. This work provides a simpler and low-cost solution for the application of acoustic tweezer in biological cell culture and filtering. [ABSTRACT FROM AUTHOR]

With the rapid development of microelectronics and flexible electronics technology, self-powered sensors have significant application prospects in human-machine interface systems and Internet of Things. However, piezoelectric- and triboelectric-based sensors have low current output and are easily affected, while electromagnetic-based sensors are difficult to miniaturize. This work proposes a high-density stacked microcoil integrated microminiaturized electromagnetic vibration energy harvester (EVEH). The double-layer high-density microcoil is fabricated on both sides of the flexible polyimide substrate interconnected via the central through-hole. Owing to reduced single coil line width, line spacing, and stacked structure, the number of turns can be substantially enhanced. Moreover, the relative position of the coils and magnet has a considerable influence on the performances; due to the huge change rate in magnetic flux when the coil is placed in the radial direction of the magnet than in the axial direction, the open-circuit voltage in the radial direction is 10 times greater. The microcoil can maintain good performance at high, low temperatures and under bending conditions. When the distance between the ends of the coil changes from 2 to 20 mm in 2 mm steps, the bending angle of the coil changes from 45° to 270° in 45° steps; furthermore, when the coil is exposed to −40 and 60°C conditions, the coil resistance is maintained at approximately 447 Ω. The peak open-circuit voltage of three-piece microcoils reaches 0.41 V at 4 Hz under 2g, and the output voltage and current increase with an increasing number of stacked layers. These excellent properties indicate that EVEH can be used for self-powered acceleration sensing. The sensitivity is measured to be 0.016 V/(m/s2) with a correlation coefficient of 0.979 over the acceleration range of 1–18 m/s2. Thus, the developed microminiaturized EVEH has enormous potential for self-powered sensing applications in confined spaces and harsh environments. [ABSTRACT FROM AUTHOR]

Harvesting energy from human movement and converting it into electricity is a promising method to address the issue of sustainable power supply for wearable electronic devices. Using traditional energy harvesters for practical applications is difficult due to their low output power. In this paper, an energy harvester with high power and efficiency is reported based on the principle of electromagnetic induction. It adopts a tiny compound mechanism comprising symmetrical lever-sector gear, which can amplify the vertical displacement of the human heel of 1.44 times without affecting the flexibility and comfort of human movement. The lever-sector gear and gear acceleration mechanism can achieve high output power from the tiny vertical movements of the heel. The results demonstrated that the average power and energy harvesting efficiency of the device are 1 W and 63%, respectively. Moreover, combining a novel controllable electric switch and energy management circuit allows the energy harvester to be worn by individuals with different weights and functions as a continuous real-time power supply for various electronic devices (mobile phones, smartwatches, etc.). Therefore, this research provides a new approach for the highly efficient harvesting of human motion energy and sustainable power supply of wearable electronics. [ABSTRACT FROM AUTHOR]

Flexible pressure sensors have broad application prospects, such as human motion monitoring and personalized recognition. However, their applicability is limited by complex structures, low output performance, low sensitivity, and narrow measurement range. In this study, we report a single-electrode spongy triboelectric sensor (SSTS) mainly composed of spongy composite multi-walled carbon nanotubes/polydimethylsiloxane (MWCNT/PDMS) film and conductive fabric, which can simultaneously generate contact electrification and electrostatic induction coupling in a single-electrode contact-separation mode. The SSTS combines the triboelectric effect, properties of doping material, and spongy porous structure (soft sugar as a sacrificial template). An SSTS with an MWCNT content of 10 wt% and a porosity of 64% exhibits high sensitivity, a wide measurement range, and excellent linearity. It also displays two sensitivity regions (slopes): 1.324 V/kPa from 1.5 to 28 kPa in the low-pressure range and 0.096 V/kPa from 28 to 316.5 kPa in the high-pressure range, with linearities of 0.980 and 0.979, respectively. Furthermore, the SSTS delivers a high-performance output and high stability, thus enhancing the monitoring of hand pressure changes, human movement, personalized spatial recognition, and other detection tasks. This new strategy for human motion monitoring shows great potential in the healthcare fields, sports rehabilitation, and human-computer interactions. [ABSTRACT FROM AUTHOR]

Designing stretchable and skin-conformal self-powered sensors for intelligent sensing and posture recognition is challenging. Here, based on a multi-force mixing and vulcanization process, as well as synergistically piezoelectricity of BaTiO3 and polyacrylonitrile, an all-in-one, stretchable, and self-powered elastomer-based piezo-pressure sensor (ASPS) with high sensitivity is reported. The ASPS presents excellent sensitivity (0.93 V/104 Pa of voltage and 4.92 nA/104 Pa of current at a pressure of 10–200 kPa) and high durability (over 10,000 cycles). Moreover, the ASPS exhibits a wide measurement range, good linearity, rapid response time, and stable frequency response. All components were fabricated using silicone, affording satisfactory skin-conformality for sensing postures. Through cooperation with a homemade circuit and artificial intelligence algorithm, an information processing strategy was proposed to realize intelligent sensing and recognition. The home-made circuit achieves the acquisition and wireless transmission of ASPS signals (transmission distance up to 50 m), and the algorithm realizes the classification and identification of ASPS signals (accuracy up to 99.5%). This study proposes not only a novel fabrication method for developing self-powered sensors, but also a new information processing strategy for intelligent sensing and recognition, which offers significant application potential in human—machine interaction, physiological analysis, and medical research. [ABSTRACT FROM AUTHOR]

The research on flexible pressure sensors has drawn widespread attention in recent years, especially in the fields of health care and intelligent robots. In practical applications, the sensitivity of sensors directly affects the precision and integrity of weak pressure signals. Here, a pressure sensor with high sensitivity and a wide measurement range composed of porous fiber paper and 3D patterned electrodes is proposed. Multi-walled carbon nanotubes with excellent conductivity were evenly sprayed on the fiber paper to form the natural spatial conducting networks, while the copper-deposited polydimethylsiloxane films with micro-pyramids array were used as electrodes and flexible substrates. Increased conducting paths between electrodes and fibers can be obtained when high-density micro-pyramids fall into the porous structures of the fiber paper under external pressure, thereby promoting the pressure sensor to show an ultra-high sensitivity of 17.65 kPa−1 in the pressure range of 0–2 kPa, 16 times that of the device without patterned electrodes. Besides, the sensor retains a high sensitivity of 2.06 kPa−1 in an ultra-wide measurement range of 150 kPa. Moreover, the sensor can detect various physiological signals, including pulse and voice, while attached to the human skin. This work provides a novel strategy to significantly improve the sensitivity and measurement range of flexible pressure sensors, as well as demonstrates attractive applications in physiological signal monitoring. [ABSTRACT FROM AUTHOR]

Effective collection, recognition, and analysis of sports information is the key to intelligent sports, which can help athletes to improve their skills and formulate scientific training plans and competition strategies. At present, wearable electronic devices used for movement monitoring still have some limitations, such as high cost and energy consumption, incompatibility of suitable flexibility and personalized spatial structure, dissatisfactory data analysis methods, etc. In this work, a novel three-dimensional-printed thermoplastic polyurethane is introduced as the elastic shell and friction layer, and it endows the proposed customizable and flexible triboelectric nanogenerator (CF-TENG) with personalized spatial structure and robust correlation to external pressure. In practical application, it exhibits highly sensitive responses to the joint-bending motion of the finger, wrist, or elbow. Furthermore, a pressure-sensing insole and smart ski pole based on CF-TENG are manufactured to build a comprehensive sports monitoring system to transmit the athletes' motion information from feet and hands through the plantar pressure distribution and ski pole action. To recognize the movement status, the self-developed automatic peak recognition algorithm (P-Find) and machine learning algorithm (subspace K-Nearest Neighbors) were introduced to accurately distinguish the four typical motion behaviors and three primary sub-techniques of cross-country skiing, with accuracy rates of 98.2% and 100%. This work provides a novel strategy to promote the personalized applications of TENGs in intelligent sports. [ABSTRACT FROM AUTHOR]

Ocean intelligent buoy is important for ocean environment monitoring. With the increase of requisite sensors and transportable data, a long power supply has become a problem to be solved urgently. In this work, a hybrid nanogenerator integrating triboelectric, piezoelectric, electromagnetic, photovoltaic, and thermotropic units is proposed to maximize ocean ambient energy harvesting, which includes static energy (solar and thermal energy) and dynamic energy (wave energy). Compared with a device with a single energy conversion mechanism, this structural design breaks the limit of harvesting time and natural conditions during the energy harvesting process, thereby increasing the harvested energy. Static energy harvesting is realized by the thermoelectric (TG) and photovoltaic (PV) units located inside the device and the PV unit attached to the device surface. Results show that the maximum open-circuit voltage and short-circuit current are 5 V and 41 mA in the external PV and 1.33 V and 49 mA in the internal PV under 30000 Lux illumination, respectively. The open-circuit voltage and short-circuit current of the TG unit are 5 V and 15 mA, respectively. The core component of the dynamic generation unit is the gimbal used to harvest wave energy by the triboelectric nanogenerator (TENG), piezoelectric generator (PENG), and electromagnetic generator. When the frequency is 2.4 Hz, the maximum peak-to-peak power of the TENG, PENG, and EMG are 0.25, 1.58, and 13.8 mW, respectively. Finally, an intelligent ocean buoy is fabricated by the integration of an energy harvester, a power management circuit, sensors, a microcontroller, and a wireless communication module. Driven by static and dynamic energy, temperature signal, humidity signal, GPS signal, and sound signal are sent to the receiving terminal wirelessly. The ocean energy harvester proposed in this work is of great significance for ocean energy harvesting and ocean wireless monitoring systems. [ABSTRACT FROM AUTHOR]

Recently, human physiological information wireless monitoring in real-time is particularly important in health analysis. As a solution, a non-contact wireless physiological monitoring system based on pyroelectric generator (PyG), whose core part consists of a wireless circuit processing module and a polyvinylidene fluoride (PVDF) film, has been successfully designed. Owing to the temperature change under the stimulation of an external heat source, the output voltage of the PyG self-powered flexible sensor increases with the heat source temperature variation in the range of 295–355 K. Furthermore, based on the natural temperature oscillation between the living body and surrounding environment, the sensor can realize human physiological information assessment, for example, temperature monitoring of the palms, fingers, respiratory heat signals from mouth or nose or non-contact spatial heat mapping recognition of finger movement via sensor array. On this basis, a portable wireless monitoring system was designed by integrating the intelligent sensor with a signal conditioning circuit, data conversion storage module, Bluetooth module, and power module. This system can acquire real-time human oral or nasal breathing signals in the personal mobile app to evaluate the physiological state of individuals. Additionally, the wireless monitoring system can be activated within 10 m, demonstrating the application of PyG sensors in remote data transmission. [ABSTRACT FROM AUTHOR]

With the evolution of power electronic system to miniaturization and integration, dielectric capacitors are extensively studied in electric power systems such as electron beam and direction energy weapons owing to outstanding energy storage density and low loss. In this work, Pb0.97La0.02ZrO3 (PLZ) films were deposited on LaNiO3 (LNO)/Pt and LNO electrodes using sol-gel method, respectively. High spontaneous polarization (Ps ~ 91.3 μC cm−2) and low remanent polarization (Pr ~ 7.3 μC cm−2) can be obtained from PLZ/LNO/Pt/TiO2/SiO2/Si with energy storage density up to 25.4 J cm−3, which could be explained by good ohmic contact between films and composite electrodes. Besides, recoverable energy storage of films exhibits outstanding temperature stability (25.9–25.3 J cm−3) over -60 - 20 °C. These results suggest that LNO/Pt composite electrodes can be used to optimize PLZ films properties, which could be considered as a valid way for developing wide temperature range energy-storage capacitors. Highlights: High quality PbLaZrO3(PLZ) films could be obtained by LaNiO3 (LNO)/Pt electrode owing to good ohmic contact and lattice matching between films and composite electrode. High spontaneous polarization (Ps ~ 91.3 μC cm−2) and low remanent polarization (Pr ~ 7.3 μC cm−2) can be obtained in PLZ/LNO/Pt/TiO2/SiO2/Si. Excellent energy storage could be obtained in PLZ films within wide temperature range (−60–200 °C). Especially, recoverable energy storage of films exhibits outstanding temperature endurance (25.9–25.3 J cm−3) over −60–20 °C. [ABSTRACT FROM AUTHOR]

SrRuO/BiFeO/SrRuO thin-film capacitors were fabricated to investigate the role of mobile oxygen vacancies in a switchable photovoltaic (PV) effect that depends on ferroelectric domain orientations. Normally, the flowing direction of the stabilized photocurrent is opposite to ferroelectric polarization orientation. However, an abnormal overshoot of initial positive transient photocurrent parallel to the ferroelectric polarization could be observed under light illumination for a poled BiFeO thin film with the polarization pointing to the bottom electrode. Moreover, the photocurrent has a strong response with respect to voltage poling time and relaxation time after poling, which seems to be correlated with time-dependent migration of oxygen vacancies and concurrent charge trapping effect. Our results not only reveal the scenario how oxygen-vacancy migration and charge trapping effect affect the switchable PV effect, besides ferroelectric polarization, but also are helpful for the understanding and designing of new switchable photoelectric devices. [ABSTRACT FROM AUTHOR]

(Pb,La)(Zr,Ti)O antiferroelectric 1.4 μm-thick films have been prepared on Pt (111)/Ti/SiO/Si(100) substrates by sol-gel process. The structures and dielectric properties of the antiferroelectric thick films were investigated. The films displayed pure perovskite structure with (100)-preferred orientation. The surface of the films was smooth, compact and uniform. The antiferroelectric (AFE) characterization have been demonstrated by P (polarization)-E (electric field) and C(capacitance)-V (DC bias) curves. The AFE-ferroelectric (FE) and FE-to-paraelectric (PE) phase transition were also investigated as coupling functions of temperature and direct current electric field. With the applied field increased, the temperature of AFE-to-FE phase transition decreased and the FE-to-PE phase shifted to high temperature. The AFE-to-FE phase transition was adjustable by direct current electric field. (Pb,La) (Zr,Ti) O antiferroelectric films have broad application prospects in microelectromechanical systems because of the phase transition. [ABSTRACT FROM AUTHOR]

(Pb, La)(Zr, Ti)O antiferroelectric thick films with (100)-preferred orientation were fabricated on Pt(111)/Ti/SiO/Si(100) substrates via a sol-gel method. The electric-field-induced antiferroelectric (AFE) to ferroelectric (FE) phase transition characteristics were studied by C (capacitance)-E (electric field) measurements at different temperature. The films were in AFE state under 0 kV/cm below 122 °C, and the switching field values decreased, with increasing temperature. The films were in FE state between 122 and 135 °C, and when the temperature above 135 °C, the films were in PE state. The temperature-dependent dielectric parameters were deconvoluted using a Gaussian fit multi-peaks showed that two typical phase transitions were discovered. The first peak is the AFE-to-FE phase transition and the second peak is the FE-to-PE phase transition which has been verified by C-E tests. [ABSTRACT FROM AUTHOR]