A high-resolution flexible sensor array based on PZT nanofibers.

Flexible tactile sensor array has drawn great attention due to its ability to mimic human skin for sensing weak pressure and distinguishing pressure distribution, but the deficiency of sensitivity, the low resolution, and the complex and costly fabrication process seriously limit its development. Hence, it is urgent to explore a fully flexible sensor array with high sensitivity and high resolution as an electronic-skin. Here, the flexible piezoelectric tactile sensor array based on the composite film of PZT nanowires and polydimethylsiloxane (PDMS) was fabricated by the simple fabrication process (electrospinning process and mixture process). The electrospun PZT nanofibers have high aspect ratio and could enhance the generation and accumulation of the piezoelectric charges in the two electrodes of the composite film. By virtue of the inherently high piezoelectric coefficient of PZT material and high aspect ratio of PZT nanofibers, the composite film (75 wt% PZT nanofibers) presents high force-electric conversion capability and high sensitivity. Owing to the bottom electrode sheet shared by all sensor units and the supporting layer with relatively high elastic modulus, the sensor array shows high resolution to qualitatively sense the distribution and size of the impact in real time. Moreover, the sensor array also shows great durability, repeatability, and large working range. Based on these excellent characteristics, the sensor array has wide potential applications in the field of bionics science, robotics science and human-machine interaction.

Hybrid Pressure Sensor Based on Carbon Nano-Onions and Hierarchical Microstructures with Synergistic Enhancement Mechanism for Multi-Parameter Sleep Monitoring.

With the existing pressure sensors, it is difficult to achieve the unification of wide pressure response range and high sensitivity. Furthermore, the preparation of pressure sensors with excellent performance for sleep health monitoring has become a research difficulty. In this paper, based on material and microstructure synergistic enhancement mechanism, a hybrid pressure sensor (HPS) integrating triboelectric pressure sensor (TPS) and piezoelectric pressure sensor (PPS) is proposed. For the TPS, a simple, low-cost, and structurally controllable microstructure preparation method is proposed in order to investigate the effect of carbon nano-onions (CNOs) and hierarchical composite microstructures on the electrical properties of CNOs@Ecoflex. The PPS is used to broaden the pressure response range and reduce the pressure detection limit of HPS. It has been experimentally demonstrated that the HPS has a high sensitivity of 2.46 V/104 Pa (50-600 kPa) and a wide response range of up to 1200 kPa. Moreover, the HPS has a low detection limit (10 kPa), a high stability (over 100,000 cycles), and a fast response time. The sleep monitoring system constructed based on HPS shows remarkable performance in breathing state recognition and sleeping posture supervisory control, which will exhibit enormous potential in areas such as sleep health monitoring and potential disease prediction.

Synergistic Enhancement Properties of a Flexible Integrated PAN/PVDF Piezoelectric Sensor for Human Posture Recognition.

The flexible pressure sensor has attracted much attention due to its wearable and conformal advantage. All the same, enhancing its electrical and structural properties is still a huge challenge. Herein, a flexible integrated pressure sensor (FIPS) composed of a solid silicone rubber matrix, composited with piezoelectric powers of polyacrylonitrile/Polyvinylidene fluoride (PAN/PVDF) and conductive silver-coated glass microspheres is first proposed. Specifically, the mass ratio of the PAN/PVDF and the rubber is up to 4:5 after mechanical mixing. The output voltage of the sensor with composite PAN/PVDF reaches 49 V, which is 2.57 and 3.06 times that with the single components, PAN and PVDF, respectively. In the range from 0 to 800 kPa, its linearity of voltage and current are all close to 0.986. Meanwhile, the sensor retains high voltage and current sensitivities of 42 mV/kPa and 0.174 nA/kPa, respectively. Furthermore, the minimum response time is 43 ms at a frequency range of 1-2.5 Hz in different postures, and the stability is verified over 10,000 cycles. In practical measurements, the designed FIPS showed excellent recognition abilities for various gaits and different bending degrees of fingers. This work provides a novel strategy to improve the flexible pressure sensor, and demonstrates an attractive potential in terms of human health and motion monitoring.

Self-Powered Acceleration Sensor Based on Multilayer Suspension Structure and TPU-RTV Film for Vibration Monitoring.

In this paper, we designed a triboelectric acceleration sensor with excellent multiple parameters. To more easily detect weak vibrations, the sensor was founded on a multilayer suspension structure. To effectively improve the electrical properties of the sensor, a surface roughening and internal doping friction film, which was refined with a room temperature vulcanized silicone rubber (RTV) and some thermoplastic polyurethanes (TPU) powder in a certain proportion, was integrated into the structure. It was found that the optimization of the RTV film increases the open circuit voltage and short circuit current of the triboelectric nanogenerator (TENG) by 223% and 227%, respectively. When the external vibration acceleration is less than 4 m/s2, the sensitivity and linearity are 1.996 V/(m/s2) and 0.999, respectively. Additionally, when it is in the range between 4 m/s2 and 15 m/s2, those are 23.082 V/(m/s2) and 0.975, respectively. Furthermore, the sensor was placed in a simulated truck vibration environment, and its self-powered monitoring ability validated by experiments in real time. The results show that the designed sensor has strong practical value in the field of monitoring mechanical vibration acceleration.

Flexible and Wearable PDMS-Based Triboelectric Nanogenerator for Self-Powered Tactile Sensing.

Flexible electronics devices with tactile perception can sense the mechanical property data of the environment and the human body, and they present a huge potential in the human health system. In particular, the introduction of ultra-flexible and self-powered characteristics to tactile sensors can effectively reduce the problems caused by rigid batteries. Herein, we report a triboelectric nanogenerator (TENG), mainly consisting of an ultra-flexible polydimethylsiloxane (PDMS) film with micro-pyramid-structure and sputtered aluminum electrodes, which achieves highly conformal contact with skin and the self-powered detection of human body motions. The flexible polyethylene terephthalate (PET) film was selected as spacer layer, which made the sensor work in the contact-separation mode and endowed the perfect coupling of triboelectrification and electrostatic induction. Moreover, the controllable and uniform micro-structure PDMS film was fabricated by using the micro-electro-mechanical system (MEMS) manufacturing process, bringing a good sensitivity and high output performance to the device. The developed TENG can directly convert mechanical energy into electric energy and light up 110 green Light-Emitting Diodes (LEDs). Furthermore, the TENG-based sensor displays good sensitivity (2.54 V/kPa), excellent linearity (R2 = 0.99522) and good stability (over 30,000 cycles). By virtue of the compact size, great electrical properties, and great mechanical properties, the developed sensor can be conformally attached to human skin to monitor joint movements, presenting a promising application in wearable tactile devices. We believe that the ultra-flexible and self-powered tactile TENG-based sensor could have tremendous application in wearable electrons.