Jikui Luo

Here we demonstrate a magnetic resonance coupling based wireless triboelectric nanogenerator (TENG) and fully self-powered wireless sensors. By integrating a microswitch and an inductor with the TENG, the pulsed voltage output is converted into a sinusoidal voltage signal with a fixed frequency. This can be transmitted wirelessly from the transmit coil to the resonant-coupled receiver coil with an efficiency of 73% for a 5 cm distance between the two coils (10 cm diameter). Analytic models of the oscillating and coupled voltage signals for the wireless energy transfer are developed, showing excellent agreement with the experimental results. A TENG of 40 × 50 mm2 can wirelessly light up 70 LEDs or charge up a 15 μF capacitor to 12.5 V in ~90 s. The system is further utilized for two types of fully self-powered wireless chipless sensors with no microelectronic components. The technologies demonstrate an innovative strategy for a wireless ‘green’ power source and sensing.

As a reliable indicator of human physiological health, respiratory rate has been utilized in more and more cases for prediction and diagnosis of potential respiratory diseases and the respiratory dysfunction caused by cystic fibrosis. However, compared with smart mobile electronics, traditional clinical respiration monitoring systems is not convenient to work as a household wearable device for real-time respiration monitoring in daily life due to its cumbersome structure, complex operability, and reliance on external power sources. Thus, we propose a wearable wireless respiration sensor based on lateral sliding mode triboelectric nanogenerator (TENG) to monitor respiratory rates by sensing the variation of the abdominal circumference. In this paper, we validate the possibility of the device as a respiration monitoring sensor via an established theoretical model and investigate the output performance of the sensor via a series of mechanical tests. Furtherly, the applications of the respiration sensor in different individuals, different breathing rhythms, different active states, and wireless transmission have been verified by a lot of volunteer tests. All the results demonstrate the potential of the proposed wearable sensor as a new alternative for detecting and monitoring real-time respiratory rates with general applicability and sensitivity.

Atomic layer deposited (ALD) ultra-thin alumina film is proposed to control the operational lifetimes of fully biodegradable (FB-) surface sensitive surface acoustic wave (SAW) devices. SAW devices encapsulated with conventional thick organic materials fail to function effectively, while devices with an ultra-thin alumina encapsulation layer (AEL) function normally with high performance. After being subjected to degradation in water, a FB-SAW device with no AEL starts to degrade immediately and fails within 8 h, due to dissolution of the tungsten electrode and piezoelectric material (ZnO). The coating of an ultra-thin AEL on the surfaces prevents SAW devices from undergoing degradation in water and enables SAW devices to perform normally before the AEL is dissolved. The stable operation lifetimes of SAW devices are linearly dependent on the AEL thickness, thus allowing for the design of devices with precisely controlled operational lifetimes and degradation times. The results show that all the materials used could be degraded; also, in vitro cytotoxicity tests indicate that the encapsulated FB-SAW devices are biocompatible, and cells can adhere and proliferate on them normally, demonstrating great potential for broader biodegradable electronic device applications.

The rapid uptake of energy harvesting triboelectric nanogenerators (TENGs) for self-powered electronics requires the development of high-performance tribo-materials capable of providing large power outputs. This work reports on the synthesis and use of aniline formaldehyde resin (AFR) for energy-harvesting applications. The facile, acidic-medium reaction between aniline and formaldehyde produces the aniline-formaldehyde condensate, which upon an in-vacuo high temperature curing step provides smooth AFR films with abundant nitrogen and oxygen surface functional groups which can acquire a tribo-positive charge and thus endow AFR with a significantly higher positive tribo-polarity than the existing state-of-art polyamide-6 (PA6). A TENG comprising of optimized thin-layered AFR against a polytetrafluomethylene (PTFE) film produced a peak-to-peak voltage of up to similar to 1000 V, a current density of similar to 65 mA m(-2), a transferred charge density of similar to 200 mu C m(-2) and an instantaneous power output (energy pulse) of similar to 11 W m(-2) (28.1 mu J cycle(-1)), respectively. The suitability of AFR was further supported through the Kelvin probe force microscopy (KPFM) measurements, which reveal a significantly higher average surface potential value of 1.147 V for AFR as compared to 0.87 V for PA6 and a step-by-step increase of the surface potential with the increase of energy generation cycles. The work not only proposes a novel and scalable mouldable AFR synthesis process but also expands with excellent prospects, the current portfolio of tribo-positive materials for triboelectric energy harvesting applications.

Triboelectric nanogenerators (TENGs), as a promising energy harvesting technology, have attracted considerable attention and various approaches have been developed to improve their output performance. An innovative strategy was proposed recently by using solid polymer electrolyte (SPE) with asymmetric pairing ions as the friction layer, showing excellent potential to achieve high-performance TENGs. However, it is far from clear what are the effects of SPE on TENG performance as only one electrolyte, CaCl2, was used for the investigation. Herein, PTFE/PVA-MClx TENGs based on SPEs with different types of electrolytes, including LiCl, ZnCl2, CaCl2, FeCl3, and AlCl3, were fabricated and their performances were investigated. All the devices demonstrated superior output performance than that of the control PTFE/PVA TENG. Specifically, the PTFE/PVA-LiCl TENG exhibited remarkably enhanced triboelectric performance with an output voltage of ~1345 V, a short-circuit current density of ~260 mA m−2 and a maximum power density of ~83 W m−2, four times higher than that of the control PTFE/PVA TENG. Detailed investigations revealed that in combination with improved triboelectric property, the enhanced interaction of SPEs with opposite triboelectric layers further significantly boost the triboelectric outputs. This work presents a new method to increase the interaction between triboelectric layers to effectively improve the outputs of TENGs, and to facilitate the development of high performance TENGs. Polyvinyl alcohol (PVA) based solid polymer electrolytes (SPEs) with different ion concentrations doping were utilized to fabricate high-performance triboelectric nanogenerators (TENG) due to their much improved triboelectric property and enhanced interaction with opposite tribolayer. The PTFE/PVA-LiCl TENG demonstrates an outstanding triboelectric output with a peak output voltage of ~1345 V, a short-circuit current density of ~260 mA m−2 and a maximum power density of ~83 W m−2, much higher than these of TENGs with specific surface micro-structures and optimized device structures reported so far. This study presents a new strategy to increase the interaction between triboelectric layers to effectively improve the outputs of TENGs, and to facilitate the development of high performance TENGs. [Display omitted] •Different types of electrolytes have been utilized to dope and modulate PVA based solid polymer electrolytes tribolayer to achieve much enhanced transferred charge density of 210 μC m−2.•The PTFE/PVA-LiCl TENG demonstrates much enhanced triboelectric performance and stability, achieving a high power density of 83 W m−2.•Electrolyte addition enhances the triboelectric property of PVA based SPE as a positive triboelectric material.•Enhanced interaction between triboelectric layers further improves the outputs of TENGs significantly.

Medical implantation of an electrocorticography (ECoG) recording system for brain monitoring is an effective clinical tool for seizure focus location and brain disease diagnosis. Planar and flexible ECoG electrodes can minimize the risks of infection and serious inflammatory response, and their good shape adaptability allows the device to fit complex cortex shape and structure to record brain signals with high spatial and temporal resolution. However, these ECoG electrodes require an additional surgery to remove the implant, which imposes potential medical risks. Here, a novel flexible and bioresorbable ECoG device integrated with an intracortical pressure sensor for monitoring swelling of the cortex during operation is reported. The ECoG device is fabricated with poly(l-lactide) and polycaprolactone composite and transient metal molybdenum. In vivo tests on rats show that the ECoG system can record the dynamic changes in brain signals for the different epilepsy stages with high resolution, while the malleable pressure sensor shows a linear relationship between the pressure and resistance in in vitro tests. In vitro degradation experiments show that the ECoG system can work stably for about five days before loss of efficacy, and the whole ECoG system degrades completely in a phosphate buffer solution in about 100 days.

For mechanical equipment or facilities, abnormal vibration and external impact can sometimes cause fatigue or even failure, which might lead to severe accidents. It's necessary to monitor the movement of important devices during their service and identify these abnormal conditions. In recent years, triboelectric nanogenerators (TENGs) have been widely used for collecting energy in many applications, and many experiments show that it is an effective method for self-powered sensing. In this paper, a mathematical model of a novel self-powered eccentric triboelectric nanosensor (Ec-TENS) has been built which can detect linear acceleration and velocity. Governing equations between output voltage and linear acceleration/velocity have been derived. Based on the theoretical model, a sliding-mode prototype has been designed and fabricated to verify the theoretical models through a series of tests. Experimental results have shown that Ec-TENS could generate output voltage once external acceleration exceeds a threshold, and amplitude of voltage could vary with velocity. The output voltage and linear velocity satisfy a specific function, and have a good repeatability and stability. Because of its self-powered feature, the novel Ec-TENS has potentially wide applications in the fields of structural health monitoring (SHM), wearable devices, security systems and aeronautic fields, especially in extreme environmental or unattended conditions. [Display omitted] •Proposed a novel design of a self-powered eccentric triboelectric nanosensor.•Proposed a theoretical model, governing equations and verified them by tests.•It can detect linear velocity and acceleration change without a power supply.

A triboelectric nanogenerator-based self-powered resonant sensor is proposed and investigated. By integrating an inductor and a microswitch with a triboelectric nanogenerator, a new type triboelectric nanogenerator is obtained, the pulse voltage output is converted to an oscillating signal with a very stable modulated resonant frequency, immune to the cross disturbance of contact-related variation (force, frequency, distance) and environmental variation, such as humidity and temperature. This is utilized for non-destructive defect detection. When the coil inductor scans the surface of a specimen with defects, varying resonant frequencies are obtained for different types of defects, showing excellent consistency between the experimental and simulated results. The results demonstrate the potential of the self-powered TENG-based resonant sensor to be a highly stable and sensitive magnetic sensor for the non-destructive defect detection applications.

Liquid metal (LM) has been used as flexible electrodes for high performance triboelectric nanogenerators (TENGs), however it is unclear how the LM in tribo-layers would affect the performance of TENGs. Here, we report the investigation on the effects of LM particles incorporated into a tribo-layer on the performance of TENGs. The TENGs consist of a polyacrylonitrile (PAN) electrospinning nanofiber membrane, and a polytetrafluoroethylene (PTFE) thin film. LM particles with different concentrations are incorporated into PAN polymer matrix, and used to make the PAN nanofibers membranes by electrospinning. Result shows that the outputs of TENGs become much larger with the increase in LM content. Specifically, the current density increases by about 40%, and both the charge density and output voltage increase by nearly 70%. The overall output power is approximately 2 times higher for the TENG with 1.5 wt% LM concentration, as compared to those of TENGs with pure PAN tribo-layer. However, the output of PAN/LM-PTFE TENGs deteriorates drastically when the LM mass content is increased to 2.5 wt%, at which the composite contains a high density of LM spheroid and spindle particles, deteriorating the generation of triboelectric charge. Liquid metal (LM) is feasible to be incorporated into electrospinning polymer (polyacrylonitrile, PAN) nanofibers as nano-particle and achieves the modification of TENG tribo-material layer on this account. Compared with TENG based on pure-PAN film, the TENG with PAN/LM composite membrane demonstrates a higher energy output, which only needs a small amount of LM concentration. The result exhibits that the current density increases by about 40% and the output voltage increase by nearly 70%, which is explained by the charge trapping mechanism. When two tribo-material layers begin to separate, a large negative bias generated by electron transfer from the external circuit will cause some electrons to be injected into the LM oxide layers, and then stored in the interface states. The low-cost approach in this study is also potential to other polymers, thus enriching the diversity of modifying tribo-material layers. In addition, it is also feasible to apply similar polymer composite membranes to the energy harvesting of wearable electronic devices. [Display omitted] •A simple process has been developed to incorporate liquid metal particles into PAN nanofibers uniformly.•Liquid metal has been used as nanoparticle dopants to improve the TENG performance significantly•The charge trapping at the liquid metal surface oxide plays the key role for the performance improvement of TENGs.

Optimized design of sliding-mode triboelectric nanogenerator (TENG) that is triggered by relative sliding between dielectric layers through a friction process forms one of the key focuses in this community since it may enhance the feasibility of real applications in industries. We propose here a theoretical model based on multi-parameter analysis to provide a rational optimization strategy for design of sliding mode TENG. By combining multiple parameters into dimensionless variables, the normalized output performance is expressed by virtue of two compound parameters. The scaling laws are achieved between the normalized electric output and these compound parameters, involving device dimensions (sizes, dielectric layer thickness), electrical properties of the electrode and dielectric materials, loading conditions (loading force, frequency and motor process), and the circuit conditions (open/short circuit and load resistance). The scaling laws may provide a more comprehensive and rational optimization strategy for sliding-mode TENG based on multi-parameter analysis and may help to enhance the output performance of the device as either a smart sensor or an energy harvester. A theoretical model for optimizing sliding-mode TENG based on multi-parameter analysis is established to simulate the normalized output performance of sliding-mode TENG in various working conditions. The theoretical results agree very well with experimental data. According to scaling laws between dimensionless output voltage and compound parameters, the optimal combination of all the parameters considered simultaneously could be acquired for the best output voltage, providing a more rational optimization strategy for device design. [Display omitted] •A theoretical approach for optimizing sliding-mode TENG based on multi-parameter analysis is proposed.•The scaling laws may help acquire the optimal combination with all the parameters considered simultaneously.•The output performance may be enhanced by tuning multiple parameters or varying single parameter with the others fixed.