Self-powered Sensor System Research Articles

High performance piezotronic logic nanodevices based on GaN/InN/GaN topological insulator

Piezotronics and piezo-phototronics have received increasing attention in flexible energy-harvesting devices, self-powered sensor systems utilizing piezoelectric semiconductor materials, such as ZnO, GaN and monolayer MoS2. Piezoelectric potentials induced by the externally applied strain can effectively control the generation, recombination and transport of the charge carriers for achieving high-performance devices. In this study, we describe the piezotronics effect on the GaN/InN/GaN quantum well, which can induce performances resembling those of topological insulators by a piezoelectric field polarized under the externally applied mechanical strain. The transport properties of bulk and edge states of this quantum well device have been investigated by calculating the electron density distribution under different widths of the quantum point contact (QPC), which is the origin of more conductance plateaus. In addition, we postulate the mechanical-electronic logic operation mechanisms based on the piezotronics effect adjusting the transport of edge states in the quantum well device. Fundamental logic units such as NOT, NAND and NOR gates have been innovatively designed for performing the logic computation functions from external mechanical stimuli. The logic nanodevices based on the topological insulator have near zero-power consumption and ultrahigh ON/OFF ratio. This work provides a deep insight into the piezotronics effect on the transport of bulk and edge states of the quantum well device, and offers novel solutions to design high-performance low-power mechanical-electronic logic devices.

Self-Powered Wind Sensor System for Detecting Wind Speed and Direction Based on a Triboelectric Nanogenerator

The development of the Internet of Things has brought new challenges to the corresponding distributed sensor systems. Self-powered sensors that can perceive and respond to environmental stimuli without an external power supply are highly desirable. In this paper, a self-powered wind sensor system based on an anemometer triboelectric nanogenerator (a-TENG, free-standing mode) and a wind vane triboelectric nanogenerator (v-TENG, single-electrode mode) is proposed for simultaneously detecting wind speed and direction. A soft friction mode is adopted instead of a typical rigid friction for largely enhancing the output performance of the TENG. The design parameters including size, unit central angle, and applied materials are optimized to enhance sensitivity, resolution, and wide measurement scale. The optimized a-TENG could deliver an open-circuit voltage of 88 V and short-circuit current of 6.3 μA, corresponding to a maximum power output of 0.47 mW (wind speed of 6.0 m/s), which is capable of driving electronics for data transmission and storage. The current peak value of the a-TENG signal is used for analyzing wind speed for less energy consumption. Moreover, the output characteristics of a v-TENG are further explored, with six actual operation situations, and the v-TENG delivers fast response to the incoming wind and accurately outputs the wind direction data. As a wind sensor system, wind speed ranging from 2.7 to 8.0 m/s can be well detected (consistent with a commercial sensor) and eight regular directions can be monitored. Therefore, the fabricated wind sensor system has great potential in wireless environmental monitoring applications.

Self-Powered Wireless Sensor Network for Automated Corrosion Prediction of Steel Reinforcement

Corrosion is one of the key issues that affect the service life and hinders wide application of steel reinforcement. Moreover, corrosion is a long-term process and not visible for embedded reinforcement. Thus, this research aims at developing a self-powered smart sensor system with integrated innovative prediction module for forecasting corrosion process of embedded steel reinforcement. Vibration-based energy harvester is used to harvest energy for continuous corrosion data collection. Spatial interpolation module was developed to interpolate corrosion data at unmonitored locations. Dynamic prediction module is used to predict the long-term corrosion based on collected data. Utilizing this new sensor network, the corrosion process can be automated predicted and appropriate mitigation actions will be recommended accordingly.

On-Skin Triboelectric Nanogenerator and Self-Powered Sensor with Ultrathin Thickness and High Stretchability.

Researchers have devoted a lot of efforts on pursuing light weight and high flexibility for the wearable electronics, which also requires the related energy harvesting devices to have ultrathin thickness and high stretchability. Hence, an elastic triboelectric nanogenerator (TENG) is proposed that can serve as the second skin on human body. The total thickness of this TENG is about 102 µm and the device can work durably under a strain of 100%. The carbon grease is painted on the surface of elastomer film to work as stretchable electrode and thus the fine geometry control of the electrode can be achieved. This elastic TENG can even work on the human fingers without disturbing body movement. The open-circuit voltage and short-circuit current from the device with a contact area of 9 cm2 can reach 115 V and 3 µA, respectively. Two kinds of self-powered sensor systems with optimized identification strategies are also designed to demonstrate the application possibility of this elastic TENG. The superior characteristics of ultrathin thickness, high stretchability, and fine geometry control of this TENG can promote many potential applications in the field of wearable self-powered sensory system, electronics skin, artificial muscles, and soft robotics.

Enhanced self-powered UV photoresponse of ferroelectric BaTiO3 materials by pyroelectric effect

ABSTRCT Ferroelectric material BaTiO 3 (BTO) with intrinsic spontaneous polarization demonstrates excellent pyroelectric effect that output current/voltage signals can be observed even by slight temperature fluctuation. Here, we report a self-powered 365 nm UV light photodetector by using the light-induced pyroelectric effect in Ag/BTO/Ag device with the response time of about 0.5 s at the rising edge. Moreover, the heating-induced pyroelectric effect has been utilized to enhance the 365 nm light response, where both the corresponding photoconductive gain and responsivity can be dramatically enhanced by larger than 1200% under a temperature variation rate of 2.1 K/s as compared with that of UV light illumination. Our study proposes a feasible method to enhance the 365 nm light response by coupling light and heating-induced pyroelectric effect in BTO, which has potential applications in thermal energy scavenging and self-powered sensor systems.

Self-Powered Viscosity and Pressure Sensing in Microfluidic Systems Based on the Piezoelectric Energy Harvesting of Flowing Droplets.

The rapid development of microscaled piezoelectric energy harvesters has provided a simple and highly efficient way for building self-powered sensor systems through harvesting the mechanical energy from the ambient environment. In this work, a self-powered microfluidic sensor that can harvest the mechanical energy of the fluid and simultaneously monitor their characteristics was fabricated by integrating the flexible piezoelectric poly(vinylidene fluoride) (PVDF) nanofibers with the well-designed microfluidic chips. Those devices could generate open-circuit high output voltage up to 1.8 V when a droplet of water is flowing past the suspended PVDF nanofibers and result in their periodical deformations. The impulsive output voltage signal allowed them to be utilized for droplets or bubbles counting in the microfluidic systems. Furthermore, the devices also exhibited self-powered sensing behavior due to the decreased voltage amplitude with increasing input pressure and liquid viscosity. The drop of output voltage could be attributed to the variation of flow condition and velocity of the droplets, leading to the reduced deformation of the piezoelectric PVDF layer and the decrease of the generated piezoelectric potential.

EHDC: An Energy Harvesting Modeling and Profiling Platform for Body Sensor Networks.

Energy harvesting is a promising solution to the limited battery lifetimes of body sensor nodes. Self-powered sensor systems capable of quasi-perpetual operation enable the possibility of truly continuous monitoring of patients beyond the clinic. However, the discontinuous and dynamic characteristics of harvesting in real-world scenarios-and their implications for the design and operation of self-powered systems-are not yet well understood. This paper presents a mobile energy harvesting and data collection (EHDC) platform designed to provide a deeper understanding of energy harvesting dynamics. The EHDC platform monitors and records the instantaneous usable power generated by body-worn harvesters, while also collecting human activity and environmental data to provide a comprehensive real-world evaluation of two energy harvesting modalities common to body sensor networks: solar and thermoelectric. The platform was initially validated with benchtop tests and later with real-world deployments on two subjects. 7-h-long multimodal energy harvesting profiles were generated, and the environmental and behavioral data were used to expand upon previously developed Kalman filter based mathematical models for energy harvesting prediction. Results confirm the validity of the EHDC platform and harvesting models, establishing the potential for longer term monitoring of energy harvesting characteristics; thus, informing the design and operation of self-powered body sensor networks.

Packaging of Small-Scale Thermoelectric Generators for Autonomous Sensor Nodes

This paper focuses on packaging of small-scale thermoelectric generators (TEGs) for energy harvesting applications in sensor nodes for industry 4.0 and for the Internet of Things. The TEGs are suitable to enable self-powered sensor systems with unlimited energy lifetime, but they have to withstand high mechanical loads during the assembly and packaging process and further stress due to the mismatch of the coefficient of thermal expansion of the different materials. Devices with different underfills (UFs) and stress decoupling thermal adhesives were evaluated with a shear force test apparatus and a four-line bending test together. In addition to these mechanical tests, the thermal influence of the UF on the system performance was investigated with measurements, finite element method, and computational fluid dynamics simulations. The shear force per area could be enhanced up to the factor of two by using capillary UF. All TEGs with and without UFs passed the reliability investigations without any electrical defects. All TEGs with UF passed the given quality criteria with the four-line bending test. With some of the stress decoupling thermal adhesives, the TEGs could withstand the loads without UF. The simulation model was evaluated with a measurement setup, and the differences between the simulation model and the measurements concerning the temperature difference of the TEGs were in an acceptable range (<21%). Furthermore, the influence of the UF on the temperature difference of the TEGs in the given measurement scenario was smaller than 15%, which makes the application of a UF a realistic approach.

Self-powered wireless sensor system application for cutting process con-trol

In the article a self-powered wireless sensor used for milling operation control is presented. Source of vibrations suitable for energy harvesting and generation has been accurately identified, experimental work on CNC machine performed and was determined that the highest amplitude vibrations for the milling tool are present during its tooth contact with the workpiece. During investigation it was determined that based on feed rate and number of teeth on the cutter, the frequency of tooth contact with workpiece is in the range of 150 – 300 Hz, based on that a piezoelectric cantilever with natural frequency falling within this frequency range scope has been chosen. In order to increase the efficiency of energy generation by the piezoelectric transducer adjustment of its natural frequency by adding proof mass for course control and connection of piezoelectric layers for fine tunning has been proposed. Proposed energy generation, storage and wireless signal representing tool condition transmition circuit for the device. Experiments were performed, that allowed to record milling tool‘s wear during machining and evaluate energy generation dependence on set milling parameters. Designed and validated prototype device is suitable for control of milling process and can be efectivelly used to increase milling accuracy of thin-walled workpieces. DOI: http://dx.doi.org/10.5755/j01.mech.23.3.17957

Effective energy storage from a hybridized electromagnetic-triboelectric nanogenerator

We report a hybridized electromagnetic-triboelectric nanogenerator including an electromagnetic generator (EMG) and a triboelectric nanogenerator (TENG) for simultaneously scavenging wind energy. The TENG can deliver a largest output power of about 1.7mW under a loading resistance of 10MΩ, while the EMG can deliver a largest output power of about 2.5mW under a loading resistance of 1kΩ. A power management circuit has been designed to store the produced energy from the TENG into a capacitor, resulting in the enhanced energy-storage efficiency of up to 112% as compared with that of using a traditional rectifier. The charging rate of the capacitor by using the TENG has been optimized by changing the inductance and the switching on/off time. As compared with the individual TENG or EMG, the hybridized nanogenerator has a much better ability for sustainably powering a temperature sensor, exhibiting the potential applications of hybridized nanogenerators in self-powered sensor systems.

Enhanced P3HT/ZnO Nanowire Array Solar Cells by Pyro-phototronic Effect.

The pyro-phototronic effect is based on the coupling among photoexcitation, pyroelectricity, and semiconductor charge transport in pyroelectric materials, which can be utilized to modulate photoexcited carriers to enhance the output performance of solar cells. Herein, we have demonstrated the largely enhanced output performance of a P3HT/ZnO nanowire array photovoltaic cell (PVC) by using the pyro-phototronic effect under weak light illuminations. By applying an external cooling temperature variation, the output current and voltage of the PVC can be dramatically enhanced by 18% and 152% under indoor light illumination, respectively. This study realizes the performance enhancement of pyroelectric semiconductor materials-based solar cells via a temperature-variation-induced pyro-phototronic effect, which may have potential applications in solar energy scavenging and self-powered sensor systems.

Development of a Nonlinear Piezoelectric Energy Harvester for Alternating Air Load

The demand for energy-harvesting technology is steadily growing in the field of self-powered wireless sensor systems for use in pneumatic systems. The purpose of this research was to study an energy harvester excited by alternating air load in a pneumatic system. The harvester was designed to consist of a power chamber and a compressed chamber, and to the bottom of the power chamber a piezoelectric patch as been affixed. The harvester is excited by the changing pressure, which can be adjusted through changing volume, and the alternating air pressure energy can be harvested through the deformation of the piezoelectric patch. A test system was built and a prototype device was tested under various experimental conditions. The test results show that the energy generation performance of the harvester can be influenced by varying the volume compression parameters, with the output voltage increasing when the flow increases. The maximal output voltage and power are 24.7 V and 1.06 mW, respectively. An effective power of 0.28 mW was measured across the 200 kΩ resistor at a pressure of 200 kPa and a cycle time of 2.5 s with a flow of 150 L/min.

A durable and stable piezoelectric nanogenerator with nanocomposite nanofibers embedded in an elastomer under high loading for a self-powered sensor system

Abstract Practical usage of piezoelectric nanogenerators (PENGs) under heavy loading environments for high power generation, such as smart shoes, has been limited due to the low mechanical endurance of many piezoelectric materials. Durability and performance under harsh environments are a stumbling block for the practical application of PENGs. Synthesis of piezoelectrically enhanced nanofibers electrospun from nanocomposite of barium titanate nanoparticles (BT NPs) dispersed in poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) enables successful fabrication of a robust, efficient, flexible and lead-free PENG. A nanofiber PENG (nf-PENG) fabricated by embedding nanocomposite nanofibers in an elastomer film is demonstrated for biomechanical energy harvesting and storage during walking. When placed inside of a shoe, a nf-PENG loaded with 15 wt% BT NPs can generate an output of 25 V at a walking frequency of 0.6 Hz with high mechanical durability under very high loads (600 N). This can charge a 4.7 µF capacitor after approximately 72 steps. The stored charge can operate a strain sensor without any external power supply. The high performance of the nf-PENG is mainly attributed to the self-poled nanocomposite nanofibers. Additionally, embedding the nanofibers into an elastomer provided high durability by protecting the nanofibers from mechanical damage. Furthermore, the devices small form factor, flexibility, and transparency make this nf-PENG suitable for applications in wearable electronics, where aesthetics and comfort are also desired (in addition to performance). This work demonstrates the possibility of highly durable, efficient, and self-powered wearable sensing systems that can work under extreme environments.

A Shared-Electrode-Based Hybridized Electromagnetic-Triboelectric Nanogenerator.

Integration of electromagnetic generators (EMGs) and triboelectric nanogenerators (TENGs) can increase the total energy conversion efficiency from one mechanical motion by connecting the two devices in parallel after using power management circuits. A critical issue is how to realize the integration of the EMG and TENG in the same current circuits. Here, a hybridized nanogenerator, including an EMG and a TENG with the same set of electrodes, has been utilized to simultaneously scavenge mechanical energy. The hybridized nanogenerator can deliver a high output current of about 3.8 mA and a high output voltage of about 245 V when the switch in the device circuit was turned on and off, respectively. A acceleration sensor can be achieved by using the hybridized nanogenerator, where the detection sensitivities are about 143.2 V/(m/s(2)) for TENG and 291.7 μA/(m/s(2)) for EMG. The fabricated hybridized nanogenerator may have practical use for scavenging mechanical energy and self-powered acceleration sensor systems.

Piezoelectric Active Humidity Sensors Based on Lead-Free NaNbO₃ Piezoelectric Nanofibers.

The development of micro-/nano-scaled energy harvesters and the self-powered sensor system has attracted great attention due to the miniaturization and integration of the micro-device. In this work, lead-free NaNbO3 piezoelectric nanofibers with a monoclinic perovskite structure were synthesized by the far-field electrospinning method. The flexible active humidity sensors were fabricated by transferring the nanofibers from silicon to a soft polymer substrate. The sensors exhibited outstanding piezoelectric energy-harvesting performance with output voltage up to 2 V during the vibration process. The output voltage generated by the NaNbO3 sensors exhibited a negative correlation with the environmental humidity varying from 5% to 80%, where the peak-to-peak value of the output voltage generated by the sensors decreased from 0.40 to 0.07 V. The sensor also exhibited a short response time, good selectively against ethanol steam, and great temperature stability. The piezoelectric active humidity sensing property could be attributed to the increased leakage current in the NaNbO3 nanofibers, which was generated due to proton hopping among the H3O+ groups in the absorbed H2O layers under the driving force of the piezoelectric potential.

A novel energy conversion method based on hydrogel material for self-powered sensor system applications

In this paper, a novel energy conversion method based on hydrogel material for self-powered sensor system applications is proposed, which can harvest energy from environment vibrations and supply power to sensors without any external power source. In this approach, hemispherical hydrogel arrays are positioned between two parallel-arranged conductive plates. The deformation of hydrogel arrays caused by ambient vibrations will result in non-equilibrium charge distribution in the conductive plates. The charge redistribution leads to electrons transfer, thereby converting mechanical vibration energy into electricity. Based on this energy conversion principle, a hydrogel-based energy harvester is fabricated and experimentally characterized. The fabricated device exhibits a superwide working bandwidth (0–80Hz) and high reliability in power generation. Moreover, favorable adaptability of the tilt angle during installation is achieved. In the feasibility experiment, an LCD screen is operated to verify the potential of the hydrogel-based energy conversion method to self-powered sensor applications under vibration environment. Finally, a visualized self-powered force sensor is also demonstrated with the fabricated hydrogel-based energy harvester, which proves its great potential in various application fields.

Integrated active sensor system for real time vibration monitoring.

We report a self-powered, lightweight and cost-effective active sensor system for vibration monitoring with multiplexed operation based on contact electrification between sensor and detected objects. The as-fabricated sensor matrix is capable of monitoring and mapping the vibration state of large amounts of units. The monitoring contents include: on-off state, vibration frequency and vibration amplitude of each unit. The active sensor system delivers a detection range of 0–60 Hz, high accuracy (relative error below 0.42%), long-term stability (10000 cycles). On the time dimension, the sensor can provide the vibration process memory by recording the outputs of the sensor system in an extend period of time. Besides, the developed sensor system can realize detection under contact mode and non-contact mode. Its high performance is not sensitive to the shape or the conductivity of the detected object. With these features, the active sensor system has great potential in automatic control, remote operation, surveillance and security systems.

A Streaming Potential/Current-Based Microfluidic Direct Current Generator for Self-Powered Nanosystems.

A simple but practical method to convert the hydroenergy of microfluids into continuous electrical output is reported. Based on the principle of streaming potential/current, a microfluidic generator (MFG) is demonstrated using patterned micropillar arrays as a quasi-porous flow channel. The continuous electrical output makes this MFG particularly suitable as a power source in self-powered systems. Using the proposed MFG to power a single nanowire-based pH sensor, a self-powered fluid sensor system is demonstrated.

Transparent Stretchable Self-Powered Patchable Sensor Platform with Ultrasensitive Recognition of Human Activities.

Monitoring of human activities can provide clinically relevant information pertaining to disease diagnostics, preventive medicine, care for patients with chronic diseases, rehabilitation, and prosthetics. The recognition of strains on human skin, induced by subtle movements of muscles in the internal organs, such as the esophagus and trachea, and the motion of joints, was demonstrated using a self-powered patchable strain sensor platform, composed on multifunctional nanocomposites of low-density silver nanowires with a conductive elastomer of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate/polyurethane, with high sensitivity, stretchability, and optical transparency. The ultra-low-power consumption of the sensor, integrated with both a supercapacitor and a triboelectric nanogenerator into a single transparent stretchable platform based on the same nanocomposites, results in a self-powered monitoring system for skin strain. The capability of the sensor to recognize a wide range of strain on skin has the potential for use in new areas of invisible stretchable electronics for human monitoring. A new type of transparent, stretchable, and ultrasensitive strain sensor based on a AgNW/PEDOT:PSS/PU nanocomposite was developed. The concept of a self-powered patchable sensor system integrated with a supercapacitor and a triboelectric nanogenerator that can be used universally as an autonomous invisible sensor system was used to detect the wide range of strain on human skin.

Enhanced performance of triboelectric nanogenerators integrated with ZnO nanowires.

We report a hybrid nanogenerator matrix integrated with ZnO nanowires (NWs) for the use of combined triboelectric and piezoelectric features, where the ZnO NWs are grown on bottom electrodes via a hydrothermal method. Along with structural properties analyzed by scanning electron microscopy, the hybrid nanogenerator displayed an output power density of 0.21 mW/cm2, which was higher than that of the triboelectric nanogenerator without NWs. Therefore, our approach can allow for the enhancement of electrical output, with a view toward the realization of functional and self-powered devices of high performance in portable electronics, such as power source and electric self-powered sensor systems.