Investigation of Self-Powered IoT Sensor Nodes for Harvesting Hybrid Indoor Ambient Light and Heat Energy.

Sensor nodes are critical components of the Internet of Things (IoT). Traditional IoT sensor nodes are typically powered by disposable batteries, making it difficult to meet the requirements for long lifetime, miniaturization, and zero maintenance. Hybrid energy systems that integrate energy harvesting, storage, and management are expected to provide a new power source for IoT sensor nodes. This research describes an integrated cube-shaped photovoltaic (PV) and thermal hybrid energy-harvesting system that can be utilized to power IoT sensor nodes with active RFID tags. The indoor light energy was harvested using 5-sided PV cells, which could generate 3 times more energy than most current studies using single-sided PV cells. In addition, two vertically stacked thermoelectrical generators (TEG) with a heat sink were utilized to harvest thermal energy. Compared to one TEG, the harvested power was improved by more than 219.48%. In addition, an energy management module with a semi-active configuration was designed to manage the energy stored by the Li-ion battery and supercapacitor (SC). Finally, the system was integrated into a 44 mm × 44 mm × 40 mm cube. The experimental results showed that the system was able to generate a power output of 192.48 µW using indoor ambient light and the heat from a computer adapter. Furthermore, the system was capable of providing stable and continuous power for an IoT sensor node used for monitoring indoor temperature over a prolonged period.

Design and Fabrication of Interdigital Supercapacitors as Force/Acceleration Sensors.

The integrated device for energy supply and sensing (IDESS) is a potential candidate for relieving the energy and space burdens caused by the rising integration degrees of microsystems. In this article, we propose a force sensor based on an interdigital supercapacitor (IDTSC). The capacitance and internal resistance of the IDTSC change under external loads, resulting in a transient current fluctuation at a constant bias voltage, which can be used to sense external force/acceleration. The IDTSC showed a specific energy and specific power of 4.16 Wh/kg and 22.26 W/kg (at 0.1 A/g), respectively, which could maintain an essential energy supply. According to the simulation analysis, the designed IDTSC's current response exhibited good linearity with the external force. In addition, benefiting from its light weight and the applied gel electrolytes, the IDTSC showed good high-g impact sensing performance (from 9.9 × 103× g to 3.2 × 104× g). This work demonstrated the feasibility of realizing an integrated energy supply and force-sensing device by empowering energy storage devices with sensing capabilities.

Recent Progress in Self-Powered Skin Sensors.

Self-powered skin sensors have attracted significant attention in recent years due to their great potential in medical care, robotics, prosthetics, and sports. More importantly, self-powered skin sensors do not need any energy-supply components like batteries, which allows them to work sustainably and saves them the trouble of replacement of batteries. The self-powered skin sensors are mainly based on energy harvesters, with the device itself generating electrical signals when triggered by the detected stimulus or analyte, such as body motion, touch/pressure, acoustic sound, and chemicals in sweat. Herein, the recent research achievements of self-powered skin sensors are comprehensively and systematically reviewed. According to the different monitoring signals, the self-powered skin sensors are summarized and discussed with a focus on the working mechanism, device structure, and the sensing principle. Based on the recent progress, the key challenges that exist and the opportunities that lie ahead are also discussed.

A Self-Powered Insole for Human Motion Recognition.

Biomechanical energy harvesting is a feasible solution for powering wearable sensors by directly driving electronics or acting as wearable self-powered sensors. A wearable insole that not only can harvest energy from foot pressure during walking but also can serve as a self-powered human motion recognition sensor is reported. The insole is designed as a sandwich structure consisting of two wavy silica gel film separated by a flexible piezoelectric foil stave, which has higher performance compared with conventional piezoelectric harvesters with cantilever structure. The energy harvesting insole is capable of driving some common electronics by scavenging energy from human walking. Moreover, it can be used to recognize human motion as the waveforms it generates change when people are in different locomotion modes. It is demonstrated that different types of human motion such as walking and running are clearly classified by the insole without any external power source. This work not only expands the applications of piezoelectric energy harvesters for wearable power supplies and self-powered sensors, but also provides possible approaches for wearable self-powered human motion monitoring that is of great importance in many fields such as rehabilitation and sports science.

Comparison between electrochemical ELISA and spectrophotometric ELISA for the detection of dentine sialophosphoprotein for root resorption.

INTRODUCTION: Root resorption is an undesirable sequela of orthodontic treatment. It is necessary to establish sensitive methods for identification of teeth at risk for resorption. The x-ray is the traditional method to diagnose root resorption, which is often at a late stage. Some researchers used enzyme-linked immunosorbent immunoassay (ELISA) combined with spectrophotometry to study some biochemical markers of root resorption. However, spectrophotometric detection often has a poor detection limit. Electrochemical detection has inherent advantages over spectrophotometric detection, which is especially suitable for small biologic samples. METHODS: We used ELISA combined with electrochemistry and ELISA combined with spectrophotometry to measure the biochemical marker dentine sialophosphoprotein in gingival crevicular fluid of orthodontic patients (treated for 8-12 months). RESULTS: Standard dentine sialophosphoprotein was used to calculate the linear regression equation. No significant difference was found between the electrochemical outcome and the spectrophotometric outcome. But the electrochemical results extended the lower end of detection from 5 pg per milliliter (by spectrophotometry) to 0.5 pg per milliliter. CONCLUSIONS: These results showed that ELISA combined with electrochemistry is a reliable and sensitive method to detect dentine sialophosphoprotein in gingival crevicular fluid.

Self-Supporting, Binder-Free, and Flexible Ti3C2Tx MXene-Based Supercapacitor Electrode with Improved Electrochemical Performance.

MXenes have shown great potential for supercapacitor electrodes due to their unique characteristics, but simultaneously achieving high capacitance, rate capability, and cyclic stability along with good mechanical flexibility is exceptionally challenging. Here, highly enhanced capacitance, rate capability, and cyclic stability, as well as good mechanical flexibility for T3C2Tx MXene-based supercapacitor electrodes are simultaneously obtained by engineering the electrode structure, modifying the surface chemistry, and optimizing the fabrication process via an optimized integration approach. This approach combines and more importantly optimizes three methods that all require a calcination process: carbonizing in situ grown polymer ("Cpolymer") on the MXene, alkali treatment ("A"), and template sacrificing ("P"); and the optimized processes lead to more abundant active sites, faster ion accessibility, better chemical stability, and good mechanical flexibility. The obtained P-MXene/Cpolymer-A electrodes are binder-free and self-supporting and not only have good mechanical flexibility but also demonstrate much larger capacitances and better rate performance than the pristine MXene electrode. Specifically, the P-MXene/CPAQ-A electrode (PAQ: quinone-amine polymer) achieves a high capacitance of 532.9 F g-1 at 5 mV s-1, together with superior rate performance and improved cyclic stability (97.1% capacitance retention after 40 000 cycles at 20 A g-1) compared with the pristine MXene (79.6% retention) and P-MXene-A (77.3% retention) electrodes. In addition, it is discovered that carbonizing in situ grown polymers can variously remove the -F group and the removal effect can be accumulated with that by the alkali treatment.

Flexible temperature sensors based on carbon nanomaterials.

Flexible temperature sensors can be attached to the surface of human skin or curved surfaces directly for continuous and stable data measurements, and have attracted extensive attention in myriad areas. Carbon nanomaterials possess great potential for temperature sensing, and flexible temperature sensors based on carbon nanomaterials have demonstrated unique advantages such as high sensitivity, fast response, good mechanical adaptability, low-cost fabrication processes, high cycling stability and reliability. In this review, the working mechanisms, device structures, material compositions, fabrication technologies, temperature sensing properties, the crucial roles of carbon nanomaterials, specific advantages and existing limitations of different types of flexible temperature sensors based on carbon nanomaterials are comprehensively elaborated and discussed. Based on recent advances, conclusions are made and challenges as well as future perspectives are systematically outlined and discussed.

Harvesting Ambient Vibration Energy over a Wide Frequency Range for Self-Powered Electronics.

Vibration is one of the most common energy sources in ambient environment. Harvesting vibration energy is a promising route to sustainably drive small electronics. This work introduces an approach to scavenge vibrational energy over a wide frequency range as an exclusive power source for continuous operation of electronics. An elastic multiunit triboelectric nanogenerator (TENG) is rationally designed to efficiently harvest low-frequency vibration energy, which can provide a maximum instantaneous output power density of 102 W·m-3 at as low as 7 Hz and maintain its stable current outputs from 5 to 25 Hz. A self-charging power unit (SCPU) combining the TENG and a 10 mF supercapacitor gives a continuous direct current (DC) power delivery of 1.14 mW at a power management efficiency of 45.6% at 20 Hz. The performance of the SCPU can be further enhanced by a specially designed power management circuit, with a continuous DC power of 2 mW and power management efficiency of 60% at 7 Hz. Electronics such as a thermometer, hygrometer, and speedometer can be sustainably powered solely by the harvested vibration energy from a machine or riding bicycle. This approach has potential applications in self-powered systems for environment monitoring, machine safety, and transportation.

Voltage Fluctuation in a Supercapacitor During a High-g Impact.

Supercapacitors (SCs) are a type of energy storage device with high power density and long lifecycles. They have widespread applications, such as powering electric vehicles and micro scale devices. Working stability is one of the most important properties of SCs, and it is of significant importance to investigate the operational characteristics of SCs working under extreme conditions, particularly during high-g acceleration. In this paper, the failure mechanism of SCs upon high-g impact is thoroughly studied. Through an analysis of the intrinsic reaction mechanism during the high-g impact, a multi-faceted physics model is established. Additionally, a multi-field coupled kinetics simulation of the SC failure during a high-g impact is presented. Experimental tests are conducted that confirm the validity of the proposed model. The key factors of failure, such as discharge currents and discharging levels, are analyzed and discussed. Finally, a possible design is proposed to avoid the failure of SCs upon high-g impact.

A highly shape-adaptive, stretchable design based on conductive liquid for energy harvesting and self-powered biomechanical monitoring.

The rapid growth of deformable and stretchable electronics calls for a deformable and stretchable power source. We report a scalable approach for energy harvesters and self-powered sensors that can be highly deformable and stretchable. With conductive liquid contained in a polymer cover, a shape-adaptive triboelectric nanogenerator (saTENG) unit can effectively harvest energy in various working modes. The saTENG can maintain its performance under a strain of as large as 300%. The saTENG is so flexible that it can be conformed to any three-dimensional and curvilinear surface. We demonstrate applications of the saTENG as a wearable power source and self-powered sensor to monitor biomechanical motion. A bracelet-like saTENG worn on the wrist can light up more than 80 light-emitting diodes. Owing to the highly scalable manufacturing process, the saTENG can be easily applied for large-area energy harvesting. In addition, the saTENG can be extended to extract energy from mechanical motion using flowing water as the electrode. This approach provides a new prospect for deformable and stretchable power sources, as well as self-powered sensors, and has potential applications in various areas such as robotics, biomechanics, physiology, kinesiology, and entertainment.