Energy Harvesting Powered Wireless Sensor Research Articles

Age of information in energy harvesting dual-sensor status update systems with HARQ-MRC

We consider an energy harvesting powered wireless sensor network consisting of two sensors and one destination, where the sensors with finite-sized batteries harvest energy to transmit the sensed status update to the destination. A two-stage communication model, containing both control data and status update transmissions, is considered. Specifically, the destination first transmits the control data to the sensors using hybrid automatic repeat request with selection combining (HARQ-SC) for allocating wireless resources. Then, trigged by a common controller, the sensors synchronously sense and transmit the same status update to the destination using truncated HARQ with maximal ratio combining (HARQ-MRC). The system is interested in not only the fresh sensed data (e.g., humidity, temperature, moisture content) as the newest data usually carries the most valuable information, but also the steady harvested energy as the battery-powered sensors are energy-limited. We first present the energy state transition diagram by a Markov chain to characterize the energy harvesting model, and then provide the corresponding energy transition matrix as well as the steady-state distribution. Considering both the preemptive and non-preemptive transmissions, we derive the average age of information (AoI) expression as a function of energy arrival probability, update generation probability, and maximum allowable number of transmissions. Simulation results validate the theoretical results and demonstrate that the preemptive and non-preemptive schemes can outperform each other for minimizing the average AoI in different system configurations.

Energy Savvy Network Joining Strategies for Energy Harvesting Powered TSCH Nodes

This article presents methods that enable batteryless energy harvesting powered time-synchronized channel hopping (TSCH) wireless sensor nodes to join a network with less energy wastage. Network joining of TSCH nodes is very power hungry yet inevitable process to form a working wireless sensor network (WSN). Since the energy level from energy harvesting is scarce, energy passive methods are essential. A duty-cycled network joining process in combination with an appropriate capacitor size is proposed here as they are among the factors that can be easily controlled without extra energy. When a node joins the network in a duty-cycled manner, other nodes may join the network during the gap time, which reduces energy wastage of the nodes in waiting. With an appropriate capacitor size, the capacitor can be charged up within a reasonable time and power up the node for a sufficiently long time, which increases the probability to complete the network joining process of the node. With the combination of a join duty cycle of 50% with a 100-mF capacitor, a WSN was successfully formed by two energy harvesting powered wireless sensor nodes in one network joining attempt.

Review of Power Conversion and Energy Management for Low-Power, Low-Voltage Energy Harvesting Powered Wireless Sensors

In this paper, state-of-the-art power electronics and energy management solutions utilized in low-power (less than 5 mW), low-voltage (less than 3 V) energy harvesting powered wireless sensors for Internet of things related applications are detailed. All aspects of an energy harvesting powered sensor system are examined, including the challenges of low-power energy harvesting sources, energy management circuits including power converters and energy storage elements, as well as the impact of wireless sensor pulsed power profiles. In particular, this paper focuses on existing voltage step-up energy management techniques, including the issues of cold-start and maximum power point tracking, as well as energy storage which is necessary for wireless sensor operation. Both academic and commercially available energy harvesting powered systems are examined to provide a comprehensive analysis of existing solutions. Issues that are limiting the current system performance are identified to help define future developments needed to enable efficient and effective energy harvesting powered wireless sensor operation.

Demonstrating the Scope of a Switched Supercapacitor Circuit for Energy Harvesting Powered Wireless Sensor Loads

This paper describes the design of a high-efficiency energy management system for low-power, low-voltage energy harvesting powered wireless sensor systems. With typical voltages of less than 1 V and power levels lower than 1 mW, there are significant challenges when applying energy harvesting sources to supply pulsed power levels of up to 120 mW at voltage levels of 1.8–4 V as required by wireless sensor loads. The proposed approach integrates energy storage elements within a voltage step-up circuit to produce a new high-efficiency energy management circuit that converts the energy produced by a low-power, low-voltage source into a series of high power pulses. An optimized switched supercapacitor energy buffer circuit including a self-powered control circuit is proposed. Efficiencies of up to 91% are shown for an indoor solar cell source with a power level of 0.5 mW, supplying an equivalent wireless sensor with pulsed power levels of 10–120 mW. This is significantly higher than 83% achieved for the dc–dc stage of the existing best solution under the same source conditions, but requires an additional conversion step to provide high power pulses.

Charge-Based Supercapacitor Storage Estimation for Indoor Sub-mW Photovoltaic Energy Harvesting Powered Wireless Sensor Nodes

Supercapacitors offer an attractive energy storage solution for lifetime “fit and forget” photovoltaic (PV) energy harvesting powered wireless sensor nodes for Internet of Things (IoT) applications. Whilst their low storage capacity is not an issue for sub-mW PV applications, energy loss in the charge redistribution process is a concern. Currently, there is no effective method to estimate the storage of the supercapacitor in IoT applications for optimal performance with sub-mW input. The existing energy-based method requires supercapacitor model parameters to be obtained and the initial charge state to be determined, consequently it is not suitable for practical applications. This paper defines a charge-based method, which can directly evaluate supercapacitor's storage with straightforward calculations. Time constant analysis and experimental tests demonstrate that with the newly proposed method, the manufacturer-specified tiny leakage current, although measured long after postcharge (e.g., 72 h), can be directly used, making the storage estimation for a supercapacitor in IoT applications as simple as that for an ordinary capacitor. In addition, the demonstrated tiny leakage current at the required energy storage for a sub-mW PV-powered IoT application enables a supercapacitor alone to be employed as the storage mechanism, thus achieving lifetime battery-replacement-free, self-powered IoT nodes.

Strain Energy Harvesting Powered Wireless Sensor System Using Adaptive and Energy-Aware Interface for Enhanced Performance

This paper presents a wireless sensor system (WSS) powered by a strain energy harvester (SEH) through the introduction of an adaptive and energy-aware interface (EAI) for enhanced performance under variable vibration conditions. The interface is realized by an adaptive power management module for maximum power transfer under different loading conditions and an EAI, which manages the energy flow from the storage capacitor to the WSS for dealing with the mismatch between energy demanded and energy harvested. The focus is to realize high harvested power and high efficiency of the system under variable vibration conditions, and an aircraft wing structure is taken as a study scenario. The SEH powered WSS was tested under different peak-to-peak strain loadings from 300 to 600 με and vibrational frequencies from 2 to 10 Hz to verify the system performance on energy generation and distribution, system efficiency, and capability of powering a custom-developed WSS. Comparative studies of using different circuit configurations with and without the interface were also performed to verify the advantages of the introduced interface. Experimental results showed that under the applied loading of 600 με at 10 Hz, the SEH generates 0.5 mW of power without the interface while having around 670% increase to 3.38 mW with the interface, which highlights the value of the interface. The implemented system has an overall efficiency of 70 to 80%, a long active time of more than 1 s, and duty cycle of up to 11.85% for vibration measurement under all the tested conditions.

Energy-Aware Approaches for Energy Harvesting Powered Wireless Sensor Nodes

Intensive research on energy harvesting powered wireless sensor nodes (WSNs) has been driven by the needs of reducing the power consumption by the WSNs and increasing the power generated by energy harvesters. The mismatch between the energy generated by the harvesters and the energy demanded by the WSNs is always a bottleneck as the ambient environmental energy is limited and time varying. This paper introduces a combined energy-aware interface with an energy-aware program to deal with the mismatch through managing the energy flow from the energy storage capacitor to the WSNs. These two energy-aware approaches were implemented in a custom developed vibration energy harvesting powered WSN. The experimental results show that, with the 3.2-mW power generated by a piezoelectric energy harvester under an emulated aircraft wing strain loading of $600~\mu \varepsilon $ at 10 Hz, the combined energy-aware approaches enable the WSN to have a significantly reduced sleep current from $28.3~\mu \text{A}$ of a commercial WSN to $0.95~\mu \text{A}$ and enable the WSN operations for a long active time of about 1.15 s in every 7.79 s to sample and transmit a large number of data (388 B), rather than a few ten milliseconds and a few bytes, as demanded by vibration measurement. When the approach was not used, the same amount of energy harvested was not able to power the WSN to start, not mentioning to enabling the WSN operation, which highlighted the importance and the value of the energy-aware approaches in enabling energy harvesting powered WSN operation successfully.

How Much Energy Needs for Running Energy Harvesting Powered Wireless Sensor Node?

Abstract There is a big challenge for research and industrial engineers to apply energy harvesting powered wireless sensors for practical applications. This is because wireless sensors is very power hungry while current energy harvesting systems can only harvest very limited energy from the ambient environment. In order for wireless sensors to be operated based on the limited energy harvested, understanding of power consumption of wireless sensors is the first task for implementation of energy harvesting powered wireless sensors systems. In this research an energy consumption model has been introduced for wireless sensor nodes and the power consumption in the life cycle of wireless communication sensors, consisting of JN5148 microcontroller and custom built sensors: a 3-axial accelerometer, a temperature sensor and a light sensor, has been studied. All measurements are based on a custom-built test bed. The power required carrying out a life cycle of wireless sensing and transmission is analysed. This paper describes how to analyse the current consumption of the system in active mode and thus power Consumption for sleeping and deployed sensors mode. The results show how much energy needs to run the energy harvesting powered wireless sensor node with JN5148 microcontroller.

Strain Energy Harvesting Powered Wireless Sensor Node for Aircraft Structural Health Monitoring

This paper presents a wireless sensor node (WSN) powered by a strain energy harvester (SEH) through an adaptive power management module (PMM) for aircraft structural health monitoring (SHM). The energy distribution in the system, the efficiencies of the whole systems, and the WSN powering capability of the SEH under different strain loadings were studied to understand the developed system performance for practical applications of an autonomous WSN. Experimental results show that the SEH is able to produce up to 3.34 mW under strain loading of 600 μɛ at 10 Hz. The WSN can be powered up through the adaptive PMM at efficiency from 70 to 80% under different test conditions.

Super-capacitor and Thin Film Battery Hybrid Energy Storage for Energy Harvesting Applications

This paper presents the design of hybrid energy storage unit (HESU) for energy harvesting applications using super-capacitor and thin film battery (TFB). The power management circuits of this hybrid energy storage unit are proposed to perform "smart" charge/discharge control in order to optimize the HESU from the perspectives of energy loss due to leakage current and equivalent series resistance (ESR). This paper shows the characterizations of ESUs for energy harvesting powered wireless sensor networks (WSN) applications. A new design of power management circuits is proposed in order to utilize the low ESR characteristics of super-capacitor and the low leakage current characteristics of the TFB in the hybrid energy storage. The average power loss due to leakage current is measured at 38μW in the proposed system. When Compared to the super-capacitor energy storage with the similar capacity, the proposed hybrid energy storage unit reduces the leakage power by approximately 45% whilst maintains a similar (<100 mΩ) ESR.