Zheng Jun Chew

Low power adaptive power management with energy aware interface for wireless sensor nodes powered using piezoelectric energy harvesting

A batteryless power management circuit incorporating an energy aware interface (EAI) for wireless sensor nodes (WSNs) powered by piezoelectric energy harvester (PEH) has been proposed and implemented. Traditional power management usually requires two DC-DC converters, each for maximum power point tracking (MPPT) and voltage regulation functionalities. The proposed circuit requires only one DC-DC converter for both the MPPT and voltage regulation. The EAI also provides a means to voltage regulation. This allows the circuit to have higher efficiency as the energy transfer does not have to go through two stages to reach the load. A PEH connected to the proposed circuit was tested under various vibration conditions. The circuit was found to have end-to-end efficiency of about 66% under most of the test conditions.

Microwatt power consumption maximum power point tracking circuit using an analogue differentiator for piezoelectric energy harvesting

A maximum power point tracking (MPPT) scheme by tracking the open-circuit voltage from a piezoelectric energy harvester using a differentiator is presented in this paper. The MPPT controller is implemented by using a low-power analogue differentiator and comparators without the need of a sensing circuitry and a power hungry controller. This proposed MPPT circuit is used to control a buck converter which serves as a power management module in conjunction with a full-wave bridge diode rectifier. Performance of this MPPT control scheme is verified by using the prototyped circuit to track the maximum power point of a macro-fiber composite (MFC) as the piezoelectric energy harvester. The MFC was bonded on a composite material and the whole specimen was subjected to various strain levels at frequency from 10 to 100 Hz. Experimental results showed that the implemented full analogue MPPT controller has a tracking efficiency between 81% and 98.66% independent of the load, and consumes an average power of 3.187 μW at 3 V during operation.

Single Piezoelectric Transducer as Strain Sensor and Energy Harvester Using Time-Multiplexing Operation

This paper presents the implementation of a single piece of macro fiber composite (MFC) piezoelectric transducer as a multifunctional device for both strain sensing and energy harvesting for the first time in the context of an energy harvesting powered wireless sensing system. The multifunction device is achieved via time-multiplexing operation for alternating dynamic strain sensing and energy harvesting functions at different time slots associated with different energy levels, that is, when there is insufficient energy harvested in the energy storage for powering the system, the MFC is used as an energy harvester for charging up the storage capacitor; otherwise, the harvested energy is used for powering the system and the MFC is used as a strain sensor for measuring dynamic structural strain. A circuit is designed and implemented to manage the single piece of MFC as the multifunctional device in a time-multiplexing manner, and the operation is validated by the experimental results. The dynamic strains measured by the MFC in the implemented system match a commercial strain sensor of extensometer by 95.5 to 99.99%, and thus the studied method can be used for autonomous structural health monitoring of dynamic strain.

Airflow energy harvesting with high wind velocities for industrial applications

An airflow energy harvester capable of harvesting energy from vortices at high speed is presented in this paper. The airflow energy harvester is implemented using a modified helical Savonius turbine and an electromagnetic generator. A power management module with maximum power point finding capability is used to manage the harvested energy and convert the low voltage magnitude from the generator to a usable level for wireless sensors. The airflow energy harvester is characterized using vortex generated by air hitting a plate in a wind tunnel. By using an aircraft environment with wind speed of 17 m/s as case study, the output power of the airflow energy harvester is measured to be 126 mW. The overall efficiency of the power management module is 45.76 to 61.2%, with maximum power point tracking efficiency of 94.21 to 99.72% for wind speed of 10 to 18 m/s, and has a quiescent current of 790 nA for the maximum power point tracking circuit.

Poster Abstract: Piezoelectric Energy Harvesting Powered WSN for Aircraft Structural Health Monitoring

In this work, we present the design and prototype of a selfpowered sensor node for the aircraft structural health monitoring. The sensor node is powered by the ambient vibrations generated by the aircraft wings. Sensing devices perform the comprehensive condition monitoring of structures and systems, as well as measurement of environmental parameters, e.g. ambient temperature, ionizing radiation levels, to help operators in assessing the aircraft status at every stage of its mission. With the wireless communication the sensor nodes can be networked with no need for wiring which implies extra weight on board.

Ultra-low-power RADFET sensing circuit for wireless sensor networks powered by energy harvesting

We evaluate an ultra-low-power radiation-sensing circuit based on a radiation sensitive MOSFET (RADFET) for use in Wireless Sensor Networks (WSN) powered by energy harvesting with a special focus on airborne applications. We estimate a worst-case energy budget below 10 μJ per readout cycle superimposed on a constant worst-case power budget below 10 μW. The sensor circuit operates successfully with a wireless sensor node powered by a piezoelectric harvester and power management unit which is able to provide up to 2.5 mW at 10 Hz, 600 με in emulated flight mode.

Combined power extraction with adaptive power management module for increased piezoelectric energy harvesting to power wireless sensor nodes

This paper, for the first time, presents a combined power extraction with adaptive full analogue power management module (PMM) for increased piezoelectric energy harvesting. The PMM is adaptive to variations in the amplitude and frequency of vibration subjected to the piezoelectric strain energy harvester (SEH) and adaptive to different connected electrical loads, where it is used to power up a wireless sensor node (WSN). The combined power extraction circuit and adaptive PMM allow up to 156 % more power to be harvested from the SEH. The combined circuit harvested 0.55 mW at peak-to-peak strain loading of 200 με at 10 Hz. This feature is especially crucial under low frequency and low vibration amplitude conditions as it greatly improves the power generated from the SEH.

A multifunctional device as both strain sensor and energy harvester for structural health monitoring

In the context of wireless sensors (WSs) autonomous in energy, this paper presents a single macro-fiber composite (MFC) piezoelectric transducer which is used for the first time as a multifunctional device as both sensor and energy harvester in a time-multiplexing manner. The MFC is used as an energy harvester to charge up a storage capacitor. When there is sufficient energy, the WS is powered up and the MFC is used as a sensor. A circuit was implemented to harvest energy from the MFC and use the MFC as a sensor. Experiment validation shows that the MFC has an accuracy of up to 97 % as sensor and the circuit harvests energy from the MFC at its maximum power point (MPP) with up to 98 % efficiency.

Energy autonomous wireless sensing system enabled by energy generated during human walking

Recently, there has been a huge amount of work devoted to wearable energy harvesting (WEH) in a bid to establish energy autonomous wireless sensing systems for a range of health monitoring applications. However, limited work has been performed to implement and test such systems in real-world settings. This paper reports the development and real-world characterisation of a magnetically plucked wearable knee-joint energy harvester (Mag-WKEH) powered wireless sensing system, which integrates our latest research progresses in WEH, power conditioning and wireless sensing to achieve high energy efficiency. Experimental results demonstrate that with walking speeds of 3~7 km/h, the Mag-WKEH generates average power of 1.9~4.5 mW with unnoticeable impact on the wearer and is able to power the wireless sensor node (WSN) with three sensors to work at duty cycles of 6.6%~13%. In each active period of 2 s, the WSN is able to measure and transmit 482 readings to the base station.