[Show abstract][Hide abstract] ABSTRACT: In this paper, a hybrid of indoor ambient light and thermal energy harvesting scheme that uses only one power management circuit to condition the combined output power harvested from both energy sources is proposed to extend the lifetime of the wireless sensor node. By avoiding the use of individual power management circuits for multiple energy sources, the number of components used in the hybrid energy harvesting (HEH) system is reduced and the system form factor, cost and power losses are thus reduced. An efficient microcontroller-based ultra low power management circuit with fixed voltage reference based maximum power point tracking is implemented with closed-loop voltage feedback control to ensure near maximum power transfer from the two energy sources to its connected electronic load over a wide range of operating conditions. From the experimental test results obtained, an average electrical power of 621 μW is harvested by the optimized HEH system at an average indoor solar irradiance of 1010 lux and a thermal gradient of 10 K, which is almost triple of that can be obtained with conventional single-source thermal energy harvesting method.
IEEE Transactions on Industrial Electronics 10/2011; · 5.17 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The satellite-based remote sensing technique has been widely used in monitoring wildfire spread. There are two prominent drawbacks with this approach of using satellites located in space: (1) very low sampling rate (temporal resolution problem) and (2) lack of accuracy (spatial and spectral resolution problem). To address these challenges, a wireless sensor network deployed at ground level with high-fidelity and low-altitude atmospheric sensing for wind speed of local wildfire spread has been used. An indirect approach in sensing wind speed has been proposed in this paper as an alternative to the bulky conventional wind anemometer to save cost and space. The wind speed is sensed by measuring the equivalent electrical output voltage of the wind turbine generator (WTG). The percentage error in the wind speed measurement using the proposed indirect method is measured to be well within the ±4% limit with respect to wind anemometer accuracy. The same WTG also functions as a wind energy harvesting (WEH) system to convert the available wind energy into electrical energy to sustain the operation of the wireless sensor node. The experimental results show that the designed WEH system is able to harvest an average electrical power of 7.7 mW at an average wind speed of 3.62 m/s for powering the operation of the wireless sensor node that consumes 3.5 mW for predicting the wildfire spread. Based on the sensed wind speed information, the fire control management system determines the spreading condition of the wildfire, and an adequate fire suppression action can be performed by the fire-fighting experts.
IEEE Transactions on Instrumentation and Measurement 05/2011; · 1.36 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In the past few years, various circuit techniques have been proposed to improve the efficiency of piezoelectric energy harvesting, among which the synchronized charge extraction (SCE) circuit has been enthusiastically pursued. In the literature, the SCE technique is claimed to increase the power output of a piezoelectric energy harvester (PEH) by four times based on the assumption that the vibration of the harvester is not affected by the energy harvesting process. Under such assumption, the circuit model of a PEH is usually over-simplified as an ideal current or voltage source with the piezoelectric internal capacitance placed in parallel or in series. In this paper, the applicability of the SCE technique is investigated by electrical simulation. First, a more accurate circuit model of a cantilevered PEH is derived, taking into account the backward electromechanical coupling effect on vibration. Subsequently, the designed SCE circuit is connected with the simplified and the accurate circuit models of the PEH for simulation. The applicability of the SCE circuit for different cases are investigated, including the PEH excited at resonance and off-resonance frequencies as well as the PEH with various degree of electromechanical coupling. The results show that when the coupling of PEH is not negligible, the SCE technique cannot improve or even reduces the efficiency of energy harvesting for the PEH vibrating at resonance. The SCE technique is found applicable for efficiency improvement only for the PEH vibrating at offresonance or with a weak coupling coefficient because of the very minimum of electrical damping effect from the energy harvesting process, in which cases, the simplified and accurate circuit models are approximately equivalent.
[Show abstract][Hide abstract] ABSTRACT: This paper presents an optimized wind energy harvesting (WEH) system that uses a specially designed ultra-low-power-management circuit for sustaining the operation of a wireless sensor node. The proposed power management circuit has two distinct features: 1) an active rectifier using MOSFETs for rectifying the low amplitude ac voltage generated by the wind turbine generator under low wind speed condition efficiently and 2) a dc-dc boost converter with resistor emulation algorithm to perform maximum power point tracking (MPPT) under varying wind-speed conditions. As compared to the conventional diode-bridge rectifier, it is shown that the efficiency of the active rectifier with a low input voltage of 1.2 V has been increased from 40% to 70% due to the significant reduction in the ON-state voltage drop (from 0.6 to 0.15 V) across each pair of MOSFETs used. The proposed robust low-power microcontroller-based resistance emulator is implemented with closed-loop resistance feedback control to ensure close impedance matching between the source and the load, resulting in an efficient power conversion. From the experimental test results obtained, an average electrical power of 7.86 mW is harvested by the optimized WEH system at an average wind speed of 3.62 m/s, which is almost four times higher than the conventional energy harvesting method without using the MPPT.
IEEE Transactions on Power Electronics 01/2011; · 4.08 Impact Factor