| With the miniaturization of electronic devices,micro-electromechanical systems(MEMS)have been further developed,and the relative power consumption of functional devices has been further reduced.The energy captured and collected by the ambient energy harvester will be sufficient to support the electronics to perform functional tasks without the need to embed conventional power supplies in the sensor system.The current market for miniature energy harvesters includes transportation infrastructure,shared bicycle power,wireless medical equipment,and tire pressure testing.The building automation market is the largest market for current device applications.In the case of building automation,the energy harvester can be combined with sensor components such as sensors,thermostats,and optical switches to form a self-powered system,thereby reducing the production cost of conventional power supply cable routing,improving installation convenience,and reducing daily operations.The electret micro energy harvester has been extensively studied for its good compatibility with MEMS.There are also some problems in the application of the current electret micro energy harvester.For example,the common electret energy harvester is indirect contact between the dielectric material of the electret material and the sensing electrode or the direct contact between the electret and the sensing electrode.And the stability of the electret charge is affected,the use of air as the medium between the column body and the electrode makes the equivalent plate capacitor have a small capacitance,a large capacitive reactance and a small output current.In addition,after researching and comparing the vibrating energy pick-up structures of common electret-based vibration energy harvesters,such as springs or cantilever beams,we found that the elastic recovery structures of these devices are not ideal.At the same time,as a kind of miniature energy harvester,its output parameter has a certain gap with respect to the condition parameters required by the electric device(such as sensor),The energy collected by the energy harvester is limited due to its large output voltage and small current.Conditions cannot directly power the sensor.Therefore,it is necessary to use a power management chip to implement storage management of the collected charge,so as to achieve the power requirement of the power device,andat the same time realize the operations of step-down,voltage regulation,and current increase.In view of the above problems,after analyzing to improve the output power of the device and increase the stability of the device structure,we propose a device structure improvement method for improving the output power of the energy harvester,and design a new device structure to improve the output power of the device.Based on the good elasticity and dielectric constant of the PDMS material,we chose it as the elastic layer between the electret and the electrode in the variable capacitor.The specific work of this paper is as follows:(1)Detailed analysis of the theoretical model of the plate capacitor of the electret energy harvester,and comparative analysis of its electrostatic capacitor structure.It is concluded that the key factor affecting the output power of the energy harvester is the dielectric layer between the electrode and the electret.The initial capacitance of the capacitor structure is different due to the difference in dielectric constant of the dielectric layer,thereby affecting the output power.Based on this we have proposed the use of polydimethylsiloxane(PDMS)as a dielectric layer to replace the air layer.(2)A four-gap energy harvester based on PDMS as an elastic layer was designed and fabricated,and the output data was analyzed.Analysis shows that the output power of the device is increased by nearly 3 times and the output current is increased by about 2.3 times compared to the device using air as the intermediate medium of the energy harvester.The capacitive reactance of the device is reduced by half.At the same time,the output power of the device is negatively correlated with the thickness of the PDMS.The existing experimental results show that the maximum output power can be obtained when the thickness of the PDMS is 50 ?m.When the thickness is 25?m,the output power of the device drops sharply.The reason for the analysis is that the thickness is too small.Makes the elasticity insufficient.(3)Verify the capacitive reactance theory of the device to analyze the influencing factors and experimental results.Theoretical analysis shows that there is an inverse relationship between capacitive reactance and output power.Experiments show that the capacitive reactance of the device is reduced to 1/2 of the air dielectric device after using PDMS material,and the experimental results are in good agreement with the theoretical analysis.(4)To design the distributed energy harvester structure for improving the output power of the device,the output power can be effectively improved by designing therectifier bridges of the energy harvesters in parallel.The experimental results show that the array structure realizes the output current superposition and power multiplication of the device.(5)The output voltage of the energy harvester fluctuates between 20-100 V with the difference of the vibration frequency.The output current at the micro-ampere level limits the application of the device.For this reason,the LTC3588 power management chip is used for charge storage.Regulate the output voltage and current,so that the output voltage is stable between 1.8-2.5V and the output current is up to the milliamp level.The output parameters of the device after power management can be applied to the experiment of powering the wireless transmitting module and lighting the LED lamp bead.The above experiments and results show that the new device structure design improves the output power of the energy harvester and increases the collection efficiency of the energy harvester,laying a foundation for the wide application of the device to wireless sensor devices. |
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