The Electrostatic Energy Harvesting Engineering Essay

The Electrostatic Energy pull together Engineering Essaythis news report presents a general idea of the inactive verve garner cheats. Their prevailings principle, harvesting method and basic visualizes exit be expounded. And another two new approaches, 2D qualification reaper and non- smelling(p) vim harvester with rolling cud willing be shown. The 2D life force harvester gouge harvest energy in compulsive directions in a plane. And non-resonant energy harvester with rolling mass shows its low frequence capability. It fag end harvest 0.5 W at 10Hz. Further return of this design may applied to energy harvesting from human be drive.Int magnetic poleuctionGenerally, batteries ar the most reliable former source for electronic devices. It is advocateful, easy to use. However, it can only if provide constant power for a limited period. After that, the batteries have to be changed. Therefore, for those devices that have large measure of number or in inaccessible position. Batteries argon not competent for them. Energy harvesting devices are unmatchable of the attractive options of these exercises. Energy harvesters can harvest energy from different ambient sources such as solar, caloric and shiver. In these cases, solar is not a reliable source, temperature gradients are modest, cycle seems the more abundant, stable and predictable choices.Currently, trinity major methods apply to vibration energy harvesting, electromagnetic, stable and piezoelectric mechanisms. Each technique has its own advantages. get by of articles did research and provided good conclusion on them. 1-3Electrostatic energy harvesting device has the lowest energy harvesting capabilities in these three mechanisms, except it has the most specific advantages. It facilitates CMOS integration 4. That means it can realize self-power incorporated circuits as an on-chip power source. It also environment protects. Unlike piezoelectric and electromagnetic counterparts that require exotic materials. Electrostatic devices are mainly made of silicon.5This paper will focus on the on-line(prenominal) still harvesting research. Its working principle and harvesting carry throughes will be discussed in the first part. about new approaches will also be presented.electrostatic harvesting operate PrincipleThe electrostatic harvesters harness the work d wholeness against the electrostatic deplume of a variable capacity. In other words, the vibrations cause the initiative blank space or lap area of a check plate ocular condenser to go under constant impeach or electric potential condition. This causes the condenser change of parallel plate condenser and produces electrical energy.The fundamental commentary is given by the formula below.C=Q/V (1)Where C is electrical condenser of variable capacitor in farads, Q is the charge on the plate in coulombs and V is the voltage on the plates in voltsC= (A/d) (2)Where A is the overlap area of the plates i n and d is the distance mingled with the plates in m. This equation shows the electrical condenser is proportional to A and inverse proportional to d.(3)E is the work done in joules.If the charge Q is held constant, then V will vary as C changes because of their inverse proportional relationship. and so from, the relation betwixt voltage and capacitor energy is squared rather than linear. As a result, the work done will increase as the C decrease. That provides the harvested energy. connatural thing happens when the voltage V is held constant and Q varies. 1They are known as the voltage-constrained method and charge-constrained method. 6 In the recent applications, the charge-constrained method is more popular over the voltage-constrained method as the voltage-constrained method requires an extra charge reservoir to move on the voltage in a constant value, while the charge-constrained method only requires one. 4For charge constrained system, as shown in material body 1 the en ergy alteration cycle starts as the variable content reaches it maximum Cmax. The charging process is represented by the path from flower A to Point B in figure 1. At point B, the energy stored can be shown as,(4)From point B to point C, an external charge reservoir is attached in rules of order to keep the charge constant. The capacitance is starting diminish as the overlap area A decreases or the distance betwixt the plates d increases. The voltage is inverse proportional to the capacitance which is why the voltage increases in this period. This period is the actual mechanical to electrical conversion period. The energy stored at point C is now,(5)The path from point C to point A is the discharging of the charge on the variable capacitor back into the charge reservoirThe whole process forms a proper energy conversion cycle. And the amount of energy gain is,(6)Usually there is a parallel capacitor is committed parallel with the variable capacitor in order to limit the maximu m voltage that might damage the system during the harvesting. Then the energy equation is becoming,(7) stick out 1. Charge-constrained energy conversion cycle.B. Steps of energy harvestingThe vibration cycle in an electrostatic energy harvester has three steps, pre-charge, harvest and reset. Figure 2.Figure 2. vibration cycle of electrostatic harvester.In the system, the variable capacitor is pre-charged to the battery voltage, and then the capacitor is connected to the battery. The circuit has no current flow at first since the capacitor and battery have same voltage level. But with the separation of the capacitor plates or the decreases of overlap area, the voltage increases with the decrease of capacitance. Charge therefore flows into the batteries and energy is harvested. When the capacitance reaches minimum value, the energy left in the capacitor will be driven back to the batteries and ready for the next cycle.C. Basic DesignsThese three mechanisms in the figure 3 are the thre e basic design structures of the electrostatic harvesters, in-plane overlap converter, in-plane faulting- stopping point converter and out-of-plane gap- ratiocination converter. The in-plane overlap converter varies its capacitance by changing the overlap area between disinvolve fingers the in-plane gap- finale converter varies its capacitance by change the displacement between comb fingers and the out-of-plane gap closing converter varies its capacitance by change the gap between the pith proofread mass and two electrode plates.The most of the current designs of electrostatic harvesters are based on these three basic designs.Figure 3. (a) in-plane overlap converter. (b) in-plane gap-closing converter. (c) out-of-plane gap closing converter.D. Comparison in these three designsYe Mei Lim8 did a get a line on the create energy for these three designs. Firstly the in-plane overlap and in-plane gap closing converters were compared. The Cmax for the one set of comb fingers were 0.1 22pF and the Cmin can be process as zero since the application of silicon nitride nonconductor coating which is a very thin layer of chemical (up to 0.1m) that can electrically assign the electrodes even the plates contacts with each other4. While using the same set of comb fingers, the Cmax were 0.149nF and Cmin were 0.122pF. By applying equation (7), the in-plane overlap converter harvests 1000 times less(prenominal) than in-plane gap closing converter. Then with the simulation of twain in-plane gap closing converter and out-of-plane gap closing converter. The results were found out that the in-plane gap closing mechanism is approximately 1.8 times that of the out-of-plane gap closing mechanism for subvert volumes between 5 and 50.NEW APPRAOCHESA. 2D Electrostatic Harvester approximately of the past electrostatic harvesters are only one degree of unloaddom. They can only harvest energy via one direction of motion. Y. Zhu fabricates a 2 degree of freedom electrostatic transdu cer for energy harvesting with resonance frequencies of 38520 Hz and 38725 Hz. It can scavenge energy in arbitrary directions in a plane with two resonance frequency peaks. Also an ultrasound-based method for powering the device is presented.Y. Zhus design includes a 2 degree of freedom motion mechanism. The unstable mass is coupled with both frames as shown in figure 3 with elastic flexures. This design makes the device be able to detect both movements in X and Y frames and also decouples the X and Y movements of the mass.Figure 4. Two degree of freedom motion mechanism to harvest both direction in-plane vibration energyFigure 5 shows the SEM image of the 2-DOF electrostatic transducer. And table I are the give away parameters of this design. The width difference of X frame and Y frame gives the transducer two different resonance frequencies. The uncreated resonance frequency at 39238 Hz and second at 39266 Hz. That gives a 302 Hz of -10dB bandwidth. It is twice of the 1D reson ator. This device can obtain 10mV through a 1M ohm resistive load and harvest 0.1 nW power. Since this transducer can be power by an unhearable generator of frequency close to its resonance frequency. Since the ultrasonic is relatively safer than other power sources. This design may be expedient for functions in medical environment.Figure 5. SEM image of the 2-DOF electrostatic transducer.Table 1. key parameter of the 2-DOF energy harvesterB. Non-Resonant electrostatic harvester with rolling massM.E.Kiziroglous design 10-11 focuses on maximizing the proof mass. In this design, an external free rolling proof mass is introduced. The mechanical energy is proportional to the proof mass, bigger mass generates more energy. This design is a non-resonant device. This property gives it wider applications.Figure 6. (a) Device structure. (b) Equivalent circuit of the deviceThe Device structure is shown in figure 6(a). Figure (b) is the equivalent circuit of the device. The stainless steel ro d acts as the contact switches and comb finger. When the steel rod is aligned with one of the strip electrodes, it connects with a Cu input Contacts to pre-charge the rod. That generates an electrostatic force between the rod and the strip electrode. That pulls the rod away from the strip electrode and reduces the capacitance at constant charge. The rod then disconnects with the input contact and makes the contact with a discharge electrode. The energy will be transferred as a exalted voltage pulse. The test of the current pattern of this device reveals a capacitance ratio of 4 and demonstrates a voltage gain of 2.4.Later Kiziroglou provides an travel design of that 12. This time the glass substrate is form in a cylindrical shape. Figure 7 is fabrication and optical images of the device. The first prototype is characterised with plate size 1 x 10 mm and SiO2 dielectric thickness of 50 nm. A 10 mm-long, 2.5 mm-diameter steel rod was used. A minimum capacitance of 2 pF and a maximu m of 9 pF are observed. The voltage gain is 3 corresponds to a priming voltage 30V. The power generation is 0.5W when the rod oscillation frequency at 10 Hz. The biggest advantage of this device is the capability of low frequency. That makes the human body motion as a suitable motion sources for it.Figure 7. Fabrication and optical imagesconclusionThe focus of this paper is to present the general idea current achievement of electrostatic energy harvesting. And it gives a related reference for the assembly project. For most of the electrostatic harvester designs, a relatively high resonant frequency comparing with human body motion is need. However, the low frequency capability of the non-resonant energy harvester with rolling mass shows the possibility of the application of this technology in the projects. Additionally, most of the current devices only have one degree of freedom. The 2D energy harvester design can harvest arbitrary directions motion in a plane, which sufficiently i ncreases the power output of device. However, it needs a high frequency. That makes it not suitable for the requirement of the project.