FEBRUARY 22, 2012
The other common source for mechanical energy harvesting is vibration energy. It has been demonstrated that the energy of mechanical vibrations present in floors, stairs, vehicles and equipment housings can be used for electrical power generation. Currently, the majority of experimental vibration harvesters have output power in the range from 10^−6 to 10^−2 W. The reverse electrowetting (REWOD) process can enable the use of novel harvester architectures with greatly increased power output. One example of the REWOD-based vibration harvester device consists of an array of conductive droplets squeezed between two dielectric-coated electrodes, as shown in Figure 4b. The electrodes are separated by a millimeter-thick elastic spacer so that the resulting structure can be used as a mounting 'pad' for the load device. Mechanical vibration of the load device causes periodic change in the solid–liquid contact area and, thus, electrical current generation. For the film stack with a capacitance of 10^2 nF cm−2, the resulting power density can be scaled up to 10^−1 W cm^−2 at 50 Hz vibration frequency, thus enabling the fabrication of practical vibration harvesters with power output of several watts.
The above examples illustrate new possibilities in portable high-power energy harvesting that can be opened by utilizing the REWOD process. High-power energy harvesting can potentially provide a valuable alternative to the use of batteries. Even though energy harvesting is unlikely to completely replace batteries in the majority of mobile applications, it can have a very important role in reducing cost, pollution, and other problems associated with battery use. We believe that the REWOD-based mechanical to electrical energy conversion process, which we have developed, can go a long way in achieving this goal.
(a) Shows energy generated per one oscillation cycle (in units of C0V2 ) as a function of dimensionless parameter ωRC0. The solid line represents equation (1). Experimental data for the droplets between sliding plates are shown in blue, and experimental data for the droplets in a channel are shown in green. The red dot represents the predicted energy for a train of 1,000 droplets. (b) Shows the predicted power for a train of 1,000 droplets as a function of the bias voltage. Calculations are for of a load impedance of 2 KΩ and a film-stack capacitance of 16 nF cm−2. The red curve corresponds to 1-Hertz stride (fast walk) and the blue curve to 0.5-Hertz stride (leisure walk).
How to use Shoe power ?
Alternatively, a Wi-Fi hot spot can be integrated into the harvester to act as a “middleman” between mobile devices and a wireless network. Such an arrangement dramatically reduces power consumption of wireless mobile devices and allows them to operate for much longer time without battery recharge. No direct physical connection between the mobile devices and the harvester unit is required in this case.
Here is a more detailed technical description. The main idea is based on the fact that long-range radio (RF) communication requires much more power to operate as compared to their other functions or to short-range RF communications such as those conforming to Bluetooth standards. The high power required for long-range RF communications leads to accelerated battery discharge in many mobile electronic devices, such as smartphones, laptops with Wide Area Network (WAN) cards, cell phones, etc. Thus substantial decrease in power consumption by these devices can be achieved if their long-range RF transmission is minimized or even completely excluded.