Remember the story about Bristol University researchers and their idea of harvesting vibration energy? Well, this is the sequel!
The old MEMS element only had a power output of 60μW but the new development goes up to 85μW of energy. The discovery was made public at the 2009 IEEE International Electron Devices Meeting (IEDM 2009).
The MEMS element is made by forming silicon MEMS on a 6-inch silicon wafer and stacking a piezoelectric material on it. The old piezoelectric material was lead zirconate titanate (PZT) but for higher energy output IMEC & TNO used aluminum nitride (AlN) as a piezoelectric material.
The stacking of AlN is three times faster than in the case of stacking PZT mostly because it is not necessary to adjust the ratio of Al and N. By changing the size of the MEMS, the resonance frequency of the element can be adjusted in the range from 150 to 1,200Hz.
Besides all this the new MEMS element was embedded in a temperature sensor capable of transmitting the data wireless. Temperature data is transmitted to the base station every 15 seconds only when vibration with an acceleration of 0.64G and a frequency of 353Hz is detected. The temperature sensor works at 10μW.