The maximum output of the MEMS energy harvester was just under 500 microWatts at its natural resonant frequency of 1 KHz. Energy generation dropped to just over 40 microWatts in automobile tire traveling at 40 miles per hour, but was still enough to qualify the part for powering the pressure sensor and wireless communications circuitry for TPMS systems, according to IMEC.
The MEMS energy harvester consists of a cantilever with a piezoelectric layer (aluminum nitride) sandwiched between metallic electrodes to form a capacitor. A mass attached to one end of the cantilever, enables it to act as a transducer converting vibrations into electricity as the piezoelectric layer flexes. The voltage across the capacitor can then be harvested to drive wireless circuits.
IMEC demonstrated that the tiny energy harvesters can be packaged using vacuum processing on six-inch wafers. IMEC predicts that its MEMS energy harvester will be used to power wireless sensor nodes in many applications where changing a battery is inconvenient—from automobile engines to industrial appliances.