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Microgen Systems has announced that vibration energy-harvesting Bolt power cells enabled a live wireless sensor network using Linear Technology’s Dust Networks LTC5800-IPM Smartmesh IP mote-on-chip device at the Sensors Expo and Conference in Rosemont, Illinois, in June 2013. The mote was powered by Microgen’s piezoelectric micro-electromechanical system (piezo-MEMS) vibrational energy harvester or micro-power generator technology.

The Bolt power cell is simply a battery replacement unit that uses vibrational energy instead of chemical energy produced by environmentally unfriendly materials. The intent is to eliminate or extend the lifetime of primary cells or rechargeable batteries in wireless sensor network industrial and building applications, where the labour to frequently change batteries is cost prohibitive for a wireless sensor network to be installed.

Linear Technology’s wireless sensor network comprised four motes and its software for efficient power-managed communication was utilised. The self-powered motes were enabled by electronic shakers set at typical industrial vibrations levels of 120Hz and acceleration G-level 0.2g (g=9.8m/sec²).

Microgen placed vibration-powered motes at the Linear Technology booth and at the X-Fab MEMS Foundry booth. These motes were about 20–30m away from Microgen’s booth. It is said that this was the first fully MEMS energy-harvesting-powered wireless sensor network completed by a commercial company.

Inside the technology

  • Within Microgen’s Bolt power cell is a small semiconductor MEMS chip fabricated using similar techniques as those utilised in the computer-chip industry. This chip is a ~1.0cm² piezo-MEMS MPG containing one end-mass-loaded micro-cantilever containing a piezoelectric thin film. As the MPG’s cantilever bends up and down due to the external vibrational force, it produces AC electricity. At resonance the AC power output is maximised, where it is ~100µW at 120Hz and ³0.1g, and ~900µW at 600Hz and ³0.5g. 
  • The AC electricity is efficiently converted to DC using Linear Technology’s LTC3588-1 piezoelectric energy-harvesting AC-to-DC converter. After the energy is scavenged, it is temporarily stored on a 300µF capacitor. The output of the power cell ranges from 25–500µW at 3.3VDC, depending on configuration and frequency. The Bolt power cell is intended to enable a wireless sensor mote from many different manufacturers.
  • Power cells will be offered at 50/60Hz harmonics between 100Hz and 1,500Hz. Microgen’s MPGs and power cells are very sensitive to low levels of g. At g-levels of less than 0.1–0.5g (depends on frequency) at a specific industrial signature frequency, then the power cell will enable the WS mote attached.
  • In volume, the MPG and power-cell production cost are estimated to be in the order of $0.50 and $1.00 each, respectively.

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