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Piezo-MEMS enables wireless sensor networks

-July 01, 2013

A group of EDN editors and bloggers were just recently discussing monitoring electric motor parameters wirelessly. The parameters discussed were not just voltage and current, but bearing vibration and related parameters in a preventive maintenance scenario as well as staying ahead of a motor failure and predicting problems before breakdown occurs.

 

Well, MicroGen Syetems BOLT Power Cells are now using Linear Technology LTC3588-1 piezoelectric energy harvesting conversion chip to power Dust Networks’ motes.

 

BOLT™ Power Cells (see Figure 1) enabled a live wireless sensor network (WSN) using Linear Technology’s Dust Networks LTC5800-IPM SmartMesh™ IP mote-on-chip at the Sensors Expo and Conference exhibition in Rosemont, IL on June 5-6, 2013 (see similar demonstration video – Linear Tech Demo below).

 

 

MicroGen BOLT energy harvester enables Linear SmartMesh IP Wireless Sensor Network

 

The Linear mote was powered by MicroGen’s piezoelectric Micro Electro Mechanical Systems vibrational energy harvester or micro-power generator (MPG) technology inside the Power Cell.

 

 

Figure 1: From left to right – (1) BOLT™ Power Cell; (2) piezo-MEMS energy harvesting generator or MPG; (3) ESM-B1 using 50 μA-hr solid state battery (Cymbet Corp); (4) ESM-B2 using 7.0 mA-hr rechargeable coin cell (Panasonic); (5) ESM-C using 22 mF ultra- Capacitor (Panasonic).

 

 

       

 

Figure 2: ESM-X (B1, B2 or C) module plugged into BOLT Power Cell powering a wireless sensor node

The Linear WSN consisted of four (4) motes, and their WSN software for efficient power managed communication was used. The self-powered motes were enabled by electronic

shakers set at typical industrial vibrations levels of 120 Hz and acceleration G-level 0.2 g (g = 9.8 m/s²).

 

MicroGen placed vibration powered motes at the Linear booth and at the X-FAB MEMS Foundry booth. These motes were on the order of 20-30 meters away from MicroGen’s booth. This was the first fully MEMS energy harvesting powered WSN completed by a commercial company.

 

Inside MicroGen’s BOLT Power Cell is a small semiconductor MEMS chip fabricated using similar techniques as the computer chip industry. This chip is a ~1.0 cm² 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 alternating current (AC) electricity. At resonance the AC power output is maximized, where it is ~100 microWatts at 120 Hz and =0.1 g, and ~900 microWatts at 600 Hz & =0.5 g.

 

You can mount this on a motor housing, fan/ventilation system, compressor or any vibrating device and the Power Cell will be charged enough to power the WSN to send out a few data bursts. Just what we were discussing in a chat session recently.

 

 

 

 

The AC electricity is efficiently converted to direct current (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 300 microFarad capacitor. The output of the Power Cell ranges from 25-500 microWatts at 3.3 Volts DC, depending upon configuration and frequency. The BOLT Power Cell is intended to enable a wireless sensor mote from many different manufacturers.

 

 

The bottom-line is that 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 WSN industrial and building applications, where the labor to frequently change batteries is cost prohibitive for a WSN to be installed. Power cells will be offered at 50/60 Hz harmonics between 100-1500 Hz. MicroGen’s MPGs and Power Cells are very sensitive to low levels of G.

 

At G-levels < 0.1-0.5g (depends upon 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 be on the order of $0.50 and $1.00 each, respectively.

 

Linear Technology’s Boston Design Center’s Director, Sam Nork added, “MicroGen’s demonstration of its piezo harvesting chip integrated with Linear Technology’s LTC3588 piezo conversion chip is a perfect match to efficiently produce DC electricity for WSN applications.”

 

I agree---we’ll be seeing a great deal more of these types of innovative EH and WSN pairings going forward as the Internet of Things evolves. The evolution has begun and will proceed at a very rapid pace.

For more information visit the Linear Technology website and the  MicroGen website

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