Getting Started with Vibration Energy Harvesting

Aug. 18, 2012
Summary: This six-page white paper discusses the fundamentals of electro-magnetic vibration energy harvesting as a perpetual power source for Wireless Sensor Networks (WSN) in an asset monitoring application. The paper immediately focuses on whether a machine is a possible candidate for energy harvesting by pointing to two essential characteristics needed: resonant frequency and vibration level.

Not all vibration is equal in the world of energy harvesting. The fact that a structure or object vibrates (even at excessive levels) does not automatically make it a viable candidate as a suitable vibration source to harvest from. The source vibration must have certain characteristics for it to be usable.

The following guidelines will shed some light on how to determine if you have a suitable vibration source for optimal use:

Resonant Frequency:  The source vibration object should have a known and repeatable frequency component within a range. This provides the optimal tuning frequency for the vibration harvester to work at its maximum potential.

Vibration Level: The RMS g level of vibration will be the next consideration. Once the Vibration Energy Harvester is frequency tuned for maximum mass/spring displacement, the RMS g level of the source vibration object will determine the power output of the vibration energy harvester (VEH). The usefulness of a VEH in industrial environments will be its ability to produce sufficient power at low levels of vibration. Higher levels of vibration generate greater power output from the VEH.

All vibration energy harvesters are in essence a mass/spring tuned resonator. Their effective operation is based upon the ability of the VEH to harvest from a vibration source within a repeatable and consistent frequency range and known sufficient vibration level. The vibration source frequency is used to tune the VEH to a resonant frequency (the frequency that will produce the maximum amount of displacement of the mass/spring structure enabling maximum power output of a VEH based upon source vibration level). In other words, they are factory tuned to a predefined resonant frequency range to match the vibration source of the application and maximize the power output of the VEH.

In the industrial world, line powered machinery are excellent vibration sources to harvest from. They will have a repeatable frequency component of 60Hz (line power frequency) or 120Hz (2X line power frequency). In non-U.S. countries the frequencies are 50Hz & 100Hz. This allows the end-user to select the optimized VEH frequency to ensure maximized power output of the VEH in the target application. This is referred to as the “Center Frequency”. The operational design of a VEH should have sufficient bandwidth to accommodate actual frequencies that deviate by the slip percentage of an AC induction motor.

Once the source frequency is determined (enabling the selection of a maximized =VEH), the next step is to determine the level of vibration the source can/will supply.  Typical balance of plant machinery will vibrate at levels below 1g. A key design requirement is to be able to produce sufficient power output from very low levels of vibration (i.e. down to 25mg/RMS on a smooth running machine) and to do it over the necessary bandwidth.

This white paper was written by Perpetuum. Publication Date: January 2012

Grant Gerke, Automation World Digital Managing Editor, edited this white paper abstract.

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