Available Energy is All Around       

There is abundant energy in our environment.  Examples of energy sources are: light, vibration, body heat, chemical . The trick is to convert that ambient energy into useable electrical energy to power a microcontroller.


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               LIGHT 

           It  able to drive down system power, combination of analog, digital, and power management, to the point where we’re reaching what we would call a sort of inflection point and that is that we’re able to make practical, useful systems down at the milliwatt or lower range.  And at that range, it becomes possible to actually look around us and harvest some energy out of the environment.  So there are the obvious things like light, both solar and electrical light.  Figure show a 100-watt light bult.Interesting to note that a human puts out about 100 watts as well.  So there are serious sources of power around us.  All we need to do is be able to harvest 100 thousandth of the power from a light bulb or from your body in order to run a practical application like a body temperature sensor or a pulse sensor or some other blood, vital sign, statistic sensor.

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Radio frequency

Other sources of energy maybe not so obvious around us are the radio frequency that’s unused of the base stations that are driving our cell phones.  Not all of that energy is needed for the cell phones, and we’ve got systems down to the point of power consumption in which they could practically harvest some of that energy and do useful things.

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Other, maybe less obvious, sources of energy are the vibration that either buildings or bridges.They’re available in either buildings or bridges at all times.  So we get to the point where we can look around us and say there’s some energy, enough energy.  If we can harvest some of that energy, we could actually drive some of these systems that we’ve driven to a low enough power that they can run off practically harvested ambient energy.

Energy Harvesting Basics

  • Energy harvesting is the process by which energy is captured and stored
  • This term frequency refers to small autonomous devices – micro energy harvesting
  • A variety of sources exist for harvesting energy

–    solar power                   – salinity gradients

–   thermal energy             – kinetic energy

–   wind energy                   – radio frequency

Energy Harvesting Application 

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        Medical and Health monitoring

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Wireless Sensor Networks

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Smart building

one particular area that can be addressed with his low and no-power type of applications is like the office environment.  Today, most offices are built of cubes, temporary arrangements of workspaces and such.  Now when the office was constructed, there was a lot of permanent things, like light switches, thermostats and such.  In an environment where you could have sensors that took low or no power, you could distribute those to where the workplace is.  So each individual cube could have its own thermostat.  The light control could be there for that particular environment, and this allows a lot more flexibility in building utilization.

Now for example, I used to work with an administrative assistant who was constantly cold, and I’m constantly hot.  So we have a little bit of a quandary when it comes to what temperature should it be, and I had control of the thermostat.  So I set it where I was comfortable, and that clearly made her uncomfortable.  So in response, the only thing that she could do was go out and get a little heater for under her desk, plug it in where she — and then could be maintained warm.  That was a terrible waste of energy since she was trying to recover from the fact I was running air conditioning full time.  If she had the opportunity to have that same device and be able to have her own thermostat, then she would be able to control her own environment.

It’s not just low power and no power that makes this possible, but it’s also this low-power and no-power approach towards communication between these devices.  It’s wireless communication.  And by doing this, you could form a network, and that network could interface with a resource-managing system and deploy the resources at the point they’re needed.  And it would greatly reduce the power utilization in office environments and benefit everybody by creating a more comfortable scenario.

Energy Harvesting Tradeoffs

Advantages

–   Mobile: no power wires

–   Easier installation

–   Lower maintenance

–   Environmentally friendly

–   Higher uptime

Disadvantages

–    Dependent on availability of harvestable energy source

–   Strict power budget

–   Upfront cost may be higher

–   Less mature technology

When Does Harvesting Make Sense?

  • Harvestable energy available
  • Difficult to install or power devices
  • Difficult to reach devices for maintenance
  • Cords too costly
  • Numerous devices
  • Environmentally friendliness required
  • High uptime demanded

One or more of these characteristics are required for energy harvesting to make sense compared to batteries

Tree Energy Harvesting

A new MIT tree sensor system taps into trees as a self-sustaining power supply. Each sensor is equipped with an off-the-shelf battery that can be slowly recharged using electricity generated by the tree.

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The sensor system produces enough electricity to allow the trees’ temperature and humidity sensors to regularly and wirelessly transmit signals. Each signal hops from one sensor to another, until it reaches an existing weather station that beams the data by satellite to a forestry command center

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Harvesting Thermal Energy

Thermoelectric  Seebeck  Effect

Temp. gradient drives heat flow—>Electrons and holes flow in   N-type and P-type lags made    of semiconductor materials
    —->       Carnot Efficiency      ≡ ∆T/TH

                                                                                                                


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 Energy Harvesting Storage Required

  • Scavenged energy is not constant
  • Power not available on-demand
  • High peak power not available
  • An ideal energy storage device:

–    Infinite shelf life

–    Negligible leakage

–    Unlimited capacity

–    Negligible volume

–    No need for energy conversion

 – Efficient energy acceptance and delivery

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