Jun 24 2014

Small Energy

Energy is what makes stuff happen. The ability to generate energy in useful amounts and locations is key to our civilization. Often when discussing energy we are focusing on big energy, how to make large amounts of energy in a cost-effective manner with minimal negative impact on our environment.

The ability to generate tiny amounts of energy is also useful, however. One particular application requiring a small but reliable source of energy is implantable devices, such as cardiac pacemakers. Right now pacemakers are run by small batteries. These batteries have a limited lifespan, and need to be surgically replaced.

What if, however, we could generate the required electrical energy from the body itself. Our bodies use a relative large amount of energy, creating movement, electrical signals, generating heat, assembling proteins and cells, and undergoing biochemical reactions. All we would need to do is tap into a tiny slice of this energy and there would be enough energy to power a pacemaker, or many other small implantable devices.

A recent paper discusses a successful demonstration of one such technology. Hwang et. al. report:

A flexible single crystalline PMN-PT piezoelectric energy harvester is demonstrated to achieve a self-powered artificial cardiac pacemaker. The energy harvesting device generates a short-circuit current of 0.223 mA and an open-circuit voltage of 8.2 V, which are enough to meet the standard for not only charging commercial batteries but also stimulating heart without an external power source.

The piezoelectric effect is a property of some materials that converts mechanical stress into electrical current. In the body, mechanical stress can derive from the beating of the heart, the movement of the chest wall in breathing, the movement of limbs, or the bouncing movement of walking. The idea of harvesting electricity from such movement through the piezoelectric effect has been around for a while, and it’s good to see a successful demonstration of this principle.

Other types of devices that could benefit from this technology include hearing aids, medication pumps, vagal nerve or deep-brain stimulators, and implantable sensors (such as blood glucose monitors).

The technology could also be used for wearable or portable electronic devices. Flexible piezoelectric devices could provide extra juice to your cell phone, extending the life of its charge, or even providing an emergency charge if you are away from an outlet.

It’s likely that the technology would also give a boost to the development of new wearable electronics applications. A major limitation of such technology is providing convenient power.

There are other technologies for harvesting electrical energy. Electromagnetic generators harvest kinetic energy by creating relative motion between a conductor and a magnetic flux to induce charge in the conductor. For at least 20 years there have been kinetic watches that use the movement of the arm to wind the mainspring. Now, there are watches that use the same motion to power electromagnetic generators for a quartz crystal mechanism.

There is also the thermoelectric effect – materials that generate an electric current when there is a temperature difference between the two sides. Electrons will flow from the hot side to the cold side, which can be harvested as an electric current. 

The pyroelectric effect is similar, but involves materials that will generate a voltage due to a change in temperature. To clarify the distinction – thermoelectric effects result from a temperature difference between one side and the other of the material, while pyroelectric effects result from a change in the temperature of the entire crystal. The latter generates a voltage difference across the crystal, which can be used to general a small current.

Of course, small photovoltaics can be used for external devices. Photovoltaics convert sunlight into electrical current.

It is possible to harvest other types of ambient energy, such as radio waves, which are fairly ubiquitous in our modern world. This is currently not a very efficient method, but could provide small amounts of energy to implantable devices, or devices that would otherwise be inaccessible.

For implantable devices it is theoretically possible to function like any other part of the body and derive power from glucose through oxidation. These are called biofuel cells. They can use bacteria to consume the glucose, or simply duplicate the necessary chemical reactions.


There are multiple technologies being developed to generate tiny amounts of electrical energy to power small devices – implantable, wearable, or inaccessible. The development of such technology could revolutionize our use of such devices, or at least make them much more convenient.

Of potential methods of harvesting ambient or otherwise wasted energy, harvesting kinetic energy through magnetic induction or piezoelectric effects seems to be the most mature. This latest study demonstrates a piezoelectric device capable of powering an implanted pacemaker – a significant milestone.

It’s always difficult to predict the development of cutting edge technology, but these technologies do seem ripe. I have been reading about such effects and their potential for decades, and now it seems we are crossing the threshold to a significant increase in actual applications.

We might be entering the age of small energy.

7 responses so far

7 thoughts on “Small Energy”

  1. banyan says:

    “Energy” from crystals and magnets? How gullible do you think we are? 😛

  2. I wonder if you mixed up 2 different things you intended to write here:

    “For at least 20 years there have been kinetic watches that use the movement of the arm to wind the mainspring. Now, there are watches that use the same motion to power electromagnetic generators for a quartz crystal mechanism.”

    Self winding watches have been around far longer than 20 years, more than 200 years if Wikipedia is to be believed. Successful self winding wristwatches have been around since 1923 (again, according to Wikipedia)

    The Seiko Kinetic technology you linked to that has been around (both the world and my wrist) for at least 20 years is a self charging technology that uses the motion of the arm to charge either a capacitor or titanium lithium ion battery, which in turn powers the quartz movement (no mainspring).

  3. Sylak says:

    This could be great! With the development of Cybernetic limbs, instead of having to recharged them all the time, or replace the battery, if the body itself could be use as a energy source, how great this could be! People with prosthetic arm will not be caught with a non functioning limb because the battery is dead!

    5-10 years? lol 😉

  4. Kawarthajon says:

    Sylak: I’m not sure we’re ready for cybernetic limbs yet. These devices produce tiny amounts of power (0.223 mA, for example), enough to run a watch, but definitely not a limb. Even a florescent light bulb requires much more power than this. I agree that it would be great if it could be used for limbs, but we’d need to up the amperage dramatically to move something big.

  5. tmac57 says:

    Karl beat me to it. According to the font of all knowledge,Abraham-Louis Perrelet had developed a credible self-winding pocket watch in 1777:


  6. Sylak says:

    @Kawarthajon : Yes of course we’re not there yet. I was talking in a hypothetical future. Prosthetic limb have made really great progress, and I remember reading in “science et vie” about a piezoelectric polymer that could be use to make artificial muscle ( Deus ex : human revolution like). Of course all this are all style hypothetical, but even with current really great protestic arm, like this one http://www.youtube.com/watch?v=_qUPnnROxvY, this power harvester could be really useful, maybe not to power the whole thing, yet, but just help making it last longer before charging.

    That’s why i was also making the 5-10 years joke 🙂

  7. Bruce says:

    So… the machines using us as batteries is one step closer…?

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