Driven by the vision of our society one day being basically self-propelled, a team of University of Houston scientists has set out to both amplify and provoke that potential in materials known as piezoelectrics, which naturally produce electricity when literally subjected to strain.

Engineers at Leeds in the U.K. are developing a way to capture the kinetic energy produced when soldiers march and use it to power their equipment. The devices will use high tech ceramics and crystals as piezoelectric transducers in order to convert mechanical stress into an electric charge.

Schema of the Piezoelectric Effect. From Wikipedia.

Schema of the Piezoelectric Effect. From Wikipedia.

The UH group’s goal is to use piezoelectrics to create nanodevices that can power electronics, such as cell phones, MP3 players and even biomedical implants.  The Leeds group is working toward soldiers one day powering electronic devices such as personal radios using just their own movements on the battlefield.  Soldiers using this technology will not have to carry extra supplies of batteries.

The UH group is addressing a very large sum of power demand.  I did a quick google to see if there is a handy statistic or graph to illustrate the power of charges for small devices to no easy avail, but I did look through the house and found 7 little chargers here.  All of them plugged in is like having just over a 50 watt bulb burning.  They are all unplugged again.  The only “smart” one is for my cell phone that when plugged into the phone scales back as the cell’s battery gets close to full.  The kill-a-watt says it runs at full power though, when its not plugged into the cell phone.  How’s that for engineering?

That sort of makes the case when those stories appear about the hundreds of millions of them in the U.S. alone.  Maybe there are a billion or more of them worldwide.  You can imagine the total draw is going to equal several power plants running full out.  All for lack of a little engineering multiplied millions of times.

Associate professor Pradeep Sharma, one of the creative minds at the Cullen College of Engineering at UH says, “Nanodevices using piezoelectric materials will be light, environmentally friendly and draw on inexhaustible energy supplies.”  Not satisfied with saving a lot of generated power his imagination goes on to, “Imagine a sensor on the wing of a plane or a satellite. Do we really want to change its battery every time its power source gets exhausted?  Hard-to-access devices could be self-powered.”  It’s a little like the potential isn’t even thought through completely.

Sharma explains and expands the topic even more, “Indeed, gas lighters used in most homes are based on this. These future piezoelectric nanodevices will also generate an electrical current in response to mechanical stimuli. Then, the energy will be stored in batteries or, even better, in nanocapacitors for use when needed.”

The UH team is exploring new possibilities by beefing up the effect in natural piezoelectrics. Doing so requires understanding the phenomenon that energizes piezoelectricity, known as “flexoelectricity.”  Sharma says, “Flexoelectricity, at the nanoscale, allows you to coax ordinary material to behave like a piezoelectric one. Perhaps more importantly, this phenomenon exists in materials that are already piezoelectric. You can make the effect even larger.”  For example, the piezoelectricity in barium titanate can be increased by 300 percent when the material is reduced to a 2-nanometer-beam and pressure is applied. “Thus, you’ll take an ordinary piezoelectric material and really give it some juice,” he says.

Sharma underscores the flexoelectric effect is a function of size – and the smaller the better, at least for generating piezoelectric power. Materials with nanoscale features – such as nanoscale thin plates stacked on each other or materials with particles or holes the size of a few nanometers – exhibit a much larger flexoelectric effect, he says.

Ramanan Krishnamoorti, chairman of the department, is working with Sharma to embed classes of nanostructures in polymers to create unusual types of piezoelectrics while Sharma and professor Ken White recently reported that the electrical activity caused by flexoelectricity also affects a material’s resiliency. They tested their theory – that the elasticity of a material would be quite altered by flexoelectricity and caused electrical activity – by poking the material with a sophisticated needle.

Sharma says, “We basically predicted that when you poke it, because of this electrical activity, depending upon how big a crater you create, your elastic behavior will change. It’s not supposed to. Ordinarily, whether you make a big crater or small crater, if you calculate how stiff it is or soft it is, it’ll give you the same answer – a constant.” White and Sharma conducted several experiments on single crystals of materials.  White says, “By monitoring the stiffness of the material as the crater became larger and larger, we discovered a change in elasticity relative to size, which could only be explained by flexoelectric effect.”

The amount of power that can be harvested is still too low to actually power wearable devices unless efficient electric storage solutions, like nanocapacitors are developed.

In the U.K. they seem to be less nano and more micro.  Prof Andrew Bell, director of the Institute for Materials Research at Leeds University and his researchers believe piezoelectric material, which converts movement into electrical energy, may be the portable answer. His group aims to make a wearable device that does not restrict a soldier’s movement on the battlefield.

Bell says, “What this project needs to deliver is not only devices that can harvest the energy, but they must do it with minimal impact to the soldier and the possibly positive impact.”  The team has suggested a device that would mount around the knee and extract energy as a soldier stretches his leg forward and cushion his knee as the leg returns. Bell said electrical engineers working on the project would optimize the electronics so that they take energy out of the device’s transducer during the part of the walking cycle when the leg extends.

‘We need to take energy out of the device at the right part of the cycle so the soldier doesn’t feel it,’ Bell explained.  But when compared to soldiers’ packs of up to 75kg in weight a little counter force might not be so noticeable.

The electricity generated would be distributed through wires weaved across a soldier’s uniform and used to charge up the batteries that power its devices. Such a power distribution system could be avoided if the piezoelectrics were self-contained in the electronic devices. His group aims to develop a personal radio that demonstrates this possibility. “The innards of the radio will move up and down as the soldier walks,” he said. “Kinetic energy can be harvested from that.” A very British perspective.

They are looking at single crystal piezoelectric materials. They have the potential to be 10 times better at energy conversion compared with PZT, the most popular piezoelectric in the world, with the potential to be 10 times better at energy conversion compared with PZT.

Bell said the strength of the material and its flexibility will also be a concern, especially for applications such as the knee-worn device. He added that it is possible to create a composite made of the fibers of the piezoelectric material so that the piezoelectrics could be worn around a soldier’s knee more like an elastic bandage.

One does wonder about the comfort of an elastic bandage, but the Leeds team is still formulating the forward planning.  But what stands out is the likelihood that the current state of the art in materials might just take those batteries of the backs of our service men out on patrol.

Both of these technologies when developed would make it to consumer products offering a relief not just from the task of remembering to charge them, but likely save weight and size.

If any of you have a reliable number on the power drain for all those little chargers of portable devices I’m sure everyone would like to know.  I’ll bet it’s a very interesting amount of power, making these researchers work very worthwhile.


4 Comments so far

  1. Jewelry on August 2, 2009 7:07 PM

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  2. bootricity « Thought Shop on March 6, 2010 1:30 PM

    […] Piezoelectricity wiki.More on Flexoelectricity. […]

  3. bootricity « syncwpmu on March 7, 2010 12:02 AM

    […] Piezoelectricity wiki.More on Flexoelectricity. […]

  4. Scientist on April 25, 2011 1:21 PM

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