Mar 31 2009
Microdynamos and the Piezoelectric Effect
In our increasingly electrified world the race is on to find new sources of energy and batteries to store that energy. Applications range from the very small to the huge. The electric car industry is essentially waiting on improvements in battery technology.
Researcher Z. L. Wang from the Georgia Institute for Technology has recently announced a breakthrough at the other end of the size spectrum – the very tiny. He has created, not a battery, but a nanoscale energy generator that uses the piezoelectric effect to convert movement into electrical current. The effects are still modest – 0.2 volts with an efficiency of 6.8%, but this is enough for some applications.
The piezoelectric effect is a property of some materials that converts mechanical energy into electrical current. Our bones have this property and it is that which causes the molding of bones under pressure (such as moving the placement of teeth in the jaw using braces). The amount of current generated is generally small – we won’ be running our cars off the piezoelectric effect, but in the aggregate can be useful.
What Wang has done is create rods with nanoscale zinc oxide bristles. When jostled the bristles move against each other, bending them and generating current through the peizoelectric effect. The innovation here is the extremely small size. While the current generated is still small, if enough of these microdynamos were put together they could be useful for some applications. But most applications will have to wait until improvements are made and higher efficiencies are achieved.
Potentially such nanoscale piezoelectric devices could be used to research all of the small electronic devices that we carry around with use – cell phones, mp3 players, beepers, watches, cameras, etc. Just from walking around we generate and waste a great deal of mechanical energy. Some of that energy can be recaptured and put to use.
One exciting potential application is in implantable medical devices. One major technical limitation of such devices is that they need energy, but once inside the body it’s hard to replace the batteries. Some devices, like even the best current artificial hearts, require external batteries. Others, like pacemakers, can be charged from the outside using a coil or need to be removed to have their batteries changed every 7-10 years.
But what if such devices could be charged by the movement of the body itself – by biological energy. Pacemakers, for example, could be charged by the energy of the beating heart. (Such systems are already in development using microgenerators.) The constant expansion and contraction of the chest and diaphragm for breathing is another source of mechanical energy.
And, of course, walking can be a significant source of mechanical energy. Every time our feet strike the ground the impact dissipated mechanical energy throughout our shoes, feet, legs, and hips. Every step could be used to harvest some of that energy. Swinging arms could also be exploited for energy.
Also – deliberate activity could be employed. If your cell phone is running a bit low, just shake it for a few minutes.
Biological activity is not the only source of ambient mechanical energy. Our world is full ove movement and much of the energy of that movement is dissipated uselessly to the environment. For example, the energy of rain striking the ground is completely wasted. If, however, it struck a piezoelectric plate the energy of the falling droplets could be harvested.
Energy is the ultimate currency of our civilization. As we search for greater efficiency of energy production and use the ability to extract ambient energy from the environment will be extremely useful. The piezoelectric effect allows us to connect mechanical energy to electricity, and this property can be exploited in numerous ways, limited only by our cleverness. This is definitely a technology to watch.
11 Responses to “Microdynamos and the Piezoelectric Effect”
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In undergrad I had an idea for a piezoelectric parking garage that uses piezoelectrics underneath the concrete plates to direct cars to open spots. Then I was told I was a materials engineer and that this wasn’t a materials problem! Oh well … I do think the nearest piezoelectric technology will be seen in clothing, and then probably it will be seen in medical equipment – an implantable insulin pump for Type 1 diabetics would be incredibly useful!
Wow, after giving Ray Kurzweil so much flack for his multitude of assumptions on the rate we acquire information, I do recall him making a prediction about microchips in clothing. Shucks!
The piezoelectrical effect would be beneficial for wheelchair bound patients receiving physical therapy as strength training to walk. I can envision an implant in the sacrum region which could assist the patient with mechanical movement. The patient’s goal to walk again might be achieved.
@medmonkey
Why would you put the electrical equipment directly into your clothing? To me this seems like a waste. You would be forced to either own several pieces of clothing with the same equipment or to use one in particular every time you needed its function. Wouldn’t it be simpler to have it attached to you as a small clip (or in a utility belt)?
I’m always curious about the impact of such energy converting devices. For example, robbing the kinetic energy of rain into electrical energy will stop the transfer of energy into the molecular motion of the ground where the water would have hit; thus, decreasing the temperature of the ground. I know this is probably not an issue, but it’s good to think about the ramifications of such devices.
Or if, as you suggested, install one of these devices in the human body to capture energy from a rotating heart, will it put too much strain on the heart and with ~7% efficiency it seems hardly worth it.
I guess you could apply this argument to any or all modern energy devices, but considering the increased probability of anthropogenic global warming, it’s important we seriously investigate these arguments.
Can anyone explain, or provide a source, that goes into a little more depth regarding the Piezoelectric effect and the manipulation of teeth by braces? I’m interested and want to delve into it further.
JonoB, Having worn braces, maybe I can answer this simply. Braces encircle each tooth, which is a hard, bony enamel in the jaw. The brace and connective parts can be metal or hard plastic. Mechanical pressure is exerted by the brace on each bony structure to move the tooth to a corrected position to allow for better mastication. Braces are tightened periodically to put additional pressure on each tooth. Sudden mechanical release of pressure can stress a tooth causing breakage/ damage to the tooth.
As a cardiac physiologist and a recipient of a pacemaker, any technology that prolongs the life of pacemakers is very welcome. However many pacemakers already utilize piezoelectric technology. Piezoelectric crystals change conformation in response to the constant expansion and contraction of the chest and diaphragm during breathing. Increases or decreases in voltage resulting from these changes in conformation are utilized by rate responsive algorithms within the pacemaker to incense or decrease heart rate as a response to increased or decreased overall activity.
It is only a small step to harnessing the voltage resulting from this activity to recharge a battery, even if it only increases battery life by a few years. This would certainly mean less operations for many pacemaker patients. From a personal point of view, i am looking at at least 5 box change procedures in my lifetime (given that i live til 80 and don’t get hit by a bus tomorrow). Reducing that number by even one procedure would be worth it.
quickly – bone itself is a piezoelectric material. Pressure on the bone causes a current which induces the bone cells to break down in advance of the pressure and to form in the wake of the pressure. So the bone remodels itself around the tooth, and the tooth is literally slowly moved through the bone.
In one of my engineering courses we were analysing the stresses on a femur bone. It was really interesting to see how bones density correlates exactly with the stress lines – increased density along the lines with gradual decreasing density between them.
Magnus –
My thought was that the first commercial uses would be for entertainment purposes. Perhaps piezoelectrics will energize lights on clothing, or something of that nature. I recall that apple already has an electronic pedometer that inserts into special Nike running shoes and sends data to your ipod. So one application of electronic clothing could be to provide status updates about body conditions: heat generation, sweat, what-have-you. At first this will be novel and expensive, of course, but overtime should become cheap and commonplace.
I tend to think that if something can be done, somebody will do it … if it proves practical or popular is another story.
@medmonkey
Lcd t-shirts are probably the most high tech clothing I’ve seen to date. I can imagine that piezoelectronic equipment could be very useful in powering the batteries.
A slight quibble regarding bone and strain effects. Yes, bone and virtually all solid materials are piezoelectric. All that is necessary for a material to be piezoelectric is for there to be charges in it, and for those charges to be separated by a distance that changes when the material is strained. Virtually all materials exhibit these properties and produce piezoelectric effects.
All piezoelectric materials produce electric fields when subjected to strain, they also all produce strain when subjected to electric fields. This is how ultrasonic transducers produce the ultrasonic vibrations, they are piezoelectric materials, and when excited at ultrasonic frequencies produce acoustic vibrations at the same frequency.
The major bone stiffness regulating mechanism is known to be NO generated via shear in fluid in bone porosity due to strain of bone. This NO activates the cells that cause deposition of bone mineral and inhibit the cells that cause resorption of bone mineral.
Aqueous biological fluids are pretty conductive. Lipids are virtually non-conductive. For conduction you need mobile charge carriers. In metal those charge carriers are electrons, in aqueous systems the carriers are hydrated ions (which are many orders of magnitude less mobile). The effects of electric fields can be mediated through the field (electrostatics) or via charge and charge carrier reactions (electrolytic effects). It is difficult to have electric field effects in conductive materials.
I suspect that the effect of electrical stimulation of bones is not mediated through electrical effects per se, but rather through electric field induced strain which activates NO via shear and so upregulates the normal NO mediated regulation of bone healing.
Another common example of piezoelectric effects that everyone is familiar with is the quartz clock. A piezoelectric quartz crystal is cut such that it has a mechanical resonance at a certain frequency that mechanical resonance interacts with its piezoelectric properties to cause a resonant electrical frequency, such that the quartz crystal generates a constant frequency when used as a component tin an oscillating circuit. That precise frequency is used as the basis of timing circuits.
There are ways of extracting energy from motion that actually increase efficiency. Biological tissues that covert chemical energy into mechanical energy are not effective at doing the reverse, converting mechanical energy into chemical energy. In some cyclical movements, there are instances where kinetic energy has to be dissipated by using mechanical energy generated by muscle. If that kinetic energy could be regenerated into electricity, then the body wouldn’t need to exert muscle power to do it, and muscle exertion would be reduced while generating positive power. It isn’t a first or second law violation, it is simply using a different mechanism for generating force used at the right time to reduce muscle work requirements.