Electricity from the nose: Engineers make power from human respiration

Electricity from the nose: Engineers make power from human respiration

  8:59:00 AM    Science Lover

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The same piezoelectric effect that ignites your gas grill with the push of a button could one day power sensors in your body via the respiration in your nose.

Graduate Student Jian Shi and Materials Science and
Engineering Assistant Professor Xudong Wang
demonstrate a material that could be used to
capture energy from respiration.

Writing in the September issue of the journal Energy and Environmental Science, Materials Science and Engineering Assistant Professor Xudong Wang, postdoctoral Researcher Chengliang Sun and graduate student Jian Shi report creating a plastic microbelt that vibrates when passed by low-speed airflow such as human respiration.

In certain materials, such as the polyvinylidene fluoride (PVDF) used by Wang’s team, an electric charge accumulates in response to applied mechanical stress. This is known as the piezoelectric effect. The researchers engineered PVDF to generate sufficient electrical energy from respiration to operate small electronic devices.



“Basically, we are harvesting mechanical energy from biological systems. The airflow of normal human respiration is typically below about two meters per second,” says Wang. “We calculated that if we could make this material thin enough, small vibrations could produce a microwatt of electrical energy that could be useful for sensors or other devices implanted in the face.”

Researchers are taking advantage of advances in nanotechnology and miniaturized electronics to develop a host of biomedical devices that could monitor blood glucose for diabetics or keep a pacemaker battery charged so that it would not need replacing. What’s needed to run these tiny devices is a miniscule power supply. Waste energy in the form or blood flow, motion, heat, or in this case respiration, offers a consistent source of power.

Wang’s team used an ion-etching process to carefully thin material while preserving its piezoelectric properties. With improvements, he believes the thickness can be controlled down to the submicron level. Because PVDF is biocompatible, he says the development represents a significant advance toward creating a practical micro-scale device for harvesting energy from respiration.

Provided by University of Wisconsin-Madison

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Generating Power from a Heart

Generating Power from a Heart

  9:07:00 PM    Science Lover

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Nanowire generators could one day lead to medical devices powered by the patient's own heart.

Live wire: A single zinc oxide nanowire can be attached to a rat’s heart, where it produces electric current as it bends with every beat.
Credit: Guang Zhu, Georgia Tech

A tiny, nearly invisible nanowire can convert the energy of pulsing, flexing muscles inside a rat's body into electric current, researchers at Georgia Institute of Technology have shown. Their nano generator could someday lead to medical implants and sensors powered by heartbeats or breathing.

Zinc oxide nanowires show the piezoelectric effect, producing electricity when they are under mechanical stress. Georgia Tech professor of materials science and engineering Zhong Lin Wang and his group first demonstrated these nanowire generators in 2005. Since then they have made devices that can harness the energy of a running hamster and tapping fingers, and have also combined their piezoelectric nanowires with solar cells.

In their latest work, published in the journal Advanced Materials, Wang's team shows that the nanogenerator works inside a live animal. The researchers deposited a zinc oxide nanowire on a flexible polymer substrate and encapsulated the device in a polymer casing to shield it from body fluids. It was then attached to a rat's diaphragm. The rodent's breathing stretched the nanowire, and the device generated four picoamperes of current at two millivolts. When attached to a rat's heart, the device gave 30 picoamperes at three millivolts.

Zinc oxide nanogenerators would be an ideal power source for nano-scale sensors that monitor blood pressure or glucose levels and detect cancer biomarkers. These can run on low power levels of about one microwatt, but they need a long-lasting nano-sized power source instead of a battery to be truly nano scale. "Our ultimate goal is to make self-powered nano devices for medical applications," says Wang.

The femtowatt scale of power generated by the devices is far too low to be practical right now (power = current x voltage). But that should change soon, Zhang says. While the researchers have only tested a single nanowire device inside a rat, they have also built a device that integrates hundreds of nanowires in an array. This device, which the researchers recently reported in the journal Nature Nanotechnology, gives an output current of about 100 nanoamperes at 1.2 volts, producing 0.12 microwatts of power. Wang says the next step is to connect this higher-output nanogenerator to a nano sensor inside an animal.

Better piezoelectric materials than zinc oxide nanowires exist and are also being considered for biomedical applications. The most efficient piezoelectric material known is PZT, a compound of lead, zirconium, and titanium. It is 10 times more efficient than zinc oxide at converting mechanical stress into electric current, says Michael McAlpine, a mechanical engineering professor at Princeton University. By sandwiching PZT between silicone pieces, he has made a material that can harvest 80 percent of the energy applied when flexed. Like Wang, he is focusing on using the material to power medical implants.

McAlpine says the material gives 10 nanowatts of power from human finger tapping. Larger sheets could generate enough power to charge a pacemaker, but the material has not been tested in animals yet. Here, zinc oxide might have an advantage over PZT because it is biocompatible. The lead in PZT would require the device to be robustly encased in silicone or another biocompatible polymer.

The biggest challenge for both materials, however, will be getting higher power outputs, McAlpine says. "It's amazing that they could implant these devices in these animals and get power out," he says. "But we still have to go far with our devices to get a meaningful power output."

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