Using Muscle Action to Power Cell Phones, iPods and Similar Devices

Cell phones, iPods, Blackberries and other personal electronic devices play important roles in many people’s lives. These devices require a portable power supply, which often runs out at very inconvenient times. It’s sometimes difficult for people to get a power top-up while they are away from their home, school or office. Researchers at the Georgia Institute of Technology may have the answer to this power dilemma. They’ve created tiny nanogenerators that produce electricity under the influence of human muscle action. The scientists predict that the nanogenerators will eventually be powerful enough to drive personal electronic devices.

Electronic equipment is useless when it has no power source. At the moment, obtaining power away from an electrical outlet is often problematic. A replacement battery, a portable charger or a solar-powered charger can be taken on trips. However, these are extra items to carry and may be heavy or awkward to pack. A convenient power source that is always available is muscle energy.

Muscle contraction and relaxation is constantly taking place in our bodies. The heart repeatedly beats and relaxes to pump blood around the body. The respiratory muscles contract and relax to allow the lungs to fill with air and then partially empty. More muscle contraction occurs as we move parts of our body through space. Muscle action is occurring wherever we go and all the time, even in people with mobility problems – it’s a property of human life. Scientists at Georgia Tech have discovered that this muscle action can be used to produce electricity.

The technology that the researchers are exploring is based on piezoelectricity – the ability of certain crystalline substances to create an electric current whenever they are bent or compressed. As a muscle contracts and relaxes it changes its shape and body parts move. If muscle activity – either conscious or unconscious - can distort a piezoelectric crystal’s shape, electricity can be generated.

Professor Zhong Lin Wang and his colleagues at Georgia Tech have created nanogenerators. The prefix “nano” means one billionth of the base measurement unit that is being used. For example, a nanometer is a billionth of a meter. In the case of a nanogenerator, nano refers to nanotechnology, which is technology that involves extremely small objects with a size on the nano scale.

The research team’s current nanogenerator contains tiny zinc oxide wires which create electricity when they are bent. Five hundred zinc oxide nanowires placed side by side would have the width of one human hair. The nanowires are placed on a flexible polymer film. The polymer layers are then arranged in a sandwich-like structure to create a nanogenerator. The generator creates electricity when a person bends it with his or her fingers.

One zinc oxide wire can create only a very small amount of electricity, but there are millions of the wires in a nanogenerator. The latest generator has a voltage of 3 volts – the same voltage as two AA batteries – and is able to light up the liquid crystal display of a calculator or drive a light-emitting diode.

Zinc oxide nanowires convert the mechanical energy present in moving objects into electrical energy. These moving objects may be found in our bodies or in our environment.

In the future, nanogenerators may be placed inside the body where the heartbeat, the activity of the breathing muscles or even the flow of blood could trigger electricity production, which could then be used to drive medical instruments. For example, the muscle movement of the heartbeat might be used to stimulate nanogenerators that power an insulin pump for diabetics. In addition, pacemakers could be recharged by nanogenerators.

Nanogenerators may also be placed in the soles of shoes so that a person’s footsteps will compress the piezolelectric substance and generate electricity. Our future clothing may contain piezoelectric nanowires that produce electricity as the clothing moves on our bodies. Nanogenerators are very small and lightweight and would be easy to carry around. They would be a very convenient source of power for our personal electronics, and could also be used to recharge batteries and to provide electric charge for storage in capacitors.

Any object that moves frequently could be used to produce electricity. For example, future nanogenerators may be placed in car tires or in flags that blow in the wind. The energy of ocean waves could also be used to deform piezoelectric crystals, generating electricity.

The present piezoelectric devices work successfully, but the power and the voltage of the nanogenerators need to increase so that they can be used in additional situations. Researchers are hoping to incorporate more nanowires on to each polymer layer and to stack more layers together to create a better generator.

Nanogenerator research is progressing rapidly. The present devices are almost a hundred times more powerful than those created a year ago. Professor Wang predicts that a nanogenerator capable of powering environmental sensors will be available within three to five years. Nanogenerators for powering or charging our mobile phones, media players and other personal electronic devices should be available at the same time, or soon afterwards.