As wireless medical devices move from the test bench to the hospital bed, product designers have turned their attention to solving the challenge of powering these technologies as well as reducing their overall need for power. Low-power draw medical body area network technologies, like ZigBee and Bluetooth 4.0 Low Energy, have reduced electric requirements to a point where these devices do not require large batteries or power cords. Advances in on-body power generation, flexible battery technology and battery-integrated devices are solving the power problem for wireless medical devices.
Solar capacitors. Two Israeli companies, Sol Chip and Cellergy, have developed a power source that uses a small solar cell to charge a super capacitor. Capacitors are electronic components that work similarly to batteries but with the ability to charge substantially faster than normal batteries. For example, leaving the window shades open for a few minutes could power a body-mounted sensor for an entire day.
- Glucose fuel cells. Small fuel cells developed by researchers at the Massachusetts Institute of Technology can use the body's glucose to generate electricity. These fuel cells are small enough to be used in implanted wireless medical devices and can draw small quantities of glucose from cerebrospinal fluid or other bodily secretions. Given that the body transfers energy in the form of glucose, it's a readily available fuel.
- Edible sodium-ion batteries. While small sodium-ion batteries may not have long life, they are an inexpensive solution for sensors that are designed to be swallowed. This is an already extant technology that is safe and non-toxic and can provide enough power to drive a sensor for a trip through the digestive system.
- Flexible batteries. The lithium-ion batteries that power cell phones, notebook computers and some power tools offer excellent density and efficiency but they remain inflexible. Researchers hope to expand the applications of such batteries by creating flexible battery cells that can be sewn into clothing or comfortably placed on the body. They could offer large enough quantities of power to serve an entire body area network of wireless medical devices. Other uses of flexible battery technology are in their use in conjunction with stick-on-tattoo-like sensors that are applied to the skin and provide their own power, data collection and wireless transmission service.
- Heat capture. The heat that a 98.6 degree human body emits can be harvested and used as a source of energy. An Oregon-based company known as Perpetua Power Source Technologies has invented a chip that converts body heat into electricity. It can be implanted in wireless medical devices to provide an always-on body source, as long as its wearer isn't hypothermic.
These technologies are just a few of the many on-body power generation and delivery systems being developed. A recent post on six promising technologies from MPMN Medtech Pulse blog covers more on-body power solutions that are in development.