New Technique is Ultrasound for Charging Through Skin

­At the moment, we rely on batteries to power many things in our homes and working lives. However, there is the potential to increase that number if we had new methods of recharging. These days, most batteries are rechargeable, especially ones that are expected to work for a long time in place. It is sensible, as the amount of waste from non-rechargeable batteries can be huge, and they can be incredibly toxic if not disposed of correctly. Recharging is just very convenient, cheaper and better for the environment if devices have to be portable.

There are some applications that are currently difficult or even impossible to recharge. There is a lot of demand from medical device manufacturers to power smart implants, particularly for joint replacement. New types of implant designs could be created that would monitor the status of the patient and the implant itself. Data could also be collected to allow the makers of the implants to design better devices and make them cheaper and longer lasting, as well as helping patients to recover faster.

New electrical therapies could also be developed. Electrical stimulation has proven to be an effective treatment for many different conditions, but at the moment, devices are normally either kept outside the body, or in some cases implanted under the patient’s skin - for example, a pacemaker battery may be inserted under the patient’s pectoral muscles to be easier to access when the batteries require changing. It is not an ideal situation, but better than the alternatives. Any surgical procedure presents a danger that the patient may have a reaction to the anaesthetic, or provides other risks. A method of charging the implant in situ would be an ideal solution and provide the impetus for innovation in the medical industry. There are other areas away from the medical industry where it is hard to charge batteries, such as underwater, where sensors could be used to monitor the condition of undersea cables.

Many researchers are currently looking at the problem. One of the first to develop a potential solution has just published. The Korea Institute of Science and Technology (KIST) announced that a research team developed an ultrasonic wireless power transmission technology that can be applied both to charge batteries under water and in the human body. Instead of using electromagnetic induction, which has a short range and heats while charging, the research team used ultrasonic waves as an energy transmission medium. This type of charging hasn’t been commercialised before due to the low transmission efficiency of acoustic energy.

The research team has developed a model that receives and converts ultrasonic waves into electrical energy using the triboelectric principle converts small mechanical vibrations into electrical energy effectively. By adding a ferroelectric material to the triboelectric generator, the ultrasonic energy transfer efficiency was significantly improved from less than 1% to more than 4%. Charging of more than 8 mW power at a distance of 6 cm was possible, which was sufficient to simultaneously operate 200 LEDs or to communicate Bluetooth sensor data underwater.