Mobile phones have become an integral part of every day life, with one main constraint for usage being the charging of the device and the need for a power supply.  It is therefore highly desirable to produce a mobile phone which can source energy from mechanical or human hosts, also providing advantages in disaster situations, as well as making the product more environmentally viable.  Recently, there have been tremendous research efforts on the development of energy harvesters that can scavenge energy from ubiquitous forms of mechanical energy.

Now, a study from researchers at Michigan State University develops a new way to harvest energy from human motion, using a film-like device that actually can be folded to create more power. The team state that with the low-cost device, known as a nanogenerator, they successfully operated an LCD touch screen, a bank of 20 LED lights and a flexible keyboard, all with a simple touching or pressing motion and without the aid of a battery.  The study is published in the journal Nano Energy.

Previous studies suggest that innovation is nearing the advent of wearable devices powered by human motion.  The most studied mechanisms are based on the use of piezoelectric and triboelectric effects.  The current study investigates an efficient, flexible, and biocompatible ferroelectret nanogenerator (FENG) device charged by human motion.

The current study develops a device called a biocompatible ferroelectret nanogenerator, or FENG. The device is as thin as a sheet of paper and can be adapted to many applications and sizes. The device used to power the LED lights was palm-sized, while the device used to power the touch screen was as small as a finger.  Results show that the device becomes more powerful when folded, whereby, each time it is folded the amount of voltage produced increases exponentially.

Data findings show that the device can be large to begin with, and folded multiple times to a smaller size to produce more energy.  The lab explain that the innovative process starts with a silicone wafer, which is then fabricated with several layers, or thin sheets, of environmentally friendly substances including silver, polyimide and polypropylene ferroelectret. They go on to add that ions are added so that each layer in the device contains charged particles. Results show that electrical energy is produced when the device is compressed by human motion, or mechanical energy.

The group state that the FENG may be folded small enough to put in a specially made heel of a shoe so it creates power each time the person’s heel strikes the ground.  They go on to add that advantages such as being lightweight, flexible, biocompatible, scalable, low-cost and robust could make FENG a promising and alternative method in the field of mechanical-energy harvesting for many autonomous electronics such as wireless headsets, cell phones and other touch-screen devices.

The team surmise that they have developed a liquid-crystal display (LCD) that harvests energy from the user’s touch.  For the future, the researchers state that they foresee, relatively soon, the capability of not having to charge a cell phone for an entire week, as that energy will be produced by the person’s own movement.  They conclude that they are now developing technology that would transmit the power generated from the heel strike to, say, a wireless headset.

Source: Michigan State University