Four technologies for wearable energy harvesting

    Wearable devices are portable devices that are integrated into the user's clothes or accessories or worn directly on the body. Wearable devices are not only a set of hardware devices, but also have powerful functions such as data interaction and cloud interaction software support. Wearable devices will greatly change the user's perception. One of the biggest problems for wearable devices is how to ensure a long enough battery life without making the device too large. The ideal situation is that the user does not need to charge the device at all, but it is not easy to never charge it, especially in such a small size as the iFind anti-lost tag. It has been questioned by many people and accused of being a fraudulent project, and the project initiator has not been able to provide solid evidence to prove that they can make such a product. It just issued a statement accepting Kickstarter's approach, while firmly denying that it is a fraud.

    Whether iFind is a fraud remains in doubt, but it reminds us that on the road to an ideal world without charging, energy collection is the most important thing. In the envisioned future, wearable devices will be able to obtain energy through light, heat or vibration. This sounds like science fiction, but wearable devices that can collect energy have actually existed for many years. For example, Seiko of Japan has invented an electromagnetic generator that powers its quartz watch through the user's body movement.

    However, for today's wearable devices that rely mainly on sensors, computing chips and communication technologies, these relatively simple energy harvesting methods are no longer sufficient. But there is still hope, and a series of new technologies have emerged to help achieve energy independence for wearable devices. In terms of energy harvesting, the scientific community and industry are currently focusing on the following technologies:

    Solar battery

    Solar cells are not limited to large-scale applications such as power plants and street lights. We will see miniature versions of solar cells provide enough energy for wearable devices. Solar watches that do not require batteries have been around for many years. Energy Bionics recently developed a solar watch that can not only meet its own needs, but also power other devices.

    A big problem with applying solar cells to wearable devices is that the devices need light to generate electricity. Once the light is blocked, such as under the sleeves, no energy can be generated. However, from another perspective, this also makes solar cells a good choice for smart clothing. Flexible batteries can even be sewn directly into fabrics.

    Traditional solar cells are designed to work with sunlight, which is much more intense than the light sources commonly found indoors. To address this problem, new materials are being developed that can generate electricity indoors with much higher efficiency.

    Thermoelectric harvesting

    Thermoelectric harvesting converts heat energy into electrical energy using a physical principle called the Seebeck effect. A Peltier element plus a pair of specific semiconductors will generate an electric current as long as there is a temperature difference.

    For wearable devices, the human body, which constantly emits heat, can be used as the hot end, and the environment can be used as the cold end. The amount of energy generated depends on the delta value between high and low temperatures. Peltier elements can collect a lot of energy, so they have great potential for devices that are close to the skin and have high energy requirements. A major advantage of thermoelectric recovery is that the energy is endless and can be used indoors or outdoors, day or night.

    Earlier, Leifeng.com reported that South Korea had developed a patch that converts thermal energy into electrical energy, and its various properties have already met the needs of wearable devices.

    Piezoelectric collection

    Piezoelectric harvesting converts mechanical energy into electrical energy. In piezoelectric components, due to the piezoelectric effect, a small current is generated whenever the component is manipulated by mechanical force. For applications in wearable devices, piezoelectric components are usually designed to generate electricity from the vibrations caused by walking, breathing or hand movement.

    The energy generated by piezoelectric harvesting is relatively small, which limits its application mainly to devices with low power consumption and parts of the body that are always in motion. The polymer piezoelectric fibers that scientists are developing are flexible and breathable, can be placed in fabrics, and have a wide range of applications.

   Optimizing power storage and consumption in wearable devices

    Energy harvesting is only one aspect of making wearable devices completely free of charging. Energy storage is another area with a lot of room for improvement. Supercapacitors and graphene have great potential in this area. The wonder material graphene can greatly improve the efficiency of batteries and capacitors, thereby improving the overall performance of wearable devices. And structural capacitors can turn wearable components into energy storage, so that no additional space is needed to place batteries.

    Another way to extend the battery life of wearable devices or even eliminate the need for charging is to significantly reduce the energy consumption of sensors, chips and communication systems. The success of smartphones has promoted the development of low-energy, high-performance chips. The processors of wearable devices require even less computing power and energy. To address this problem, chip manufacturers including Intel are integrating processors, memory and communication modules into a single chip to reduce some common energy losses.

    Choosing the most efficient networking technology can also go a long way in reducing energy consumption. Looking ahead, as more and more sensors and devices are worn on different parts of the body, efficient communication methods called "body zone networks" have great potential for saving energy. Companies such as EnOcean have developed optimized protocols that use shorter data telegrams than IPv6, which significantly reduces the energy consumed for the same amount of information transmission.

    All of these different improvements are pushing wearables into an era where they don’t need to be charged, while significantly improving performance. Add in technologies like wireless charging, and consumers may soon see a significant improvement in the user experience of wearable devices, which will further push wearables into a wider market.