Powering the Future

Wearable sensors are a growing field of technology with diverse applications ranging from healthcare to fitness and beyond. These compact devices are equipped with various sensors capable of monitoring physiological parameters, movement, environmental conditions, and more. However, a significant challenge hindering the widespread adoption of wearable sensors lies in the method of supplying them with power.

Traditional solutions, such as batteries, present a dilemma as they tend to make the devices bulky and uncomfortable to wear for extended periods. Additionally, the need for regular recharging poses practical challenges, often requiring users to remove the devices, which can interrupt continuous data collection. This inconvenience diminishes the seamless integration of wearable sensors into users' daily lives, impacting the reliability and effectiveness of the collected data.

In an attempt to address these challenges, researchers have explored alternative power sources, with energy harvesting emerging as a promising candidate. Energy harvesting technologies aim to generate power from the surrounding environment, converting ambient energy into electrical power for the sensors. Despite its potential, energy harvesting faces several limitations, including the variability and intermittency of energy sources, inefficiencies in conversion, and the difficulty of obtaining sufficient power for demanding sensor applications.

Energy harvesting may become practical for a wider range of applications in the near future thanks to the work of a team led by researchers at Tohoku University in Japan. They have developed a new fabrication procedure that can unlock the potential of piezoelectric composite materials to convert mechanical energy into electrical energy. Typically, the poor mechanical strength of these materials limits their ability to be used for energy harvesting. But the researchers have demonstrated that they can produce strong, flexible piezoelectric composite materials that are well-suited for harvesting mechanical energy.

The novel fabrication method leverages the piezoelectric ceramic material known as potassium sodium niobate. Nanoparticles of this material are reinforced with unidirectional carbon fibers and an epoxy resin to give it mechanical strength. The new material also exhibits excellent stretchability and a strong piezoelectric response. These properties make it ideal for comfortably conforming to the curves of the body and producing electricity to power wearable sensors over long periods of time.

The material was put to the test in a series of experiments. It was discovered that it could maintain a high level of performance even after being stretched 1,000 times. And when pulled in the direction of the carbon fibers, the material showed that it had great strength. This strength did not come at the expense of performance — it was shown that the energy output density of the material was notably higher than other piezoelectric polymers.

To test the real-world utility of the material, it was utilized to create a battery-free piezoelectric motion sensor. This device was integrated into a baseball glove, where it was used to accurately record the timing of catches of a ball. A similar device was attached to a shoe, which was then found to be capable of recording the wearer’s stepping frequency.

In addition to being strong, the material is also very light in weight. The team believes that this combination of properties could make it very useful for applications in the aerospace and automotive industries, as well as in sports equipment, and medical equipment. It is their hope that this work will help to further research in the field of motion detection in the future.