Powering Electronics with Human Movement
Wearable devices work best when they are constantly on and continually worn. That’s a difficult ask for devices powered by rechargeable batteries. Now, researchers at the University of Waterloo in Ontario and Wilkes University in Pennsylvania have developed a wearable generator that captures electricity from movement, promising a way to recharge devices without taking them off.
The compact, scalable technology harnesses vibrations and small body motions to generate power.
Asif Abdullah Khan, an assistant professor in the Department of Mechanical and Electrical Engineering at Wilkes University in Pennsylvania and a party to this research, explained that the method is based on the piezoelectric effect. The effect, discovered in 1880 by the French physicists Pierre and Jacques Curie, is found in materials that generate electricity when stretched or compressed.
“Piezoelectric materials can convert ambient vibration to electricity by their inherently possessed electric dipoles,” Khan said. The effect is stronger when the dipoles are aligned.
When flexed, the material made from a sandwich of organometal halide perovskite polymers generated enough electricity to power a tiny radio transmitter. Photo: University of Waterloo
Many piezoelectric materials are ceramics or crystals, including quartz. These materials form the basis of devices as varied as cell phone microphones and atomic force microscopes.
One class of piezoelectric material getting new attention is organometal halide perovskite (OHP) composites, which as a type of polymer is flexible and easy to synthesize. While OHPs could be ideal for energy harvesting applications, they the piezoelectric effect is orders of magnitude lower than other materials. Researchers have been looking to boost the effect.
“Existing piezoelectric devices rely on some tiny nanoparticles inside a polymer matrix to more efficiently align those dipoles, but it is very challenging,” Khan continued, “as such devices get damaged very quickly (breakdown) before all the dipoles are aligned.
Khan’s team looked for another method to strengthen the piezoelectric effect.
“We proposed a new approach to break this dilemma: including a very small amount of electrical insulating molecules with these nanoparticles,” he said. “It helps more effective dipole alignment and enhances the piezoelectric response. Breaking this fundamental limit helped us to design a piezoelectric device, that can generate high output current with a small amount of force applied to it. Let us imagine, you just touched the device with a finger, and it can glow a light."
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The insulating material was simple polystyrene. The research team placed layers of OHP and styrene in a sandwich, with the electric field alternating directions from one layer to the next. The team discovered that more layers led to a greater current density when a force was applied to the material. Not only were these OHP sandwiches durable enough to survive more than 1,000 flexes, but they produced enough current to charge a capacitor under experimental conditions.
In fact, as the team reported in their paper “Breaking dielectric dilemma via polymer functionalized perovskite piezocomposite with large current density output,” published in Nature Communications, a couple dozen touches by a finger were capable of charging a 1 µF capacitor, and 30 flexes a second could power a small radio-frequency transmitter.
“Because of this research, we can say that we will be able now to harness those vibrations more easily,” Khan said. “A very small vibration still can produce high electricity. Another fact is that current technologies are relying on decades-old (piezoelectric) materials, which are brittle ceramics and require high temperatures to grow them. Our materials are flexible and require low processing temperatures and cost."
The hope is that OHP sandwiches could be developed to power small-scale electronics for biomedical applications such as blood-pressure monitoring or systems on machines that feature constant vibrations, such as internal combustion engines or gas turbines.
Jim Romeo is a technology writer in Chesapeake, Va.
The compact, scalable technology harnesses vibrations and small body motions to generate power.
Asif Abdullah Khan, an assistant professor in the Department of Mechanical and Electrical Engineering at Wilkes University in Pennsylvania and a party to this research, explained that the method is based on the piezoelectric effect. The effect, discovered in 1880 by the French physicists Pierre and Jacques Curie, is found in materials that generate electricity when stretched or compressed.
“Piezoelectric materials can convert ambient vibration to electricity by their inherently possessed electric dipoles,” Khan said. The effect is stronger when the dipoles are aligned.
When flexed, the material made from a sandwich of organometal halide perovskite polymers generated enough electricity to power a tiny radio transmitter. Photo: University of Waterloo
One class of piezoelectric material getting new attention is organometal halide perovskite (OHP) composites, which as a type of polymer is flexible and easy to synthesize. While OHPs could be ideal for energy harvesting applications, they the piezoelectric effect is orders of magnitude lower than other materials. Researchers have been looking to boost the effect.
“Existing piezoelectric devices rely on some tiny nanoparticles inside a polymer matrix to more efficiently align those dipoles, but it is very challenging,” Khan continued, “as such devices get damaged very quickly (breakdown) before all the dipoles are aligned.
Khan’s team looked for another method to strengthen the piezoelectric effect.
“We proposed a new approach to break this dilemma: including a very small amount of electrical insulating molecules with these nanoparticles,” he said. “It helps more effective dipole alignment and enhances the piezoelectric response. Breaking this fundamental limit helped us to design a piezoelectric device, that can generate high output current with a small amount of force applied to it. Let us imagine, you just touched the device with a finger, and it can glow a light."
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The insulating material was simple polystyrene. The research team placed layers of OHP and styrene in a sandwich, with the electric field alternating directions from one layer to the next. The team discovered that more layers led to a greater current density when a force was applied to the material. Not only were these OHP sandwiches durable enough to survive more than 1,000 flexes, but they produced enough current to charge a capacitor under experimental conditions.
In fact, as the team reported in their paper “Breaking dielectric dilemma via polymer functionalized perovskite piezocomposite with large current density output,” published in Nature Communications, a couple dozen touches by a finger were capable of charging a 1 µF capacitor, and 30 flexes a second could power a small radio-frequency transmitter.
“Because of this research, we can say that we will be able now to harness those vibrations more easily,” Khan said. “A very small vibration still can produce high electricity. Another fact is that current technologies are relying on decades-old (piezoelectric) materials, which are brittle ceramics and require high temperatures to grow them. Our materials are flexible and require low processing temperatures and cost."
The hope is that OHP sandwiches could be developed to power small-scale electronics for biomedical applications such as blood-pressure monitoring or systems on machines that feature constant vibrations, such as internal combustion engines or gas turbines.
Jim Romeo is a technology writer in Chesapeake, Va.
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