A new concept in energy harvesting could capture energy that is currently mostly wasted due to its characteristic low frequency and use it to power next-generation electronic devices. In a project funded by electronics giant Samsung, a team of Penn State materials scientists and electrical engineers has designed a mechanical energy transducer based on flexible organic ionic diodes that points toward a new direction in scalable energy harvesting of unused mechanical energy in the environment, including wind, ocean waves and human motion.
Devices to harvest ambient mechanical energy to convert to electricity are widely used to power wearable electronics, biomedical devices and the so-called Internet of Things (IoT) — everyday objects that wirelessly connect to the internet. The most common of these devices, based on the piezoelectric effect, operate most efficiently at high frequency, greater than 10 vibrations per second. But at lower frequencies their performance falls off dramatically.
“Our concept is to specifically design a way to turn low-frequency motion, such as human movement or ocean waves, into electricity,” said Qing Wang, professor of materials science and engineering, Penn State. “That’s why we came up with this organic polymer p-n junction device.”
Called an ionic diode, their device is composed of two nanocomposite electrodes with oppositely charged mobile ions separated by a polycarbonate membrane. The electrodes are a polymeric matrix filled with carbon nanotubes and infused with ionic liquids. The nanotubes enhance the conductivity and mechanical strength of the electrodes. When a mechanical force is applied, the ions diffuse across the membrane, creating a continuous direct current. At the same time, a built-in potential that opposes ion diffusion is established until equilibrium is reached. The complete cycle operates at a frequency of one-tenth Hertz, or once every 10 seconds.
For smart phones, the mechanical energy involved in touching the screen could be converted into electricity that can be stored in the battery. Other human motion could provide the energy to power a tablet or wearable device.
“Because the device is a polymer, it is both flexible and lightweight,” Wang said. “When incorporated into a next-generation smart phone, we hope to provide 40 percent of the energy required of the battery. With less demand on the battery, the safety issue should be resolved.”
According to the authors on the paper “Flexible Ionic Devices for Low-Frequency Mechanical Energy Harvesting” published online in the journal Advanced Energy Materials, “The peak power density of our device is in general larger than or comparable to those of piezoelectric generators operated at their most efficient frequencies.”
Michael Hickner, associate professor of materials science and engineering, produced the ionic polymers, with Liang Zhu, a postdoctoral scholar in his group. Qiming Zhang, distinguished professor of electrical engineering, and his group focused on device integration and performance. Wang’s group, including coauthors postdoctoral scholar Qi Li and graduate student Yong Zhang, focused on materials optimization. The co-lead authors are visiting scholar Ying Hou, recent Ph.D graduate Yue Zhou and visiting scholar Lu Yang, all part of Zhang’s group.
“Right now, at low frequencies, no other device can outperform this one. That’s why I think this concept is exciting,” Wang said.
Future work will involve further optimization and integration into smart phones and tablet devices.
Learn more: Capturing the Energy of Slow Motion
The day of charging cellphones with finger swipes and powering Bluetooth headsets simply by walking is now much closer.
Michigan State University engineering researchers have created a new way to harvest energy from human motion, using a film-like device that actually can be folded to create more power. With the low-cost device, known as a nanogenerator, the scientists 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 (click the respective links to see a short video of each demonstration).
The groundbreaking findings, published in the journal Nano Energy, suggest “we’re on the path toward wearable devices powered by human motion,” said Nelson Sepulveda, associate professor of electrical and computer engineering and lead investigator of the project.
“What I foresee, relatively soon, is the capability of not having to charge your cell phone for an entire week, for example, because that energy will be produced by your movement,” said Sepulveda, whose research is funded by the National Science Foundation.
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. Ions are added so that each layer in the device contains charged particles. Electrical energy is created when the device is compressed by human motion, or mechanical energy.
The completed device is 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, for example, while the device used to power the touch screen was as small as a finger.
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 study says.
Remarkably, the device also becomes more powerful when folded.
“Each time you fold it you are increasing exponentially the amount of voltage you are creating,” Sepulveda said. “You can start with a large device, but when you fold it once, and again, and again, it’s now much smaller and has more energy. Now it may be small enough to put in a specially made heel of your shoe so it creates power each time your heel strikes the ground.”
Sepulveda and his team are developing technology that would transmit the power generated from the heel strike to, say, a wireless headset.
A two-stage power management and storage system could dramatically improve the efficiency of triboelectric generators that harvest energy from irregular human motion such as walking, running or finger tapping.
The system uses a small capacitor to capture alternating current generated by the biomechanical activity. When the first capacitor fills, a power management circuit then feeds the electricity into a battery or larger capacitor. This second storage device supplies DC current at voltages appropriate for powering wearable and mobile devices such as watches, heart monitors, calculators, thermometers – and even wireless remote entry devices for vehicles.
By matching the impedance of the storage device to that of the triboelectric generators, the new system can boost energy efficiency from just one percent to as much as 60 percent. The research was reported December 11 in the journal Nature Communications.
“With a high-output triboelectric generator and this power management circuit, we can power a range of applications from human motion,” said Simiao Niu, a graduate research assistant in the School of Materials Science and Engineering at the Georgia Institute of Technology. “The first stage of our system is matched to the triboelectric nanogenerator, and the second stage is matched to the application that it will be powering.”
Triboelectric nanogenerators use a combination of the triboelectric effect and electrostatic induction to generate small amounts of electrical power from mechanical motions such as rotation, sliding or vibration. The triboelectric effect takes advantage of the fact that certain materials become electrically charged after they come into moving contact with a surface made from a different material. However, the output is alternating current, which can power applications such as LED lighting – but is not ideal for mobile devices.
Ordinary alternating current can be converted to direct current by using a transformer – but such a device requires consistency in the number of cycles per second. Because biomechanical energy sources such as walking or finger tapping produce fluctuating amplitude and variable frequencies, a standard transformer can’t be used. In addition, the output from a triboelectric generator tends to have high voltage and low current – while applications for it require just the opposite: low voltage and higher current.
To address the problem, Niu and collaborators under the supervision of Professor Zhong Lin Wang at Georgia Tech developed their power management system, which converts the fluctuating power amplitudes and variable frequencies to a continuous direct current.
The power management system can work with any triboelectric generator that produces a minimum of 100 microwatts. The system requires some power to operate, but compensates by increasing the overall output as much as 330 times to reach milliwatt levels.
“It doesn’t matter what kind of mechanical motion or what frequency of mechanical motion you have as long as the energy input is high,” said Niu. “This is a critical step in the commercialization of triboelectric nanogenerators because it opens up a range of new applications.”
With finger tapping as the only energy source, the power unit provides continuous direct current of 1.044 milliwatts. The unit can work continuously with the motion, allowing devices to be operated even as the device charges the battery or capacitor.
Beyond portable electronics, Niu believes the system could be useful in powering networks of sensors, allowing long-term operation without the need for replacing batteries.
“In a sensor network, you would have so many devices that you could not replace all of the batteries,” he said. “This technology would allow you to power the sensors by harvesting energy from the environment and then directly providing energy for each component of the network.”
With the energy management circuitry demonstrated in this proof-of-concept, the next step will be to miniaturize the circuitry to fit into an overall system, said Zhong Ling Wang, a Regents professor in the Georgia Tech School of Materials Science and Engineering who led development of the original triboelectric nanogenerators.
“This new device provides a bridge between the triboelectric nanogenerator and many different types of applications,” he said. “This work will allow us to build a package that can power wearable and mobile devices from the motion of humans. With constant output from a battery or large capacitor, you can drive just about any device that you want.”
The power management system could also be applied to piezoelectric and pyroelectric generators, which also produce alternating current.
In 2012, Wang and his research team announced triboelectric nanogenerators that produce small amounts of electricity from motion in the world around us – by capturing the electrical charge produced when two different kinds of plastic materials rub against one another. Based on flexible polymer materials, the triboelectric generators provide alternating current (AC) from activities such as walking.
Variations in generator structures allow a variety of applications depending on the source of mechanical energy. Wang’s team has reported four major groups of generators including those that operate by (1) vertical contact-separation mode, (2) lateral sliding mode, (3) single-electron mode, and (4) freestanding triboelectric-layer mode. There are also hybrid combinations of these major structural modes.
Martian colonists could use an innovative new technique to harvest energy from carbon dioxide thanks to research pioneered at Northumbria and Edinburgh Universities.
Dry ice may not be abundant on Earth, but increasing evidence from NASA’s Mars Reconnaissance Orbiter suggests it may be a naturally occurring resource on Mars as suggested by the seasonal appearance of gullies on the surface of the red planet.
If utilised in a Leidenfrost-based engine dry-ice deposits could provide the means to create future power stations on the surface of Mars.
One of the co-authors of Northumbria’s research, Dr Rodrigo Ledesma-Aguilar, said: “Carbon dioxide plays a similar role on Mars as water does on Earth. It is a widely available resource which undergoes cyclic phase changes under the natural Martian temperature variations.”Perhaps future power stations on Mars will exploit such a resource to harvest energy as dry-ice blocks evaporate, or to channel the chemical energy extracted from other carbon-based sources, such as methane gas.
‘This unassisted water splitting, which is very rare, does not require expensive or scarce resources.’
Team reports first ‘unassisted’ water splitting using only hematite and silicon as solar absorbers,
Finding an efficient solar water splitting method to mine electron-rich hydrogen for clean power has been thwarted by the poor performance of hematite. But by ‘re-growing’ the mineral’s surface, a smoother version of hematite doubled electrical yield, opening a new door to energy-harvesting artificial photosynthesis, according to a report published online today in the journal Nature Communications.
Re-grown hematite proved to be a better power generating anode, producing a record low turn-on voltage that enabled the researchers to be the first to use earth-abundant hematite and silicon as the sole light absorbers in artificial photosynthesis, said Boston College associate professor of chemistry Dunwei Wang, a lead author of the report.
The new hydrogen harvesting process achieved an overall efficiency of 0.91 percent, a ‘modest’ mark in and of itself, but the first ‘meaningful efficiency ever measured by hematite and amorphous silicon, two of the most abundant elements on Earth,’ the team reported.
‘By simply smoothing the surface characteristics of hematite, this close cousin of rust can be improved to couple with silicon, which is derived from sand, to achieve complete water splitting for solar hydrogen generation,’ said Wang, whose research focuses on discovering new methods to generate clean energy. ‘This unassisted water splitting, which is very rare, does not require expensive or scarce resources.’
Wang said the findings represent an important step toward realizing the potential performance theoretical models have predicted for hematite, an iron oxide similar to rust.
‘This offers new hope that efficient and inexpensive solar fuel production by readily available natural resources is within reach,’ said Wang. ‘Getting there will contribute to a sustainable future powered by renewable energy.’
The team, which included researchers from Boston College, UC Berkeley and China’s University of Science and Technology, decided to focus on hematite’s surface imperfections, which have been found in earlier studies to limit ‘turn-on’ voltage required to jump-start photoelectrochemistry, the central process behind using artificial photosynthesis to capture and store solar energy in hydrogen gas.
The team re-evaluated hematite surface features using a synchrotron particle accelerator at the Lawrence Berkeley National Laboratory. They established a new ‘re-growth’ strategy that applied an acidic solution to the material under intense heat, a process that simultaneously reduced ridges and filled depressions, smoothing the surface.
Tests immediately showed an improvement in turn-on voltage, as well as an increase in photovoltage from 0.24 volts to 0.80 volts, a dramatic increase in power generation.
The team reported that further modifications to the new hematite-silicon method make it amenable to large-scale utilization. Furthermore, the ‘re-growth’ technique may be applicable to other materials under study for additional breakthroughs in artificial photosynthesis.
A research team at American University of Sharjah (AUS) has made an important breakthrough in energy harvesting technology that can benefit many sectors, from bio-medicine to construction.
The device works by harnessing electromagnetic radiation from different sources and then reusing it to energize low-power circuits.
Potential uses of the technology include being placed in a medical chip that measures blood sugar levels in diabetes patients; powering wireless sensors on bridges, roads and buildings to monitor structural safety factors; or improving the battery life of mobile phones.
Team members include Dr. Lutfi Albasha, Associate Professor in Electrical Engineering; Dr. Nasser Qaddoumi, Professor and Interim Head of the Department of Electrical Engineering; a full-time research associate and six undergraduate students including three UAE nationals.
“One of the main obstacles present when it came to energy harvesting technology was low efficiency. Despite many innovations in the field, one common problem, in most cases, was that the harvester itself utilized most of the collected energy,” Dr. Albasha commented.
Typically, harvesters would provide 5 percent efficiency. However, the AUS team was able to minimize its harvester’s energy consumption and to raise efficiency to more than 80 percent. Launched in 2011, the project is set to have its final testing soon.
Sponsored by Semiconductor Research Corporation (SRC) and Mubadala Technologies Company, the AUS team taped-out a chip using Global Foundries 65 nanometer advanced analog CMOS process. The chip comprises dedicated harvester circuits with very high conversion efficiencies.
In addition, the team was also equally successful in designing a novel wide-band antenna for the same system. “The antenna, reported to be the smallest and best-in-class, is very small and enjoys a wide frequency bandwidth. Tests have shown that this flat antenna can pick up signals from mobile phones, TV signals and even Wi-Fi and toll systems at 5GHz,” said Dr. Qaddoumi.