Energy harvesting is the process of collecting low-level ambient energy and converting it into electrical energy to be used as a power source for miniaturized autonomous devices. Examples of this can be seen in structural health monitoring, smart packaging solutions, communication systems, transportation, air and aerospace vehicles, structural biology, robotics, microelectromechanical systems (MEMS) devices, sensor networks, wearable electronics, agriculture, forest fire detection, or various Internet of Things (IoT) components
The large growth of internet of things (IoT) and sensor networks is predicted in the future. Cisco predicts, by 2020 the world will have trillions of sensor units distributed on the earth. For trillions of batteries that are vastly distributed and each having a limited life time, monitoring, replacing, recycling and exchanging batteries would be a huge and even an impossible task. Batteries have several disadvantages in: the need to either replace or recharge them periodically from fixed power sources, and their relatively large size and weight. Many batteries are rated for a typically 3- to 10-year lifetime; but in most practical applications they last for significantly less, often months rather than years.
Therefore researchers are therefore looking for alternative models to power the future IOT sensors. One of them is to integrate an energy harvester together with a battery to form a self-powered system. Human energy harvesting is a term used to describe systems that utilize the human body as a primary generator. Biomechanical energy harvesting from human motion, such as walking step; ankle, knee, hip, shoulder, and elbow joint motion; and center of mass vertical motion, are potential anchors for electrical power generators. However, human energy harvesters are not capable of generating sufficient energy to perform mechanical work, but could still power low-energy electronics.
Militaries are also exploring Energy harvesting technologies to tackle the issues with solar power like in extreme cold when the batteries fail to hold a charge, and in heavy shade the panels don’t operate. Researchers at the Natick Soldier Research, Development and Engineering Center are working to develop wearable energy-harvesting technology solutions including wearable solar panels as well as backpack and knee kinetic, energy-harvesting devices to reduce weight and the quantity of batteries soldiers required to power their devices.
The possibility and the effectiveness of extracting energy from human activities has been under study for years. As a matter of fact, continuous and uninterrupted power can potentially be available: from typing (~mW), motion of upper limbs (~10 mW), air exhalation while breathing (~100 mW), and walking (1 W). Reimer and Shapiro theoretically proved that up to 4 W could be generated with a 4-mm compression of a shoe sole that is easily achieved at natural pace, that is, two steps per second (or 1 Hz per insert) by a person of 80 kg. The maximum energy that can be generated, assuming that 50–80% of the energy during walk is stored as elastic energy in the shoe would be 2 W.
The increase in minitarization and energy efficiency of electronic components are also aiding in employment of energy harvesting solutions. “Technology advances have enabled modification of the size and shape of the electronic components to the microscale, with commensurate scaling down of their power requirements to milliwatts and microwatt range. Consequently, many complex electronic systems and devices such as wearable medical and autonomous devices consume power in the range less than 200 μW, and wireless sensor networks in the range μW to 100 mW are operated on battery power,” write Vikrant Bhatnagar, and Philip Owende.
“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, in a press release. “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.”
Nanotechnology research, development and application are relevant and potentially beneficial to almost every facet of our lives, including health, energy, infrastructure, information technology, transportation, food safety, environmental science, as well as defence. Nanotechnologies can greatly aid in meeting the future demand for energy harvesting. Some nanotechnologies can operate without a traditional electricity source and can draw the energy they require from the environment in which they operate.
Global warming and the resultant energy crisis has motivated scientists to search for renewable and green energy resources in order to ensure sustainable development of our human civilization. Nanotechnologies will significantly assist in meeting the future demand for energy harvesting. The goal of energy-harvesting technologies is to develop nanogenerators which operate over a broad range of conditions for extended time periods with high reliability. The discovery of nanogenerators is one of the top ten world discoveries in science, according to academics from the Chinese Academy of Science. Their discovery could have equal importance as the invention of mobile phones in 10 to 30 years, according to the New Scientist. Nanogenerators are in the top six future and emerging technologies selected by European Commission for support in the next 10 years.
Nanotechnologies for Energy Harvesting
Scientists are close to using people as device chargers. Nano generators can harvest energy from the human body and that energy can power wearable and implantable devices such as pacemakers, muscle sensors and tumour detectors. The human body generates a great amount of mechanical energy that is available for harvesting and potential utilisation, through processes such as body movement, respiration and blood flow.
The body also generates thermal energy in the form of body heat and biochemical energy from physiological processes and metabolism. A bio-nano generator is an electrochemical device which works like a fuel cell, except it draws power from blood glucose in a living body. An enzyme is capable of stripping glucose of its electrons, freeing them for use in electrical devices. The electricity generated is able to power devices embedded in the body. The design and development of appropriate energy-harvesting strategies for miniaturised powering packages is therefore critical.
Piezoelectric generation is the ability of certain materials to generate an electric charge in response to applied mechanical stress. Piezoelectric ceramic thin film nanomaterials transform miniature movements of the human body into electrical energy. Although its definition may include any type of energy harvesting devices using nano-structures to convert various types of ambient energy (e.g. solar power and thermal energy), a piezoelectric nanogenerator is an energy harvesting device capable of converting external kinetic energy into electrical energy via action by a nano-structured piezoelectric material.
Among various piezoelectric materials studied for nanogenerators, much research has focused on materials with wurtzite structure, a crystal structure for various binary compounds. The greatest advantage of these materials arises from the cost-effective fabrication technique – hydrothermal synthesis. These flexible nanogenerators, that efficiently convert mechanical energy into electrical energy, have been extensively studied because of their great potential for driving low-power personal electronics and self-powered sensors.
Bio-mechanical forces produced by the human body are able to produce non-polluting energy. This technology can be used to power an LED and can operate touchable flexible displays. The nanogenerator gives a high output voltage and the output current is small and, because of this, not only can it be used as a potential power source but also as a sensor for measuring temperature variation.
Nanogenerator that harvest human energy from walking, talking, breathing, typing and more by utilize mainly two effects: piezoelectricity and triboelectricity. Piezoelectric nanogenerators (PENG) depend on the strain induced piezoelectric polarization in certain crystals, such as ZnO and PZT. The potential created by polarization charges can drive the flow of electrons across two electrodes placed on the top and bottom surfaces of the crystal.
The demand for energy has not only increased, but the size and shape of energy sources have also adapted and evolved to meet the challenges presented by an electronically evolving age. As a result of the increasing requirement for inexpensive renewable energy sources, organic-based energy harvesters have been introduced. A team of researchers at Jadavpur University in Kolkata, India, started recycling fish by-products into piezoelectric energy harvesters. The scientists’ concept was to create a bio-piezoelectric nanogenerator or energy harvester out of fish scales. Fish scales contain collagen fibres that generate an electric charge in response to mechanical stress. It also has the potential for portable electronics with reduced e-waste elements. Scientists are thinking of various ways to put such inedible by-products to good use, especially food waste.
The triboelectric effect (also known as triboelectric charging) is a type of contact electrification in which certain materials become electrically charged after they come into frictional contact with a different material. Rubbing glass with fur, or a plastic comb through the hair, can build up triboelectricity. The contact induced triboelectric charges can generate a potential drop when the two surfaces are separated by mechanical force, which can drive electrons to flow between the two electrodes built on the top and bottom surfaces of the two materials. This is the birth of the triboelectric nanogenerator (TENG).
Ever since the first report on the TENG in January 2012, the area power density reaches 500 W m2 , volume power density reaches 15 MW m3 , and an instantaneous conversion efficiency of 70% has been demonstrated. For low frequency agitation and if the energy generated by all the residual vibrations are acquired, a total energy conversion efficiency of up to 85% has been shown experimentally.
Ultrathin device harvests electricity from human motion
Vanderbilt University’s Nanomaterials and Energy Devices Laboratory has developed a new, ultrathin energy harvesting system based on battery technology and made from layers of black phosphorus that are only a few atoms thick. The new device generates small amounts of electricity when it is bent or pressed even at the extremely low frequencies characteristic of human motion.
Pint’s device is based on battery construction with both positive and negative electrodes made from the same material. Vanderbilt researchers used black phosphorus nanosheets, a material has become the latest darling of the 2D materials research community because of its attractive electrical, optical and electrochemical properties. Although this prevents the device from storing energy, it allows it to fully exploit the voltage changes caused by bending and twisting and so produce significant amounts of electrical current in response to human motions. They have found that bending their prototype devices produces as much as 40 microwatts per square foot and can sustain current generation over the full duration of movements as slow as 0.01 Hertz, one cycle every 100 seconds.
Number of research groups are developing energy harvesters based on piezoelectric materials that convert mechanical strain into electricity. However, these materials often work best at frequencies of more than 100 Hertz. This means that they don’t work for more than a tiny fraction of any human movement so they achieve limited efficiencies of less than 5-10 percent even under optimal conditions. “Our harvester is calculated to operate at over 25 percent efficiency in an ideal device configuration, and most importantly harvest energy through the whole duration of even slow human motions, such as sitting or standing,” Pint said.
“Compared to the other approaches designed to harvest energy from human motion, our method has two fundamental advantages,” said Pint. “The materials are atomically thin and small enough to be impregnated into textiles without affecting the fabric’s look or feel and it can extract energy from movements that are slower than 10 Hertz—10 cycles per second—over the whole low-frequency window of movements corresponding to human motion.”
One of the more futuristic applications of this technology might be electrified clothing. It could power clothes impregnated with liquid crystal displays that allow wearers to change colors and patterns with a swipe on their smartphone. “When incorporated into clothing, our device can translate human motion into an electrical signal with high sensitivity that could provide a historical record of our movements. Or clothes that track our motions in three dimensions could be integrated with virtual reality technology. There are many directions that this could go.”
Smart Textile’ Turns Body Movements Into Power Source
Scientists in China and the United States have designed a fabric that can power wearable devices by harvesting energy from both sunlight and body movements and can be produced on a standard industrial weaving machine. Combining two types of electricity generation into one textile paves the way for developing garments that could provide their own source of energy to power devices such as smart phones or global positioning systems.
The fabric is based on low-cost, lightweight polymer fibers coated with metals and semiconductors that allow the material to harvest energy. The solar cells constructed from lightweight polymer fibers are weaved with fiber-based triboelectric nanogenerators along with wool on high-throughput commercial weaving equipment to create a textile just 0.01 inches (0.32 millimeters) thick.Wang envisions that the new fabric could be integrated into tents, curtains or wearable garments.
“It is highly deformable, breathable and adaptive to human surface curves and biomechanical movement,” said Xing Fan, one of the fabric’s inventors and an associate professor of chemical engineering at Chongqing University in China. “And this approach enables the power textile to be easily integrated with other functional fibers or electronic devices to form a flexible, self-powered system.”
In a paper published online in the journal Nature Energy, the researchers described how they used a layer-by-layer process similar to those employed in the semiconductor industry. Using this method, they coated polymer fibers with various materials to create cable-like solar cells that generate electricity from sunlight and also so-called triboelectric nanogenerators (TENG).
The TENGs rely on the triboelectric effect, by which certain materials become electrically charged when rubbed against another type of material. When the materials are in contact, electrons flow from one to the other, but when the materials are separated, the one receiving electrons will hold a charge, Fan said.
If these two materials are then connected by a circuit, a small current will flow to equalize the charges. By continuously repeating the process, an alternating electrical current can be produced to generate power, Fan added.
By tweaking the patterns and configurations of the textile, the researchers found they could tune the power output and customize it for specific applications by aligning the TENGs with the direction of body movements so that they can capture as much energy as possible, or by using different patterns for high-light and low-light environments.
“This is very important. Different applications have different requirements. For example, the voltage requirement of a cellphone is different from that of an electronic watch,” Fan told Live Science. “Also, people walking between buildings in London may have less sunshine than those running on the beach in California.”
The team has yet to conduct long-term durability tests, but after 500 cycles of bending, there was no drop in performance, Fan said. However, the study noted that electrical output of the TENG did gradually drop to 73.5 percent of its original performance when relative humidity was increased from 10 percent to 90 percent.
Still, the fabric’s full performance can be recovered if the device is dried out, Fan said. He added that encapsulating the textile in an inert material using a common heat-wrapping process should counteract the issue.
Electricity-Generating Textiles Power Small Electronics
A team from Chalmers University of Technology in Sweden has created a fabric that converts kinetic energy into electric power, where the greater the load applied to the textile and the wetter it becomes the more electricity it can generate. The new woven fabric has generated enough power to light an LED, send wireless signals or drive small electric units like pocket calculators or digital watches.
The technology is based on the piezoelectric effect, which results in the generation of electricity from deformation of a piezoelectric material, like when it is stretched. The researchers weaved a piezoelectric yarn together with an electrically conducting yarn to create the new fabric.
“The textile is flexible and soft and becomes even more efficient when moist or wet,” Anja Lund, a postdoctoral researcher at Chalmers, said in a statement. “To demonstrate the results from our research we use a piece of the textile in the shoulder strap of a bag. The heavier the weight packed in the bag and the more of the bag that consists of our fabric, the more electric power we obtain. When our bag is loaded with three kilos of books, we produce a continuous output of four microwatts. That’s enough to intermittently light an LED. By making an entire bag from our textile, we could get enough energy to transmit wireless signals.”
According to the study, textiles are an ideal format for low-power electronics because textiles can interact with the user as displays based on electrochromic or electroluminescent fibers or by movement, such as artificial muscles.
Taking wearable technology to a whole new level, smart textiles are known to enhance the overall functionality of the apparel by integrating electronic components into the fabric. What makes smart fabric technology revolutionary is its ability to communicate, transform, and even grow!
‘Smartness’ amid fabrics initially emerged in the form of passive smart textiles, which could sense and react to only environmental conditions. Today, we also have active smart textiles and ultra-smart textiles. The ultra-smart textiles have units that work similar to a human brain, with reasoning, cognition, and activating capabilities.
Smartphones, Wearable Devices powered by human motion
Engineering researchers from the Michigan State University have developed a pioneering nanotechnology that may soon power up smartphones and wearable devices using simple human motions, such as finger swipe over a smartphone screen to charge it, typing on keyboards that will charge laptop batteries, and kinetics of jogging feet charging wearable devices. Even biological functions e.g. heartbeats or diaphragm activities involve mechanical energy that has recently been tapped as renewable energy sources.
The new nanotechnology, described in a paper published in the journal Nano Energy, was able to successfully operate an LCD touch screen, a bank of 20 LED lights and a flexible keyboard with the help of simple touching and pressing motions, even without the aid of a battery.
Dubbed as biocompatible ferroelectret nanogenerator or FENG, the new device is as thin as a sheet of paper and can be molded to adapt to many applications and sizes. The researchers noted that the filmlike nanogenerator is a low-cost device that becomes more powerful and efficient when folded. The innovative device is consisted of a silicone wafer fabricated with several thin layers that include silver, polyimide and polypropylene ferroelectret. These layers are all environmentally friendly. Ions were added to each layer, making the device contain charged particles. FENG produces electrical energy when human motions or mechanical energy compresses the layers.
Due to the ability of FENG to become more powerful when folded, the researchers noted that it can start as a large device then be folded again and again to make a smaller more powerful device. Each fold is said to exponentially increase the amount of voltage the device can create. Furthermore, FENG is considered to be “a promising and alternative method in the field of mechanical-energy harvesting” due to its many advantages, such as being lightweight, flexible, biocompatible, scalable, low-cost and robust.
The authors introduce Polypropylene ferroelectret (PPFE) as the active material in an efficient, flexible, and biocompatible ferroelectret nanogenerator (FENG) device. PPFE is charged polymers with empty voids and inorganic particles that create giant dipoles across the material’s thickness. Upon applied pressure, the change in the dipole moments generate a change of the accumulated electric charge on each surface of the PPFE film, resulting in a potential difference between the two electrodes of the FENG.
Energy-harvesting nanotechnology yarns generate electricity
An international research team led by scientists at The University of Texas at Dallas and Hanyang University in South Korea has developed “twistron” yarns that generate electricity when they are stretched or twisted. The easiest way to think of twistron harvesters is, you have a piece of yarn, you stretch it, and out comes electricity,” said Dr. Carter Haines, associate research professor in the Alan G. at UT Dallas.
The yarns are constructed from carbon nanotubes, which are hollow cylinders of carbon 10,000 times smaller in diameter than a human hair. The researchers first twist-spun the nanotubes into high-strength, lightweight yarns. To make the yarns highly elastic, they introduced so much twist that the yarns coiled like an over-twisted rubber band.
In order to generate electricity, the yarns must be either submerged in or coated with an ionically conducting material, or electrolyte, which can be as simple as a mixture of ordinary table salt and water.
“Fundamentally, these yarns are supercapacitors,” said Dr. Na Li, a research scientist at the NanoTech Institute and co-lead author of the study. “In a normal capacitor, you use energy — like from a battery — to add charges to the capacitor. But in our case, when you insert the carbon nanotube yarn into an electrolyte bath, the yarns are charged by the electrolyte itself. No external battery, or voltage, is needed.”
When a harvester yarn is twisted or stretched, the volume of the carbon nanotube yarn decreases, bringing the electric charges on the yarn closer together and increasing their energy, Haines said. This increases the voltage associated with the charge stored in the yarn, enabling the harvesting of electricity. Stretching the coiled twistron yarns 30 times a second generated 250 watts per kilogram of peak electrical power when normalized to the harvester’s weight, said Dr. Ray Baughman, director of the NanoTech Institute and a corresponding author of the study.
The researchers also sewed twistron harvesters into a shirt. Normal breathing stretched the yarn and generated an electrical signal, demonstrating its potential as a self-powered respiration sensor. “Electronic textiles are of major commercial interest, but how are you going to power them?” Baughman said. “Harvesting electrical energy from human motion is one strategy for eliminating the need for batteries. Our yarns produced over a hundred times higher electrical power per weight when stretched compared to other weavable fibers reported in the literature.”
“Although numerous alternative harvesters have been investigated for many decades, no other reported harvester provides such high electrical power or energy output per cycle as ours for stretching rates between a few cycles per second and 600 cycles per second.”
Even though the investigators used very small amounts of twistron yarn in the current study, they have shown that harvester performance is scalable, both by increasing twistron diameter and by operating many yarns in parallel. “If our twistron harvesters could be made less expensively, they might ultimately be able to harvest the enormous amount of energy available from ocean waves,” Baughman said. “However, at present these harvesters are most suitable for powering sensors and sensor communications. Based on demonstrated average power output, just 31 milligrams of carbon nanotube yarn harvester could provide the electrical energy needed to transmit a 2-kilobyte packet of data over a 100-meter radius every 10 seconds for the Internet of Things.”
AMPY MOVE, the world’s first wearable motion charger
AMPY Move transforms the kinetic energy from all your motion throughout the day into power for your phone or other devices. AMPY Move is a wearable about the size of a deck of cards and weighs as much as your phone.
AMPY MOVE consists of a circuit board, a battery and two inductors. An inductor is a coil with a magnet suspended inside. When your motion moves the magnet, it induces a current within the coil. Using several types of circuits, this current is then converted into energy that can be stored in the battery.
“Inductors have been used to convert kinetic energy into electrical energy for decades in a variety of applications. But these devices are typically big and bulky, about the size of your forearm. So, we set out to find a way to generate more power in a small form factor that could fit into your daily life. In doing so, we came up with a patent-pending inductor architecture that brought AMPY MOVE to life,” says the company.
References and Resources also include:
Li, et al., Flexible and biocompatible polypropylene ferroelectret nanogenerator (FENG): On the path toward wearable devices powered by human motion, Nano Energy (2016), http://dx.doi.org/10.1016/j.nanoen.2016.10.007i