Energy harvesting also known as power harvesting or energy scavenging or ambient power is the process by which energy is derived from external sources e. Energy harvesters provide a very small amount of power for low-energy electronics.
While the input fuel to some large-scale generation costs resources oil, coal, etc. For example, temperature gradients exist from the operation of a combustion engine and in urban areas, there is a large amount of electromagnetic energy in the environment because of radio and television broadcasting. One of the earliest applications of ambient power collected from ambient electromagnetic radiation EMR is the crystal radio.
The principles of energy harvesting from ambient EMR can be demonstrated with basic components. Energy harvesting devices converting ambient energy into electrical energy have attracted much interest in both the military and commercial sectors. Some systems convert motion, such as that of ocean waves, into electricity to be used by oceanographic monitoring sensors for autonomous operation. Future applications may include high power output devices or arrays of such devices deployed at remote locations to serve as reliable power stations for large systems.
Another application is in wearable electronics, where energy harvesting devices can power or recharge cellphones, mobile computers, radio communication equipment, etc.
All of these devices must be sufficiently robust to endure long-term exposure to hostile environments and have a broad range of dynamic sensitivity to exploit the entire spectrum of wave motions. Energy can also be harvested to power small autonomous sensors such as those developed using MEMS technology.
These systems are often very small and require little power, but their applications are limited by the reliance on battery power. Scavenging energy from ambient vibrations, wind, heat or light could enable smart sensors to be functional indefinitely.
Typical power densities available from energy harvesting devices are highly dependent upon the specific application affecting the generator's size and the design itself of the harvesting generator.
Energy harvesting autonomous sensor systems pdf file
In general, energy can be stored in a capacitor , super capacitor , or battery. Capacitors are used when the application needs to provide huge energy spikes. Batteries leak less energy and are therefore used when the device needs to provide a steady flow of energy. Compared to batteries, super capacitors have virtually unlimited charge-discharge cycles and can therefore operate forever enabling a maintenance-free operation in IoT and wireless sensor devices .
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Current interest in low power energy harvesting is for independent sensor networks. The history of energy harvesting dates back to the windmill and the waterwheel. People have searched for ways to store the energy from heat and vibrations for many decades. One driving force behind the search for new energy harvesting devices is the desire to power sensor networks and mobile devices without batteries. Energy harvesting is also motivated by a desire to address the issue of climate change and global warming.
There are many small-scale energy sources that generally cannot be scaled up to industrial size in terms of comparable output to industrial size solar, wind or wave power:. A possible source of energy comes from ubiquitous radio transmitters.
Historically, either a large collection area or close proximity to the radiating wireless energy source is needed to get useful power levels from this source. The nantenna is one proposed development which would overcome this limitation by making use of the abundant natural radiation such as solar radiation. One idea is to deliberately broadcast RF energy to power and collect information from remote devices:  This is now commonplace in passive radio-frequency identification RFID systems, but the Safety and US Federal Communications Commission and equivalent bodies worldwide limit the maximum power that can be transmitted this way to civilian use.
This method has been used to power individual nodes in a wireless sensor network  . Airflow can be harvested by various turbine and non-turbine generator technologies. For example, Zephyr Energy Corporation's patented Windbeam micro generator captures energy from airflow to recharge batteries and power electronic devices. The generator consists of a lightweight beam suspended by durable long-lasting springs within an outer frame.
Energy Harvesting Systems
The beam oscillates rapidly when exposed to airflow due to the effects of multiple fluid flow phenomena. A linear alternator assembly converts the oscillating beam motion into usable electrical energy.
A lack of bearings and gears eliminates frictional inefficiencies and noise. The generator can operate in low-light environments unsuitable for solar panels e.
HVAC ducts and is inexpensive due to low cost components and simple construction. The scalable technology can be optimized to satisfy the energy requirements and design constraints of a given application. The flow of blood can also be used to power devices. For instance, the pacemaker developed at the University of Bern, uses blood flow to wind up a spring which in turn drives an electrical micro-generator. Photovoltaic PV energy harvesting wireless technology offers significant advantages over wired or solely battery-powered sensor solutions: virtually inexhaustible sources of power with little or no adverse environmental effects.
Indoor PV harvesting solutions have to date been powered by specially tuned amorphous silicon aSi a technology most used in Solar Calculators.
The dyes absorbs light much like chlorophyll does in plants. Electrons released on impact escape to the layer of TiO 2 and from there diffuse, through the electrolyte, as the dye can be tuned to the visible spectrum much higher power can be produced. The piezoelectric effect converts mechanical strain into electric current or voltage. This strain can come from many different sources.
Human motion, low-frequency seismic vibrations, and acoustic noise are everyday examples. Except in rare instances the piezoelectric effect operates in AC requiring time-varying inputs at mechanical resonance to be efficient.
Most piezoelectric electricity sources produce power on the order of milliwatts, too small for system application, but enough for hand-held devices such as some commercially available self-winding wristwatches.
One proposal is that they are used for micro-scale devices, such as in a device harvesting micro-hydraulic energy. In this device, the flow of pressurized hydraulic fluid drives a reciprocating piston supported by three piezoelectric elements which convert the pressure fluctuations into an alternating current. As piezo energy harvesting has been investigated only since the late s,   it remains an emerging technology.
Nevertheless, some interesting improvements were made with the self-powered electronic switch at INSA school of engineering, implemented by the spin-off Arveni. In , the proof of concept of a battery-less wireless doorbell push button was created, and recently, a product showed that classical wireless wallswitch can be powered by a piezo harvester. Other industrial applications appeared between and ,  to harvest energy from vibration and supply sensors for example, or to harvest energy from shock.
Piezoelectric systems can convert motion from the human body into electrical power. DARPA has funded efforts to harness energy from leg and arm motion, shoe impacts, and blood pressure for low level power to implantable or wearable sensors.
The nanobrushes are another example of a piezoelectric energy harvester.
Energy Harvesting Applications
Multiple other nanostructures have been exploited to build an energy-harvesting device, for example, a single crystal PMN-PT nanobelt was fabricated and assembled into a piezoelectric energy harvester in These energy harvesting sources by association affect the body. The Vibration Energy Scavenging Project  is another project that is set up to try to scavenge electrical energy from environmental vibrations and movements.
Microbelt can be used to gather electricity from respiration. The use of piezoelectric materials to harvest power has already become popular.
Piezoelectric materials have the ability to transform mechanical strain energy into electrical charge. Piezo elements are being embedded in walkways    to recover the "people energy" of footsteps. They can also be embedded in shoes  to recover "walking energy".
Energy Harvesting Autonomous Sensor Systems: Design, Analysis, and Practical Implementation
The stretching strain in a doubly clamped beam shows a nonlinear stiffness, which provides a passive feedback and results in amplitude-stiffened Duffing mode resonance. One drawback is that the piezoelectric cantilever has gradient strain distribution, i. To address this issue, triangle shaped and L-shaped cantilever are proposed for uniform strain distribution. In , Soochow University researchers reported hybridizing a triboelectric nanogenerator and a silicon solar cell by sharing a mutual electrode.
This device can collect solar energy or convert the mechanical energy of falling raindrops into electricity.
Brothers Pierre Curie and Jacques Curie gave the concept of piezoelectric effect in Pyroelectric crystals that have a unique polar axis and have spontaneous polarization, along which the spontaneous polarization exists.
These are the crystals of classes 6mm , 4mm , mm2 , 6 , 4 , 3m , 3 , 2 , m. Consequently, the electric centers of positive and negative charges are displaced of an elementary cell from equilibrium positions, i. Since piezoelectric effect in pyroelectric crystals arises as a result of changes in their spontaneous polarization under external effects electric fields , mechanical stresses. PZT thin films have attracted attention for applications such as force sensors, accelerometers , gyroscopes actuators, tunable optics, micro pumps, ferroelectric RAM, display systems and smart roads,  when energy sources are limited, energy harvesting plays an important role in the environment.
Smart roads have the potential to play an important role in power generation. Embedding piezoelectric material in the road can convert pressure exerted by moving vehicles into voltage and current. Piezoelectric sensors are most useful in Smart-road technologies that can be used to create systems that are intelligent and improve productivity in the long run. Imagine highways that alert motorists of a traffic jam before it forms.
Or bridges that report when they are at risk of collapse, or an electric grid that fixes itself when blackouts hit. For many decades, scientists and experts have argued that the best way to fight congestion is intelligent transportation systems, such as roadside sensors to measure traffic and synchronized traffic lights to control the flow of vehicles.
But the spread of these technologies has been limited by cost. There are also some other smart-technology shovel ready projects which could be deployed fairly quickly, but most of the technologies are still at the development stage and might not be practically available for five years or more. The pyroelectric effect converts a temperature change into electric current or voltage. It is analogous to the piezoelectric effect , which is another type of ferroelectric behavior.
Pyroelectricity requires time-varying inputs and suffers from small power outputs in energy harvesting applications due to its low operating frequencies. One way to directly convert waste heat into electricity is by executing the Olsen cycle on pyroelectric materials.
The Olsen cycle consists of two isothermal and two isoelectric field processes in the electric displacement-electric field D-E diagram.
The principle of the Olsen cycle is to charge a capacitor via cooling under low electric field and to discharge it under heating at higher electric field.
Several pyroelectric converters have been developed to implement the Olsen cycle using conduction,  convection,     or radiation. Additionally, a pyroelectric scavenging device that does not require time-varying inputs was recently introduced. The energy-harvesting device uses the edge-depolarizing electric field of a heated pyroelectric to convert heat energy into mechanical energy instead of drawing electric current off two plates attached to the crystal-faces.
In , Thomas Johann Seebeck discovered that a thermal gradient formed between two dissimilar conductors produces a voltage.
At the heart of the thermoelectric effect is the fact that a temperature gradient in a conducting material results in heat flow; this results in the diffusion of charge carriers. The flow of charge carriers between the hot and cold regions in turn creates a voltage difference.
In , Jean Charles Athanase Peltier discovered that running an electric current through the junction of two dissimilar conductors could, depending on the direction of the current, cause it to act as a heater or cooler.