potential ambient energy

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Potential Ambient Energy-Harvesting Sources andTechniquesFaruk Yildiz

AbstractAmbient energy harvesting is also known as energy scavenging or power harvesting, and it isthe process where energy is obtained from the environment. A variety of techniques areavailable for energy scavenging, including solar and wind powers, ocean waves,

piezoelectricity, thermoelectricity, and physical motions. For example, some systems convertrandom motions, including ocean waves, into useful electrical energy that can be used byoceanographic monitoring wireless sensor nodes for autonomous surveillance. Ambientenergy sources are classified as energy reservoirs, power distribution methods, or power-scavenging methods, which may enable portable or wireless systems to be completely batteryindependent and self sustaining. The students from different disciplines, such as industrialtechnology, construction, design and development and electronics, investigated the

effectiveness of ambient energy as a source of power. After an extensive literature review,students summarized each potential ambient energy source and explained future energy-harvesting systems to generate or produce electrical energy as a support to conventionalenergy storage devices. This article investigates recent studies about potential ambientenergy-harvesting sources and systems.

Introduction

Today, sustaining the power requirement for autonomous wireless and portable devices is animportant issue. In the recent past, energy storage has improved significantly. However, this

progress has not been able to keep up with the development of microprocessors, memorystorage, and wireless technology applications. For example, in wireless sensor networks,

battery-powered sensors and modules are expected to last for a long period of time. However,conducting battery maintenance for a large-scale network consisting of hundreds or eventhousands of sensor nodes may be difficult, if not impossible. Ambient power sources, as areplacement for batteries, come into consideration to minimize the maintenance and the costof operation. Power scavenging may enable wireless and portable electronic devices to becompletely self-sustaining, so that battery maintenance can be eventually removed.Researchers have performed many studies in alternative energy sources that could providesmall amounts of electricity to electronic devices, and this will be explained in anothersection of this article.

Energy harvesting can be obtained from different energy sources, such as mechanicalvibrations, electromagnetic sources, light, acoustic, airflow, heat, and temperature variations.

Energy harvesting, in general, is the conversion of ambient energy into usable electricalenergy. When compared with energy stored in common storage elements, such as batteries,capacitors, and the like, the environment represents a relatively infinite source of availableenergy.

Systems continue to become smaller, yet less energy is available on board, leading to a shortrun-time for a device or battery life. Researchers continue to build high-energy density

batteries, but the amount of energy available in the batteries is not only finite but also low,which limits the life time of the systems. Extended life of the electronic devices is veryimportant; it also has more advantages in systems with limited accessibility, such as thoseused in monitoring a machine or an instrument in a manufacturing plant used to organize achemical process in a hazardous environment. The critical long-term solution shouldtherefore be independent of the limited energy available during the functioning or operatingof such devices. Table 1 compares the estimated power and challenges of various ambient


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energy sources in a recent study byYildiz , Zhu, Pecen , and Guo (2007). Values in the tablewere derived from a combination of published studies, experiments performed by the authors,theory, and information that is commonly available in textbooks. The source of informationfor each technique is given in the third column of the table. Though this comparison is notcomprehensive, it does provide a broad range of potential methods to scavenge and store

energy from a variety of ambient energy sources. Light, for instance, can be a significantsource of energy, but it is highly dependent on the application and the experience to whichthe device is subjected. Thermal energy, in contrast, is limited because temperaturedifferences across a chip are typically low. Vibration energy is a moderate source, but again,it is dependent on the particular application, as cited by Torres and Rincon-Mora (2005).

Table 1. Comparison of Power Density of Energy Harvesting Methods

Energy Source Power Density & Performance Source of Information

Acoustic Noise0.003 W/cm3 @ 75Db0.96 W/cm3 @ 100Db

(Rabaey, Ammer, Da Silva Jr,Patel, & Roundy, 2000)

Temperature Variation 10 W/cm3(Roundy, Steingart , Frchette ,Wright, Rabaey , 2004)

Ambient Radio Frequency 1 W/cm2 (Yeatman, 2004)

Ambient Light100 mW/cm2 (direct sun)100 _W/cm2 (illuminated office)

Available

Thermoelectric 60 _W/cm2 (Stevens, 1999)

Vibration(micro generator)

4 _W/cm3 (human motionHz)

800 _W/cm3 (machineskHz)

(Mitcheson, Green, Yeatman,& Holmes, 2004)

Vibrations (Piezoelectric) 200 W/cm3 (Roundy, Wright, & Pister , 2002)

Airflow 1 W/cm2 (Holmes, 2004)

Push buttons 50 _J/N (Paradiso & Feldmeier, 2001)

Shoe Inserts 330 W/cm2 (Shenck & Paradiso, 2001)Hand generators 30 W/kg (Starner & Paradiso, 2004)

Heel strike 7 W/cm2(Yaglioglu, 2002)(Shenck & Paradiso, 2001)

Ambient Energy Sources

Ambient energy harvesting, also known as energy scavenging or power harvesting, is theprocess where energy is obtained and converted from the environment and stored for use inelectronics applications. Usually this term is applied to energy harvesting for low power andsmall autonomous devices, such as wireless sensor networks, and portable electronicequipments. A variety of sources are available for energy scavenging, including solar power,

ocean waves, piezoelectricity, thermoelectricity, and physical motions (active/passive humanpower). For example, some systems convert random motions, including ocean waves, intouseful electrical energy that can be used by oceanographic monitoring wireless sensor nodesfor autonomous surveillance.

The literature review shows that no single power source is sufficient for all applications, andthat the selection of energy sources must be considered according to the applicationcharacteristics. Before going into details, a general overview of ambient energy sources are

presented, and summarized the resources according to their characteristics:

Human Body: Mechanical and thermal (heat variations) energy can be generated froma human or animal body by actions such as walking and running;

Natural Energy: Wind, water flow, ocean waves, and solar energy can providelimitless energy availability from the environment;
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Mechanical Energy: Vibrations from machines, mechanical stress, strain from high-pressure motors, manufacturing machines, and waste rotations can be captured andused as ambient mechanical energy sources;

Thermal Energy: Waste heat energy variations from furnaces, heaters, and frictionsources;

Light Energy: This source can be divided into two categories of energy: indoor roomlight and outdoor sunlight energy. Light energy can be captured via photo sensors,

photo diodes, and solar photovoltaic (PV) panels; and

Electromagnetic Energy: Inductors, coils, and transformers can be considered asambient energy sources, depending on how much energy is needed for the application.

Additionally, chemical and biological sources and radiation can be considered ambientenergy sources. Figure 1 shows a block diagram of general ambient energy-harvestingsystems. The first row shows the energy-harvesting sources. Actual implementation and toolsare employed to harvest the energy from the source are illustrated in the second row. Thethird row shows the energy-harvesting techniques from each source. The research efforts are

employed by the above listed sources to explore in general how practical devices that extractpower from ambient energy sources are. A broad review of the literature of potential energy-scavenging methods has been carried out by the authors. The result of this literature review iscategorized for each source, and follows in the next few sections of this paper.

Figure 1. Ambient Energy Systems


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Mechanical Energy Harvesting

An example of electric power generation using rotational movement is the self-powered,battery-less, cordless wheel computer mouse cited by Mikami , Tetsuro , Masahiko, Hiroko(2005). The system is called Soc and is designed as an ultra low power wireless interface forshort-range data communication as a wireless battery-less mouse. The system was designed

uniquely to capture rotational movements by the help of the mouse ball to generate andharvest electric power. The electric generator is powered through exploiting rolling energy bydragging the mouse. The energy-harvesting system was intended to power the electronicsystem of a mouse device, such as the ultra low power RF transmitter and microcontroller.The experimental results of the study showed that the mouse only needed 2.2mW energy tooperate. The total energy captured using an energy-harvesting system was bigger than 3mW,which was enough for the wireless mouse operations in a transmit range of one meter.

Another example of mechanical energy harvesting is an electrets-based electrostatic microgenerator, which was proposed by Sterken , Fiorini , Baert , Puers , and Borghs (2003). In thissystem, a micro machined electrostatic converter consisted of a vibration sensitive variablecapacitor polarized by an electret. A general multi domain model was built and analyzed inthe same study, and it showed that power generation capabilities up to 50w for a 0.1cm2surface area were attainable.

Mechanical Vibrations

Indoor operating environments may have reliable and constant mechanical vibration sourcesfor ambient energy scavenging. For example, indoor machinery sensors may have plentifulmechanical vibration energy that can be monitored and used reliably. Vibrationenergyharvesting devices can be either electromechanical or piezoelectric. Electromechanicalharvesting devices, however, are more commonly researched and used.Roundy, Wright, andRabaey (2004) reported that energy withdrawal from vibrations could be based on themovement of a spring-mounted mass relative to its support frame. Mechanical acceleration is

produced by vibrations that, in turn, cause the mass component to move and oscillate. Thisrelative dislocation causes opposing frictional and damping forces to be applied against themass, thereby reducing and eventually extinguishing the oscillations. The damping forceenergy can be converted into electrical energy via an electric field (electrostatic), magneticfield (electromagnetic), or strain on a piezoelectric material. These energy conversionschemes can be extended and explained under the three listed subjects because the nature ofthe conversion types differs even if the energy source is vibration. In the section below, themain differences of the three sources are discussed.

Electromagnetic

This technique uses a magnetic field to convert mechanical energy to electrical energy

(Amirtharajah & Chandrakasan, 1998). A coil attached to the oscillating mass is made to passthrough a magnetic field, which is established by a stationary magnet, to produce electricenergy. The coil travels through a varying amount of magnetic flux, inducing a voltageaccording to Faraday's law. The induced voltage is inherently small and therefore must beincreased to become a viable source of energy. (Kulah & Najafi, 2004). Techniques toincrease the induced voltage include using a transformer, increasing the number of turns ofthe coil, or increasing the permanent magnetic field (Torres & Rincn -Mora, 2005).However, each of these parameters is limited by the size constraints of the microchip as wellas its material properties.

Piezoelectric

This method alters mechanical energy into electrical energy by straining a piezoelectric

material (Sodano, Inman, & Park, 2004). Strain or deformation of a piezoelectric materialcauses charge separation across the device, producing an electric field and consequently a
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voltage drop proportional to the stress applied. The oscillating system is typically a cantileverbeam structure with a mass at the unattached end of the lever, which provides higher strainfor a given input force (Roundy & Wright, 2004). The voltage produced varies with time andstrain, effectively producing an irregular AC signal on the average. Piezoelectric energyconversion produces relatively higher voltage and power density levels than the

electromagnetic system. Moreover, piezoelectricity has the ability of some elements, such ascrystals and some types of ceramics, to generate an electric potential from a mechanical stress(Skoog, Holler, & Crouch, 2006). This process takes the form of separation of electric chargewithin a crystal lattice. If the piezoelectric material is not short circuited, the appliedmechanical stress induces a voltage across the material. There are many applications based on

piezoelectric materials, one of which is the electric cigarette lighter. In this system, pushingthe button causes a spring-loaded hammer to hit a piezoelectric crystal, and the voltage that is

produced injects the gas slowly as the current jumps across a small spark gap. Following thesame idea, portable sparkers used to light gas grills, gas stoves, and a variety of gas burnershave built-in piezoelectric based ignition systems.

Electrostatic (Capacitive)

This method depends on the variable capacitance of vibration-dependent varactors.(Meninger, Mur-Miranda, Amirtharajah, Chandrakasan, & Lang, 2001). A varactor, orvariable capacitor, which is initially charged, will separate its plates by vibrations; in thisway, mechanical energy is transformed into electrical energy. Constant voltage or constantcurrent achieves the conversion through two different mechanisms. For example, the voltageacross a variable capacitor is kept steady as its capacitance alters after a primary charge. As aresult, the plates split and the capacitance is reduced, until the charge is driven out of thedevice. The driven energy then can be stored in an energy pool or used to charge a battery,generating the needed voltage source. The most striking feature of this method is its IC-compatible nature, given that MEMS (Micro-electromechanical system) variable capacitorsare fabricated through relatively well-known silicon micro-machining techniques. This

scheme produces higher and more practical output voltage levels than the electromagneticmethod, with moderate power density.

In a study conducted to test the feasibility and reliability of the different ambient vibrationenergy sources by Marzencki (2005), three different vibration energy sources (electrostatic,electromagnetic, and piezoelectric) were investigated and compared according to theircomplexity, energy density, size, and encountered problems. The study is summarized inTable 2.

Table 2. Comparison of Vibration Energy-Harvesting Techniques

Electrostatic Electromagnetic Piezoelectric

Complexity of process flow Low Very High High

Energy density 4 mJ cm-3 24.8 mJ cm-3 35.4 mJ cm-3Current size Integrated Macro Macro

ProblemsVery high voltage and need

of adding charge source

Very low outputvoltages

Low outputvoltages

Thermal (Thermoelectric) Energy Harvesting

Thermal gradients in the environment are directly converted to electrical energy through theSeebeck (thermoelectric) effect, as reported byDisalvo (1999) and Rowe (1999).Temperature changes between opposite segments of a conducting material result in heat flowand consequently charge flow since mobile, high-energy carriers diffuse from high to low

concentration regions. Thermopiles consisting of n- and p-type materials electrically joined atthe high-temperature junction are therefore constructed, allowing heat flow to carry the
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dominant charge carriers of each material to the low temperature end, establishing in theprocess a voltage difference across the base electrodes. The generated voltage and power isrelative to the temperature differential and the Seebeck coefficient of the thermoelectricmaterials. Large thermal gradients are essential to produce practical voltage and power levels(Roundy, Wright, & Rabaey , 2004). However, temperature differences greater than 10C are

rare in a micro system, so consequently such systems generate low voltage and power levels.Moreover, naturally occurring temperature variations also can provide a means by whichenergy can be scavenged from the environment with high temperature. Stordeur and Stark(1997) have demonstrated a thermoelectric micro device, which is capable of converting 15

_W/cm3 from 10 C temperature gradients. Although this is promising and, with theimprovement of thermoelectric research, could eventually result in more than 15 _W/cm3,situations in which there is a static 10 C temperature difference within 1 cm3 are, however,very rare, and assume no losses in the conversion of power to electricity.

One of the latest designs of thermoelectric energy harvester is the thermoelectric generator(TEG) designed and introduced by Pacific Northwest National Laboratory (2007). This newthermoelectric generator is used to convert environmental (ambient) thermal energy into

electric power for a variety of applications that necessitates low power use. Thisthermoelectric energy harvester includes an assembly of very small and thin thermocouples ina unique configuration that can exploit very small (>2C) temperature variations that areoccurring naturally in the environment of the application such as ground to air, water to air,or skin to air interfaces. The body of the TEG consisted of reliable and stable componentsthat provided maintenance free, continuous power for the lifetime of the application claimed

by the manufacturer. Depending on the temperature range, the TEGs electrical output can bechanged from a few microwatts to hundreds of milliwatts and more by modifying the design.Applications of this energy-harvesting design are diverse, including automotive performancemonitoring, homeland and military security surveillance, biomedicine, and wilderness andagricultural management. It is also documented that the thermoelectric energy harvester may

be appropriate for many other stand-alone, low-power applications, depending on the natureof the application.

In addition to PNNLs patent-pending thermoelectric generator, Applied Digital SolutionsCorporation has developed and presented a thermoelectric generator as a commercial product(PNNL, 2007). This thermoelectric generator is capable of producing 40mw of power from 5C temperature variations using a device that is 0.5 cm2 in area and a few millimeters thick(Pescovitz, 2002). This device generates about 1V output voltage, which can be enough forlow- power electronic applications. Moreover, the thermal-expansion-actuated piezoelectricgenerator has also been proposed as a method to convert power from ambient temperaturegradients to electricity by Thomas, Clark and Clark (2005).

Pyroelectricity Energy Harvesting

The pyroelectric effect converts temperature changes into electrical voltage or current(Lang, 2005). Pyroelectricity is the capability of certain materials to generate an electrical

potential when they are either heated or cooled. As a result of the temperature change,positive and negative charges move to opposite ends through migration (polarized) and thus,an electrical potential is established. Pryroelectric energy-harvesting applications requireinputs with time variances which results in small power outputs in energy-scavengingapplications. One of the main advantages that pyroelectric energy harvesting has overthermoelectric energy harvesting is that most of the pyroelectric materials or elements arestable up to 1200 C or more. Stability allows energy harvesting even from high temperaturesources with increasing thermodynamic efficiency.

Light Energy (Solar Energy) Harvesting
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A photovoltaic cell has the capability of converting light energy into electrical energy (Kasap,2001; Raffaelle , Underwood, Scheiman , Cowen, Jenkins, Hepp , Harris, & Wilt, 2000). Eachcell consists of a reverse biased pn+ junction, in which the light crosses with the heavilyconservative and narrow n+ region. Photons where the light energy exists are absorbed withinthe depletion region, generating electron-hole pairs. The built-in electric field of the junction

immediately separates each pair, accumulating electrons and holes in the n+ and p regions,respectively, establishing an open circuit voltage. With a load connected, accumulatedelectrons travel through the load and recombine with holes at the p-side, generating a

photocurrent that is directly proportional to the light intensity and independent of the cellvoltage. Several research efforts, have been conducted so far have demonstrated that

photovoltaic cells can produce sufficient power to maintain a micro system. Moreover, athree-dimensional diode structure constructed on absorbent silicon substrate helps increaseefficiency by significantly increasing the exposed internal surface area of the device (Sun,Kherani , Hirschman, Gadeken , & Fauchet , 2005). Overall, photovoltaic energy conversion isa well-known integrated circuit compatible technology that offers higher power output levels,when compared with the other energy-harvesting mechanisms. Nevertheless, its power output

is strongly dependent on environmental conditions; in other words, varying light intensity.Acoustic Noise

Acoustic noise is the result of the pressure waves produced by a vibration source. A humanear detects and translates pressure waves into electrical signals. Generally a sinusoidal waveis referred to as a tone, a combination of several tones is called a sound, and an irregularvibration is referred to as noise. Hertz (Hz) is the unit of sound frequency; 1 Hz equals 1cycle, or one vibration, per second. The human ear can perceive frequencies between 20 Hzand 20 000 Hz. Acoustic power and acoustic pressure are types of acoustic noise. Acoustic

power is the total amount of sound energy radiated by a sound source over a given period oftime, and it is usually expressed in Watts. For acoustic pressure, the reference is the hearingthreshold of the human ear, which is taken as 20 microPa. The unit of measure used to

express these relative sound levels is the Bel or decibel (1 Bel equals 10 decibels). The Beland decibel are logarithmic values that are better suited to represent a wide range ofmeasurements than linear values (Rogers, Manwell , & Wright, 2002).

Rare research attempts have been made of harvesting acoustic noise from an environmentwhere the noise level is high and continuous, to transfer it into electrical energy. For example,a research team at the University of Florida examined acoustic energy conversion. Theyreported analysis of strain energy conversion using a flyback converter circuit (Horowitz etal. 2002). The output of a vibrating PZT piezoceramic beam is connected to an AC to DCflyback converter, which is estimated to provide greater than 80 percent conversionefficiency at an input power of 1 mW and 75% efficiency at an input power of 200 W(Kasyap, Lim, et al. 2002). It was finalized that there is far too insufficient amount of poweravailable from acoustic noise to be of use in the scenario being investigated, except for veryrare environments with extremely high noise levels.

Human Power

Researchers have been working on many projects to generate electricity from active/passivehuman power, such as exploiting, cranking, shaking, squeezing, spinning, pushing, pumping,and pulling (Starner & Paradiso, 2004). For example some types of flashlights were poweredwith wind-up generators in the early 20th century (US patent 1,184,056, 1916). Laterversions of these devices, such as wind-up cell phone chargers and radios, became availablein the commercial market. For instance, Freeplays (a commercial company) wind-up radiosmake 60 turns in one minute of cranking, which allows storing of 500 Joules of energy in a

spring. The spring system drives a magnetic generator and efficiently produces enough powerfor about an hour of play.
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A battery-free wireless remote control for Zenith televisions was another human-powereddevice. The design, called Space Commander, was introduced by Robert Adler in 1956.The system consisted of a set of buttons that hit aluminum material to produce ultrasound.The produced ultrasound energy was decoded at the television to turn it on, change channelsand mute the volume (Adler, Desmares , & Spracklen , 1982). Adlers Space Commander

design was then replaced by the active infrared remote controls and is being used in manycurrent remote control systems.

Another similar architecture, developed byParadiso and Feldmeier (2001) is a piezoelectricelement, which was comprised of a resonantly matched transformer and conditioningelectronics. This system was actuated when hit by a button, and it produced about 1mJ at 3V

per 15N push. The generated power was enough to run a digital encoder and radio that wasable to transmit over 50 feet. Materials used for this device were off-the-shelf components,which enabled placing compact digital controllers independently without any battery or wiremaintenance.

An average human body burns approximately 10.5 MJ every day, which is equal to about121W of power dissipation. Power dissipation occurs in the average human body eitheractively or passively in daily life motions, making the human body and motions an attractiveambient energy source. Researchers have proposed and conducted several studies to capture

power from the human body. For example Starner has researched and investigated some ofthese energy- harvesting techniques to power wearable electronics (Starner, 1996). MITresearchers considered these studies and suggested that the most reliable and exploitableenergy source occurs at the foot during heel strikes when running or walking (Shenck &Paradiso, 2001). This research initiated the development of piezoelectric shoe inserts capableof producing an average of 330 W/cm2 while an average person is walking. The firstapplication of shoe inserts was to power a low power wireless transceiver mounted to theshoe soles. The ongoing research efforts mostly focused on how to get power from the shoe,where the power is generated, to the point of interest or application. Such sources of power

are considered as passive power sources in that the person is not required to put extra effort togenerate power because power generation occurs while the person is doing regular dailyactivities, such as walking or running. Another group of power generators can be classified asactive human-powered energy scavengers. These types of generators require the human to

perform an action that is not part of the normal human performance. For instance, Freeplayhas self-powered products that are powered by a constant-force spring that the user mustwind up to operate the device (FreePlay Energy, 2007). These types of products are veryuseful because of their battery-free systems.

For an RFID (Radio frequency identification) tag or other wireless device worn on the shoe,the piezoelectric shoe insert offers a good solution. However, the application space for suchdevices is extremely limited, and as mentioned previously, they are not very applicable tosome of the low-powered devices, such as wireless sensor networks. Active human power,which requires the user to perform a specific power-generating motion, is common and may

be referred to separately as active human-powered systems (Roundy, 2003).

Conclusion

In conclusion, several currently developed, and overlooked ideas and options exist, and thesecan provide new energy resources to portable or wireless electronics devices within theenergy-harvesting systems. The possibility of overall dependence on ambient energyresources may remove some constraints required by the limited reliability of standard

batteries. Ambient energy harvesting can also provide an extended lifespan and support toconventional electronics systems. Students involved in this paper learned different ambient

energy-harvesting, conversion, and storage systems. Students agreed to start a new researchidentify various ambient energy sources and design unique energy-harvesting systems.
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Dr. Faruk Yildiz is an assistant professor in the Department of Agricultural and IndustrialSciences at Sam Houston State University, Huntsville Texas. He is a Member-at-large ofEpsilon Pi Tau.

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Mitcheson, P. D., Green, T. C., Yeatman, E. M., & Holmes, A. S. (2004). Analysis ofoptimized micro-generator architectures for self-powered ubiquitous computers. ImperialCollege of Science Technology and Medicine. Exhibition Road, London, SW7 2BT.

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Paradiso, J., & Feldmeier, M. (2001). A compact, wireless, self-powered pushbuttoncontroller. ubicomp: Ubiquitous Computing.

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Pending, Battelle Number(s): 12398-E, 13664-B, Retrieved October 6, 2009, fromhttp://availabletechnologies.pnl.gov/technology.asp?id=85


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Robot Systems

Robots are comprised of several systems working together as a whole. The type of job the

robot does dictates what system elements it needs. The general categories of robot systems

are:

Controller

Body

Mobility

Power

Sensors

Tools

Controller

The controller is the robot's brain and controls the robot's movements. It's usually a computer

of some type which is used to store information about the robot and the work environment and

to store and execute programs which operate the robot. The control system contains programs,

data algorithms, logic analysis and various other processing activities which enable the robot to

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The picture above is an AARM Motion control system. AARM stands for Advanced Architecture

Robot and Machine Motion and it's a commercial product from American Robot for industrial

machine motion control. Industrial controllers are either non-servos, point-to-point servos orcontinuous path servos. A non-servo robot usually moves parts from one area to another and is

called a "pick and place" robot. The non-servo robot motion is started by the controller and

stopped by a mechanical stop switch. The stop switch sends a signal back to the controller which

starts the next motion. A point-to-point servo moves to exact points so only the stops in the

path are programmed. A continous path servo is appropriate when a robot must proceed on a

specified path in a smooth, constant motion.

More sophisticated robots have more sophisticated control systems. The brain of the Mars

Sojourner rover was made of two electronics boards that were interconnected to each other

with Flex cables. One board was called the "CPU" board and the other the "Power" board and

each contained items responsible for power generation, power conditioning, power distributionand control, analog and digital I/O control and processing, computing (i.e., the CPU), and data

storage (i.e., memory). The control boards for Sojourner are shown below. For more info, visit

Rover Control and Navigation at JPL.

Mobile robots can operate by remote control or autonomously. A remote control robot receives

instructions from a human operator. In a direct remote control situation, the robot relaysinformation to the operator about the remote environment and the operator then sends the
http://mars.jpl.nasa.gov/MPF/roverctrlnav/rovercntrlnav.htmlhttp://mars.jpl.nasa.gov/MPF/roverctrlnav/electronics.htmlhttp://prime.jsc.nasa.gov/ROV/images/controller.gifhttp://mars.jpl.nasa.gov/MPF/roverctrlnav/rovercntrlnav.html


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robot instructions based on the information received. This sequence can occur immediately

(real-time) or with a time delay. Autonomous robots are programmed to understand their

environment and take independent action based on the knowledge they posess. Some autonomous

robots are able to "learn" from their past encounters. This means they can identify a situation,

process actions which have produced successful/unsuccessful results and modify their behavior

to optimize success. This activity takes place in the robot controller.

Body

The body of a robot is related to the job it must perform. Industrial robots often take the

shape of a bodyless arm since it's job requires it to remain stationary relative to its task. Space

robots have many different body shapes such as a sphere, a platform with wheels or legs, or a

ballon, depending on it's job. The free-flying rover, Sprint Aercam is a sphere to minimize

damage if it were to bump into the shuttle or an astronaut. Someplanetary rovershave solar

platforms driven by wheels to traverse terrestrial environments. Aerobotbodies are balloons

that will float through the atmosphere of other worlds collecting data. When evaluating whatbody type is right for a robot, remember that form follows function.

Mobility

How do robots move? It all depends on the job they have to do and the environment they

operate in.

In the Water: Conventional unmanned, submersible robots are used in

science and industry throughout the oceans of the world. You probably

saw the Jason AUV at work when pictures of the Titanic discovery were

broadcast. To get around, automated underwater vehicles (AUV's) use

propellers and rudders to control their direction of travel. One area of

research suggests that an underwater robot likeRoboTuna could propel

itself as a fish does using it's natural undulatory motion. It's thought that robots that move likefish would be quieter, more maneuverable and more energy efficient.

On Land: Land based rovers can move around on

legs, tracks or wheels. Dante II is a frame walking

robot that is able to descend into volcano craters

by rapelling down the crater. Dante has eight legs;

four legs on each of two frames. The frames are

separated by a track along which the frames slide

relative to each other. In most cases Dante II has

at least one frame (four legs) touching the ground.

An example of a track driven robot is Pioneer, a robot developed to clearrubble, make maps and acquire samples at the Chornobyl Nuclear Reactor
http://spaceflight.nasa.gov/station/assembly/sprint/http://robotics.jpl.nasa.gov/http://robotics.jpl.nasa.gov/http://robotics.jpl.nasa.gov/http://www.jpl.nasa.gov/adv_tech/balloons/summary_overview.htmhttp://www.jpl.nasa.gov/adv_tech/balloons/summary_overview.htmhttp://www.marine.whoi.edu/ships/rovs/jason_med.htmhttp://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/titanic.htmlhttp://web.mit.edu/afs/athena/org/t/towtank/www/tuna/pictures.htmlhttp://web.mit.edu/afs/athena/org/t/towtank/www/tuna/pictures.htmlhttp://web.mit.edu/afs/athena/org/t/towtank/www/tuna/pictures.htmlhttp://spacelink.nasa.gov/NASA.Projects/Space.Science/Solar.System/Dante/http://spacelink.nasa.gov/NASA.Projects/Space.Science/Solar.System/Dante/http://www.frc.ri.cmu.edu/projects/pioneer/http://www.frc.ri.cmu.edu/projects/pioneer/http://spacelink.nasa.gov/NASA.Projects/Space.Science/Solar.System/Dante/http://web.mit.edu/afs/athena/org/t/towtank/www/tuna/pictures.htmlhttp://robotics.jpl.nasa.gov/tasks/aerobot/homepage.htmlhttp://robotics.jpl.nasa.gov/http://spaceflight.nasa.gov/station/assembly/sprint/http://spaceflight.nasa.gov/station/assembly/sprint/http://robotics.jpl.nasa.gov/http://www.jpl.nasa.gov/adv_tech/balloons/summary_overview.htmhttp://www.marine.whoi.edu/ships/rovs/jason_med.htmhttp://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/titanic.htmlhttp://web.mit.edu/afs/athena/org/t/towtank/www/tuna/pictures.htmlhttp://spacelink.nasa.gov/NASA.Projects/Space.Science/Solar.System/Dante/http://www.frc.ri.cmu.edu/projects/pioneer/


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site. Pioneer is track-driven like a small bulldozer which makes it suitable for driving over and

through rubble. The wide track footprint gives good stability and platform capacity to deploy

payloads.

Many robots use wheels for locomotion. One of the first US

roving vehicles used for space exploration went to the moon

on Apollo 15 (July 30, 1971) and was driven by astronauts

David R. Scott and James B. Irwin. Two other Lunar Roving

Vehicles (LRV) also went to the moon on Apollo 16 and 17.

These rovers were battery powered and had radios and

antenna's just like the Mars Pathfinder rover Sojourner.

But unlike Sojourner, these rovers were designed to seat

two astronauts and be driven like a dune buggy.

The Sojourner rover's wheels and suspension use a rocker-bogie

system that is unique in that it does not use springs. Rather, its joints

rotate and conform to the contour of the ground, which helps it

traverse rocky, uneven surfaces. Six-wheeled vehicles can overcomeobstacles three times larger than those crossable by four-wheeled

vehicles. For example, one side of Sojourner could tip as much as 45 degrees as it climbed over

a rock without tipping over. The wheels are 13 centimeters (5 inches) in diameter and made of

aluminum. Stainless steel treads and cleats on the wheels provide traction and each wheel can

move up and down independently of all the others.

In the Air/Space: Robots that operate in the air use engines and

thrusters to get around. One example is the Cassini, an orbiter on it's

way to Saturn. Movement and positioning is accomplished by either

firing small thrusters or by applying a force to speed up or slow down

one or more of three "reaction wheels." The thrusters and reactionwheels orient the spacecraft in three axes which are maintained with

great precision. The propulsion system carries approximately 3000

kilograms (6600 lbs) of propellant that is used by the main rocket

engine to change the spacecraft's velocity, and hence its course. A

total velocity change of over 2000 meters per second (6560 ft/s) is

possible. In addition, Cassini will be propelled on its way by two

"gravity assist" flybys of Venus, one each of Earth and Jupiter, and

three dozen of Saturn's moon Titan. These planetary flybys will provide twenty times the

propulsion provided by the main engine.

Deep Space 1 is an experimental spacecraft of the future sent

into deep space to analyze comets and demonstrate new

technologies in space. One of it's new technologies is a solar

electric (ion) propulsion engine that provides about 10 times the

specific impulse of chemical propulsion. The ion engine works by

giving an electrical charge, or ionizing, a gas called xenon. The

xenon is electrically accelerated to the speed of about 30

km/second. When the xenon ions are emitted at such a high

speed as exhaust from the spacecraft, they push the

spacecraft in the opposite direction. The ion propulsion system

requires a source of energy and for DS1 the energy comes from electrical power generated by

it's solar arrays.
http://www.lpi.usra.edu/expmoon/Apollo15/Apollo15.htmlhttp://mars.jpl.nasa.gov/MPF/index1.htmlhttp://saturn.jpl.nasa.gov/spacecraft/index.cfmhttp://nmp.jpl.nasa.gov/ds1/http://nmp.jpl.nasa.gov/ds1/tech/sep.htmlhttp://nmp.jpl.nasa.gov/ds1/tech/sep.htmlhttp://www.jpl.nasa.gov/cassini/Spacecraft/design_feats.htmlhttp://mars.jpl.nasa.gov/MPF/rovercom/rovintro.htmlhttp://www.lpi.usra.edu/expmoon/Apollo15/A15_surfops.htmlhttp://www.lpi.usra.edu/expmoon/Apollo15/Apollo15.htmlhttp://mars.jpl.nasa.gov/MPF/index1.htmlhttp://saturn.jpl.nasa.gov/spacecraft/index.cfmhttp://nmp.jpl.nasa.gov/ds1/


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Power

Power for industrial robots can be electric, pneumatic or hydraulic. Electric

motors are efficient, require little maintenance, and aren't very noisy.

Pneumatic robots use compressed air and come in a wide variety of sizes. A

pneumatic robot requires another source of energy such as electricity,

propane or gasoline to provide the compressed air. Hydraulic robots use oil

under pressure and generally perform heavy duty jobs. This power type is

noisy, large and heavier than the other power sources. A hydraulic robot also

needs another source of energy to move the fluids through its components.

Pneumatic and hydraulic robots require maintenance of the tubes, fittings and

hoses that connect the components and distribute the energy.

Two important sources of electric power for mobile robots are solar

cells and batteries. There are lots of types of batteries like carbon-

zinc, lithium-ion, lead-acid, nickel-cadmium, nickel-hydrogen, silver zinc

and alkaline to name a few. Battery power is measured in amp-hourswhich is the current (amp) multiplied by the time in hours that current

is flowing from the battery. For example, a two amp hour battery can

supply 2 amps of current for one hour. Solar cells make electrical power

from sunlight. If you hook enough solar cells together in a solar panel

you can generate enough power to run a robot. Solar cells are also used

as a power source to recharge batteries.

Deep space probes must use alternate power

sources because beyond Mars existing solar arrays would have to be so

large as to be infeasible. The lifespan of batteries is exceeded at these

distances also. Power for deep space probes is traditionally generated byradioisotope thermoelectric generators or RTGs, which use heat from

the natural decay of plutonium to generate direct current electricity.

RTGs have been used on 25 space missions including Cassini,Galileo, and

Ulysses.

Sensors

Sensors are the perceptual system of a robot and measure physical quantities like contact,

distance, light, sound, strain, rotation, magnetism, smell, temperature, inclination, pressure, or

altitude. Sensors provide the raw information or signals that must be processed through therobot's computer brain to provide meaningful information. Robots are equipped with sensors so

they can have an understanding of their surrounding environment and make changes in their

behavior based on the information they have gathered.

Sensors can permit a robot to have an adequatefield of view, a range of detection and the

ability to detect objects while operating in real or near-real time within it's power and size

limits. Additionally, a robot might have an acoustic sensor to detect sound, motion or location,

infrared sensors to detect heat sources, contact sensors, tactile sensors to give a sense of

touch, or optical/vision sensors. For most any environmental situation, a robot can be equipped

with an appropriate sensor. A robot can also monitor itself with sensors.

The Big Signal robotNOMAD uses sensing instruments like a camera, aspectrometer and a metal-detector. The high resolution video camera can
http://www.howstuffworks.com/solar-cell.htmhttp://www.howstuffworks.com/solar-cell.htmhttp://www.grc.nasa.gov/WWW/Electrochemistry/doc/batteries.htmlhttp://www.grc.nasa.gov/WWW/RT1999/5000/5420manzo.htmlhttp://nuclear.gov/space/space-history.htmlhttp://nuclear.gov/space/space-history.htmlhttp://www.jpl.nasa.gov/cassini/http://galileo.jpl.nasa.gov/http://galileo.jpl.nasa.gov/http://galileo.jpl.nasa.gov/http://ulysses.jpl.nasa.gov/http://www.hhmi.org/senses/http://www.bores.com/courses/intro/basics/1_whatis.htmhttp://www.vision1.com/systems/fovmath.shtmlhttp://www.vision1.com/systems/fovmath.shtmlhttp://www.frc.ri.cmu.edu/projects/bigsignal/2000http://www.frc.ri.cmu.edu/projects/bigsignal/2000http://www.frc.ri.cmu.edu/projects/bigsignal/2000http://nuclear.gov/space/space-history.htmlhttp://www.grc.nasa.gov/WWW/RT1999/5000/5420manzo.htmlhttp://jewel.morgan.edu/~salimian/courses/IEGR470/223_lab.htmlhttp://www.howstuffworks.com/solar-cell.htmhttp://www.howstuffworks.com/solar-cell.htmhttp://www.grc.nasa.gov/WWW/Electrochemistry/doc/batteries.htmlhttp://nuclear.gov/space/space-history.htmlhttp://www.jpl.nasa.gov/cassini/http://galileo.jpl.nasa.gov/http://ulysses.jpl.nasa.gov/http://www.hhmi.org/senses/http://www.bores.com/courses/intro/basics/1_whatis.htmhttp://www.vision1.com/systems/fovmath.shtmlhttp://www.frc.ri.cmu.edu/projects/bigsignal/2000


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identify dark objects (rocks, meterorites) against the white background of the Antarctic snow.

The variations in color and shade allow the robot to tell the difference between dark grey rocks

and shadows. Nomad uses a laser range finder to measure the distance to objects and a metal

detector to help determine the composition of the objects if finds.

Very complex robots like Cassini have full sets of sensing equipment much like human senses.

It's skeleton must be light and sturdy, able to withstand extreme temperatures and monitor

those temperatures. Cassini determines it's location by using three hemisperical resonant

gyroscopes or HRG's which measures quartz crystal vibrations. The eyes of Cassini are the

Imaging Science Subsystem (ISS) which can take pictures in the visible range, the near-

ultraviolet and near-infrared ranges of the electromagnetic spectrum.

Tools

As working machines, robots have defined job duties and carry all the tools they need to

accomplish their tasks onboard their bodies. Many robots carry their tools at the end of a

manipulator. The manipulator contains a series of segments, jointed or sliding relative to oneanother for the purpose of moving objects. The manipulator includes the arm, wrist and end-

effector. An end-effector is a tool or gripping mechanism attached to the end of a robot arm to

accomplish some task. It often encompasses a motor or a driven mechanical device. An end-

effector can be a sensor, a gripping device, a paint gun, a drill, an arc welding device, etc. There

are many examples of robot tools that you will discover as you examine the literature associated

with this site. To get you going, two good examples are listed below.

Tools are unique to the task the robot must perform. The goal of the robot

mission Stardust is to capture both cometary samples and interstellar

dust. The trick is to capture the high velocity comet and dust particles

without physically changing them. Scientists developed aerogel, a silicon-based solid with a porous, sponge-like structure in which 99.8 percent of

the volume is empty space. When a particle hits the aerogel, it buries itself in the material,

creating a carrot-shaped track up to 200 times its own length. This slows it down and brings the

sample to a relatively gradual stop. Since aerogel is mostly transparent - with a distinctive

smoky blue cast - scientists will use these tracks to find the tiny particles.

Robonaut has one of the many ground breaking dexterous robot hands

developed over the past two decades. These hand devices make it possible

for a robot manipulator to grasp and manipulate objects that are not

designed to be robotically compatible. While several grippers have been

designed for space use and some even tested in space, no dexterousrobotic hand has been flown in Extra Vehicular Activity (EVA) conditions.

The Robonaut Hand is one of the first under development for space EVA

use and the closest in size and capability to a suited astronaut's hand. The

Robonaut Hand has a total of fourteen degrees of freedom. It consists of

a forearm which houses the motors and drive electronics, a two degree of

freedom wrist, and a five finger, twelve degree of freedom hand. The forearm, which measures

four inches in diameter at its base and is approximately eight inches long, houses all fourteen

motors, 12 separate circuit boards, and all of the wiring for the hand.
http://saturn.jpl.nasa.gov/index.cfmhttp://vesuvius.jsc.nasa.gov/er_er/html/robonaut/robonaut.htmlhttp://stardust.jpl.nasa.gov/tech/aerogel.htmlhttp://saturn.jpl.nasa.gov/index.cfm


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Energy harvestingFrom Wikipedia, the free encyclopedia

Energy harvesting (also known as power harvesting orenergy scavenging) is the processby whichenergy is derived from external sources (e.g., solar power, thermal energy, windenergy, salinity gradients[citation needed], and kinetic energy), captured, and stored for small,wireless autonomous devices, like those used inwearable electronics and wirelesssensornetworks.

Energy harvesters provide a very small amount of power for low-energy electronics. Whilethe input fuel to some large-scale generation costs money (oil, coal, etc.), the energy sourcefor energy harvesters is present as ambient background and is free. For example, temperaturegradients exist from the operation of a combustion engine and in urban areas, there is a largeamount of electromagnetic energy in the environment because of radio and television

broadcasting.

Contents[hide]

1 Operation

1.1 Accumulating energy

1.2 Storage of power

1.3 Use of the power

2 Motivation

3 Devices

3.1 Ambient-radiation sources

3.2 Biomechanical harvesting

3.3 Photovoltaic harvesting

3.4 Piezoelectric energy harvesting

3.5 Pyroelectric energy harvesting

3.6 Thermoelectrics

3.7 Electrostatic (capacitive) energy harvesting

3.8 Magnetostatic energy harvesting

3.9 Blood sugar energy harvesting

3.10 Tree metabolic energy harvesting

3.11 Future directions

4 See also

5 References
http://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wearable_computerhttp://en.wikipedia.org/wiki/Wearable_computerhttp://en.wikipedia.org/wiki/Sensor_networkhttp://en.wikipedia.org/wiki/Sensor_networkhttp://en.wikipedia.org/wiki/Sensor_networkhttp://en.wikipedia.org/wiki/Energy_harvestinghttp://en.wikipedia.org/wiki/Energyhttp://en.wikipedia.org/wiki/Wikipedia:Citation_neededhttp://en.wikipedia.org/wiki/Wearable_computerhttp://en.wikipedia.org/wiki/Sensor_networkhttp://en.wikipedia.org/wiki/Sensor_networkhttp://en.wikipedia.org/wiki/Energy_harvesting


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6 External Links

[edit] OperationEnergy 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 sensorsfor autonomous operation. Future applications may include high power output devices (orarrays of such devices) deployed at remote locations to serve as reliable power stations forlarge systems. Another application is in wearable electronics, where energy harvestingdevices can power or recharge cellphones, mobile computers, radio communicationequipment, etc. All of these devices must be sufficiently robust to endure long-term exposureto hostile environments and have a broad range of dynamic sensitivity to exploit the entirespectrum of wave motions.

[edit] Accumulating energy

Energy can also be harvested to power small autonomous sensors such as those developedusing MEMS technology. These systems are often very small and require little power, buttheir applications are limited by the reliance on battery power. Scavenging energy fromambient vibrations, wind, heat or light could enable smart sensors to be functionalindefinitely. Several academic and commercial groups have been involved in the analysis anddevelopment of vibration-powered energy harvesting technology, including theControl andPower Group and Optical and Semiconductor Devices Groupat Imperial College London,IMEC and the partnering Holst Centre,[1]AdaptivEnergy , LLC,ARVENI, MIT Boston,Georgia Tech, UC Berkeley, Southampton University,University of Bristol,[2]NanyangTechnological University,[3]PMG Perpetuum,Vestfold University College,NationalUniversity of Singapore,[4] NiPS Laboratory at the University of Perugia,[5]ColumbiaUniversity,[6]Universidad Autnoma de Barcelona andUSN & Renewable Energy Lab at theUniversity of Ulsan (Ulsan, South Korea).

Typical power densities available from energy harvesting devices are highly dependent uponthe specific application (affecting the generator's size) and the design itself of the harvestinggenerator. In general, for motion powered devices, typical values are a few W/cm forhuman body powered applications and hundreds of W/cm for generators powered frommachinery.[7] Most energy scavenging devices for wearable electronics generate very little

power.[8][verification needed]

[edit] Storage of power

In general, energy can be stored in a capacitor, super capacitor, orbattery. Capacitors areused when the application needs to provide huge energy spikes. Batteries leak less energy andare therefore used when the device needs to provide a steady flow of energy.

[edit] Use of the power

Current interest in low power energy harvesting is for independent sensor networks. In theseapplications an energy harvesting scheme puts power stored into a capacitor then

boosted/regulated to a second storage capacitor or battery for the use in the microprocessor.[9]

The power is usually used in a sensorapplication and the data stored or is transmittedpossibly through a wireless method. [10]

[edit] MotivationThe history of energy harvesting dates back to the windmill and the waterwheel. People havesearched for ways to store the energy from heat and vibrations for many decades. One drivingforce behind the search for new energy harvesting devices is the desire to power sensor
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Energy_Lab_at_the_University_of_Ulsan_(Ulsan,_South_Korea)&action=edit&redlink=1http://en.wikipedia.org/wiki/Wikipedia:Verifiabilityhttp://en.wikipedia.org/w/index.php?title=Energy_harvesting&action=edit&section=3http://en.wikipedia.org/wiki/Capacitorhttp://en.wikipedia.org/wiki/Super_capacitorhttp://en.wikipedia.org/wiki/Battery_(electricity)http://en.wikipedia.org/w/index.php?title=Energy_harvesting&action=edit&section=4http://en.wikipedia.org/wiki/Microprocessorhttp://en.wikipedia.org/wiki/Sensorhttp://en.wikipedia.org/wiki/Transmitterhttp://en.wikipedia.org/w/index.php?title=Energy_harvesting&action=edit&section=5


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networks and mobile devices without batteries. Energy harvesting is also motivated by adesire to address the issue of climate change and global warming.

[edit] Devices

Energy harvesting system based on "APA" amplified piezoelectric actuator

There are many small-scale energy sources that generally cannot be scaled up to industrialsize:

Piezoelectric crystals or fibers generate a small voltage whenever they aremechanically deformed. Vibration from engines can stimulate piezoelectricmaterials, as can the heel of a shoe.

Some wristwatches are already powered by kinetic energy (called kineticwatches), in this case movement of the arm. The arm movement causesthe magnet in the electromagnetic generator to move. The motionprovides a rate of change of flux, which results in some induced emf onthe coils. The concept is simply related to Faraday's Law.

Photovoltaics is a method of generating electrical power by convertingsolar radiation (both indoors and outdoors) into direct current electricityusing semiconductors that exhibit the photovoltaic effect. Photovoltaicpower generation employs solar panels composed of a number of cellscontaining a photovoltaic material.

Thermoelectric generators (TEGs) consist of the junction of two dissimilarmaterials and the presence of a thermal gradient. Large voltage outputsare possible by connecting many junctions electrically in series andthermally in parallel. Typical performance is 100-200 V/K per junction.

These can be utilized to capture mW.s of energy from industrialequipment, structures, and even the human body. They are typicallycoupled with heat sinks to improve temperature gradient.

Micro wind turbine are used to harvest wind energy readily available in theenvironment in the form of kinetic energy to power the low powerelectronic devices such as wireless sensor nodes. When air flows acrossthe blades of the turbine, a net pressure difference is developed betweenthe wind speeds above and below the blades. This will result in a lift force

generated which in turn rotate the blades. This is known as theaerodynamic effect.
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Special antennae can collect energy from stray radio waves [11] ortheoretically even light (EM radiation).[citation needed]

[edit] Ambient-radiation sources

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 toget useful power levels from this source. Thenantenna is one proposed development whichwould overcome this limitation by making use of the abundant natural radiation (such as solarradiation).

One idea is to deliberately broadcast RF energy to power remote devices: This is nowcommonplace in passive Radio Frequency Identification (RFID) systems, but the Safety andUS Federal Communications Commission (and equivalent bodies worldwide) limit themaximum power that can be transmitted this way to civilian use.

[edit] Biomechanical harvesting

Biomechanical energy harvesters are also being created. One current model is the

biomechanical energy harvester ofMax Donelan which straps around the knee.

[12]

Devices asthis allow the generation of 2.5 watts of power per knee. This is enough to power some 5 cellphones.

[edit] Photovoltaic harvesting

Photovoltaic [PV] energy harvesting wireless technology offers significant advantages overwired or solely battery-powered sensor solutions: virtually inexhaustible sources of powerwith 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 SolarCalculators. In recent years new PV technologies have come to the forefront in EnergyHarvesting such as Dye Sensitized Solar Cells DSSC. The dyes absorbs light much likechlorophyll does in plants. Electrons released on impact escape to the layer of TiO2 and fromthere diffuse, through the electrolyte, as the dye can be tuned to the visible spectrum muchhigher power can be produced. At 200 lux DSSC can provide over 15 micro watts per cm2.

TV batteryless remote control from Arveni for Philips

[edit] Piezoelectric energy harvesting

Thepiezoelectric effectconverts mechanicalstraininto electric current or voltage. This straincan come from many different sources. Human motion, low-frequency seismic vibrations,and acoustic noise are everyday examples. Except in rare instances the piezoelectric effectoperates in AC requiring time-varying inputs at mechanical resonance to be efficient.
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Most piezoelectric electricity sources produce power on the order of milliwatts, too small forsystem application, but enough for hand-held devices such as some commercially availableself-winding wristwatches. One proposal is that they are used for micro-scale devices, such asin a device harvesting micro-hydraulic energy. In this device, the flow of pressurizedhydraulic 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 '90s, it remains anemerging technology. Nevertheless some interesting improvements were made with the self-

powered electronic switch at INSA school of engineering, implemented by the spin-offArveni. In 2006, the proof of concept of a battery-less wireless doorbell push button wascreated, and recently, a demonstrator showed that classical TV infra-red remote control can

be powered by a piezo harvester. Other industrial applications appeared between 2000 and2005,[13] to harvest energy from vibration and supply sensors for example, or to harvestenergy 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 pressurefor low level power to implantable or wearable sensors. The nanobrushes ofDr. Zhong Lin Wang are another example of a piezoelectric energy harvester. [14] They can beintegrated into clothing. Careful design is needed to minimise user discomfort. These energyharvesting sources by association have an impact on the body. The Vibration EnergyScavenging Project[15] is another project that is set up to try to scavenge electrical energy fromenvironmental vibrations and movements. Xudong Wang's microbelt can be used to gatherelectricity from respiration.[16]Finally, a millimeter-scale piezoelectric energy harvester hasalso already been created.[17]

The use ofpiezoelectric materials to harvest power has already become popular. Piezoelectricmaterials have the ability to transform mechanical strain energy into electrical charge. Piezo

elements are being embedded in walkways

[18][19][20]

to recover the "people energy" offootsteps. They can also be embedded in shoes[21]to recover "walking energy".

[edit] Pyroelectric energy harvesting

The pyroelectric effectconverts a temperature change into electric current or voltage. It isanalogous to thepiezoelectric effect, which is another type offerroelectric behavior. Like

piezoelectricity, pyroelectricity requires time-varying inputs and suffers from small poweroutputs in energy harvesting applications. One key advantage of pyroelectrics overthermoelectrics is that many pyroelectric materials are stable up to 1200 C or more, enablingenergy harvesting from high temperature sources and thus increasing thermodynamicefficiency. There is a pyroelectric scavenging device that was recently introduced whichdoesn't require time-varying inputs. The energy-harvesting device uses the edge-depolarizing

electric field of a heated pyroelectric to convert heat energy into mechanical energy instead ofdrawing electric current off two plates attached to the crystal-faces. Moreover, stages of thenovel pyroelectric heat engine can be cascaded in order to improve the Carnot efficiency. [22]

[edit] Thermoelectrics

In 1821, Thomas Johann Seebeckdiscovered that a thermal gradient formed between twodissimilar conductors produces a voltage. At the heart of the thermoelectric effect is the factthat a temperature gradient in a conducting material results in heat flow; this results in thediffusion of charge carriers. The flow of charge carriers between the hot and cold regions inturn creates a voltage difference. In 1834, Jean Charles Athanase Peltierdiscovered thatrunning 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. The heatabsorbed or produced is proportional to the current, and the proportionality constant is known
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as the Peltier coefficient. Today, due to knowledge of the Seebeck and Peltier effects,thermoelectric materials can be used as heaters, coolers and generators(TEGs).

Ideal thermoelectric materials have a high Seebeck coefficient, high electrical conductivity,and low thermal conductivity. Low thermal conductivity is necessary to maintain a highthermal gradient at the junction. Standard thermoelectric modules manufactured today consist

of P- and N-doped bismuth-telluride semiconductors sandwiched between two metallizedceramic plates. The ceramic plates add rigidity and electrical insulation to the system. Thesemiconductors are connected electrically in series and thermally in parallel.

Miniature thermocouples have been developed that convert body heat into electricity andgenerate 40W at 3V with a 5 degree temperature gradient, while on the other end of thescale, large thermocouples are used in nuclearRTG batteries.

Practical examples are the finger-heartratemeter by the Holst Centre and thethermogenerators by the Fraunhofer Gesellschaft.[23][24]

Advantages to thermoelectrics:

1. No moving parts allow continuous operation for many years. TellurexCorporation[25] (a thermoelectric production company) claims thatthermoelectrics are capable of over 100,000 hours of steady stateoperation.

2. Thermoelectrics contain no materials that must be replenished.

3. Heating and cooling can be reversed.

One downside to thermoelectric energy conversion is low efficiency (currently less than10%). The development of materials that are able to operate in higher temperature gradients,and that can conduct electricity well without also conducting heat (something that was untilrecently thought impossible), will result in increased efficiency.

Future work in thermoelectrics could be to convert wasted heat, such as in automobile enginecombustion, into electricity.

[edit] Electrostatic (capacitive) energy harvesting

This type of harvesting is based on the changing capacitance of vibration-dependentvaractors. Vibrations separate the plates of an initially charged varactor (variable capacitor),and mechanical energy is converted into electrical energy. An example of a electrostaticenergy harvester with embedded energy storage is the M2E Power Kinetic Battery. Anotherexample is CSIROs Flexible Integrated Energy Device (FIED)[26] Yet another example is theTremont Electric nPower PEG.[27] Finally, there is the Regenerative shock absorber.

[edit] Magnetostatic energy harvesting

This type of energy harvesting is based on changes in magnetic flux through a coil of magnetwire as

potential ambient energy

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