No wire

Presenting By

A.S.krishna

Contents Abstract

Introduction

History

WPT

Advantages

Disadvantages

Biological Impacts

Applications

Conclusion

Reference

Acknowledgement

I’d like to thank our beloved H.O.D sir’s Mr. N.Sreekanth and Mr. M.L.Dwarakanath Sir and my guide for their help and guidance . I am also thankful to my friend’s for their help.

AbstractIn this presentation I’d like to provide the complete

details about the wireless power transmission. Here, we have the contents like Introduction, History, WPT which means Wireless Power Transmission, Conclusion and References. In this presentation we’ll see the different types of the wireless transmission techniques and their details.

Introduction

Wireless Technology is improving widely in this days. We have number of applications on this wireless technology. Such as WPT, in electrical and communication departments also.

Wireless power transfer (WPT) or wireless energy transmission is the transmission of electrical power from a power source to a consuming device without using solid wires or conductors.

Wireless communication is the transfer of information between two or more points that are not connected by an electrical conductor.

Wireless operations permit services, such as long-range communications, that are impossible or impractical to implement with the use of wires.

Information is transferred in this manner over both short and long distances.

In this presentation we are mainly looking at the wireless power transmission and their types and applications.

In wireless power transfer, a transmitter device connected to a power source, such as the mains power line, transmits power by electromagnetic fields across an intervening space to one or more receiver devices, where it is converted back to electric power and utilized.

HistoryThe world's first wireless telephone conversation occurred in 1880, when

Alexander Graham Bell and Charles Sumner Tainter invented and patented the photophone, a telephone that conducted audio conversations wirelessly over modulated light beams (which are narrow projections of electromagnetic waves).

There were no practical applications for their invention, which was highly limited by the availability of both sunlight and good weather.

The photophone also required a clear line of sight between its transmitter and its receiver.

Bell and Tainter's photophone, of 1880.

David E. Hughes transmitted radio signals over a few hundred yards by means of a clockwork keyed transmitter in 1878.

In 1888, Heinrich Hertz demonstrated the existence of electromagnetic waves, the underlying basis of most wireless technology.

Hertz demonstrated that electromagnetic waves traveled through space in straight lines, could be transmitted, and could be received by an experimental apparatus.

Jagadish Chandra Bose around this time developed an early wireless detection device and helped increase the knowledge of millimeter-length electromagnetic waves.

The term "wireless" came into public use to refer to a radio receiver or transceiver(a dual purpose receiver and transmitter device), establishing its use in the field of wireless telegraphy early on; now the term is used to describe modern wireless connections such as in cellular networks and wireless broadband Internet.

It is also used in a general sense to refer to any type of operation that is implemented without the use of wires, such as "wireless remote control" or "wireless energy transfer", regardless of the specific technology (e.g. radio, infrared, ultrasonic) used.

Guglielmo Marconi and Karl Ferdinand Braun were awarded the 1909 Nobel Prize for Physics for their contribution to wireless telegraphy.

Marconi transmitting the first radio signal across the Atlantic

Inventor Nikola Tesla performed the first experiments in wireless power transmission at the turn of the 20th century, and may have done more to popularize the idea than any other individual.

In the period 1891 to 1904 he experimented with spark-excited radio frequency resonant transformers, now called Tesla coils, which generated high AC voltages on elevated capacitive terminals.

With these he was able to transmit power for short distances without wires.

Wireless Power Transmission (WPT)

Wireless power transfer (WPT) or wireless energy transmission (WET) is the transmission of electrical power from a power source to a consuming device without using solid wires or conductors.

Wireless transmission is useful to power electrical devices in cases where interconnecting wires are inconvenient, hazardous, or are not possible. In wireless power transfer, a transmitter device connected to a power source, such as the mains power line, transmits power by electromagnetic fields across an intervening space to one or more receiver devices, where it is converted back to electric power and utilized.

There are two different fundamental methods for wireless energy transfer. They can be transferred using either far-field methods that involve beam power/lasers, radio or microwave transmissions or near-field using induction. Both methods utilize electromagnetism and magnetic fields.

In near-field or non-radiative techniques, power is transferred over short distances by magnetic fields using inductive coupling between coils of wire or in a few devices by electric fields using capacitive coupling between electrodes.

In radiative or far-field techniques, also called power beaming, power is transmitted by beams of electromagnetic radiation, like microwaves or laser beams. These techniques can transport energy longer distances but must be aimed at the receiver. Proposed applications for this type are solar power satellites, and wireless powered drone aircraft.

Wireless power techniques fall into two categories, non-radiative and radiative.

This two categories are also called as the Near-field and Far-filed Techniques.

Near-Field or Non-Radiative Techniques:

The near-field components of electric and magnetic fields die out quickly beyond a distance of about one diameter of the antenna (Dant). Outside very close ranges the field strength and coupling is roughly proportional to (Drange/Dant)

−3 . Since power is proportional to the square of the field strength, the power transferred decreases with the sixth power of the distance (Drange/Dant)

−6 or 60 dB per decade. In other words, doubling the distance between transmitter and receiver causes the power received to decrease by a factor of 26 = 64.

Here we have three types of the near-field or non-radiative techniques.

Inductive Coupling

Capacitive Coupling

Magneto-dynamic Coupling

Inductive Coupling:

This coupling is also known as the electro-dynamic induction technic.

The electro-dynamic induction wireless transmission technique relies on the use of a magnetic field generated by an electric current to induce a current in a second conductor.

This effect occurs in the electromagnetic near field, with the secondary in close proximity to the primary. As the distance from the primary is increased, more and more of the primary's magnetic field misses the secondary.

Even over a relatively short range the inductive coupling is grossly inefficient, wasting much of the transmitted energy.

This action of an electrical transformer is the simplest form of wireless power transmission. The primary coil and secondary coil of a transformer are not directly connected; each coil is part of a separate circuit.

Energy transfer takes place through a process known as mutual induction. Principal functions are stepping the primary voltage either up or down and electrical isolation.

Mobile phone and electric toothbrush battery chargers, are examples of how this principle is used. Induction cookers use this method.

The main drawback to this basic form of wireless transmission is short range. The receiver must be directly adjacent to the transmitter or induction unit in order to efficiently couple with it.

Capacitive Coupling:

In capacitive coupling (electrostatic induction), the dual of inductive coupling, power is transmitted by electric fields between electrodes such as metal plates.

The transmitter and receiver electrodes form a capacitor, with the intervening space as the dielectric. An alternating voltage generated by the transmitter is applied to the transmitting plate, and the oscillating electric field induces an alternating potential on the receiver plate by electrostatic induction, which causes an alternating current to flow in the load circuit.

The amount of power transferred increases with the frequency and the capacitance between the plates, which is proportional to the area of the smaller plate and (for short distances) inversely proportional to the separation.

Capacitive coupling has only been used practically in a few low power applications, because the very high voltages on the electrodes required to transmit significant power can be hazardous, and can cause unpleasant side effects such as noxious ozone production.

In addition, in contrast to magnetic fields, electric fields interact strongly with most materials, including the human body, due to dielectric polarization.

However capacitive coupling has a few advantages over inductive. The field is largely confined between the capacitor plates, reducing interference, which in inductive coupling requires heavy ferrite "flux confinement" cores. Also, alignment requirements between the transmitter and receiver are less critical.

Capacitive coupling has recently been applied to charging battery powered portable devices and is being considered as a means of transferring power between substrate layers in integrated circuits.

Magneto-dynamic Coupling:

In this method, power is transmitted between two rotating armatures, one in the transmitter and one in the receiver, which rotate synchronously, coupled together by a magnetic field generated by permanent magnets on the armatures.

The transmitter armature is turned either by or as the rotor of an electric motor, and its magnetic field exerts torque on the receiver armature, turning it. The magnetic field acts like a mechanical coupling between the armatures.

The receiver armature produces power to drive the load, either by turning a separate electric generator or by using the receiver armature itself as the rotor in a generator.

This device has been proposed as an alternative to inductive power transfer for noncontact charging of electric vehicles. A rotating armature embedded in a garage floor or curb would turn a receiver armature in the underside of the vehicle to charge its batteries. It is claimed that this technique can transfer power over distances of 10 to 15 cm (4 to 6 inches) with high efficiency, over 90%.

Also, the low frequency stray magnetic fields produced by the rotating magnets produce less electromagnetic interference to nearby electronic devices than the high frequency magnetic fields produced by inductive coupling systems.

A prototype system charging electric vehicles has been in operation at University of British Columbia since 2012. Other researchers, however, claim that the two energy conversions (electrical to mechanical to electrical again) make the system less efficient than electrical systems like inductive coupling.

Far-Field or Radiative Techniques:

Far field methods achieve longer ranges, often multiple kilometer ranges, where the distance is much greater than the diameter of the device(s). The main reason for longer ranges with radio wave and optical devices is the fact that electromagnetic radiation in the far-field can be made to match the shape of the receiving area (using high directivity antennas or well-collimated laser beams). The maximum directivity for antennas is physically limited by diffraction.

In general, visible light (from lasers) and microwaves (from purpose-designed antennas) are the forms of electromagnetic radiation best suited to energy transfer.

The Rayleigh criterion dictates that any radio wave, microwave or laser beam will spread and become weaker and diffuse over distance; the larger the transmitter antenna or laser aperture compared to the wavelength of radiation, the tighter the beam and the less it will spread as a function of distance (and vice versa). Smaller antennae also suffer from excessive losses due to side lobes.

However, the concept of laser aperture considerably differs from an antenna. Typically, a laser aperture much larger than the wavelength induces multi-moded radiation and mostly collimators are used before emitted radiation couples into a fiber or into space.

Here we are mainly implementing the two things to transfer the power.

Microwaves

Lasers

Microwaves:

Power transmission via radio waves can be made more directional, allowing longer distance power beaming, with shorter wavelengths of electromagnetic radiation, typically in the microwave range.

A rectenna may be used to convert the microwave energy back into electricity.

Rectenna conversion efficiencies exceeding 95% have been realized. Power beaming using microwaves has been proposed for the transmission of energy from orbiting solar power satellites to Earth and the beaming of power to spacecraft leaving orbit has been considered.

Power beaming by microwaves has the difficulty that, for most space applications, the required aperture sizes are very large due to diffraction limiting antenna directionality.

For example, the 1978 NASA Study of solar power satellites required a 1-km diameter transmitting antenna and a 10 km diameter receiving rectenna for a microwave beam at 2.45 GHz.

These sizes can be somewhat decreased by using shorter wavelengths, although short wavelengths may have difficulties with atmospheric absorption and beam blockage by rain or water droplets. Because of the "thinned array curse," it is not possible to make a narrower beam by combining the beams of several smaller satellites.

Wireless high power transmission using microwaves is well proven. Experiments in the tens of kilowatts have been performed at Goldstone in California in 1975 and more recently (1997) at Grand Bassin on Reunion Island. These methods achieve distances on the order of a kilometer.

Under experimental conditions, microwave conversion efficiency was measured to be around 54%.

More recently, a change to 24 GHz has been suggested as microwave emitters similar to LEDs have been made with very high quantum efficiencies using negative resistance, i.e. Gunn or IMPATT diodes, and this would be viable for short range links.

Lasers:In the case of electromagnetic radiation closer to the visible region of the spectrum

(tens of micrometers to tens of nanometres), power can be transmitted by converting electricity into a laser beam that is then pointed at a photovoltaic cell. This mechanism is generally known as "power beaming" because the power is beamed at a receiver that can convert it to electrical energy.

Compared to other wireless methods:

Collimated monochromatic wavefront propagation allows narrow beam cross-section area for transmission over large distances.

Compact size: solid state lasers fit into small products.

No radio-frequency interference to existing radio communication such as Wi-Fi and cell phones.

Access control: only receivers hit by the laser receive power.

Laser "powerbeaming" technology has been mostly explored in military weapons and aerospace applications and is now being developed for commercial and consumer electronics. Wireless energy transfer systems using lasers for consumer space have to satisfy laser safety requirements standardized under IEC 60825.

Other details include propagation and the coherence and the range limitation problem.

Geoffrey Landis is one of the pioneers of solar power satellites and laser-based transfer of energy especially for space and lunar missions. The demand for safe and frequent space missions has resulted in proposals for a laser-powered space elevator.

NASA's Dryden Flight Research Center demonstrated a lightweight unmanned model plane powered by a laser beam. This proof-of-concept demonstrates the feasibility of periodic recharging using the laser beam system.

Drawbacks include:

Laser radiation is hazardous. Low power levels can blind humans and other animals. High power levels can kill through localized spot heating.

Conversion between electricity and light is inefficient. Photovoltaic cells achieve only 40%–50% efficiency. (Efficiency is higher with monochromatic light than with solar panels).

Atmospheric absorption, and absorption and scattering by clouds, fog, rain, etc., causes up to 100% losses.

Requires a direct line of sight with the target.

Advantages of WPT:Wireless Power Transmission system would completely eliminates the existing high-tension

power transmission line cables, towers and sub stations between the generating station and consumers and facilitates the interconnection of electrical generation plants on a global scale.

It has more freedom of choice of both receiver and transmitters. Even mobile transmitters and receivers can be chosen for the WPT system.

The cost of transmission and distribution become less and the cost of electrical energy for the consumer also would be reduced.

The power could be transmitted to the places where the wired transmission is not possible. Loss of transmission is negligible level in the Wireless Power Transmission; therefore, the efficiency of this method is very much higher than the wired transmission.

Power is available at the rectenna as long as the WPT is operating. The power failure due to short circuit and fault on cables would never exist in the transmission and power theft would be not possible at all.

Disadvantages of WPT:

The Capital Cost for practical implementation of WPT seems to be very high and the other disadvantage of the concept is interference of microwave with present communication systems.

Biological Impacts of WPT:

Common beliefs fear the effect of microwave radiation. But the studies in this domain repeatedly proves that the microwave radiation level would be never higher than the dose received while opening the microwave oven door, meaning it is slightly higher than the emissions created by cellular telephones. Cellular telephones operate with power densities at or below the ANSI/IEEE exposure standards. Thus public exposure to

WPT fields would also be below existing safety guidelines.

Applications of WPT:

Generating power by placing satellites with giant solar arrays in Geosynchronous Earth Orbit and transmitting the power as microwaves to the earth known as Solar Power Satellites (SPS) is the largest application of WPT. Another application of WPT is moving targets such as fuel free airplanes, fuel free electric vehicles, moving robots and fuel free rockets. The other applications of WPT are Ubiquitous Power Source (or) Wireless

Power Source, Wireless sensors and RF Power Adaptive Rectifying Circuits (PARC).

ConclusionThe concept of Microwave Power transmission (MPT) and Wireless Power

Transmission system is presented. The technological developments in Wireless Power Transmission

(WPT), the advantages, disadvantages, biological impacts and applications of WPT are also discussed. This concept offers greater possibilities for transmitting power with negligible losses and ease of transmission than any invention or discovery heretofore made.

Dr. Neville of NASA states “You don’t need cables, pipes, or copper wires to receive power. We can send it to you like a cell phone call – where you want it, when you want it, in real time”. We can expect with certitude that in next few years’ wonders will be wrought by its applications if all the conditions are favourable.

References:Agbinya, Johnson I., Ed. (2012). Wireless Power Transfer. River Publishers.

ISBN 8792329233. Comprehensive, theoretical engineering text

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Kurs, André; Karalis, Aristeidis; Moffatt, Robert (July 2007). "Wireless Power Transfer via Strongly Coupled Magnetic Resonances". Science (American Association for the Advancement of Science) 317: 83–85.

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