Abstract
As (Vallone, Thomas, & Vallone, Jacqueline, 2009) observe, the area of wireless power transmission s but an undeveloped area of study. Many a promising applications have been posited for this area, owing to the fact that t provides for the transmission f power over great distances as, along with boundaries, less the need for transmission lines. On juxtaposition with current electronic technology, the latter makes use of microwaves, given that the energy and economic efficiency provides form some leveraging via products which are already in production. In retrospect, the last couple years have seen attempts to develop new technology which would otherwise accommodate this propagating by means of electromagnetic waves, in and around the visual light spectrum. In retrospect, as already mentioned, the technologies herein are but emergent.
Introduction
Despite the fact that the technology is merely in its infancy, the potential benefits are immense on its attaining of maturation. These could be significant for generations as well as society hitherto, given that on extrapolation, the global population is projected to increase exponentially. Five sixths of the global population currently hails from developing countries. As such, countries the likes of India, China, along with Pakistan are on a campaign to alleviate the standards of living. Per se, such are the trends which hint at a demand for energy of extreme proportions, and whose demand rate is directly proportional to the population increase. Along these lines, the WTP technology provides for the generation of solar power on a satellite, subsequent to which it is beamed down to earth. Similarly, power can also be transmitted to a water treatment plan in the instance of a disaster for the purposes of disaster relief. Conversely, if it reaches maturation, it will be possible to power a flying communication relay station from a terrestrial station. In light of these sentiments, this treatise will focus on the history of this piece of technology, tracing its development over the years to the current state it’s in.
The technology is yet to come to viability owing to technological impediments which present minute engineering hurtles. However, with the increasing energy demand, along with the rapid improvements, it is but a matter of time before the conceptualization of WTP comes into being, and the industry materializes (Sarka, Maillox, Oliner, & Dipak, 2006). It is a common presumption of the association between the propagation of electromagnetic waves to electromagnetic power. Hypothetically, the epicenter of the wireless power transmission technology is electromagnetic waves. As such, the disparity between the common communication systems and wireless power technology, WPT comes in the issue of efficiency (Sarka, Maillox, Oliner, & Dipak, 2006). As extrapolated from Maxwell’s equations, it emerges that an electromagnetic field, along with its power, diffuse in all directions. This is also evident in the communication systems of today. This owes to the fact that, on transmission of energy in a communication system, it diffuses in all directions. In retrospect, despite the fact that the power received is enough to transmit information, the efficiency from the transmitter to the receiver is to a certain extent low. Owing to this, it passes not as a WTP system.
History of Wireless power Transmission
An archetypical WTP is but a point-to-point power transmission. Similarly, as opposed to a communication system, the efficiency levels attained in a typical WTP approach 100% (Sarka, Maillox, Oliner, & Dipak, 2006). This owes to the fact that, in WTP, the power distribution via the taper method of the transmitting antenna comes to play in the transmission of the microwave power to the recipient apertures. The most common tapers linked to the transmitting antenna are inclusive of Taylor distribution, Gaussian tapers, along with Chepachet distribution. As such, these methods of taper distribution are effective in that, they are commonly used in the suppression of side lobes. Per se, this phenomenon corresponds to the increment in efficiency when transmitting power. On the issue of power efficiency in Wireless Power Transmission, a myriad of relevant optical approaches have been made by the Russians (Choi, & Seo, 2010).
In 1864, James C. Maxwell posited the ideology that, radio waves were conceivable by means of mathematical extrapolation. Subsequent to this, John H. pointing, in 1884, came to the realization that, the Poynting vector played a quintessential role in the quantification of electromagnetic energy. Along these, Heinrich Hertz, bolstered by Maxwell’s theory, was successful in showing experimental evidence of radio waves, by means of his spark-gap radio transmitter. As such, this prediction along with evidence of the existence of the radio wave, at the end of the 19thg century, marks the conception of wireless power transmission.
In the same era, Marchese G. Marconi, along with Reginald Fessenden, pioneered communication by means of radio waves. Subsequent to this, Nikola Tesla proposed that, wireless transmission of power was a viable ideology, subsequent to which he carried out the first known experiment on WTP in 1899. He is quoted as asserting that, the new form of energy would be collected on a global spectrum, in small amounts, which would range from but a fraction of one to a few horse powers. Its main application, according to him, would be primarily illumination of isolated homes. In the wake of this, he built a gigantic coil which he connected to a high mast 200 feet long, with a ball of diameter 3 ft atop it. On feeding power of up to 300 kw to it, the Tesla coil reacted by resonating at 150kHz. At the top of the sphere, the RF potential reached 100 MV. However, he was unsuccessful owing to the fact that, the power which was transmitted resulted to diffusing in all directions, with radio waves resonation at a speed of 150 kHz, and with a wavelength of 21 km.
In a bid to concentrate the transmitted power, in addition to increase the efficiency of transmission, it was imperative to use a frequency much higher than that used by Tesla in his experiment. In the 1930’s, further progress came about n the generation of high power microwaves, namely the 1-10 GHz radio waves. This occurred following the invention of the klystron, as well as the magnetron. In the wake of World war II, high power microwaves tubes, with characteristically higher efficiency, were also advanced, following the development of radar technology. Owing to this technology stride, it was possible to concentrate a given power onto a receiver with microwaves. This transmission of wireless power by use of microwaves was coined microwave power transmission, abbreviated MPT. W. C. Brown, basing his research on the development of microwave tubes in the course of World War II, attempted the first MPT research and development. This was in 1960.
To start with, he built up a retina, along with rectifying antenna, which he coined, for the purposes of receipt and rectification of microwaves. In terms of efficiency, the first retina developed in 1963 had an efficiency of 50%, at an output of 4WDC. At 7WDC however, the efficiency dropped to 40%. Brown, therefore, in developing the rectifying antenna, or rather, the rectenna, succeeded in MPT experiments to a wired helicopter in 1964 and to a free-flied helicopter in 1968. In the 1970s, he also attempted to increase the total efficiency in a DC-RF-transmission-RF-DC-transmission. This he did by use of a 2.45 GHz microwave. By 1970, the total efficiency at 39WDC was a mere 26.5% at the Marshall Flight Centre. In parallel, Brown and his team were successful in the largest ever demonstration of MPT at JPL Goldstone’s Venus Site, in 1975. The distance between the transmitting parabolic antennas, with a diameter of 26m, along with a rectenna array of size 7.2m by 3.4 m, was 1 mile.
After the 1990s, a myriad of MPT field and laboratory experiments were carried out all over the world. The ISM bands in use to date s either the 2.45 GHz or the 5.8GHZ one for the MPT. In recent times, a Canadian group has demonstrated the fuel-free airplane flight experiment by use of MPT. This was in 1987. They coined it the Stationary High Altitude Relay Platform, abbreviated SHARP, using 2.4 GHz voltage.
Not willing to be left behind, the US was also a site for a series of successive experiments on MPT. Research and development projects, after W.C. brown, were carried out as well. An instance of this is evident in the retro directive microwave transmitters, a myriad of new devices and microwave circuit technologies, as well as the rectenna. In Japan, also, an array of field experiments n the area of MPT were also carried out. These are inclusive of the fuel-free airplane flight, which made use of MPT phased array with a 1.411 frequency in the year 1992. Similarly, ground-to-ground MPT experiments on not only universities, but also power plants, have been carried out between 1994 and 1995 (Vallone, & Vallone, 2009).
Recent trends
Antennas for Microwave Power Transmission: All antennas can be applied for both the MPT system and communication systems, for example, Yagi-Uda antenna, horn antenna, parabolic antenna, micro strip antenna, phased array antenna or any other type of antenna.
To fixed target of the MPT system, we usually select a large parabolic antenna, for example, in MPT demonstration in 1975 at the Venus Site of JPL Goldstone Facility and in ground-to-ground MPT experiment in 1994-95 in Japan. In the fuel-free airship light experiment with MPT in 1995 in Japan, they changed a direction of the parabolic antenna to chase the moving airship.
However, we have to use a phased array antenna for the MPT from/to moving transmitter/receiver which include the SPS because we have to control a microwave beam direction accurately and speedily. The phased array is a directive antenna which generates a beam form whose shape and direction by the relative phases and amplitudes of the waves at the individual antenna elements.
It is possible to steer the direction of the microwave beam. The antenna elements might be dipoles [1], slot antennas, or any other type of antenna, even parabolic antennas [2, 3]. In some MPT experiments in Japan, the phased array antenna was adopted to steer a direction of the microwave beam
All SPS is designed with the phased array antenna. experiments were carried out in Japan with phased array of semiconductor amplifiers.
Typical semiconductor devices for microwave circuits are FET (Field Effect Transistor), HBT (Hetero junction Bipolar Transistor), and HEMT (High Electron Mobility Transistor). Present materials for the semiconductor devices are Si for lower frequency below a few GHz and GaAs for higher frequency.. It is easy to control phase and amplitude through the microwave circuits with semiconductor devices, for example, amplifiers, phase shifters, modulators, and so on.
Currently, new materials are under development to enable semiconductor devices yield increased output power and efficiency.
Transmitter Issues and Answers for Space Use: Largest MPT application is a SPS in which over GW microwave will be transmitted from space to ground at distance of 36,000km. In the SPS, we will use microwave transmitters in space. For space use, the microwave transmitter will be required lightness to reduce launch cost and higher efficiency to reduce heat problem.
A weight of the microwave tube is lighter than that of the semiconductor amplifier when we compare the weight by power-weight ratio (kg/kW). The microwave tube can generate/amplify higher power microwave than that by the semiconductor amplifier. Kyoto University’s groups have developed a light weight phase controlled magnetron called COMET, Compact Microwave Energy Transmitter with a power-weight ratio below 25g.

References
Choi, J., & Seo, C. (2010). High efficiency wireless energy transmission using magnetic resonance based on Meta-material equal to-1. Informally published manuscript, Department of Electronic Engineering, Soongsil University, Dongjak-gu,Seoul 156-743-Republic of Korea. Retrieved from http://www.jpier.org/PIER/pier106/03.10050609.pdf
Kurs, Andre. (2007). Power transfer through strongly coupled resonances. (Master's thesis, Massachusetts Institute of Technology).
Sarka, Tapan, K., Maillox, Robert, J., Oliner, Arthur, A., & Dipak, Sengupta, (2006). History of wireless. Hoboken, New Jersey: John Wiley & Sons Inc. Retrieved from http://books.google.com/books?id=NBLEAA6QKYkC&printsec=frontcover&dq=history of wirelesselectricity&source=bl&ots=1H2KiqR7qp&sig=TWDQA4Vgf5IA7sQQXsDvMOvyLZ8
Vallone, Thomas, F., & Vallone, Jacqueline, P. (2009). The future of energy: An emerging science. (First Soft Cover Edition ed.). Beltsville, MD: Integrity Research Institute.
Valone, Thomas. (2002). Harnessing the wheelwork of nature, Tesla's science of energy. Kempton, Illinois: Adventures Unlimited Press. Retrieved from http://books.google.com/books?id=ZNqo1zaZRTYC&printsec=frontcover&dq=wirelesselectricity&source=bl&ots=ZJ_IJlqgVK&sig=gy9a7OSVx6tGV4IuFAwQNTdIDU&hl=en&sa=X&ei=RjUMUMfzIoG49QT0sa28Cg&ved=0CEAQ6AEwAg