19-04-2011, 03:32 PM
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1.INTRODUCTION
The area of wireless power transmission is very interesting. One of the major issue in power system is the losses occurs during the transmission and distribution of electrical power. As the demand increases day by day, the power generation increases and the power loss is also increased. The major amount of power loss
occurs during transmission and distribution. The percentage of loss of power during transmission and distribution is approximated as 26%. The main reason for power loss during transmission and distribution is the resistance of wires used for grid. The efficiency of power transmission can be improved to certain level by using high strength composite over head conductors and underground cables that use high temperature super conductor. But, the transmission is still inefficient.
The technology is in its infancy but the overall benefits from its maturation could be significant to society as a whole. World population is expected to continue to grow exponentially. Five sixths of the world’s population lives in developing nations. Most developing nations such as China, India, and Pakistan are rapidly improving their standard of living. All of these trends point to an energy demand that will grow at even a larger rate. Wireless power transmission could one day allow us to generate solar power on a satellite and beam it down to Earth, transmit power to a water treatment plant for a disaster relief operation or power a flying communication relay station from a terrestrial station. There are a few engineering hurtles yet to overcome to make this technology viable to today’s investors, but with the rising demand for energy and the rapid improvements being made it is just a matter of time before wireless power transmission becomes an industry of its own.
It is known that electromagnetic energy is associated with the propagation of electromagnetic waves. Theoretically, we can use all electromagnetic waves for a wireless power transmission (WPT). The difference between the WPT and communication systems is only efficiency. Maxwell’s Equations indicate that the electromagnetic field and its power diffuse to all directions. Though we transmit energy in a communication system, the transmitted energy is diffused to all directions. Though the received power is enough for a transmission of information, the efficiency from the transmitter to receiver is quiet low. Therefore, we do not call it the WPT system.
Typical WPT is a point-to-point power transmission. For the WPT, we had better concentrate power to receiver. It was proved that the power transmission efficiency can approach close to 100%. We can more concentrate the transmitted microwave power to the receiver aperture areas with taper method of the transmitting antenna power distribution. Famous power tapers of the transmitting antenna are Gaussian taper, Taylor distribution, and Chepachet distribution. Such taper of the transmitting antenna is commonly used for suppression of side lobes. It corresponds to increase in the power transmission efficiency. Concerning the power transmission efficiency of the WPT, there are some good optical approaches in Russia.
Future suitable and largest application of the WPT via microwave is a Space Solar Power Satellite (SPS). The SPS is a gigantic satellite designed as an electric power plant orbiting the Geostationary Earth Orbit (GEO). It consists of mainly three segments; solar energy collector to convert the solar energy into DC (direct current) electricity, DC-to-microwave converter, and large antenna array to beam down the microwave power to the ground. The first solar collector can be either photovoltaic cells or solar thermal turbine. The second DC-to-microwave converter of the SPS can be either microwave tube system and/or semiconductor system. It may be their combination. The third segment is a gigantic antenna array.
Table 1.1 shows some typical parameters of the transmitting antenna of the SPS. An amplitude taper on the transmitting antenna is adopted in order to increase the beam collection efficiency and to decrease side lobe level in almost all SPS design. A typical amplitude taper is called 10 dB Gaussian in which the power density in the center of the transmitting antenna is ten times larger than that on the edge of the transmitting antenna.
The SPS is expected to be operational around 2030.Before realization of the SPS, we can consider other applications of WPT. In recent years, mobile devices advanced significantly and require decreasing power consumption . It means that we can use the diffused weak microwave power as power source of the mobile devices with low power consumption such as RF-ID. The RF-ID is radio IC-tug with wireless power transmission and wireless information. This is a new WPT
Application like broadcasting.
2.HISTORY OF WIRELESS POWER TRANSMISSION
The discussion of wireless power transmission as an alternative to transmission line power distribution started in the late 19th century. In 1888, bolstered by Maxwell's theory, Heinrich Hertz succeeded in showing experimental evidence of radio waves by his spark-gap radio transmitter. The prediction and evidence of the radio wave in the end of 19th century was start of the wireless power transmission.
Both Heinrich Hertz and Nicolai Tesla theorized the possibility of wireless power transmission. Tesla demonstrated it in 1899 by powering fluorescent lamps 25 miles from the power source without using wires. Despite the novelty of Tesla’s demonstration and his personal efforts to commercialize wireless power transmission, he soon ran out of funding because it was much less expensive to lay copper than to build the equipment necessary to transmit power through radio waves.
Nicolai Tesla suggested an idea of the wireless power transmission and carried out the first WPT experiment in 1899. He said “This energy will be collected all over the globe preferably in small amounts, ranging from a fraction of one to a few horse-powers. One of its chief uses will be the illumination of isolated homes”.
William C. Brown contributed much to the modern development of microwave power transmission which for many reasons dominates research and development of wireless transmission today. In the early 1960s brown invented the rectenna which directly converts microwaves to DC current.
To concentrate the transmitted power and to increase transmission efficiency, we have to use higher frequency than that used by Tesla. In 1930s, much progress in generating high-power microwaves, namely 1-10 GHz radio waves, was achieved by invention of the magnetron and the klystron. After World War II, high power and high efficiency microwave tubes were advanced by development of radar technology. We can concentrate a power to receiver with microwaves. We call the wireless power transmission with microwaves as microwave power transmission (MPT). Based on the development of the microwave tubes during the World War II, W. C. Brown started the First MPT research and development in 1960.
Despite these advances wireless power transmission has not been adopted for commercial use except for the sole exception of pacemakers and electric toothbrush rechargers. However, research is ongoing because of the many promising applications suited for wireless power transmission.
First of all, he developed a rectenna, rectifying antenna which he named, for receiving and rectifying microwaves. The efficiency of the first rectenna developed in 1963 was 50 % at output 4WDC and 40% at output 7WDC respectively.
With the rectenna, he succeeded in MPT experiments to wired helicopter in 1964 and to free-flied helicopter in1968 (Fig. 1). In 1970s; he tried to increase DC-RF-transmission-RF-DC total efficiency with 2.45 GHz microwave. In 1970, overall DC-DC total efficiency was only 26.5 % at 39WDC in Marshall Space Flight Center.
After 1990s, many MPT laboratory and field experiments were carried out in the world. We often use 2.45 GHz or 5.8 GHz of the ISM band (ISM=Industry, Science, and Medical) for the MPT system. A Canadian group demonstrated fuel-free airplane flight experiment with MPT in 1987 which was called SHARP (Stationary High Altitude Relay Platform) with 2.45 GHz.
In USA, there were many MPT research and development projects after W. C. Brown: for instance, retro directive microwave transmitters, rectenna, new devices and microwave circuit technologies.
1.INTRODUCTION
The area of wireless power transmission is very interesting. One of the major issue in power system is the losses occurs during the transmission and distribution of electrical power. As the demand increases day by day, the power generation increases and the power loss is also increased. The major amount of power loss
occurs during transmission and distribution. The percentage of loss of power during transmission and distribution is approximated as 26%. The main reason for power loss during transmission and distribution is the resistance of wires used for grid. The efficiency of power transmission can be improved to certain level by using high strength composite over head conductors and underground cables that use high temperature super conductor. But, the transmission is still inefficient.
The technology is in its infancy but the overall benefits from its maturation could be significant to society as a whole. World population is expected to continue to grow exponentially. Five sixths of the world’s population lives in developing nations. Most developing nations such as China, India, and Pakistan are rapidly improving their standard of living. All of these trends point to an energy demand that will grow at even a larger rate. Wireless power transmission could one day allow us to generate solar power on a satellite and beam it down to Earth, transmit power to a water treatment plant for a disaster relief operation or power a flying communication relay station from a terrestrial station. There are a few engineering hurtles yet to overcome to make this technology viable to today’s investors, but with the rising demand for energy and the rapid improvements being made it is just a matter of time before wireless power transmission becomes an industry of its own.
It is known that electromagnetic energy is associated with the propagation of electromagnetic waves. Theoretically, we can use all electromagnetic waves for a wireless power transmission (WPT). The difference between the WPT and communication systems is only efficiency. Maxwell’s Equations indicate that the electromagnetic field and its power diffuse to all directions. Though we transmit energy in a communication system, the transmitted energy is diffused to all directions. Though the received power is enough for a transmission of information, the efficiency from the transmitter to receiver is quiet low. Therefore, we do not call it the WPT system.
Typical WPT is a point-to-point power transmission. For the WPT, we had better concentrate power to receiver. It was proved that the power transmission efficiency can approach close to 100%. We can more concentrate the transmitted microwave power to the receiver aperture areas with taper method of the transmitting antenna power distribution. Famous power tapers of the transmitting antenna are Gaussian taper, Taylor distribution, and Chepachet distribution. Such taper of the transmitting antenna is commonly used for suppression of side lobes. It corresponds to increase in the power transmission efficiency. Concerning the power transmission efficiency of the WPT, there are some good optical approaches in Russia.
Future suitable and largest application of the WPT via microwave is a Space Solar Power Satellite (SPS). The SPS is a gigantic satellite designed as an electric power plant orbiting the Geostationary Earth Orbit (GEO). It consists of mainly three segments; solar energy collector to convert the solar energy into DC (direct current) electricity, DC-to-microwave converter, and large antenna array to beam down the microwave power to the ground. The first solar collector can be either photovoltaic cells or solar thermal turbine. The second DC-to-microwave converter of the SPS can be either microwave tube system and/or semiconductor system. It may be their combination. The third segment is a gigantic antenna array.
Table 1.1 shows some typical parameters of the transmitting antenna of the SPS. An amplitude taper on the transmitting antenna is adopted in order to increase the beam collection efficiency and to decrease side lobe level in almost all SPS design. A typical amplitude taper is called 10 dB Gaussian in which the power density in the center of the transmitting antenna is ten times larger than that on the edge of the transmitting antenna.
The SPS is expected to be operational around 2030.Before realization of the SPS, we can consider other applications of WPT. In recent years, mobile devices advanced significantly and require decreasing power consumption . It means that we can use the diffused weak microwave power as power source of the mobile devices with low power consumption such as RF-ID. The RF-ID is radio IC-tug with wireless power transmission and wireless information. This is a new WPT
Application like broadcasting.
2.HISTORY OF WIRELESS POWER TRANSMISSION
The discussion of wireless power transmission as an alternative to transmission line power distribution started in the late 19th century. In 1888, bolstered by Maxwell's theory, Heinrich Hertz succeeded in showing experimental evidence of radio waves by his spark-gap radio transmitter. The prediction and evidence of the radio wave in the end of 19th century was start of the wireless power transmission.
Both Heinrich Hertz and Nicolai Tesla theorized the possibility of wireless power transmission. Tesla demonstrated it in 1899 by powering fluorescent lamps 25 miles from the power source without using wires. Despite the novelty of Tesla’s demonstration and his personal efforts to commercialize wireless power transmission, he soon ran out of funding because it was much less expensive to lay copper than to build the equipment necessary to transmit power through radio waves.
Nicolai Tesla suggested an idea of the wireless power transmission and carried out the first WPT experiment in 1899. He said “This energy will be collected all over the globe preferably in small amounts, ranging from a fraction of one to a few horse-powers. One of its chief uses will be the illumination of isolated homes”.
William C. Brown contributed much to the modern development of microwave power transmission which for many reasons dominates research and development of wireless transmission today. In the early 1960s brown invented the rectenna which directly converts microwaves to DC current.
To concentrate the transmitted power and to increase transmission efficiency, we have to use higher frequency than that used by Tesla. In 1930s, much progress in generating high-power microwaves, namely 1-10 GHz radio waves, was achieved by invention of the magnetron and the klystron. After World War II, high power and high efficiency microwave tubes were advanced by development of radar technology. We can concentrate a power to receiver with microwaves. We call the wireless power transmission with microwaves as microwave power transmission (MPT). Based on the development of the microwave tubes during the World War II, W. C. Brown started the First MPT research and development in 1960.
Despite these advances wireless power transmission has not been adopted for commercial use except for the sole exception of pacemakers and electric toothbrush rechargers. However, research is ongoing because of the many promising applications suited for wireless power transmission.
First of all, he developed a rectenna, rectifying antenna which he named, for receiving and rectifying microwaves. The efficiency of the first rectenna developed in 1963 was 50 % at output 4WDC and 40% at output 7WDC respectively.
With the rectenna, he succeeded in MPT experiments to wired helicopter in 1964 and to free-flied helicopter in1968 (Fig. 1). In 1970s; he tried to increase DC-RF-transmission-RF-DC total efficiency with 2.45 GHz microwave. In 1970, overall DC-DC total efficiency was only 26.5 % at 39WDC in Marshall Space Flight Center.
After 1990s, many MPT laboratory and field experiments were carried out in the world. We often use 2.45 GHz or 5.8 GHz of the ISM band (ISM=Industry, Science, and Medical) for the MPT system. A Canadian group demonstrated fuel-free airplane flight experiment with MPT in 1987 which was called SHARP (Stationary High Altitude Relay Platform) with 2.45 GHz.
In USA, there were many MPT research and development projects after W. C. Brown: for instance, retro directive microwave transmitters, rectenna, new devices and microwave circuit technologies.
