06-08-2011, 10:34 AM
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1. Theoretical Background
It is known that electromagnetic energy also associated with the propagation of the
electromagnetic waves. We can use theoretically all electromagnetic waves for a wireless power
transmission (WPT). The difference between the WPT and communication systems is only efficiency.
The Maxwell’s Equations indicate that the electromagnetic field and its power diffuse to all
directions. Although we transmit the energy in the communication system, the transmitted energy is
diffused to all directions. Although 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 Chebychev distribution. These taper of the
transmitting antenna is commonly used for suppression of sidelobes. It corresponds to increase the
power transmission efficiency. Concerning the power transmission efficiency of the WPT, there are
some good optical approaches in Russia[5][6].
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 in 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 sidelobe 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 realize around 2030. Before the realization of the SPS, we can consider the
other application of the WPT. In resent years, mobile devices advance quickly and require
decreasing power consumption. It means that we can use the diffused weak microwave power as a
power source of the mobile devices with low power consumption such as RF-ID. The RF-ID is a
radio IC-tug with wireless power transmission and wireless information. This is a new WPT
application like broadcasting.
1. Theoretical Background
It is known that electromagnetic energy also associated with the propagation of the
electromagnetic waves. We can use theoretically all electromagnetic waves for a wireless power
transmission (WPT). The difference between the WPT and communication systems is only efficiency.
The Maxwell’s Equations indicate that the electromagnetic field and its power diffuse to all
directions. Although we transmit the energy in the communication system, the transmitted energy is
diffused to all directions. Although 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 Chebychev distribution. These taper of the
transmitting antenna is commonly used for suppression of sidelobes. It corresponds to increase the
power transmission efficiency. Concerning the power transmission efficiency of the WPT, there are
some good optical approaches in Russia[5][6].
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 in 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 sidelobe 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 realize around 2030. Before the realization of the SPS, we can consider the
other application of the WPT. In resent years, mobile devices advance quickly and require
decreasing power consumption. It means that we can use the diffused weak microwave power as a
power source of the mobile devices with low power consumption such as RF-ID. The RF-ID is a
radio IC-tug with wireless power transmission and wireless information. This is a new WPT
application like broadcasting.
