Effective radiated power

Abstract: This paper is concerned with the properties of the radiation from a high energy accelerated electron, as recently observed in the General Electric synchrotron. An elementary derivation of the total rate of radiation is first presented, based on Larmor's formula for a slowly moving electron, and arguments of relativistic invariance. We then construct an expression for the instantaneous power radiated by an electron moving along an arbitrary, prescribed path. By casting this result into various forms, one obtains the angular distribution, the spectral distribution, or the combined angular and spectral distributions of the radiation. The method is based on an examination of the rate at which the electron irreversibly transfers energy to the electromagnetic field, as determined by half the difference of retarded and advanced electric field intensities. Formulas are obtained for an arbitrary charge-current distribution and then specialized to a point charge. The total radiated power and its angular distribution are obtained for an arbitrary trajectory. It is found that the direction of motion is a strongly preferred direction of emission at high energies. The spectral distribution of the radiation depends upon the detailed motion over a time interval large compared to the period of the radiation. However, the narrow cone of radiation generated by an energetic electron indicates that only a small part of the trajectory is effective in producing radiation observed in a given direction, which also implies that very high frequencies are emitted. Accordingly, we evaluate the spectral and angular distributions of the high frequency radiation by an energetic electron, in their dependence upon the parameters characterizing the instantaneous orbit. The average spectral distribution, as observed in the synchrotron measurements, is obtained by averaging the electron energy over an acceleration cycle. The entire spectrum emitted by an electron moving with constant speed in a circular path is also discussed. Finally, it is observed that quantum effects will modify the classical results here obtained only at extraordinarily large energies.

Abstract: A new framework for the analysis of multiple-input multiple-output (MIMO) wireless systems is introduced to account for mutual coupling effects in the antenna arrays. The multiport interactions at transmit and receive are characterized by representing the channel using a scattering parameter matrix. A new power constraint that limits the average radiated power is also introduced. The capacity of the MIMO system with mutual coupling is defined as the maximum mutual information of the transmit and receive vectors over all possible transmit signaling and receive loading. Full-wave electromagnetic antenna simulations combined with a simple path-based channel model are used to demonstrate the utility of the method.

Abstract: Expressions for the total power radiated by magnetic and electric dipoles of arbitrary orientation located in a medium 1 at distance z0 from the interface to a homogeneous or planar stratified medium 2 are derived. A relation between the normalized powers radiated by magnetic and electric dipoles is established. For a homogeneous loss-free medium 2, curves of the normalized powers L(z0)/L∞ radiated by magnetic and electric dipoles versus the normalized distance z0/λ1 are presented for different values of the relative refractive index n = n2/n1 as the only parameter. The computer calculations are compared with analytical expressions derived for small and large distances. For n > 1, the contribution of the evanescent waves to the radiated power is calculated separately. We show that the classical results for the normalized radiated power yield the correct normalized spontaneous emission rates from an excited atomic state for electric and magnetic dipole transitions, respectively. We point out that the results for the electric dipole also give the change of the total power scattered by a small dielectric scattering particle when it is placed close to an interface.

Abstract: This paper presents a fully integrated remotely powered and addressable radio frequency identification (RFID) transponder working at 2.45 GHz. The achieved operating range at 4 W effective isotropically radiated power (EIRP) base-station transmit power is 12 m. The integrated circuit (IC) is implemented in a 0.5 /spl mu/m silicon-on-sapphire technology. A state-of-the-art rectifier design achieving 37% of global efficiency is embedded to supply energy to the transponder. The necessary input power to operate the transponder is about 2.7 /spl mu/W. Reader to transponder communication is obtained using on-off keying (OOK) modulation while transponder to reader communication is ensured using the amplitude shift keying (ASK) backscattering modulation technique. Inductive matching between the antenna and the transponder IC is used to further optimize the operating range.

Abstract: Expressions are derived for the power radiated in the compressional, shear and surface waves set up by a circular disk vibrating normally to the free surface of a semi-infinite isotropic solid. The total radiated power is also calculated independently by integrating the displacement velocity over the area of the source. The theory is extended to a general type of multi-element radiator in the form of an array of elements on the circumference of a circle. The calculation of the total power here involves a ‘mutual admittance’ function, a table of which is given for the case when the Poisson’s ratio of the medium is equal to ¼. The theory is applied to a three-element radiator of a type used in a recent geophysical investigation, and it is shown that the efficiency of radiation in the compressional mode can be varied between wide limits by varying the distance between the elements. Finally, an approach is suggested for problems in which the most suitable idealized boundary condition is one of known displacement under the radiator, the stress being zero elsewhere on the free surface. It is shown that the stress under the radiator satisfies an integral equation whose kernel is derived from the mutual admittance function.