Uniform Energy Density Research Articles

New developments in multiconductor slow-wave transmission lines of circular cross-section

Equispaced parallel wires located around the circumference of a circle are used to form a cylindrical grid structure operating as a waveguide at 3 GHz. It is shown that a number of distinctive slow-wave modes can propagate along such a guide and among them one finds the Goubau wave, a variety of TEM configurations and the dipole mode. Launching filters enable each mode in turn to be identified and preserved for individual measurements. At the same time, a theoretical investigation is made applying superposition of separate circularly symmetrical surface waves assumed to be associated with each conductor as a single-wire transmission line. Calculations from the theory show good agreement with experiment. It is found that dipole-mode propagation along an 8-wire guide of the kind considered here, has an attenuation 40% below that of the corresponding 2-wire line and provides for a close approach to uniform energy-density over the cross-section of the structure. Moreover, the field outside the surface of the guide is much smaller than in the case of the 8-wire Goubau line.

Comparison of Two Types of Structural Optimization Procedures for Flutter Requirements

A comparison is made of results obtained from mathematical programing and optimality criteria procedures for the minimum-mass design of typical aircraft wing structures to satisfy prescribed flutter requirements. The mathematical programing method is based on an interior penalty function approach. A Langrangian optimality criterion and an intuitive optimality criterion based on uniform strain energy density are considered. An intuitive resizing procedure is used for both optimality criterion solutions. All results are calculated using the same computer program, changing only the optimization procedure. Both high- and low-aspect-ratio wings are examined. Finite elements are used for structural modeling, and the generalized coordinates for the flutter solution are based on the natural vibration modes of the structure. Second-order piston theory aerodynamics is used for supersonic conditions and kernel function aerodynamics for subsonic conditions. Convergence of the optimality criteria procedures with respect to the number of natural modes is considered. [A ] [B] [Bti] Nomenclature

Applications of the variational formulation of geometrical room acoustics

This paper extends and improves the variational formulation previously described by A.D. Pierce at the Los Angeles meeting [J. Acoust. Soc. Am. 55, 431(A) (1974)] for estimating the directional spectral density as a function of propagation direction and/or position in reverberant rooms. The revised formulations specifically exclude the contribution of waves coming directly from the source and include the case when the walls are either diffuse or specular reflectors. The insertion of a directionally independent spectral density in the variational indicator for the specular reflecting wall case leads to that derived for the diffusely reflecting wall case. Numerical techniques are described and specific cases are reported which give the reverberant field at each of the six walls as a function of source position and wall absorption. For small absorption, the deviation from that corresponding to uniform energy density is independent of absorption, suggesting that the state of ideal diffuseness (as regards spatial uniformity) cannot be achieved, even in the limit of perfectly reflecting walls.

Uniform energy density at the output of high-power glass lasers

Uniform energy density at the output of high-power glass lasers

Design Considerations for Microwave Oven Cavities

The heating mechanism in a microwave oven results from the interaction of a high-frequency electromagnetic field and the food within it. In most ovens the field is generated by a magnetron which converts dc energy to high-frequency energy at approximately 2450 MHz. This energy is then propagated into the oven chamber which is, in reality, a multimode resonant cavity where the energy is reflected from the walls to create standing wave patterns. To properly design a microwave oven, one must consider not only the magnetron but also the dimensions and resonant properties of the oven cavity. The designer must strive for a uniform energy density within the cavity for uniform cooking of the food and must be sure the cavity presents the proper load to the magnetron. These objectives are discussed, and a procedure for obtaining them is outlined.

A “Twisted-Mode” Technique for Obtaining Axially Uniform Energy Density in a Laser Cavity

A “Twisted-Mode” Technique for Obtaining Axially Uniform Energy Density in a Laser Cavity