Phoenix Hospital Chelmsford

This paper describes a small land based closed cycle Ocean Thermal Energy Plant which is being designed to supply deep nutrient rich sea water to an aquaculture facility and to produce a net electric power output of up to 300 kW. In addition the plant will also demonstrate a small air condenser for producing potable water at a rate of 2650 US gallons per day. The work is being done for ALCAN International and the plan is to build and operate such a plant at Keahole Point in Hawaii.

This paper outlines the theoretical background and describes confirmatory trials of an angle-diversity principle which can usefully supplement the frequency-and space-diversity techniques currently used in troposcatter communications.The trials involved modifying the feed of a 25 m steerable antenna to produce twin receiving beams, each about 20 arc minutes wide and splayed vertically by 20 arc minutes at operating frequencies near 2 GHz. Measurements were made of the signal loss due to specified beam deviations from the optimum angle of shoot, together with the crosscorrelation between the signals from the splayed beams. Tests on two troposcatter paths, terminating at the 25 m antenna at Chilbolton, Hants, gave working beam-deviation losses (mean values) of 1.1 and 0.7 dB for the respective paths, compared with 0.8 and 1.2dB predicted theoretically. Measured median-crosscorrelation coefficients between angle-diversity channels were, respectively, 0.22 and 0.16, underthese conditions, against theoretical values of 0.31 and 0.24. The trials have endorsed the supporting theory as a reliable guide to the angle-diversity behaviour of vertically splayed beams, while confirming some design procedures based thereon.

The loss in signal strength by diffraction over two knife-edges in succession is solved, with the usual approximations, by a double application of Huyghens' principle expressed in terms of simple Fresnel theory. The solution is shown to depend on a Fresnel surface integral which will be discussed in a companion paper. Some typical curves of decibel loss as a function of knife-edge heights and position are given which illustrate the physical properties of the solution. In particular, a notable obstacle-gain phenomenon is revealed which shows that the simple treatment of a hilly ground profile as a single equivalent knife-edge can lead to considerable errors in field-strength predictions. The formal extension to three or more knife-edges is indicated, though the detailed development would be very laborious. An approximate treatment in terms of the loss at each edge in succession, treated as a single knife-edge between neighbouring points, is shown to agree well with the accurate method, provided that it is used with judgment gained by experience. It affords a practical method for the engineer who has many ground profiles to assess in predicting the service area of a broadcasting transmitter.

A comprehensive treatment of the subject is given, with a large number of computed results of cut-off points and phase constants for the case of a guide containing a concentric ferrite rod of arbitrary radius. The wave equation for the ferrite is derived in cylindrical co-ordinates, and solved. The wave equation for the isotropic medium surrounding the ferrite is also solved. The boundary conditions are then applied and the characteristic equations obtained for the case of the filled guide, the partly filled guide, and the guide filled with dielectric. By putting the phase constant s equal to 0 in the characteristic equation, it has been possible to solve for the ratio of ferrite radius to guide radius at cut-off. By plotting cut-off curves, a study of the normal mode spectrum can be made. This paves the way for an attack upon the characteristic equation proper, and curves of phase constant against radius ratio are obtained for various values of the properties of the ferrite and the geometry of the system. Faraday rotation, power flow, and losses are next discussed. The paper ends with an account of checking methods and accuracy of the computed results.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation H. Jefferson; Violation of the Reciprocity Theorem in Linear Passive Electromechanical Systems. J Acoust Soc Am 1 May 1947; 19 (3): 502. https://doi.org/10.1121/1.1916509 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAcoustical Society of AmericaThe Journal of the Acoustical Society of America Search Advanced Search |Citation Search