The propagation of waves supported by capacitively loaded loops is investigated using a circuit model in which each loop is coupled magnetically to a number of other loops. Since the coupling is due to induced voltages the waves are referred to as magnetoinductive (MI) waves. The mathematical formulations are mostly analytical thanks to long standing previous work on the magnetic and electric fields generated by currents flowing in loops. Retardation is neglected, i.e., dimensions of the structure are assumed to be small relative to the free space wavelength. The dispersion relations, derived in the most general case for a tetragonal three-dimensional structure, exhibit both forward and backward waves within a pass band. It is shown that for reproducing the salient features of the waves it is sufficient to take nearest neighbor coupling into account but coupling between loops further away must also be considered if higher accuracy is required. The investigations include that of resonances, conditions for the existence of traveling waves, tolerances, and streamlines of the Poynting vector. Waveguide components, like bends, power dividers and couplers are considered due to the potential applications of the MI waves as magnetic guides. Generality of the results, their possible implications for transverse electromagnetic wave propagation, previous work on similar waves, including the possibility of phase conjugation, are discussed in a separate section.

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A simple approximate expression is derived for the resonant frequency of a singly split single ring that is among the first microwave resonators designed to be small relative to the wavelength. In addition to the usual gap capacitance the concept of surface capacitance is introduced. The surface capacitance is determined analytically by two different methods, first using analytical expressions for the electric field of a split cylinder, and second by using conformal mapping. Taking two practical examples the resonant frequency, found analytically, is shown to agree with that obtained by numerical simulations. The model could be used for studies of the resonant properties of split rings in the terahertz region.

Using data pertaining to the elementary radiator feeding and geometrical arrangement, expediently selected characteristics of ah aerial system are defined, viz. : geometrical gain, geometrical quality and tolerance sensitivity. The geometrical gain gives the gala of an array of isotropic radiators ; the geometrical quality shows how many times less is the band width of the array than that of the elementary radiator ; the tolerance sensitivity is the numerical expression of the extent to which the system is sensitive to current distribution variations. These characteristic properties ate arrived at by making such simplifications in the strict physical definitions as result, on the one hand, in the separation of the properties relevant to the constructional details of the elementary radiator and to those of the aerial system ; on the other hand, in formulas more amenable to mathematical treatment. These simplifications yield a simpler relationship of the three aforementioned quantities. Four of the current distributiong dealt with in the literature ate selected to show on hand of a few concrete examples, the values taken up by the newly introduced constants. Lastly, a generalisation of the solutions is attempted in seeking the current distribution which gives the highest geometrical gain in case of varioug numbers of components anda prescribed geometrical quality. Mathematically, the originaI problem is reduced to ah extremum problem with given auxiliary conditions. I/1. IntroductionFora long time papers have been published dealing with the theory of the so-called "supergain" gr super-directive antennae. Its essence is that with finite dimensions of the antenna any desired gain can be obtained. This end is achieved by means of continuous current distribution, or by the juxtaposition of a sufficient number of discrete radiators. The present paper deals only with the theory of the discrete radiators.SCH~LXU~OFr [2] was the first to take up this problem. He evolved a method for linear equidistant arrays whereby substantial gains ate obtainable, he did, however, not deal with the upper limit of gain in case of a constant number of elements for variable current distributions. He mentions, all the same, that with a marked increase in gain both radiation eff/ciency and band width decrease. DOLP• [3] took up the problem of maximum gain taking for his point of departure the requirements of radar technique and setting himself the task of determining the minimum main beato width at a given side-lobe attenuation. The angular resolving power of the locator depends indeed not on the gain but

Radio-frequency experimental measurements of magnetically coupled chains of L-C resonators supporting magneto-inductive (MI) waves are presented. MI waveguides are constructed using printed circuit board (PCB) inductors and external capacitors. Methods for increasing the nearest-neighbour coupling and reducing the non-nearest neighbour coupling using double-sided PCBs are demonstrated. Conditions for low propagation loss are determined, and a method of approximate matching to 50 transmission lines is presented. Propagation losses of 0.12 dB per element and coupling losses of 0.4 dB are achieved, using elements with Q-factors of 110 at ≈150 MHz frequency. Simple recursive Fabry-Perot filters are demonstrated by inserting reflectors into the waveguide.

We sought to determine if a higher dose of heparin would reduce arterial complications in patients weighing 10 kg or less undergoing cardiac catheterization to investigate congenital heart disease. Sixty patients were given either 100 (group A) or 150 (group B) IU x kg(-1) of heparin in a double-blinded randomized manner. Initial arterial access was established using a 4F cannula in all patients. Mean activated clotting time measured 20 minutes following heparin administration was significantly lower in group A than in group B (199 versus 251 seconds). Only 3 out of 60 patients (5%) required treatment for loss of femoral pulse. The age, weight, activated clotting time, length of catheterization procedure, time taken to establish arterial access, and the duration of arterial cannulation were comparable between the groups. Weight under 4 kg, age under 1 month, and cannula size larger than 4F were identified as independent risk factors for the development of arterial complications. Arterial access using a 4F cannula is a safe procedure in children weighing 10 kg or less. The incidence of significant arterial complications is low, and they do not appear to be preventable by a higher dose of heparin.