Short Electromagnetic Waves Research Articles

Determination of the velocity of short electromagnetic waves by interferometry

A new measurement of the velocity of electromagnetic radiation is described. The result has been obtained, using micro-waves at a frequency of 24005 Mc/s ( λ = 1∙25 cm), with a form of interferometer which enables the free-space wave-length to be evaluated. Since the micro-wave frequency can also be ascertained, phase velocity is calculated from the product of frequency and wave-length. The most important aspect of the experiment is the application to the measured wave-length of a correction which arises from diffraction of the micro-wave beam. This correction is new to interferometry and is discussed in detail. The result obtained for the velocity, reduced to vacuum conditions, is c 0 = 299792∙6 ± 0∙7 km/s.

On Sahánek's relation for the generation of short electromagnetic waves in electron tubes

Sahanek has done work on electromagnetic oscillations originating in valves. In 1928 he was the first to deduce a relation for the regions of these oscillations. But others who later worked on this problem achieved results which were in contradiction to Sahanek's relation and the aim of this work is to explain this disagreement. Sahanek's derivation is given and the assumptions from which he started are pointed out in the first part of this article. In the second part Kleinsteuber's derivation is shown and the assumptions on which the calculation was based, and in the third part the contradiction between the two relations is solved. Sahanek's relation is proved by the application of Kleinsteuber's mathematical procedure to Sahanek's assumptions and it is shown that the disagreement only lies in a difference in assumptions.

ReviewUltrasonics in Medicine (Der Ultraschall in der Medizin). Kongressbericht der Erlanger Ultraschall-Tagung, 1949 (S. Hirzel Verlag, Zurich, 1949). 486 pp., with 27 plates.

The spectacular advances in the applications of physics in medicine which have resulted from the development of machines for accelerating particles at very high voltages, and from the increasing availability of radioactive isotopes, have overshadowed what may ultimately prove to be very valuable contributions along other lines. The Institute took cognisance of this when it devoted its March 1950 meeting to “Biological Effects of Non-Ionizing Radiations”. The papers read then were concerned with short electro-magnetic waves. The book under review deals with another type of vibration, ultrasonics, or very high frequency sound waves, a subject which has hitherto received most attention from continental workers. It consists of 72 original papers covering technical, biological and clinical aspects, and the discussions which followed each of them, together with tables summarising the clinical results obtained from some thousands of applications of ultrasonics to a wide range of conditions and diseases in about 30 hospitals and institutions. There is also a valuable bibliography which contains 554 references.

The Magnetic Antenna

The theory of the magnetic antenna, consisting of a cylindrical rod of cemented magnetic powder around the center of which is wound a few turns of wire, is investigated. This antenna is shown to be more efficient than an electric antenna in receiving short electromagnetic waves of a few meters length. For such waves it exhibits an interesting selectivity.

THE HEATING OF ELECTROLYTES IN HIGH FREQUENCY FIELDS

In this investigation the heating of solutions of simple electrolytes of varying concentrations when irradiated by short electromagnetic waves from 10 to 200 metres in length was measured. It was found that for a given wave-length there is a maximum heating effect produced in a medium, the specific conductivity and dielectric constant of which are connected with the frequency by a simple law. This law, proved theoretically as well as shown experimentally to hold for dilute solutions is [Formula: see text] where C = specific conductivity in absolute units, K = dielectric constant and n = frequency of wave."Skin effect" was shown theoretically and experimentally to be negligible for substances having the low conductivities studied and deep-seated heating effects were shown to be attainable with the radio waves used. The possibility of directed selective heating effects is suggested and illustrated by experiments on blood. The law shown to apply in these experiments was used to evaluate the dielectric constant of water.

Popis aparatury pro buzení velmi krátkých, netlumených elektromagnetických vln

Popis aparatury pro buzení velmi krátkých, netlumených elektromagnetických vln

Short Electromagnetic Waves of Wave-length up to 82 Microns

UP to the present date, short electromagnetic waves have been generated only by the method of the Hertz vibrator. This method offers very serious difficulties when we try to produce electromagnetic waves of the smallest possible length, as the vibrator burns out very soon, so that the amount of the energy and the length of the waves produced do not remain constant, and also as the length of the waves decreases slowly, if the dimensions of the vibrator are diminished, when we approach the region of the very shortest waves. The experiments of many investigators who have tried to fill the interval between the short electromagnetic waves of Lebedew and the long heat-waves of Rubens, have proved how difficult it is to obtain the shortest electromagnetic waves by the Hertz method, and have shown the necessity of finding a new method.

VI. The production and measurement of short continuous electromagnetic waves

VI. <i>The production and measurement of short continuous electromagnetic waves</i>

The Specular Reflection of X-rays.

IT has been shown by Herr Laue and his colleagues that the diffraction patterns which they obtain with X-rays and crystals are naturally explained by assuming the existence of very short electromagnetic waves in the radiations from an X-ray bulb, the wave length of which is of the order 10-9 cm. The spots of the pattern represent interference maxima of waves diffracted by the regularly arranged atoms of the crystal. Now, if this is so, these waves ought to be regularly reflected by a surface which has a sufficiently good polish, the irregularities being small compared with the length 10-9 cm. Such surfaces are provided by the cleavage planes of a crystal, which represent an arrangement of the atoms of the crystal in parallel planes, and the amount by which the centres of atoms are displaced from their proper planes is presumably small compared with atomic dimensions.