Ultrashort Electromagnetic Waves Research Articles

The Structural Design Method of Multi-Layer Parabolic Reflective Surface for X-Ray Focusing

As an ultra-short electromagnetic waves, X-ray has a strong ability to penetrate with high-energy. The method for focusing visible spectral bands is not suitable for X-ray spectrum. At present, in X-ray astronomy, the X-ray focus mode which uses grazing incidence less than critical angle has been widely used. However, the small critical angle limits its effective aperture of the X-ray collection. This paper presents a multi-layer reflective structure working with grazing incidence and the surfaces coated multilayer high reflective for X-ray. It can guarantee the large effective entrance pupil and high energy collection. The 200mm diameter X-ray focusing device is designed as an example. It is found from simulation that a good focusing result is acquired.

Terahertz radiation from superconducting YBa2Cu3O7−δ thin films excited by femtosecond optical pulses

Ultrashort electromagnetic waves (600 fs width) from superconducting YBCO thin films have been observed by irradiating current-biased samples with femtosecond optical laser pulses (80 fs width). The Fourier component of the pulse extends up to ∼2 THz. The characteristics of the radiation are studied and the radiation mechanism is ascribed to the ultrafast supercurrent modulation by the laser pulses, which induce the nonequilibrium superconductivity.

Complex Permittivity for an Ideal Dielectric of Stochastic Structure

AbstractThe effective complex permittivity is calculated of a microheterogeneous dielectric, which is a composite material or a polycrystal. The Bourret approximation is used and the binary correlation function of the permittivity tensor is taken to be exponential. Asymptotic formulas are presented for long, short, and ultrashort electromagnetic waves. The results are presented in the form of plotted frequency dependences of the imaginary and real parts of the effective permittivity and the Cole‐Cole diagrams for real and virtual waves.

Ultrashort electromagnetic waves from arc discharges at the plasma frequency and its second harmonic

The radiation detected at four discrete frequency bands from the positive column in argon at low pressure is compatible with that from a source comprising two modes of plasma waves—oscillations of a plasma plate and cylinder.

INfluence of Ultra-Short Electromagnetic Waves on the Development of Cotton Plants

INfluence of Ultra-Short Electromagnetic Waves on the Development of Cotton Plants

Ultrashort electromagnetic waves VI — Reception

Mr. Trevor deals with the reception of ultrashort electromagnetic waves over line-of-sight paths under practical conditions. He shows that, when directive antennas are employed, there is an optimum antenna height for which the direct and reflected rays are received in phase producing maximum effect. The concept of excess-noise ratio is developed which evaluates the merit of a receiver in a manner independent of band width, receiver impedance, signal-generator impedance, or frequency. This is the concluding article in a series of six on ultrashort electromagnetic waves. The material contained in these articles was originally presented as a series of lectures before the basic science group of the New York Section at Columbia University. A consolidated reprint will be available (see announcement elsewhere in this issue). PAUL C. CROMWELL, Chairman, Symposium Committee (College of Engineering, New York University, New York 53, N. Y.)

Ultrashort electromagnetic waves v-radiation (continued)

This article is the concluding portion of the fifth lecture in the series on ultrashort waves sponsored by the basic science group of the AIEE New York Section. In the design of radiators or antennas for ultrashort waves a complete solution of Maxwell's field equations usually is not practicable, and engineering approximations are resorted to. The first installment (July issue) presented a method to be used when the distribution of current and charge over the radiator surface is known. This concluding portion presents a second method for the calculation of the field in space on the basis of known field distribution in the immediate vicinity of the radiator.

Ultrashort electromagnetic waves IV — Guided propagation

When Doctor S. A. Schelkunoff presented the material contained in this article as a lecture before the basic science group of the New York Section, he remarked that it was “nonmathematical.” Certainly the electrical engineer will welcome any concept which allows an easier approach to the solution of certain problems involved in wave guides than the more complete equivalent field-theory method. In this fourth article in a series of six on ultrashort electromagnetic waves, Doctor Schelkunoff combines transmission-line theory with optical analogy and derives useful relations for both wave guides and cavity resonators. The three preceding articles appeared in the March, April, and May issues of “Electrical Engineering.”

Ultrashort electromagnetic waves: II — Transmission lines at Ultrahigh frequencies

This article is the second in a series of six on ultrashort electromagnetic waves, all presented originally before the basic science group of the AIEE New York Section as a symposium of six lectures surveying ultrahigh-frequency theory. The first article, “Electromagnetic Theory,” by Doctor Ernst Weber, appeared in the March issue. This second article presents simplifications and approximations of the usual engineering solutions for the transmission line that are valid only for very high frequencies. The resulting expressions are of great practical advantage in designing transmission-line circuit elements.

Ultrashort electromagnetic waves: I — Electromagnetic theory

Ultrashort electromagnetic waves are of vital importance at the present time. In keeping with the policy of the Institute to concentrate its efforts on matters closely related to the war effort, the basic science group of the AIEE New York Section is now presenting a series of lectures on this topic. The editor of “Electrical Engineering,” believing that this material should be made available to the entire AIEE membership, has asked the lecturers to prepare articles to be published in this journal. This first article lays the groundwork in fundamental theory for the entire series. Succeeding articles, all being prepared by recognized authorities, will cover: (II) transmission-line theory at ultrahigh frequencies; (III) generation; (IV) guided propagation; (V) radiation; (VI) reception. If sufficient interest is shown, a consolidated reprint will be made available after the full series has appeared. PAUL C. CROMWELL, Chairman, Symposium Committee (College of Engineering, New York University, New York, N. Y.)

55. Ultrashort Electromagnetic Waves Generated in a Vacuum Tube by Ordinary Electric Discharge

55. Ultrashort Electromagnetic Waves Generated in a Vacuum Tube by Ordinary Electric Discharge

Rectangular Hollow-Pipe Radiators

The open hollow pipe of rectangular cross section is discussed from both practical and theoretical standpoints as a radiator and absorber of ultra-short electromagnetic waves. A theory of operation is derived and it is verified by a series of measured radiation patterns taken at wavelengths of 50 to 100 centimeters.

Grating Theory and Study of the Magnetostatic Oscillator Frequency

A special type of echelette grating for wavelength measurements of ultra-short electromagnetic waves is described. The one grating may be used over the entire wavelength range from 1 to 10 cm without loss of effectiveness due to an automatically changing groove form which keeps the direction of the center of the diffraction pattern fixed. The formula for the distribution of the energy diffracted from the grating is given and found to agree with the experimental values. The magnetostatic oscillator produces a band of frequencies unless it is adjusted for the conditions at which the tube gives the maximum output, in which case no conclusions as to the width of the band could be drawn as the resolution of the spectrometer was too low.

Investigations in the Field of the Ultra-short Electromagnetic Waves. IV. On the Dependence of the Ultra-short Electromagnetic Waves upon the Heating Current and upon the Amplitude of the Oscillations

An investigation has been made of the dependence of the length of the ultrashort electromagnetic waves generated by vacuum tubes on the magnitude of the heating current. It is shown that the normal waves (i.e., waves the frequency of which corresponds to the frequency of the oscillations of the electrons about the grid of the tube) differ from the dwarf waves (i.e., waves with frequency ceeding several times the frequency of electronic oscillations) in their dependence on the heating current. The length of the normal waves increases, while the length of the dwarf waves of all orders decreases as the heating current is decreased. Therefore, as the heating current is decreased, there is a better agreement between the observed and computed values of wave-lengths of the normal and of the dwarf waves. At low heating currents the product ${\ensuremath{\lambda}}^{2}{E}_{g}$ for dwarf waves of different orders is very close to the theoretical values ${\ensuremath{\lambda}}^{2}{E}_{g}=\frac{{\mathrm{const}.}_{0}}{{n}^{2}} n=2, 3, 4, \ensuremath{\cdots}$ where ${\mathrm{const}.}_{\mathrm{o}}$ corresponds to the value of the product ${\ensuremath{\lambda}}^{2}{E}_{g}$ for normal waves. The results of the experiments are in agreement with the theory of P. S. Epstein, which explains the discrepancy between the calculated and the observed length of the normal and the dwarf waves being due to the influence of the alternating potentials appearing on the electrodes of the tube during oscillations. In the limit, at infinitely low amplitudes of these potentials, the ratio of the values of the products ${\ensuremath{\lambda}}^{2}{E}_{g}$ for normal and for dwarf waves approaches the theoretical value within the limits of the experimental error. Neglecting these alternating potentials introduces the largest error in the results of the existing theories of the generation of ultra-short waves. At sufficiently intensive oscillations, this error exceeds all the others taken together, including the error introduced through the simplifying assumption of plane electrodes. The limiting value of ${\mathrm{const}.}_{0}$ corresponding to infinitely low amplitudes of the alternating potentials, approaches very closely the value of the product ${\ensuremath{\lambda}}^{2}{E}_{g}$ calculated from the formulas of H. Barkhausen and A. Scheibe. This shows that normal waves really do correspond to a complete period of oscillations of the electrons about the grid, i.e., to the time the electrons take to pass from the filament to the grid and back to the filament.

Imperial Academy of Japan

AT a meeting of the Imperial Academy of Japan on May 10, annual medals and prizes were awarded to the following: Kyosuke Kindaichi for his studies on the Ainu epic Yukar Kiyoo Wadati for his investigations on deep focus earthquakes Ikutaro Hirai for his work on the cause of the meningitislike disease frequently observed among Japanese suckling children Tatuo Aida for genetical studies on the body colour of Aplocheilus latipes Motojiro Matuyama for his geophysical investigations on gravity anomalies and magnetism of basaltic rocks Shintaro Uda for research on ultra-short electro-magnetic waves. The Mendenhall Memorial Prize was awarded to Seishi Kikuchi for his studies on the diffraction of electron rays through thin mica plates.

Investigations in the Field of the Ultra-short Electromagnetic Waves III. Electronic Oscillations in Vacuum Tubes and the Causes of the Generation of the Dwarf Waves

Investigations in the Field of the Ultra-short Electromagnetic Waves III. Electronic Oscillations in Vacuum Tubes and the Causes of the Generation of the Dwarf Waves

Investigations in the Field of the Ultra-Short Electromagnetic Waves I. The Generator for the Production of Ultra-Short Undamped Waves

A description of apparatus for the production of ultra-short undamped electromagnetic waves by the method of Barkhausen and Kurz is given. An investigation has been made of the method of detecting the oscillations by observing the current in the plate circuit of the generator. At a constant plate potential the current is approximately proportional to the amplitude of the oscillations. A comparison of generators with one and with two tubes shows the advantages of the former. In certain cases the energy of oscillations produced by generators with one tube can be considerably increased by a suitable choice of the "ballast" capacity of the generator.

Investigations in the Field of the Ultra-Short Electromagnetic Waves II. The Normal Waves and the Dwarf Waves

The results are presented of an investigation of the production of ultra-short undamped electromagnetic waves by using the method of H. Barkhausen and K. Kurz.Method of working diagrams. Normal waves and dwarf waves. A method is developed for the graphic representation of the work of generators of ultra-short waves. This method is based on the construction of special "working diagrams." These diagrams define the location of "regions of oscillations," which show the values of the natural periods of the oscillating circuits and the values of the grid potentials at which oscillations are generated. Vacuum tubes can generate two kinds of ultra-short waves. The first kind have a wave-length approximating that computed by Barkhausen's formula ${\ensuremath{\lambda}}^{2}{E}_{g}={{d}_{a}}^{2}{10}^{6}$. Their period is nearly equal to the time required for the electrons to move from the filament to the plate and back (normal waves). The second kind of waves are considerably shorter (dwarf waves). Both kinds of waves satisfy the equation ${\ensuremath{\lambda}}^{2}{E}_{g}=\mathrm{const}.$ for points on the working diagram where the plate current (the amplitude of the oscillations) has its maximum value.Complex working diagrams. Dwarf waves of higher orders. Vacuum tubes can have complex working diagrams with a large number of regions of oscillations. In such a case the tube generates different dwarf waves. Their length is two, three and four times shorter than that of the normal waves. Dwarf waves are accordingly divided into waves of the ${1}^{\mathrm{st}}$, ${2}^{\mathrm{nd}}$, ${3}^{\mathrm{rd}}$, etc. orders. The shortest dwarf waves of the ${4}^{\mathrm{th}}$ order, generated by tubes of the type $R5$, had a wave-length $\ensuremath{\lambda}=9.4$ cm. The presence of dwarf waves of higher orders shows that vacuum tubes can generate oscillations of a frequency considerably greater than the frequency of the electronic oscillations. Both the normal and dwarf waves belong to the same type of GM-oscillations. Limits were determined within which Barkhausen's formula is applicable. It is shown that the difference in the number of regions of oscillations on the working diagrams depends on the difference in the time required for the electrons to pass in different directions within the tube. The latter depends on the asymmetry in the arrangement of the electrodes.The nature of dwarf waves. Dwarf waves are oscillations of the circuits within the tube or coupled with the tube which are excited in such a manner that during the time $\ensuremath{\tau}$ it takes for the electrons to pass from the filament to the plate and back, the circuits perform two complete oscillations (dwarf waves of the ${1}^{\mathrm{st}}$ order), three complete oscillations (dwarf waves of the ${2}^{\mathrm{nd}}$ order) etc. Thus the wave-lengths are equal to: ${\ensuremath{\lambda}}_{0}={c}_{0}\ensuremath{\tau}$ (normal waves), ${\ensuremath{\lambda}}_{1}=\frac{{c}_{0}\ensuremath{\tau}}{2}$ (dwarf waves of the ${1}^{\mathrm{st}}$ order), ${\ensuremath{\lambda}}_{2}=\frac{{c}_{0}\ensuremath{\tau}}{3}$ (dwarf waves of the ${2}^{\mathrm{nd}}$ order), ${\ensuremath{\lambda}}_{3}=\frac{{c}_{0}\ensuremath{\tau}}{4}$ (dwarf waves of the ${3}^{\mathrm{rt}}$ order), etc. Dwarf waves 9.5-18.5 cm long originate in oscillating circuits, which are inside the tube. The advantages of dwarf waves of higher orders are shown, owing to the possibility of using lower grid potentials, which leads to a greater steadiness in the operation of the tube.

Popis aparatury pro buzení velmi krátkých, netlumených elektromagnetických vln

Popis aparatury pro buzení velmi krátkých, netlumených elektromagnetických vln