ARTIFICIAL REFRACTIVE MEDIUM FOR RADIO LENSES

(Historical Note)

I. G. Kobylyansky

In connection with the assertions of a number of American and English authors concerning the “discovery” of artificial refractive media for radio lenses and with their claims of priority, the Soviet scientific and engineering community has already raised the question of the actual creators of the artificial dielectric and of the first prototypes of modern waveguide radio lenses—N. A. Gezekhus,^1 N. A. Kaptsov,^2 and M. A. Bonch-Bruevich.^3 However, in view of the complete absence of references to the priority of N. P. Kasterin and taking into account a certain incompleteness in the materials on the work of N. A. Gezekhus, as well as the fact that even very recently attempts have continued to suppress the works of Russian scientists in this field,^4 it seems useful to us to restore the historical truth with sufficient fullness.

The idea of creating lenses from an artificial inhomogeneous medium belongs to the prominent Russian physicist of the late nineteenth and early twentieth centuries, Nikolai Aleksandrovich Gezekhus (1845–1919).

Proceeding from the fact that sound in tubes of small cross section propagates considerably more slowly than in air, N. A. Gezekhus decided to make a lens for sound waves out of a porous material, since, as he pointed out, “the propagation of sound through tubes represents a special case of its propagation through the pores or channels of a sound-conducting body.”^5 As was to be expected, the results of tests of lenses that he made from down and ebonite shavings confirmed the correctness of this premise. A considerable number of experiments made it possible to determine a number of properties of such “porous” bodies, in particular “the influence of the pitch of sound on its refrangibility in a loose medium at different densities of the latter,” in other words, the dependence of the dispersion properties of an artificial refractive medium on the dimensions of the channels and, at the same time (which is very important, but apparently was not noticed by the author), on the concentration of particles,

this medium of constituents. In the lens of N. A. Gesehus, as is not difficult to note, the foundations are laid both for waveguide (“porous”) lenses and for lenses made of an artificial dielectric.

N. A. Gesehus reported on the results of his investigations at a meeting of the physics section of the Russian Physico-Chemical Society on April 29, 1886.[^5]

N. A. Gesehus foresaw that the results of his work could also be used in the field of electromagnetic phenomena. This is confirmed, for example, by the following statement of the author.

“Propagation of sound in porous, loose, or ‘sound-transmitting’ bodies... presents an analogy with the propagation of light in transparent media or of electrical oscillations in dielectrics. The interest and importance of a detailed study of the laws of propagation of sound in porous bodies lies, among other things, in the fact that the study of this comparatively simple acoustic phenomenon... may lead to useful conclusions concerning similar, but more complex, optical and electrical phenomena.”

A further contribution to the development of the theory and experimental study of artificial refracting media was made by Nikolai Petrovich Kasterin (1869—1947). His work “On the Propagation of Waves in an Inhomogeneous Medium,”[^6] a preliminary communication on which was published in 1898,[^7] contains, in particular, interesting considerations on the theory of the polarization of dielectrics and their models. In N. P. Kasterin’s work three variants of inhomogeneous media are considered: a layered medium, a medium composed of immobile spheres, and an inhomogeneous medium composed of immobile resonators. The author carries out a rigorous theoretical analysis of wave propagation in each of the named media, determines the refractive indices and wavelengths in these media, and finds their dispersion and absorption characteristics. Unlike all his predecessors, Kasterin pays special attention to elucidating the dependence of the parameters of the medium on the degree to which it is filled with spheres or other particles.

However, the significance of N. P. Kasterin’s work is by no means exhausted by the creation of a theory of sound dispersion in an inhomogeneous medium, and this is usually not noted even in recent investigations.[^8] Indeed, upon attentive reading of the indicated work, the clearly expressed purposefulness of the author becomes evident—to give a rigorous explanation of electromagnetic phenomena in periodically inhomogeneous media. This follows with complete clarity from the following, for example, statements by N. P. Kasterin:

“In order better to clarify for ourselves the mechanism of wave propagation in such an (artificially inhomogeneous.—I. K.) medium, we first investigate sound waves; the methods that make it possible to carry out this investigation for sound waves are also applicable to the case of waves

ARTIFICIAL REFRACTING MEDIUM

electromagnetic”... “The application... of the results obtained to optical phenomena... can, by analogy, be made already now.”

N. P. Kasterin boldly generalizes the results he obtained and shows that “the theories of Poisson, Mossotti, Clausius, and Lord Rayleigh concerning magnetization, dielectric polarization, and the electrical conductivity of an inhomogeneous conductor are the simplest special case of the problem considered.” Indeed,

the solutions of all the indicated problems follow from the results obtained by N. P. Kasterin, if one assumes that the wavelength incident on the artificial medium is infinitely large.

For experimental verification the author creates an artificial periodically inhomogeneous medium of immobile spheres. The experiments confirmed the theoretical relations obtained (see the figure).

N. P. Kasterin’s work was highly valued by his contemporaries, in particular by P. N. Lebedev.

The next major contribution, which in essence completed the development of the artificial dielectric, was the widely known work of N. A. Kaptsov[^2], dating to 1920, when he created a model of a crystal lattice in the form of metallic particles uniformly distributed in an air volume and investigated the diffraction of radio waves with wavelengths of 2.1 and 3.5 cm on this model.

Finally, in 1936 M. A. Bonch-Bruevich put forward the idea of creating highly directional radiators for ultrahigh frequencies on the basis of an artificial dielectric. He constructed and tested in the decimeter ...

range a series of lenses and prisms in the form of a corresponding set of metallic elements (disks, rings)^3.

As follows from the foregoing survey of the principal works on the creation of lenses from artificial media, the entire history of radio lenses is inseparably connected with the names of outstanding Russian scientists—N. A. Gezehus, N. P. Kasterin, N. A. Kaptsov, and M. A. Bonch-Bruevich—who by many years anticipated foreign work in this field.

CITED LITERATURE

1. L. D. Rozenberg, Sound Focusing Systems, Moscow–Leningrad, Publishing House of the Academy of Sciences of the USSR, 1949.
2. N. A. Kaptsov, Ann. d. Physik, 69, 112 (1922).
3. Information Bulletin, No. 18, 3 (1950).
4. Ch. Süsskind, Journal of the British Institution of Radio Engineers, 12, 49 (1952).
5. N. A. Gezehus, ZhRFKhO, 22, 233 (1890).
6. N. P. Kasterin, Scientific Notes of the Imperial Moscow University, Physical-Mathematical Section, issue 20 (1904).
7. N. P. Kasterin, ZhRFKhO, 30, 61 (1898).
8. Essays on the History of Physics in Russia, Moscow, Uchpedgiz, 1949.