摘要:

From lessons learned in the late 1960s and early 1970s, skilled teams of interdisciplinary investigators have formed that are making technical and scientific contributions to knowledge of the biological response to non‐ionizing electromagnetic radiations. Examples of technological advances in the US and other Western nations are nonperturbing thermal sensors, and dosimeters for measuring whole‐body absorption of energy and for determining differential uptake of energy in tissues of interest. These advances have enabled considerable gains in knowledge and prediction of energy capture by human and infrahuman bodies as functions of wavelength and orientation of an object in the field. Complementing these advances are those by Eastern investigators, who have performed many epidemiological surveys and have pioneered studies of behavioral and nervous reactions to long‐term, low‐level irradiation. The resulting accretion of data, including those from international programs of scientific exchange, will help provide a sound basis for standards of safety and for beneficial applications of radio frequency energy. Especially promising in the area of medicine are microwave techniques for non‐invasive diagnostic “imaging” of deep tissues, and for treatm

ISSN:0048-6604    

DOI:10.1029/RS014i001p00001

年代:1979

数据来源: WILEY

摘要:

Research on biological effects of RF radiation has undergone a turbulent series of swings in the United States during the last three decades. A peak of activity during the Tri‐Service era of the late 1950s and early 1960s was followed by a nadir—in 1965, not a single federal agency was supporting research in the area. The resurgence of research during the past decade—13 federal agencies or departments are now annually supporting a multi‐million dollar effort—is examined in the light of two related projects involving NASA: the proposed Space Power Station (SPS) and the Search for Extraterrestrial Intelligence (SETI). Interwoven in the complex of technological, economic, and political considerations that affect both projects is the eventuation of a new pragmatism—a moral retrenchment—that the author sees as a potential decline in the national spirit of outreach and enterprise. In the entirely justifiable search for bread and energy, the US may also be pursuing a course that starves and chills its

ISSN:0048-6604    

DOI:10.1029/RS014i001p00005

年代:1979

数据来源: WILEY

摘要:

The diffraction of anH‐polarized plane wave is investigated when the wave is obliquely incident on a flanged parallel‐plate waveguide or on a slit in a thick screen. Using discrete spectra of periodic functions inside the waveguide and of Mathieu functions in a half‐space, the solution can be obtained by matching the different field representations in the aperture plane. The technique has the advantage that it operates in a wide frequency range,ka>0 throughka≈ 20, and yields rapid convergent results of excellent accuracy (kis the free‐space wavenumber, 2ais the aperture width). The calculated fields satisfy the edge condition. Investigations into a proper ratio between series truncation numbers to avoid relative convergence appear to be unnecessary. A number of numerical results are presented. The transmission coefficient is critically dependent on the cutoff frequencies of the waveguide modes and on the thickness of the screen, which causes strong resonances, whereas the near‐ and far‐field patterns are influenced by the thickness, especially for obli

ISSN:0048-6604    

DOI:10.1029/RS014i001p00011

年代:1979

数据来源: WILEY

摘要:

In 1960 I suggested that Deception Island, near the northern end of the Antarctic Peninsula, might serve as a useful naturally resonant VLF slot antenna. Connection across the island was subsequently made and impedance measurements were obtained. Contrary to theoretical predictions by Galejs and by Staras, a strong resonance was obtained. However, it occurred at 9.5 kHz, rather than at 5 kHz as anticipated. This is ascribed to a short, low cut through one of the arms of the island which otherwise range from 500 to 1000 ft high. A composite transmission line model is constructed to represent the data. A first approximation to the efficiency suggests that it is in the range of 10–25

ISSN:0048-6604    

DOI:10.1029/RS014i001p00019

年代:1979

数据来源: WILEY

摘要:

Approximate expressions for the ac quasi‐static fields produced by a horizontal electric dipole (HED) antenna located within a conducting slab have been derived by employing finitely conducting earth image theory techniques. Asymptotic results have also been obtained by applying the quasi‐near approximation to the basic Sommerfeld integrals. The resulting approximations agree with previously derived numerical integration results. The resulting expressions are particularly applicable to short‐range electromagnetic propagation in a shallo

ISSN:0048-6604    

DOI:10.1029/RS014i001p00027

年代:1979

数据来源: WILEY

摘要:

Explicit expressions for the self admittance and the mutual admittanceYijbetween two arbitrarily polarized circular apertures are presented. The aperture field distribution is that of TE11circular waveguide mode. The analysis makes use of a spherical mode expansion and of the addition theorem for tesseral harmonics. Numerical results showYijas a function of angular separation θ. TheE‐plane coupling exhibits asymptotic (large θ) behavior consistent with the lowest “hard” surface ray order results. The slope of theH‐plane coupling for large values of θ does not correspond to the lowest‐order “soft” surface ray attenuation, but rather to that of the lowest‐order “hard” ray. This

ISSN:0048-6604    

DOI:10.1029/RS014i001p00035

年代:1979

数据来源: WILEY

摘要:

Low‐frequency radiation characteristics of an electric dipole antenna in an isotropic plasma with warm electrons and cold ions are studied. The electron distribution function is approximated by the multiple water‐bag model. The current distribution on the antenna is calculated by solving a boundary‐value problem. It is found that at low frequencies (ω ≲ ωpi, ωpibeing the ion‐plasma frequency), the propagation constant for the current wave on an infinitely long wire is approximately (ω/ωpe)2λd−1where ωpeis the plasma frequency and λdis the Debye length. At very low frequency (ω ≪ ωpi), the dipole resistanceRvaries as (l/λd)2× (ω/ωpe)4× (M/m)5/2, wherelis the half length of the dipole andMandmare respectively the ion and electron masses. When ωpi.<ω ≪ ωp, the resistance is the same as previously reported in the literature;R∝ (l/λd)−l. At the frequency ω = ωpi, the dipole impedance has a resonance; the dipole is inductive for

ISSN:0048-6604    

DOI:10.1029/RS014i001p00043

年代:1979

数据来源: WILEY

摘要:

The predicted performance of tropospheric scatter transmission is investigated in terms of spectrum slope, refractive index variance, and scale of turbulence. The common volume integral is evaluated to yield a useful expression for path loss in terms of these parameters. Formulas for the coupling loss in the asymptotic case of very wide and very narrow antenna beams are derived. Approximate formulas for intermediate size antenna beams are deduced and compared with more exact computer calculations. Our results suggest that previous path loss prediction methods do not place enough emphasis on turbulent scatter and that a model with spectrum slope 11/3 should be used. The resulting model provides an initial step toward the development of a simpler and more realistic alternative to the NBS model, and also refines a related approach by Gjessing.

ISSN:0048-6604    

DOI:10.1029/RS014i001p00049

年代:1979

数据来源: WILEY

摘要:

A numerical integration technique is used to compute the amplitudes of the quasi‐static electromagnetic fields produced on and above the surface of a sea of finite depth by a submerged vertically‐directed harmonic magnetic dipole. The purpose of these computations is to determine the conditions under which an electrically conducting sea floor can produce significant changes in the fields, as compared with the fields produced on and above an infinitely deep sea, for frequencies in the ULF/lower‐ELF bands (frequencies less than 300 Hz). It is shown that even a comparatively highly conducting sea floor (conductivity σƒ∼ 0.4 mho/m) can produce substantial changes in the field amplitudes for certain source‐receiver configurations and that alterations of two orders of magnitude or more can occur in the amplitudes on the sea surface for smaller values of σƒ. The changes generally become smaller as the altitude of the receiver is increased, but even at altitudes equal to ten sea water skin depths (10 δ) the field quantities may be doubled by the presence of a sea floor. As might be expected, the sea floor effects are most marked in seas that are electrically shallow, i.e., for seas that are only a few skin depths deep. The largest changes are produced when the VMD is within 1 δ of the sea floor, and there is essentially no sea floor effect when the VMD is more than 3 δ

ISSN:0048-6604    

DOI:10.1029/RS014i001p00059

年代:1979

数据来源: WILEY

摘要:

A technique for the study of traveling ionospheric disturbances has been developed using the incoherent scatter radar at Chatanika, Alaska. Using one wave event, the technique is employed to compute the period of oscillation (36.5 min), southward velocity (208 m sec−1), and power profile. A possible source event for the traveling ionospheric disturbance has been identified as being a filamentary auroral arc moving southward toward Chatanik

ISSN:0048-6604    

DOI:10.1029/RS014i001p00075

年代:1979

数据来源: WILEY