Metallic Dipole Research Articles

Semiconductor dipole: possible radiating element for microwave/millimetre-wave monolithic integrated circuits (MIMICs)

A wideband, semiconductor-compatible dipole, derived from the conventional metallic half-wavelength dipole is described. This dipole is resistively loaded along its length, producing a travelling wave current distribution that is insensitive to frequency variations. The resistive loading, however, produces a reduction in efficiency but an increase in bandwidth. Graphs are presented which relate the resistive loading, with efficiency and bandwidth for a given length to diameter ratio of the dipole. These graphs could be useful as design curves in the tradeoff between bandwidth and efficiency. The current distributions along the length of the dipole under various resistive loading conditions are also plotted, as well as the radiation patterns due to these current distributions. The resistive loading for a conventional dipole can be achieved by varying the thickness of the resistive material coating along the length of the dipole. For a semiconductor, however, the resistivity can be varied by changing the doping concentration (ND) of the impurities. Hence, a wideband resistively loaded dipole can now be realised on a semiconductor substrate.

Antennas in material media near boundaries with application to communication and geophysical exploration, Part I: The bare metal dipole

The properties of the bare metal dipole embedded in a dissipative medium near a boundary are examined. These include the distribution of current, the driving-point admittance and impedance, and the effective length, with particular reference to antennas in the earth near the air surface at frequencies in the range from 30 to 300 kHz and antennas on the sea floor at frequencies in the range from 0.3 to 3 Hz. The effects of the internal impedance of the copper conductor are included at the low frequencies where they are important.

Infrared mesh filters fabricated by electron-beam lithography

Capacitive and inductive infrared mesh filters have been fabricated using electron-beam lithography combined with a lift-off procedure. A single level of PMMA was used to create positive tone patterns while a two-level metal-on-polymer process was used to create negative tone patterns. Resonant structures consisting of arrays of crossed metal dipoles and arrays of crossed slots in otherwise continuous metal films have been fabricated that have linewidths less than 0.25 μm, and which exhibit bandstop and bandpass transmissive properties, respectively.

Study of a neutrally charged electron gas with a surface

A charge-neutral electron-gas system with a surface is studied over a wide range of densities including the metallic range, by application of certain theoretical and physical constraints to a model surface effective potential. The properties derived are metallic surface dipole barriers, work functions, and surface energies, the behavior of the work function for densities higher than those existing in metals, and low-density surface energies. The finite-linear-potential model employed is one which varies linearly over a finite region and is constant beyond some point, the parameters of the system being the edge of the neutralizing positive charge (jellium) background, the field strength, and the barrier height. For this model effective potential the determination of all properties is primarily analytic. The jellium edge and barrier height are determined by the condition of charge neutrality and requirement of self-consistency of the surface dipole barrier, respectively, whereas the field strength is either adjusted so as to satisfy the constraint set on the electrostatic potential by the Budd-Vannimenus theorem (BVT) or varied in an application of the variational principle for the energy. The results obtained on use of the BVT constraint indicate that although the work function decreases with increasing density, it does not saturate at some finite value in the high-density limit as concluded by Peuckert, but rather that it vanishes at a density corresponding to ${r}_{s}\ensuremath{\simeq}0.4$. For metallic densities, the surface dipole barriers and work functions thus determined lie within three tenths of an electron volt of the fully self-consistent calculations of Lang and Kohn (LK). The upper bounds obtained by a variational-self-consistent calculation of metallic surface energies as determined within the local-density approximation (LDA) are within 5 ergs/${\mathrm{cm}}^{2}$ of the LK values for ${r}_{s}\ensuremath{\ge}2.5$ and differ by less than 3% for ${r}_{s}=2$. Surface energies for metallic and lower densities are also determined by use of the Vannimenus-Budd theorem in conjunction with the physical criterion of the vanishing of the surface energy in the low-density limit. For the same choice of single-particle Hamiltonian, determined by the BVT sum rule, these results lie significantly below those of a LDA calculation over the entire range of densities considered.

The average backscattering cross section of clouds of randomized resonant dipoles

The average backscattering cross section of clouds of linear metallic dipoles of resonant length and random orientation is investigated. The effects of mutual coupling among dipoles is included in the analysis by use of computer techniques currently available or being developed. Average backscattering cross sections are Presented for random clouds containing up to 200 dipoles with average spacings from 0.5\lambda to 2.0\lambda . Results show that coupling is insignificant at the largest spacings but causes a 2-3-dB degradation in average echo area at the smallest spacings.

Avibrating-Dipole Technique for Measuring Mlillimeter-Wave Fields in Free Space

EM field measuring techniques, based on the modulated-scattering principle, are well established at microwave frequencies. The main difficulty in extending measurements to the millimeter-wave region is that of scaling the scatterer for operation at these wavelengths. The technique of modulated scattering described in this paper overcomes this limitation. A thin metallic dipole, attached to a vibrating nylon cord, forms the modulated scatterer which interacts with the electric field and gives rise to a phase-modulated reflected wave. The reflected wave is then combined with preference wave in a coherent detection system. The detected signal contains information about the amplitude and phase of the field at the midpoint of the dipole's vibration. An analysis of the technique is presented and the factors affecting the accuracy of measurement are fully discussed. It is shown how the measurement errors can be minimized. Amplitude and phase measurements, taken at a wavelength of 4.8mm, verify the validity and accuracy of the technique.

Electrooptical Characteristics of Dipole Suspensions

The theory of a suspension of submicron dipoles in a fluid medium, and their interconection with light is given. The electrooptical characteristics in a herapathite dipole suspension, and a metal dipole suspension, is also presented.

A Modulated Scattering Technique for Measurement of Field Distributions

Electric field distributions can be measured accurately by passing a short metal dipole through the field and recording the wave scattered by the dipole. Ordinarily the method is difficult to use since the scattered signal is small, critical tuning adjustments are required, and careful attention to stability is necessary. However, by placing a nonlinear impedance at the center of the dipole and applying an audio voltage though slightly conducting threads, the scattered wave can be modulated. This makes it possible to relax the tuning and stability requirements and at the same time to increase the sensitivity of the measurements.