Circular Dipole Research Articles

Compact dielectric resonator antenna for microwave breast cancer detection

A compact stair-shaped dielectric resonator antenna (DRA) is designed and fabricated for microwave breast cancer detection. A quarter-wavelength choke was incorporated to reduce the finite ground plane size. A more than 40% return loss of 10 dB centred at 6.5 GHz is achieved with a 50 Ω coaxial port. Parametric studies are carried out to provide practical insights into sensor design. The design is performed numerically and confirmed experimentally. A simple model for the tissue is considered and the interaction of the sensor with the tissue is investigated. Good matching is retained without adding any matching medium or lumped loads when the sensor is in contact with the tissue. A two-element sensor array is investigated numerically. A dipole antenna and a circular ultra-wideband dipole antenna are compared with the stair-shaped DRA with a choked ground plane. Preliminary results are obtained for the cases with different tumour locations. The DRA type of sensor reveals good potential for frequency-domain detection.

Circular Dipole Antenna for Mode 1 UWB Radio With Integrated Balun Utilizing a Flex-Rigid Structure

A fully integrated dipole antenna with balun for ultrawideband (UWB) radio utilizing a flexible and rigid printed circuit board is presented in this paper. The concept in this paper is to take advantage of the respective possibilities of the rigid and flexible parts. The balun utilizes broadside-coupled microstrips and is integrated in the rigid part of the printed circuit board, whereas the radiator is placed in the flexible part. The antenna with the balun covers the mode 1 UWB frequency-band 3.1-4.8 GHz (with margin) at voltage standing wave ratio (VSWR) <. Furthermore, good radiation characteristics and a linear phase response are observed with measurements.

ПОКАЗАТЕЛИ ЭЛЕКТРИЧЕСКОГО ПОЛЯ СЕРДЦА ПРИ ПЕРЕДНЕМ И ПЕРЕДНЕБОКОВОМ ИНФАРКТЕ МИОКАРДА ПО ДАННЫМ ЭКТГ

Abstract. Quantitative and qualitative parameters of the electric fi eld of the heart (EFH) are studied, localizations of the typical changes in the anterior and anterolateral myocardial infarction (MI) are specifi ed on the data of electrocardiotopography (ECTG). ECTG was performed in 78 healthy subjects (control groupp — CG) and 147 patients with MI of different localization on the 3-4 week of disease (9pts with anterior and 20 pts with anterolateral MI among them). The areas of overlapping zones (OZ) in electropositivity (EP) and electronegativity (EN) are reduced due to the direction changes of the vectors of initial and fi nal forces in comparison with CG. Length of the reliable dicreasing of potential and zero zone (ZZ), appearing in EP, is more in anterolateral MI, than in anterior MI. In patients with anterolateral MI the determinant importance of the prevalence of the process has the registration of QS wave in V1 lead. In anterolateral MI with QS in V1 the area of lesion is maximal. In assessment of the length of the process in anterior and anterolateral MI ZZ in EP differs. In anterior MI it spreads more to the upper levels of registration, affecting the posterior part of interventricular septum (IVS) and high posterior-septal area or the high part of IVS ( in the inferior third). In the anterolateral MI it spreads more to the lower levels of registration, involving the inferior-septal and inferior-apical areas. Quantitative indices of EFH in MI of anterior localisations ststistically reliable differ from CG and characterize the prevalence of EN in the second half of the circular dipole motion, especially on the front surface of the torax in the anterior and anterolateral MI and sharp dicreasing EP on the anterior and posterior thoracic surface.

Simulation of Vibrational Spectra of Large Molecules by Arbitrary Time Propagation.

Modern ab initio and multiscale methods enable the simulation of vibrational properties of very large molecules. Within the harmonic approximation, the traditional generation of the spectra based on the force field diagonalization can become inefficient due to the excessive demands on computer time and memory. The present study proposes to avoid completely the matrix diagonalization with a direct generation of the spectral shapes. For infrared absorption (IR) and vibrational circular dichroism (VCD) electric and magnetic dipole moments are propagated in a fictitious time and spectral intensities are obtained by Fourier transformation. The algorithm scales quasi-linearly, and for model polypeptide molecules the method was found numerically stable and faithfully reproduced exact transition frequencies and relative intensities.

Characterization of the Angular Orientation Distribution of Discotic Molecules in Thin-Film Assemblies: Combinations of Polarized Transmission and Reflection−Absorption Infrared Spectroscopies

We present a protocol to determine the angular orientation of surface-confined discotic molecules in ordered thin-film assemblies through a combination of polarized reflection absorption infrared spectroscopy (RAIRS) and polarized transmission infrared (IR) spectroscopy. We focus here on the determination of the orientation of side-chain-modified disk-like phthalocyanine molecules that self-organize to form parallel columnar aggregates in Langmuir-Blodgett (LB) films. This work complements and follows on work published previously (Langmuir 2005, 21, 360-368) where we used the visible absorbance dichroism in similar assemblies to determine the tilt angles of discotic molecules. The approach described here is applicable to all disk-like molecules that possess distinct in-plane or out-of-plane IR transitions. Molecular orientation is determined by comparison of absorbance intensities that are measured using (i) a RAIRS spectrum of the thin-film material on a gold surface, (ii) transmission spectra taken at two different polarizations of the thin-film material on an IR-transparent silicon substrate, and ( iii) a transmission IR spectrum of an isotropic sample. We chose two distinct IR transitions of this molecule (a C-O-C “in-plane” stretch, OC-O-C ,a nd aC -H out-of-plane bend, ‰C-H), which we initially assume are orthogonal to each other. The OC-O-C transition is modeled as an inplane circular dipole, and the ‰C-H transition is modeled as a linear out-of-plane dipole. Formalisms are described that allow the determination of two independent values for order parameters within the thin film using the dichroism in these transitions in all three IR spectra, assuming that the microstructure of these thin films is the same on both the gold and silicon substrates. The spectra from the ‰C-H transition appear to best describe the orientation of these molecules within the molecular assembly, these IR results agreeing best with earlier visible absorbance and X-ray diffraction studies. The preferential alignment of the ‰C-H transition is parallel to the substrate, arising from Pc molecules that are nearly upright, edge-on to the substrate plane. The approach described here provides a means of complete description of the tilt angles of the monomer building blocks in any discotic assembly in thin-film formats, where distinct in-plane and out-of-plane optical transitions are available.

A COMPARISON BETWEEN CIRCULAR AND HEXAGONAL ARRAY GEOMETRIES FOR SMART ANTENNA SYSTEMS USING PARTICLE SWARM OPTIMIZATION ALGORITHM

In this paper, circular and hexagonal array geometries for smart antenna applications are compared. Uniform circular (UCA) and hexagonal arrays (UHA) with 18 half-wave dipole elements are examined; also planar (2 concentric rings of radiators) uniform circular (PUCA) and hexagonal arrays (PUHA) are considered. The effect of rotating the outer ring of the PUCA is studied. In our analysis, the method of moments is used to compute the response of the uniform circular and hexagonal dipole arrays in a mutual coupling environment. The particle swarm optimization (PSO) algorithm is used to optimize the complex excitations, amplitudes and phases, of the adaptive arrays elements for beamforming.

Polarization of luminescence and site symmetry of the Xe center in diamond

We report on polarized photoluminescence studies of the Xe ion-related optical center in diamond. The sample was a single crystal CVD diamond film grown along the (0 0 1) crystallographic plane. The film was irradiated with 180 keV Xe + ions at room temperature at a dose 5×10 12 cm −2 and annealed at 1400 °C. The emission of the sample with laser excitation at 647 nm exhibits the first and second order Raman spectra of diamond, a broad band due to the phonon sideband of the GR1 center, and the Xe center-related features: two zero phonon lines at 813 nm and at 794 nm and a respective vibrational sideband. The Huang–Rhys factor for the Xe center was estimated to be exp(− S)=0.3 at room temperature. The polarization of the Xe center photoluminescence was studied as a function of the sample rotation. The center was established to be a 〈1 1 1〉 oriented defect with a circular dipole absorption transition at 647 nm, a circular dipole emission transition at 794 nm, and a linear dipole emission transition at 813 nm. Possible models of the center were discussed.

Resonance analysis of a circular dipole array antenna in cylindrically layered media for directional borehole radar

In this paper, we discuss the influence of a resonance on estimating direction of arrival (DOA) with a circular dipole array in a borehole (CAB). The resonance is caused by the phase-sequence of currents on the dipole antennas. Making use of method of moments (MoM) analysis, we predict resonant frequencies of the CAB and describe a mechanism for the resonance theoretically, making use of the fact that a plane wave can be broken down into cylindrical harmonics. In order to examine the agreement between the MoM and experimental data, we propose a signal processing method to extract phase-sequence components from the actual received array signal. This method is useful for confirming excitation of the phase-sequence resonance in experimental data, as predicted by the MoM. Using the MoM, we examine the influence of the resonances on DOA estimation, and we conclude that the resonances give some spurious solutions. In order to confirm these results, we conduct experiments at a field test site. We arrange the CAB, which consisted of seven receiving dipole antennas. In this experiment, a plane wave is incident on the CAB from a transmitter in another borehole. We apply the proposed signal method, and the measured results demonstrate the existence of the phase-sequence resonance in a physically real CAB. The spurious solutions found to occur in the DOA estimation at the resonant frequencies are also found experimentally.

Determination of Molecular Anisotropy in Thin Films of Discotic Assemblies Using Attenuated Total Reflectance UV−Visible Spectroscopy

We report here an investigation of absorbance anisotropy in highly ordered, single bilayer (ca. 5.6 nm) Langmuir-Blodgett (LB) thin films of discotic liquid-crystalline phthalocyanines, using a recently introduced broad-band attenuated total reflectance (ATR) spectroscopic technique, capable of measuring dichroism in such films in the UV--visible optical region down to absorbances of ca. 0.003 absorbance units. On the basis of the ATR measurements of LB-deposited films, a thorough treatment was established to determine the ensemble average of the Cartesian components and the associated optical anisotropy of transition dipoles in the molecular film. In an effort to recover order parameters of molecular orientation, those results were interpreted with a circular dipole model, which is the expected model for the isolated molecule based on symmetry properties. We measured a strong dipole component normal to the film plane that cannot be explained in terms of a truly circular model, indicating that the molecular transition dipoles were perturbed upon aggregation. The utility of the experimental approach was further demonstrated by (a) investigating the effect of substrate modifiers (methyl- and phenyl-terminated silanes) on the ordering within the phthalocyanine film and (b) the effect of water immersion and re-annealing of the thin film on molecular ordering and optical anisotropy.

Optimizing Light-Source Aperture for Off-Axis Illumination in Optical Nanolithography: Theoretical Consideration

A theoretical analysis is given of ultimate-resolution imaging in optical lithography by off-axis illumination, a common approach to image quality improvement. On this basis, the optimization of light-source aperture configuration is addressed. The types of aperture considered are the circular dipole, the circular quadrupole, the simple annular aperture, the annular dipole, and the annular quadrupole. They are compared in terms of simultaneous transfer of transverse and longitudinal mask features.

Effective skin depth of EM fields due to large circular loop and electric dipole sources

Definition and concept of plane wave skin depth is applied to study the effective skin depth due to large circular loop and horizontal electric dipole sources, and attempt is made to illustrate its application to the real field survey design and data interpretation problems. The effective skin depth, the depth at which the amplitude of a frequency-domain electromagnetic field due to a large circular loop source or an electric dipole source falls to 1/e of its value at surface of a homogeneous half space, is compared with the usual plane wave skin depth for variation of different survey and model parameters, viz. source frequency, source moment or loop dimension, source-receiver offset and half space conductivity. The results show their characteristic variations, and depict that the effective skin depth due to large loop source and/or electric dipole source depends on source-frequency, source moment, source-receiver offset and half-space conductivity. The effective skin depth may vary from a fraction of plane wave skin depth in near vicinity of the source to more than twice the plane wave skin depth at points away from the source. However, for large source-receiver offsets and/or high source frequencies and half-space conductivities, it tends to the plane wave skin depth. For receiver positions in near vicinity of the source, the effective skin depth curves exhibit variations specific to the source, and show different characteristic variations for different sources, whereas for receiver positions away and far away from the source, the effective skin depth curves show similar characteristic variations for all sources, irrespective of nature and geometry of the source. The results depict distinctive effect of geometry and nature of the source on effective skin depth. The examples presented for illustrating the application of effective skin depth depict that effective skin depth has direct relation with the EM response of the local source over the layered earth and thus, can be used as an aid for estimating the optimum parameters in EM survey design and data interpretations.

Properties and applications of the large circular resonant dipole array

Large closed-curve antenna arrays have been a subject of research for many years and have been shown to have many interesting properties. The paper investigates some of the properties of such a dipole array when the closed curve is a circle. Recently, because of its unique horizontal field pattern, a 90-element circular array of this type has been proposed as a microwave beacon for the coastal navigation of ships and airplanes. In the design of these arrays, it is suggested that the array be rotated mechanically. The question arises: can the mechanical rotation be replaced by an electronic rotation? We show that electronic rotation is not possible for the 90-element circular array originally described, but is possible for a modified array. The subtle difference between these two arrays is clarified and a simple criterion is given for the general case. Also presented is the derivation of an asymptotic formula for the radiation pattern of a resonant circular array of N equal elements with only one element driven. Since the theory for such an array is complicated and involves numerous numerical difficulties, a simple asymptotic formula for the field pattern has advantages over other methods. The simple formula is shown to produce a vertical field pattern that is indistinguishable from its numerically calculated counterpart. Generalization to noncircular arrays is discussed briefly.

Numerical analysis of cylindrical dipole antennas using an auxiliary sources model

In this paper, the problem of the radiation from a circular cylindrical dipole antenna, which is either symmetrically or asymmetrically fed by an idealized voltage source, is analyzed using the method of auxiliary sources (MAS). This method is applied by introducing a set of fictitious sources carrying unknown currents inside the dipole for the direct description of the radiated electromagnetic (EM) field. The unknown currents are determined by imposing the electric field continuity boundary conditions on the physical surface of the dipole. The solution is formed using spatially overlapped small sinusoidal dipoles, instead of elementary dipoles that are usually used in conventional implementations of current‐model based techniques. It is shown that this choice leads to a significant acceleration in the rate of convergence of the solution and, as a direct outcome, to a noteworthy reduction of the relevant computational cost. Since the currents of the fictitious sources are determined, various quantities of great theoretical and practical interest, are readily computable. Several examples illustrating the well‐behaved convergence of the proposed method are presented, concerning various geometrical configurations. In each case, the accuracy of the resultant solution is verified by checking the stability of the input impedance/admittance of the dipole for an increasing number of fictitious sources and comparing the computed values with previously published data.

A circular cylindrical dipole antenna

AbstractThe problem of a circular cylindrical dipole antenna is revisited. The Fourier transform and mode matching are used to obtain its rigorous solution in a convergent series. Our solution is compared with other results in terms of antenna admittance and current distribution. The angular radiation patterns of a circular cylinder antenna are shown for different circular cylinder radii of a dipole antenna. © 2001 John Wiley &amp; Sons, Inc. Microwave Opt Technol Lett 31: 322–324, 2001.

Antenna Model for Conductive Omega Particles

Analytical models for small Ω-shaped conductive particles in free space or embedded in isotropic materials are presented and discussed. The electromagnetic analysis is based on the antenna theory for circular loop antennas and dipole wire antennas. Analytical expressions for the polarizabilities valid in the frequency area covering the two lower resonances are given. Mutual coupling between two portions of the particle: the loop and the straight wire is considered in terms of the mutual impedance, which is analytically calculated with the use of the induced electromotive force method. Approximate analytical expressions are compared with numerical simulations and are seen to be in good agreement. The results can be used in analytical modeling of omega and chiral composite materials and in the antenna theory.

A new method of geoelectrical prospecting by vertical electric current soundings

Some advantages and problems of a new geoelectrical prospecting method, vertical electric current soundings (VECS) are discussed. This method is based on using a new source, circular electric dipole (CED). The source is installed in the following way. One of the transmitter poles is grounded in the central point. The other pole is uniformly grounded around with a radius determined by the depth of investigation desired. It can be defined as a noninductive source. The most interesting CED properties in the low frequency regime are as follows. CED has no magnetic field of its own. It is a pure galvanic source, which differs from a loop (a pure inductive source) and from a line, which is both galvanic and inductive (a ‘line’ here means a cable or insulated wire grounded at its end points). The normal magnetic field on the earth's surface (and above it) of a horizontally layered medium is absent (within the quasi-static approximation), and only a radial electric component exists. A CED field is at right angles to the loop field and has azimuthal symmetry. The CED field is always governed by a vertical medium structure (at the latter transient stage as well) rather than by the total longitudinal conductivity. An interesting result was obtained: in marine electrical prospecting a sea water layer will not play such a crucial role when a CED is used as in applying a loop or a line. In a medium with non-conducting basement the decay of the CED field is exponential. The transient process is more fast than in the case of a loop or a line. The CED can be also considered as a ground analogue of another known source, a vertical electric line. Besides, the CED is a pure galvanic source that does not excite a long-term transient field. Thus it seems to be a new useful means to study IP processes. The mathematical apparatus is represented in the frequency and time domain. The authors consider the results of the initial field tests.

Excitation of a half-space by a radial current sheet source

Some advantages and problems of the new geoelectrical prospecting method, i.e., vertical electric current soundings (VECS) are discussed. This method is based on using a new source, namely a circular electric dipole (CED). The source is installed by one of the transmitter poles grounded in the central point and the other pole uniformly grounded around with a radius determined by the depth of investigation desired. It can be defined as a noninductive source. The previous research was based on the diffusion approach. In this paper the author uses the solution with due regards for displacement currents in the frequency and time domain. A major disadvantage of the CED scheme is the need to provide a symmetrical grounding of the outer ring electrode. A possible way to avoid this requirement is to adopt an ungrounded CED array.

On the effect of gap width on the admittance of solid circular cylindrical dipoles

A center-fed, solid, circular cylindrical dipole of radius a with feed gap of width 2d radiating in a circular waveguide of radius b terminated in infinite ground planes is rigorously analyzed by applying both the conservation-of-complex-power technique and the multiple-reflections technique. The analysis begins by studying the dependence of the dipole admittance on its feed gap width and on its length, 2l, as well as on b, with ka (k=2 pi / lambda is the number) as a parameter. From the decreasing amplitudes of the almost periodic oscillations of these input admittances as b/ lambda is increased, the input admittances of dipoles radiating in free space (b to infinity ) are estimated using a variable-bound approach. The effect of gap width (d/a >

A horizontal small sized backfire antenna using circular dipole

In this paper, a horizontal small sized (≈ 0.5 λ) backfire antenna with the circular dipole is described. The antenna structure and experimental results are given. The experimental results demonstrate that the antenna has better electrical performances.

Synthesis and conformation of asymmetric rigid polyamides

AbstractAsymmetric polyamides from the reaction of either optically active trans‐1,2‐cyclopropanedicarboxylic acid (C3) or trans‐1,2‐cyclohexanedicarboxylic acid (C6) with 2,7‐diazaspiro[4,4]nonane(DSN) were synthesized. The possible conformations of these polymers and their model compounds in 2,2,2‐trifluoroethanol (TFE), water, methanesulfonic acid (MSA), and sulfuric acid were examined by circular dichroism (CD), NMR, viscosity, and dipole moment measurements. The racemic polyamides (±)C3·(±)DSN and (±)C6·(±)DSN exist in extended forms. No intrinsic viscosity changes were observed for these two polymers in TFE and MSA. Certain viscosity and spectral changes have been observed for the optically active polyamides, although no specific ordered conformations can be assigned. The optically active diacid units incorporated into the polymer give a conformation unique from the totally extended chain. CD studies seem to evidence some conformational differences among the polyamide derived from (+)C6 diacid and the optically active DSN. By changing the solvent from TFE to MSA a blue shift of the trough was observed for (+)C6·(±)DSN, a red shift for (+)C6·(−)DSN, and an inversion of the CD spectrum for (+)C6·(+)DSN polyamides. The results of the work with (+)C6·(−)DSN in dilute acid solution suggest that the rotation around the C–N bond is a relatively low‐energy process. The spectral and intrinsic viscosity data are consistent with this suggestion. No drastic spectral changes have been observed for the C3·DSN polyamides by changing the solvent from TFE to MSA. The amide group in the C3·DSN polyamide and the corresponding model compound prefer a similar conformation with the carbonyl group bisecting the cyclopropane ring. The C3·DSN polyamide seems to exist in an extended form.