Spectral Domain Analysis Research Articles

Numerical and experimental studies of split ring resonators loaded on the sidewalls of rectangular waveguides

This work investigates the use of a lattice comprising split ring resonators (SRRs) as a negative permeability medium to achieve backward travelling modes within a rectangular waveguide. The loadings of such SRR-type periodic structures into a waveguide can be tailored such that the backward mode exists in a passband below the ordinary basic modal cutoff frequency, thus affording filtering capabilities and miniaturisation. Theoretical studies by two approaches are performed here, a moment method spectral domain analysis, and a commercial simulation tool. Parametric studies that characterise the effects of various dimensional and electrical properties on the dispersion behaviour of the SRR-loaded waveguide shall also be conducted. The SRR parameters are then optimised using the ant colony optimisation (ACO) algorithm to achieve a low backward passband, for a high degree of miniaturisation and isolation. Experimental results of measurements performed on a manufactured prototype of the optimised SRR-loaded waveguide will also be presented.

Efficient double-filtering with a single acousto-optic tunable filter

We describe an efficient double-filtering method that uses a single acousto-optic tunable filter (AOTF) to improve the spectral resolution and intrinsic sidelobes for the spectral domain analysis systems. Double filtering with a single AOTF is realized by applying a unique feedback scheme based on the fact that incident light can be diffracted into two orthogonally polarized beams of light by an AOTF. Our theoretical explanation attempts to address and satisfy the main prerequisite for the proposed idea. The experimental results confirm that the proposed method achieves a 20% to 30% improvement in spectral resolution and 10 dB suppression of sidelobes with minimized light loss for the extraordinary incident light. We believe that the results of using an AOTF are comparable to the results achieved with two AOTFs in tandem.

Autonomic cardiac control of very preterm newborns: A prolonged dysfunction

Background Autonomic nervous system (ANS) activity is fundamental to infant health. ANS activity of preterm newborns seems to be reduced at term equivalent age, but follow-up of ANS activity has rarely been performed in that population during the weeks after birth. The aim of the study was to perform such a follow-up in preterm newborns of different gestational ages, up to their term equivalent ages. Methods Prolonged electrocardiographic recordings were prospectively performed in a group of 39 premature newborns, each week, up to term equivalent age before discharge. Control values were obtained from a group of 19 full-term newborns, recorded at the first week of their life. ANS indices were calculated from recordings during quiet sleep periods by spectral-domain analysis (Fourier transform): Ptot (total power), VLF (very low-frequencies), LF (low-frequencies), HF (high-frequencies), LF/HF ratio, LFnu (normalized low-frequencies) and HFnu (normalized high-frequencies) values. Results Ptot, VLF, LF and HF were significantly lower in the preterm group at birth compared to the control group, while LFnu, HFnu and LF/HF ratio were not significantly different. The results were similar when comparing the control group to any ANS values at a given post-natal corrected age of preterm newborns. Furthermore, preterm newborns did not demonstrate any significant increase in ANS values from birth to theoretical term. Conclusion The finding of substantial reduced ANS activity and failure of maturation in preterm infants up to term equivalent age needs confirming by other research groups, and mechanisms and implications for infant health explored.

Electrophysiological markers of skill-related neuroplasticity

Neuroplasticity involved in acquiring a new cognitive skill was investigated with standard time domain event-related potentials (ERPs) of scalp-recorded electroencephalographic (EEG) activity and frequency domain analysis of EEG oscillations looking at the event-related synchronization (ERS) and desynchronization (ERD) of neural activity. Electroencephalographic activity was recorded before and after practice, while participants performed alphabet addition (i.e., E + 3 = G, true or false?). Participant's performance became automated with practice through a switch in cognitive strategy from mentally counting-up in the alphabet to retrieving the answer from memory. Time domain analysis of the ERPs revealed a prominent positive peak at ∼300 ms that was not reactive to problem attributes but was reduced with practice. A second prominent positive peak observed at ∼500 ms was found to be larger after practice, mainly for problems presented with correct answers. Frequency domain spectral analyses yielded two distinct findings: (1) a frontal midline ERS of theta activity that was greater after practice, and (2) a beta band ERD that increased with problem difficulty before, but not after practice. Because the EEG oscillations were not phase locked to the stimulus, they were viewed as being independent of the time domain results. Consequently, use of time and frequency domain analyses provides a more comprehensive account of the underlying electrophysiological data than either method alone. When used in combination with a well-defined cognitive/behavioral paradigm, this approach serves to constrain the interpretations of EEG data and sets a new standard for studying the neuroplasticity involved in skill acquisition.

Radiation and resonant frequency of a resistive patch and uniaxial anisotropic substrate with entire domain and roof top functions

This paper develops and describes briefly the spectral domain analysis of microstrip patch antennas in which two sets of basis functions are used to model the patch current: the entire domain sinusoid basis functions and roof-top sub-domain basis functions. The moment method technique based on Galerkin's procedure is developed to examine the resonant frequency of a perfectly or an imperfectly conducting microstrip rectangular patch, which is printed on isotropic or uniaxial anisotropic substrate. It is seen that the results obtained by the roof top basis functions provides a significant improvement in the computations time with less iterations in the evaluation of the resonant frequency of a microstrip patch compared with the entire domain basis functions. Numerical results for the effects of surface resistance and uniaxial substrate on the radiation and the directivity of the rectangular microstrip structure are also presented. The accuracy of the computed technique is presented and compared with other computed results.

Abstract 3315: Therapeutic Implications of Sympathetic Stimulus in Orthostatic Patients: Measured by Spectral Domain Analysis

Upon assuming an upright, head up posture, a sympathetic surge is expected. Sympathetic Withdrawal (SW) is abnormal and can differentiate Orthostasis. SW, with blood pressure (BP) and heart rate (HR), can fully define the continuum that is Orthostasis, including pre-clinical forms: Orthostatic Hypotension (OH-), Orthostatic Intolerance (OI), Orthostatic Hypertension (OH+), and Postural Orthostatic Tachycardia Syndrome (POTS). Our objective was to test the therapeutic implications of SW in Orthostatic patients. Autonomic profiling of 210 consecutive Orthostatic patients recruited from ambulatory clinics was performed using the ANX-3.0 Autonomic Monitoring System (Ansar, Inc., Philadelphia, PA). The cohort (age=58.9±11.6; 30 Diabetics; 132 Females, 28 Controls) was followed over a two year period. Autonomic profiling was based on patient responses to a standard clinical study that includes a resting baseline and periods of deep (relaxed) breathing, short Valsalva maneuvers, and quick stand immediately followed by quiet standing. The control group were patients with known diagnoses. The experimental group were prescribed 2.5 mg Midodrine once a day around dinner. Control patients were administered Flourinef, or support hose, or when possible were requested to modify their diets to add salt and build fluid volume. Patients with dysautonomia, with symptoms of elevated BP when supine were omitted from the study. In 89% of the experimental cases, SW was reversed in approximately 6 months and weaned from the medication. The remaining cases were reversed and weaned before the end of the two year follow up. In the control group, 46% of the patients on Flourinef, 4% of the support hose patients and 12% of the diet modification patients corrected SW within the two year period. The application of an alpha-adrenergic agonist seems to have greater efficacy than a mineralo-corticoid, mechanical intervention, or dietary modification in correcting SW associated with Orthostasis.

Impact of Withdrawal of 450 ml of Blood on Respiration-Induced Oscillations of the Ear Plethysmographic Waveform

It has been widely appreciated that ventilation-induced variations in systolic blood pressure during mechanical ventilation correlate with changes in intravascular volume. The present study assessed whether alterations in volume status likewise can be detected with noninvasive monitoring (ear plethysmograph) in non-intubated subjects (awake volunteers). Eight healthy adults were monitored with EKG, noninvasive blood pressure, an unfiltered ear plethysmograph, and a respiratory force transduction belt before (PRE) and after (POST) withdrawal of 450 ml of blood from an antecubital vein. Spectral-domain analysis was used to determine the peak ventilatory frequency and the power of the associated variation in the ear plethysmographic tracing; Interphase differences in the respiration-induced plethysmographic variations were assessed by Wilcoxon signed rank test. In addition, the changes in the ear plethysmographic tracing were compared to changes in heart rate and blood pressure. There was a significant increase in respiratory-associated oscillations at the respiratory frequency between the PRE and POST phases (p = 0.012). These changes were detected despite lack of changes in heart rate or blood pressure. Respiration-induced changes of the ear plethysmographic waveform during spontaneous ventilation increase significantly as a consequence of withdrawal of approximately one unit of blood in healthy volunteers.

Spectral domain analysis of frequency-selective surfaces on biaxially anisotropic substrate

A full-wave analysis is presented of frequency-selective surfaces (FSSs) on a biaxially anisotropic substrate. The integral equations are first transformed into the spectral domain ones through the use of the Floquet theorem and then solved by the method of moments. Since the wave immittance of the biaxially anisotropic substrate is derived in a closed form, the resulting impedance matrix can be obtained conveniently by using the spectral domain immittance approach (SDI). The validity of theoretical formulations is verified by illustrative numerical results and their comparisons. The obtained results are compared with the existing data and other analyses and good agreements are observed. The effects of biaxially anisotropy on the FSS have been studied and discussed.

Seismic risk analysis of modified fan type cable stayed bridges

A seismic risk analysis of modified fan type cable stayed bridges is presented using the concept of damage probability matrix. The cable stayed bridge is modeled as a two dimensional system with the deck idealized as a continuous beam subjected to bending action and axial compression. The response of the bridge is obtained by the frequency domain spectral analysis. A double filtered power spectral density function with seismic intensity parameter taken as the magnitude of an earthquake and a correlation function between the support excitations are considered as seismic inputs. For a given magnitude of earthquake, the damage probability matrix is determined by defining three damage states namely, major, moderate and minor. The seismic risk index is determined by combining the damage probability matrix with the probability of occurrence of different magnitudes of earthquake. As an illustrative example, a three span modified fan type cable stayed bridge is analyzed for an extensive parametric study. The parameters include degree of correlation, angle of incidence of earthquake, ratio of the components of ground motion, and soil condition. Some of the important conclusions of the study indicate that (i) the longitudinal component of ground motion has a considerable effect on the annual probabilities of failure of the bridge deck; (ii) annual probabilities of failure are significantly more for soft soil condition; (iii) fully correlated ground motion between support excitation provides less value of the damage indices as compared to the uncorrelated ground motion; and (iv) annual probabilities of failure are not very sensitive to the variation of angle of incidence of an earthquake.

Electromagnetic Characterization of a Magnetic Material Using an Open-ended Waveguide Probe and a Rigorous Full-wave Multimode Model

In this paper a material characterization technique employing a flanged opened-ended rectangular waveguide probe is presented that now allows extraction of both permittivity and permeability from a conductor-backed lossy shielding material. As an added benefit, this non-destructive technique reduces sample preparation time leading to rapid measurement. Calculation of both material parameters is accomplished using experimental reflection measurements from two different thicknesses of a given material sample. A theoretical solution to the reflection coefficients is developed through a rigorous magnetic field integral equation (MFIE) formulation. The double integral that results from the spectral domain analysis is reduced to a single integral through careful application of Cauchy's Integral Theorem leading to improved convergence and is an additional contribution that is believed to be new for this particular structure. A comparison between the theoretical and experimental reflection coefficients allows extraction of the material parameters using a two-dimensional Newton root search algorithm. Parameter extraction results incorporating dominant and higher-order modes are presented and compared to results from traditional waveguide material characterization techniques. An uncertainty analysis is also performed to determine sensitivity to errors in sample and probe flange thickness.

Spectral synchronization in chaotic optical communication systems

The ability of chaotic carriers to synchronize in optical chaotic communication systems is studied experimentally under a spectral domain analysis. Synchronization of high-frequency components up to tens of gigahertz of the chaotic carriers can thus be evaluated. On the contrary, the traditional method of measuring the synchronization through chaotic carrier time-traces is constrained by the limited bandwidth of the real-time oscilloscopes used for such measurements, excluding the contribution of the high-frequency components of the chaotic carriers to the synchronization characterization of the system.

Full-wave analysis of coupled strip-slot guiding structures

In this paper, the coupled strip-slot lines are modeled using hybrid mode analysis. Standard spectral-domain analysis is employed to solve the eigenvalue problem in multilayered media and a novel formulation is proposed to obtain strip and slot modal impedances. Comparisons with available published data are presented. The model is used to obtain scattering parameters of a bandpass filter with a novel topology. These scattering parameters are then compared with those obtained using rigorous Sonnet simulations, thereby confirming the reliability of the model.

Numerical analysis of ground plane size effects on patch array antenna characteristics for mobile satellite communications

In this research, a patch array antenna for mobile satellite communications aiming at ETS-VIII applications has been developed. The ground plane size effects on the antenna characteristics were investigated. Finite and infinite ground planes were analysed by the finite integration technique (FIT) for time domain analysis, the finite element method (FEM) and the method of moments (MoM) for spectral domain analysis. Then measurements of the fabricated antenna were performed to confirm the analysis results. It is clear that the frequency characteristics of the axial ratio are influenced by the variation in the ground plane size. When the ground plane size is increased, the edge-diffracted field causes tilting of the beam in the direction of low elevation angles and causes a decrease in the maximum gain and in the 3 dB-beamwidth of axial ratio in the elevation plane. In the conical-cut direction, an increase in ground plane size induces a decrease in the 3 dB-beamwidth of axial ratio for FEM, but shows the opposite result for FIT and measurement. In addition, an increase in ground plane size also induces increases in maximum gain and its 6 dBic-beamwidth along with a shift in the maximum gain in the direction of low azimuth angle. Copyright © 2004 John Wiley & Sons, Ltd.

Different spectral components of 24 h heart rate variability are related to different modes of death in chronic heart failure

To assess whether analysis of heart rate variability (HRV) from 24 h Holter recordings provides information about the mode of death (pump failure vs. sudden death) in chronic heart failure (CHF). We analysed 24 h HRV in 330 consecutive CHF patients in sinus rhythm. Indices derived from time domain, spectral domain, and fractal analyses of 24 h automatic HRV were evaluated. Data from clinical assessment, echocardiography, right heart catheterization, exercise test, blood biochemical examination, and arrhythmia pattern were analysed. Patients were followed up for 3 years. Two simple multivariable models, both including 24 h spectral indices, were able to identify patients at higher risk of progressive pump failure and sudden death, respectively. Depressed power of night-time HRV (< or = 509 ms(2)) below 0.04 Hz [very low frequency (VLF)], high pulmonary wedge pressure (PWP > or = 18 mm Hg) and low left ventricular ejection fraction (LVEF < or = 24%) were independently related to death for progressive pump failure, while the reduction of power between 0.04 and 0.15 Hz at night (LF < or = 20 ms(2)) and increased left ventricular end-systolic diameter (LVESD > or = 61 mm) were linked to sudden mortality. Automatic spectral analysis of 24 h HRV provides independent risk indices related to mode of death in sinus rhythm CHF patients.

Spectral domain analysis of large (M)MIC‐structures using novel quadrature methods

AbstractThe spectral domain approach for the solution of integral equations is especially attractive for planar circuits and antennas in multilayered environments characterized by analytically derived Green's functions. However, for circuits with large lateral dimensions the spectral integrands are strongly oscillatory and accurate evaluation of the integrals is extremely difficult and often time‐consuming. In this paper, we propose higher‐order Legendre quadrature rules optimized for the integration of the oscillating integrands using the Filon principle. The Legendre–Filon quadrature weights are computed for the specific oscillations by solving a small linear system of equations. The method is applied within a spectral domain solution approach evaluating the spectral integrals in cartesian wavenumbers and using asymptotic extraction techniques as well as complex integration path deformation for improved convergence. Since the asymptotic extraction causes a singularity in the origin of the wavenumber domain that is not annihilated by cartesian wavenumber integration, a special procedure for the treatment of this singularity is also introduced. The overall method needs very few sampling points for the numerical evaluation of the spectral integrals but is still applicable to very large structures as compared to the wavelength. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Characteristics of a Circular Patch Microstrip Antenna on Uniaxially Anisotropic Substrate

Resonant characteristics of a circular patch microstrip antenna on the uniaxially anisotropic substrate are determined via spectral domain analysis. Green's functions of the structure in Hankel transform domain are determined by using Hertz vector formulation. The variations in the resonant characteristics depending on the replacement of the isotropic substrate with the uniaxially anisotropic one are analyzed for different permittivity tensor element cases. The results of the study indicate that resonant frequency and bandwidth characteristics of the antenna can be considerably changed due to proper selection of substrate anisotropy ratio and other structural parameters. Depending on the arrived results, operational performance of the antenna will be improved in future studies.

Efficient numerical evaluation of superconducting microstrip structures with bianisotropic layers

An efficient procedure is developed for characterizing the frequency-domain behavior of superconducting microstrip planar structures with non conventional (bianisotropic) layers. Most of the frequency domain techniques in computational electromagnetics result in a matrix equation, which is solved at a single frequency. In the proposed technique, a rational function expansion around that frequency is applied to the matrix equation. This paper addresses three aspects in employing such an expansion: a) a generalization of the spectral domain analysis of superconducting patch antennas over bianisotropic layers, b) a robust and reliable estimation of confidence in the interpolated values, c) a criterion for selecting new sample frequencies. As a first numerical example, the radiation efficiency as a function of thickness for a copper and superconducting square patch antenna is presented.

New Method for the Efficient Summation of Double Infinite Series Arising From the Spectral Domain Analysis of Frequency Selective Surfaces

When the method of moments (MoM) in the spectral domain is applied to the analysis of frequency selective surfaces, the entries of the MoM matrix are slowly convergent double infinite series. In this paper, a two-step acceleration technique is developed which makes it possible the fast and accurate computation of these double series in the particular case where subsectional rooftops are used as basis functions. The technique is based on a combination of the use of Kummer's transformation, the use of Poisson's transformation, and the determination of judicious Chebyshev polynomial interpolations of some of the spectral discrete functions involved in the infinite series. The results obtained show that when all the double series of the MoM matrix are to be computed with an accuracy of three significant figures, the new acceleration technique turns out to be about one thousand times faster than brute-force computation, and a few times faster than the acceleration technique based on fast Fourier transform.

Spectral‐domain modeling of superconducting microstrip structures: Transmission lines and resonators

AbstractWe present a spectral‐domain analysis of thin superconducting microstrip structures in which the effects of superconducting materials, finite conductivity, and finite thickness are taken into account, using the concept of complex surface impedance. Numerical simulations showing variation of the propagation and attenuation characteristics of transmission lines and the quality factor of resonators with regard to temperature and frequency are presented. Some of the theoretical results are compared with the available data to document the validity of the approach. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 41: 55–59, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20045

방향 스펙트럼 파 해석을 위한 GUI 프로그램 개발

GUI program for analyzing directional spectrum waves is introduced in this paper Basically, MLM (Maximum Likelihood Method) was used for this program which was additionally consisted of performing spectral and time domain analysis for two dimensional irregular waves. Moreover, the directionality of directional spectrum waves generated by single summation and double summation method was investigated based on MLM. The directionality from each summation method has good agreement compared with that of target wave spreading function in the case of single wide directional spectrum waves. In addition to this, the resolution of directionality in double summation method was investigated as introducing coherence function between each wave component