Change In Reflection Coefficient Research Articles

Design of an ultrawideband conformal metal antenna

ABSTRACTIn this article, a novel design of volcano smoke antenna is proposed as an ultrawideband (UWB) conformal antenna. The radiating element and CPW feed line are in the same plane that makes the antenna completely planar. The proposed planar metal antenna is bent on a cylindrical surface, and the characteristics of the antenna for different bent conditions are studied. This study shows no significant change of reflection coefficient and radiation pattern characteristics of the bent antenna compared to that of flat position. The impedance bandwidth for S11 < −10 dB of the bent antenna covers the UWB (3.1–10.6 GHz). Variation of absolute gain and group delay of the antenna under flat and bent conditions are shown in this article. The measured reflection coefficient agrees with the simulated results. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:430–434, 2014

Exercise Central (Aortic) Blood Pressure Is Predominantly Driven by Forward Traveling Waves, Not Wave Reflection

Exercise hypertension independently predicts cardiovascular mortality, although little is known about exercise central hemodynamics. This study aimed to determine the contribution of arterial wave travel and aortic reservoir characteristics to central blood pressure (BP) during exercise. We hypothesized that exercise central BP would be principally related to forward wave travel and aortic reservoir function. After routine diagnostic coronary angiography, invasive pressure and flow velocity were recorded in the ascending aorta via sensor-tipped intra-arterial wires in 10 participants (age, 55±10 years; 70% men) free of coronary artery disease with normal left ventricular function. Measures were recorded at baseline and during supine cycle ergometry. Using wave intensity analysis, dominant wave types throughout the cardiac cycle were identified (forward and backward, compression, and decompression), and aortic reservoir and excess pressure were calculated. Central systolic BP increased significantly with exercise (Δ=19±12 mm Hg; P<0.001). This was associated with increases in systolic forward compression waves (Δ=12×10(6)±17×10(6) W·m(-2)·s(-1); P=0.045) and forward decompression waves in late systole (Δ=9×10(6)±6×10(6) W·m(-2)·s(-1); P<0.001). Despite significant augmentation in BP (Δ=9±6 mm Hg; P=0.002), reflected waves did not increase in magnitude (Δ=-1×10(6)±3×10(6) W·m(-2)·s(-1); P=0.2). Excess pressure rose significantly with exercise (Δ=16±9 mm Hg; P<0.001), and reservoir pressure integral fell (Δ=-5×10(5)±5×10(5) Pa·s; P=0.010). Change in reflection coefficient negatively correlated with change in central systolic BP (r=-0.68; P=0.03). We conclude that elevation of exercise central BP is principally because of increases in aortic forward traveling waves generated by left ventricular ejection. These findings have relevance to understanding central BP waveform morphology and pathophysiology of exercise hypertension.

On the stability of optical properties of antireflection coatings for solar cells based on a silicon-silicon-oxide mixture

It is investigated how the storage duration influences the optical properties of antireflection coatings based on silicon-silicon-oxide mixture intended for silicon solar cells. It is shown that the spectral reflection coefficient changes by 2.7% for 22 years; i.e., the antireflection effect is retained. We draw the conclusion that coatings based on silicon-silicon-oxide mixture can greatly increase the lifetime of solar cells and a solar battery.

The Research of Acoustic Characteristic from a Submerged Viscoelastic Functionally Graded Materials

In this paper, we designed a FGM which can be used as the cover of underwater target and research its mid-low frequency acoustic characteristic just as reflection and absorption coefficient. Based on transfer matrix method, we research the FGM acoustic reflection and absorption coefficient change with the variation of constituent material property, number of hierarchy, and volume fraction. We found that its reflection and absorption coefficient are determinated by material property and volume fraction, and could be equivalent to multi-layer composite structure with specific number of layers to address acoustic problems. If elastic layer added, both acoustic characteristic and mechanics characteristic could be improved, which contributes to the research and design of structure/acoustic stealth FGM.

Label-free DNA microarray bioassays using a near-field scanning microwavemicroscope

A near-field scanning microwave microscope (NSMM) is used to readout and visualize homemade 10-mer oligonucleotide microarrays and an Agilent 60-mer DNA microarray as a realistic test of NSMM applicability to multiplexed sequence analysis. Sensitive characterization of DNA coverage and high resolution mapping of DNA spots in the microarray were realized by measuring the change of microwave reflection coefficient (S11) at about 4GHz operating frequency. Hybridization between target (free) and capture (immobilized) sequences leads to changes in the microwave reflection coefficient, which were measured by the NSMM. These changes are caused by hybridization-induced modification of the dielectric permittivity profile of the DNA film. The dynamic range based on analysis of the 10-mer microarrays is over 3orders of magnitude with the detection limit estimated below 0.01strands/μm2. The NSMM method should be readily capable of detecting target coverages down to 98% of probe coverage. We also directly image the patterned DNA microarray by NSMM with a 2μm resolution. The complementary optical image of the DNA microarray visualized by using a relative fluorescent intensity metric agrees well with the NSMM results.

Effect of stress on reflection and refraction of plane wave at the interface between fluid and stressed rock

Reflection and refraction of plane wave through an interface between fluid and rock with elastic deformations on the basis of the acoustoelastic theory are considered. The effects of stress on the anisotropy and energy reflection and transmission coefficients are investigated. The incident wave plane can coincide with or deviate from planes of material symmetry. Elastic deformations are assumed to be locally homogeneous and to satisfy static boundary conditions. Numerical computations are carried out and comparisons are made with the results predicted in the presence and absence of initial stress. The changes in phase velocity, group velocity, and energy reflection and refraction coefficients due to the presence of stress are displayed graphically and discussed. The results show that the effect of stress depends on its magnitude, direction and form (uniaxial and biaxial).

Scattering and embedded trapped modes for an infinite nonhomogeneous Timoshenko beam

We consider an infinite Timoshenko beam whose density is weakly perturbed on a finite interval. The plane waves of the unperturbed system form the continuous spectrum, which has multiplicity 2 for \({0 \omega^2_0}\) (here \({\omega}\) is the frequency and \({\omega_0}\) is the cut-off frequency). The first branch of the spectrum (the flexural mode) corresponds to the range \({\omega^2 >0 }\), and the second (the shear mode) to the range \({\omega^2>\omega_0^2}\). The perturbation gives rise to a resonance (a pole of the analytic continuation of the reflection coefficient of the corresponding scattering problem) in a neighborhood of the point β = 0, where \({\beta^2=\omega_0^2-\omega^2}\), in the complex plane of the parameter β. When the pole is real and positive, it becomes an eigenvalue of the problem. It turns out that this is the case for certain perturbations (e.g., a square barrier of certain length); the pole then defines an eigenvalue (a trapped mode) embedded in the continuous spectrum of the first branch. When the conditions for the existence of an eigenvalue are not satisfied, the reflection coefficient changes abruptly in a neighborhood of the real part of the pole, rapidly growing from almost zero to almost one and then back to zero, as β passes through the resonant value, according to a formula of Breit–Wigner type familiar from quantum mechanics.

Detection of DNA-Hybridization Using a Near-Field Scanning Microwave Microscope

A near-field scanning microwave microscope (NSMM) is used to detect sequence-specific hybridization between surface-immobilized and free DNA single strands. Hybridization between target (free) and capture (immobilized) sequences leads to changes in the reflection coefficient (S11) which are measured by the NSMM. These changes are caused by hybridization-induced modification of the dielectric constant profile of the DNA film. NSMM instrumentation does not require labeling of target sequences with fluorophores or other tagging groups. The physical basis of reflection coefficient changes underpinning the NSMM approach is discussed.

Application of Generalized EPR Entangled State in Quantum Teleportation

We show how the generalized EPR entangled state |η,θ〉 generated by an asymmetric beamsplitter can be directly applied to quantum teleportation to make detailed analysis and calculation. In the whole process of teleportation, the entanglement source is more flexible with the change of transmission and reflection coefficients of the beam splitter. When the squeezed state of |η,θ〉 is used as quantum channel, the fidelity depends on the degrees of squeezing for entanglement and the reflection coefficient. Our calculation has been greatly simplified by using the Schmidt decomposition of |η,θ〉.

Characterization of magnetoresistance hysteresis of Permalloy thin-film using near-field microwave microscope

A near-field scanning microwave microprobe (NSMM) technique has been used to investigate the magnetic properties of the Permalloy (Ni 81Fe 19) thin film. To characterize the hysteresis behavior of the magnetoresistance (MR) of Permalloy (Py) thin films, the microwave reflection coefficient, S 11 was measured. The change of the estimated MR was observed under in-plane external magnetic fields, and was confirmed with variation of MR measured by the 4-probe method. The magnetic properties of the Py thin film were examined by a vibrating sample magnetometer. The observed MR was correlated with the changes of the relative magnetic permeability, Δ μ of the Py. We also directly imaged the Py thin film changes by NSMM. MR of Py was determined from the visualized microwave reflection coefficient changes Δ S 11 at the thin film interface with high sensitivity. The present methodology can be extended to investigations of other magnetic thin films or magnetic materials using the NSMM system.

Improving Backscatter Radio Tag Efficiency

This paper studies tag properties for optimized tag-to-reader backscatter communication. The latter is exploited in RF identification (RFID) systems and utilizes binary reflection coefficient change of the tag antenna-load circuit. It is shown that amplitude maximization of complex reflection coefficient difference between the two states is not sufficient for optimized tag-to-reader backscatter communication, contrary to what is commonly believed in the field. We provide a general tag load selection methodology that applies to any tag antenna, including minimum scattering antennas as a special case. The method is based on tag antenna structural mode closed-form calculation (given three values of tag radar cross section), employs simple antenna/communication theory, and applies to both passive, as well as semipassive RFID tags.

Optical metrology of Ni and NiSi thin films used in the self-aligned silicidation process

The thickness-dependent optical properties of nickel metal and nickel monosilicide (NiSi) thin films, used for self-aligned silicidation process, were characterized using spectroscopic ellipsometry. The thickness-dependent complex dielectric function of nickel metal films is shown to be correlated with the change in Drude free electron relaxation time. The change in relaxation time can be traced to the change in grain boundary (GB) reflection coefficient and grain size. A resistivity based model was used as the complementary method to the thickness-dependent optical model to trace the change in GB reflection coefficient and grain size. After silicidation, the complex dielectric function of NiSi films exhibit non-Drude behavior due to superimposition of interband absorptions arising at lower frequencies. The Optical models of the complete film stack were refined using x-ray photoelectron spectroscopy, Rutherford backscattered spectroscopy, and x-ray reflectivity (XRR).

Preliminary Study of Coagulation Monitoring by Antenna for Treatment during Microwave Coagulation Therapy

Microwave coagulation therapy (MCT) has been employed mainly for treatment of small size tumors. In the treatment, thin microwave antenna is inserted into the tumor and microwave energy heats up the tumor up to at least 60°C for generation of enough coagulated volume including the target tumor. During the microwave radiation, reflection coefficient of treatment antenna changes significantly. In this paper, possibility of coagulation monitoring was found observing the reflection coefficient change of the antenna by numerical calculations and measurements.

Preliminary Study of Coagulation Monitoring by Antenna for Treatment during Microwave Coagulation Therapy~!2009-09-07~!2009-12-29~!2010-02-04~!

Microwave coagulation therapy (MCT) has been employed mainly for treatment of small size tumors. In the treatment, thin microwave antenna is inserted into the tumor and microwave energy heats up the tumor up to at least 60°C for generation of enough coagulated volume including the target tumor. During the microwave radiation, reflection coefficient of treatment antenna changes significantly. In this paper, possibility of coagulation monitoring was found observing the reflection coefficient change of the antenna by numerical calculations and measurements.

RTM法によるFRP成形における電磁超音波センサを用いた樹脂硬化モニタリング

Electromagnetic acoustic transducer (EMAT) is applied to resin cure monitoring in manufacturing process of fiber reinforced plastic (FRP) by resin transfer molding (RTM) method. The RTM is suitable for fabrication of FRP products of three-dimensional complex shape. In order to reduce the cost by minimizing the cycle time, cure monitoring is required. Authors have already ensured that the EMAT can detect the resin flow front in RTM process by monitoring the change in reflection coefficient at mold surface due to resin impregnation. The reflection factor is also affected by the resin viscosity. In this study, during the curing process, we measure the attenuation coefficient of standing wave introduced in the mold. Results are compared with impedance of dielectric sensor located inside the mold, showing that the degree of cure can be evaluated by EMAT at outer surface of the mold.

Direct imaging of photoconductivity of solar cells by using a near-field scanning microwave microprobe

A near-field scanning microwave microprobe (NSMM) technique has been used to investigate the photovoltaic effect in solar cells. As the photoconductivity of the n-type silicon layer in the solar cells was varied due to the incident light intensities and the wavelength, we could directly observe the photoconductivity changes inside the solar cells by measuring the change of reflection coefficient S11 of the NSMM at an operating frequency near 4.1 GHz. We also directly imaged the photoconductivity changes by NSMM. Photoconductivity in solar cells is determined from the visualized microwave reflection coefficient changes at the interfaces with high sensitivity.

Transmission and Reflection Coefficients for Damage Identification in 1D Elements

According to the latest research results presented in the literature changes in propagating waves are one of the most promising parameters for damage identification algorithms. Numerous publications describe methods of damage identification based on the analysis of signals reflected from damage. They also include complicated signal processing techniques. Such methods work well for damage localisation, but it is rather difficult to use them in order to estimate the size of damage. It is natural that propagating wave reflects from any structural discontinuity. The bigger the disturbance the bigger part of a propagating wave reflects from it. The amount of energy reflected and transmitted through any discontinuity can expressed as reflection and transmission coefficients. In the literature different application for these coefficients may be found – the most often cited application is connected with localising changes in the geometry of structures. Changes in the coefficients due to cross section variations in rods and beams or due to existence of stiffeners in plates are well documented. However there are no application of using the reflection and transmission coefficients for damage size identification. For this reason the analysis presented in this paper has been carried out. The article presents a method of damage identification in 1D elements based on the wave propagation phenomenon and changes in reflection and transmission coefficients. The changes in transmission and reflection coefficients for waves propagating in isotropic rods with different types of damage have been analysed. The rods have been modelled with the elementary, two and three mode theories or rods. For numerical modelling the Spectral Finite Element Method has been used. Several examples are given in the paper.

Characterization of self-assembled monolayers by using a near-field microwave scanning microprobe

A near-field microwave scanning microprobe (NSMM) technique has been used to investigate the material properties of n-alkanethiol self-assembled monolayers (SAMs) on a gold (Au) surface. We demonstrate that near-field microwave probing technique can achieve the noncontact detection of the thickness of SAMs by measuring the microwave reflection coefficient S 11 at an operating frequency near 5.3 GHz. We also directly image the patterned SAMs by NSMM. The thickness (chain length) of SAMs is determined from the visualized microwave reflection coefficient changes on the Au surface with high sensitivity. This nano-scale measurement of SAMs has a great potential for investigating the surface profile with high sensitivity.

Hard disk magnetic domain nano-spatial resolution imaging by using a near-field scanning microwave microscope with an AFM probe tip

A near-field scanning microwave microscope (NSMM) incorporating an atomic force microscope (AFM) probe tip was used for the direct imaging of magnetic domains of a hard disk under an external magnetic field. We directly imaged the magnetic domain changes by measuring the change of reflection coefficient S 11 of the NSMM at an operating frequency near 4.4 GHz. Comparison was made to the magnetic force microscope (MFM) image. Using the AFM probe tip coupled to the tuning fork distance control system enabled nano-spatial resolution. The NSMM incorporating an AFM tip offers a reliable means for quantitative measurement of magnetic domains with nano-scale resolution and high sensitivity.

Investigation of photoconductivity of silicon solar cells by a near-field scanning microwave microscope

The photovoltaic effect in silicon solar cells were investigated by using a near-field scanning microwave microscope (NSMM) technique by measuring the microwave reflection coefficient at an operating frequency near 4 GHz. As the photoconductivity in the solar cells was varied due to the incident light intensities and the wavelength, we could observe the photoconductivity changes at heterojunction interfaces inside the solar cells by measuring the change of reflection coefficient S 11 of the NSMM. By measuring the change of reflection coefficient, we also directly imaged the photoconductivity changes at heterojunction interfaces inside the solar cells.