Measured Reflection Coefficient Research Articles

Reduced-scale ultrasonic modelling of Rayleigh wave transmission over seismic barriers formed by periodic arrays of vertical holes

Seismic barriers are used widely to protect buildings from traffic-induced ground vibrations, mainly from propagating Rayleigh surface waves. Experimental investigations of real size seismic barriers at frequencies typical for traffic-induced ground vibrations, i.e. at 10-100 Hz, are costly and time consuming. In the present work, an alternative and much less expensive approach is proposed - a reduced-scale experimental modelling using ultrasonic Rayleigh wave propagation over very small-scale replicas of real seismic barriers. Experimental investigations of propagation of Rayleigh wave pulses with the central frequency of 1 MHz have been carried out for seismic barriers formed by periodic arrays of vertical holes in Aluminium samples. Measurements of transmission and reflection coefficients of Rayleigh waves for different types of arrays and for different incident angles have been carried out and compared with the earlier published results obtained for real seismic barriers.

Local Quasioptical Resonator Diagnostics of Semiconductor Wafers

The method of measurement of reflection coefficient behind an orifice in one of reflectors of the quasioptical open resonator is considered. According to the applied mathematical model, the method has the restriction which is consist in use of a short-wave approximation for the orifice size (it dimension is much more than a wavelength). For evaluation of limits of applicability of this method the experimental setup in the threecentimetric range of wavelengths consist of the quasioptical open resonator and the system of positioning of the measuring probe is created. By the experimental study of distribution of fields behind an orifice in the reflector of the open resonator it is found that the method, except restriction of mathematical model, has also restrictions, due to the wave’s interference, reflected from edges of this orifice. It causes a deviation from the uniform amplitude distribution of the field in an opening that can lead to increase in an error of a reflection coefficient measuring. It is also shown that by decrease of the sizes of an orifice formation of a bunch with small divergence, but with significantly more expressed distribution of the field localized about a bunch axis in an aperture is possible. It can be used for diagnostics of inhomogeneity of samples with higher locality.

Design and Characterization of Ultra-Wideband Horn Antenna in Quasi-TEM Mode

This paper describes the ultra-wideband horn antenna design operating in quasi TEM mode. The antenna consist of a triangular plate with an inclination angle above a ground plane and directly feed by a coaxial cable. Broadband characteristics, radiation pattern, high gain and small reflection coefficient were achieved. Its performance analysis and main parameters effects were obtained by using ANSYS HFSS software. In the numerical analysis, an optimized model was obtained in 1.57 to 12.85 GHz bandwidth a 11 to 14 dBi gain. The proposed antenna was manufactured and the measured reflection coefficient results show an operation frequency range between 1.48 and 10.12 GHz, agreeing very well with simulations.

3-D Microwave Holographic Imaging With Probe and Phase Compensations

A 3-D microwave holographic imaging algorithm compatible with reflection-coefficient measurement setup is proposed. It can be divided into four parts. First, starting from the open-circuit voltage of antenna, the algorithm compensates for both transmitting and receiving properties of the probe antenna, leading to antenna-independent least squares problems. However, the problems tend to be ill-conditioned. An auxiliary equation is thus derived and exploited to effectively improve the numerical stability and image quality. Third, to accurately locate the unknown target in range direction, a phase compensation method that requires only phase correction to the associated entries of the kernel matrix is proposed based on a simple ray model. Last, considering the finite size of the scanning aperture and beamwidth of the probe antenna, a numerical low-pass filter in the spatial-frequency domain is utilized to effectively locate the worth-solving area. For verification, a series of images reconstructed from the simulated and measured data using the proposed algorithm are presented. Thanks to the enhanced image quality, the geometry, location, and dielectric constant of the target can be retrieved. The range and cross-range resolutions achieved are about $\lambda /10$ and $\lambda /4$ , respectively.

Predicting the Frequency of Combustion Instability Using the Measured Reflection Coefficient through Acoustic Excitation

Predicting the Frequency of Combustion Instability Using the Measured Reflection Coefficient through Acoustic Excitation

Broadening the beam‐width of microstrip antenna by the induced vertical currents

In this study, a method to broaden the beamwidth of an aperture couple feed microstrip antenna is investigated. Two metal walls are put at the bilateral sides of an original microstrip antenna in the E -plane ( xoz -plane). The vertical current on the metal walls is induced by E -field from the horizontal current on the radiating patch of the microstrip antenna. The beamwidth of the antenna is broadened by both the horizontal and vertical currents. A novel wide beamwidth aperture couple feed microstrip antenna (WBMA) is designed according to the proposed method. The simulated and measured reflection coefficients and radiation patterns of the WBMA are presented and compared with the original microstrip antenna. Compared with the original microstrip antenna, the half-power beamwidth (HPBW) is obviously improved, which the HPBW is 236° in the E -plane and 124° in the H -plane at 9.0 GHz. Good radiation characteristics of the new structure antenna have been obtained in the whole operating frequency band.

Investigations on flexural wave propagation and attenuation in a modified one-dimensional acoustic black hole using a laser excitation technique

Abstract Acoustic Black Holes (ABHs), as a new type of passive structure for vibration damping enhancement and noise attenuation, have been drawing increasing attentions of many researchers. Due to the difficulty in manufacturing the sharp edges required by the ABH structures, it is important to understand the wave propagation and attenuation process in the presence of damping layers in non-ideal ABHs with a truncated edge. In this paper, an analytical expression of the wave reflection coefficient in a modified one-dimensional ABH is derived and a time-domain experimental method based on a laser excitation technique is used to visualize the wave propagation. In the experimental studies, the flexural waves in the ABH were excited by a scanning pulse laser and measured by a Laser Doppler Vibrometer (LDV). The incident wave and reflected wave were separated from the measured original wave field and the decrease of the wave velocity in the ABH was exhibited. The reflection coefficient was calculated from the ratio of the amplitude of the reflected wave to that of the incident wave for different ABH parameters and different thicknesses of the damping layer. The measured reflection coefficients were used to identify the unknown coefficients in the theoretical formula. The results confirm that there exists an optimal thickness for the damping layer, which leads to the minimum wave reflection. Based on the laser-induced visualization technique and various signal processing and feature extraction methods, the entire process of the wave propagation in a non-ideal one-dimensional ABH structure can be visualized and scrutinized.

Gain enhancement of the ultra-wideband tapered slot antenna using broadband gradient refractive index metamaterial

In this article, a broadband gradient refractive index (GRIN) metamaterial is designed and used to enhance the gain of the tapered slot antenna (TSA). The proposed GRIN is implemented using nonresonant parallel-line unit cell with different refractive index values. GRIN lens are placed in front of the tapered slot direction in the direction of x-axis. The designed GRIN metamaterials have broad bandwidth (2-12 GHz) characteristics due to the nonresonant parallel-line elements which is suitable for the ultra-wideband frequency band. The measurement results indicates that the radiated beam becomes more directive with narrow beam width. The measured reflection coefficient is below −10 dB over the frequency bandwidth of 3-11 GHz. The peak gain of TSA is obtained up to 14 dB at 10 GHz using GRIN lens.

Temperature dependence of dynamical permeability characterization of magnetic thin films using shorted microstrip line probe

A temperature dependence microwave permeability characterization system of magnetic thin film up to 10 GHz is designed and fabricated. This system can be used at temperatures ranging from room temperature to 200 °C, and is based on a shorted microstrip probe, which is made by microwave printed circuit board. Without contacting the magnetic thin films to the probe, the microwave permeability of the film can be detected without any limitations of sample size and with almost the same accuracy, as shown by comparison with the results obtained from a shorted microstrip transmission-line fixture. The complex permeability can be deduced by an analytical approach from the measured reflection coefficient of a strip line (S11) with and without a ferromagnetic film material on it. The procedures are the same with the shorted microstrip transmission-line method. The microwave permeability of an oblique deposited CoZr thin film was investigated with this probe. The results show that the room temperature dynamic permeability of the CoZr film is in good agreement with the results obtained from the established short-circuited microstrip perturbation method. The temperature dependence permeability results fit well with the Landau–Lifshitz–Gilbert equation. Development of the temperature-dependent measurement of the magnetic properties of magnetic thin film may be useful for the high-frequency application of magnetic devices at high temperatures.

A Reconfigurable MIMO Antenna System for Wireless Communications

A reconfigurable antenna system is proposed to improve data throughput limitations in multiple input multiple output wireless communication systems in this investigation. The 4×4 MIMO antenna is designed to operate in the 2.4 and 2.6 GHz for Wireless Local Area Network (WLAN) and Long Term Evolution (LTE) applications. The system's radiation pattern re-configurability is realized by using the microcontroller-driven PIN diode switching concept. Simulations and measurements exhibited good agreements for the single, 2×2 MIMO and 4×4 MIMO configurations. The antenna is operational between 2.387 to 2.628 GHz, while the simulated and measured reflection coefficients are at least −24.3 dB. All configurations produced a narrow beam forward radiation, while the envelope correlation coefficient (ECC) and diversity gain for the two MIMO configurations are below 0.5 and at least 9 dBi, respectively.

Wideband Matching of Full-Wavelength Dipole With Reflector for Base Station

This communication introduces a wideband hybrid feeding method for full-wavelength dipole antennas with a reflector. A full-wavelength dipole is designed to cover the band from 698 to 960 MHz for cellular base station applications. Its matching circuit consists of a triple-tuned circuit and a quasi-quarter-wavelength impedance transformer. The proposed matching circuit can provide balanced feeding as a balun and has a compact size. The working mechanism and a complete design scheme of the proposed matching circuit are elaborated. The matching circuit is designed and optimized using a circuit theory model and then physically realized using microstrip lines based on full-wave simulation. The measured reflection coefficient $|S_{11}|$ is lesser than −14 dB across the entire band from 698 to 960 MHz, exhibiting a bandwidth of 32%. This is the first time that a wideband center-fed full-wavelength dipole is proposed.

Compact, Frequency-Reconfigurable Filtenna With Sharply Defined Wideband and Continuously Tunable Narrowband States

A compact, frequency-reconfigurable filtenna with sharp out-of-band rejection in both its wideband and continuously tunable narrowband states is presented. It is intended for use in cognitive radio applications. The wideband state is the sensing state and operationally covers 2.35–4.98 GHz. The narrowband states are intended to cover communications within the 3.05–4.39 GHz range, which completely covers the Worldwide Interoperability for Microwave Access (WiMAX) band and the satellite communications C-band. A p-i-n diode is employed to switch between these wide and narrowband operational states. Two varactor diodes are used to shift the operational frequencies continuously among the narrowband states. The filtenna consists of a funnel-shaped monopole augmented with a reconfigurable filter; it has a compact electrical size: $0.235\lambda _{\textrm {L}} \times 0.392\lambda _{\textrm {L}}$ , where the wavelength $\lambda _{\textrm {L}}$ corresponds to the lower bound of its operational frequencies. The measured reflection coefficients, radiation patterns, and realized gains for both operational states are in good agreement with their simulated values.

Geoacoustic inferences from seabed reflection measurements on the New England mud patch

The vast majority of sediment acoustics research has been aimed at understanding propagation in granular (sandy) sediments. The focus of the ONR Seabed Characterization Experiment was to improve understanding of fine-grained/cohesive sediments. A variety of measurement techniques by various researchers were conducted to that end. Here, we report on initial results from broadband wide-angle reflection measurements at two sites, one with a ∼2 m “mud” layer thickness and the other ∼11 m thick. The measured reflection coefficient exhibits features that permit estimation of geoacoustic properties including the critical angle (with a rather weak frequency dependence, 200-2500 Hz) and interference patterns in frequency-angle space (which provide information on properties in individual layers). Modeling permits insight into the information content of the data and some initial estimates of the geoacoustic properties. [This research was funded by the Office of Naval Research, Ocean Acoustics Program.]

Flexible and reversibly deformable radio-frequency antenna based on stretchable SWCNTs/PANI/Lycra conductive fabric

We demonstrated a flexible and reversibly deformable radio-frequency antenna based on SWCNTs/PANI/Lycra conductive fabric and semipermeable film for wireless wearable communications applications. The conductive fabric fabricated by using the ‘dip and dry’ process exhibits good flexibility, electrical stability, stretchability and mechanical properties, and a high electrical conductivity (with low sheet resistance of ∼35 Ω/sq) was obtained based on the SWCNTs/PANI synergistic conductive network. The morphology of the semipermeable film was investigated to further illustrate the waterproof breathable features. Meanwhile, the modeling, fabrication procedure and radiating properties of the radio-frequency textile antenna worked at 2.45 GHz were systematically illustrated. The measured reflection coefficient, VSWR and the −10 dB bandwidth is ∼−18.6 dB, 1.58 and ∼270 MHz respectively, which agreed well with the simulation results. Furthermore, the results indicate that the design methodology for the radio-frequency textile antenna could have promising applications in flexible and reversibly deformable antennas for wearable wireless communications systems.

A Method of Measuring the S-parameters of Transistors on a Simulator-Analyzer of Amplifiers and UHF Self-Excited Oscillators

A method of measuring the S-parameters of transistors in the case of specified operating characteristics is proposed. The following techniques are considered: sequential normalization of the S-parameters relative to the natural impedance of a matched microstrip design calibrator used for additional calibration of a simulator-analyzer; measurement of the complex reflection coefficient and complex transmission coefficient of a transistor; and determination of the complex reflection coefficient of the matching circuits of a transistor. The flow diagram and a mathematical model of a simulator-analyzer are presented.

Nondestructive measurement of complex permittivity by a microwave technique: detection of contamination and food quality

In this paper, we interested of wideband measurement system that permits to characterize high- and low-loss materials according to physical and chemical properties of cheddar cheese and beef. The proposed measurements system, spanning a frequency range of 1–18 GHz, is constituted by one port junction of a small diameter ( mm, mm) coaxial probe and a standard rectangular waveguide. Theoretical reflection coefficient is obtained using the generalized equivalent circuit method that takes into account most of the involved physical phenomena. Thus, the effect of higher order modes as well as the dominant modes is considered. The complex permittivity of material is extracted by minimizing the difference between the theoretical and measured reflection coefficient. The complexity of the electromagnetic analysis does not allow to find an analytical relation between these two parameters. A computer code based on genetic algorithm is developed to numerically solve the inverse problem. To validate this program, we perform measurements on standard materials of known permittivity as air and FR4 (Flame Resistant 4) in the 1–18 GHz range.

Microstrip Spiral Resonator For Microwave-Based Gas Sensing

This paper presents the design of a new microstrip gas sensor based on a trapezoidal spiral resonator covered by a titanium dioxide nanoparticle layer. Reflection and transmission coefficient measurements between 1 and 8GHz revealed multiple resonances that can be used in the context of gas detection. The sensor response upon ammonia adsorption has been evaluated on the whole frequency span with a simple spectral analysis. Kinetic parameters such as response time, reversibility, and measurement stability have been determined with a monofrequential temporal analysis. The sensor showed at each resonance a good sensitivity to ammonia for concentrations between 50 and 300ppm, with a response time less than 1 min. The maximal response was reported at 7.76GHz with a reflection coefficient variation of 0.45dB after the injection of 300ppm of ammonia, which is 3.5 times higher than previously reported.

Monitoring of Microalgae Lipid Accumulation Using RF Open Ended Biosensor

This letter presents an original approach to monitor the lipid intracellular content of microalgae by the radio frequency (RF) analysis of the broadband dielectric characterization. This study shows that the lipid quantification can be deduced from the complex dielectric spectra properties extracted from the reflection coefficient ( S11 ) measurement. A calibration of the open-ended coaxial biosensor is performed using three different conditions (vacuum, water, and methanol) from which the complex dielectric behavior is well known. From the microalgae RF measurements, the complex permittivity spectrum of the biological samples is estimated up to 3 GHz. In this way, the microalgae lipid content and, thus, its state of accumulation can be further monitored using this RF biosensor.

Planar High-efficiency Antenna Array Using New Printed Ridge Gap Waveguide Technology

High-efficiency millimeter wave antenna array is proposed. A cooperate feeding network is designed using the new printed ridge gap waveguide technology, which is self-packaged with low loss. The feeding network is designed to couple to narrow slots arranged in a planar array that is coupled to printed broadband magnetoelectric (ME) dipoles. An array of $4 \times 4$ ME dipoles is designed. The simulated results are verified with measurements. The measured reflection coefficient is less than −10 dB over 16.5% bandwidth (28.8–34 GHz). The measured antenna gain is higher than 19 dBi, and the cross polarization measured gain is around −35 dB within the main beam. Furthermore, the measured total radiation efficiency is 70%, and the measured aperture efficiency corresponds to 90% at 30.2 GHz.

Compact uniplanar UWB MIMO antenna with band-notched characteristic

A compact uniplanar ultrawideband (UWB) multiple-input–multiple-output (MIMO) antenna with band-notched characteristic is presented in this paper. The antenna consists of two half circle-slot antennas serving as the radiators and a simple rectangular slot etched on the ground plane. The utilization of a half circle-slot antenna structure results in a significant size reduction compared with the traditional circle-slot antennas. A T-shaped open slot is employed to create a band rejection in WLAN 5.2 GHz. To enhance the port isolation, the back-to-back placement and a rectangular slot on the common ground are utilized. To verify the antenna performance, the proposed antenna is constructed. Over the UWB band of 3.1–10.6 GHz, the measured reflection coefficient is better than −10 dB and the port isolation less than −15 dB with a compact size of 33 × 26 mm2. In addition, the reasonable radiation pattern, gain, and ECC are also obtained.