Amplitude Of Reflection Coefficient Research Articles

Interdigitated-comb piezoelectric phononic crystals for innovative SAW devices

In this paper, piezoelectric phononic crystals made up of interdigitated combs in floating potential condition are studied. Calculation of the dispersion curves shows that, in addition to Bragg bandgaps due to the presence of periodic electrodes, supplementary bandgaps are present corresponding to electrical resonance/antiresonance of the comb pairs. Calculation of the reflection coefficient of finite-sized mirrors reveals the presence of high amplitude reflection coefficient lobes near these bandgap frequencies. The electrical response of single port resonators using these interdigitated comb mirrors fabricated with Al metallization on LiTaO3 POI substrate is contrasted with that of a resonator with classical mirrors, providing experimental verification of this mechanism for bandgap opening. Possible applications for SAW device design are finally discussed.

WITHDRAWN: Perfect asymmetric transmission for linear polarization in background reflection-free bilayer dielectric metasurfaces

In spite of the importance of asymmetric transmission (AT) with near-unity value and significantly high contrast of transmission, such a perfect AT has not yet been realized in reciprocal systems. For single resonance, it is already known that the upper limit of AT is identical to the background amplitude reflection coefficient. Nevertheless, if multiple resonances simultaneously contribute to AT, their coherent coupling enables us to obtain perfect AT, even when background reflection completely vanishes. Taking bilayer dielectric metasurfaces composed of orthogonal silicon nanorods embedded in silica glass as examples, here we show that perfect AT can be realized for linear polarization with characteristics comparable with bulky optical isolators based on Faraday effect: AT of 0.9994 with dramatically high contrast 35.1dB at telecom wavelength, the spectral position of which is tunable by properly changing the structural parameters. The analytical model based on the quasinormal-mode expansion well agrees with numerical results, revealing the concurrent contributions of multiple resonances. The presented perfect AT has the advantages of excellent performances of AT and compact structures without bulky devices for field bias or temporal modulations, enabling practical applications for optical computing, high-contrast polarization multiplexing and conversion.

Design and analysis of a metamaterial based biosensor to determine blood glucose concentration

In this paper, a biosensor utilizing metamaterials is designed and simulated to detect blood glucose concentration. The proposed sensor comprised of a microstrip patch antenna designed on a Rogers RT5880 substrate. A circular-shaped complementary split ring resonator (CSRR) cell is integrated onto the patch of the antenna which acts as the sensing region. The sensor is analyzed in order to ascertain the blood glucose concentration ranging from 50-300 mg/dL in a human finger model. The sensing parameter is amplitude of reflection coefficient, which exhibits variation in response to alterations in the dielectric characteristics of the sample being tested. The Cole-Cole relaxation model is employed to predict the dielectric properties of different finger tissues. An analysis of the characteristics of the CSRR was conducted to illustrate its significance in the realm of glucose detection. The glucose level is determined through the utilization of a linear regression model that describes the relationship between the reflection coefficient of the sensor and glucose level. The sensor demonstrates an impressive sensitivity of 1.792 dB per (mgdL<sup>-1</sup>) and has the ability of determining glucose levels with a good accuracy, as verified by the application of Clarke error grid. This sensor exhibits enhanced performance compared to some other recent glucose sensors.

An accurate measurement method for center oil film thickness in high-speed roller bearing using ultrasound

A multicycle focal spot mapping method is proposed to design the specific pulse emission frequency and the recorded pulse number. A great number of successive ultrasonic pulses with a specific emission frequency are utilized to examine the lubricant film in the roller bearing so that at least one ultrasonic pulse will interrogate the center of the contact region. Subsequently, the center oil film thickness is calculated by the selected minimum ultrasonic reflection coefficient amplitude. A statistical test analysis and an experimental analysis are performed to validate the proposed method. The results show that the proposed method can be used to accurately measure the center oil film thickness in high-speed roller bearings, which overcomes the speed limitation of the existing method.

Measurement of coating–substrate interface stiffness using a constructed ultrasonic echo phase derivative spectrum

Measurement of coating–substrate interface stiffness can indirectly characterize interface bonding quality. This paper proposes a noval quantitative inversion coating–substrate interface stiffness method based on the multi-resonance frequencies of a constructed ultrasonic echo phase derivative spectrum (UEPDS). The theoretical relationship between UEPDS resonance frequencies and interface stiffness is derived. The detection frequency and high-sensitivity interface stiffness range are optimized based on the sensitivity analyzed. Numerical simulation and experiment are implemented on a 0.48 mm aluminum layer/carbon steel substrate specimen to prove the validity of the proposed ultrasonic method. The simulation results show that the maximal relative error between the inversion and the preset interface stiffnesses is reduced from 23% to 8% compared with the traditional ultrasonic reflection coefficient amplitude spectrum-based (URCAS-based) method. The experiment results indicate that the UEPDS-based inversion interface stiffnesses have the same trend as the nominal contact pressures between the coating–substrate interface.

Near-unity asymmetric transmission of linearly polarized light with high Q-factor based on the coherent coupling of dual resonances in bilayer dielectric chiral metasurfaces

This report shows that near-unity asymmetric transmission (AT) of linearly polarized light with high Q-factor can be realized in bilayer dielectric chiral metasurfaces, the unit cell of which consists of silicon slab with rectangular holes on its both sides which are arranged perpendicularly to each other. The preceding work has revealed that the theoretical upper limit of the AT is given as the amplitude reflection coefficient of background system without nanostructure, when a single resonance mainly contributes. If double resonances with overlapping spectral shapes concurrently contribute to the AT, however, their coherent coupling enables breaking the above upper limit and near-unity AT can be obtained. As one of the contributing resonances in the metasurface is quasi-BIC, the resultant AT has also high Q-factor in addition to the near-unity value. Thus, the presented photonic system exhibits highly efficient asymmetric third-harmonic generation behavior, which has the efficiency ratio between forward and backward pumping in the orders from several hundreds to thousands. High-Q near-unity AT shown in this work will find practical applications for direction-dependent nonlinear frequency conversion, information processing, optical sensing, and polarization multiplexing.

Characterization and analysis of attenuation anisotropy in viscoelastic vertical transverse isotropic media

AbstractDue to the intrinsic attenuation of the earth, the study of wave propagation characteristics, considering seismic attenuation plays an important role in high‐precision reservoir prediction. Therefore, we investigate the propagation and reflection characteristics of seismic waves in viscoelastic vertical transverse isotropic media in the complex frequency domain. Specifically, we analyse the response characteristics of velocity, propagation vector and attenuation vector with respect to viscosity media with different attenuation intensities. Furthermore, based on the quasi‐Zoeppritz equation, the variation of reflection coefficient amplitude with offset at different attenuation angles and different attenuation intensities is studied. We also compare the trends in the amplitude variation of reflection coefficients with offset in elastic isotropic, elastic anisotropic and viscoelastic anisotropic media. Due to the complexity of the exact reflection coefficient expression, we first propose the approximate expression of the attenuation–anisotropy parameters and then derive the approximate expression of the reflection coefficient. The numerical simulation results show that the approximate expression of the reflection coefficient is still accurate, even in media with strong anisotropy. Finally, the accuracy evaluations of the reflection coefficient formulas using four typical theory models demonstrate that the approximate reflection coefficient formulas are highly accurate in both weak and strong anisotropic media.

A sensitivity-improved amplitude method for determining film thickness based on the partial reflection waves

A sensitivity-improved reflection coefficient amplitude method for determining wide-range lubricating oil film thickness is proposed based on partial reflection waves, which are obtained by removing the first reflection wave. Numerical analysis and experimental testing are conducted to verify the proposed method. The results show the lubricating oil film thickness ranging from the spring model region to the resonant region can be calculated based on the proposed partial-wave reflection coefficient amplitude method. In comparison to the existing reflection coefficient amplitude method, the measurement accuracy of the lubricating oil film thickness is significantly improved for the transition region which locates between the spring model region and the resonant region, for instance, the observed maximum relative error is decreased to 9% from 60%.

Sensitivity evaluation of miniature microstrip line‐based sensors using multiple sensing parameters for non‐invasive blood glucose monitoring

AbstractA number of high‐sensitivity microwave sensors with compact resonators are designed, fabricated, and tested for non‐invasive blood glucose monitoring. In the first step, a split ring resonator (SRR)‐based sensor is designed, and then it’s sensing parameters, viz. the reflection coefficient magnitude and phase coupled with its input impedance, are extracted and calibrated by different glucose solutions. The results of this structure are subsequently saved as a reference sensor. During the second step, the swastika‐shaped and electric‐LC (ELC) geometries are substituted for the SRR to enhance the sensitivity of the reference sensor, and the sensing parameters of these structures, which are sensitive to the glucose solutions, are obtained. In the third step, the sensitivity of the three proposed designs is calculated and compared, using the reflection coefficient amplitude, phase, and input impedance. The comparisons typically demonstrate that the sensitivity of the swastika‐shaped structure is equal to 148.367 (Ω/mgmL−1) if the sensitivity is acquired from the imaginary part of the input impedance, which is better than the SRR and ELC geometries. On the contrary, the sensitivity of the SRR geometry is at a maximum and equal to 16.79 (deg/mgmL−1) if the sensitivity is calculated in terms of the reflection coefficient phase.

The Effect of Random Characteristics of Ionosphere on the Propagation of ELoran Sky Waves

In this study, the effect of random characteristics of the ionosphere on the enhanced Loran (eLoran) sky-wave signal was analyzed. First, the bilinear transform stochastic finite-difference time-domain (S-BT-FDTD) method in layered half-space isotropic plasma is derived, and the correctness of the calculation of the mean value and standard deviation of the field components of the eLoran sky-wave signal is verified. Second, the mean value and standard deviation of the amplitude and time delay of the eLoran sky-wave signal were analyzed by combining the International Reference Ionosphere, pseudo-1-D BT-FDTD method, and Monte Carlo method. The simulation results show that the mean value of the amplitude of the reflection coefficient amplitude (RA) in the eLoran signal bandwidth remains unchanged. The larger the standard deviation of the electron density, the larger is the standard deviation of RA. The standard deviation of RA during the day is greater than that at night. The mean value of the time delay remains unchanged, and the standard deviation of the time delay is related to the way the electron density varies randomly. When the incident angle increases, the RA increases, the standard deviation of RA decreases, the time delay decreases, the standard deviation of the time delay decreases, and the signal becomes more stable.

Four-wave mixing on thermal and resonant nonlinearities with feedback for object and signal waves

Background. The need to create highly efficient four-wave radiation converters in order to use them in adaptive optics systems, for real-time processing of complex spatio-temporal fields, in interferometry, quantum cryptography, etc. requires along with the use of traditional methods to increase the efficiency of such converters by increasing the interaction length, radiation power density, effective value of the nonlinear susceptibility of the development of new methods. One of these methods is a method based on the imposition of feedback on one or more interacting waves. Aim. The influence of feedback on the amplitude reflection coefficient of the degenerate four-wave radiation converter on thermal and resonant nonlinearities has been considered. Methods. The amplitude reflection coefficient of a degenerate four-wave radiation converter on thermal and resonant nonlinearities in the presence of feedback for both object and signal waves has been analyzed by a numerical method based on the multiple passage of the signal and object waves of the nonlinear layer in the ring resonator. Results. It was shown, that the difference in the reflection coefficients in the presence and absence of feedback for both object and signal waves increase monotonically with a growth in the pumping waves intensity and does not depend on the parameter characterizing the relationship between thermal and resonant nonlinearities at the approximation of a small reflection coefficient. Conclusion. The range of values of the absorption coefficient in which the imposition of feedback for both object and signal waves leads to an increase in the efficiency of the four-wave radiation converter has been established.

Identification of the Damages and Abnormal Objects in Tibetan Stone Walls Based on GPR Data Analysis

ABSTRACT Based on the amplitude attribute analysis of ground penetrating radar (GPR) data, this paper applies GPR to the identification of internal damages and abnormal objects in stone walls of Tibetan ruins. The corresponding relationship between the characteristics of internal damages and abnormal objects and the radar data is explored through the Tibetan stone walls (TSWs) simulation test. The identification of location and size of the damages and abnormal objects in TSWs is realized based on the Mahalanobis distance abnormal data discrimination method. Using the normal distribution and the noncentral chi-square distribution, the identification law of types of the damages and abnormal objects is constructed, which takes root mean square (RMS) amplitude and interface reflection coefficient as the characteristic values. The field detection results of TSWs at three Tibetan sites are taken as an extension and supplement to the simulation results, and a set of identification atlas for the location, size and type of the internal damages and abnormal objects in TSWs is established. The application results of the identification atlas were verified by the field detection and the results show that the atlas has a high accuracy, which can significantly improve the efficiency of the identification, and can provide a basis for the performance research, protection and maintenance of TSWs.

Design and Implementation Unit Cell for 6G Reconfigurable Intelligent Surface Application

This article presents a model through which the reflection coefficient amplitude as well as phase of reflective intelligent surfaces can be estimated accurately. The reconfigurability of the surface was achieved by incorporating the varactor diodes into the surface of the cell unit. The manipulation of the phase of the reflection coefficient can be achieved by making adjustments to the biasing state of the varactors. The model, which makes use of a physics-based methodology and is based on a transmission-line circuit description of the Reconfigurable Intelligent surfaces (RIS) unit cells, considers every pertinent electrical and geometrical characteristics of the proposed surface. With the method proposed in this paper, fast and accurate RIS-based communication lines can be created. The recommended accuracy of the proposed method was confirmed through the use of a CST microwave studio full-wave simulations.

Ultrasonic in-situ measurement method and error analysis of wear of PEEK water-lubricated bearing materials

Water-lubricated polymer bearing is the key component to guarantee the function of ship propulsion systems, nuclear main pumps, hydraulic turbines and other important equipment. Abnormal wear of the water-lubricated polymer thrust bearing is a common failure under harsh working conditions such as low speed, heavy load, and sediment. Accurate acquisition of bearing wear is of great value for revealing the bearing wear mechanism and evaluating the bearing service life. Therefore, this paper proposes an in-situ measurement method of bearing wear based on ultrasound and parameter inversion. The objective function is defined as the correlation coefficient of the ultrasonic reflection coefficient amplitude spectrum. Different parameters, such as thickness, acoustic velocity, density and attenuation factor, are inverted by the particle swarm algorithm. Simulations are performed to analyze the influence of single-parameter to multi-parameter inversions on the objective function and the inversion of thickness. Taking the PEEK material as the subject, the experiment shows that the parameter inversion of thickness, density and attenuation factor has the highest accuracy, with errors within 0.15%, 2% and 95%, and the maximum absolute error of wear is 20 μm. If the amplitude of the reflected signal is small, the intensity of the transmission signal will affect the identification result of thickness.

A wear monitoring method and influencing factors of water-lubricated polymer bearings based on improved ultrasonic reflection coefficient amplitude spectrum and ultrasonic reconfiguration calculation

The water-lubricated thrust bearings of the marine Rim-Driven Thruster (RDT) are usually composed of polymer composites, which are prone to serious wear under harsh working conditions. Ultrasonic is an excellent non-destructive monitoring technology, but polymer materials are characterized by viscoelasticity, heterogeneity, and large acoustic attenuation, making it challenging to extract ultrasonic echo signals. Therefore, this paper proposes a wear monitoring method based on an improved ultrasonic reflection coefficient amplitude spectrum, introducing an ultrasonic transfer function to mathematically resolve the attenuation coefficients in the propagation model, and using a differential evolutionary algorithm to invert the thickness, sound velocity, density, and attenuation coefficients of polymer bearings simultaneously. The effects of different influencing factors on the ultrasonic signal and identification results are explored, including probe contact pressure, surface roughness and surface inclination; In order to remove the influence of water film overlap on the identification of polymer bearing thickness, a water film separation method based on time-frequency domain ultrasonic reconfiguration is proposed to construct the ultrasonic theoretical time domain waveform of the bearing. An ultrasonic wear measurement system is built to record the ultrasonic echoes of PEEK test blocks with different pressures to the probe, surface roughness, and tilt angles. The experiment is carried out on the water film calibration test rig, using a high-precision spiral micrometer to simulate the mixing of water films of different thicknesses with polymer test block and collecting ultrasonic signals. The results show that the method has a thickness identification error of approximately 0.5% for PEEK specimens with different probe contact pressure, roughness, and tilt angle, and the reconfiguration thickness identification error is less than 1% for the full range of water film overlap.

Second-Order Statistics for IRS-Assisted Multiuser Vehicular Network With Co-Channel Interference

In this paper, we consider a downlink multi-user vehicular communication network empowered by an intelligent reflecting surface (IRS) with the base station (BS) employing the orthogonal frequency division multiple access (OFDMA) scheme. The performance of the considered system is evaluated in terms of second-order statistics (SOS) in the presence of multiple co-channel interferers with varying powers and speeds. In particular, we develop the analytical expressions of level crossing rate (LCR) and average outage duration (AOD) of the received signal envelope at a desired vehicle by considering a generalized fading model as - distribution. The impact of various system and channel parameters such as number of reflecting elements, amplitude of reflection coefficients, number of interferers, Doppler frequencies of desired and interfering vehicles, and different channel fading environments has been shown on the LCR and AOD performances. Moreover, we derive an expression for asymptotic LCR under high transmit power conditions. It has been shown that the asymptotic LCR is independent of the threshold and transmit power. In addition, we consider a stop and wait automatic repeat request (SW-ARQ) protocol for reliable data packet transmission and derive the expressions for packet error rate (PER) and throughput by utilizing the finite-state Markov channel (FSMC) model. The optimal packet length is also determined which maximizes the throughput under SW-ARQ protocol. The impact of various system parameters is also shown on the PER and throughput performances.

Wear monitoring method of water-lubricated polymer thrust bearing based on ultrasonic reflection coefficient amplitude spectrum

The water-lubricated thrust bearings of the marine rim-driven thruster (RDT) are usually composed of polymer composites, which are prone to serious wear under harsh working conditions. Ultrasonic is an excellent non-destructive monitoring technology, but polymer materials are characterized by viscoelasticity, heterogeneity, and large acoustic attenuation, making it challenging to extract ultrasonic echo signals. Therefore, this paper proposes a wear monitoring method based on the amplitude spectrum of the ultrasonic reflection coefficient. The effects of bearing parameters, objective function, and algorithm parameters on the identification results are simulated and analyzed. Taking the correlation coefficient and root mean square error as the matching parameters, the thickness, sound velocity, density, and attenuation factor of the bearing are inversed simultaneously by utilizing the differential evolution algorithm (DEA), and the wear measurement system is constructed. In order to verify the identification accuracy of this method, an accelerated wear test under heavy load was executed on a multi-functional vertical water lubrication test rig with poly-ether-ether-ketone (PEEK) fixed pad and stainless-steel thrust collar as the object. The thickness of pad was measured using the high-precision spiral micrometer and ultrasonic testing system, respectively. Ultimately, the results demonstrate that the thickness identification error of this method is approximately 1%, and in-situ monitoring ability will be realized in the future, which is of great significance to the life prediction of bearings.

Identification interface stiffness of coating/substrate structure based on ultrasonic pressure reflection coefficient amplitude spectrum

Due to the variation of interface stiffness, interface morphology, and testing frequency, coating/substrate interface stiffness identified through ultrasonic methods are usually non-unique and inaccuracy. This paper, a method for quantitative inversion interface stiffness of coating/substrate structure is proposed based on a constructed ultrasonic pressure reflection coefficient amplitude spectrum (URCAS). The URCAS of coupling medium/non-metallic coating/metal substrate structure is derived based on interfacial spring model. The high-sensitivity frequency and interface stiffness ranges are determined by analyzing the sensitivity of URCAS to testing frequency and interface stiffness in advance. The accurate inversion of interface stiffness is achieved through a least square objective function under the high-sensitivity frequency and interface stiffness ranges. The feasibility of proposed ultrasonic method was verified by numerical simulations and ultrasonic experiments implemented on epoxy resin coating/aluminum substrate specimens. Simulation results show that the inverted interface stiffnesses are in good agreement with the preset values, and the maximum relative error is less than 6% in the high-sensitivity interface stiffness range, while the inversion accuracy of interface stiffness significantly reduces, and the relative error exceeds 21% in the low-sensitivity range. Experimental results show that the tested tensile strength and interface stiffness have similar trends. The proposed ultrasonic method can quantitatively identify the interface stiffness and effectively characterize the bonding quality of coating/substrate interface.

Four-wave mixing on thermal nonlinearity with feedback for signal or object waves

The coincidence of the amplitude reflection coefficients, half-widths of the spatial frequencies bands of a four-wave radiation converter on thermal nonlinearity with feedback for signal or object waves has been shown at equal pump waves intensity. The dependence of the amplitude reflection coefficient, spatial selectivity of the four-wave radiation converter on thermal nonlinearity on the pump waves intensity has been analyzed. An increase in the half-width of the spatial frequency band is observed with an increase in the pump waves intensity at the compensation for the phase shift arising as a result of the propagation of the pump waves in the medium. There is a threshold value of the pump waves intensity, above which the value of the amplitude reflection coefficient of the four-wave converter with feedback for signal or object waves, is less than in the absence of feedback.

Effect of mesoscopic-flow loss on seismic reflections in media with penny-shaped inclusions

Summary We obtain the amplitude and energy reflection coefficients of seismic waves in porous media with penny-shaped inclusions, based on the generalized Biot-Rayleigh model that takes into account the attenuation due to mesoscopic local fluid flow (LFF). We consider two cases, including a contact between two porous media having either different fluids (gas-water contact) or crack density/aspect ratio, as well as a water half-space overlying a porous medium, and study the frequency-dependent reflection-transmission (scattering) coefficients for open- and sealed-pore boundary conditions. Our examples show that the LFF mechanism mainly reduces the reflection coefficients (amplitude and energy) at the gas-water contact and at a water/porous-medium interface for frequencies less than 10 kHz, due to the fact that the velocity in the lower medium decreases. For the latter case, if the fluid is gas, the LFF effect becomes only important at frequencies between 0.0001 and 10 Hz for the open-pore case. This is due to the fact that the acoustic impedance contrast between water and gas is high. At frequencies less than 0.0001 Hz, the interface is equivalent to a water/elastic-medium one, and hence the results are the same as those of the sealed-pore case. Moreover, the crack density and aspect ratio affect the mesoscopic attenuation and relaxation frequency, and therefore the reflection coefficients.