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A LiNbO3 (LN)/SiO2/Si multilayered structure was recently reported as a new platform for achieving wideband radio frequency (RF) filters. However, the in-band ripples in filters resulting from the spurious Rayleigh mode lead to deteriorated performance, and thus, a wide Rayleigh elimination window (REW) is highly desired for realizing spurious-free wideband surface acoustic wave (SAW) filters with a wide design space and good process tolerance. Here, we investigated the spurious mode suppression on the LN/SiO2/Si platform theoretically and experimentally through modulating the cut angle ($\theta $) of LN. The ${K}^{{2}}$ dispersion characteristics of the main mode (shear-horizontal wave) and spurious mode (Rayleigh wave) on LN/SiO2/Si substrates were systematically analyzed by the finite-element method (FEM), along with bulk LN for comparison. It is found that the REW is wider on LN/SiO2/Si than bulk LN, as Rayleigh wave can be totally eliminated with Cu electrode normalized thickness (${h}_{\text {Cu}}/\lambda $) ranging from 0.1 to 0.19 when $\theta $ is between 19° and 22° on the LN/SiO2/Si platform, in contrast to the quite narrow REW on bulk LN restricted to some specific ${h}_{\text {Cu}}/\lambda$. To verify the simulation results, resonators were prepared on 15°YX-LN/SiO2/Si, 20°YX-LN/SiO2/Si, bulk 15°YX-LN, and bulk 20°YX-LN. In addition, the typical spurious-free wideband SAW filter with ${h}_{\text {Cu}} = {200}$ nm based on the 20°YX-LN/SiO2/Si platform demonstrates high performance with a center frequency (${f}_{\text {c}}$) of 1.27 GHz, a minimum insertion loss (ILmin) of 0.7 dB, and a 3-dB fractional bandwidth (FBW) of ~20.1%. This work provides a workable solution in fabricating spurious-free wideband and low-loss SAW filters for fifth-generation (5G) applications. [ABSTRACT FROM AUTHOR]

To obtain optimal system throughput for semiconductor device fabrications, fast vacuum pump-down operations are frequently performed to quickly depressurize processing chambers for desirable pressure conditions. However, sudden and drastic temperature variations could occur at the beginning of a fast vacuum pump-down session, resulting in catastrophic consequences such as thermal shock and condensation-induced contamination, profoundly disturbing the otherwise well-conditioned mini-environment. To this end, the vacuum pump-down processes taking place between a pair of parallel isothermal disks resembling typical industrial applications (e.g., high-throughput load lock) are investigated by computational fluid dynamics (CFD) simulation and space-invariant theoretical modeling. It is discovered that the gas temperature first drops rapidly in a manner resembling isentropic gas expansion, and then quickly recovers at a rate governed by the pumping speed and a near-constant Nusselt number. In addition, it is discovered that attenuated temperature variations can be achieved with smaller disk separations and lower pumping speeds. Furthermore, a new empirical formula is proposed to calculate the Nusselt number based on a normalized time parameter, which not only better reflects the heat-transfer characteristics during pump-down than its well-known counterparts based on the Rayleigh number, but also enable efficient evaluations of various pump-down configurations with the space-invariant theoretical modeling. [ABSTRACT FROM AUTHOR]

How to determine the velocity of an S-wave from measured seismic data is an important topic in seismology. A modern technique for obtaining the S-wave velocity is to solve an inverse problem so that the simulated dispersion curve (the relation between the frequencies and phase velocities) coincides with the actual experimental results. In this work, by using the seismic impedance tensor, we propose a new function describing Rayleigh wave dispersion in the layered medium model of the Earth, which offers an efficient way to compute the dispersion curve. With this newly established forward model, based on mixture density networks (MDNs), we develop a physics-informed neural network, named MDN based on a physics informed forward model (FW-MDN), to estimate the S-wave velocity from dispersion curves. The FW-MDN method deals with the nonuniqueness issue encountered in the inversion of dispersion curves for the crust and upper mantle models, and attains satisfactory performance on an artificial dataset with various noise structures. Numerical simulations are performed to show that the FW-MDN offers easy calculation, efficient computation, and high precision for model characterization. [ABSTRACT FROM AUTHOR]

A non-invasive fetal electrocardiogram (FECG) is used to monitor the electrical pulse of the fetal heart. Decomposing the FECG signal from the maternal ECG (MECG) is a blind source separation problem, which is hard due to the low amplitude of the FECG, the overlap of R waves, and the potential exposure to noise from different sources. Traditional decomposition techniques, such as adaptive filters, require tuning, alignment, or pre-configuration, such as modeling the noise or desired signal to map the MECG to the FECG. The high correlation between maternal and fetal ECG fragments decreases the performance of convolution layers. Therefore, the masking region of interest based on the attention mechanism was performed to improve the signal generators' precision. The sine activation function was also used to retain more details when converting two signal domains. Three available datasets from the Physionet, including the A&D FECG, NI-FECG, and NI-FECG challenge, and one synthetic dataset using FECGSYN toolbox, were used to evaluate the performance. The proposed method could map an abdominal MECG to a scalp FECG with an average of 98% R-Square [CI 95%: 97%, 99%] as the goodness of fit on the A&D FECG dataset. Moreover, it achieved 99.7% F1-score [CI 95%: 97.8-99.9], 99.6% F1-score [CI 95%: 98.2%, 99.9%] and 99.3% F1-score [CI 95%: 95.3%, 99.9%] for fetal QRS detection on the A&D FECG, NI-FECG and NI-FECG challenge datasets, respectively. Also, the distortion was in the “very good” and “good” ranges. These results are comparable to the state-of-the-art results; thus, the proposed algorithm has the potential to be used for high-performance signal-to-signal conversion. [ABSTRACT FROM AUTHOR]

In this letter we investigate phonon-dominated mobilities for carriers in a diamond field effect transistor with a cubic Boron Nitride (cBN) overlayer. We investigate the intra-subband scattering due to interaction of electrons with acoustic phonons, treated properly as quantized surface acoustic Rayleigh waves, and include, for the first time, the interaction with remote polar phonons originating in the cBN overlayer. We conclude that the surface acoustic phonon scattering is the dominant mechanism limiting the mobility of electrons for temperatures below 375 K. [ABSTRACT FROM AUTHOR]

Batteryless, wireless, and packageless acoustic wave sensors are particularly desirable for harsh high-temperature environments. In this letter, an acoustic wave sensor based on a lithium niobate (Y + 128° cut, abbreviated LN-Y128) substrate with a buried platinum interdigital transducer (IDT) in an aluminum nitride (AlN) overlayer is investigated. Previously, it was demonstrated theoretically that due to the specific properties of LN-Y128, Rayleigh-type guided waves can propagate at the AlN/IDT(Pt)/LN-Y128 interface. Here, this structure is, for the first time, studied experimentally, including the growth and properties of the AlN layer onto irregular platinum IDTs. Both Shear Horizontal and Rayleigh-type waves have been identified after the AlN deposition and the velocities are consistent with the fitted SDA-FEM-SDA (a combination of finite element modeling with spectral domain analysis) simulations. Electrical measurements with a surface perturbation and temperature measurements show that the AlN/IDT(Pt)/LN-Y128 bilayer structure is promising as a packageless high-temperature sensor. [ABSTRACT FROM AUTHOR]

In an attempt to include the effects of natural porosity of lung parenchyma into the mathematical study of lung diagnostics, a model describing the propagation of low-frequency Rayleigh waves in relation to the porous architecture of the lung parenchyma is presented. The wave motion is analyzed by assuming that the lung parenchyma behaves as an isotropic elastic half-space containing a distribution of vacuous pores with the visceral pleura as a taut elastic membrane in smooth contact with the half-space. The thinness of the pleural membrane in comparison with the large surface area of contact enables it to be modeled as a material surface in contact with the parenchyma. Utilizing the perturbation technique, an approximate formula for the Rayleigh wave velocity in the parenchyma with allowance for surface tension, mass density, and porosity is derived. In addition, the effect of the tension in the pleural membrane and the porosity in the parenchyma on the propagation of the low-frequency Rayleigh waves is brought out through the dispersion spectrum. It is hoped that the results of this paper would enable a better understanding of the porosity and surface-tension effects on lung parenchyma.

Ultrasound shear wave elastography (SWE) is a technique used to measure mechanical properties to evaluate healthy and pathological soft tissues. SWE typically employs an acoustic radiation force (ARF) to generate laterally propagating shear waves that are tracked in the spatiotemporal domains, and algorithms are used to estimate the wave velocity. The tissue viscoelasticity is often examined through analyzing the shear wave phase velocity dispersion curves, which is the variation of phase velocity with frequency or wavelength. A number of available methods to estimate dispersion exist, which can differ in resolution and variance. Moreover, most of these techniques reconstruct dispersion curves for a limited frequency band. In this work, we propose a novel method used for dispersion curve calculation. Our unique approach uses a generalized Stockwell transformation combined with a slant frequency-wavenumber analysis (GST-SFK). We tested the GST-SFK method on numerical phantom data generated using a finite-difference-based method in tissue-mimicking viscoelastic media. In addition, we evaluated the method on numerical shear wave motion data with different amounts of white Gaussian noise added. Additionally, we performed tests on data from custom-made tissue-mimicking viscoelastic phantom experiments, ex vivo porcine liver measurements, and in vivo liver tissue experiments. We compared results from our method with two other techniques used for estimating shear wave phase velocity: the two-dimensional Fourier transform (2D-FT) and the eigenvector (EV) method. Tests carried out revealed that the GST-SFK method provides dispersion curve estimates with lower errors over a wider frequency band in comparison to the 2D-FT and EV methods. In addition, the GST-SFK provides expanded bandwidth by a factor of two or more to be used for phase velocity estimation, which is meaningful for a tissue dispersion analysis in vivo. [ABSTRACT FROM AUTHOR]

In the last decade, the development of new flexible electronics is producing pervasive technologies for the Internet of Things (IoT), robotics and wearables transducers, pushing towards the demonstration of highly compliant low cost components on disposable or recyclable substrates. In recent years, there was a marked improvement in these technologies using organic or inorganic transistors. However, the lack of a high-performance passive-wireless devices in flexible electronics is one of the key bottlenecks for compliant IoT and wearables sensing nodes. One of the main building blocks for sorting this issue out is the development of flexible, bendable and stretchable acoustic-based devices, controllable via wireless antenna. In this work, a flexion characterization of a polymeric-based surface acoustic wave (SAW) device is presented. The flexible SAW is fabricated on polyethylene naphthalate (PEN), employing the high performance of the aluminum nitride (AlN) as a piezoelectric layer. The dual-wave modes, Rayleigh and Lamb, have been characterized. The Lamb waves show better results, in terms of strain sensitivity (1.81E- $04~\varepsilon $) and responsivity (1.156 kHz/ $\mu \varepsilon $), as compared to the Rayleigh wave (4.29E- $04~\varepsilon $ and 0.577 kHz/ $\mu \varepsilon $ , respectively). This polymeric flexible- based SAW device could pave the way for the development of a passive wireless strain sensor. [ABSTRACT FROM AUTHOR]

This article extends the solution to an electromagnetic wave propagating along a thin wire parallel to the interface between two homogeneous half-spaces to wires coated with insulation. The solution presented in this article includes half-spaces with different magnetic permeability and wires with finite conductance. The solution agrees with earlier works after appropriate restrictions are applied. The effects of varying the parameters representing the half-spaces and conductor insulation on the system attenuation constant are investigated. Equivalent line parameters for the propagation are extracted from the full wave modal equation and analytical approximations of these parameters are provided for conductors located above or below the interface assuming the half-spaces are formed by the earth and air. The limitations of the approximations are investigated and compared with previous approximations that have been identified as used outside the range of their applicability. As well as reviewing some of the more fundamental works on the subject, this article contributes to understanding the limitations of existing theory and establishes an alternate process for further extensions in the field. [ABSTRACT FROM AUTHOR]

Surface acoustic waves, such as Rayleigh or Lamb waves, can be used to characterise the geometry of surface-breaking defects. For accurate measurement of defect length and depth, the in-plane (IP) and out-of-plane (OP) components of the displacement or velocity can be measured and compared. Electromagnetic acoustic transducers (EMATs) offer a simple, non-contact method of doing this, as it is possible to design detection EMATs such that they are sensitive predominantly to either the IP or the OP velocity component. Here we present a new design of differential coil EMAT which measures both components simultaneously, and through simple processing gives the IP and OP velocities. This is compared to previous designs, showing that these components are obtained accurately. The system is used to characterise three artificial surface-breaking defects in aluminium and one thermal fatigue crack in 10 mm thick steel plate under thin coating. [ABSTRACT FROM AUTHOR]

The parallel propagating waves (Langmuir, R and L waves) are studies in different plasma environments by choosing the different values of $\eta =({mc^{2}}/{k_{B}T})$ and $({\omega ^{2}_{\mathrm{ pe}}}/{\omega ^{2}_{\mathrm{ ce}}})$. The dispersion relations of these waves are derived under a weak magnetic field limit for a fully relativistic plasma environment. The analytical solution of the integrals in the dispersion relations is not possible, so we use a numerical quadrature approach for their solution. We observe that in both relativistic and weakly relativistic plasmas, these modes shifted to lower values of frequency. The cutoff points of R- and L-waves shifted to further lower values in high-density plasma compared to low density. [ABSTRACT FROM AUTHOR]

The simultaneous wireless information and power transfer (SWIPT) has recently attracted much attention since both information and energy are integrated within radio frequency signals, which is considered to be one of the most important technologies for future networks. However, security becomes one of the most critical issues in SWIPT networks due to its broadcasting features over wireless media and the transferring requirements for strong signal strength. To improve the security of SWIPT networks, in this paper, a SWIPT system enabled by full-duplex (FD) jamming is proposed, where an FD energy-limited receiver with the power splitting (PS) structure, powered by a transmitter, generates jamming signals. Both linear and nonlinear energy harvesting (EH) models are considered. To evaluate the secrecy throughput (ST) of the system, we derive the closed-form connection outage probability and secrecy outage probability for the proposed PS-based scheme in the delay-constrained transmission (DCT) mode. The ST is maximized by optimizing the PS ratio based on the asymptotic cases of the high signal-to-noise ratio as well as the perfect self-interference cancellation (SIC). Besides, the exact integral forms of the ergodic secrecy capacity and their closed-form lower bounds are presented for both the PS-based and the time switching (TS)-based schemes in the delay-tolerant transmission (DTT) mode. Simulation results suggest that the PS-based scheme outperforms the TS-based scheme for the DTT mode. For the DCT mode, the PS-based scheme can achieve better performance than the TS-based scheme only in low target communication rate, small PS/TS ratio, high transmit power, and weak path loss. Meanwhile, given a tolerable amount of SIC, the ST obtained in the linear EH model is higher than that achieved in the nonlinear EH model. [ABSTRACT FROM AUTHOR]

Nondestructive testing for identifying defects on the surface of metal materials is important for industries and infrastructures. The Rayleigh wave is widely used for detecting these surface defects. For replacing piezoelectric transducers with electromagnetic acoustic transducers (EMATs) for the surface inspection of metal materials, this article proposes a new magnet and coil combination consisting of a periodic-permanent-magnet (PPM) and a returned dislocation meander line coil. The returned dislocation meander line coil was developed using a traditional meander line coil, whose wires return from one side to another and shift for a certain distance. A 2-D finite-element simulation was conducted to analyze the performance of the proposed Rayleigh wave EMAT. The simulation results revealed that, compared with a large conventional magnet, the PPM increased the maximum magnetic flux density, and made the magnetic flux density distribution more concentrated on the specimen’s surface, particularly below the coil. In the middle part of the coil, the PPM greatly increased the intensity of the horizontal magnetic field. Additionally, the returned dislocation meander line coil made full use of the strong magnetic field below the center of each small magnet and at the adjacent magnets. The designed Rayleigh wave EMAT was fabricated, and the experimental results revealed that the new design of the Rayleigh wave EMAT increased the received signal by 57.9% compared with the conventional Rayleigh wave EMAT. [ABSTRACT FROM AUTHOR]

Ultrasound shear wave elastography (SWE) is an increasingly used noninvasive modality for quantitative evaluation of tissue mechanical properties. SWE typically uses an acoustic radiation force to produce laterally propagating shear waves that are tracked in the spatial and temporal domains, in order to obtain the wave velocity. One of the ways to study the viscoelasticity is through studying the shear wave phase velocity dispersion curves. Shear wave attenuation can be also characterized in viscoelastic tissues with methods that use multiple lateral data samples. In this article, we present an alternative method for measuring the shear wave attenuation without using a rheological model two-point frequency shift (2P-FS). The technique uses information related to the amplitude spectra FS of shear waves measured at only two lateral locations. The theoretical basis for the 2P-FS is derived and validated. We examined how the first signal position and the distance between the two locations affect the shear wave attenuation estimation in the 2P-FS method. We tested this new method on digital phantom data created using the local interaction simulation approach (LISA) in viscoelastic media. Moreover, we tested data acquired from custom-made tissue-mimicking viscoelastic phantom experiments and ex vivo porcine liver measurements. We compared results from the 2P-FS method with the other two techniques used for assessing a shear wave attenuation: the FS-based method and the attenuation-measuring ultrasound shear wave elastography (AMUSE) technique. In addition, we evaluated the 2P-FS algorithm with different levels of added white Gaussian noise to the shear wave particle velocity using numerical phantoms. Tests conducted showed that the 2P-FS method gives robust results based on only two measurements and can be used to measure attenuation of viscoelastic soft tissues. [ABSTRACT FROM AUTHOR]

The objective of this study was to investigate the measurement instrument-dependent variability in the morphology of the ballistocardiogram (BCG) waveform in human subjects and computational methods to mitigate the variability. The BCG was measured in 22 young healthy subjects using a high-performance force plate and a customized commercial weighing scale under upright standing posture. The timing and amplitude features associated with the major I, J, K waves in the BCG waveforms were extracted and quantitatively analyzed. The results indicated that 1) the I, J, K waves associated with the weighing scale BCG exhibited delay in the timings within the cardiac cycle relative to the ECG R wave as well as attenuation in the absolute amplitudes than the respective force plate counterparts, whereas 2) the time intervals between the I, J, K waves were comparable. Then, two alternative computational methods were conceived in an attempt to mitigate the discrepancy between force plate versus weighing-scale BCG: a transfer function and an amplitude-phase correction. The results suggested that both methods effectively mitigated the discrepancy in the timings and amplitudes associated with the I, J, K waves between the force plate and weighing-scale BCG. Hence, signal processing may serve as a viable solution to the mitigation of the instrument-induced morphological variability in the BCG, thereby facilitating the standardized analysis and interpretation of the timing and amplitude features in the BCG across wide-ranging measurement platforms. [ABSTRACT FROM AUTHOR]

We present laser-induced full-matrix imaging of complex-shaped objects that combines the advantages of noncontact laser ultrasound inspection and high-contrast array imaging based on total focusing method (TFM). Full-matrix data were acquired by synthesizing a laser ultrasonic array through an alternate scanning of the generation and detection laser beams. Taking advantage of the simultaneous generation of all wave modes, surface Rayleigh waves were extracted for surface profiling, and longitudinal waves were utilized for imaging. To gain a better understanding, we analyzed the full-wave dynamics in generation, propagation, and scattering by using numerical simulations. TFM was adapted to accommodate complex surface and suppress interference from other waves, including surface waves and straightforward traveling bulk waves between emission and reception. Numerical and experimental studies on an aluminum sample with a sinusoidal surface and side-drilled holes were conducted, and results agreed well. [ABSTRACT FROM AUTHOR]

Planar glass-etalon Fabry–Pérot (FP) optical ultrasound sensors offer an alternative to piezoelectric sensors for the measurements of high-intensity focused ultrasound (HIFU) fields and other metrological applications. In this work, a model of the frequency-dependent directional response of the FP sensor was developed using the global matrix method, treating the sensor as a multilayered elastic structure. The model was validated against the experimentally measured directional response of an air-backed cover-slip FP sensor with well-known material properties. In addition, the model was compared with the measurements of an all-hard-dielectric sensor suitable for HIFU measurements. The model was then used to calculate modal dispersion curves for both glass-etalon sensors, allowing the features of the directional response to be linked to specific wave phenomena. The features in the directivity of the air-backed cover-slip sensor are due to guided Lamb waves. Symmetric Lamb modes give rise to regions of high sensitivity, whereas anti-symmetric modes cause regions of low sensitivity. For the all-hard-dielectric sensor, two features correspond to the water-substrate and water-spacer compressional and shear critical angles. A region of high sensitivity close to the shear critical angle is associated with a leaky-Rayleigh wave, which has a frequency-dependent phase speed. At higher frequencies, this feature is counteracted by a region of low sensitivity, which occurs when there is no difference in the vertical displacement of the mirrors forming the FP cavity. The model may be used to improve and optimize the design of FP sensors or could be used to assist with the accurate deconvolution of the directional response from array measurements in metrological and imaging applications. [ABSTRACT FROM AUTHOR]

A modified 2-D reverse-time migration algorithm in the energy flow domain, called EF-RTM, is proposed for short impulse borehole radar (BHR) imaging. The key of the approach is based on Poynting’s theorem, which allows decomposition of the energy flux density (EFD) derived from the source and receiver wave fields in different wave-propagation directions. Then, imaging conditions, for example, zero-lag cross correlation (prestack migration) and zero-time imaging principle (poststack migration), are applied to the decomposed EFD-field components to obtain the migrated sections. The characteristics of the resulting images can be optionally combined or separately used for better BHR data imaging, interpretation, and analysis. In this paper, the EF-RTM algorithm is validated by numerical modeling and real field data and compared with the conventional RTM algorithm. All the results show that this new EF-RTM method is superior to the conventional RTM method: it inherits the high precision of RTM with additional imaging advantages, such as natural wave-field decomposition in different directions, improved migrated cross-range resolution, a better focus of the target’s shape, and migration noise reduction. [ABSTRACT FROM AUTHOR]

In this paper, we study the problem of beam alignment for millimeter wave (mmWave) communications, where a hybrid analog and digital beamforming structure is employed at the transmitter (i.e., base station), and an omni-directional antenna or an antenna array is used at the receiver (i.e., user). By exploiting the sparse scattering nature of mmWave channels, the beam alignment problem is formulated as a sparse encoding and phaseless decoding problem. More specifically, the problem of interest involves finding a sparse sensing matrix and an efficient recovery algorithm to recover the support and magnitude of a sparse signal from compressive phaseless measurements. A sparse bipartite graph code algorithm is developed for sparse encoding and phaseless decoding. Our theoretical analysis shows that, in the noiseless case, our proposed algorithm can perfectly recover the support and magnitude of the sparse signal with a probability exceeding a pre-specified value from $\mathcal {O}(K^2)$ measurements, where $K$ is the number of nonzero entries of the sparse signal. The proposed algorithm has a simple decoding procedure which is computationally efficient and noise robust. Simulation results show that our proposed method renders reliable beam alignment even in the low signal-to-noise ratio regime and presents a clear performance advantage over existing methods. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of coupling between Rayleigh and shear-horizontal (SH) surface acoustic waves (SAWs) on rotated Y-cut LiNbO3 to their electromechanical coupling. For the purpose, a coupling-of-mode (COM) model including the coupling between two SAWs is developed, and the coupling influences to their excitation in addition to electromechanical coupling factors are discussed. Then, its validity is confirmed by comparison of its results with the finite-element method analysis. Comparing with the conventional COM shows this extended COM model could fit the complex value area much better in the dispersion curve analysis. After that, variation of COM parameters with the device design is discussed. Then, all COM parameters are fit by polynomial equations and the procedures to find the optimal rotation angle are obtained in terms of the SH mode suppression. It indicates that the optimal angle changes rapidly at certain Cu thickness, which is due to decoupling between two SAW modes. At last, structure based on the low-cut LiNbO3 is discussed and the validity of this COM model is further confirmed. [ABSTRACT FROM AUTHOR]

Surface acoustic wave sensors find their application in a growing number of fields. This interest stems in particular from their passive nature and the possibility of remote interrogation. Still, the sensor package, due to its size, remains an obstacle for some applications. In this regard, packageless solutions are very promising. This paper describes the potential of the AlN/ZnO/LiNbO3 structure for packageless acoustic wave sensors. This structure, based on the waveguided acoustic wave principle, is studied numerically and experimentally. According to the COMSOL simulations, a wave, whose particle displacement is similar to a Rayleigh wave, is confined within the structure when the AlN film is thick enough. This result is confirmed by comprehensive experimental tests, thus proving the potential of this structure for packageless applications, notably temperature sensing. [ABSTRACT FROM AUTHOR]

The feasibility of obstacle detection along a railway track through Rayleigh wave sensing was empirically studied using a laser vibrometer mounted along railway tracks at specific test sites. The impact of obstacles like rock and timber of varying weights dropped on rail head, rail ballast, and sleeper was recorded using the laser vibrometer. It could detect the vibrations generated by the impact of rock and timber drop from a distance of 2 km. The results were cross-verified using finite-element simulation and it was established that the waves propagating along the railway track are indeed Rayleigh waves. Sensing of Rayleigh wave generation under object drop along railway track can pave way to a technology on real-time railway track monitoring for obstacle detection. [ABSTRACT FROM AUTHOR]

This paper considers the performance analysis of sparse code multiple access (SCMA) with receive diversity arrays and randomly deployed users in a cellular uplink scenario. The impact of path loss on the performance of SCMA is characterized, by assuming independent Rayleigh fading and joint maximum likelihood (ML) receivers. A tight upper bound on the probability of symbol detection error is derived, and the achievable diversity and coding gains are investigated. The analytical results are validated by using simulations, and show that a diversity order which is equal to the product of the number of receive antennas and the signal-space diversity can be achieved, and the large-scale path-loss decreases only the coding gain. [ABSTRACT FROM AUTHOR]

Objective: For long-term electrocardiography (ECG) recordings, accurate R-wave detection is essential. Several algorithms have been proposed but not yet compared on large, noisy, or pathological data, since manual ground-truth establishment is impossible on such large data. Methods: We apply the simultaneous truth and performance level estimation (STAPLE) method to ECG signals comparing nine R-wave detectors: Pan and Tompkins (1985), Chernenko (2007), Arzeno et al. (2008), Manikandan et al. (2012), Lentini et al. (2013), Sartor et al. (2014), Liu et al. (2014), Arteaga-Falconi et al. (2015), and Khamis et al. (2016). Experiments are performed on the MIT-BIH database, TELE database, PTB database, and 24/7 Holter recordings of 60 multimorbid subjects. Results: Existing approaches on R-wave detection perform excellently on healthy subjects (F-measure above 99% for most methods), but performance drops to a range of F = 90.10% (Khamis et al.) to F = 30.10% (Chernenko) when analyzing the 37 million R-waves of multimorbid subjects. STAPLE improves existing approaches (ΔF = 0.04 for the MIT-BIH database and ΔF = 0.95 for the TELE database) and yields a relative (not absolute) scale to compare algorithms’ performances. Conclusion: More robust R-wave detection methods or flexible combinations are required to analyze continuous data captured from pathological subjects or that is recorded with dropouts and noise. Significance: STAPLE algorithm has been adopted from image to signal analysis to compare algorithms on large, incomplete, and noisy data without manual ground truth. Existing approaches on R-wave detection weakly perform on such data. [ABSTRACT FROM AUTHOR]

This paper reports post-annealing of zinc oxide (ZnO) films on flexible foil substrates in order to improve the functional and acoustic wave sensing performance. ZnO films of 5 \mu \textm thick were deposited onto aluminum foils (50 \mu \textm thick) using magnetron sputtering and then annealed in air at different temperatures between 300 °C and 500 °C. Effects of post-annealing on structural, optical, and device properties of the ZnO films and ZnO/Al foil acoustic wave devices were investigated. A temperature of 350 °C was identified as the optimized annealing temperature, which resulted in good light transmission, improved crystallinity, reduced film stress/defects, and increased amplitude of reflection signals of both Lamb and Rayleigh waves. The annealed ZnO/Al acoustic wave devices demonstrated a large temperature coefficient of frequency and a good linearity, revealing the potential for precise temperature sensing. [ABSTRACT FROM AUTHOR]

Typically, meander-line-coil electromagnetic acoustic transducers (EMATs) with wires of a constant length are used to generate Rayleigh waves. However, significant side lobes are observed in this design. In this paper, a novel meander-line-coil with variable-length wires is proposed to suppress side lobes of the Rayleigh waves’ beam. This novel EMAT is simulated by using a wholly analytical method, which involves the coupling of an analytical EM model and an analytical US model to generate the radiation pattern of Rayleigh waves. The Rayleigh waves’ beam directivity of this novel variable-length meander-line-coil (VLMLC) is quantitatively analyzed by the half power beamwidth and the sidelobe level; the effect of the length step on the Rayleigh waves’ beam directivity is discussed. A 50-mm VLMLC with a length step of 8 mm is fabricated and experimentally analyzed; experimental results showed that novel VLMLCs are capable of suppressing side lobes of the Rayleigh waves’ beam, which is not achievable by the conventional meander-line-coil. To the best of our knowledge, there has been no report so far of the VLMLCs EMAT. [ABSTRACT FROM PUBLISHER]

This paper presents a new method for sensing and the quantification of the number of solid microparticles using surface acoustic wave (SAW) devices. In contrast to the standard mass loaded delay line approach, microcavities with varying geometrical shapes and sizes are formed between SAW interdigitated transducer pairs. The system operation relies on the resonance condition occurring inside the microcavity through the coupling of Rayleigh waves to the sample, and the output phase angle is used for obtaining measurement results. It is shown through measurements that it is possible to interact with polystyrene solid microbeads trapped inside the microcavity and extract information about the size of the sample. Furthermore, the number of microbeads placed in a single file along the microcavity width can be quantified using this platform. Experimental results are compared and verified with finite-element method simulations. In essence, this novel approach resulted in a platform capable of analyzing sample volumes less than 10 pL in a non-invasive manner. For size differentiation, experimental phase shifts of 0.14° ± 0.05°, 0.81° ± 0.26°, and 3.54° ± 0.49° were obtained in rectangular microcavities for 10, 15, and 20 \mu \textm microbeads, respectively. On the other hand, a distribution of phase shifts as 0.51° ± 0.19°, 0.98° ±0.12°, and 1.34° ± 0.15° are obtained for counting one, two, or three microbeads, respectively. The proposed system was designed, simulated, fabricated, and tested successfully. [ABSTRACT FROM PUBLISHER]

The elastic waves generated by traditional meander- line coil electromagnetic acoustic transducers (EMATs) propagate in two directions, overlapping the echo signals from defects with the same distances, and the defect echo signal is hard to distinguish from the edge-reflected signal when the EMATs are near the edge of a specimen. In this paper, a unidirectional EMAT with two meander-line coils is proposed. A finite element model is used to simulate the directivity of the Rayleigh and shear vertical waves generated by these EMATs. Six transducers are fabricated using the printed circuit technique. The unidirectional Rayleigh wave and shear vertical wave are tested, and the results agree well with the simulation. [ABSTRACT FROM AUTHOR]

We present a novel method for the calculation of the 2D and 3D free-space periodic Green's function (PGF), especially efficient when observation points are in the vicinity of the array plane, a case for which both spatial and spectral domain forms of PGF are known to be slowly convergent. The PGF is approximated by a truncation of the original array, and the assignment of new fictitious amplitudes to maintained sources. Both 2D and 3D numerical tests show that a highly accurate approximation of the PGF can be obtained with such an equivalent finite array composed of a few sources, making the method especially relevant for fast electromagnetic computation of periodic structures, with the method of moments (MoM) for example. [ABSTRACT FROM PUBLISHER]

The interference channel with a relay (ICR) is the fundamental building block of cooperation in wireless networks where there are multiple communicating pairs interfering with each other. This paper considers ICRs in which the links are subject to i.i.d. fading, and each node has channel state information (CSI) only on its incoming links (receive CSI). Two channel models are considered: phase fading and Rayleigh fading. Strong interference conditions are derived for the case where the links from the sources to the relay are good in the sense that the achievable region for decoding both messages at the relay contains the maximal achievable region at the destinations. This leads to the characterization of the capacity region for such scenarios. This is the first time the capacity region of the ICR is characterized for a nondegraded, noncognitive scenario, with a causal relay when all links are active. [ABSTRACT FROM PUBLISHER]

A main target of seismic data processing is to remove the surface waves and improve the quality of seismic records. Here, we propose a Co-Core Trace (CCT) transform filtering based on the Trace transform from image processing and apply it to seismic surface wave attenuation. The CCT transform is designed according to the distribution and propagation of the surface waves. In the CCT transform domain, the energies of surface waves are significantly enhanced and could be filtered out with a relative threshold, while the reflection events are saved due to the conspicuous disparity. Experiments on both synthetic model and field data demonstrate that the proposed algorithm performs well both in surface wave attenuation and reflected signal preservation, besides presenting advantages over some conventional methods. [ABSTRACT FROM AUTHOR]

Minimum-selection generalized selection combining (MS-GSC) has been proposed as a power-saving variant of conventional generalized selection combining (GSC). Existing performance results of this scheme are limited to interference-free environments under multipath fading. This paper addresses the scenario when the received desired signal on each diversity branch is corrupted by multiple interfering signals and background noise, wherein desired and undesired signals undergo mutually independent Rayleigh fading. In the absence of perfect tracking of the instantaneous interference power on diversity branches, the adaptation thresholds that are set on the combined signal-to-noise ratio (SNR) to enhance either the spectral efficiency or power efficiency in noise-limited environments may not guarantee the target performance. This paper aims to study the effect of cochannel interference on the performance of bandwidth- and power-efficient SNR-based MS-GSC. Through the analysis, new analytical results for some important performance measures of adaptive MS-GSC schemes are presented. Numerical comparisons to clarify the impact of cochannel interference on the achieved performance of the adaptation schemes under consideration are provided. [ABSTRACT FROM PUBLISHER]

In this paper, the exact closed-form expressions for the level crossing rate (LCR) and the temporal autocorrelation function (ACF) of the signal-to-noise ratio (SNR), at the output of the spatially correlated multiple-input–multiple-output (MIMO) systems with orthogonal space-time block codes (OSTBCs), are derived. The expressions are derived for the case of an arbitrary number of Rayleigh distributed branches and any form of the covariance matrix. The derived identities can be applied to isotropic and nonisotropic scattering environments, and they are validated by Monte Carlo simulations. [ABSTRACT FROM PUBLISHER]

This paper presents analytical upper and lower bounds on the information rate of a multiuser Rayleigh fading channel with no channel state information (CSI) at the transmitters or the receivers. These bounds are shown to converge whenever an individual user's data rate is small compared with the bandwidth, e.g., when users can employ CDMA. The amount of spreading required for a given degree of convergence depends on the number of receive antennas. The number of users can be sufficient for the aggregate spectral density to be large. The paper presents exact analytical expressions for the information rates of both the block fading and the continuous correlated fading channel models in this regime. Finally, the results are extended to more general channel models. [ABSTRACT FROM AUTHOR]

In this correspondence, we evaluate the symbol error rate (SER) and information outage probability (IOP) of space-time block codes (STBCs) from coordinate interleaved orthogonal designs (CIODs) in the composite channel of lognormal shadowing and Rayleigh fading. By applying the Gauss–Hermite quadrature integration, we derive an accurate closed-form approximation for the symbol pairwise error rate (SPER) and corresponding tight upper and lower bounds on the SER of STBCs from CIODs. An accurate closed-form approximate formula for the IOP is also derived by formulating the composite squared lognormal/chi-square probability density function and exploiting the high-signal-to-noise-ratio (SNR) approximation technique. Furthermore, we investigate the achievability of full diversity in Rayleigh fading channels with shadowing effects. Finally, various Monte Carlo simulations are performed to validate our theoretical results. [ABSTRACT FROM PUBLISHER]

With imperfect channel state information (CSI) acquired by channel estimation at the receiver, the performance of basic automatic-repeat-request (ARQ) and hybrid ARQ (HARQ) systems is evaluated as a function of the accuracy of channel estimation. A link between data-link-layer performances and physical-layer parameters is therefore established. Upper and lower bounds on the accepted packet error rate (APER), the goodput, and the drop rate are derived. These upper and lower bounds are close to one another and therefore enable the behavior of the exact performance parameters to be investigated. The results show that the effect of the MSE on the system performance is nonlinear. At high values of the MSE, the performance very rapidly deteriorates, whereas, at low values of the MSE, the performance gently improves toward that of the perfect CSI case. The study here shows how accurate the CSI should be to achieve a specified performance level in ARQ schemes. [ABSTRACT FROM PUBLISHER]

Wireless network coding is a useful technology that can increase the total throughput of wireless networks. There are, however, few works focusing on wireless network coding over fading channels, which is an important characteristic of many real wireless channels and may result in performance degradation. To investigate the fading channel's impact on network coding, based on the constant transmission power scheme and the channel inversion-transmission scheme, we analyze network throughput over Rayleigh fading channels. It is shown that, when the difference between average channel gains over two broadcasting channels is very large, the throughput of network coding greatly decreases, and the advantage of network coding almost disappears. To address this issue and to maximize the throughput of network coding over fading channels, we formulate the fading compensation for network coding as optimization problems and present the optimal transmission data rate and transmission power level of the relay node. Furthermore, to consider the realization problem of network coding over fading channels, including unbalanced traffic load and asynchronization of packet arrivals, we present two opportunistic optimal network coding (OONC) schemes. Performance evaluation has shown that the proposed opportunistic schemes perform well in various scenarios. [ABSTRACT FROM PUBLISHER]

Consider a cooperative diversity network that consists of a source, N cooperating relays, and a destination. The relays cooperate with the source through the decode and forward protocol to transmit a data symbol from the source to the destination. In a conventional signal-to-noise ratio based selection combining scheme at the destination, the effect of the source-to-relay links is not accounted for when choosing one link from the set consisting of the source-to-destination and N relay-to-destination links. To overcome this drawback, we modify the conventional scheme by including, in the selection process, a deterministic scale factor that incorporates the effect of the source-to-relay links. For statistically independent links that undergo flat Rayleigh fading, we derive, in closed form, the exact end-to-end symbol error probability (SEP) of this modified scheme, which we call a scaled selection combining scheme for M-ary phase-shift keying constellation. We also give a method of obtaining the optimum scale factor that minimizes the end-to-end SEP. A system designer should select the optimum scale factor to achieve the best performance of the scheme. [ABSTRACT FROM PUBLISHER]

An experimental setup for acoustoseismic detection of shallow buried objects is presented. The seismic (Rayleigh) waves were generated by exciting an acoustic airborne source by a series of sine-wave bursts, which were designed to cover a frequency range (100-1000 Hz) large enough to distinguish the vibrational characteristics of buried compliant objects. The signals were recorded by means of contact-acceleration microelectromechanical- system sensors moved above different buried objects (compliant and rigid). Signal acquisitions on only sandy soil revealed the natural variability of the outdoor test bed. This variability of soil parameters pointed out the difficulties of buried-object detection based on the amplitude thresholding of the signal spectrum. For this aim, the signals were processed in both time and frequency domains. An audio-channel output was devised to avail of the human hearing apparatus in distinguishing the buried objects according to spatial variations of the acceleration signals obtained by scanning the soil surface. [ABSTRACT FROM AUTHOR]

Thanks to colorless operation and cost-effectiveness, an incoherent-light-injected Fabry-Perot laser diode (FP-LD) is considered as a promising optical transmitter for wavelengthdivision- multiplexed (WDM) passive optical networks (PONs). However, the wide spectral linewidth of the transmitter output, which comes from wide linewidth of injected seed light to offer a sufficient signal-to-noise ratio and colorless operation, makes the transmitter output vulnerable to fiber dispersion. Hence, we propose and demonstrate a return-to-zero (RZ) transmitter based on incoherent-light-injected FP-LDs which offers the improved tolerance to fiber dispersion for wide-linewidth transmitter output. For incoherent light, RZ signals have the same spectral linewidth as non-return-to-zero (NRZ) signals but they have wider timing margin between adjacent bits, and thus offer better dispersion tolerance than NRZ. For the generation of RZ signals in cost-sensitive WDM-PON systems based on incoherent-lightinjected FP-LDs, we simply add electrical NRZ signals to a clock signal and then apply them to the FP-LD for direct modulation. The nonlinear light-output versus current (LI) curve of the FP-LD converts the applied electrical signals into optical RZ signals. Our experimental demonstration for 1.25-Gb/s upstream transmission shows ~50% improvement of dispersion tolerance compared to NRZ signals. The back-to-back receiver sensitivity is also improved by 1.4 dB by using the proposed transmitter. Thus, we successfully transmit 1.25-Gb/s RZ signals over 45- km standard single-mode fiber without dispersion compensation. This is achieved at a low signal-to-Rayleigh-crosstalk ratio of 13.8 dB, thanks to the incoherence and wide spectral linewidth of the output light. [ABSTRACT FROM AUTHOR]

In this paper, we examine the effect of channel estimation errors on the performance of multiple-input--multiple-output (MIMO) systems that employ code-division multiple-access (CDMA) transmission. Channel estimation based on training techniques has widely been considered throughout the literature. However, employing these training techniques in MIMO-CDMA systems degrades system performance due to multiuser interference. This degradation is clear as the diversity advantage of the MIMO system diminishes with the increased level of interference. As a remedy to this problem, we propose a channel-estimation and data-detection scheme based on the superimposed training technique for space-time spreading systems. The proposed scheme enhances the performance of the space-time system by eliminating the interference effect from both the channel and data estimates using two decorrelators: channel and data decorrelators. We investigate the performance of the proposed estimation technique considering an asynchronous CDMA uplink transmission over frequency-selective slow-fading channels. In particular, we analyze the bit-error-rate (BER) performance of the multiuser system with two-transmit-antenna and V -receive-antenna configuration over Rayleigh fading channels. Compared with other conventional estimation techniques, our results show that the proposed estimation technique is more robust to channel-estimation errors. Furthermore, both simulations and analytical results indicate that full system diversity is achieved. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the performance of multicarrier code-division multiplexing (MC-CDM) systems with minimum mean square error combining (MMSEC) over a Rayleigh fading channel. An approximated expression on the symbol error rate (SER) for MMSEC is derived. The approximated expression provides an accurate approximation of the true SER, particularly for systems with higher modulation and a small spreading factor. Through the derived error performances, we also calculate the achievable diversity order. MC-CDM systems with MMSEC achieve the same asymptotical diversity order of 1, regardless of the spreading factor. Within practical signal-to-noise ratio (SNR) ranges, the effective diversity order is further increased as a larger spreading factor is used. The derived analytical expressions are verified by numerical and simulation results. [ABSTRACT FROM AUTHOR]

We present an ultracompact and fast hardware simulator for Rayleigh and Rician fading channels. To ensure numerical robustness and an efficient mapping onto hardware, the fading simulator uses the sum-of-sinusoids technique with N = 32 sinusoids added up to model each fading path. Fading samples are generated at a low rate and then are passed to an interpolator, which computes the final samples at the desired baseband rate. We propose a new time-multiplexed datapath that uses a differential approach. Instead of directly generating the fading samples, the datapath generates the discrete difference between fading samples. The proposed simulator is so compact that an entire 4 x 4 multiple-input--multiple-output (MIMO) fading channel can be implemented on a small fraction of a single field-programmable gate array (FPGA). On a Xilinx Virtex-4 XC4VLX200-11 FPGA, up to 1184 different paths can be simultaneously implemented while generating 1184 x 342 million 2 x 16-bit complex-valued fading samples per second. [ABSTRACT FROM AUTHOR]

Asymptotic error rate expressions are derived for multi-branch equal gain combining and selection combining operating on arbitrarily correlated Rayleigh fading channels. These closed-form solutions are used to provide rapid and accurate estimation of the error rates in large signal-to-noise ratio regions. More importantly, they reveal additional insights into the transmission characteristics of linear diversity combining schemes operating on correlated Rayleigh fading channels. It is shown that the asymptotic error rates over correlated branches can be obtained by scaling the asymptotic error rates over independent branches with a factor, det(M), where det( M) is the determinant of the normalized channel correlation matrix. This relationship is valid for both coherent and noncoherent signalings. A similar relationship is also established for the outage probabilities of fading wireless systems employing multi-branch diversity reception. [ABSTRACT FROM AUTHOR]

In this paper, we propose an adaptive-power-control scheme for a cognitive radio system (CRS) in a Rayleigh fading channel. By allowing transmit power adaptation at the secondary user (SU) transmitter to maintain a constant output SNR to the SU receiver, this scheme maximizes the output SNR and limits the interference to a primary user (PU) within an interference constraint. To calculate this maximum constant output SNR at the SU receiver subject to the interference constraint of the PUs, we have developed an analytical model for the distribution of the interference to the PU while considering the detection performance at the SU. The analytical model takes into account multiple antennas at SUs, including a single antenna as a special case. It is found that the proposed adaptive-power control scheme outperforms the fixed-power control scheme. Typically, with SUs using two transmit and two receive antennas at the bit error rate (BER) of 10-3, the proposed adaptive-power control scheme achieves a 3-dB gain in the SNR. [ABSTRACT FROM AUTHOR]