Wave Frequency Research Articles

Radiation mechanism of twin kilohertz quasi-periodic oscillations in neutron star low-mass X-ray binaries

Context. The connection between quasi-periodic oscillations (QPOs) and magnetic fields has been investigated in various celestial bodies. Magnetohydrodynamic (MHD) waves have been employed to explain the simultaneous upper and lower kilohertz (kHz) QPOs. Nevertheless, the intricate and undefined formation pathways of twin kHz QPOs present a compelling avenue for exploration. This study area holds great interest as it provides an opportunity for deriving crucial parameters related to compact stars. Aims. We strive to develop a self-consistent model elucidating the radiation mechanism of twin kHz QPOs, which we then compare it with observations. Methods. A sample of 28 twin kHz QPOs detected from the X-ray binary 4U 1636–53 was used for a comparison with the results of the Markov chain Monte Carlo calculations based on our model of the radiation mechanism of twin kHz QPOs, which is related to twin MHD waves. Results. We obtained 28 groups of parameters of 4U 1636–53 and a tight exponential fit between the flux and the temperature of seed photons to Compton up-scattering and find that the electron temperature in the corona around the neutron star decreases with increasing seed photon temperature. Conclusions. The origin of twin kHz QPOs are dual disturbances that arise from twin MHD waves that are generated at the innermost radius of an accretion disc. The seed photons can be transported through a high temperature corona and are Compton up-scattered. The photons that vary the frequencies of twin MHD waves lead to the observed twin kHz QPOs.

Numerical investigation on the effect of an orifice plate on the flow-induced and acoustically induced vibration of a gas transmission pipe

In this paper, a numerical method is proposed for investigating the flow-induced vibration (FIV) and acoustically induced vibration (AIV) of a straight pipe with an orifice plate. First, the turbulent pressure (TP) and acoustic pressure (AP) signals on the pipe wall were obtained through the simulation of an unsteady flow field and the application of Mohring's analogy, respectively. Subsequently, the FIV and AIV of the pipe were calculated by means of one-way fluid-structure interaction and acoustic-structure interaction, respectively. The calculated pressures, flow velocities, and sound powers at the monitoring point were in good agreement with the experimental results reported in the literature. The numerical results revealed that the power spectral densities of the AP were significantly higher than those of the TP on the surface of the tested end pipe, particularly at the natural frequencies of the acoustic modes. In the low-frequency regime, FIV was the dominant factor, whereas in the medium-high frequency regime, particularly above the cutoff frequency of the plane wave, AIV was the dominant factor. The findings of the parametric studies demonstrated that the AP and AIV of the pipe exhibited a considerable increase with the Mach number. Conversely, the TP and FIV demonstrated a more pronounced rise when the Mach number increased from 0.1 to 0.2, followed by a less pronounced increase when the Mach number increased from 0.2 to 0.3. A reduction in the orifice diameter resulted in an increase in the AP and AIV. In contrast, the TP and FIV exhibited a comparatively minor increase.

Finite element simulation and experimental study of the coupling acoustic field characteristics of ultrasonic waves with internal defects inside microelectronic packaging

The miniaturization, ultra-thin and multi-layer complex structure of microelectronic packaging complicates the coupling acoustic field of ultrasonic waves and internal defects in the packaging, making accurate defect detection very difficult. In this paper, the finite element models of flip chip (FC) packaging and ball grid array (BGA) packaging are established to investigate the coupling acoustic field characteristics of ultrasonic waves and defects. In addition, based on the ultrasonic pitch and catch technique, the coupling laws of ultrasonic waves of different frequencies and the defects of different types, positions and sizes are analyzed by simulation, and the relationship between the relative amplitudes of the bottom waves and the sizes of different defects is revealed. Two specimens of microelectronic packaging are designed and fabricated to carry out the experimental studies using an ultrasonic signal acquisition system. The simulation and experimental results show that the relationship between the defects with small changes in the same location and the relative amplitudes of the bottom waves is basically linear, while the relationship between the solder ball extension defects with large changes and the relative amplitudes of the bottom waves is basically logarithmic, which provides a theoretical guidance for accurate evaluation of the type, size and location of defects in the practical detection.

Statistical Properties of Quasi‐Periodic Electromagnetic Ion Cyclotron Waves: ULF Modulation Effects

AbstractElectromagnetic ion cyclotron (EMIC) waves effectively scatter relativistic electrons in Earth's radiation belts and energetic ions in the ring current. Empirical models parameterizing the EMIC wave characteristics are important elements of inner magnetosphere simulations. Two main EMIC wave populations included in such simulations are the population generated by plasma sheet injections and another population generated by magnetospheric compression due to the solar wind. In this study, we investigate a third class of EMIC waves, generated by hot plasma sheet ions modulated by compressional ultra‐low frequency (ULF) waves. Such ULF‐modulated EMIC waves are mostly observed on the dayside, between magnetopause and the outer radiation belt edge. We show that ULF‐modulated EMIC waves are weakly oblique (with a wave normal angle ) and narrow‐banded (with a spectral width of of the mean frequency). We construct an empirical model of the EMIC wave characteristics as a function of ‐shell and MLT. The low ratio of electron plasma frequency to electron gyrofrequency around the EMIC wave generation region does not allow these waves to scatter energetic electrons. However, these waves provide very effective (comparable to strong diffusion) quasi‐periodic precipitation of plasma sheet protons.

Traveling wave vibration characteristics of rotating FGM conical shell

Abstract Conical shell is common structural component in various rotating machinery. The study of traveling wave vibration performance of conical shell is of great significant for the design of rotating machinery. This paper addresses the traveling wave vibration performance of rotating functionally graded material (FGM) conical shells. Artificial springs, uniformly distributed, are employed to simulate the boundary constraints of rotating FGM conical shell. Accounting for the effects of Coriolis and centrifugal forces caused by rotation, the energy equation of rotating FGM conical shell is calculated, and then the dynamical model of the rotating FGM conical shell under elastic supported constraints is established using the Lagrange equation. The influence of key factors on traveling wave frequency and response characteristics of rotating FGM conical shell are investigated including rotational speed, half-cone angle and material components.

Numerical investigation on the liquid jet and the dynamics of the near-wall cavitation bubble under an acoustic field

The dynamics of the near-wall cavitation bubble in an acoustic field are the fundamental forms of acoustic cavitation, which has been associated with promising applications in ultrasonic cleaning, chemical engineering, and food processing. However, the potential physical mechanisms for acoustic cavitation-induced surface cleaning have not been fully elucidated. The dynamics of an ultrasonically driven near-wall cavitation bubble are numerically investigated by employing a compressible two-phase model implemented in OpenFOAM. The corresponding validation of the current model containing the acoustic field was performed by comparison with experimental and state-of-the-art theoretical results. Compared to the state without the acoustic field, the acoustic field can enhance the near-wall bubble collapse due to its stretching effect, causing higher jet velocities and shorter collapse intervals. The jet velocity in the acoustic field increases by 80.2%, and the collapse time reduces by 40.9% compared to those without an acoustic field for γ = 1.1. In addition, the effects of the stand-off distances (γ), acoustic pressure wave frequency (f), and initial pressure (p*) on the bubble dynamic behaviors were analyzed in depth. The results indicate that cavitation effects (e.g., pressure loads at the wall center and the maximal bubble temperature) are weakened with the increase in the frequency (f) owing to the shorter oscillation periods. Furthermore, the maximum radius of bubble expansion and the collapse time decrease with increasing f and increase with increasing p*. The bubble maximum radius reduces by 12.6% when f increases by 62.5% and increases by 20.5% when p* increases by 74%.

Numerical study of wave resonance characteristics in gaps of a floating array

Wave resonance in the gaps formed by a four-float array for various drafts and incident wave frequencies is investigated using a numerical wave tank based on OpenFOAM. In the gap perpendicular to the direction of wave propagation, the resonant wave height is higher than that between two side-by-side floats under the same draft, and the resonant frequency is also different. Significant variations in wave height distribution are observed along the gap parallel to the wave propagation direction under different incident wave frequencies. When the incident wave frequencies are higher than the resonant frequency, the lateral force amplitude on the front floats increases, while the force amplitude on the rear floats does not show this effect. Using the dynamic mode decomposition method, we discover that the irregular distribution of wave heights across different frequencies leads to an increase in the lateral force amplitude on the front floats at non-resonant frequencies.

Phase coded waveforms for integrated sensing and communication systems

AbstractNowadays, especially with the developments in the automotive industry, it has become a highly popular topic for radar and communication systems to operate on the same platform and perform joint tasks to increase situational awareness. Sharing the hardware of the radar and communication systems and using a joint waveform for both functions eliminate interference problems between the systems, increasing the effectiveness of the joint task. In studies where radar signals are utilised for communication functions, continuous wave frequency modulation or intra‐pulse frequency modulation is generally employed to transmit communication signals. There are a few studies in the literature on joint radar and communication waveforms using phase modulation. In these studies, phase modulation is not employed directly for both functions. As a contribution to the literature, this study evaluates the usage of joint radar and communications waveforms, such as Barker sequences and Zadoff–Chu sequences as opposed to linear frequency modulation. We compare these waveforms terms of range‐speed detection and symbol error rate.

Coupling analysis between wave resonance in the moonpool and heave motion of the twin hulls with mooring effect

Fluid resonance in the moonpool formed by two identical rectangular hulls in water waves is investigated by employing the Computational Fluid Dynamics (CFD) package OpenFOAMⓇ. The influence of vertical stiffness on the behavior of moonpool resonance coupling with the heave motion response is presented. Numerical simulations show that the free surface oscillation in the moonpool exhibits a two-peak variation with the incident wave frequency, defined as the first and second peak frequencies. A local Keulegan–Carpenter (KC) number is introduced for describing the influence of fluid viscosity and flow rotation on the fluid resonance and heave motion resonance. At the first peak frequency, the free surface oscillation and heave motion response show an in-phase relationship, where increase in the vertical stiffness can increase the relative motion between them. This finally leads to an increase in the KC number, indicating the increased effect of energy dissipation with increase in the vertical stiffness. At the second peak frequency with an out-of-phase relationship between the free surface oscillation and heave motion response, the variation of the KC number is not sensitive to the vertical stiffness. Correspondingly, the influence of energy dissipation is not strongly dependent on the vertical stiffness.

Thermal Wave and Pennes’ Models of Bioheat Transfer in Human Skin: A Transient Comparative Analysis

The primary focus of this study is to analyze comparative heat transfer in a two-dimensional (2D) multilayered human skin using thermal waves and Pennes' bioheat transfer models. The model comprises the epidermis, dermis, hypodermis tissue, and inner cells, and aims to understand their response to microwave (MW) power and electromagnetic (EM) frequency. The system of equations involves EM wave frequency and bioheat equations and uses the finite element method (FEM) for solving. It encompasses a range of microwave power levels (4-16 W), frequencies (0.9-4 GHz), and exposure durations (0-180 s). It examines how MW power and frequency affect temperature predictions due to different relaxation times. The results are visually represented, illustrating microwave power dissipation, isothermal profiles within the skin tissue, temperature trends at several locations, relaxation times, specific absorption rate (SAR), and the mean surface temperature of the multilayered dermal cell. Thermal analysis shows that Pennes' equation predicts higher temperatures than the thermal wave model of bioheat transfer (TWMBT). A notable disparity in temperature evolution is observed between the two models, especially in high-frequency transient heating scenarios. The TWMBT forecasts a delay in heat transfer, offering valuable insights into the more realistic short-term thermal behavior that the classical Pennes' model fails to capture. This comparative study underscores the significance of selecting an appropriate bioheat transfer model for precise thermal analysis in biomedical applications, such as hyperthermia treatment and thermal diagnostics. The findings emphasize the potential of the TWMBT to enhance the accuracy of thermal treatments in clinical settings.

Parametric Subharmonic Instability of the M2 Internal Tides in the Tokara Strait

AbstractThe Tokara Strait is a mixing hotspot due to the coexistence of complex bottom topographies and strong composite flow including both the Kuroshio and tidal currents. Although previous studies have revealed several mechanisms from the view of Kuroshio‐Topography interaction, the role of tides in driving mixing is still not clear. Given that it is located at the M2 critical latitude (29°N), parametric subharmonic instability (PSI) is expected as an important process responsible for the mixing. Here, we study PSI of the M2 internal tides in the Tokara Strait based on a high‐resolution model. Our model results indicate that intense near‐inertial waves are generated via PSI, which exhibit a horizontally layered structure and have much larger vertical wavenumbers than the M2 internal tides. Energy is transferred from the M2 internal tides to the near‐inertial waves around the generation sites, and most of the near‐inertial energy is dissipated locally. The dissipation rates of near‐inertial waves are comparable to those of the M2 internal tides. Simulations with and without the Kuroshio Current revealed the suppression of PSI along the Kuroshio path, which could be attributed to two mechanisms. First, the Kuroshio Current modifies the local minimum internal wave frequency by its horizontal and vertical shear, making the condition for PSI not satisfied. Second, the Kuroshio Current advects the near‐inertial waves downstream in the Okinawa Trough, which inhibits the accumulation of near‐inertial energy there. However, in most of the areas outside the Kuroshio path, PSI majorly contributes to mixing in and around the Tokara Strait.

The rebar corrosion length evaluation technique based on nonlinear ultrasonic guided wave energy flow

In offshore reinforced concrete (RC) structures, phenomena of rebar corrosion are widespread, seriously threatening the durability of the structures. However, the issue of entire rebar corrosion process detection, especially for the evaluation of local corrosion states and the scope, is also challengeable. The paper aims at utilizing the nonlinear ultrasonic guided wave (UGW) energy flow to identify reinforcement corrosion level and length during the entire corrosion process in RC structures and establishing a corresponding corrosion evaluation algorithm. Therefore, a corroded rebar with the surrounding concrete cover is simplified into a cylindrical layered structural model. Meanwhile, piezoelectric transducers are used for the actuation and reception of UGWs, and a granular material contact (GMC) model is applied to illustrate the mechanism for generating surface-contact-induced nonlinear components in scattering waves. Then, the propagation behavior of the nonlinear UGWs is analyzed by regarding the corrosion layer as a secondary sound source changing the wave energy flow. A corrosion evaluation algorithm based on the GMC model is established and validated by both experiment and finite element (FE) analysis. The results show that for a harmonic UGW excitation signal, the periodic relationship between the second-order nonlinear coefficient of received signal and the corrosion length is found in which the period is associated with the difference (kd) of 2 times of fundamental frequency wave number (2 kω) and double frequency wave number (k2ω). Particularly, as kd trends to zero, a degraded linear relationship is found for establishing the corrosion length evaluation algorithm with the relatively high evaluation precision and convenient evaluation technique.

A Higher-Order Theory for Nonlinear Dynamic of an FG Porous Piezoelectric Microtube Exposed to a Periodic Load

This paper investigates the nonlinear dynamic deflection, natural frequency, and wave propagation in functionally graded (FG) porous piezoelectric microscale tubes under periodic load, hygrothermal conditions, and an external electric field. The piezoelectric material used to make the smart microtubes has pores that may be smoothly changed or uniformly distributed over the tube wall. Here, three types of porosity distribution are taken into consideration. The nonlinear motion equations are constructed using a novel shear deformation beam theory and the modified couple stress theory (MCST). The nonlinear motion equations are solved using the fourth-order Runge–Kutta technique and the Galerkin approach. The effects of various geometric parameters, porosity distribution type, porosity factor, periodic load amplitude and frequency, material length scale parameter, moisture, and temperature on the nonlinear dynamic deflection, natural frequency, and wave frequency of FG porous piezoelectric microtubes are explored through a number of parametric investigations.

Wave Height Estimation with a Short Return Period

Bisection and grid search methods are proposed as wave height estimation techniques for short return periods (hereafter RP; reference, one year) using long-term wave monitoring data. The proposed method is compared and evaluated with the estimation results using GP (generalized Pareto) and GEV (generalized extreme value) distribution functions, which are widely used as extreme value analysis methods. The wave height data used for the estimation were KMA Ulleungdo Ocean Buoy’s wave height data observed for 12 years from 2012 to 2023. The estimation results show that the annual frequency wave height is 4.55 m, the 90% confidence interval (±5%) is [4.18, 4.69] (m), and the confidence interval for the RP is [0.58, 1.42] (years). The difference from the GP and GEV estimation results (4.61 m and 4.53 m, respectively) was statistically ‘no significance difference.’ The method proposed in this study can estimate design variables for RPs without assumptions on candidate extreme distribution functions or parameter estimation procedures, so it can be used to estimate wave heights for short RPs of one year or less when observation data of approximately ten years or more are available.

Rancang Bangun Pengusir Hama Burung dan Belalang Pada Padi Menggunakan Gelombang Ultrasonik Berbasis Lora

Indonesia, as an agricultural country, faces the challenge of pests in the agricultural sector, one of which is the sparrow that often attacks rice plants, causing a decrease in rice yields. The use of traditional methods such as canned sound is considered less effective, so ultrasonic technology is chosen as a safer alternative to pesticides that can cause side effects to the environment. This research aims to design and test a sparrow and locust pest repellent tool on rice plants using ultrasonic waves based on LoRa technology, with the hope of offering a more efficient and environmentally friendly solution. Tests were conducted to determine the effectiveness of ultrasonic frequencies against sparrow and locust pests, as well as the maximum distance the tool can work. The device was tested with various wave frequencies (30 kHz, 35 kHz, 40 kHz) at different distances, and the LoRa communication range was measured until the signal was lost. The test results show that the optimal frequency to repel sparrows and locusts is 40 kHz with an effective range of up to 3 meters, and the LoRa module is able to transmit signals up to a distance of 63 meters. This research offers an alternative solution for farmers to repel pests effectively without harmful chemicals, as well as providing ease of tool control in areas without internet connection.

Ultra-Low Frequency Waves of Foreshock Origin Upstream and Inside of the Magnetospheres of Earth, Mercury, and Saturn Related to Solar Wind–Magnetosphere Coupling

This review examines ultra-low frequency (ULF) waves across different planetary environments, focusing on Earth, Mercury, and Saturn. Data from spacecraft missions (CHAMP, Swarm, and Oersted for Earth; MESSENGER for Mercury; and Cassini for Saturn) provide insights into ULF wave dynamics. At Earth, compressional ULF waves, particularly Pc3 waves, show significant power near the equator and peak around Magnetic Local Time (MLT) = 11. These waves interact complexly with Alfvén waves, impacting ionospheric responses and geomagnetic field line resonances. At Mercury, ULF waves transition from circular to linear polarization, indicating resonant interactions influenced by compressional components. MESSENGER data reveal a lower occurrence rate of ULF waves in Mercury’s foreshock compared to Earth’s, attributed to reduced backstreaming protons and lower solar wind Alfvénic Mach numbers, as ULF wave activity increases with heliocentric distance. Short Large-Amplitude Magnetic Structures (SLAMS) observed at Mercury and Saturn show distinct characteristics compared to those of Earth, including the presence of whistler precursos waves. However, due to the large differences in heliospheric distances, SLAMS (their temporal scale size correlate with the ULF wave frequency) at Mercury are significantly shorter in duration than at Earth or Saturn, since the ULF wave frequency primarily depends on the strength of the interplanetary magnetic field. This review highlights the variability of ULF waves and SLAMS across planetary environments, emphasizing Earth’s well-understood ionospheric interactions and the unique behaviours observed for Mercury and Saturn. These findings enhance our understanding of space plasma dynamics and underline the need for further research regarding planetary magnetospheres.

Performance Analysis of Millimeter-Wave Propagation Characteristics for Various Channel Models in the Indoor Environment

Due to the recent surge in the proliferation of smart wireless devices that feature higher data speeds, there has been a rise in demand for faster indoor data communication services. Moreover, there is a sharp increase in the amount of mobile data being generated worldwide, and much of this data comes from residential wireless applications like high-definition TV, device-to-device communication, and high data rate indoor networks (i.e., local and cellular). These technologies need large capacity, high data rate indoor wireless networks with huge bandwidth. Consequently, a greater interest exists in implementing an effective and trustworthy indoor propagation model for next-generation wireless systems operating in the massively bandwidth-rich millimeter wave (mm-wave) frequency range. The analysis of mm-wave propagation characteristics in an indoor environment using the ray tracing approach is proposed in this paper. Propagation modeling for 60 GHz bands is included. The aspects of wideband propagation characteristics such as angular spread, path loss, delay spread, and power delay profile are modeled in this paper. The position of transceivers, antenna effect, and attenuation, in the hallways, and stairwells will all be considered while determining the propagation parameters. This includes wave propagation characteristics like absorption, reflection, and diffraction by building structures and furniture. The specifications for propagation characteristics are included in the article for developing indoor local and cellular networks. In this paper, the IRT model has been tested at 60 GHz for potential mobile communication and is identified as the best method for predicting signal attenuation caused by objects, barriers, or humans within buildings in internal millimeter wave transmission.

ULTRASONIC INTERROGATION TECHNIQUE FOR DETECTING HATCH ANGLE VARIATIONS IN ADDITIVE MANUFACTURING BY PHONONIC LATTICE STRUCTURES

Abstract Additive Manufacturing/3D Printing (AM/3DP) has revolutionized part production by enabling the creation of intricate internal structures and complex geometries from diverse materials directly from digital design files. Among powder-based metal AM/3DP methods, Selective Laser Melting (SLM) is widely used in advanced applications such as biomedical devices and aerospace parts. Despite considerable progress in AM/3DP and SLM, at present, challenges in print quality persist, and vast resources for post-production quality assessment are allocated. The quality of SLM prints is influenced by various process and design parameters, such as the accuracy of hatch angle deposition, laser intensity/power, scanning speed of the laser beam, print line spacing, layer depth, printing chamber conditions, and the material's physical and chemical properties. Direct ultrasonic Non-Destructive Evaluation (NDE) offers comprehensive internal inspection and real-time data acquisition ability; however, in AM/3DP it faces severe limitations due to a build's intricate internal and external geometric features. In the current study, we present a Phononic Crystal Artifact (PCA)-based real-time ultrasonic NDE quality monitoring framework and show offline its utility in detecting and evaluating hatch angle variations, a critical process parameter. A PCA is substantially simpler and smaller than the actual build but represents its critical geometric and structural intricacies and mechanical properties. The current offline study demonstrates that hatch angle variations can be monitored from ultrasonic responses' spectral modal frequency peaks and wave dispersion relations.

Advances in Cardiovascular Wearable Devices

Cardiovascular diseases are a leading cause of death worldwide. They mainly include coronary artery disease, rheumatic heart disease, andcerebrovascular disease, and. Cardiovascular diseases can be better managed and diagnosed using wearable devices. Wearable devices, in comparison to traditional cardiovascular diagnostic tools, are not only inexpensive but also have the potential to provide continuous real-time monitoring. This paper reviews some of the recent advances in cardiovascular wearable devices. It discusses traditional implantable devices for cardiovascular diseases as well as wearable devices. The different types of wearable devices are categorized based on different technologies, namely using galvanic contact, photoplethysmography (PPG), and radio frequency (RF) waves. It also highlights the use of artificial intelligence (AI) in cardiovascular disease diagnostics as well as future perspectives on cardiovascular devices.

Expected insights into Type Ia supernovae from LISA’s gravitational wave observations

The nature of progenitors of Type Ia supernovae has long been debated, primarily due to the elusiveness of the progenitor systems to traditional electromagnetic observation methods. We argue that gravitational wave observations with the upcoming Laser Interferometer Space Antenna (LISA) offer the most promising way to test one of the leading progenitor scenarios – the double-degenerate scenario, which involves a binary system of two white dwarf stars. In this study we review published results, supplementing them with additional calculations for the context of Type Ia supernovae. We discuss the fact that LISA will be able to provide a complete sample of double white dwarf Type Ia supernova progenitors with orbital periods shorter than 16–11 minutes (gravitational wave frequencies above 2–3 millihertz). Such a sample will enable a statistical validation of the double-degenerate scenario by simply counting whether LISA detects enough double white dwarf binaries to account for the measured Type Ia merger rate in Milky Way-like galaxies. Additionally, we illustrate how LISA’s capability to measure the chirp mass will set lower bounds on the primary mass, revealing whether detected double white dwarf binaries will eventually end up as a Type Ia supernova. We estimate that the expected LISA constraints on the Type Ia merger rate for the Milky Way will be 4–9%. We also discuss the potential gravitational wave signal from a Type Ia supernova assuming a double-detonation mechanism and explore how multi-messenger observations could significantly advance our understanding of these transient phenomena.