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Multimode silicon photonics, leveraging mode-division multiplexing technologies, offers significant potential to increase capacity of large-scale multiprocessing systems for on-chip optical interconnects. These technologies have implications not only for telecom and datacom applications, but also for cutting-edge fields such as quantum and nonlinear photonics. Thus, the development of compact, low-loss and low-crosstalk multimode devices, in particular mode exchangers, is crucial for effective on-chip mode manipulation. This work introduces a novel mode exchanger that exploits the properties of subwavelength grating metamaterials and symmetric Y-junctions, achieving low losses and crosstalk over a broad bandwidth and a compact size of only 6.5 µm × 2.6 µm. The integration of SWG nanostructures in our design enables precise control of mode exchange through different propagation constants in the arms and metamaterial, and takes advantage of dispersion engineering to broaden the operating bandwidth. Experimental characterization demonstrates, to the best of our knowledge, the broadest operational bandwidth covering from 1,420 nm to 1,620 nm, with measured losses as low as 0.5 dB and extinction ratios higher than 10 dB. Enhanced performance is achieved within a 149 nm bandwidth (1,471–1,620 nm), showing measured losses below 0.4 dB and extinction ratios greater than 18 dB.

Copyright of Journal of Guangdong University of Technology is the property of Journal of Guangdong University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The lowest-order shear horizontal (SH0) guided wave in a plate is crucial for nondestructive testing and structural health monitoring due to its nondispersive nature. However, mode conversion at the interface for the SH0 wave complicates the received information and increases the difficulty of signal analysis. In this work, an elastic metasurface is proposed to suppress mode conversion at the interface and to reflect the SH0 wave directionally. The metasurface comprises a series of rectangular elements with a specific phase gradient covering the 2 π phase range. The effectiveness of the proposed metasurface is confirmed through finite element simulations and experimental validation. The results indicate that the metasurface can significantly reduce the amplitude of the reflected lowest-order symmetric Lamb wave when compared to the reflection without the metasurface, while simultaneously allowing the reflected SH0 wave to propagate at the designed angle. Furthermore, the metasurface maintains its functionality for SH0 wave with incident angles varying from 0° to 25°. This study provides a viable approach for suppressing mode conversion and modulating the reflection behavior of SH0 wave, which is expected to find applications in nondestructive testing and structural health monitoring. [ABSTRACT FROM AUTHOR]

The high‐power characteristic of the coaxial to waveguide transition plays an important role in modern communication and radar systems. In this letter, a novel design of a high‐power transition from a 50 Ω coaxial line with an N‐type connector to a WR‐90 rectangular waveguide. The power handling capability (PHC) of the proposed structure is significantly enhanced by a cone‐shaped excitation probe with a bold end, a transitional cavity, and a mode conversion cavity with a curved shorted back wall. The simulated results reveal that the transition possesses high PHC of 257 kW at 8.5 GHz, which is the upper limit of the power tolerance for the N‐type connector. The measured results show that the return loss and insertion loss are better than 15 and 0.15 dB, respectively, in the range of 7.96–9.16 GHz. In addition, experimental validation confirms the normal operation of the structure under a 250 kW power level test, demonstrating the applicability of the proposed transition in high‐power microwave systems. [ABSTRACT FROM AUTHOR]

This paper investigates the method for water ingress detection in an aluminum honeycomb sandwich structure by laser ultrasonics. To clarify the propagation of Scholte waves generated at the solid-liquid interface, the theoretical dispersion curves in the water-aluminum layered structure are calculated by the global matrix method. Using a laser ultrasonic visualizing inspector, the guided wave propagation in the wavefields has been visualized, which shows the mode conversion behaviors occurring in the water ingress area. The clarification of mode conversion is then investigated by the finite element method. The Scholte modes at the solid-fluid interface and the Lamb modes in the face sheet are interconverted because of the change in the waveguide structure. Wavenumber filter reconstruction and the resulting energy maps are applied to illustrate the mode conversion in the wavefields and to detect the water ingress area. Results show that the appearance of the water layer contributes to the mode conversion behaviors during the guided wave propagation in the honeycomb sandwich structure, which offers the potential for water ingress detection based on the mode conversion behaviors. [ABSTRACT FROM AUTHOR]

An ultrasonic-based method was developed to enable in-line measurements of foam structure parameters for highly aerated batters by mode conversion. Biscuit batters were foamed to different degrees (density: 364–922 g/L) by varying the mixing head speed and pressure. Density and foam structure changes were detected by efficient offline analytics (nref measurement = 96). Ultrasonic signal data were recorded using two ultrasonic sensors attached to an industry-standard tube. Mode conversion effects in the ultrasonic signals were obtained to predict the rheological parameters of the batters. The frequency range in which surface waves are expected was particularly suitable for detecting rheological changes in highly aerated batters. An ultrasonic-based, online-capable method for process monitoring was implemented and established regarding feature selection in combination with machine learning and 5-fold cross-validation. The developed ultrasonic sensor system shows high accuracy for online density measurement (R2 = 0.98) and offers decent accuracy for measurements of foam structure parameters (Bubble count: R2 = 0.95, Relative span: R2 = 0.93, Sauter diameter: R2 = 0.83). The main benefit of this novel technique is that integrating ultrasonic signal features based on mode conversion leads to a robust foam structure analysis, which has the advantage of being retrofitable into existing processes. [ABSTRACT FROM AUTHOR]

A high-power ultrasonic transducer for minimally invasive treatments is proposed, capable of treating areas inaccessible by high-intensity focused ultrasound treatments. This transducer employs two elliptical reflectors that efficiently focus ultrasound waves into a thin waveguide by utilizing mode conversion. Additionally, a slit structure is introduced to suppress wave diffraction, further enhancing the focusing capabilities of the transducer. Finite element analysis demonstrates that the proposed transducer achieves an impressive energy density magnification factor of 325, with an energy efficiency of 24.2 %. This efficiency is 3.4 times higher than that of a conventional transducer, Double Parabolic refLector wave-guided Ultrasonic transducer. [ABSTRACT FROM AUTHOR]

With the proliferation of smart devices, the Internet of Things (IoT) is rapidly expanding. This study proposes a miniaturized controllable metamaterial with low control voltage for achieving low-power and compact designs in IoT node devices. Operating at a target frequency of 2.4 GHz, the proposed metamaterial requires only a 3.3 V control voltage and occupies approximately one-third of the wavelength in size. Experimental validation demonstrates its excellent reflective control performance, positioning it as an ideal choice for low-power IoT systems, particularly in the context of miniaturized and low-power IoT node applications. [ABSTRACT FROM AUTHOR]

This study investigates the propagation characteristics of Saturn's Narrowband (NB) emissions using a 3D ray‐tracing code incorporating Saturn's magnetic field and electron density parameters. The potential source regions and propagation zones of the L‐O mode, Z mode and whistler mode NB emissions are distinguished. The L‐O mode NB emissions, generated along local electron plasma frequency surfaces through mode conversion, exhibit straight‐line propagation but undergo reflections between the ionosphere, the plasma torus, and the magnetosheath. The slot region, characterized by a lower electron density distributed around the plasma torus boundary, significantly influences emission propagation, potentially leading to trapping and depolarization. The 5 kHz Z mode NB emissions propagate and fill the trapping region delineated by lower cut‐off and upper hybrid resonance frequencies. In contrast, the 20 kHz Z mode NB emissions are primarily confined near source regions at the north and south edges of the plasma torus, with the possibility of escaping under variable plasma conditions. Plain Language Summary: Scientists have discovered low‐frequency radio waves near Saturn, roughly at 5 and 20 kHz, using data from the Voyager and Cassini spacecrafts. These waves are referred to as narrowband (NB) emissions. The NB emissions are thought to originate from Saturn, but exhibit a puzzling propagation pattern when they propagate far away from their source region. Recent studies propose that the 5 kHz waves might be bouncing off a dense plasma area in Saturn's magnetosheath, introducing intriguing yet not fully understood propagation characteristics. This study employs a numerical approach, that is, the ray‐tracing technique, to trace the likely paths of these waves. Drawing on earlier theoretical studies, we pinpoint the potential origins of these waves. Our results indicate that most of these waves, particularly the so‐called L‐O mode emissions, tend to travel toward Saturn's high latitudes. This directional preference is due to interference from a dense plasma torus in Saturn's equatorial region. The boundary of this torus can trap these waves. Meanwhile, the so‐called Z mode waves are confined to a specific region near Saturn. Our study unveils intricate features such as multiple reflections and refractions of these waves near Saturn, shedding light on various data observations. Key Points: A 3D ray‐tracing analysis is conducted for Saturn Narrowband (NB) emissionsThe L‐O mode NB emissions propagate toward high latitudes and the Z mode NB emissions are trapped near SaturnSmall electron density structures on the plasma torus can lead to trapping and depolarization of NB emissions [ABSTRACT FROM AUTHOR]

[Objective] The damage detection technology based on ultrasonic guided waves has broad application prospects in the rapid damage detection of long-distance pipes. The technology can identify and locate the damages based on the analysis of signals of ultrasonic guided waves scattered by damages. However, for welded pipes, welds will also cause ultrasonic guided waves to scatter, influencing the extraction of waves scattered by damages and increasing the difficulty in pipe damage detection. [Methods] To solve the problem that damage detection is affected by the welds, a method using ultrasonic guided waves based on mode conversion was proposed to track down the axial location of damages according to different characteristics of signals of waves scattered by welds and damages. A piezoelectric sensor was used to excite the single L(0, 2) mode ultrasonic guided waves as the incident waves. Based on the circumferential characteristics of axisymmetric and bending modes, the F(1, 3) mode signals generated by mode conversion were extracted from the signals received by the sensor, and the waves reflected by damages were identified. Based on the propagation velocity of ultrasonic guided waves in L(0, 2) and F(1, 3) modes, the axial location of damages in the pipes was realized. Numerical simulations and experiments were conducted on welded pipes with damages set at different locations to verify this damage location method. [Results] The results of numerical simulations and experiments suggest that the damages in the whole pipe, including those in the weld zones and the non-weld zones, could be detected by extracting the mode conversion signals, and that the error in the axial location of damages was less than 3%. With the increase of damage depth, the amplitude of the F(1, 3) mode increased, which provided the basis for identifying the damage depth. It was difficult for traditional methods based on reflected waves in the L(0, 2) mode to identify the damages in the weld zones. [Conclusion] Compared with the traditional damage detection methods based on the reflected waves, this method can, during the damage detection, reduce the interference of waves reflected by damages based on different characteristics of waves reflected by welds and damages, showing its potential advantages in damage detection of welded pipes, especially in weld zones.

Traditional mode conversion ultrasonic motors are typically composed of the superposition of multiple vibration modes, making them more complex than single-mode ultrasonic motors. This complexity makes it difficult to miniaturize. A micro radial-torsional vibration mode ultrasonic motor is proposed and tested in this work. It is excited by a single-phase excitation signal. The proposed motor utilizes the radial in-plane vibration mode of the stator to convert the torsional vibration mode of the inner ring through the beams. The torsional vibration of the inner ring causes the rotor to rotate due to the friction force between the inner ring and the rotor. Based on the designed structure and verified using the finite element method, a prototype motor with a mass of 2.6 g and overall dimensions of Ô20 mm in diameter and 15 mm in height is fabricated and characterized. During the mechanical output performance test, the prototype achieved a maximum no-load speed of 3300 r/min and a stall torque of 0.2 mN $\cdot $ m at the driving voltage of 100 V $_{\mathrm {p-p}}$ .

Undesired conversion between common-mode (CM) and differential-mode (DM) noise often occurs in modern electronic and electrical systems, posing challenges in terms of Electromagnetic Compatibility (EMC). Modal analysis represents a crucial tool in EMC investigation and provides insight into the mechanism underlying mode conversion. By inspecting CM and DM behaviors and their interconversion, it allows for understanding of conducted emission propagation mechanisms, drives electromagnetic interference (EMI) filter design towards optimal/tailored solutions, and enables the possibility to identify the main contributors to the radiated emission phenomenon. This paper offers a comprehensive review of mathematical methodologies and modelling strategies for EMC-oriented modal analysis, with particular emphasis on mode conversion phenomena. To this end, modal decomposition techniques and standard parameters for quantifying mode conversion are summarized and compared. Additionally, the paper provides an overview and in-depth discussion of different scenarios and test cases in which mode conversion occurs, with the final goal to achieve a systematic comprehension of its root causes and consequences within power and communication systems. Eventually, a survey of circuit modelling approaches for mode conversion is presented, offering insights into addressing this phenomenon effectively.

Implementing a compact optical integrated circuit by utilizing subwavelength plasmonic devices requires the design of compact and efficient photonic to plasmonic mode converters. Especially for plasmonic multiple-input devices such as logic gates that require multiple converters, the footprint can be largely penalized by the photonic waveguides, which should be considered in the design. In this work, we simulate and benchmark five photonic to plasmonic mode converter topologies for the application of multiple-input plasmonic devices. Our design includes both directional and end coupling schemes of plasmonic waveguide and Si photonic waveguides of wire and slot configurations. We optimize the performance of the converters considering the pitch mismatch between the photonic and plasmonic waveguides, the total footprint, and mode conversion efficiency.

Optimization of the structure of piezoelectric transducers such as the proper design of matching layers can increase maximum wave energy transmission to the host structure and transducer sensitivity. A novel configuration of an ultrasonic transducer, where elastic metamaterial insertion is introduced to provide bulk wave mode conversion and to increase wave energy transfer into a substrate, is proposed. Configurations of layered elastic metamaterials with crack-like voids are examined theoretically since they can provide wide band gaps and strong wave localization and trapping. The analysis shows that the proposed metamaterial-based matching layers can sufficiently change wave energy transmission from a piezoelectric active element for various frequency ranges (relatively low frequencies as well as higher ones). The proposed configuration can also be useful for advanced sensing with higher sensitivity in certain frequency ranges or for demultiplexing different kinds of elastic waves. [ABSTRACT FROM AUTHOR]

Reflection control of elastic wave is of great importance. Recently, reflective metasurfaces governed by the generalized Snell’s law offer a new degree of freedom to control the direction as well as the polarization of the reflected elastic waves. However, the underlining mechanism of the reflective metasurfaces is frequency-dependent, which significantly limits their practical applications. Here, we propose frequency-independent metamaterials called singly polarized solids (SPSs) for broadband reflection control of elastic waves. With the engineered SPSs, perfect mode conversion (PMC) and switching between positive reflection (PR) and negative reflection (NR) are achieved. Our work opens an approach to control the reflected elastic waves in a broad frequency range, and could find potential applications in structural health monitoring, nondestructive detection, and elastic wave devices. [ABSTRACT FROM AUTHOR]

Efficient mode conversion is crucial for hybrid photonic systems. We present efficient light transition from a standard single-mode fiber (SMF) to a subwavelength-diameter microfiber via a relatively short tapered fiber. Numerical simulations were performed to design the tapered morphology with high transmittance (approximately 86%) for the fundamental modes. The designed tapered fiber was successfully fabricated on the top of a cleaved SMF tip by the direct laser writing (DLW) method. For the 1550 nm wavelength, the transmittance from the standard SMF to the subwavelength-diameter microfiber was determined to be 77%, accompanied by a change in the effective mode area from 38 μm2 to 0.47 μm2 within a very short length of 150 μm. Our result demonstrated the versatility of the DLW technique for boosting the mode conversion efficiency of fiber-to-chip devices, enabling various applications in the future. [ABSTRACT FROM AUTHOR]

Acoustic manipulation is a set of versatile platforms with excellent manipulation capabilities. In recent years, researchers have increasingly achieved specific manipulations beyond the translation and capture of particles. Here, we focus on the acoustic field momentum mechanism that generates an acoustic radiation force (ARF). A phononic crystal (PC) waveguide is established to amplify the forward momentum of the acoustic beam through the mode conversion of the acoustic field. Based on the conservation of momentum, the object gains reverse momentum. Thus, acoustic pulling can be achieved through the mode conversion of the acoustic field. Furthermore, we analyze the ARFs of two identical objects. It turns out that they can be manipulated separately by opposing forces. Our study provides a new way to achieve stable long-range acoustic pulling, and will explore, beneficially, the interaction between acoustic waves and matter. [ABSTRACT FROM AUTHOR]

In this work, we propose a slab waveguide structure based on a magneto-photonic crystal, formed by a triangular lattice of circular air holes in a cerium-substituted yttrium iron garnet (Ce-YIG) medium grown on a silica (SiO2) substrate; in this structure, we have studied the width of the photonic band gap (PBG) using the expansion plane waves method in three dimensions to reach and optimize the complete PBG, centered at the telecommunication wavelength, also a theoretical study of the conversion mode, reported and studied the effect of some parameters such as the radius and the thickness using a beam propagation method in two dimensions. In our proposed structure, the maximum conversion modes ratio equal to 98% with a low coupling length LC = 15 µm is obtained for gyrotropy g = 0.36 and Faraday rotation FR = 1500 × 104 deg/cm. [ABSTRACT FROM AUTHOR]

Over the past few decades, on-chip photonic integrated circuits based on silicon photonics (SiPh) platforms have gained widespread attention due to the fact that they offer many advantages, such as high bandwidth, low loss, compact size, low power consumption, and high integration with different photonic devices. The demand for high-speed and high-performance SiPh devices is driven by the significant increase in demand for Internet traffic. In photonic integrated circuits, controlling optical signals to make them circulate in a specific direction is a highly researched area of study. However, achieving a purely passive on-chip optical circulating network on a SiPh platform is very challenging. Therefore, we propose and demonstrate, through simulations, an on-chip optical circulator network on a silicon-on-insulator (SOI) platform. The proposed device can also support mode conversion. The proposed on-chip optical circulating network consists of two kinds of tailor-made multi-mode interferometer (MMI) structures and waveguide crossings. Through the optical power division and mode combination capabilities of the MMI, an optical circulating network supporting high optical isolation and mode conversion is achieved. The proposed optical circulating network has a loss of 1.5 dB at each output port, while maintaining a high isolation of 35 dB in the transmission window from 1530 nm to 1570 nm. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the proliferation of smart devices, the Internet of Things (IoT) is rapidly expanding. This study proposes a miniaturized controllable metamaterial with low control voltage for achieving low-power and compact designs in IoT node devices. Operating at a target frequency of 2.4 GHz, the proposed metamaterial requires only a 3.3 V control voltage and occupies approximately one-third of the wavelength in size. Experimental validation demonstrates its excellent reflective control performance, positioning it as an ideal choice for low-power IoT systems, particularly in the context of miniaturized and low-power IoT node applications.

Electromagnetic ion cyclotron (EMIC) waves can scatter radiation belt electrons with energies of a few hundred keV and higher. To accurately predict this scattering and the resulting precipitation of these relativistic electrons on short time scales, we need detailed knowledge of the wave field’s spatio-temporal evolution, which cannot be obtained from single spacecraft measurements. Our study presents EMIC wave models obtained from two-dimensional (2D) finite-difference time-domain (FDTD) simulations in the Earth’s dipole magnetic field. We study cases of hydrogen band and helium band wave propagation, rising-tone emissions, packets with amplitude modulations, and ducted waves. We analyze the wave propagation properties in the time domain, enabling comparison with in situ observations. We show that cold plasma density gradients can keep the wave vector quasiparallel, guide the wave energy efficiently, and have a profound effect on mode conversion and reflections. The wave normal angle of unducted waves increases rapidly with latitude, resulting in reflection on the ion hybrid frequency, which prohibits propagation to low altitudes. The modeled wave fields can serve as an input for test-particle analysis of scattering and precipitation of relativistic electrons and energetic ions.

In this article, the anisotropic microstructure of a nickel IN718 sample fabricated on a forged nickel alloy base plate by the Additive Manufacturing (AM) method using the Direct Laser Deposition (DLD) technique was characterized by the mode-converted (Longitudinal to Transverse, L-T) ultrasonic scattering. The L-T ultrasonic measurements were conducted using two same focused transducers in a pitch-catch configuration on both forged and AM regions in two perpendicular directions. The ultrasonic scattered signal was converted to the two-dimensional scalogram through the Continuous Wavelet Transform (CWT). The energy distribution of ultrasonic scattering over the whole traveling path was obtained in the Time-Frequency (TF) domain. The apparent integrated scatter (AIS) was calculated to represent scattering energy by selecting the time window over the focal zone and the right frequency range. The AIS ratio of L z - T y / L z - T x measured in two perpendicular directions was used to quantify the microstructural anisotropy at each measurement spot. Then the variation of the microstructural anisotropy can be imaged over the whole sample, from which it can be seen that the microstructural anisotropy increased progressively towards the interface between the AM region and the forged base plate, and reached the maximum near the interface. The dependence of the characterization of microstructural anisotropy on the selection of the time window was also investigated by choosing several different time windows around the focal zone. The results show that the characterization of microstructural anisotropy was barely influenced, a result which indicates the measurement stability of this method. The mode-converted diffuse ultrasonic scattering technique demonstrates a strong sensitivity to anisotropic microstructure, an outcome that can be applicable for quality control during additive manufacturing. [ABSTRACT FROM AUTHOR]

Previous studies show that fast magnetosonic (MS) wave with frequency of tens of Hz may propagate to low L‐shells (L < 2.0) in the inner plasmasphere and mode convert to electromagnetic ion cyclotron (EMIC) wave where its wave frequency is close to the local crossover‐cutoff‐resonance frequency triplet through different propagation paths. In this study, we investigate how this mode conversion process may depend on the ion composition and electron density by full‐wave simulation with various plasma density profiles and initial wave normal angles (WNAs) of incoming MS wave from magnetic equator and a higher latitude of 15°. We find that critical fraction of minority ion (He+ or M/Q = 2 ion − D+ or He++) exists during the mode conversion, over which the conversion from MS wave to H+ band right‐handedly polarized EMIC wave starts to become negligible. This critical fraction decreases with the incident WNA of MS wave from equator. The efficiency of this conversion process also decreases with the electron density. As incoming MS is from higher latitudes off equator, optimal fraction of minority ion exists, with which the efficiency of conversion from MS wave to H+ band left‐handedly polarized EMIC wave reaches a maximum. Moreover, this maximum conversion efficiency varies with the incident WNA and may approach 100% with WNA close to 90° at the magnetic latitude of 15°. We also find that localized wave structure may be formed when the converted H+ band EMIC wave is trapped between local H+ − D+(He++) bi‐ion resonance frequency and D+(He++) − He+ left‐handed polarization cut‐off frequency with a small M/Q = 2 ion fraction and a relatively larger He+ fraction as incoming MS wave is near equator. Key Points: Tunneling efficiency from fast magnetosonic (MS) to electromagnetic ion cyclotron (EMIC) decreases with electron density, minority ions and wave normal angle (WNA)Maximum conversion efficiency to left‐handedly polarized H+ band EMIC varies with incident WNA and may approach 100% with optimal fraction of minority ionsMode converted right‐handedly polarized H+ band EMIC may be trapped between local H+ − D+(He++) bi‐ion frequency and D+(He++) − He+ left‐handed polarization cut‐off frequency forming local wave structure [ABSTRACT FROM AUTHOR]

The propagation of fast magnetosonic (MS) waves from high to extremely low L shells and their conversion into electromagnetic ion cyclotron (EMIC) waves is investigated with a ray tracing model and a full‐wave model. The ray tracing simulations show that MS waves in the vicinity of the local H+−He+ ${\mathrm{H}}^{+}{-\text{He}}^{+}$ crossover frequency at low L shells have a latitudinal range from −20° ${-20}^{{}^{\circ}}$ to 20° ${20}^{{}^{\circ}}$ with wave normal angles from 0° ${0}^{{}^{\circ}}$ to 180° ${180}^{{}^{\circ}}$, both of which provide the opportunity for their mode conversion to EMIC waves. Results from ray tracing are fed into the full‐wave model as initial conditions. The full‐wave simulations show that the incoming MS waves with small (20° ${20}^{{}^{\circ}}$) and intermediate (40° ${40}^{{}^{\circ}}$) wave normal angles may be efficiently converted to right‐handedly polarized H+ ${\mathrm{H}}^{+}$ band EMIC waves, which may be further converted to right‐handedly polarized He+ ${\text{He}}^{+}$ band EMIC waves or to guided left‐handedly polarized H+ ${\mathrm{H}}^{+}$ band EMIC waves through bi‐ion resonance reflection and polarization reversal. With intermediate (40° ${40}^{{}^{\circ}}$) or larger wave normal angles, via polarization reversal and left‐handed polarization cut‐off reflection, the incoming MS waves may be efficiently converted to guided left‐handedly polarized H+ ${\mathrm{H}}^{+}$ band EMIC waves and the optimal wave normal angles corresponding to the maximum conversion efficiencies decrease with magnetic latitudes. Our study verifies the mode conversion mechanism of MS waves to EMIC waves proposed with a previous ray tracing study and examines the dependence of the efficiency of the wave energy transfer on the magnetic latitudes and wave normal angles, which may help to understand the wave properties and distribution of MS and EMIC waves observed at extremely low L shells. Key Points: Propagation and mode conversion of fast magnetosonic (MS) to electromagnetic ion cyclotron (EMIC) waves at extremely low L shells is studied with ray tracing and full‐wave simulationsRight‐handedly polarized H+ ${\mathrm{H}}^{+}$ band EMIC converted from MS with small (20° ${20}^{{}^{\circ}}$) and intermediate (40° ${40}^{{}^{\circ}}$) wave normal angles may be efficiently converted to right‐handedly polarized He+ ${\text{He}}^{+}$ band EMIC or guided left‐handedly polarized H+ ${\mathrm{H}}^{+}$ band EMICMS with intermediate (40° ${40}^{{}^{\circ}}$) or larger wave normal angles may be efficiently converted to guided left‐handedly polarized H+ ${\mathrm{H}}^{+}$ band EMIC and the optimal wave normal angles corresponding to the maximum conversion efficiencies decrease with magnetic latitudes [ABSTRACT FROM AUTHOR]

In this work, we propose a design of a double-scatterer structure to achieve complete conversion for elastic bulk waves. Every unit of the elastic metamaterial slab contains a pair of scatterers with a relatively oblique direction. When the slab attaches on a semi-infinite solid background, it can completely convert the normal incident longitudinal wave into the reflected shear wave, or vice versa. The conversion can be attributed to the in-phase coupling of the double scatterers' quadrupolar resonances. The coupled two quadrupoles could interact with the background and bring oblique displacements. Consequently, the oblique displacements generate horizontal displacements for reflected waves. [ABSTRACT FROM AUTHOR]

To overcome the limitations of traditional frequency selective surfaces in flexible state switching at the same frequency, this paper proposes a novel active frequency selective surface (AFSS) that simultaneously exhibits conversion between absorption and transmission modes at the same frequency band. By welding PIN diodes on the bottom structure of the AFSS, the conversion between band-pass (transmission) and band-stop (absorption) filters can be controlled electronically. In the common-frequency switch between absorption and transmission modes, the impedance matching of the AFSS is attained by altering the capacitance value of the varactors embedded on the top structure of the AFSS. The functionalities of the proposed AFSS design are investigated by full-wave simulations (in HFSS software) at 11.4 GHz. Furthermore, the operating principle is analyzed using an equivalent circuit model (in AWR software). To verify the concept, a prototype is manufactured, and the responses of mode switching are measured by adjusting the bias voltage. The measurement result is consistent with the simulation analysis. Owing to the tunability of the varactors, the structural asymmetry is compensated to achieve 80% absorptivity and transmissivity within a field of view of ±35°. The developed AFSS structure is highly valuable to be used in scenarios such as antenna domes, etc. [ABSTRACT FROM AUTHOR]

Background: Transcranial ultrasound imaging and therapy depend on the efficient transmission of acoustic energy through the skull. Multiple previous studies have concluded that a large incidence angle should be avoided during transcranial‐focused ultrasound therapy to ensure transmission through the skull. Alternatively, some other studies have shown that longitudinal‐to‐shear wave mode conversion might improve transmission through the skull when the incidence angle is increased above the critical angle (i.e., 25° to 30°). Purpose: The effect of skull porosity on the transmission of ultrasound through the skull at varying incidence angles was investigated for the first time to elucidate why transmission through the skull at large angles of incidence is decreased in some cases but improved in other cases. Methods: Transcranial ultrasound transmission at varying incidence angles (0°–50°) was investigated in phantoms and ex vivo skull samples with varying bone porosity (0% to 28.54% ± 3.36%) using both numerical and experimental methods. First, the elastic acoustic wave transmission through the skull was simulated using micro‐computed tomography data of ex vivo skull samples. The trans‐skull pressure was compared between skull segments having three levels of porosity, that is, low porosity (2.65% ± 0.03%), medium porosity (13.41% ± 0.12%), and high porosity (26.9%). Next, transmission through two 3D‐printed resin skull phantoms (compact vs. porous phantoms) was experimentally measured to test the effect of porous microstructure alone on ultrasound transmission through flat plates. Finally, the effect of skull porosity on ultrasound transmission was investigated experimentally by comparing transmission through two ex vivo human skull segments having similar thicknesses but different porosities (13.78% ± 2.05% vs. 28.54% ± 3.36%). Results: Numerical simulations indicated that an increase in transmission pressure occurs at large incidence angles for skull segments having low porosities but not for those with high porosity. In experimental studies, a similar phenomenon was observed. Specifically, for the low porosity skull sample (13.78% ± 2.05%), the normalized pressure was 0.25 when the incidence angle increased to 35°. However, for the high porosity sample (28.54% ± 3.36%), the pressure was no more than 0.1 at large incidence angles. Conclusions: These results indicate that the skull porosity has an evident effect on the transmission of ultrasound at large incidence angles. The wave mode conversion at large, oblique incidence angles could enhance the transmission of ultrasound through parts of the skull having lower porosity in the trabecular layer. However, for transcranial ultrasound therapy in the presence of highly porous trabecular bone, transmission at a normal incidence angle is preferable relative to oblique incidence angles due to the higher transmission efficiency. [ABSTRACT FROM AUTHOR]

In this paper, two‐dimensional hybrid simulations are used to study wave excitation and evolution throughout a low‐Mach number quasi‐parallel shock. Simulation results show that quasi‐parallel fast magnetosonic waves, ion Bernstein waves with harmonics and possible Alfven/ion cyclotron waves can be excited in the upstream region, and their small phase velocities compared to injected flow velocity results in the convection to the shock front where they are mode converted into several groups of downstream waves, including Alfven waves along the directions parallel to downstream average magnetic fields and perpendicular to the shock normal, the quasi‐perpendicular kinetic slow waves and possible kinetic Alfven waves. We suggest that downstream Alfven waves originate from the mode conversion of upstream quasi‐parallel fast magnetosonic waves with left‐hand polarization in the downstream rest frame under helicity conservation, while the downstream left‐hand polarized kinetic slow waves and right‐hand polarized kinetic Alfven waves can be from the upstream quasi‐perpendicular ion Bernstein waves. Key Points: Upstream and downstream waves at a low‐Mach number quasi‐parallel shock are investigated by 2‐D hybrid simulationsUpstream quasi‐parallel and quasi‐perpendicular waves are excited by the interaction of injected flow and backstreaming ionsDownstream waves are generated by the mode conversion of upstream waves [ABSTRACT FROM AUTHOR]

An ultrasonic wave mode-based method for density measurement in highly foamed batters was developed. Therefore, a non-contact ultrasonic sensor system was designed to generate signals for batch-wise processes. An ultrasonic sensor, containing a piezoelectric ceramic at the fundamental longitudinal frequency of 2 MHz, was used to take impedance measurements in pulse-echo mode. The ultrasonic signals were processed and analysed wave-mode wise, using a feature-driven approach. The measurements were carried out for different mixing times within a container, with the attached ultrasonic sensor. Within the biscuit batter, the change to the ultrasonic signals caused by density changes during the batter-mixing process was monitored (R2 = 0.96). The density range detected by the sensor ranges between 500 g/L and 1000 g/L. The ultrasonic sensor system developed also shows a reasonable level of accuracy for the measurements of biscuit batter variations (R2 > 0.94). The main benefit of this novel technique, which comprises multiple wave modes for signal features and combines these features with the relevant process parameters, leads to a more robust system as regards to multiple interference factors. [ABSTRACT FROM AUTHOR]

In this work, we design a twisting metamaterial for longitudinal-torsional (L-T) mode conversion in pipes through exploring the theory of perfect transmodal Fabry-Perot interference (TFPI). Assuming that the axial and radial motions in pipes can be decoupled, we find that the metamaterial can be designed in a rectangular coordinate system, which is much more convenient than that in a cylindrical system. Numerical calculation with detailed microstructures shows that an efficient L-T mode conversion can be obtained in pipes with different radii. In addition, we fabricate mode-converting microstructures on an aluminum pipe and conduct ultrasonic experiments, and the results are in good agreement with the numerical calculations. We expect that the proposed L-T mode-converting metamaterial and its design methodology can be applied in various ultrasonic devices. [ABSTRACT FROM AUTHOR]

In this paper, a multi-way THz power combiner based on H-T branch circular waveguide mode conversion is presented. The two-stage H-plane T-junction waveguide-mode converter is used from the rectangular waveguide TE10 mode to the circular waveguide TM01 mode. To verify the performance of the presented THz power combiner circuit, a THz four-way waveguide power combiner based on H-T branch circular waveguide mode conversion has been developed, fabricated, and measured with reasonable agreement between the simulated and measured results. The measured center frequency of the circuit is 155 GHz, the measured input return loss is greater than 13 dB in the frequency band of 140–167 GHz, and the relative bandwidth is about 17.5%. The presented THz four-way power combiner has the advantages of high-power capacity, low insertion loss, and high-power combining efficiency. The presented THz four-way power combiner can be used in the THz power-combining source. [ABSTRACT FROM AUTHOR]

The helicon plasma source is of great significance for the magnetoplasma rocket engine (MPRE) to be used as an effective propulsion device. In this paper, a multi-fluid, two-dimensional, axisymmetric model coupled with the electromagnetic field was developed to simulate the helicon plasma source in the MPRE. The simulation results demonstrate that the operation mode of the helicon plasma source in the MPRE gradually converts to a high-order wave mode and the resonance between the electromagnetic field and electrons is observed; due to the resonance, the deposit power density inside the plasma increases significantly, and the plasma density is two orders of magnitude higher than that in the inductively coupled plasma source. As the magnetic field intensity increases, the helicon plasma source enters into a high-order wave mode, which suggests that the MPRE can improve the utilization rate of the working medium by a stronger magnetic field.

A high-power ultrasonic transducer for minimally invasive treatments is proposed, capable of treating areas inaccessible by high-intensity focused ultrasound treatments. This transducer employs two elliptical reflectors that efficiently focus ultrasound waves into a thin waveguide by utilizing mode conversion. Additionally, a slit structure is introduced to suppress wave diffraction, further enhancing the focusing capabilities of the transducer. Finite element analysis demonstrates that the proposed transducer achieves an impressive energy density magnification factor of 325, with an energy efficiency of 24.2 $ \% .$ This efficiency is 3.4 times higher than that of a conventional transducer, Double Parabolic refLector wave-guided Ultrasonic transducer.

Experiments were conducted on risers with different mass ratios to study the effect of mode conversion and spanwise correlation. The slenderness ratio of the riser model was set as 169, and the Reynolds numbers are 1600–14400. The dynamic responses of riser models versus reduced velocity were analyzed, and the spanwise displacement, frequency, and trajectory of the mode conversion from the lower to the higher mode were explored. The results revealed that the riser model with a higher mass ratio excites a higher number of modes. The conversion region of multi-mode competition exists and narrows with the increasing mass ratio. Mode conversion is continuous and manifests as the transmission of peaks and troughs in mode shape: the peaks and troughs of mode shape move up in the mode stable development region and move down in the mode conversion region. The single-mode dominating vibration exhibits a standing wave feature, and the traveling wave feature is significant in the mode conversion region. Furthermore, the frequency jump is always transmitted from the trough to the peak of the mode shape, and finally, all the axial positions vibrate at the same frequency. The trajectory in the mode conversion region deviates from the 8-shape and recovers the standard 8-shape at the middle and late stages of the mode stable development region. [ABSTRACT FROM AUTHOR]

Compared with thrombus dissolution using only thrombolytic agents, an advanced therapy of direct stirring of the blood clot can yield shorter recanalization time and higher recanalization velocity. Our previous research presented the design of a novel micro-stirrer, which can convert longitudinal vibration into transverse vibration and eventually generate opposite transverse vibration at the end-effort, like a scissor, for efficient blood clot stirring and thrombus dissolution acceleration. Transverse vibration is the most effective movement to dissolve thrombi. However, the small size of blood vessels has strict limits, which will greatly affect the output transverse vibration. Therefore, to improve the output performance of the micro-stirrer in curved and narrow vascular spaces, the analysis and structure optimization of the micro-stirrer is expected to increase the vibration mode conversion efficiency from longitudinal to transverse mode. The design concept and theoretical analysis of the micro-stirrer are presented in detail. Aiming to obtain the optimal structure parameters of the micro-stirrer, the mathematical model is established and analyzed. Next, a series of finite element models involving important structure parameters are designed and investigated. Finally, the optimal structure parameters are obtained, and the stirring effect in a blood vessel is verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

Asymmetry in a differential pair leads to deterioration of signal integrity. Differential pairs on a meshed ground often encounter asymmetry in return current paths. In this paper, we propose an offset mesh as an improved mesh structure that offsets asymmetry between a solid region and an aperture region. The offset mesh mitigates the asymmetry in the conventional mesh structure without additional design elements. The proposed structure has been verified to be effective in reducing mode conversion, intra-pair and inter-pair skews, and characteristic impedance variation in the time and frequency domains. This enables high-density routing of differential pairs.

One barrier, preventing the wide applications of elastic metamaterials (EMMs), is their limited ability to attenuate waves at low frequencies. Rainbow metamaterials (RMs), characterized by spatially varying structural parameters, can exhibit outstanding performance, boosting wider wave attenuation frequency ranges (stopbands) at lower frequencies compared to their counterparts of finite EMMs. However, attributed to the intricate topologies and constitutive relationships in 3D RMs, effectively configuring them to achieve enhanced wave-suspending capability is challenging. In most existing design approaches, frequency response analysis (FRA) method is frequently employed to iteratively calculate reliable stopband characteristics, leading to a significant computational burden. Herein, to address these challenges, a novel mode conversion approach is developed, underpinned by a recently proposed modal-based evaluation method (MEM) to estimate stopband characteristics, and a novel layer-based energy manipulation strategy to redirect energy, originating in excitation place, away from the output. The proposed approach is demonstrated to be effective for 3D RM design, through guiding the adjustment of geometrical parameters (GPs) of unit cells in each layer on 3D RMs. Moreover, the structure robustness is tested through experiments, facilitating the applications of 3D metamaterials. • Proposed a modal analysis-aided approach for 3D metastructure design. • Able to Estimate starting and cut-off frequencies via dominant eigenmode superposition. • Tuned geometrical parameters based on mode classification results. • Tuning geometrical parameters lowered starting frequency and enlarged normalized bandwidth simultaneously. [ABSTRACT FROM AUTHOR]

Optimization of the structure of piezoelectric transducers such as the proper design of matching layers can increase maximum wave energy transmission to the host structure and transducer sensitivity. A novel configuration of an ultrasonic transducer, where elastic metamaterial insertion is introduced to provide bulk wave mode conversion and to increase wave energy transfer into a substrate, is proposed. Configurations of layered elastic metamaterials with crack-like voids are examined theoretically since they can provide wide band gaps and strong wave localization and trapping. The analysis shows that the proposed metamaterial-based matching layers can sufficiently change wave energy transmission from a piezoelectric active element for various frequency ranges (relatively low frequencies as well as higher ones). The proposed configuration can also be useful for advanced sensing with higher sensitivity in certain frequency ranges or for demultiplexing different kinds of elastic waves.

Acoustic manipulation is a set of versatile platforms with excellent manipulation capabilities. In recent years, researchers have increasingly achieved specific manipulations beyond the translation and capture of particles. Here, we focus on the acoustic field momentum mechanism that generates an acoustic radiation force (ARF). A phononic crystal (PC) waveguide is established to amplify the forward momentum of the acoustic beam through the mode conversion of the acoustic field. Based on the conservation of momentum, the object gains reverse momentum. Thus, acoustic pulling can be achieved through the mode conversion of the acoustic field. Furthermore, we analyze the ARFs of two identical objects. It turns out that they can be manipulated separately by opposing forces. Our study provides a new way to achieve stable long-range acoustic pulling, and will explore, beneficially, the interaction between acoustic waves and matter.

Efficient mode conversion is crucial for hybrid photonic systems. We present efficient light transition from a standard single-mode fiber (SMF) to a subwavelength-diameter microfiber via a relatively short tapered fiber. Numerical simulations were performed to design the tapered morphology with high transmittance (approximately 86%) for the fundamental modes. The designed tapered fiber was successfully fabricated on the top of a cleaved SMF tip by the direct laser writing (DLW) method. For the 1550 nm wavelength, the transmittance from the standard SMF to the subwavelength-diameter microfiber was determined to be 77%, accompanied by a change in the effective mode area from 38 μm2 to 0.47 μm2 within a very short length of 150 μm. Our result demonstrated the versatility of the DLW technique for boosting the mode conversion efficiency of fiber-to-chip devices, enabling various applications in the future.

Over the past few decades, on-chip photonic integrated circuits based on silicon photonics (SiPh) platforms have gained widespread attention due to the fact that they offer many advantages, such as high bandwidth, low loss, compact size, low power consumption, and high integration with different photonic devices. The demand for high-speed and high-performance SiPh devices is driven by the significant increase in demand for Internet traffic. In photonic integrated circuits, controlling optical signals to make them circulate in a specific direction is a highly researched area of study. However, achieving a purely passive on-chip optical circulating network on a SiPh platform is very challenging. Therefore, we propose and demonstrate, through simulations, an on-chip optical circulator network on a silicon-on-insulator (SOI) platform. The proposed device can also support mode conversion. The proposed on-chip optical circulating network consists of two kinds of tailor-made multi-mode interferometer (MMI) structures and waveguide crossings. Through the optical power division and mode combination capabilities of the MMI, an optical circulating network supporting high optical isolation and mode conversion is achieved. The proposed optical circulating network has a loss of 1.5 dB at each output port, while maintaining a high isolation of 35 dB in the transmission window from 1530 nm to 1570 nm.