Parasitic Modes Research Articles

Investigation of the spatial distribution of deformations in quartz piezo elements by x-ray topography

Using X-ray topography on laboratory and synchrotron X-ray sources, the distribution of deformations in the volume of two types of AT-cut quartz resonators of different sizes were obtained. From a comparison of X-ray data and the amplitude-frequency characteristics of the resonators, a correlation between the deformation patterns and the features of oscillatory processes for operating modes and their harmonics, as well as for parasitic modes, was established. A connection between oscillations in parasitic modes, which manifest themselves in the amplitude inhomogeneity, and the topology of the resonators is found. The applied significance of the obtained results for the development and optimization of new designs of piezoelectric elements and the development of their manufacturing technology is noted.

The influence of parasitic modes on stable lattice Boltzmann schemes and weakly unstable multi-step Finite Difference schemes

Numerical analysis for linear constant-coefficient multi-step Finite Difference schemes is a longstanding topic, developed approximately fifty years ago. It relies on the stability of the scheme, and thus—within the L2 setting—on the absence of multiple roots of the amplification polynomial on the unit circle. This allows for the decoupling, while discussing the convergence of the method, of the study of the consistency of the scheme from the precise knowledge of its parasitic/spurious modes, so that the methods can be essentially studied as if they had only one step. Furthermore, stability alleviates the need to delve into the complexities of floating-point arithmetic on computers, which can be challenging topics to address. In this paper, we demonstrate that in the case of “weakly” unstable Finite Difference schemes with multiple roots on the unit circle, although the schemes may remain stable, considering parasitic modes is essential in studying their consistency and, consequently, their convergence. This research was prompted by unexpected numerical results on stable lattice Boltzmann schemes, which can be rewritten in terms of multi-step Finite Difference schemes. Unlike Finite Difference schemes, rigorous numerical analysis for lattice Boltzmann schemes is a contemporary topic with much left for future discoveries. Initial expectations suggested that third-order initialization schemes would suffice to maintain the accuracy of fourth-order schemes. However, this assumption proved incorrect for weakly unstable Finite Difference schemes and for stable lattice Boltzmann methods. This borderline scenario underscores that particular care must be adopted for lattice Boltzmann schemes, and the significance of genuine stability in facilitating the construction of Lax-Richtmyer-like theorems and in mastering the impact of round-off errors concerning Finite Difference schemes. Despite the simplicity and apparent lack of practical usage of the linear transport equation at constant velocity considered throughout the paper, we demonstrate that high-order lattice Boltzmann schemes for this equation can be used to tackle nonlinear systems of conservation laws relying on a Jin-Xin approximation and high-order splitting formulæ.

A broadband and compact TE01 mode bend with hexagonal section for high-power microwave applications

The conventional circular waveguide 90° TE01 bend makes it difficult to achieve broadband because of the serious interference from TM11 mode. To solve this problem, the mode coupling characteristics in the hexagonal waveguides are investigated in this paper, and it is found that when the deformation amplitude is appropriate, not only the degradation between TE01 and TM11 is broken but other parasitic modes can be efficiently suppressed. Based on the analysis, an oversized broadband TE01 waveguide bend with variable curvature is proposed, and its transmission efficiency is over 95% from 8.5 to 11 GHz, while its structure length is only 26.16 times wavelength. Measurement results indicate that the S21 of the bend is about −0.4 dB from 8.5 to 11 GHz, and it works stably under a microwave output power of 1 MW. The consistency between theoretical calculations, simulation, and experiments indicates the feasibility of this novel TE01 bend.

Suppression of Parasitic Modes in a Cylindrical Gyrotron Beam Tunnel by a Wall Corrugation With Schroeder Diffuser Structures

Suppression of Parasitic Modes in a Cylindrical Gyrotron Beam Tunnel by a Wall Corrugation With Schroeder Diffuser Structures

Immunomodulatory effects of hydatid antigens on mesenchymal stem cells: gene expression alterations and functional consequences.

Cystic echinococcosis, caused by the larval stage of Echinococcus granulosus, remains a global health challenge. Mesenchymal stem cells (MSCs) are renowned for their regenerative and immunomodulatory properties. Given the parasite's mode of establishment, we postulate that MSCs likely play a pivotal role in the interaction between the parasite and the host. This study aims to explore the response of MSCs to antigens derived from Echinococcus granulosus, the etiological agent of hydatid disease, with the hypothesis that exposure to these antigens may alter MSC function and impact the host's immune response to the parasite. MSCs were isolated from mouse bone marrow and co-cultured with ESPs, HCF, or pLL antigens. We conducted high-throughput sequencing to examine changes in the MSCs' mRNA expression profile. Additionally, cell cycle, migration, and secretory functions were assessed using various assays, including CCK8, flow cytometry, real-time PCR, Western blot, and ELISA. Our analysis revealed that hydatid antigens significantly modulate the mRNA expression of genes related to cytokine and chemokine activity, impacting MSC proliferation, migration, and cytokine secretion. Specifically, there was a downregulation of chemokines (MCP-1, CXCL1) and pro-inflammatory cytokines (IL-6, NOS2/NO), alongside an upregulation of anti-inflammatory mediators (COX2/PGE2). Furthermore, all antigens reduced MSC migration, and significant alterations in cellular metabolism-related pathways were observed. Hydatid disease antigens induce a distinct immunomodulatory response in MSCs, characterized by a shift towards an anti-inflammatory phenotype and reduced cell migration. These changes may contribute to the parasite's ability to evade host defenses and persist within the host, highlighting the complex interplay between MSCs and hydatid disease antigens. This study provides valuable insights into the pathophysiology of hydatid disease and may inform the development of novel therapeutic strategies.

Optimal waveguide structure for low-threshold InGaN/GaN-based photonic-crystal surface-emitting lasers

We analyzed the optimal waveguide structure of two types of InGaN-based photonic crystal surface-emitting lasers (PCSELs) to suppress the coupling with leaky modes via mode simulations. To minimize the threshold material gain (gth), we calculated the confinement factor and quality factor of PCSELs with varying waveguide layer thicknesses in the separate confinement heterostructure (SCH) layer. The optical mode intensity profile revealed the coupling between the fundamental mode of SCH and parasitic leaky modes in the cladding layer or substrate as the primary root cause of the low-quality factor and high threshold gain of PCSELs. The asymmetric nature of the SCH structure yielded the optimal waveguide structure to be dependent on the position of the air holes. With a proper waveguide thickness and air hole depth, the optimized threshold modal gain of PCSELs with the n-side air holes can be less than 30 cm−1.

Investigations on the multiple-sector hard-copper X-band accelerating structures

The development of advanced, high gradient accelerating structures is one of the leading activity of the particle accelerator community. In the technological research of new construction methods for these devices, high-power testing is a critical step for the verification of their viability.Recent experiments showed that accelerating cavities made out of hard copper, fabricated without high-temperature processes, can achieve better performance as compared with soft copper ones. Recently, we have built cavities using Tungsten Inert Gas welding and the high-power experiments confirmed that this joining process is a robust and low-cost alternative to brazing or diffusion bonding. This is a good solution for high-gradient operation, with a gradient of about 150 MV/m in X-band, at a breakdown rate of 10−3/pulse/meter using a shaped RF pulse with a 150 ns flat part.We continue the design, construction and high power tests of three-cells standing-wave X-band accelerating cavities fabricated with a split-open geometry, made of hard copper and vacuum-sealed by welding. Our aim is the fabrication of accelerating structures made out of hard copper alloys by using innovative cost-effective technologies. Moreover, our method of multiple-sector structures opens the way to new technological approaches and design methods, for example providing the possibility of placing dampers of the parasitic higher-order modes. Such structures with dampers allow for acceleration of multi-bunch beams, both in standing and in travelling-wave accelerating modality.This paper describes the design of two cavities made of multiple sectors that were fabricated at the Italian Institute for Nuclear Physics in Frascati, Italy (INFN-LNF), assembled by means of clamping and then joined with the Tungsten Inert Gas welding in order to preserve the hardness of the metal. These are three-cell standing-wave X-band accelerating cavities, to be operated in the π-mode. We report the low-power RF tests of the first one, made of two halves, and the RF design of the second one, made of four quadrants. Both structures were built for high-gradient tests at SLAC National Accelerator Laboratory.

Initialisation from lattice Boltzmann to multi-step Finite Difference methods: Modified equations and discrete observability

Latitude on the choice of initialisation is a shared feature between one-step extended state-space and multi-step methods. The paper focuses on lattice Boltzmann schemes, which can be interpreted as examples of both previous categories of numerical schemes. We propose a modified equation analysis of the initialisation schemes for lattice Boltzmann methods, determined by the choice of initial data. These modified equations provide guidelines to devise and analyze the initialisation in terms of order of consistency with respect to the target Cauchy problem and time smoothness of the numerical solution. In detail, the larger the number of matched terms between modified equations for initialisation and bulk methods, the smoother the obtained numerical solution. This is particularly manifest for numerical dissipation. Starting from the constraints to achieve time smoothness, which can quickly become prohibitive for they have to take the parasitic modes into consideration, we explain how the distinct lack of observability for certain lattice Boltzmann schemes—seen as dynamical systems on a commutative ring—can yield rather simple conditions and be easily studied as far as their initialisation is concerned. This comes from the reduced number of initialisation schemes at the fully discrete level. These theoretical results are successfully assessed on several lattice Boltzmann methods.

Noise analysis of the observatory superconducting gravimeter in the normal mode frequency range using gravity data of Ghuttu, Garhwal Himalaya, India

We present a study on gravity data from the Observatory Superconducting Gravimeter (OSG-051) located at MPGO Ghuttu in the Garhwal Himalaya, India. Ambient noise observed at this site is compared with other worldwide SGs and computed seismic noise magnitude for the OSG-051. Instrumental noise has been observed at frequencies ranging from ∼0.0239 to ∼0.03207 Hz in the form of parasitic mode for the lower and upper sensors of SG, whose quality factor has been estimated in different modes of oscillations. The signal is enhanced at noise reduction below 2.0 mHz using local barometric pressure data and modelled tidal effect of the site. Other seismic noise factors are discussed through data analysis of OSG-051. OSG-051 and trillium 240 Broad Band Seismometer data are analysed and compared in the seismic normal mode frequency band. Several observations have been made regarding noise sources that affect the gravity data in the seismic normal mode’s frequency band. Residual gravity data after removal of atmospheric pressure, tidal, and co-seismic effects, respond very well to long-period seismometers than any conventional seismometer. This characteristic and low noise level of the MPGO Ghuttu site makes it a suitable station for long-period seismometer studies.

Equal-strength beam design of acoustic wave accelerometers

Abstract Surface acoustic wave (SAW) based accelerometers have received significant attention due to their digital output, low cost, mass production and easy implementation of wireless passive function. However, conventionally rectangular cantilever-beam based SAW accelerometers often have non-uniform strains generated along the beams, which cause emergence of parasitic wave modes and measurement errors. In this paper, a simulation platform was developed to analyze and optimize designs of SAW accelerometers and variable-thickness and equal-strength beams were designed to solve the critical issue of non-uniform strain distribution along the beam. Frequency responses of SAW accelerometers under the acceleration were successfully obtained using the simulation platform, with the visualized strain/stress distribution and particle displacement field. The accuracy of this simulation platform was verified using the experimental result reported in literature. A highly sensitive and equal-strength beam SAW accelerometer was achieved with a sensitivity up to 1.40 kHz g−1, a linearity coefficient of ∼1, and a measurement range of 0∼15 g. Furthermore, a high-G accelerometer was designed, with the capability of enduring large shocks up to 11,500 g and a sensitivity of 6.96 Hz g−1.

Design and verification of a backward wave oscillation suppression circuit for the Ka-band gyrotron travelling-wave tube.

Backward wave oscillation seriously degrades the stability of gyrotron travelling-wave tubes (gyro-TWTs), especially during high average/continuous wave operation. To solve this problem, a selective mode suppression structure (SMSS) based on the mode coupling principle is proposed and applied in the nonlinear beam-wave interaction region to suppress the parasitic TE11 mode. It is capable of obtaining a high power and improving the tube stability. Simulation results demonstrate that the SMSS can raise the starting current from 10 to 18A and the starting pitch factor from 1.2 to 1.6. Based on this proposed circuit, a Ka-band TE01 mode gyro-TWT was designed, and the particle-in-cell simulation shows that it can achieve a saturated output power of over 150 kW from 29.7 to 31.7GHz with a velocity spread of 2.2%. For verification, a SMSS is manufactured and cold tested. The measurement of S-parameters reveals that it can effectively suppress the parasitic TE11 mode.

Drought Resistant Resting Cysts of Paraphysoderma sedebokerense Preserves the Species Viability and Its Virulence.

The blastocladialean fungus P. sedebokerense is a facultative parasite of economically important microalgae and for this reason it has gained a lot of interest. P. sedebokerense has a complex life cycle which includes vegetative and resting stages. The resting cysts were assumed to play an essential role in survival by resisting drought, but this ability was never tested and the factors that trigger their formation were not evaluated. This study was aimed to induce resting cyst formation and germination in P. sedebokerense. At first, we tested the survival of P. sedebokerense liquid cultures and found that infectivity is retained for less than two months when the cultures were stored on the bench at room temperature. We noticed that dry cultures retained the infectivity for a longer time. We, thus, developed a method, which is based on dehydration and rehydration of the biomass, to produce, maintain, and germinate resting cysts of P. sedebokerense in both saprophytic and parasitic modes of growth. When the dry cultures were rehydrated and incubated at 30 °C, resting cysts asynchronously germinated after 5 h and the "endosporangium" was protruding outside of the cyst. Our method can be used to preserve P. sedebokerense for research purposes with the advantage of no need for expensive equipment.

Robustness Improvement for Chipless RFID Reading Using Polarization Separation

In this article, a novel method to improve the readability of chipless tags is presented. When the EM wave falls upon the tag’s surface at normal incidence or with a known incidence, the proposed approach permits to obtain a higher signal-to-noise ratio (SNR) of resonators whose orientation with respect to the normal to the plane in which the tag is positioned is unknown and, thus, to increase the reading distance of the tag. It introduces a technique based on the detection of this tag orientation in relation to the antennas; a projection of the signals will allow correcting this misalignment in order to always be able to decode the tag identifier on a signal that corresponds to an ideal alignment between the tag and the antennas. With this principle, it is also possible to separate the resonance mode of the resonator that is connected to the identifier from other parasitic resonance modes that may appear due to a possible misalignment between the tag and the antenna. This principle is applied to loop resonators commonly used in chipless radio frequency identification (RFID), which can present strong parasitic modes of resonance. Also, this method makes the reading orientation invariant, allowing to read the resonator whatever its orientation with respect to the normal to the plane in which the tag is positioned. Likewise, the proposed method can be also used to sense this resonator orientation. This method requires a dual-polarization antenna and a two-port vector network analyzer (VNA). Results are validated in simulation and with real-environment measurements for a single resonator and multiple resonators, as it is classically used in chipless RFID technology. Measurements in a harsh environment, as well as comparisons with classical techniques, such as time gating (TG), are presented. A study on the improvement of the read range is achieved to highlight the potential of the proposed technique. A reading distance of more than 80 cm was, thus, obtained, which represents 20 cm more than with the classic use of a postprocessor based on time gating. Finally, the principle of the measurement is generalized by applying it to a tag with a ground plane and considering that the antenna is not necessarily placed in normal incidence with respect to the plane of the tag.

Exploration of the construction path of artificial intelligence big data "integrated" innovation and entrepreneurship ecosystem from the perspective of land use ecological suitability

Ecological environment has always been an important prerequisite while reflecting people and nature. The construction reflects the degree of development and civilization of a country as a whole, so it is related to the future of mankind. The deep integration of land use is a major breakthrough in solving the complex problems in the process of ecological civilization development and transformation. By establishing a "fusion" innovation and entrepreneurship ecological civilization system, this paper applies artificial intelligence and big data in the construction path of innovation and entrepreneurship ecological system from the perspective of land use and ecological suitability. Simulation studies were conducted in parasitic mode, biased symbiosis mode, asymmetric symbiosis mode, and symmetric symbiosis mode respectively through Matlab software. According to the results of the study, the subject size of the relevant subjects in the parasitic mode is only 70.43% of the subject size of the entrepreneurial enterprise. In the biased symbiosis model, the subject size of the relevant subject is 87.82% of the subject size of the entrepreneurial enterprise.

A quasi‐optical resonator with new coupling method and parasitic‐mode‐suppressing in 110–170 GHz

AbstractIn this paper, a quasi‐optical resonator with new coupling method and parasitic‐mode‐suppressing in 110–170 GHz is proposed. The coupling of terahertz (THz) quasi‐optical resonator in this paper is realized by PCB substrate processing and pressurized flange. At the same time, the parasitic mode is effectively suppressed by slitting the plane mirror to reduce the influence on the main mode during the test. And the fused quartz sample was tested to verify the feasibility of the system for complex dielectric testing of materials in 110–170 GHz.

Compact single-band and multiband terahertz plasmonic absorbers using hybrid graphene-metal resonators with switching and modulation capability

THz thermal and single-pixel imaging need compact tunable absorbers with features like high modulation depth and multi bandwidth in the case of multispectral imaging. Here we are going to propose compact switchable absorbers based on a hybrid graphene-metal resonator that is designed through a genetic algorithm and numerical method. The proposed absorbers have a thickness as small as λmax/120 and can acquire perfect modulation depth. The special shape of the proposed resonator helps to gather 6 resonance bands in a very compact unit-cell. A theoretical formula is proposed to predict the resonance frequencies of the absorber based on Fabry-Perot concepts and graphene-metal plasmons. The role of local and propagating surface plasmon and their hybridization in the absorption mechanism is clarified. The modulation capabilities and tunability of the absorbers are analyzed. The absorbers work very well in a wide range of incident angles. Based on numerical analysis the hybrid resonators were capable of suppressing parasitic resonance modes making the designed absorbers ideal for emitter applications. The proposed absorbers have applications in THz thermal imaging, modulators, and emitters.

Design and low-power measurement of 1.5 GHz TM020-type harmonic cavity for KEK future synchrotron light source

We designed a normal-conducting (NC) 1.5 GHz harmonic cavity that can be used in a future synchrotron light source at High Energy Accelerator Research Organization (KEK). By utilizing a higher TM020 mode for beam acceleration, this cavity has lower R/Q and higher unloaded Q as compared to those of conventional NC cavities. These features are advantageous in reducing the fluctuations in harmonic RF voltages when the bunch gaps are introduced. Harmful parasitic modes other than the TM020 mode can be heavily damped using coaxial slots located at the node of the TM020 mode. We made a concerted effort to lower the coupling impedances of parasitic modes while maintaining high Q value of the accelerating mode. We found that maintaining the axial symmetry of the cavity is essential for minimizing the leakage power of the accelerating mode into the coaxial slots. In this article, we present the optimization of the cavity shape, low-power measurement, and the basic design of a high-power model.

Mode Recognition by Shape Morphing for Maxwell’s Eigenvalue Problem in Cavities

In electrical engineering, for example during the design of superconducting radio-frequency cavities, eigenmodes must be identified based on their field patterns. This allows to understand the working principle, optimize the performance of a device and distinguish desired from parasitic modes. For cavities with simple shapes, the eigenmodes are easily classified according to the number of nodes and antinodes in each direction as is obvious from analytical formulae. For cavities with complicated shapes, the eigenmodes are determined numerically. Thereby, the classification is cumbersome, if not impossible. In this paper, we propose a new recognition method by morphing the cavity geometry to a pillbox and tracking its eigenmodes during the deformation.

Dual-Polarized Ka-Band Phased Array Using Hybrid Magnetic-/Electric-Dipole With Low Profile for Low Cross-Polarization Leakage Inside ±60° Scan Volume

This paper presents a 26–40-GHz 16×16 dual-polarized phased array. For the dual-polarized phased array antennas, the sources of cross-polarization leakage mainly include the polarization coupling from the feedlines and the radiators. Electric dipole (E-dipole) and magnetic-dipole (M-dipole) are the most common radiators, which both suffer from the deteriorated polarization isolation when scanning in D-plane. Here, the hybrid M-/E-dipole is employed to overcome this issue. To avoid the serious cross-polarization leakage from the typical 1/4 wavelength feedline of E-dipole, the M-dipole is chosen to form the primary radiator with the typical 1/10 wavelength feedline. Therefore, the excited electric-/magnetic-current field vectors on the radiators and the feedlines can be significantly weakened. However, the low-profile M-dipole introduces the half-patch TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode due to the coupling between the horizontal feedline and the ground plane. This parasitic radiation mode with the slant polarization seriously deteriorates the polarization isolation of the M-dipole. The shorted posts are employed to suppress the half-patch TM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> mode without breaking the M-dipole mode. Through that, the high polarization isolation characteristic of the dual-polarized M-dipole radiator is maintained. Then, the double-layer meta-surface (MS) is designed to act as the secondary radiator, i.e. the E-dipole. The MS also plays the role of the impedance matching layer. Based on these methods, the cross-pol. level better than {–66, –59, –52} dB in E-/H-planes and {–66, –28, –17} dB in D-plane when scanning to {broadside, 30°, 60°} is achieved, respectively.

A Pattern-Reconfigurable Cylindrical Dielectric Resonator Antenna With Three Switchable Radiation Patterns

A pattern-reconfigurable antenna with three switchable radiation patterns is investigated. It consists of a three-layer cylindrical dielectric resonator antenna (DRA) and a parasitic monopole antenna. Its feed network comprises a Y-shaped feedline, a square ring slot, and seven diodes. For the first time, by controlling the operation states of the diodes, the radiation pattern of the antenna can be switched between the omnidirectional, broadside, and unilateral modes. The omnidirectional pattern is obtained by virtue of the parasitic monopole, whereas the broadside pattern can be obtained when the DRA and radiation mode of the feeding ring slot are excited. If the parasitic monopole, DRA, and radiation mode of the slot are all excited, their radiation fields can be superimposed to give a unilateral radiation pattern. The radiated <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E</i> -field is vertically polarized for all of the three radiation modes. A prototype working in 2.4-GHz ISM band was fabricated and tested to verify the idea, and reasonable agreement between the measured and simulated results is observed.