Low-frequency Loss Research Articles

Sound transmission characteristics of piezoelectric metamaterial plates with resonant shunt circuits

Abstract In this study, a comprehensive investigation is conducted into the sound transmission characteristics of piezoelectric metamaterial plates, which feature five distinct resonant shunt circuits. To begin with, the intrinsic equations that pertain to piezoelectric materials, along with their equivalent models under external circuit conditions are established. Subsequently, the sound transmission loss of the plate and its corresponding equivalent bending stiffness model are constructed. Five resonant shunt circuits are employed, encompassing a basic resonant shunt circuit, one with series/parallel capacitance, and another with series/parallel negative capacitance. Ultimately, the influence of these diverse shunt circuits and their respective parameters on the sound insulation capabilities of piezoelectric metamaterial plates is comprehensively calculated and analyzed. Research results show that the inductance and resistance within the resonant shunt circuit influence the sound transmission characteristics exhibited by the piezoelectric metamaterial plate. Irrespective of whether the capacitance is configured in parallel or series within the resonant shunt circuit, the low-frequency sound transmission loss of the piezoelectric metamaterial plate experiences a notable modification. The effect of negative capacitances in the resonant shunt circuit on the sound transmission loss of the plate exhibits a contrasting pattern compared to the influence of the capacitances within the resonant shunt circuit on the sound transmission loss.

Estimation of Water-Like Bottom Length along an Acoustic Track in Shallow Water

Analytically and within the framework of numerical simulations, remote sensing of the water-like bottom in shallow water based on low-frequency sound propagation loss is considered. Water-like bottom sediments are understood as sediments in which the sound speed is close to the sound speed in water, but having a significantly higher density. A model statistical analysis of depth-averaged transmission loss is carried out for acoustic tracks of a fixed range in one of the areas of the Kara Sea with a known structure of the upper layer of the bottom, which includes water-like areas. A good correlation between low-frequency transmission loss and the length of water-like bottom is demonstrated. Based on this result, a method for remote integral estimation of the water-like bottom size at an acoustic track between a single source and a vertical array of hydrophones is proposed.

A vibroacoustic model for low-frequency sound transmission loss in circular membranes with added strip mass

Noise control strategies involve physical barriers in the transmission path. Conventional barriers conform to the mass law which states an inverse relation between sound transmission, barrier mass, and incident frequency. Practical scenarios for low-frequency noise attenuation require prohibitively thick barriers making them infeasible. Mass-loaded membranes exhibit marked differences in their dynamic nature from that of bare membranes as they do not necessarily conform to the mass law. Being thin, compact, and lightweight makes them geometrically ideal for most applications. The paper presents an analytical model based on the Newtonian approach for the vibroacoustic behavior of a pre-stretched elastic circular membrane with rigidly attached strip mass under normal incidence. The point collocation approach distributes the effect of the strip mass on the membrane as a collection of discretized concentrated loads along the interfacial boundary resulting in a summation that is easier to solve. The peak and dip frequencies of sound transmission are determined for circular membranes with eccentric and central strip mass. The present study evaluates strip mass-loaded membranes' capability to attenuate noise at low frequencies as an unconventional physical barrier.

A Transformer-based invertible neural network for robust image watermarking

For the existing encoder-noise-decoder (END) based watermarking models, since the coupling between the encoder and the decoder is weak, the encoder generally embeds certain redundant features into the cover image to enable the decoder to extract watermark completely, which will affect watermarking invisibility. To address this problem, this paper proposes a Transformer-based invertible neural network (INN) for robust image watermarking (IWFormer). In order to effectively reduce redundant features, the INN framework is utilized for the watermark embedding and extracting processes, so that the encoded features are highly consistent with the features required for decoding. For enhancing watermarking robustness, an affine Transformer module is designed by mining the global correlation of the cover image. In addition, considering that the human visual system is sensitive to low-frequency variations, the wavelet low-frequency sub-band loss is deployed to guide watermark to be embedded in middle- and high-frequency components, thus further increasing the quality of the encoded images. Experimental results demonstrate that compared with the existing state-of-the-art watermarking models, the proposed IWFormer owns remarkable advantages in terms of both watermarking invisibility and robustness.

User Behavior Analysis and Optimization Countermeasures in Shopping APP Interface Design

In this study, the interface design and marketing strategy of shopping APP were deeply discussed, and a series of optimization countermeasures were put forward. The principles of interface design and user behavior are analyzed, and the design problems such as information overload, complicated navigation, low usage frequency and high user loss are pointed out. The countermeasures of interface design optimization, user behavior guidance and marketing strategy adjustment are put forward, including simplifying interface, optimizing navigation, personalized recommendation, incentive mechanism, brand building and marketing promotion. These measures are aimed at improving user experience, enhancing user stickiness and enhancing market competitiveness. Through this research, it provides theoretical basis and practical guidance for shopping APP interface design optimization and market strategy adjustment.

Single-beam low-frequency loss modulation technique for two-photon absorption measurement

We present a straightforward and reliable single-beam configuration designed for the assessment of two-photon absorption (2PA) through the utilization of the loss modulation technique. Mechanical rotation of a half-wave plate induces a sinusoidal modulation in the envelope of the probe pulse train. The elimination of spurious signals is achieved by determining the difference of the lock-in amplifier output at the focused and defocused positions of the sample. Our findings, based on measurements with dye solutions and crystalline silicon, demonstrate the feasibility of determining the 2PA coefficient, subject to preliminary calibration of the setup with reference samples. Remarkably, the acquisition of the 2PA signal in silicon at 1030 nm is accomplished with less than 200 pJ energy of the laser pulse, overcoming the challenge posed by concurrent linear absorption. Additionally, a signal of 3PA is revealed despite the presence of 2PA and linear absorption.

Nd-, La-induced precipitate/defect in cobalt-iron magnetic alloy for strong and broadband microwave absorption

Soft magnetic microwave absorbents have merits of sufficient magnetic loss and unique magnetism-frequency response characteristics, yet are limited by the low natural resonance frequencies and simplex loss mechanism. Introducing second phase has been proven to be efficient in evoking structure, magnetism and conductivity changes, but the effects on the microwave absorption is still unbeknown. In this work, the Co0.72Fe0.28 alloy magnetic absorbents with dispersedly distributed NdCo5/LaCo5 nano precipitates were prepared. By fine-tuning the doping ratios of the rare earth (RE) of Nd/La, the coercivity and conductivity show an upward trend with enhanced magnetic and dielectric losses on 2–18 GHz. On one hand, the high magneto-crystalline anisotropic RECo5 phases uplifted the holistic resonance frequency ranges and enhanced the C/X/Ku band attenuations. On the other hand, the as-spawn vacancies, heterogeneous interfaces and dislocations boosted the conductive/polarization losses of the individual magnetic alloys. As a result, the high-frequency performance was significantly improved when ensuring the impressive low-frequency loss. A remarkable minimum reflection loss (RLmin) of −76 dB was achieved in the S band, and the effective absorption bandwidth (EAB) of 7.34 GHz was obtained at only 1.7 mm, covering most of the X/Ku bands. The performance sets it apart as the highest among the reported RE-transitional alloy absorbents so far. Overall, this work provides a feasible way and novel strategy for improving the microwave absorption properties for the traditional metal alloys and their compounds.

The preparation and performances of Co-Zn 18H hexagonal ferrite with an ultra-high magnetic resonance frequency and low-loss characteristics

Modern 5G communication technologies require evolution of antennas towards high frequency and miniaturization. The search for magneto-dielectric materials with simultaneous high permeability, matched dielectric constant, and low loss properties for sub-6 GHz band applications has received considerable attention from both academic and industrial circles. Due to the low magnetic resonance frequency and high magnetic loss, traditional spinel and hexagonal ferrites hardly meet these requirements. In this study, polycrystalline Co-Zn 18H ferrites (Ba5Co2-xZnxTi3Fe12O31) were synthesized by co-precipitation method with only one-step sintering process. The polycrystalline Co-Zn 18H hexagonal ferrite possesses an ultra-high natural resonance frequency (14.5 GHz) and low magnetic loss (tanδμ≤0⊡10), which provides a better performance factor (PF= 68.6 GHz) at a higher operating frequency (4.97 GHz) compared to traditional microwave ferrites. The miniaturization rate of the planar inverted F antenna (PIFA) with Co-Zn 18H ferrite working at 4.0 GHz reaches 13.3 %. These results demonstrate the high potential of Co-Zn 18H ferrites for high frequency and low loss applications.

Intercomparison of eddy-covariance software for urban tall-tower sites

Abstract. Long-term tall-tower eddy-covariance (EC) measurements have been recently established in three European pilot cities as part of the ICOS-Cities project. We conducted a comparison of EC software to ensure a reliable generation of interoperable flux estimates, which is the prerequisite for avoiding methodological biases and improving the comparability of the results. We analyzed datasets covering 5 months collected from EC tall-tower installations located in urbanized areas of Munich, Zurich, and Paris. Fluxes of sensible heat, latent heat, and CO2 were calculated using three software packages (i.e., TK3, EddyPro, and eddy4R) to assess the uncertainty of flux estimations attributed to differences in implemented postprocessing schemes. A very good agreement on the mean values and standard deviations was found across all three sites, which can probably be attributed to a uniform instrumentation, data acquisition, and preprocessing. The overall comparison of final flux time series products showed a good but not yet perfect agreement among the three software packages. TK3 and EddyPro both calculated fluxes with low-frequency spectral correction, resulting in better agreement than between TK3 and the eddy4R workflow with disabled low-frequency spectral treatment. These observed flux discrepancies indicate the crucial role of treating low-frequency spectral loss in flux estimation for tall-tower EC systems.

Improving low-frequency sound transmission loss of double panels with a plate-type acoustic metamaterial

The sound insulation performance of double-leaf partitions is crucially affected by the mass-air-mass resonance phenomenon, whose frequency reduction can shift the high sound insulation to lower frequencies. In this work, an alternative strategy for exceeding the low limit of the mass-air-mass resonance frequency of conventional double panels is proposed in terms of the effective surface mass density. An equivalent spring-mass model based on the effective medium theory is implemented to intuitively understand the characteristics. A simple double-panel metamaterial is designed by replacing one of the panels with a single-plate metamaterial attached strip masses to decrease the structural complexity. The extended semi-analytical method is applied to predict efficiently the sound transmission loss in the low-frequency range, which is verified by the coupled vibro-acoustic finite element method with excellent agreement. The results demonstrate that the proposed double-panel metamaterial can reduce the minimum of the resonant frequency without changing the areal mass density and panel spacing. The sound insulation can be significantly improved between the reduced mass-air-mass resonance and the anti-resonance frequencies. To provide a better understanding of the sound transmission loss improvement, parametric studies are conducted. The design strategy is validated through experiments conducted in an impedance tube, and the results corroborate the findings. This study is instrumental in designing double-panel partitions that require sound insulation in specific low-frequency regions.

Ladder broadband damping filters

RELEVANCE. The large proliferation of various nonlinear loads has led to serious power-quality related problems in power systems. THE PURPOSE. In this paper, we consider design procedure of broadband passive filters with flat frequency characteristics. METHODS. A general method for optimally design the arbitrary order broadband passive filters (BBF) is considered. The base structure of BBF has the form of resistively loaded reactive two-port. Conditions of low fundamental frequency loss and required filer selectivity have been determined. The BBF design procedure minimizes the grid total current distortion and takes into account the power system performance. RESULTS. New broadband passive filter scheme are proposed. Compensating performances of different BBF configurations are discussed. Case studies demonstrated that proposed scheme can filter characteristic and damp non-characteristic harmonic simultaneously. CONCLUSION. The results show that proposed broadband damping filters are the effective instrument for the power quality normalization in industrial power systems.

Interface-induced dual-pinning mechanism enhances low-frequency electromagnetic wave loss

Improving the absorption of electromagnetic waves at low-frequency bands (2-8 GHz) is crucial for the increasing electromagnetic (EM) pollution brought about by the innovation of the fifth generation (5G) communication technology. However, the poor impedance matching and intrinsic attenuation of material in low-frequency bands hinders the development of low-frequency electromagnetic wave absorbing (EMWA) materials. Here we propose an interface-induced dual-pinning mechanism and establish a magnetoelectric bias interface by constructing bilayer core-shell structures of NiFe2O4 (NFO)@BiFeO3 (BFO)@polypyrrole (PPy). Such heterogeneous interface could induce distinct magnetic pinning of the magnetic moment in the ferromagnetic NFO and dielectric pinning of the dipole rotation in PPy. The establishment of the dual-pinning effect resulted in optimized impedance and enhanced attenuation at low-frequency bands, leading to better EMWA performance. The minimum reflection loss (RLmin) at thickness of 4.43 mm reaches -65.30 dB (the optimal absorption efficiency of 99.99997%), and the effective absorption bandwidth (EAB) can almost cover C-band (4.72 ~ 7.04 GHz) with low filling of 15.0 wt.%. This work proposes a mechanism to optimize low-frequency impedance matching with electromagnetic wave (EMW) loss and pave an avenue for the research of high-performance low-frequency absorbers.

Older adults' decision-making following bad advice.

There is minimal research investigating the influence of advice on decision-making in older age. The present study investigated the effect of different types of bad advice, relative to no advice, on young and older adults' decision-making in the Iowa Gambling Task (IGT). Fifty-four older adults and 59 young adults completed the IGT after receiving no advice, or advice to select from disadvantageous deck A (small, high-frequency losses), or disadvantageous deck B (larger, low-frequency losses). Corrugator EMG, memory and fluid intelligence were assessed. Averaged across advice conditions, older adults made more disadvantageous selections than young adults. There were no age-related differences in responding to bad advice, nor in corrugator activity in response to losses (i.e. frowning), or in learning to avoid deck A faster than deck B. Selecting from deck B was associated with reduced education among older adults, and reduced fluid intelligence among young adults. The data suggest that older adults make more disadvantageous decisions than young adults, and this is not exacerbated by bad advice. Both young and older adults are slower at learning to avoid choices resulting in low frequency relative to high-frequency losses, and this may be associated with individual differences in cognitive processing.

New bell plate controlled multi-inertia channel magnetorheological fluid mount wide frequency vibration isolation control study

This paper introduces a novel type of magnetorheological fluid (MRF) mount designed to achieve wide-frequency vibration isolation for engines. While previous studies have explored vibration isolation using hydraulic mounts, there has been limited research on achieving wideband isolation with MRF mounts. Consequently, this paper presents an innovative MRF mount structure and investigates wideband vibration isolation control for engines. Initially, experiments with a multi-channel MRF damper validate the switchable operation of controllable channels. A novel controllable multi-inertia channel MRF mount system is proposed, aligning the working mode of controllable inertia channels with that of the MRF damper. The lumped parameter method is employed to derive the mathematical model of the MRF mount, and its high and low-frequency dynamic characteristics are thoroughly examined. Subsequently, a real-time multi-island genetic algorithm-optimized controller is developed to investigate wideband vibration isolation within the MRF mount system. The findings indicate that: (1) The MRF mount demonstrates adjustable low-frequency dynamic stiffness and loss angle within the frequency range of f = 0–50 Hz. In the frequency range of f = 50–100 Hz, the mount achieves its lowest dynamic stiffness value, effectively addressing the issue of high-frequency stiffening. (2) The real-time multi-island genetic optimized controller exhibits superior vibration isolation performance compared to traditional sky-hook control and hybrid sky-hook control methods, achieving optimal vibration isolation for the mount.

Experimental and Theoretical Realization of Morphology and Frequency Tuned Charge Transport Dynamics in Co-Zn Doped SrM Hexaferrite: Electrical, Impedance and Relaxation Realm

The present report comprehensively investigates the influence of sol-gel synthesized cobalt and zinc-substituted SrFe12O19 on the morphological, structural, dielectric, and electrical characteristics. XRD analysis revealed that the substituents successfully replaced Fe3+ ions, leading to the existence of magneto-plumbite structure of M-type hexaferrite in all synthesized samples with some minor traces of CoFe2O4 in Sr Co0.8Zn0.8Fe10.4O19. With increasing the substitution level, SEM micrographs exhibited the formation of grain clusters. The electrical parameters had been investigated in the 20 Hz to 2 MHz frequency range. In the low-frequency region, both dielectric constant and loss tangent decreased with Co-Zn substitution. Sr Co0.8Zn0.8Fe10.4O19 sample shows the minimum value of AC conductivity 3.95 × 10−5 Ω−1m−1 in the high-frequency region. Both the electric modulus and impedance spectra exhibit non-Debye behavior in all samples. The Cole-Cole plots ( M'' versus M') reveal the existence of a single semicircular arc in the x = 0.0 sample, caused by the grain boundary contribution.

Dimensional design of Fe0.9Co0.1 nano-alloys with enhanced low-frequency microwave absorption

Low-frequency microwave absorbing materials are critical for enabling radar stealth and interference resistance in gigahertz communication devices and electronic equipment. However, long-wavelength electromagnetic waves are not easily attenuated, due to the limitations of current absorbing materials, including low permeability and a lack of electromagnetic wave loss mechanisms at low frequencies. Herein, we design and prepare one- and two-dimensional Fe0.9Co0.1 nanoalloys with high permeability through an organic templating method combined with a constrained transformation strategy. We systematically investigate the impact of the anisotropy of monodisperse Fe0.9Co0.1 nanoalloys on low-frequency microwave absorption performance. The generous specific surface area of Fe0.9Co0.1 nanosheets facilitate multiple reflections and the scattering of electromagnetic waves within the absorber. This phenomenon, coupled with dielectric resonance, culminates in a maximum reflection loss value of − 48.7 dB at 4.2 GHz. More significantly, Fe0.9Co0.1 nanorods exhibit an absorption intensity of − 35.3 dB at a notably lower frequency of 2.5 GHz, outperforming existing materials, in addition to an efficient absorption bandwidth of 4.2 GHz at a thickness of only 0.7 mm. Through a combination of experimental investigations and finite element simulations, we identify that highly anisotropic magnetic nanorods demonstrate a robust magnetic coupling interaction, substantial interface polarization and quasi-antenna effect. These characteristics result in enhanced low-frequency electromagnetic losses. Our findings indicate that the high anisotropy of the Fe0.9Co0.1 nanoalloys significantly improves their microwave absorption performance, thus emphasizing their substantial potential in the development of efficient low-frequency microwave absorbers.

Effects of Zr4+ and Hf4+ substitution on the structure and dielectric response of Ba4Sm9.33Ti18O54 ceramics

Microwave dielectric ceramics with high relative permittivity (εr) are commonly used for the miniaturation of microwave devices. The dielectric loss mechanism of microwave dielectric ceramics, as well as the property modification, has been a concerned topic among scholars. Herein, the lattice structure, defects, and broadband dielectric response of Zr4+ and Hf4+ substituted Ba4Sm9.33Ti18O54 (BST) ceramics are systematically examined. The negative temperature coefficient of resonant frequency (τf) of BST ceramics can be tuned to near zero via ion substitution, owing to the Sm2Ti2O7 second phase with a large positive τf. Optimal microwave dielectric properties of εr = 81.3, Q × f = 10,800 GHz, and τf = −4.6 ppm/°C are achieved. The lattice vibration behavior and defect concentration are analyzed by Raman spectra and thermally stimulated depolarization currents (TSDC), respectively. The increasing volume of the unit cell and TiO6 octahedra, which is because of the large-radius substitution ions, leads to an increase in lattice vibration damping factor and the generation of more oxygen vacancies (VO∙∙). Therefore, the dielectric losses in the microwave and terahertz (THz) bands increase after substitution. Meanwhile, the low-frequency dielectric losses at high temperatures also increase due to the weak restraint of carriers by the lattice. The broadband loss mechanism of Zr4+ and Hf4+ substituted BST ceramics related to lattice vibration and defects might be referenced for developing low-loss dielectric ceramics.

Enhancing grain boundary contributions to improve the dielectric properties of (In0.5Nb0.5)0.05Ti0.95O2 ceramics by Bi aided sintering

The internal barrier layer capacitance effect substantially contributes to the colossal permittivity in In and Nb co-doped TiO2 (INTO) ceramics. Therefore, enhancing grain boundary density and ceramic compactness can efficaciously reduce their low-frequency dielectric loss. In this investigation, Bi2O3 addition was utilized to aid sintering and refine grains for INTO ceramics. The results reveal that Bi-doped INTO ceramics, in contrast to their undoped counterparts, exhibit a more refined and compact grain structure with a significant increase in the quantity of grain boundaries. Moreover, a noticeable reduction in low-frequency dielectric loss from above 0.1 to below 0.05 and enhanced frequency stability of permittivity from below 10 Hz to approximately 10 kHz were observed, along with a decrease in the sintering temperature to 1300 °C. In comparison to undoped INTO ceramics, Bi doping also enhances the withstand voltage capability by a factor of 1.5–4 for Bi-doped INTO ceramics. However, as the sintering temperature of Bi-doped INTO ceramics increases and the grain size enlarges, their breakdown voltage gradually decreases, but the non-linear coefficient of current-voltage characteristics progressively increases. Analysis of complex impedance spectra confirms that the increased grain boundary density and resistance in Bi-doped INTO ceramics is the primary factor for the enhanced dielectric properties and withstand voltage capability.

Reduce the low-frequency dielectric losses of (In0.5Nb0.5)0.05Ti0.95O2 ceramics by increasing grain boundary density and resistance

(In0.5Nb0.5)0.05Ti0.95O2 (INTO) ceramics exhibits unusual colossal permittivity properties. However, the high dielectric loss limits their practical applications. Increasing the contribution of grain boundaries to dielectric properties can reduce their dielectric loss. Therefore, La was added to increase the number of grain boundaries, while annealing was performed to improve the grain boundary resistance. The results show that La addition and annealing in air indeed reduce the grain size of INTO ceramics and low their dielectric loss due to increased grain boundary resistance. Specifically, the permittivity of annealed La-doped INTO ceramic remains at 2 × 104, and its dielectric losses are less than 0.05 from 30 Hz to 6.5 kHz, with a minimum of approximately 0.02. The dielectric loss at 1 kHz is below 0.05 from below −60 °C to about 90 °C. The effects of La-doping and annealing on INTO ceramics, as well as the origin of the colossal permittivity properties, were discussed.

Improvement of the low-frequency sound insulation performance of hollow double-leaf panels by inserting a bending panel

Air-borne sound transmission loss of building materials generally follows the mass law. Transmission loss decreases at lower frequencies and is minimal at the fundamental natural frequency f0. On the other hand, transmission loss increases below f0, and is controlled by stiffness. Moreover, the stiffer the materials, the higher the f0. In the other words, even without increasing the mass, increasing the stiffness can improve low-frequency transmission loss. We focus on the fact that flexible lightweight panels are easily stiffened by bending deformation. We conduct a basic study on the effect of inserting a bending panel into hollow double-leaf panels. Experimental results on single panels showed a correspondence between the increase of f0 by bending deformation and the improvement of low-frequency sound insulation performance. In the case of the double-leaf panels with the lightweight bending panel inserted inside, the stronger the bending, the more low-frequency sound insulation performance tended to be improved.