Working Frequency Research Articles

Quadruple and Quintuple Helix Innovation: A Multi-Actor Approach in Reducing the Prevalence of Stunting at Jeneponto Regency, Indonesia

This study aims to determine collaboration between government actors, industry, universities, non-governmental organizations and the media in reducing the prevalence of stunting at Jeneponto Regency. Qualitative methods used by collecting data through interviews, documentation and observation. The results of the data obtained then transcribed into an accurate tool called Nvivo 12 plus. The analysis units used main map and work frequency. This study found that collaboration between government, private, university, non-governmental organizations and media actors had a significant influence in reducing the prevalence of stunting at Jeneponto Regency. To overcome the high stunting rate in Jeneponto Regency, collaboration between actors was needed, including government actors, industry, educational institutions, non-governmental organizations and media. All these actors must work well together. Apart from that, it was also important to know the causes of stunting rate to remain high in Jeneponto Regency. The cause of stunting was the environment, including sanitation and access to clean water, which was very important to prevent stunting.

Combining Microstrip Meander Line and Dipole Antennas: Dual-Band Solution for PIR Equipment

One of the aviation navigation tools is the Instrument Landing System (ILS), which functions to provide guidance signals to aircraft in the final approach position toward the runway. The ILS consists of three components: the Localizer, Glide Path, and Marker Beacon. To ensure aviation safety and security, navigation equipment must be regularly inspected through Ground Inspection. With current technological advancements, Ground Inspection is being conducted using UAVs or drones. One of the components to be installed on the UAV is the PIR, which requires two antennas of different lengths to receive signals from the Localizer and Glide Path.In this study, a dual-band antenna was developed that combines a dipole antenna and a meander line microstrip antenna for frequencies 108-112 MHz and 328.6-335.4 MHz, using CST Studio Suite 2021 software and FR-4 substrate material. Simulation results showed good performance with a return loss value of -19.43471 dB, VSWR of 1.238951, and a bandwidth of 2 MHz at a frequency of 110.5 MHz, and a return loss value of -27.41626 dB, VSWR of 1.119686, and a bandwidth of 2.5 MHz at a frequency of 329.6 MHz.Measurement parameter values for the VHF band were a return loss of -14.1680 dB, VSWR of 1.487, and a bandwidth of 14.6 MHz. Meanwhile, for the UHF band, there was a shift in the resonance frequency to 368.5 MHz with a return loss value of -15.4202 dB, VSWR of 1.408, and a bandwidth of 11.4 MHz. In this antenna design, a dual-band combination of a dipole and a meander line microstrip antenna with dimensions of 320 mm was achieved, capable of operating in both the VHF and UHF frequency bands simultaneously. However, this antenna can only operate at the Localizer working frequency.

Bidirectional DC/DC Converter Based on Interleaved Parallel Buck/Boost Cascades CLLLC

ABSTRACTIn this paper, a two‐stage bidirectional DC/DC converter is suggested to handle the energy transfer for electric vehicles between high‐voltage and low‐voltage batteries. The converter enables bidirectional power transfer, a broad range of input voltage, and a high ratio of voltage. The front stage adopts the bidirectional CLLLC resonant converter, which possesses excellent soft switching characteristics because of its symmetrical structure in both forward and reverse directions. Open‐loop fixed frequency control is used in the forward direction to set the working frequency of the switching transistors near the resonance frequency, and the voltage and current double closed loop control is employed to achieve a constant voltage ratio and efficient power transmission in the reverse direction. The rear stage adopts an interleaved parallel bidirectional Buck/Boost converter, and the interleaved parallel structure helps to lessen the output current ripple. The duty cycle secondary distribution method is used on the basis of the voltage and current double closed loop control to regulate the output voltage and make the converter operate stably. The principle and characteristics of the bidirectional DC/DC converter are analyzed, and by modeling and experimentation, the theoretical analysis's viability and correctness are confirmed.

A Polarization‐Insensitive and Adaptively‐Blazed Meta‐Grating Based on Dispersive Metasurfaces

AbstractThe diffraction efficiency of blaze gratings is optimized only at a specific frequency due to a fixed blaze angle, resulting in reduced and variable diffraction efficiencies over the working frequency band. Additionally, blazed gratings demonstrate polarization dependence due to their groove structures and the interaction of light with their surfaces. Consequently, designing gratings with constant diffraction efficiencies across a wide frequency bandwidth while maintaining polarization independence remains a challenge. Here, a design paradigm of dispersion engineerable meta‐grating inspired by orthogonal harmonic oscillations (OHO) is presented. Utilizing the OHO model, the phase dispersion of a metasurface can be precisely controlled, which applies to any unit cell featuring two orthogonal electromagnetic resonances. As a proof of concept, a polarization‐insensitive meta‐grating is showcased, where the blazed angle adapts with the incident frequency, ensuring broadband performance. In the experiment, the adaptively‐blazed grating measured an optimized and constant diffraction efficiency of ≈80% over the working wavelength range, i.e., 8.7–12.2 µm. The difference in diffraction efficiency between the two perpendicular linear polarization states remains within 4.6%. The proposed paradigm paves the way for meta‐device design based on precise dispersion engineering, which has potential applications in spectrometers, broadband beam forming and steering, hyperspectral imaging, etc.

Investigating the Annual Cross-Correlation between HPF, OWF and BUF Ionospheric Parameters over Middle East Region

In this work various correlation methods were employed to investigate the annual cross-correlation patterns among three different ionospheric parameters: Optimum Working Frequency (OWF), Highest Probable Frequency (HPF), and Best Usable Frequency (BUF). The annual predicted dataset for these parameters were generated using VOCAP and ASASPS models based on the monthly Sunspot Numbers (SSN) during two years of solar cycle 24, minimum 2009 and maximum 2014. The investigation was conducted for Thirty-two different transmitter/receiver stations distributed over Middle East. The locations were selected based on the geodesic parameters which were calculated for different path lengths (500, 1000, 1500, and 2000) km and bearings (N, NE, E, SE, S, SW, W, NW) using a Matlab program that was designed and implemented for this purpose. Depending on the investigation results of the cross-correlation, a third order polynomial equation provides a better representation of the correlation between the tested parameters. Also, the annual values of the HPF, OWF, and BUF parameters were predicted using the proposed mathematical correlation equations. These equations were confirmed by comparing their results with the observed datasets for the studied years. Several statistical methods were used to validate the presented data, all of which gave good results for all tested cases. Also, contour plot diagrams were used to visually illustrate the annual average distribution pattern of the tested ionospheric parameters for all geodetic factors for the minimum and maximum years of Solar Cycle 24.

On the directionality of membrane coupled Helmholtz resonators under open air conditions

Controlling the absorption and diffusion of sound in the audible range constitutes an exciting field of research. Acoustic absorbers and diffusers perform extraordinarily well at high frequencies with sizes comparable to the wavelength of the working frequency. Conversely, efficient low-frequency attenuators demand large volumes leading to unpractical sizes, and there is now interest in determining whether the size of the resonator can be reduced while not compromising – or perhaps even decreasing – the working frequency. One viable approach is through the use of metamaterials to enable the control of device dynamics such that heavy sub-wavelength attenuation can be efficiently realised. To achieve this goal, the theoretical (including a mathematical model and the use of finite element analysis) and experimental characterisation of 3D-printed membrane-coupled Helmholtz resonator (HR) acoustic metamaterials (AMMs) is explored. The results reveal good agreement between theory and experiments, and show that membrane-coupled HR AMMs feature heavy sub-wavelength acoustic attenuation (λ/55) while also showcasing directional responses under open air conditions. These features are explained by the interplay between resonator size, membrane characteristics, and the presence of two acoustic ports. It is anticipated that, together with recent advances on smart AMMs, these systems will foster new progress in the development of dynamic AMMs for wideband attenuation.

Ultra-miniaturized HMSIW cavity-backed reconfigurable antenna diplexer employing dielectric fluids with wide frequency tuning range

This communication presents an ultra-miniaturized two-way frequency tunable antenna diplexer based on cavity-backed slots and dielectric fluids. The proposed antenna utilizes two half-mode substrate-integrated rectangular cavities loaded with slots and fluidic pockets. The conventional size reduction is achieved by employing half-mode cavities, whereas ultra-miniaturization is obtained by applying the slots, which provides additional capacitive loading. As the cavities are of unequal sizes, a weak cross-coupling path is created between the ports to obtain high isolation (> 30 dB). The isolation is further enhanced by loading the slots. Two mechanisms are analyzed to tune the frequency bands individually or simultaneously. Firstly, the width of the slots can be altered to tune the frequency bands. However, this method involves modification of the physical dimensions of the antenna. Secondly, fluidic vias are created on the bottom plane of the cavities. These can be filled with various dielectric liquids to achieve frequency reconfigurability without altering the physical dimensions of the antenna. To demonstrate the concepts considered, the prototype of the proposed antenna was fabricated and experimentally validated. The structure has a footprint of 0.045λg2 and an isolation exceeding 33.4 dB. The operating frequencies are tunable in the range from 3.08 to 3.84 GHz (lower band) and from 4.97 to 6.33 GHz (upper band) by varying the dimensions of the slots whereas the operating frequencies are reconfigurable in the range from 2.74 to 3.38 GHz (lower band) and from 4.54 to 5.58 GHz (upper band), by employing microfluidic approach. As a result, the working frequencies may be varied in the range from 2.74 to 3.84 GHz (lower band) and from 4.54 to 6.33 GHz (upper band), making this antenna diplexer a competitive candidate for several communication systems. The cross-polarization levels, front-to-back ratio, and realized gain are greater than 19 dB, 18 dB, and 2. dBi, respectively. Excellent consistency is observed between full-wave simulation results and the measurement data.

Noise-induced stochastic internal resonance in nonlinear energy harvesting.

We analytically study the dynamic behavior of a linear mechanical energy harvester nonlinearly coupled to a linear oscillating mode, driven by stochastic Gaussian forces. Using renormalization theory and Feynman diagrams, we determine the renormalization of three key system parameters: the natural frequencies of the oscillating components and the parameter associated with the driving force amplitude. Our results show that random forces can induce the well-known internal resonance state, where the renormalized quantities exhibit a nontrivial dependence on the working frequency. In this state, coherent synchronization between the two oscillatory systems leads to qualitative changes in their respective spectral densities, with direct implications for the harvested electrical energy. Finally, we numerically validate our analytical findings.

Boosting Low-E electro-strain via high-electronegativity B-site substitution in lead-free K0.5Na0.5NbO3-based ceramics

Lead-free piezoelectric actuators emerge as promising substitutes for their lead-containing counterparts to address environmental concerns. However, they often confront a trade-off between low driving electric fields and high electro-strain. Herein, a novel strategy to boost electro-strain under low electric fields is proposed by doping high-electronegativity B-site atoms into perovskite potassium sodium niobate-based ceramics. Our findings reveal that high-electronegativity B-site atoms elevate the covalency of B-O bonding, softening the short-range repulsion and introducing local multiphase coexistence. This leads to more nanoscale domain structures and lower coercive field, thereby enabling large strains to be produced at lower electric fields. Notably, a substantial 0.2 % bipolar electro-strain and 0.1 % unipolar electro-strain under 10 kV cm-1 is achieved in Sr, Sb co-doped potassium sodium niobate ceramics, with a broad working frequency and temperature range, as well as excellent fatigue resistance. This study unveils innovative insights into designing lead-free piezoelectric ceramics with remarkable electro-strain performance and low driving electric field, promising a significant advancement in lead-free piezoelectric materials science and piezoelectric actuators.

Phase-cancellation of velocity oscillations in a flow duct using a slow-sound metamaterial

Self-sustained acoustic oscillations in industrial systems with mean flow can cause unwanted vibrations or noise pollution. Acoustic metamaterials can be engineered and integrated in such systems to prevent these limit cycles. In this study, an acoustic metamaterial is proposed for decreasing the acoustic admittance at the outlet of a contraction in a pipe. It can reduce velocity oscillations by more than 50%, without requiring an enlargement of the pipe or increasing the static resistance to the mean flow significantly. The acoustic metamaterial consists of an array of slow-sound and regular channels, which form a contraction in a pipe. The slow-sound effect shifts the resonances of the respective slow-sound channels. For the frequency of interest, the velocity oscillations of these two types of channels are out of phase, which reduces the spatially averaged velocity oscillations at the outlet of the contraction and therefore decreases its acoustic admittance. The effect is demonstrated experimentally, using impedance measurements and particle image velocimetry. A key achievement of this work is the demonstration of a device that is nearly lossless for the mean (steady) flow, i.e. having a low pressure drop, while being very stiff for the acoustic (oscillating) flow at its nominal working frequency, i.e. low admittance, which was so far a difficult challenge to address.

Harvesting both wind energy and vibration energy by a zigzag structure with hybrid magnetic and piezoelectric effects

In practical environments, wind energy and vibration energy often coexist. Considering this, we introduce a new energy harvester designed to concurrently harness wind energy and vibration energy by integrating magnetic and piezoelectric effects. This harvester is composed of a zigzag structure and a bluff body. The bluff body is designed to execute galloping under incoming fluid flow and produce outputs, while the zigzag bi-stable structure can harness the energy of base excitation effectively. The introduction of magnetic interaction leads tothe softening-spring characteristic, which is verified by the nonlinear analysis. This softening-spring nonlinearity canenhance the working frequency range of the harvester. The results obtained from the numerical simulations indicate that the interaction of base excitation and wind flow can significantly improve the non-resonance region output. Corresponding validation experiments are carried out. The results are in good agreement with the numerical ones. Under stochastic excitations, the output power obtained from the hybrid scenario can reach 73.04 μW, representing a 16 % increase compared to the pure base excitation scenario.

Anomalous wavefront control of Lamb wave with metasurfaces via superposed prism resonance

As a special branch of metamaterials characterized by phase discontinuity, elastic metasurfaces have presented extraordinary capacity for elastic wave manipulation. This class of metamaterials has received extensive attention in recent years. In this paper, a subwavelength elastic metasurface with locally resonant prisms is employed to steer the propagation of the A0 Lamb wave. Based on the dispersion curve and transmission ratio, we establish that the resonant feature of prisms is influenced by the diagonal ratio of cross section. By gradually tuning the diagonal ratio of prism cross section, the pattern of resonance modes and the mechanism of resonance superposition are clarified. In this regard, two different resonant modes can be superimposed at a certain frequency. A complete 2 π phase shift that is crucial for redirecting wave propagation can therefore be realized. To have a broader working frequency range, the influence of prism height on the resonance superposed frequency and the effect of plate thickness on the incident flexural wave are explored. Based on the generalized Snell’s law, negative refraction is verified numerically through a metasurface assembled from unit cells with constant phase change. In addition, other wavefront modulations such as eccentric focusing, nonparaxial propagation are also demonstrated. This novel design introduces new degrees of freedom in many engineering applications such as seismic wave protection, structural health monitoring and energy harvesting.

Reconfigurable super‐low‐frequency magnetoelectric antenna for underwater frequency‐hopping communication

AbstractBased on the mechanical regulation mechanism, a super‐low‐frequency (SLF) reconfigurable magnetoelectric (ME) antenna is proposed for underwater frequency‐hopping communication. By constructing the mechanical model of the ME antenna loaded with an adjustable spring, the antenna's working frequency is predicted to be tuned in an extensive dynamic range from 148 to 331 Hz by changing the states of a loaded spring. The experiment is implemented in the frequency‐response test platform and the practical communication system using the minimum shift keying modulation. The former experiment well validates the tunable frequency response of the reconfigurable ME antenna, while the latter successfully achieves the information transmission at different working frequencies. The proposed SLF reconfigurable ME antenna serves as a potential candidate for under‐water frequency‐hopping communication.

Ultra-low frequency reconfigurable magnetoelectric antenna based on mechanical regulation mechanism

Based on the mechanical oscillation principle of the magnetoelectric (ME) antenna, an ultra-low frequency (ULF) reconfigurable ME antenna based on the mechanical regulation method was proposed in this study, which can effectively serve as an underwater electromagnetic sensor. The ME antenna’s multidimensional performance, such as working frequency, bandwidth, and the quality factor (Q), can be tuned in an extensive dynamic range without damaging the antenna’s structure. Based on the oscillation theory of the ME antenna, the corresponding equivalent circuit model was also constructed, and the multidimensional tuning method of the ME antenna was quantitatively analyzed. Finally, a prototype was fabricated, and the reconfigurable characteristics of the ME antenna were tested in the mechanical domain and the electromagnetic domain, respectively, which verified the feasibility and effectiveness of the mechanical regulation method. Experimental results demonstrated that the working frequency, bandwidth and Q value regulation ranges were 138 ∼ 1133 Hz, 14 ∼ 222 Hz and 2.85 ∼ 22.57, respectively. The proposed work based on the mechanical actuators is the first reported reconfigurable ME antenna without structural damages. This technique has potential in solving the realistic narrow-band problem of the existing ME antennas and working frequency deviation problem in the ME antenna array application. These benefits help increase the information capability and the array scale, thus pave the way for realizing high-quality underwater sensing.

A Versatile Shared-Aperture Antenna for Vehicle Communications

This communication introduces a versatile, multi-service, shared-aperture antenna system for multiple vehicle applications. The design comprises three antenna elements: a rotatable microstrip antenna for global positioning system (GPS) communication, a cross-dipole circularly polarized antenna for satellite communication in the S-band, and a pattern reconfigurable antenna for V2V (vehicle-to-vehicle) communication. These antennas collectively support GPS, satellite communication (Satcom), and V2V communication in a single, shared-aperture design. This shared-aperture antenna system offers cost savings and occupies less space compared to using separate antennas for each service. The microstrip antenna covers the 1575 MHz frequency band used for GPS communication. The cross-dipole circularly polarized antenna provides continuous wideband coverage for S-band satellite communication. The pattern reconfigurable antenna, tailored for the specific application scenario, covers the 5.9 GHz V2V working frequency band (5.855–5.925 GHz). Practical testing and simulation results confirm the effectiveness of this antenna system for the intended applications. In summary, the microstrip antenna has a bandwidth of 1.565–1.578 GHz and a realized gain of 7 dBi with radiation efficiency of 81%, the cross-dipole antenna has a bandwidth of 2.2–3.8 GHz (53.3%) and a realized gain of 8.3 dBi with radiation efficiency of 90%, and the pattern reconfigurable antenna has a 5.8–6 GHz bandwidth and a realized gain of 3.7 dBi with radiation efficiency of 85%, and the isolation between antennas with different frequencies is 25 dB, 20 dB, and 30 dB in three frequency bands.

Tunable flexural waves by piezoelectric metasurface with shunt circuits

Elastic metasurfaces have been rapidly developed for effective modulation of elastic wave propagation. Among them, utilizing the electromechanical coupling effect of piezoelectric materials provides a promising way to design tunable and multifunctional elastic metasurfaces, but piezoelectric metasurfaces still face big challenges in theoretical guidance and experiments. In this paper, a tunable piezoelectric metasurface is proposed for achieving modulation of flexural wave in broad working frequency range. Based on the developed electromechanical coupling model, the piezoelectric patch with shunt resistor–inductor circuit is analyzed, and the functional unit of metasurface with only two piezoelectric patches is designed for modulating the flexural wave in thin plate. By using Antoniou’s circuit and considering the effect of impedance in circuit, the arbitral phase shift of functional unit is experimentally achieved by adjustable shunt circuits to verify the turnability in a full 2π range. Further, the piezoelectric metasurface by assembling functional units can realize multiple functions, like tunable anomalous refraction and wave focusing, by adjusting shunt circuits.

Computer use and cardiovascular risk biomarkers in midlife and older adults

With increased computer usage amongst midlife and older adults, concerns are emerging with regards to the potential adverse health effects of computer use given the sedentary habits it may encourage. The current study aims to investigate the relationship between computer use and cardiovascular risk in midlife and older adults. From the National Survey of Midlife Development in the United States II: Biomarker Project (2004–2009) and the National Survey of Midlife Development in the United States (MIDUS II), 2004–2006, we examined five cardiovascular risk biomarkers—high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides, interleukin-6, and C-reactive protein—in relation to self-reported general computer use frequency and computer use at work frequency. Our results show that general computer use frequency and computer use at work frequency were not significant predictors of any of the five cardiovascular risk biomarkers—HDL cholesterol, LDL cholesterol, triglycerides, interleukin-6, and C-reactive protein. However, our exploratory analysis showed that employment status significantly moderated the relationship between general computer use frequency and LDL cholesterol. Our study highlights the importance of a more nuanced approach to understanding the health implications of computer use and sedentary behaviour in general.

Design and Construction of a 500–800 MHz Square Spiral Dipole Microstrip Antenna Structure

An antenna can be used to detect an object. The dimensions of the antenna also affect the working frequency, the smaller dimensions, the higher the working frequency and the closer the antenna range to radiate waves. Therefore, a microstrip antenna with a small dimension size is needed, but the antenna radiation distance capability for radar systems still needs to be reduced. A microstrip dipole antenna with a spiral shape, measuring 5 cm, was meticulously designed and fabricated. The square dipole antenna, featuring an optimal design with the arm structure rotated in a clockwise direction, achieved an impressive return loss of -27.54dB with a VSWR of 1.83. The engineering refinement of the antenna design involved the addition of a square shape, which led to a significant and impressive improvement in performance. The second spiral antenna, operating at a frequency of 805MHz with an impressive bandwidth of 57MHz, exhibited a remarkable return loss of -30.83dB and a VSWR of 1.07.

Low-frequency broadband acoustic ventilation meta-barrier based on consecutive multiple Fano resonances

Acoustic metamaterials utilizing Fano resonance provide the possibility of simultaneous airborne sound insulation and high-performance ventilation. However, the ultra-sharp line shape results in a narrow working frequency range, which is still insufficient for practical applications. In this work, we propose a low-frequency acoustic meta-barrier supporting consecutive multiple Fano resonances (CMFRs) with broadband (~75%) capability, efficient ventilation, and ultra-thin thickness, etc. The barrier features a binary metastructure, incorporating a chiral space coiling tunnel and a hollow pipe in a planar arrangement. This configuration offers discrete and continuous states within the composed Fano system, corresponding to the tunnel and the pipe, respectively. By means of superposition of multi-order Fano resonance modes, the destructive interference between the discrete and continuum states keeps effective in a broad frequency range, while simultaneously achieving high air permeability. Numerical results of transmission loss show significant attenuation of incident energy in the range of 479-1032 Hz. Our work lays the groundwork for next generation of Fano-based metamaterial applications, with far-reaching implications for noise control and related fields.

Simulation and fabrication of a 20 kHz single-beam transducer

Abstract With the vigorous development of underwater acoustic technology in China, underwater acoustic transducers are constantly moving towards broadband, low-frequency, and high-power directions. How to obtain piezoelectric transducers with lower frequencies is still a research direction that scholars from various countries are striving to study. This article mainly studies and manufactures a 20 kHz single-beam piezoelectric transducer, using the classic Tonpilz transducer structure. Firstly, the Tonpilz transducer is theoretically analyzed using the classical equivalent circuit method. Secondly, the transducer is analyzed using ANSYS finite element analysis software to study the influence of piezoelectric ceramics on the frequency of the transducer, and the size of the piezoelectric ceramics is optimized to determine the size of the piezoelectric ceramic structure of the transducer. The working frequency of the transducer was calculated using software, and it was determined that the working frequency was approximately 20 kHz.