Prescribed Frequency Band Research Articles

Surrogate Model for Design Uncertainty Estimation of Nonlinear Electromagnetic Vibration Energy Harvester

The paper proposes a solution to the problem of estimating the uncertainty of the output power with respect to the design parameters for an electromagnetic vibration energy harvesting converter. Due to costly utilisation of time-domain mathematical models involved in the procedure of determination of the average output power of the system, an algorithm for developing the surrogate model that enables rapid estimation of this quantity within the prescribed frequency band limits is proposed. As a result, the metamodel sensitive to the most impactful design parameters is developed using Kriging with successive refinement of the design grid for gaining the accuracy. Under operational conditions with a constant magnitude of the acceleration signal and the prescribed frequency band limits, the surrogate model enables evaluation of the average output power of the system at 105 design points in less than 2 s of computer execution time. The consistency and accuracy of the results obtained from the surrogate model is confirmed by comparison of selected results of computations with measurements carried out on the manufactured prototype. Based on the latter and the surrogate model, the confidence intervals for the design procedure were determined and the most important spread quantities were estimated, providing quantitative information on the accuracy of the design procedure developed for the considered system.

Integration of Sub-6-GHz and mm-Wave Bands With a Large Frequency Ratio for Future 5G MIMO Applications

The integration of sub-6-GHz and millimeter-wave (mm-wave) bands has become an important issue for future fifth generation (5G) wireless communications owing to their large frequency ratios. This paper proposes a compact-size dual-function antenna operating at 3.5 GHz and the mm-wave band (28 GHz) for 5G mobile applications using a frequency reconfigurability technique. The proposed antenna comprises a microstrip patch linked with a meandered radiating structure through a radio frequency PIN diode to achieve frequency reconfigurability between the two bands. A significant size reduction up to 15.3 mm × 7.2 mm × 0.508 mm for the proposed antenna was achieved using a meandered line structure and truncated ground plane. To enhance the functionality, 8 × 8 multiple-input multiple-output (MIMO) with possible long- and short-edge antenna placement configurations were demonstrated. The system exhibited satisfactory MIMO characteristics with wide decoupling -10 dB bandwidths of 7.4% and 4.8% at the low- and high-frequency bands, respectively, without utilizing any external decoupling structure. The simulated results were validated using fabricated prototypes, and good agreement was observed. Additionally, a safety analysis based on the specific absorption rate and power density at the prescribed frequency bands was conducted using a realistic human model, and the results were found to be in accordance with the safety guidelines. Owing to the integration of sub-6-GHz and mm-wave bands in a single compact structure with a large frequency ratio and good MIMO performance, the proposed antenna system is suitable for future 5G mobile handheld devices.

Layout optimization of porous sound-absorbing material in mid-frequency vibro-acoustic systems

In this paper, a new layout optimization technique is integrated with a statistical modal energy distribution analysis (SmEdA) model to obtain the optimal layout of a porous sound-absorbing material for noise control in mid-frequency vibro-acoustic systems. The considered optimization problem is minimizing the total energy of the internal acoustic cavity within the prescribed frequency range by reasonably positioning porous sound-absorbing material patches under a given volume constraint. The principle of SmEdA is based on the power balance between different modes of coupled structural and acoustic subsystems. A modal strain and kinetic energy (MSKE) method is employed to estimate the acoustic modal damping loss factors that are associated with the energy attenuation between different modes of the coupled subsystems. The developed real-valued optimization formulation provides the feasibility of adopting an accurate sensitivity analysis technique, the complex variable method (CVM). The effectiveness of the optimization procedure is demonstrated through a significant reduction in the total acoustic energy. Additionally, some conclusions with realistic significance are obtained: (a) The optimal material layout creates a more uniform distribution of modal energies in the SmEdA model; (b) The acoustic modes tend to move out of the prescribed frequency band through optimization.

Genetic Algorithm-Based Approach for Minimising Losses in Substrate-Integrated Waveguide

The transitions in air-filled substrate-integrated waveguide (SIW) are studied here for millimetre-wave applications. A good design of an air-filled SIW (AFSIW) must allow for minimum losses in its interconnects between the air-filled and dielectric-filled regions of the SIW. This paper assesses the influence of the geometry of transition taper in an AFSIW on the return and insertion losses using full-wave analysis of a complete AFSIW structure. The data from the return and transmission losses provide a basis in the optimisation of the design of the transition tapers. The optimisation approach uses the multi-objective genetic algorithm (GA) with full-wave analysis to find an optimum profile of the transition. Defining the profile of the transition taper with a clamped cubic spline as a phenotype, the developed procedure shows that further losses are possible within the prescribed frequency bands. Furthermore, the length of the transition taper can be significantly reduced while maintaining an optimal quality of signal transmission in the transition. The simulation results show the efficacy of the proposed strategy where the optimal taper geometry is shown to provide a wider band of operating frequencies with lower return loss compared to a more established taper geometry.

Active Radar Cross Section Reduction of an Object Using Microstrip Antennas

AbstractThe research performed in this paper suggests that the radar cross section of an arbitrarily shaped object can be reduced by canceling the scattering from the object with the radiation from an antenna (implemented here as a microstrip antenna) placed on the surface of the object. Assuming that the direction of arrival of the incident signal is known, the radiation from the defending antenna can be adjusted in real‐time to cancel the scattering from the object in order to produce a negligible total field at the distant receiver so that the object becomes invisible to a monostatic radar working in a given known frequency band. This is implemented using an analog sensor on the object to measure the time domain field on the object, which is then connected to the antenna through an amplifier and phase shifter to control the radiation from the patch antenna. The system is implemented in real time and does not require any digitization or signal processing. The radar cross section reduction can thus be achieved with a wide variety of incident signals in the prescribed frequency band.

A wideband triple-layer microperforated panel sound absorber

Microperforated panels are light, clean and tunable sound absorbers, which fundamentals were already established in the previous century. They consist of a distribution of minute holes of diameter d on a panel of thickness t with perforation ratio ϕ in front of an air layer of thickness D. Therefore, the frequency band of absorption of a single-layer microperforated panel depends on (d, t, ϕ, D). In noise control applications, such a simple structure provides absorption in the frequency range of interest if holes are of sub-millimetric diameter. The former single-layer microperforated panels had two main weaknesses: narrow frequency band of absorption and a high manufacturing cost. However, nowadays these deficiencies can be easily surpassed. The absorption frequency band can be drastically increased by means of multiple-layer structures. The manufacturing cost may be reduced with the application of techniques currently used in the advanced circuitry industry. This is illustrated by the design of a triple-layer microperforated panel yielding absorption in almost four and a half octaves. The parameters of the triple-layer microperforated panel are optimised by Simulated Annealing to provide maximum absorption within a prescribed frequency band.

Experimental Validation of Generating Two Spaced Beams With Reflectarrays by VRT

The concept of generating two spaced beams in dual-CP by variable rotation technique (VRT) is validated for the first time by manufacturing and measuring. A reflectarray demonstrator has been designed, manufactured, and tested to deviate ±10° the beam of a dual-CP multiflared horn at 19.7 GHz. The proposed reflectarray cell for VRT is made of a conductive cross printed on a grounded dielectric. The experimental results show that two adjacent beams in dual-CP maintain the correct directions in the prescribed frequency band (19.2–20.2 GHz). The results are satisfactory and validate the concept for generating two spaced beams in orthogonal CP by VRT with a single feed.

Multiple-Layer Microperforated Panels as Sound Absorbers in Buildings: A Review

Sound absorbing materials are used in buildings to dissipate sound energy into heat using viscous and thermal processes. Sound absorbers increase the transmission loss of walls, decrease the reverberation time of rooms, and attenuate the noise generated by internal sound sources. Porous absorbers (fibrous, cellular, or granular) are the most used materials in noise control applications because of their high performance-to-cost ratio in the frequency band of interest. However, when cleaning conditions and health reasons are of concern, microperforated panel (MPP) absorbers may be the preferred choice. MPPs, consisting of many minute (sub-millimetric) holes in a panel, are tunable absorbers in a prescribed frequency band, whose main shortcomings are high manufacturing cost and limited absorption frequency band. Currently, the production cost of MPPs can be drastically reduced by means of modern techniques. The absorption frequency band can be considerably enlarged by designing multiple-layer MPPs (ML-MPPs). The aim of this article is to review the high potential of ML-MPPs as a modern, clean, and healthy alternative to porous materials for sound absorption.

Piecewise convergence behavior of the condensed transfer function approach for mid-to-high frequency modelling of a panel-cavity system

The vibro-acoustic modelling of a panel-cavity system is of prime importance for the building industries, exemplified by the noise insulation of single or double skin façade. The vibro-acoustic analysis of such systems in the mid-to-high frequency range is computational costly and technically challenging due to the complex wavelength composition. In the present paper, the Condensed Transfer Function (CTF) approach is revisited to tackle this problem. It is demonstrated that the calculation efficiency of the CTF method can be greatly increased by properly selecting the Condensation Functions (CFs) and exploiting their physical characteristics. In particular, owing to their spatial wavy features, the complex exponential functions can better match the structural wavelength variations so that the velocity on the plate-cavity interface can be described by using a much reduced CF set as compared with the gate functions which are widely used in the previous works. Numerical results show a piecewise convergence behavior of the calculation which is further exploited for establishing a criterion for the truncation of the CFs. The proposed criterion allows the determination of a sub-set of the CFs for any prescribed frequency band for the calculation of the system response in a progressive and piecewise manner, resulting in a great increase in the computational efficiency.

Reconfigurable origami silencers for tunable and programmable sound attenuation

Recent research has discovered that origami-inspired structures possess great versatility in properties and functionalities. In this research, through an integration of origami geometry and duct acoustics, we reveal that the folding-induced shape reconfiguration of a modular origami silencer could yield great tunability and programmability in sound attenuation. This has been made possible through exploring the kinematics of the folding and the extensibility of the modular origami. Numerical and experimental results indicate that by reconfiguring the silencer via a single degree-of-freedom folding mechanism, the sound attenuation bandwidth can be effectively tuned. Meanwhile, based on a comprehensive understanding on the correlations between the origami geometries and the acoustic characteristics, we exemplify that, by incorporating multiple origami layers in a silencer and by programming their geometries, on-demand sound control can be achieved, e.g., attenuation in the prescribed frequency bands, improved attenuation levels, and broadband attenuations. This proof-of-concept study shows that the proposed folding-based mechanism, along with the modularization design concept, would provide a new way to reconfigure the silencer for acoustic adaptability and inspire new innovation in designing acoustic devices.

Broadband transmission-type coding metamaterial for wavefront manipulation for airborne sound

The recent advent of coding metamaterials, as a new class of acoustic metamaterials, substantially reduces the complexity in the design and fabrication of acoustic functional devices capable of manipulating sound waves in exotic manners by arranging coding elements with discrete phase states in specific sequences. It is therefore intriguing, both physically and practically, to pursue a mechanism for realizing broadband acoustic coding metamaterials that control transmitted waves with a fine resolution of the phase profile. Here, we propose the design of a transmission-type acoustic coding device and demonstrate its metamaterial-based implementation. The mechanism is that, instead of relying on resonant coding elements that are necessarily narrow-band, we build weak-resonant coding elements with a helical-like metamaterial with a continuously varying pitch that effectively expands the working bandwidth while maintaining the sub-wavelength resolution of the phase profile that is vital for the production of complicated wave fields. The effectiveness of our proposed scheme is numerically verified via the demonstration of three distinctive examples of acoustic focusing, anomalous refraction, and vortex beam generation in the prescribed frequency band on the basis of 1- and 2-bit coding sequences. Simulation results agree well with theoretical predictions, showing that the designed coding devices with discrete phase profiles are efficient in engineering the wavefront of outcoming waves to form the desired spatial pattern. We anticipate the realization of coding metamaterials with broadband functionality and design flexibility to open up possibilities for novel acoustic functional devices for the special manipulation of transmitted waves and underpin diverse applications ranging from medical ultrasound imaging to acoustic detections.

Method of test signal design for estimating the aircraft aerodynamic parameters

A method of test signal design is proposed for studying the aircraft aerodynamic characteristics with the use of the technology of dynamically scaled free-flight models. Simultaneous excitation of all input channels in a prescribed frequency band by a set of mutually orthogonal signals is applied to increase the efficiency. A modified method of calculating the set of mutually orthogonal sinusoidal signals with a small normalized peak factor is presented. Results of simulating the aircraft motion in the MATLAB/Simulink environment with the use of the developed method of test signal design are reported.

Antenna Radiation Characteristics Optimization by a Hybrid Topological Method

A hybrid topology optimization method that integrates material distribution and level set methods (LSMs) is proposed. The topology of the antenna is optimized first by the material distribution method, and then, the derived structure, which has a zig-zag boundary, is further optimized by the LSM. By adopting this hybrid strategy, the powerful topology-searching ability of the material distribution method and the advantageous feature of producing structures with smooth and low sensitivity boundary of the LSM are fully exploited. To optimize antenna’s radiation characteristics, sensitivity analysis of the power density of the far-field is formulated. To demonstrate the capability of this hybrid topology optimization method and verify the sensitivity analysis formulation, three microstrip antennas with different desired polarizations, beam directions, and bandwidths are designed and tested. The measured results show that all the antennas not only achieve low reflection in the prescribed frequency band, but also give good performances in gain and polarization in the desired beam directions.

A fully integrated CMOS 60-GHz transceiver for IEEE802.11ad applications

A fully integrated 60-GHz transceiver for 802.11ad applications with superior performance in a 90-nm CMOS process versus prior arts is proposed and real based on a field-circuit co-design methodology. The reported transceiver monolithically integrates a receiver, transmitter, PLL(Phase-Locked Loop) synthesizer, and LO (Local Oscillator) path based on a sliding-IF architecture. The transceiver supports up to a 16QAM modulation scheme and a data rate of 6 Gbit/s per channel, with an EVM (Error Vector Magnitude) of lower than −20 dB. The receiver path achieves a configurable conversion gain of 36∼64 dB and a noise figure of 7.1 dB over 57∼64 GHz, while consuming only 177 mW of power. The transmitter achieves a conversion gain of roughly 26 dB, with an output P1dB of 8 dBm and a saturated output power of over 10 dBm, consuming 252 mW of power from a 1.2-V supply. The LO path is composed of a 24-GHz PLL, doubler, and a divider chain, as well as an LO distribution network. In closed-loop operation mode, the PLL exhibits an integrated phase error of 3.3° rms (from 100 kHz to 100 MHz) over prescribed frequency bands, and a total power dissipation of only 26 mW. All measured results are rigorously loyal to the simulation.

Topology optimization based methods and the realization programs for designing microstructures of patched metamaterials with prescribed electromagnetic properties

This paper aims to establish a design tool to design the metamaterial microstructures with specific electromagnetic properties easily and conveniently, including the design methods of metamaterial microstructures and the corresponding program codes. For the patch type microstructure and several typical metamaterials (such as the single-negative metamaterials with specific negative permeability, left-handed metamaterials with specific material constants at the prescribed frequency; single negative metamaterials and left-handed metamaterials in prescribed frequency bands), the topology optimization models, solving schedules and corresponding implementation program codes for microstructure design are presented in detail. Several typical metamaterial microstructures with different design requirements are designed concretely. The results illustrated the correctness and validity of the design methods and the corresponding program codes. The designing method proposed and the program codes developed in this paper provide an effective tool for the design of metamaterial microstructure with specific function for the designers.

Analysis of trapped oscillation modes in magnetized PPC and its tunability for variable plasma parameters

In this study, analysis of magnetized plasma photonic crystal (PPC) using 1-D modeling has been presented where effect of extra-ordinary modes of plasma on Photonic bandgaps (PBGs) is highlighted. The PPC characteristic has been studied in range of 1–140GHz for the different structural parameters, plasma frequency, angle of incidence, collision frequency and applied magnetic field. In the PPC, presence of static magnetic field yields the extra-ordinary mode in plasma that introduces trapped oscillations in the PBGs. This has been comprehensively analyzed and presented in detail. A procedure has been developed to identify the frequency range of the trapped oscillation in PBG. Study also explores that the trapped oscillations can be shifted at any other position in a prescribed frequency band by having suitable parameters like electronics concentration, hybrid frequency and applied magnetic field etc. Presented work can be utilized to avoid the trapped oscillation which yields non linearity in PBG.

A single sensor and single actuator approach to performance tailoring over a prescribed frequency band

Restricted sensing and actuation control represents an important area of research that has been overlooked in most of the design methodologies. In many practical control engineering problems, it is necessitated to implement the design through a single sensor and single actuator for multivariate performance variables. In this paper, a novel approach is proposed for the solution to the single sensor and single actuator control problem where performance over any prescribed frequency band can also be tailored. The results are obtained for the broad band control design based on the formulation for discrete frequency control. It is shown that the single sensor and single actuator control problem over a frequency band can be cast into a Nevanlinna–Pick interpolation problem. An optimal controller can then be obtained via the convex optimization over LMIs. Even remarkable is that robustness issues can also be tackled in this framework. A numerical example is provided for the broad band attenuation of rotor blade vibration to illustrate the proposed design procedures.

Automated Reduced Model Order Selection

This letter proposes to automate generation of reduced-order models used for accelerated S-parameter computation by applying a posteriori model error estimators. So far, a posteriori error estimators were used in Reduced Basis Method (RBM) and Proper Orthogonal Decomposition (POD) to select frequency points at which basis vectors are generated. This letter shows how a posteriori error estimators can be applied to automatically select the order of the reduced model in second-order Model Order Reduction (MOR) methods. Three different error estimators are investigated and compared in order to arrive at a new MOR scheme that is fast, reliable, and fully automated. The effectiveness of the proposed approach is verified by very high accuracy of the computed scattering parameters ( S-parameters) for an example of a waveguide filter over a prescribed frequency band.

Corrugated Surfaces With Tailorable Dark Sectors Within Prescribed Frequency Bands

Electromagnetic bandgap (EBG) surfaces have customarily been defined as being prohibitive of surface-waves within frequency ranges called bandgaps, for all directions along the surface, this latter specification being an understood presumed condition. However, not all practical applications require such an entire bandgap in terms of surface directions. Rather, there could be situations where surface-wave suppression is needed along directions only within an angular sector but are instead desirable towards others outside, over a frequency band, termed herein as a sectoral dark band (SDB). This work investigates this aspect using planar corrugated surfaces as the vehicle for study, in virtue of its ease of surface-wave modal analysis of dispersion by asymptotic corrugations boundary conditions (ACBC). A systematic design procedure for tailoring surfaces to any specified dark sector of weak signals prevailing over any prescribed band is presented.

Assessing the utility of frequency dependent nudging for reducing biases in biogeochemical models

Bias errors, resulting from inaccurate boundary and forcing conditions, incorrect model parameterization, etc. are a common problem in environmental models including biogeochemical ocean models. While it is important to correct bias errors wherever possible, it is unlikely that any environmental model will ever be entirely free of such errors. Hence, methods for bias reduction are necessary. A widely used technique for online bias reduction is nudging, where simulated fields are continuously forced toward observations or a climatology. Nudging is robust and easy to implement, but suppresses high-frequency variability and introduces artificial phase shifts. As a solution to this problem Thompson et al. (2006) introduced frequency dependent nudging where nudging occurs only in prescribed frequency bands, typically centered on the mean and the annual cycle. They showed this method to be effective for eddy resolving ocean circulation models. Here we add a stability term to the previous form of frequency dependent nudging which makes the method more robust for non-linear biological models. Then we assess the utility of frequency dependent nudging for biological models by first applying the method to a simple predator–prey model and then to a 1D ocean biogeochemical model. In both cases we only nudge in two frequency bands centered on the mean and the annual cycle, and then assess how well the variability in higher frequency bands is recovered. We evaluate the effectiveness of frequency dependent nudging in comparison to conventional nudging and find significant improvements with the former.