Filter Design Method Research Articles

Event-Triggered Reduced-Order Filtering for Continuous Semi-Markov Jump Systems With Imperfect Measurements.

This article conducts the issue of event-triggered reduced-order filtering for continuous-time semi-Markov jump systems with imperfect measurements as well as randomly occurring uncertainties (ROUs). Specifically, the sojourn-time-dependent transition probability matrix (TPM) is presumed to be polytopic and a quantizer is introduced to quantize output signals aiming to reflect the reality. Both ROUs and sensor failures are generated by individual random variables belonging to be mutually independent Bernoulli-distributed white sequences. First, sufficient conditions for the existence of the event-triggered reduced-order filter are obtained by utilizing the dissipativity-based technique to ensure the asymptotical stability with a strictly dissipative performance of the filtering error system. The time-varying TPM is then fractionalized, which enhances the results as stated. Furthermore, the required reduced-order filter parameters are obtained by introducing slack symmetric matrix as well as cone complementarity linearization algorithm. The effectiveness of the suggested event-triggered reduced-order filter design method is shown through simulation results.

A Fresh Revisit of the Issues and Improvements in Impulse Invariance Filter Design for Infinite Impulse Response Filters

The objective of this paper is to first present some issues with impulse invariance filter (IIF) design during the design of digital infinite impulse response (IIR) filters. Engineers are often confused about some inconsistent observations. For instance, if the impulse response of a digital filter is designed using the impulse invariance procedure, then the analog and digital filters’ frequency and step responses are very different. Two simple remedies are presented in this paper. One is a post-processing approach that scales the frequency and step responses of the digital filter by the sampling interval T. Another one is a pre-processing approach that scales the impulse response of the analog filter by T. However, even after these remedies, there is still a steady state bias in the step response of the digital filter for certain cases where there is discontinuity in the analog impulse response. A recommendation is to include a correction term in the digital filter. After that, the steady state bias in the digital filter is then suppressed. Moreover, the MATLAB R2021a command “impinvar” needs to also include a correction term so that the frequency and step responses can be more accurate in the digital filter. Two comparative studies were carried out to compare the improved IIF filter with three competing digital IIR filter design methods. Although the above issues and improvements have been proposed by researchers in the past, many researchers, engineers, and students are still not aware of them. This paper provides a fresh revisit of these issues and improvements by using figures, equations, and examples. Proper credits are also given to those researchers who first pointed out those issues and improvements. It is hoped that through an open access journal, future rediscovery of issues and improvements in IIF can be prevented.

E-plane waveguide bandpass filters based on high-order modes of spoof surface plasmon polaritons

In this paper, a new design method of E-plane waveguide bandpass filter (BPF) using high-order modes of spoof surface plasmon polaritons (SSPPs) is proposed. The high-order modes of the double-layer SSPP (DL-SSPP) unit cell can be effectively manipulated by adjusting the dimensions of grounded metallic patterns in SSPP array, which mainly determines the filtering characteristics of E-plane waveguide BPFs. For improving the out-of-band rejection, two extra transmission zeros (TZs) are designed at the upper and lower stopbands of E-plane waveguide BPF, and then the operating mechanism of TZs is clearly investigated. Moreover, the filtering characteristics of the E-plane waveguide BPF with different transition parts are discussed to demonstrate the generalization of proposed design method. To verify the design feasibility, two examples of E-plane waveguide BPF are fabricated and measured. Good agreement between measurements and simulations shows that the proposed design method possesses good potential for the applications of high-performance E-plane waveguide BPF design.

A General and Effective Design Method for Compact Bandpass Filters With Extensible Orders/Channels on a Modified Patch Resonator

A General and Effective Design Method for Compact Bandpass Filters With Extensible Orders/Channels on a Modified Patch Resonator

Design of a tunable center frequency and small size cavity bandpass filter by separating capacitor-loaded resonators

This paper presents a tunable center frequency and small size cavity bandpass filter design method. In this method, a capacitor-loaded open terminal coaxial resonator is employed to reduce the size of cavity filters. The resonator is designed and fabricated separately into two parts to achieve the flexible operating frequency purpose. The first part is called the base of the resonator which is simply a pillar and directly fabricated integrally with the cavity housing. The second part called the hat of the resonator is the main part causing the load capacitance in cavity filters. By using different heights of the base part or/and different shapes and sizes of the hat, the operating frequency of cavity filters can be changed flexibly. This method not only reduces the difficulty and cost of cavity filter processing but also makes cavity filters reconfigurable. To demonstrate the effectiveness of the method, a cavity filter sample with a center frequency of 3.45 GHz and a bandwidth of 80 MHz was designed, fabricated, and measured. The measured results show that the insertion loss was smaller than 1.33 dB in the whole bandwidth, one zero-point at 3.350 GHz reaching -68 dB, the rejection at 3.550 GHz was -41 dB, unloaded Q was 5,898, and the dimension of the filter was 128 mm×86 mm×23 mm.

A novel energy-focused slow-time MIMO radar and signal processing scheme

In this paper, we propose a novel energy-focused slow-time MIMO radar and signal processing scheme, aimed at addressing key challenges in slow-time coding and signal processing technology. Conventional slow-time MIMO radar faces issues such as energy waste due to the omnidirectional transmit beampattern of orthogonal coding and the velocity ambiguity problem. To overcome these limitations, the proposed radar system utilizes a method based on Doppler frequency offset diversity (DFOD) for slow-time coding design. This method enables the adjustment of Doppler offset parameters to achieve a rectangular transmit beampattern with any mainlobe width within a single coherent processing interval (CPI), offering the advantage of low computational complexity. Through an analysis of the ambiguity function for DFOD-based coding, we evaluate both Doppler and angular resolution. To further improve Doppler frequency resolution, a slow-time coding design is introduced based on Pulse Random Permutation (PRP). Subsequently, a signal processing scheme based on matched filtering is presented. To tackle the high Doppler sidelobe issue associated with PRP-based coding, we propose a mismatch filter (MMF) design method utilizing convex optimization. Ultimately, the performance enhancement of the proposed slow-time MIMO radar is verified through simulation analysis in comparison to existing technologies.

An efficient low-delay polyphase implementation method for active noise control systems

When implementing active noise control systems on signal processing hardware, the time delay introduced by electronic components (especially components requiring additional lowpass filters or introducing fixed-sample-size delays) may adversely affect the noise control performance. One common approach to reducing this delay is to use a high sampling rate, but this increases the computation significantly when implementing the ANC filters in real time. In the current work, a polyphase-structure-based filter design method is developed for active noise control systems that can reduce the computation load for real-time filter implementation but do not introduce an additional time delay. Although the computation reduction capability of a polyphase filter structure is well known for multi-rate systems, the traditional use of such multi-rate systems requires additional anti-aliasing and reconstruction filters which introduces an additional time delay. Thus, in delay-sensitive applications, such as active noise control, this method was previously applied only on the filter adaption phase, instead of directly on the real-time filtering process. In this article, a filter decomposition method using the minimum-phase technique is proposed to decompose an ANC filter into two multiplicative causal filters both of which have lowpass frequency response shapes at high frequencies such that the polyphase structure can be applied directly to the two multiplicative causal control filters without introducing additional anti-aliasing and reconstruction filters. Results show that, compared with various traditional low sampling rate implementations, the proposed method can significantly improve the noise control performance. Compared with the non-polyphase high-sampling rate method, the real-time computations that increase with the sampling rate are improved from quadratically to linearly.

A novel design method for wideband bandpass filters with fewer inductors

Inductors that are widely used in wideband filter designs could result in large filter size and high insertion loss. A novel design method using admittance matrix based on direct circuit implementation is introduced for wideband bandpass filters. Firstly, a frequency transformation is performed on cross-couplings to realize the conversion between inductor and capacitor, thereby reducing usage of inductors. Moreover, by virtue of an enhanced resonator (type I), an approach of adding extra transmission zero is proposed to improve the out-of-band rejection without any additional usage of inductors. Thirdly, based on the frequency transformation, another enhanced resonator (type II) is introduced to further improve the frequency characteristics without compromising usage of inductors. Finally, by cascading the enhanced resonators of type I and type II, a novel filter can be constructed. This novel filter is designed and fabricated using a glass-based integrated passive device (IPD) technology. The measurement results are highly consistent with the simulation results. It is shown that the proposed design method can reduce the filter size and thus improve the chip integration. It enriches the freedoms during the filter design.

A New LCL Filter Design Method for Single-Phase Photovoltaic Systems Connected to the Grid via Micro-Inverters

A New LCL Filter Design Method for Single-Phase Photovoltaic Systems Connected to the Grid via Micro-Inverters

An optimized filter design approach for enhancing imaging quality in industrial linear accelerator.

The polychromatic X-rays generated by a linear accelerator (Linac) often result in noticeable hardening artifacts in images, posing a significant challenge to accurate defect identification. To address this issue, a simple yet effective approach is to introduce filters at the radiation source outlet. However, current methods are often empirical, lacking scientifically sound metrics. This study introduces an innovative filter design method that optimizes filter performance by balancing the impact of ray intensity and energy on image quality. Firstly, different spectra under various materials and thicknesses of filters were obtained using GEometry ANd Tracking (Geant4) simulation. Subsequently, these spectra and their corresponding incident photon counts were used as input sources to generate different reconstructed images. By comprehensively comparing the intensity differences and noise in images of defective and non-defective regions, along with considering hardening indicators, the optimal filter was determined. The optimized filter was applied to a Linac-based X-ray computed tomography (CT) detection system designed for identifying defects in graphite materials within high-temperature gas-cooled reactor (HTR), with defect dimensions of 2 mm. After adding the filter, the hardening effect reduced by 22%, and the Defect Contrast Index (DCI) reached 3.226. The filter designed based on the parameters of Average Difference (AD) and Defect Contrast Index (DCI) can effectively improve the quality of defect images.

A novel design algorithm for low complexity sparse 2‐D FIR filters

SummaryThe hardware implementation complexity of traditional two‐dimensional (2‐D) finite impulse response (FIR) filters with high order is very high. In this paper, a novel sparse 2‐D FIR filter design algorithm has been proposed by combining the common subexpression elimination technique and sparse filter design algorithms to reduce hardware implementation complexity. First, an initial 2‐D FIR filter with sparse coefficients that meets frequency‐domain specifications is obtained by the sparse filter design algorithm. Then, each filter coefficient is quantized in canonical signed digit, and the sensitivities of all weight‐two subexpressions and isolated non‐zero bits are calculated. Finally, the filter coefficients with low implementation cost are reconstructed via iteratively choosing subexpressions and isolated non‐zero bits in terms of their sensitivities. Simulation results show that the proposed algorithm saves about of adders compared with other low complexity filter design method, which reduces effectively the implementation cost.

Optimized MMC passive impedance shaping method for high frequency oscillation suppression

Recent years, there have been several high-frequency oscillation events in modular multilevel converter (MMC) based DC current projects. Considering the wideband oscillation characteristics of this issue, passive MMC impedance shaping methods are superior solutions for their advantages over the active methods in enhancing the broadband damping level. However, the optimization of parallel passive devices mainly focused on reactive power compensation and the suppression of characteristic harmonics generated by low-level inverters, which is not applicable to MMC systems. To address the optimization design problem of passive damping devices, this paper proposes an optimized design method for passive filters by analyzing the relationship between the passive damping device and the impedance shaping effect of the inverter. The proposed method reduces the capacity of the passive damping device while ensuring system stability margin. Finally, the effectiveness of the proposed passive impedance shaping strategy is verified through time-domain simulations considering changes in AC side operating conditions and power reduction operation of the MMC.

Metatronics-inspired high-selectivity metasurface filter

Abstract Metatronic circuits extend the concept of subwavelength-scaled lumped circuitry from electronics to optics and photonics, providing a distinctive design paradigm for versatile optical nanocircuits. Here, based on the design of optical nanocircuits using metatronics concept, we introduce a general approach for dispersion synthesis with metasurface to achieve high-selectivity filtering response. We theoretically and numerically demonstrate how to achieve basic circuit lumped elements in metatronics by tailoring the dispersion of metasurface at the frequency of interest. Then, following the Butterworth filter design method, the meticulously designed metasurface, acting as lumped elements, are properly stacked to achieve a near-rectangular filtering response. Compared to the conventional designs, the proposed approach can simultaneously combine high selectivity with the theoretically widest out-of-band rejection in a considerably simple and time-efficient manner of circuit assembly, similar to electronic circuits, without extensive numerical simulations and complex structures. This dispersion synthesis approach provides exciting possibilities for high-performance metasurface design and future integrated circuits and chips.

Switchable Dual-Wavelength Thulium-Doped Fiber Laser Based on Polarization-Maintaining Fiber Bragg Grating and Compound Cavity Filter

This paper presents experimental evidence regarding a novel switchable dual-wavelength thulium-doped fiber laser (TDFL). Wavelength switching is achieved by combining a polarization-maintaining fiber Bragg grating (PM-FBG) with a polarization controller (PC). The three-coupler double-ring compound cavity (TC-DRC) structure, acting as a mode-selection filter, is designed to select a single longitudinal mode (SLM) from the dense longitudinal modes. This paper introduces the design and fabrication method of the TC-DRC filter and analyzes, in detail, the mechanism for SLM selection. The experimental results demonstrate that the designed filter exhibits excellent performance. By adjusting the PC, the TDFL achieves stable SLM operation at the wavelengths of 1940.54 nm and 1941.06 nm, respectively. The optical signal-to-noise ratio (OSNR) is superior to 65 dB. When the TDFL is tested at room temperature, there is no significant wavelength drift, and power fluctuations are less than 1.5 dB. The operation of the SLM is verified through the self-heterodyne method, and the laser maintains stable SLM states for both wavelengths after continuous operation for an hour. Furthermore, based on the phase noise demodulation method, the linewidths of both wavelengths are measured to be less than 10 kHz at the integration time of 0.001 s.

Performance and harmonic detection algorithm of phase locked Loop for parallel APF

As the boost of power electronics technology, the harmonic problem in the power system is becoming increasingly prominent. Fourier decomposition is performed on the load current in the power system, and components with a frequency that is an integer multiple of the fundamental wave are referred to as harmonic components. Harmonic control is essential to establish a safe and reliable power grid environment and provide high-quality and clean electricity to power users. The study focused on parallel active power filters, proposed a specific harmonic detection method on the grounds of synchronous harmonic rotating coordinate system, and developed a phase-locked loop design on the grounds of order generalized integrator. Meanwhile, a compensation current control method on the grounds of space vector pulse width modulation was introduced. The results showed that in the full compensation simulation experiment, the compensated A-phase grid side current waveform was significantly improved and presented a sinusoidal shape. After 0.05 s, the actual output compensation current closely followed the command current. Meanwhile, after compensation, the total harmonic distortion rate decreased from 26.58 to 3.06%. In specific harmonic compensation simulation experiments, when the sum of 5th, 7th, and 11th harmonic components was used as the command current for compensation, the distortion of the current waveform was improved after the load undergoes a sudden change. After compensation, the 5th, 7th, and 11th harmonic content significantly decreased, and the total harmonic distortion rate decreased to 4.08%. This indicated that the proposed phase-locked loop design and harmonic detection method for active power filters had high stability and effectiveness. The study’s primary contribution is to enhance the utilization efficiency of DC voltage and improve the dynamic response ability of current. Additionally, it offers a new method for reducing the impact of harmonics on the power grid and improving power quality. It provided an effective method reference for technological progress in related fields such as power electronics and control engineering.

Tunable bandpass filter based on epsilon-near-zero metamaterials using liquid crystals

ABSTRACT In the article, a design method of tunable bandpass filter based on epsilon-near-zero (ENZ) metamaterials using liquid crystals (LCs) is proposed. Thanks to the strong and directionally consistent electric field distribution caused by energy tunnelling effect of ENZ metamaterials, the ENZ unit cell with filled LC in the narrow tunnel can theoretically achieve the bandpass filtering characteristic with a large tuning rate. On this basis, a third-order LC-based tunable bandpass filter is constructed by three series unit structures, which achieves obviously tunable bandpass filtering characteristic with different external biased voltages. Finally, one prototype is designed, fabricated and measured, respectively. The measurement results show that the proposed bandpass filter based on ENZ materials with LCs can achieve effective tuning of the operating frequency with different external biased voltages, which verifies the effectiveness of the proposed design method. In addition, the impact of shape variation of the proposed ENZ-based tunable filter on electromagnetic characteristics is also further discussed and analysed in experiments, which is of great significance for achieving RF miniaturisation and high integration.

New Robust Model for Stability and H∞ Analysis for Interconnected Embedded Systems

This paper presents a novel approach to analyzing the robust stability of interconnected embedded systems. The paper starts by discussing the challenges associated with designing stable and robust embedded systems, particularly in the context of interconnected systems. The proposed approach combines the H∞ control theory with a new model for interconnected embedded systems, which takes into account the effects of communication delays and data losses. The paper provides a detailed mathematical analysis of the new model and presents several theorems and proofs related to its stability. The effectiveness of the proposed approach is demonstrated through several practical examples, including a networked control system and a distributed sensor network. The paper also discusses the limitations of the proposed approach and suggests several directions for future research. The proposed filter design method establishes a sufficient condition for the asymptotic stability of the error system and the satisfaction of a predefined H∞ performance index for time-invariant bounded uncertain parameters. This is achieved through the use of the strict linear matrix inequalities (LMI) approach and projection lemma. The design is formulated in terms of linear matrix inequalities (LMI). Numerical examples are provided to demonstrate the effectiveness of the proposed filter design methods.

Learning a physics-based filter attachment for hyperspectral imaging with RGB cameras

Countless RGB cameras are ubiquitously distributed in our daily lives, serving to perceive and depict the diverse colors of the world. Reconstructing hyperspectral images (HSI) from these trichromatic cameras emerges as a promising solution to address the limitations of existing, costly hyperspectral imaging systems. The performance of HSI reconstruction relies heavily on the camera spectral response (CSR). Thus, designing a better CSR and putting it into practice is the critical issue for RGB-based HSI reconstruction. However, the CSR curves designed in the existing works are overly random, making them challenging to manufacture directly. Additionally, the designed CSR curves require modifications to the camera hardware, resulting in the loss of RGB imaging functionality. In this paper, we propose a hyperspectral imaging system, which involves enhancing the CSR curve of existing RGB cameras and preserving RGB imaging functionality by adding a learnable physics-based spectral filter. Specifically, we first parameterize the spectral filter transmittance as a function of the filter thicknesses, based on the physical constraints of the multilayer interference principle. Then, we propose a joint optimization framework in which the thicknesses of the filter and the hyperspectral reconstruction network are optimized. In this manner, the thicknesses of the filter are obtained and used to manufacture the filter directly. Finally, we construct a prototype and verify the benefits of our spectral filter design method through experiments including both synthetic data and real images.

Frequency selective surface filters with high-quality factors based on a Fano resonance.

In this work, we propose a design method of the narrow passband filter with a high Q-factor based on a Fano resonance. A single-layer metallic frequency selective surface (FSS) with a simple structure is first designed according to this idea, but the result is not satisfying since the filter transmittance will significantly decrease with the increase of the Q-factor due to the presence of an inherent ohmic damping. Further, to improve the design, a ceramic-based FSS filter based on the similar mechanism is proposed, and the requirements of the ultrahigh Q-factors can be met owing to the high permittivity and low loss tangent of microwave ceramics. The design strategy proposed in this paper may have a promising potential in modern wireless communication and related fields.

Output feedback containment fuzzy control for multi-agent systems with quantitative input and tunable reference signals

For multi-agent systems with quantitative input, we propose a novel containment control scheme to guarantee that the agents can enter a convex hull generated by the leader's signals after starting from any initial position. The problem with existing schemes is that the reference signals of the agents are affected by the communication topology such that the position of the reference signal cannot be changed when this communication topology is determined. To solve this problem, the proposed scheme can generate a flexible and adjustable reference signal for each agent. This has the advantage of reducing the probability of collisions among agents. Meanwhile, to address the situation where some agents cannot receive reference signals, we design an estimator to generate an adjustable estimation signal for each specific agent to ensure that all agents continue moving within the convex hull. In addition, by combining the fuzzy observer with the command filter design method, we devise a novel controller design scheme for quantitative input, which ensures that all signals in closed-loop multi-agent systems are uniformly and ultimately bounded. Finally, the simulation results demonstrate the feasibility and superiority of the proposed scheme for controlling multi-agent systems.