Filter Structure Research Articles

Novel absolute length measurement method for etalon sensor using optical comb pulsed interference and harmonic etalon reflections

A Fabry–Perot interferometer, also called an etalon, is used in various applications such as resonant structures for lasers, wavelength filters, length and frequency standards, and sensors. When the etalon is used as sensor, both the high resolution and simplicity of the measurement mechanism are required. We propose a method using an optical comb and an etalon harmonically. Using this method, it is possible to achieve measurements with resolution of less than a few nanometers and improved sensitivity. This method can be implemented with a simple system, and traceability can be easily achieved from the characteristics of the optical comb without the need for a high-precision wavelength meter. In this study, in addition to proposing a method, we implemented measurement system including a repetition frequency scanning optical comb and verified it experimentally. The repeatability of the measurement was approximately 3.0 nm (σ = 2) when 175 mm etalon was used. The measured absolute value of the etalon length was compared to the coordinate measuring machine (CMM) measurement results and difference between the two values was <1 μm that indicated the absolute values agreed well with the maximum permissible length error range of the CMM. The etalon displacement was measured, and the result was compared to that of the conventional He–Ne interferometer. The difference between the two was less than 1 nm, indicating the validity of the measurement and its applicability as sensor. These results demonstrated that the proposed measurement method is feasible and functional for etalon sensor.

Diesel particulate filter regeneration mechanism of modern automobile engines and methods of reducing PM emissions: a review.

Diesel particulate filter (DPF) is considered as an effective method to control particulate matter (PM) emissions from diesel engines, which is included in the mandatory installation list by more and more national/regional laws and regulations, such as CHINA VI, Euro VI, and EPA Tier3. Due to the limited capacity of DPF to contain PM, the manufacturer introduced a method of treating deposited PM by oxidation, which is called regeneration. This paper comprehensively summarizes the most advanced regeneration technology, including filter structure, new catalyst formula, accurate soot prediction, safe and reliable regeneration strategy, uncontrolled regeneration and its control methods. In addition, due to the change of working conditions in the regeneration process, the additional emissions during regeneration are discussed in this paper. The DPF is not only the aftertreatment device but also can be combined with diesel oxidation catalyst (DOC), selective catalytic reduction (SCR) and exhaust recirculation (EGR). In addition, the impact of DPF modification on the original system of some old models has been reasonably discussed in order to achieve emission targets.

Reconfigurable Architecture for Noise Cancellation in Acoustic Environment Using Single Multiply Accumulate Adaline Filter

The creation of multiple applications with a higher level of complexity has been made possible by the usage of artificial neural networks (ANNs). In this research, an efficient flexible finite impulse response (FIR) filter structure called ADALINE (adaptive linear element) that makes use of a MAC (multiply accumulate) core is proposed. The least mean square (LMS) and recursive least square (RLS) algorithms are the most often used methods for maximizing filter coefficients. Despite outperforming the LMS, the RLS approach has not been favored for real-time applications due to its higher design arithmetic complexity. To achieve less computation, the fundamental filter has utilized an LMS-based tapping delay line filter, which is practically a workable option for an adaptive filtering algorithm. To discover the undiscovered system, the adjustable coefficient filters have been developed in the suggested work utilizing an optimal LMS approach. The 10-tap filter being considered here has been analyzed and synthesized utilizing field programmable gate array (FPGA) devices and programming in hardware description language. In terms of how well the resources were used, the placement and postrouting design performed well. If the implemented filter architecture is compared with the existing filter architecture, it reveals a 25% decrease in resources from the existing one and an increase in clock frequency of roughly 20%.

Outlier-resistant sequential filtering fusion for cyber-physical systems with quantized measurements under denial-of-service attacks

In this paper, an outlier-resistant sequential fusion problem is concerned for cyber-physical systems with quantized measurements under denial-of-service attacks. The multi-sensor measurements are quantized by a bank of logarithmic quantizers before entering into communication networks. The denial-of-service attack is, from the defenders' perspective, regarded to be randomly occurring and such an occurrence is governed by a Bernoulli-distributed sequence of certain probability distribution. To suppress effects from measurement outliers onto innovations, tailored saturation functions are dedicatedly introduced to filter structures at both local and fusion stages, thereby keeping satisfactory fusion performance. By finding solutions to a set of matrix difference equations, upper bounds are initially acquired on estimator error covariances, and associated estimator parameters are subsequently secured via minimizing these acquired bounds. Two examples are finally presented to showcase the applicability of this outlier-resistant sequential fusion algorithm.

A High Efficiency and Wide Voltage Gain sLC_LCC DC–DC Converter With SiC Devices

A novel s <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> _ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCC</i> resonant dc–dc converter is proposed in this article. With the combination of a notch filter and a new s <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> excitation structure of the transformer, wide and fast gain characteristics are obtained. With the frequency modulation, the notch filter structure helps the converter realize a wide output voltage range adjustable from zero theoretically. Besides, the fast voltage gain regulation capacity is achieved in a narrow frequency range with the s <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC</i> excitation structure. In the text, topology structure, operation principle, and characteristics analysis are illustrated in detail. For numerous passive components, an effective design method is necessary to guide parameter determination. And a detailed parameter design process is discussed. With the selected parameters, the soft-switching feature is realized. Finally, a 500 W experimental prototype is fabricated to verify the feasibility and effectiveness of theoretical analysis. The converter achieves 59.3–16.3 V output voltage regulation ability in a narrow frequency range (86 kHz, 189 kHz) under the condition of power 500 W and input voltage 375 V. High efficiency is maintained in the full load range, and the maximal efficiency of the converter reaches 97.7% at 99.5 kHz.

Compact Parallel Coupled Line Microstrip BPF Design for 5G Applications

A compact parallel coupled line microstrip bandpass filter (BPF) for sub-6 GHz fifth generation (5G) applications is designed operating between edge frequencies of 3.40 and 3.80 GHz. The design is designed and simulated by means of the Advanced Design System (ADS) software using the flame retardant-4 (FR-4) board as the substrate. The BPF design applies the insertion loss method (ILM) to generate a parallel coupled line filter structure that performs passband permission and unwanted noise attenuation below 3.40 GHz and above 3.80 GHz, respectively. Consistent and relevant performances in terms of matching impedance, return loss (S11), insertion loss (S21), voltage standing wave ratio (VSWR), far field radiation pattern, gain, directivity, and radiated efficiency promise the microstrip BPF design has a potential for sub-6 GHz 5G applications.

Stable narrow-linewidth single-longitudinal-mode thulium-doped fiber laser by exploiting double-coupler-based double-ring filter

A stable single-longitudinal-mode (SLM) thulium-doped fiber laser (TDFL) was combined with a phase-shift fiber Bragg grating (PS-FBG), uniform fiber Bragg grating (UFBG), and a double-coupler-based double-ring (DCDR) filter. Mode selection was achieved by using a sub-ring cavity design. For the first time, the structure of the DCDR filter was used to select a single mode from dense longitudinal modes in a ring cavity TDFL. The theoretical analysis of the DCDR filter and the principle for achieving SLM operation are presented in detail. The experimental results demonstrated the exceptional performance of the proposed DCDR filter. Within the observation period of an hour, the maximum fluctuations of center wavelength and optical power are 0.02 nm and 0.47 dB, respectively. The linewidth of the lasing wavelength is 4.8 kHz and the relative intensity noise is below −129.48 dB/Hz at frequency above 2 MHz. The power scaling, slope efficiency, and threshold power of the TDFL were also investigated. The proposed SLM TDFL shows great potential for free-space optical communication applications.

Machine learning based asynchronous computational framework for generalized Kalman filter

SummaryAlthough the Kalman filter algorithms are well suited to be executed on most digital systems, they become slow when applied to large‐scale dynamic systems. Therefore, efficient execution of Kalman filter for the time‐critical and large‐scale applications is of the essence. This work aims to address this necessity by developing a novel framework to improve the performance of a generalized Kalman filter with unknown inputs (GKF‐UI) using multithreaded‐multicore processors and machine learning (ML) classification methods. An asynchronous execution model based on OpenMP message‐passing framework is developed and integrated with a novel supervised ML‐based thread classifier for the GKF‐UI algorithm to enhance execution efficiency. The experimental results show that the proposed approach can achieve up to 35.5× speedup over the serial single‐threaded implementations with no losses in the accuracy or changes to the generality of the filter structure. Moreover, this framework can play a significant role in realizations of computational advantages in large‐scale systems as well as for the time‐critical prediction applications.

Three-dimensional numerical simulation and structural optimization of filtration performance of pleated cylindrical metal fiber filter

Cylindrical metal fiber filters have the advantages of high-temperature resistance, radiation resistance, and large filtration area. They have been widely used in the filtration and emission systems of nuclear power plants and are mainly used to remove radioactive aerosols in the containment under severe accidents. To optimize the filter structure, this research uses the numerical calculation method to verify the flat metal fiber's flow resistance and filtration efficiency. Based on the verification results, the performance of pleated cylindrical filter element is calculated (including pressure distribution, velocity distribution and efficiency distribution, etc.), the flow resistance and filtration efficiency of the cylindrical structure are analyzed, and the performance of the cylindrical filter is compared with that of the flat filter. The comparison found that due to the uneven flow distribution in the vertical direction of the cylindrical structure, the filtration efficiency will be lost after the flat filter is processed into a filter cartridge. Based on the research results, the flow resistance and filtration efficiency of filters of different sizes are also calculated, and the structural size of the cylindrical filter element is optimized. The results show that increasing the outer diameter of the filter element and reducing the height of the filter element can reduce the resistance, improve the filtration efficiency, and flatten the distribution of velocity and efficiency. For a filter element with a height of 500 mm, it is recommended to set the outer diameter to 175 mm. The research results can provide a design reference for engineering filter elements processing and manufacturing.

Advanced nitrogen removal performance and microbial community structure of a lab-scale denitrifying filter with in-situ formation of biogenic manganese oxides

Advanced nitrogen removal faces the challenges of high operational cost resulted from the additional carbon source and secondary pollution caused by inaccurate carbon source dosage in municipal wastewater. To address these problems, a novel carbon source was developed, which was the oxidation products of refractory organic matters in the secondary effluent of municipal wastewater treatment plant (MWWTP) by in-situ generated biogenic manganese oxides (BMOs) in the denitrifying filter. In the steady phase, the effluent chemical oxygen demand (CODcr), NO3−-N and total nitrogen (TN) in the denitrifying filter 2# with BMOs was 11.27, 9.03 and 10.36 mg/L, and the corresponding removal efficiency was 54.79%, 51.85% and 48.03%, respectively, which was significantly higher than those in the control denitrifying filter 1# that the removal efficiency of CODcr, NO3−-N and TN was only 32.30%, 28.58% and 29.36%, respectively. Kinds of denitrifying bacteria (Candidatus Competibacter, Defluviicoccus, Dechloromonas, Candidatus Competibacter, Dechloromonas, Pseudomonas, Thauera, Acinetobacter, Denitratisoma, Anaerolineae and Denitratisoma) and anammox bacteria (Pirellula, Gemmata, Anammoximicrobium and Brocadia) were identified in the denitrifying filters 1# and 2#, which explained why the actual CODcr consumption (1.55 and 1.44 mg) of reducing 1 mg NO3−-N was much lower than the theoretical CODcr consumption. While manganese oxidizing bacteria (MnOB, Bacillus, Crenothrix and Pedomicrobium) was only identified in the denitrifying filter 2#. This novel technology presented the advantages of no additional carbon source, low operational cost and no secondary pollution. Therefore, the novel technology has superlative application value and broad application prospect.

Active disturbance rejection controller design for alleviation of gust-induced aeroelastic responses

This paper develops an active disturbance rejection control technology that uses the equivalent input disturbance (EID) approach to reduce the aeroelastic vibrations and structural loads caused by wind gusts. The influence of gust disturbance is evaluated by the EID estimator and actively compensated in the control input channel, giving a high disturbance rejection performance of the aeroelastic system. The suitable design of the state observer and low-pass filter is essential for the disturbance estimation and rejection. However, the conventional low-pass filter simply specified by a cutoff frequency may lead to a degraded estimation performance. To this end, a new structure of low-pass filter is proposed, and the design algorithms for the observer gain and filter parameters are also given. By specifying bandwidth constraints, the control system with guaranteed performance can be automatically generated. Numerical results show that for the acceleration measurement-based control, the proposed design method can achieve better disturbance estimation performance than that obtained by the conventional one, resulting in smaller gust responses. Finally, the proposed design method is further extended to the folding wing parameter-varying system. A parameterized version of the EID-based controller is constructed by using the concept of gain-scheduling. It is demonstrated that the gust responses can be significantly reduced in the entire range of folding angle. This study provides an effective solution for gust alleviation of the aeroelastic system with fixed or variable configurations.

Filtenna with Frequency Reconfigurable Operation for Cognitive Radio and Wireless Applications.

A reconfigurable wideband monopole antenna is introduced in this paper for cognitive radio and wireless applications. The reconfigurability was achieved by four varactor diodes embedded in the band pass filter (BPF) structure which was integrated with the suggested antenna through its feed line. The simulated impedance characteristics coped with the measured ones after fabricating the suggested model with/without the reconfigurable BPF. Furthermore, the model achieved the desired radiation characteristics in terms of radiation pattern with acceptable gain values at the selected frequencies within the achieved frequency range (1.3-3 GHz).

Application of a novel rectangular filtering microfluidic device for microfilarial detection.

The rectangular filtering microfluidic chip was invented using microfluidics device fabrication technology and can separate living microfilariae from blood samples without a syringe pump. The diagnostic results are highly effective. The device is based on the principle of separating millions of blood cells from microfilariae using a rectangular filter structure. It disperses fluid evenly into the flow-passage channel, and its rectangular filter structure is the key to success in reducing the pressure and separating blood cells from microfilariae effectively. The flow rate and blood cell concentration were optimized in our study. The chip is intended to be a point-of-care device that can reduce the use of superfluous instrumentation in the field. The technology is designed to be rapid, accurate, and easy-to-use for all users, especially those in remote areas.

Design, manufacturing and properties of controllable porosity of ceramic filters based on SLA-3D printing technology

The ceramic foam filters are commonly applied in metal casting. However, this kind of filter has a number of drawbacks, such as weak impact resistance, uncontrollable technical parameters, and a long producing cycle. Our work developed a better manufacturing method for ceramic filters based on SLA-3D printing technology in which the structure of filters can be designed according to demands of porosity and hole density. Firstly, it is to propose a ceramic filter model with good mechanical properties under various porosities and hole densities using mechanical simulation and topology optimization. Secondly, SLA-3D printing technology was used to manufacture ceramic filter models with various characteristics. The results demonstrate that the porosity can be achieved with a wide range, and the higher porosity and hole density can approach 90% and 50 PPI, respectively. The preparation error of the internal pillars inside the filters model also can be revised to precisely control the porosity error of filters. Finally, the pore characteristics and compressive performance of the SLA printed ceramic filters were much better than that of the ceramic foam filters.

A 3-D Printed Ku-Band Waveguide Filter Based on Novel Rotary Coupling Structure

A Ku-band (12–18 GHz) waveguide bandpass filter has been designed, fabricated using stereolithography (SLA) printing, measured, and presented. The filter is composed of five coupled TE101 resonators, where the external/internal couplings are implemented through the rotation of resonators. This novel filter structure is superior to conventional filters based on irises, in terms of reduced sensitivity to fabrication inaccuracies (i.e., allowing larger tolerance in the fabrication process), as the coupling strength depends on the mutual rotation angle between resonators and input/output waveguides. This simple inline filter structure also allows the generation of transmission zero (TZ), by altering the rotation angles of resonators. A Ku-band prototype filter, with a center frequency of 14 GHz, a bandwidth of 0.8 GHz, a return loss of 20 dB, and a TZ at 14.8 GHz, has been successfully demonstrated, and this verifies the proposed concept.

Mathematical modeling of wastewater treatment facilities of transport enterprises

Wastewater is purified by mechanical, biological, physicochemical and chemical methods. Mechanical treatment plants are the main stage of treatment and remove most of the harmful substances contained in wastewater. The mechanical treatment facilities include a sand trap, a sump, a hydrocyclone, a grid, etc. Among them, the most common and basic design are sumps, which are divided into types according to design and function. In this article, a new mathematical model for calculating vertical sediments used in local treatment for small enterprises has been improved, and design parameters have been calculated. Theoretical studies of the proposed sump were carried out on the basis of molecular kinetic theory, and its accuracy was verified by the author in experimental tests. In the sump, an expression for the distribution of the concentration of suspended solids in wastewater was found. Thus, a filter structure with a filtration efficiency above 60% was created.

Resonator Reuse Approach for Implementing Narrowband Bandpass–Bandstop Cascade Based on Mode Orthogonality

This brief is to present a resonator reuse approach in implementing a high-attenuation notch next to a passband. Each resonator is utilized twice in producing bandpass and bandstop responses at the same time, which leads to size reduction. The filter structure employs cylindrical cavity resonators and utilizes the two orthogonal TM110 modes in each cavity resonator. The proposed filter has an excellent insertion loss since the TM110 mode has a high unloaded Q-factor. For verifying the proposed filter structure, we have designed and fabricated a second-order waveguide filter having a second-order bandpass-bandstop filter cascade response.

Lightweight Deep Neural Networks for Ship Target Detection in SAR Imagery.

In recent years, deep convolutional neural networks (DCNNs) have been widely used in the task of ship target detection in synthetic aperture radar (SAR) imagery. However, the vast storage and computational cost of DCNN limits its application to spaceborne or airborne onboard devices with limited resources. In this paper, a set of lightweight detection networks for SAR ship target detection are proposed. To obtain these lightweight networks, this paper designs a network structure optimization algorithm based on the multi-objective firefly algorithm (termed NOFA). In our design, the NOFA algorithm encodes the filters of a well-performing ship target detection network into a list of probabilities, which will determine whether the lightweight network will inherit the corresponding filter structure and parameters. After that, the multi-objective firefly optimization algorithm (MFA) continuously optimizes the probability list and finally outputs a set of lightweight network encodings that can meet the different needs of the trade-off between detection network precision and size. Finally, the network pruning technology transforms the encoding that meets the task requirements into a lightweight ship target detection network. The experiments on SSDD and SDCD datasets prove that the method proposed in this paper can provide more flexible and lighter detection networks than traditional detection networks.

Compact broadband bandpass filter with wide stopband based on halberd-shaped spoof surface plasmon polariton

In this paper, a compact broadband bandpass filter with wide out-of-band rejection characteristics based on halberd-shaped spoof surface plasmon polariton (SSPP) is proposed. The filtering structure is achieved by etching a periodic halberd-shaped groove at the bottom of the substrate and a microstrip-to-slot line transition with a crescent-shaped patch at the top. Compared with the traditional dumbbell-shaped SSPP, the halberd-shaped SSPP has good slow-wave property, and the designed bandpass filter based on halberd-shaped SSPP can achieve a more compact size. The upper cutoff frequency and lower cutoff frequency of the passband can be adjusted by regulating the SSPP structure and the transition structure from microstrip-to-slot line, respectively. The simulation results show that the center frequency of broadband bandpass filter is 2.85 GHz, with the relative bandwidth of 130%, and the return loss in the passband is better than –10 dB, and the extreme strong out-of-band rejection of –40 dB from 5.6 GHz to 20.0 GHz. The size of the broadband bandpass filter is compact, only 1.08&lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;g &lt;/sub&gt;× 0.39&lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;g&lt;/sub&gt;, where &lt;i&gt;λ&lt;/i&gt;&lt;sub&gt;g&lt;/sub&gt; is the wavelength at the center frequency. In order to verify the effectiveness of the wideband bandpass filter, the traditional printed circuit board technology is used to fabricate the wideband bandpass filter. The measurement results are in good agreement with the simulation results, verifying the feasibility of the design. The proposed broadband bandpass filter shows promising prospects for developing SSPP functional devices and circuits at microwave frequencies.

K-/Ka-Band Shared-Aperture Phased Array With Wide Bandwidth and Wide Beam Coverage for LEO Satellite Communication

A K-/Ka-band shared-aperture endfire phased array antenna is presented in this article. The antenna has the properties of dual wide bandwidths, orthogonal circular polarizations (CPs), wide beam coverage, and high isolation between the K-band and Ka-band channels. In this work, a new array topology is proposed to enhance the design freedom and the periodicity of the antenna array. Then, the filtering structures used to reflect the crossband coupled power also enhance the isolation between the K-band and Ka-band channels. The crossband mutual coupling is reflected and reradiated to generate the wideband CP beams. The high-order parallel plate waveguide (PPW) mode is suppressed to realize the wide CP beam coverage. The working bands at the boresight are 17.7–21.2 and 27.5–31.0 GHz, respectively. The polarizations are right-hand CP (RHCP) in K-band and left-hand CP (LHCP) in Ka-band. The maximal scan angles are ±60°. The axial ratios (ARs) are below 3 dB at boresight and below 5 dB when the beam scans to ±60°. The isolation between the K-band and Ka-band channels is higher than 40 dB.