Channel Filter Research Articles

Reconfigurable Frequency Response Masking Multi-MAC Filters for Software Defined Radio Channelization

Mobile technology is currently trending toward supporting multiple communication standards on a single device. This means that some reconfigurable techniques must be the foundation of their design. The two essential requirements of channel filters are minimized complexity and reconfigurability. In this research, a novel extension of Frequency Response Masking (FRM) was investigated by employing Time Division Multiplexing (TDM)-based single Multiply and Accumulate (MAC) architecture using the principle of resource sharing to realize multiple sharp filter responses from a single prototype constant group delay low pass filter. This paper uses a single multiply and add units regardless of the quantity of channels and taps. The suggested reconfigurable filter was synthesized on technology based on 0.18-µm CMOS and put into practice. Further trials were carried out on Virtex-II 2v3000ff1152-4 FPGA device. The outcomes revealed that the suggested channel filter, which was synthesized using FPGA, provides 21.36% of the area curtail and 14.88% of power scaling down on average and put into practice using ASIC provides 5.18% of the area reduction and 9.08% of power scaling down on average.

Computational spectrometer with multi-channel cascaded silicon add-drop micro-ring resonators.

The increasing demand for portable spectral analysis has driven the development of miniaturized spectrometers. Computational spectrometers, based on algorithmic reconstruction, are a potential solution to meet this demand. We report on the design and implementation of an integrated computational spectrometer on a silicon-on-insulator (SOI) substrate. The device is based on a 5-stage binary tree of cascaded silicon add-drop micro-ring resonators (MRRs). One of the 32 branches serves as the reference channel. Each of the other 31 branches has 4 cascaded MRRs with arbitrary coupling coefficients, cavity perimeters, and center distances. By using add-drop MRRs, we have 62 filter channels with 31 branches. It has no intrinsic structural reflection and scattering losses other than the excess loss in the 1 × 2 splitters and the waveguide propagation loss. The chip has a footprint of 1.5 mm2 and a resolution of 0.11 nm in the C-band. Broadband spectrum reconstruction with bandwidth >10 nm is also demonstrated.

Effect of ash-bridge deposition in asymmetric diesel particulate filter channels on the pressure drop and particulate matter trapping characteristics

A diesel particulate filter (DPF) is commonly used to trap particulate matter (PM). The collapse and sintering of carbon and ash deposits during exhaust gas flow and DPF regeneration frequently result in the formation of ash bridges, which are buildups of ash and PM that clog the filter channels. To investigate the impact of an ash bridge formed by accumulated ash on the pressure drop and PM trapping characteristics of asymmetric DPFs, an asymmetric DPF channel with an ash bridge was constructed. The analysis employed computational fluid dynamics to examine how the ash bridge affects the pressure drop and PM trapping characteristics in an asymmetric DPF. This study reveals that the asymmetric DPF design effectively enhances the ash-holding capacity, thereby mitigating the risk of channel blockage. The presence of ash bridges in DPF channels has a more substantial impact on the pressure drop through radial congestion than through axial congestion. The application of asymmetric thin-wall DPFs can counteract the increase in exhaust backpressure caused by ash bridges. An ash bridge located in the middle of a DPF channel intensifies the uneven deposition of PM. However, implementing an asymmetric DPF structure enhances the uniformity of PM deposition.

A High-Speed Train Axle Box Bearing Fault Diagnosis Method Based on Dimension Reduction Fusion and the Optimal Bandpass Filtering Demodulation Spectrum of Multi-Dimensional Signals

The operating state of axle box bearings is crucial to the safety of high-speed trains, and the vibration acceleration signal is a commonly used bearing-health-state monitoring signal. In order to extract hidden characteristic frequency information from the vibration acceleration signal of axle box bearings for fault diagnosis, a method for extracting the fault characteristic frequency based on principal component analysis (PCA) fusion and the optimal bandpass filtered denoising signal analytic energy operator (AEO) demodulation spectrum is proposed in this paper. PCA is used to measure the dimension reduction and fusion of three-direction vibration acceleration, reducing the interference of irrelevant noise components. A new type of multi-channel bandpass filter bank is constructed to obtain filtering signals in different frequency intervals. A new, improved average kurtosis index is used to select the optimal filtering signals for different channel filters in a bandpass filter bank. A dimensionless characteristic index characteristic frequency energy concentration coefficient (CFECC) is proposed for the first time to describe the energy prominence ability of characteristic frequency in the spectrum and can be used to determine the bearing fault type. The effectiveness and applicability of the proposed method are verified using the simulation signals and experimental signals of four fault bearing test cases. The results demonstrate the effectiveness of the proposed method for fault diagnosis and its advantages over other methods.

Tunable terahertz filter based on graphene photonic crystals with defective layers

In this paper, we design a high-precision tunable terahertz filter by using transfer matrix method. The filter structure mainly consists of graphene embedded photonic crystals (GPCs). The front part of the GPCs contains artificial synthetic material and air layer, the back part of the GPCs is composed by and periodic stack of isotropic dielectric slabs (MgF2) embedded with graphene sheets, where air defect layer is located in the middle of the GPC as a central layer. Our simulation reveals that graphene layer and air defective layer strongly affect the filter performance. And we can get a relatively pure transmission peak in a wide frequency region. Additionally, the influence of incidence angle of terahertz wave, thickness of air layer, the unit number of front periodic structure and chemical potential of the graphene sheets can also modulate the function of the filter. And the filter has strong stability when the temperature changes from 150 K to 350 K.The results indicate that single channel, dual and multiple channels filter in a narrow frequency can be obtained by optimizing the structure parameter.

Conditional computation in neural networks: Principles and research trends

This article summarizes principles and ideas from the emerging area of applying conditional computation methods to the design of neural networks. In particular, we focus on neural networks that can dynamically activate or de-activate parts of their computational graph conditionally on their input. Examples include the dynamic selection of, e.g., input tokens, layers (or sets of layers), and sub-modules inside each layer (e.g., channels in a convolutional filter). We first provide a general formalism to describe these techniques in an uniform way. Then, we introduce three notable implementations of these principles: mixture-of-experts (MoEs) networks, token selection mechanisms, and early-exit neural networks. The paper aims to provide a tutorial-like introduction to this growing field. To this end, we analyze the benefits of these modular designs in terms of efficiency, explainability, and transfer learning, with a focus on emerging applicative areas ranging from automated scientific discovery to semantic communication.

Perceptual authentication hashing for digital images based on multi-domain feature fusion

In recent decades, numerous perceptual authentication hashing schemes have been proposed for image content authentication. However, most of these schemes are based on a single spatial or transform domain, and they fail to provide satisfactory robustness and discrimination capability when facing complex image manipulations in real scenarios. In this work, we present a perceptual authentication hashing scheme based on Convolutional Neural Network (CNN) that leverages both spatial and frequency domains. Specifically, we construct two separate streams for spatial and transform domains. Then, we introduce a feature fusion module to merge the features of these two domains to generate a hash sequence. Besides, we design a frequency domain channel filter and a frequency attention module for the frequency domain, and introduce a frequency domain loss function to optimize model training. Based on large-scale testing datasets, our scheme demonstrates superior performance compared to state-of-the-art schemes, as evidenced by Receiver Operating Characteristic (ROC) curves.

A diplexer antenna with extremely high isolation for co-site duplex applications

Co-site full-duplex communication system is facing self-interference (SI) issues caused by tremendous gap between Tx power and Rx sensitivity. SI suppression in the propagation domain is addressed by a co-polarized diplexer antenna with high port isolation in this paper. It shares a dual-band microstrip antenna with a small frequency ratio, at 1.5 and 2.0 GHz as an example. A shorting pin directly connects the antenna and diplexer, avoiding 50-Ω interface and impedance matching circuit. The diplexer is composed of open-loop resonators (OLRs) and step-impedance resonators (SIRs). Compact channel filters are constituted by OLRs, and SIRs are adopted to improve the filtering response of the diplexer. General guidelines of the diplexer are given through rigorous analysis. The fractional bandwidths of the lower and higher channels of the diplexer are 4% and 3%, and the fractional bandwidths of the diplexer antenna are 1.5% and 1%, respectively. The port isolation is greater than 53 dB for both channels. Size of the diplexer antenna is 0.65 λ×0.60 λ×0.016 λ, where λ is the free-space wavelength at the lowest operation frequency. Potential advantages of the proposed antenna in suppressing SI are validated using Software-Defined Radio, which is potentially useful in full-duplex communications.

The analytical solutions of squeezing flow and heat transfer in an horizontal filtering channel

Flow and heat transfer dynamics inside different industrial chambers play a vital role in understanding momentum and heat transfer during industrial operations. Analysis of such flow and heat transfer helps operators to know how the system works. To better understand the filtration process, the current study analytically investigated the internal flow and heat transfer through a porous horizontal filter channel under the influence of a uniform magnetic field while removing unwanted contaminations from the fluid inside the filter chamber. Thus, the novelty of the current study is to advance the filtration process by investigating how the top moving wall, which aims to minimise filter cake formation, affects permeates outflow (the current design). The partial differential equations (PDEs) model representing the internal flow and heat transfer during filtration is transformed into a system of ordinary differential equations (ODEs) using Lie point symmetry reduction without changing the dynamics under investigation. After that, the transformed equations are solved analytically using the perturbation approximation technique. The comparative analysis between the obtained semi-analytical and NDSolve numerical solutions was used to show the correlation of internal flow, temperature, and pressure profiles. The obtained solutions are used to find the best combination of dimensionless parameters that arise from flow and heat transfer dynamics that lead to optimum outflow. Graphical analysis of flow and heat transfer dynamics are used to indicate the combination of parameters that leads to maximum outflow based on scientific evidence. It is observed that, on average, the velocity increases significantly by 122.55% across all cases of Re ranging from 0 to 3.2 at the top permeable wall y=1. This significant increase is due to the motion of the moving wall and fluid injection happening at y=1. The results show that more chamber volume, small pores size, weak injection, weak magnetic force, and less Joule heating are crucial to increase internal temperature and permeate outflow velocity during filtration.

Filter channel network based on contextual position weight for aspect-based sentiment classification

Filter channel network based on contextual position weight for aspect-based sentiment classification

Analysis of gas flow and PM movement characteristics inside diesel particulate filter channel

Based on experimental data from engine after-treatment tests, the diesel particulate filter (DPF) microscopic channel model was constructed using UG, and the accumulation of particulate matter (PM) in the deep bed filter layer and carbon deposit layer was analyzed through computational fluid dynamics (CFD). A comprehensive study was conducted on the exhaust gas flow characteristics and PM movement within the DPF channel, and focus on the effects of PM distribution type on capture and regeneration characteristics. The results show that with the increase in particle size in the exhaust, the distribution of PM concentration along the axial position of the channel shows a trend of gradually shifting from 0.2 to 0.25 m (rear section) to 0.125–0.2 m (front section). In particular, PM with 1 μm particle size has a large motion inertia, which is easy to move out of the airflow and deposit in the middle part of the channel. For PM in the front and middle sections of the channel, the airflow obstruction is relatively small, but the heat transfer loss is large, which is not beneficial for PM regeneration in the rear section. Therefore, with the distribution of LID, PD-1, and PD-2, the regeneration efficiency is relatively low, at 50.84%, 55.01%, and 54.59%, respectively.

Design of coherent passive quantum equalizers using robust control theory

The paper develops a methodology for the design of coherent equalizing filters for quantum communication channels. Given a linear quantum system model of a quantum communication channel, the aim is to obtain another quantum system which, when coupled with the original system, mitigates degrading effects of the environment. The main result of the paper is a systematic equalizer synthesis algorithm which relies on methods of state–space robust control design via semidefinite programming.

Research Progress on Router Devices for the OAM Optical Communication

Vortex beams carrying orbital angular momentum (OAM) provide a new degree of freedom for light waves in addition to the traditional degrees of freedom, such as intensity, phase, frequency, time, and polarization. Due to the theoretically unlimited orthogonal states, the physical dimension of OAM is capable of addressing the problem of low information capacity. With the advancement of the OAM optical communication technology, OAM router devices (OAM-RDs) have played a key role in significantly improving the flexibility and practicability of communication systems. In this review, major breakthroughs in the OAM-RDs are summarized, and the latest technological standing is examined. Additionally, a detailed account of the recent works published on techniques related to the OAM-RDs has been categorized into five areas: channel multicasting, channel switching, channel filtering, channel hopping, and channel adding/extracting. Meanwhile, the principles, research methods, advantages, and disadvantages are discussed and summarized in depth while analyzing the future development trends and prospects of the OAM-RDs.

Key Factors that Negatively Affect Performance of Imitation Learning for Autonomous Driving

Conditional imitation learning (CIL) has proven superior to other autonomous driving (AD) algorithms. However, its performance evaluation through physical implementations is still limited. This work contributes a systematic evaluation to identify key factors potentially improving its performance. It modified convolutional neural network parameter values, such as reducing the number of filter channels and neuron units, and implemented the model into a vision-based autonomous vehicle (AV). The AV has front-wheel steering with an Ackermann mechanism since it is commonly used by passenger cars. Using the Inertia Measurement Unit, we measured the vehicle’s location and yaw angle along the experimental route. The AV had to move autonomously through new road sectors in the morning, afternoon, and night. First, an overall performance evaluation was carried out. The results showed a 99% success rate from 648 evaluation experiments under different conditions in which the 1% failure rate happened at new intersections. Then, a turning performance evaluation was conducted to identify key factors leading to failure at new intersections. They include fast speed, dazzling light reflection, late navigation command change instant, and the untrained turning driving pattern. The AV never failed while driving on the trained routes. It had a 100% success rate when driving slower, even under various lighting conditions and at various driving patterns, including untrained intersections. Although this study is limited to identifying key factors at three constant speeds, the results become the foundation for future research to improve CIL performance for AD, including by incorporating multimodal fusion and multi-route networks.

A self-cleaning micro-fluidic chip biospired by the filtering system of manta rays.

Size-based particle filtration has become indispensable in numerous biomedical and environmental applications. In this study, bioinspired by the filter-feeding mechanism (lobe filtration) of manta rays, we designed a U-shaped biomimetic gill rake filter that combined lobe filtration and Dean flow to filter monodisperse suspensions, bi-disperse suspensions and yeast cells. Compared with other equipment using the inertial focusing technology, our equipment can perform high-throughput (up to 8 mL min-1) and high-efficiency filtration of particles (maximum filtration efficiencies of 96.08% and 97.14% for 10 and 15 μm monodisperse suspensions at the optimum flow rate of 6 mL min-1). The complex velocity field of the micro-fluidic flow within the filter is numerically simulated, and in combination with experiments, a threshold for the flow rate is identified. When the inlet flow rate exceeds the threshold value, the efficiency of particle filtration is increased rapidly. Afterwards, by analysing the filtration mechanism, we develop three novel filtration processes. The equilibrium positions of the particles and yeast cells in the main channel are close to the outer wall at high flow rate, which diminishes the likelihood of particles and yeast cells entering the side channel. This configuration establishes a self-cleaning mechanism, ensuring prolonged and efficient operation of the filter with high-throughput processing. Furthermore, the influence of the filter lobe angle and channel width on the filtration efficiency and outlet flow rate ratio are explored, and an optimisation plan is prepared.

Switching Capacitor Filter with Multiple Functions, Adjustable Bandwidth in the Range of 5 Hz–10 kHz

This article proposes a second-order switch-capacitor filter that integrates low-pass, high-pass, band-pass, band-stop, and all-pass, and achieves flexible bandwidth adjustment of the filter through clock rate and capacitance ratio. The final filter design consists of two completely independent second-order switch-capacitor filter channels, and a 4-order Butterworth low-pass filter is designed through two-stage cascades. The two completely independent second-order switch-capacitor filters are integrated on a single chip and manufactured using the Huahong BCD350GE high-voltage 24 V process. The measurement results indicate that the proposed switch-capacitor filter achieves various functional filtering characteristics and achieves a bandwidth of 5 Hz to 10 kHz. The chip area is 5.1 × 3.1 mm2, powered by a dual power supply of ± 5 V, and the power consumption is 80 mW.

Applied Cavity Perturbation Used for Frequency Identification of Channel Ports in Manifold-Coupled Multiplexers

We investigate a practical technique for deembedding the channel filter S-parameters of manifold-coupled multiplexers (MUXs), without detaching filters from the manifold. The method is applicable for MUXs with an arbitrary number of channels and can be used for the device regardless of its bandwidth, guard band, or loss of filters. We reconfigure the N-port MUX to two simpler networks cascaded to each other. We assume that the manifold response is unknown and use the idea of applied perturbation on the channel filter, and then by comparing the response of the overall cascaded network, before and after the perturbation, we approximate the channel port response. The technique is useful in fast detecting the unexpectedly detuned channels or likely faults in the device without unnecessary plugging/unplugging; it is also useful in roughly tuning of the channel filers at the early stage of MUX tuning. The technique can be easily traced by the telecommunication community.

Design of a novel stripline diplexer using frequency‐dependent couplings

AbstractA novel stripline diplexer design using frequency‐dependent couplings (FDC) to achieve multiple transmission zeros is developed in this paper. The transmission zeros generated by FDCs are flexible and controllable; on the basis of the existing cross‐coupled, more transmission zeros are introduced to improve the frequency selection characteristics. Based on this characteristic, the authors synthesized and designed a 2.6‐GHz diplexer, its transmitting channel filter is five orders with three transmission zeros, and the receiving channel filter is four orders with three transmission zeros. The authors fabricated and measured it, in narrowband, the tested results, synthesis responses and simulation results are well matched with each other, which will provide more flexibility in the design of diplexers for wireless communication system.

Wideband signal combining circuit based on multichannel different‐/same‐frequency power combiner

AbstractA wideband signal combining circuit with continuous bandwidth based on multichannel different‐/same‐frequency power combiner is presented. Two‐way signals with the same frequency can be combined to a higher power signal. Two‐way signals with different frequencies can be combined into a broadband signal. A stepped impedance resonator (SIR) is used as a multimode resonator. The wider bandwidth is got by SIR. And the selectivity of the two filtering channels is improved by the introduction of SIR stubs, which generate four transmission zeros on both sides of the passbands. The high 3‐dB point of the low‐frequency channel overlaps with the low 3‐dB point of the high‐frequency channel. Therefore, the output passband is continuous. The measured frequency ranges of two channels are 1.34–2.21 GHz/2.21‐2.87 GHz, respectively, and from 1.46 to 2.74 GHz, the input reflection coefficient is such that the return loss is higher than 15.5 dB. The insertion loss of the two channels is 0.71/1.18 dB, and the measured isolation is higher than 15.4 dB. The measured bandwidth of the combining signal is 1.5 GHz (1.34–2.84 GHz).

Integrated α-MnO2 nanowires PVDF catalytic membranes for efficient purification of dye wastewater with high permeability

Catalytic membranes have been studied and reported widely, but ideal catalytic membranes with high rejection ratio and high permeability simultaneously are still a challenge to develop. Herein, integrated α-MnO2 nanowires polyvinylidene fluoride (PVDF) catalytic membranes were fabricated by a vacuum filtration method. Based on the intercalation structures of GO formed by α-MnO2 nanowires and the spatial stacking of nanowires, filter channels with high water flux were constructed. While CS displayed as anchor point to fix α-MnO2 nanowires and also endow the membrane surface with electro-positivity. Then, a sequence of catalytic membranes with different content of α-MnO2 were prepared, and detailed characterizations of structure were taken out. Finally, all of the membranes displayed excellent stability in harsh conditions (pH values from 3 to 11), and M-5 with the most content of α-MnO2 displayed the best separation ability, for which the rejection ratio reached 99.26 % along with a high permeability about 923.72 L·m−2·h−1·Bar−1, when it was used to separate methyl blue (MBE) wastewater. In addition, M-5 also displayed excellent reusability, such as the rejection ratio still maintained above 92.62 % after 9th cycles and reduced to 86.74 % after 10th cycle, while the permeability still remained 612.09 L·m−2·h−1·Bar−1 after the 10th cycle. Therefore, this work developed an outstanding catalytic membrane, which displayed good application prospect for treatment of dye wastewater.