Flexible Filter Research Articles

Flexible bandpass filter with silver conductive layer for GPS, ISM, PCS, LTE and WLAN applications

In this work a flexible wide bandpass filter with silver conducting layer on polyimide substrate have been used. The placed silver layer has good mechanical and electrical flexibility. Measured results are showing the fractional bandwidth value of 44% with return loss value of below −15 dB and insertion loss of −1dB. At various bending conditions, the proposed bandpass filter showing constant performance value. The formed silver layer also presents good adhesion with polyimide layer. Surface roughness and skin depth of the silver layer also analysed in order to know the variation in the performance value of the proposed bandpass filter. The conformality of proposed bandpass filter across 15 0 , 30 0 , 45 0 , 60 0 and 90 0 bending are analysed and found negligible variation in the performance characteristics. Prototyped microstrip bandpass filter results are measured using ANRITSU-MS2037C combinational analyser and found suitable validation with simulation results.

Bottom temperature warming and its impact on demersal fish off the Pacific coast of northeastern Japan

Global climate change occurs not only at the ocean surface but also at the ocean bottom, which is the main habitat of demersal fish. To clarify the current status of bottom temperature warming off the Pacific coast of northeastern Japan, we examined gridded bottom temperature fields from 2003 to 2019. These fields were created by a newly developed gridding method using flexible Gaussian filter weighting with time, distance, and depth. Spatially averaged bottom temperature had a strong, significant warming trend of 0.083 to 0.115°C yr-1 in depth zones of 150-300 m, indicating bottom temperature warming. Corresponding to the warming, increases in landing amounts were found for warm-water species such as searobin in the middle region of our study area (37°50’-39°N). Seasonal catch amounts suggest that ribbon fish and swimming crab recently began to overwinter and reproduce in the area. The distribution shifts of non-target species in fisheries were also analyzed using bottom otter trawl survey data from the area from 2003 to 2019. Northward distribution shifts and increases in density were observed in blackbelly lantern shark and bighand grenadier, indicating that bottom temperature warming led to habitat expansion. Conversely, darkfin sculpin and jelly eelpout shifted northward with decreasing density, suggesting that bottom temperature warming had a negative effect on them. Deepsea bonefish shifted deeper into colder waters with increasing density and mean body weight. Thus, changes and responses of demersal fish to bottom temperature warming in the area were revealed.

Dual‐Color Flexible Metasurfaces with Polarization‐Tunable Plasmons in Gold Nanorod Arrays

AbstractOptical metasurfaces have attracted growing attention in plasmonic structural color in recent years due to their supreme performance in display and imaging technologies. However, real‐life applications of optical metasurfaces so far are often hindered by their complex, expensive, and time‐consuming nanofabrication methods, as well as sophisticated optical measurement systems. Herein, a flexible metasurface filter, based on periodic gold nanorods, capable of changing the output color by simple rotation of a linear polarizer is proposed and demonstrated. This phenomenon is enabled by switching of resonance plasmons in the gold nanorods with the polarization of incident light. Subsequent rotation of the input polarizer leads to an output of two distinct colors and their combinations. Moreover, metasurfaces consisting of Au nanorods with different orientations are integrated into a single flexible substrate. Information can be therefore encoded into the orientations of Au nanorods and readily decoded with the color of the metasurface under polarized illumination of white light‐emitting diode without complex optical components.

Flexible and Ultranarrow Transmissive Color Filters by Simultaneous Excitations of Triple Resonant Eigenmodes in Hybrid Metallic–Optical Tamm State Devices

We demonstrate a flexible transmissive color filter based on a hybrid metallic–optical Tamm state device composed of a thin metallic film on top of dual dielectric distributed Bragg reflectors (DBR...

Ag nanocubes decorated 1T-MoS2 nanosheets SERS substrate for reliable and ultrasensitive detection of pesticides

Surface-enhanced Raman scattering (SERS) is a rapid and sensitive analytical technique for detecting fingerprint structures of analyte at low concentrations. However, the lack of uniform and stable substrate limits its wide applications. Here, we demonstrate a novel 1T-MoS2/AgNCs nanocomposite SERS substrate fabricated on a flexible filter paper for sensitive analysis of pesticide residues in apple fruit. The 1T-MoS2 nanosheets were synthesized by hydrothermal method and subsequently decorated with AgNCs. Importantly, the MoS2 nanosheets form a scaffold that physically holds the AgNCs, resulting in the 1T-MoS2/AgNCs for the adsorption of more target analytes. More importantly, the fibrous structure of the filter paper endows excellent sample collection efficiency. Interestingly, the substrate has remarkable SERS activity attributed to the synergistic effects of (i) the high electromagnetic enhancement generated from the plasmonic AgNCs, and (ii) charge transfer between the MoS2 nanosheets and the target molecules. The results showed that 1T-MoS2/AgNCs nanocomposite substrate achieved a record enhancement factor (AEF = 1.78 × 107), a low detection limit (LOD) of 10−12 M, and good reproducibility (RSD = 9.46%) for R6G compared to the other substrates. Also, the SERS substrate is capable of label-free detection of thiram (TRM) and thiabendazole (TBZ) pesticides in real apple juice and peel. The LOD of thiram and thiabendazole were down to 0.15 ppb and 10 ppb, respectively. As a proof-of-concept application, multi-component detection of a mixture of TRM and TBZ was successfully analyzed. Thus, 1T-MoS2/AgNCs nanocomposite SERS substrate is promising for the ultrasensitive and label-free analysis of diverse pesticide biomarkers in real samples.

Hardware structures, control strategies, and applications of electric springs: a state‐of‐the‐art review

The popularity of electric springs (ESs) has been grown in the last years mainly due to the boost in the growth of smart grids (SGs) and micro-grids (μGs), as well as the high penetration of renewable energy sources. In general, ESs have a hardware structure similar to other compensator devices such as distributed flexible AC transmission systems or active filters. ESs offer the exchange of active and reactive powers with the electrical grid and the demand-side load management. Their ability to simultaneously perform multiple tasks without the need of modifying their hardware structure classifies them as smart loads, distinguishing them from other types of compensators such as active filters, hybrid filters, dynamic voltage restorers, and distribution static VAR compensators, among others. In this work, an exhaustive review of ESs is carried out to cover their three main research trends, i.e. hardware structure evolution, different types of controllers, and applications in electric power distribution systems, SGs, and μGs. Moreover, their main advantages, disadvantages, and contributions in the power quality improvement are discussed. This review clarifies future research trends that have to be explored to advance the subject.

Self-cleaning and flexible filters based on aminopyridine conjugated microporous polymers nanotubes for bacteria sterilization and efficient PM2.5 capture

The capture and elimination of harmful particulate matter (PM) both in air and water is of great importance for human health and environmental sustainability. Here, we demonstrate a novel strategy for the exploitation of conjugated microporous polymer bearing aminopyridine moiety (A-CMPs) as an advanced filter for bacteria sterilization and efficient PM capture. The A-CMPs network shows a hierarchically porous structure with mechanical robustness and flexibility, which facilitates to filtration especially for PM with different particle sizes. The capture efficiency of A-CMPs aerogels for PM2.5 and PM10 were respectively up to PM2.5 ≥ 99.57 ± 0.19% and PM10 ≥ 99.98 ± 0.01% in a long-term durability test and easy to be regenerated. Moreover, the A-CMPAs features excellent superhydrophobicity, which is difficult to saturate with water aerosols in humid air (RH: 89 ± 3%) and in turn shows superior stability and high-performance in terms to capture efficiency. More importantly, the A-CMP monolith exhibits excellent antimicrobial activity and high concentrations of bacterial suspension (e.g., using E. coli as probe bacterial) could be effectively captured and quickly killed during filtration, which endows the A-CMPs additional sterilization performance and thus is of great technological significance with remarkable potentials as a new kind of advanced filter for multifunctional filtration in both air and water.

Flexible and reconfigurable radio frequency electronics realized by high-throughput screen printing of vanadium dioxide switches

Smart materials that can change their properties based on an applied stimulus are in high demand due to their suitability for reconfigurable electronics, such as tunable filters or antennas. In particular, materials that undergo a metal–insulator transition (MIT), for example, vanadium dioxide (VO2) (M), are highly attractive due to their tunable electrical and optical properties at a low transition temperature of 68 °C. Although deposition of this material on a limited scale has been demonstrated through vacuum-based fabrication methods, its scalable application for large-area and high-volume processes is still challenging. Screen printing can be a viable option because of its high-throughput fabrication process on flexible substrates. In this work, we synthesize high-purity VO2 (M) microparticles and develop a screen-printable VO2 ink, enabling the large-area and high-resolution printing of VO2 switches on various substrates. The electrical properties of screen-printed VO2 switches at the microscale are thoroughly investigated under both thermal and electrical stimuli, and the switches exhibit a low ON resistance of 1.8 ohms and an ON/OFF ratio of more than 300. The electrical performance of the printed switches does not degrade even after multiple bending cycles and for bending radii as small as 1 mm. As a proof of concept, a fully printed and mechanically flexible band-pass filter is demonstrated that utilizes these printed switches as reconfigurable elements. Based on the ON and OFF conditions of the VO2 switches, the filter can reconfigure its operating frequency from 3.95 to 3.77 GHz without any degradation in performance during bending.

Augmented extended Kalman filter with cooperative Bayesian filtering and multi‐models fusion for precise vehicle localisations

Self-localisation is vital for autonomous vehicles. In this study, the authors present an augmented extended Kalman filter (AEKF) framework for intelligent vehicle localisation applications. Compared to the previous approach, the proposed AEKF is enhanced through a model fusion, which incorporates a constant velocity model, constant acceleration model, constant turn rate and velocity, and constant turn rate and acceleration model by using the Takagi–Sugeno fuzzy inference technique, where the typical prediction procedure in the extended Kalman filter is modified by a fusion of those various motion models for the state estimation. Furthermore, they proposed a flexible cooperative Bayesian filter to incorporate the data from nearby-vehicles’ position and lateral distance from the host vehicle to the lane lines, to improve the raw global positioning system (GPS) performance under multi-sensor observation environments. They conduct simulation experiments under vividly, near-realistic scenarios with random traffic-flows to show the superiorities of the proposed framework when compared with the consumer-grade GPS implementation. The results show that the obtained positioning enhancement can significantly reduce the positioning error from the original larger than 5 m to the sub-meter level under various scenarios.

A Flexible Low-Pass Filter Based on Laser-Induced Graphene

A graphene-based flexible filter was obtained via one-step laser heating of a polyimide film. The key parameters of a laser have been confirmed by comparing simulated results and experimental data. High-frequency components of input signals were filtered out effectively for different waveforms, such as sine, rectangular, triangle and pulse waveforms. In order to study filtering performance, this paper focused on amplitude frequency curve, phase frequency curve, transient response and mechanical stability. The phase frequency curve is linear distribution, indicating that it is convenient to control phase shift. The mechanical stability of the device remains good even after 5000 bends, which is unreported in previous work. This paper demonstrated that a graphene-based flexible filter prepared by one-step laser heating has excellent performance and opens new way of thinking about flexible electronics in the future.

A Non-Invasive Flexible Glucose Monitoring Sensor Using a Broadband Reject Filter

In this paper, a novel, highly accurate, non-invasive glucose-monitoring sensor that is based on a flexible broadband reject filter is presented. The filter topology comprises a tapered feed line at a top layer that excites four open loop resonators on the bottom layer. The broadband reject response is achieved by relying on a modified log-periodic distribution of the open loop resonators. The embedded resonators are reduced in size and are designed to exhibit an enhanced sensitivity to track the variations of the glucose level across the 1.25-2.65 GHz frequency span. The proposed flexible filter is tested within in-vitro, ex-vivo and in-vivo setups. A high correlation between the scattering parameters of the proposed sensor and the variations in glucose levels is attained. Regression models are developed using experimental data obtained from healthy patients that are subjected to glucose tolerance tests. Results demonstrate less than 4% mean absolute relative difference between the reference and estimated glucose levels, and the predicted glucose levels lie 100% within the clinically acceptable zones as shown by the Clarke Error Grid analysis.

Optical analysis of methyl violet thin films/polymeric substrate for flexible organic technology

In this research, the spin coating as a low-cost non-vacuum preparation technique was used to deposit high-quality thin films of Methyl Violet-10B (MV-10B) with different thicknesses on flexible polymeric substrates. X-ray diffraction technique was applied to distinguish the crystal structure of MV-10B films with different thicknesses. The X-ray diffraction patterns revealed the amorphous nature of all MV-10B films on the polymeric substrates. The optical band gap (direct and indirect) was measured using Tauc's relationship with the various thicknesses of MV-10B films. The linear optical parameters such as refractive index, dielectric constant, and loss were investigated with the difference in thickness of these films. The dispersion parameters of the studied films were estimated according to the single oscillator model provided by Wemple and Di-Domenico. As regards the film thickness, the spectral distribution of linear and nonlinear susceptibilities of MV-10B films was studied. The optical limiting behavior of MV-10B films on the polymeric substrates also has been examined to know how to control the laser beam power as a function of the film thickness. Methyl violet 10B thin films/polymeric substrate for flexible organic technology and Laser power attenuation, and flexible CUT-OFF laser filters in optoelectronic devices.

New flexible directional filter bank by tuning Hermite transform parameters for content based medical image retrieval

This study presents a flexible directional filter bank (DFB) by tuning Hermite transform parameters for content-based medical image retrieval (CBMIR). Two imperative Hermite transform parameters such as the scale of Gaussian kernel and the order of Hermite polynomial are tuned to adapt the flexible Hermite orthogonal basis to improve the retrieval performance of the CBMIR system. First, the tuned 1D Hermite filter transformed into 2D diamond shape filter by McClellan transformation and made it adequate for the directional decomposition of images using DFB structure. The dominant features of these directionally decomposed images are extracted by the rotation-invariant local neighbourhood frequency pattern. The mean retrieval precision is used as a high-level criterion to measure retrieval performance. The proposed method is assessed on three medical image databases: two for computed tomography and one for magnetic resonance imaging and achieved 99.41, 89.07, and 88.71% mean precision, respectively, when ten images are returned by the system.

Numerical simulation of a neotype fluidic sensing system based on side-polished optical fiber

Theoretical design of a neotype fluidic controlling sensor system based on side-polished optical fiber is proposed. Numerical investigations demonstrate that the higher birefringence and resonance coupling can be achieved by flexible design of the polishing shape and depth in the research wavelength. The fluidic system is beneficial to selective integration of functional materials. The material is integrated into the fluidic system, which can achieve a birefringence up to 6.98×10−5, and the application of Sagnac thermometer in temperature sensing is studied, and a group of dips with different temperature sensitivities would be observed in the transmission spectra, which is about 1.6 nm/°C by calculating. furthermore, by introducing resonant coupling, single mode single polarization at 1 310 nm is realized. The refractive index (RI) response of the sensing system for a low RI range of 1.39–1.37 is approximately linear, and exhibits a sensitivity of 6 338 nm/RIU. The results show that the proposed neotype fluidic controlling system can be used as a flexible polarization filter or as a potential two-parameter sensor.

Ensemble patch transformation: a flexible framework for decomposition and filtering of signal

This paper considers the problem of signal decomposition and filtering by extending its scope to various signals that cannot be effectively dealt with existing methods. For the core of our methodology, we introduce a new approach, termed “ensemble patch transformation” that provides a framework for decomposition and filtering of signals; thus, as a result, it enhances identification of local characteristics embedded in a signal that is crucial for signal decomposition and designs flexible filters that allow various data analyses. In literature, there are some data-adaptive decomposition methods such as empirical mode decomposition (EMD) by Huang (Proc. R. Soc. London A 454:903–995, 1998). Along the same line of EMD, we propose a new decomposition algorithm that extracts essential components from a signal. Some theoretical properties of the proposed algorithm are investigated. To evaluate the proposed method, we analyze several synthetic examples and real signals.

A Bearing Fault Diagnosis Method Based on Enhanced Singular Value Decomposition

For the two shortcomings of singular value decomposition (SVD), the determination of the reconstruction order and the poor noise reduction ability, an enhanced SVD is introduced in this article. The core ideas include: first, an efficient method to determine the reconstructed order of SVD and the relative-change rate of the singular envelope kurtosis is presented, composed of improved SVD (ISVD). Then, the method to select the optimal node of wavelet packet transform (WPT) by the criterion of envelope kurtosis maximum is presented, composed of improved WPT (IWPT). The flexible filter design and superior noise reduction abilities of the IWPT and the passband denoise ability of the ISVD are organicly combined to form enhanced singular value decomposition (E-SVD) method. In addition, an indicator is introduced to evaluate the performance of the results. First, the reconstructed signal is obtained by performing ISVD on the original signal. Second, IWPT is executed on the reconstructed signal to achieve the optimal node. Finally, the filtered signal is combined with the envelope power spectrum to extract the bearing fault characteristic frequency. The method's validity and superiority are verified by the analysis of simulated data and actual cases of rolling bearing.

Waveguide Filters With Central-Post Resonators

In this letter, a class of rectangular waveguide filters with central-post resonators is introduced. By introducing a central post in an oversized rectangular cavity, the resonant frequency of TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">301</sub> -mode can be brought close to that of TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</sub> -mode. The two resonant modes are coupled to adjacent fundamental mode resonators by inductive irises. A doublet coupling topology can be used to model the physical configuration, and flexible filter responses with finite-position transmission zeros (TZs) can be realized. Four 4-pole filters with different TZ positions are designed and simulated. A seven-pole filter with two cascaded central-post resonators is fabricated and measured. In the seven-pole filter, each central-post resonator independently controls one TZ on the lower side and very close to the passband. The measurement results of the seven-pole filter agree with the simulated counterparts very well, thus validating this filter design technique.

Accelerating Convolutional Neural Network via Structured Gaussian Scale Mixture Models: A Joint Grouping and Pruning Approach

Despite the great success of deep convolutional neural networks (DCNNs), their heavy computational complexity remains a key obstacle to the wide use in practical applications. To meet this challenge, DCNN pruning has been recently developed as a technique of compressing DCNNs to facilitate their applications in the real world. In this paper, we propose a hybrid network compression technique for exploiting the prior knowledge of network parameters by Gaussian scale mixture (GSM) models. Specifically, the collection of network parameters are characterized by GSM models and network pruning is formulated as a maximum a posteriori (MAP) estimation problem with a sparsity prior. The key novel insight brought by this work is that groups of parameters associated with the same channel are similar, which is analogous to the grouping of similar patches in natural images. Such observation inspires us to leverage powerful structured sparsity prior from image restoration to network compression - i.e., to develop a flexible filter- grouping strategy that not only promotes structured sparsity but also can be seamlessly integrated with the existing network pruning framework. Extensive experimental results on several popular DCNN models including VGGNet, ResNet and DenseNet have shown that the proposed GSM-based joint grouping and pruning method convincingly outperforms other competing approaches (including both pruning and non-pruning based methods).

A novel flexible broadband photodetector based on flower-like MoS2 microspheres

Flexible photodetectors based on two-dimensional (2D) transitional metal dichalcogenides (TMDCs) can be used in wearable photoelectronic devices, which have attracted a lot of attention for the last few years. However, most photodetectors based on single layer materials often have low light absorption, and it generally requires complicated and elaborate preparation processes. In this work, we synthesized MoS2 flower-like microspheres with a hydrothermal method, and then a flexible broadband photodetector was prepared by combining MoS2 with a flexible microporous filter membrane. The photodetectors show broad spectral response from 405 nm to 808 nm, with superior responsivity and detectivity reached 0.963 A W−1 and 2.9x1010 Jones respectively under a 405 nm light of 1.77 mW cm−2. Furthermore, these devices also exhibit stable photoelectric responsivity even under various bending conditions. We believe this work will inspire the future development of flexible wearable optoelectronic device.

An optimized MAC based architecture for adaptive digital filter

Filter design in signal processing field plays a vital role in achieving low power dissipation, which is essential for portable gadgets. This paper proposes an effective flexible FIR filter structure, which is adaptive and utilizes multiply–accumulate (MAC) core. Most common algorithm for filter coefficient optimization includes least mean square (LMS) and recursive least square (RLS). Though the performance of the recursive least square (RLS) algorithm is superior as compared to the least mean square (LMS); because of higher arithmetic complexity in design, it has not been preferred for real time applications. The fundamental filter has used a LMS based tapped delay line filter, which is practically a feasible choice for adaptive filtering algorithm in order to attain lesser computation. In the proposed work, the adjustable coefficient filters using an optimized LMS approach has been implemented for the utilization of determining the unexplored system. The filter tap considered here is a 32-tap and its analysis and synthesis has been carried out using hardware description language (HDL) programming and synthesized in field programmable gate array (FPGA) devices. The placement and post routing design has offered good performance in terms of utilized resources. The implemented filter architecture requires 80% reduction in resources and has enhanced the clock frequency by about five times when examined with the reported architecture.