Metal Mesh Filters Research Articles

Evaluation of the effect of respiratory airflow on captured speech quality: application to pop filters

Recording speech is often a matter of proper experimental design to obtain the best signal quality. This notably includes appropriate microphone positioning and gain adjustment. However, some radio communication devices require that the microphone be placed in a very close proximity to the mouth, therefore capturing the respiratory airflow, as well as the air bursts from plosive consonants. In this paper, we assess an objective evaluation method for the quality of speech signals captured in such adverse conditions. It employs an artificial mouth coupled with a steady airflow to compute the Speech Transmission Index (STI). We apply this method to the evaluation of four commercially available pop filters. The addition of a 30~L/min airflow reduces the STI with the microphone alone from excellent to fair. With soft fabric filters, we gain back the original STI, while it remains very slightly degraded with a metal mesh filter. The objective metric is finally confronted with a listening test. The perceived quality of simulated samples with the added airflow is similar to the STI results. However, no significant difference between the filters is found with real speech samples containing plosive consonants and no respiration noise.

Metal Mesh Metasurfaces as Dual-Band Bandpass Filters for Terahertz Frequencies

In the paper, we propose a new strategy to design of metal mesh filters (MMFs) based on spatial symmetry analysis of bound states in the continuum(BICs) and manipulating and control with resonances, when BICs transformed to the resonances due to spatial perturbations in the MMF structure. The design of a dual-band polarization-insensitive terahertz bandpass filter with wide upper stopband characteristics using a single conducting layer patterned with rectangular holes is presented. The transmission response of the MMF with two poles is obtained to realize dual-band characteristics and three zeros to suppress the stopband. The proposed design has achieved broadband bandpass transmission characteristics under both TE and TM polarizations with canter frequencies at 0.516THz and 0.734THz and 3dB bandwidths of 25% and 17%, respectively, and upper stopband from 0.887THz to 1.6THz with over 10dB suppression.

Novel metal mesh filter equipped with pulse-jet regeneration for small-scale biomass boilers

Wood is a renewable fuel, however the combustion of wood can lead to significant dust emissions. The application of fabric filters is one possibility to ensure low particulate matter emissions. Nevertheless, these filters are so far not used for small-scale firing systems. In this work, the mitigation potential of a newly developed fabric filter concept with pulse-jet regeneration, based on a stainless-steel mesh was studied. The filter was tested on a commercially available 24 kW biomass boiler, which was operated with wood pellets and wood chips. Experiments showed a linear dependency of the separation efficiencies and clean gas concentrations on average pressure drop while a logarithmic dependency of the clean gas concentrations on an empirical factor k was proven. The filter showed good regenerability and dust separation efficiencies up to 83 % and 90 % during combustion of wood pellets and wood chips. The pulse-jet regeneration showed a short-time peak of dust emissions behind the filter which can represent between 24 and 60 % of the total dust emissions during a whole filtration cycle. Nevertheless, the application of different filters with 25 and 50 μm mesh size guarantees an efficient dust removal. In a first phase during filter cake formation, the concentrations can exceed the limit value, but once a filter cake had built up, the concentrations drop drastically below 0.01 g m−3. In summary, the filters show good regenerability and efficient dust separation and thus further development potential.

Evaluation of a metal mesh filter prototype with wet regeneration

Wood combustion is a major part of the current efforts to reduce CO2 emissions. However, wood combustion leads to emissions of other pollutants like fine particulate matter. A new option to reduce particulate matter emissions is a metal mesh filter with counter current flushing. An automatic prototype was tested under realistic conditions including starts and stops of the boiler. For regeneration, the filter was flushed using water in opposite flow direction. The water was recycled multiple times to limit water consumption. The results are very promising. Regeneration was successful and no signs of decay could be observed over 419.5 h of operation and 234 regenerations. The filter can be operated during all phases of boiler operation, which is a major step forward compared to alternative secondary measures. Separation efficiency was high with 80–86%, even though the filter showed internal leakage, which reduced the separation efficiency. Additionally, waste products were examined. About 1000 l wastewater can be expected to be produced every month, which could be disposed using the communal waste water system, given the low heavy metal loading. A part of the fine particulate matter is unsoluble and has to be removed from the regeneration water before reuse. The unsoluble fraction contains the majority of heavy metals and has to be disposed as fly ash or used for urban mining. Generally spoken, the metal mesh filter is a new, promising option which can overcome limitations of current secondary measures without increasing costs given its simple and robust construction.

Novel metal mesh filter using water-based regeneration for small-scale biomass boilers

Particulate matter emissions are a key issue of modern biomass boilers. A novel gas cleaning method using a metal mesh filter combined with water-based cleaning was developed and tested. The filter was tested batch-wise. Flue gas of a commercial 50-kW boiler was filtered until a pressure drop of 2000 Pa was reached. Afterwards, the filter was regenerated. The initial prototype used ultrasound in order to remove the filter cake from the filter candles. Regeneration was complete and, even after boiler malfunctions producing tar, the filter cake could still be removed. Given the good results, a second cleaning mode, flushing the filter candles with water, was tested. The results were as good as with ultrasonic cleaning. Peak mass collection efficiency was very high with 98 ± 2% (burning wood pellets). However, directly after cleaning, the first layer of filter cake has to be developed. In this initial phase, collection efficiency is low. Service time until maximum pressure drop was reached depended on the gas velocity. Using pellets as fuel, at a gas velocity of 66.6 m/h, 12-h service time was reached and 4.1 g dust was collected per square meter filter surface, while at 33.3 m/h, service time increased to 55 h and collected dust to 13.9 g/m2. Using low-quality wood chips, the raw gas dust loading was much higher but also the maximum loading of the filter was higher with 13.3 to 28.9 g dust separated per square meter. Still, the service time decreased to 3.4 respective 38 h. Peak collection efficiency increased to 99.5 ± 0.8%. The overall collection efficiency including the buildup of the filter cake depends on the gas velocity and fuel. It ranges from 74 ± 4 to 91 ± 1%. The feasibility of the filter concept could be proven, and further development towards a commercial application is in progress. Metal mesh filters with countercurrent cleaning showed a high potential given their simple and robust design, as well as high collection efficiency.

Demonstration of wideband metal mesh filters for submillimeter astrophysics using flexible printed circuits.

We developed a wideband quasi-optical band-pass filter covering 170-520 GHz by exploiting the recent advancements in commercially available flexible printed circuit (FPC) fabrication technologies. We designed and fabricated a three-layered stack of loaded hexagonal grid metal meshes using a copper pattern with a narrowest linewidth of 50µm on a polyimide substrate. The measured frequency passband shape was successfully reproduced through a numerical simulation using a set of parameters consistent with the dimensions of the fabricated metal meshes. FPC-based metal mesh filters will provide a new pathway toward the on-demand development of millimeter/submillimeter-wave quasi-optical filters at low cost and with a short turnaround time.

Effective removal of fluorescent microparticles as Cryptosporidium parvum surrogates in drinking water treatment by metallic membrane

The diarrhoea-causing parasitic protozoan Cryptosporidium parvum (C. parvum) cannot be efficiently removed by conventional drinking water treatment and poses a biological threat to public health. To ensure the biological safety, three kinds of metallic membranes, laminating metal mesh filter, non-woven metal filter and sintered metal fiber filter were employed to compare their properties. The results showed that the sintered membrane possessed the best filtration performance and lowest membrane resistance among three metallic membranes. Therefore, the sintered membrane was selected for subsequent experiments. Due to the low infectious dose of C. parvum and sophisticated detection methods, fluorescent particle tracers, Crypto-tracer-1, were chosen as a feasible surrogate was proposed to investigate the removal efficiency of sintered membrane for C. parvum. The results indicated that the tracer log removal value (LRV) ranged between 5.1 and 5.4 log10 under different filtration flux, which equivalently means that C. parvum could be completely removed and further tests are needed to confirm the results obtained using C. parvum. Furthermore, a pilot-scale study was performed for 10 weeks in full-scale drinking water treatment systems. The turbidity could be efficiently removed (outlet water of membrane was 0.08 ± 0.04 NTU) and the average transmembrane pressure recovery rate was 84.6% after physical backwash. Fouling mechanism analysis indicated that the interaction energy between foulants and membrane material became stronger over time. The practical operation results showed that sintered membrane performed well in continuous operation for a long time and also had a good anti-pollution ability. These findings could facilitate application of metallic membrane in drinking water treatment.

Transmission properties of metal mesh filters at 90 GHz

Freestanding frequency-selective surfaces with cross-shaped aperture elements are investigated numerically and experimentally. Transmission characteristics of such two-dimensional periodic structures as functions of geometrical sizes are analyzed using the 3D finite element method. These structures find application in modern microwave and terahertz engineering as band-pass metal mesh filters. Utilizing the conjugate gradient method narrowband, 90 GHz filters have been developed and optimized numerically. The results of measurements carried out in the present study agree well with the obtained theoretical data. It is shown that some parameters of such metal mesh filters can be improved by the proper selection of structure periodicity. A single-layer filter with a fractional bandwidth of 5.3% and an insertion loss of − 0.5 dB at the central frequency is demonstrated.

Twin-Slot Antenna-Coupled Superconducting Ti Transition-Edge Sensor at 350 GHz

We have developed four-leg-supported superconducting Ti transition-edge sensors (TES) formed by KOH wet etching. Energy relaxation mechanism is changed from electron–phonon coupling to diffusive phonon after wet etching. The current–voltage curves of the same TES device were measured before and after wet etching. After wet etching, its thermal conductance (G) is reduced to 500 pW/K from 8950 pW/K. The measured effective response time (τeff) is 143 μs, about 30 times larger. In addition, we have studied the optical noise equivalent power (NEP) with a cryogenic blackbody in combination with metal-mesh filters to define the radiation bandwidth. The obtained optical NEP is 5 × 10−16 W/√Hz, which is suitable for ground-based astronomical applications.

Metal mesh filters based on Ti, ITO and Cu thin films for terahertz waves

In this study, we have investigated the spectral performance of resonant terahertz (THz) bandpass filters which were produced from thin films with a metal-mesh shape. The aforementioned filters were fabricated from titanium, copper and indium tin oxide thin films on fused silica substrates by UV lithography with an array of cross-shaped apertures. Since the mesh period, cross-arm length and its width specify the spectral characteristics of the filters, we were able to reveal the performance of these filters experimentally using both a THz time domain spectrometer and a Fourier transform infrared spectrometer. A commercial electromagnetic simulation software, CST microwave studio, was used to verify the experimental data. The transmission of the filters are in the range 20–55 % at their relevant center frequencies. To our knowledge this study is the first to show that fabricated patterns based on ITO thin films can be used to filter THz radiation.

Metamaterial composite bandpass filter with an ultra-broadband rejection bandwidth of up to 240 terahertz

We present a metamaterial, consisting of a cross structure and a metal mesh filter, that forms a composite with greater functional bandwidth than any terahertz (THz) metamaterial to date. Metamaterials traditionally have a narrow usable bandwidth that is much smaller than common THz sources, such as photoconductive antennas and difference frequency generation. The composite structure shown here expands the usable bandwidth to exceed that of current THz sources. To highlight the applicability of this combination, we demonstrate a series of bandpass filters with only a single pass band, with a central frequency (f0) that is scalable from 0.86–8.51 THz, that highly extinguishes other frequencies up to >240 THz. The performance of these filters is demonstrated in experiment, using both air biased coherent detection and a Fourier transform infrared spectrometer (FTIR), as well as in simulation. We present equations—and discuss their scaling laws—which detail the f0 and full width at half max (Δf) of the pass band, as well as the required geometric dimensions for their fabrication using standard UV photolithography and easily achievable fabrication linewidths. With these equations, the geometric parameters and Δf for a desired frequency can be quickly calculated. Using these bandpass filters as a proof of principle, we believe that this metamaterial composite provides the key for ultra-broadband metamaterial design.

Large-Area Reflective Infrared Filters for Millimeter/Sub-mm Telescopes

Ground-based millimeter and sub-millimeter telescopes are attempting to image the sky with ever-larger cryogenically-cooled bolometer arrays, but face challenges in mitigating the infrared loading accompanying large apertures. Absorptive infrared filters supported by mechanical coolers scale insufficiently with aperture size. Reflective metal-mesh filters placed behind the telescope window provide a scalable solution in principle, but have been limited by photolithography constraints to diameters under 300 mm. We present laser etching as an alternate technique to photolithography for fabrication of large-area reflective filters, and show results from lab tests of 500 mm-diameter filters. Filters with up to 700 mm diameter can be fabricated using laser etching with existing capability.

Experimental Study on the Reverse Cleaning and Regeneration of Diesel Engine's Metal Mesh Filter

This paper puts forward the suitable conditions of high sulphur fuel oil in China wire mesh particle trap counter blowing regeneration technology. The regeneration process is characterized by the filter body is separated from particle combustion, solve the problem of broken filter body and burning-out, at the same time remove the not burning material in the trap. By filtering body regeneration experiment made the counter blowing regeneration scheme, design and optimization of the diesel exhaust particulate trap wire mesh filter body and counter blowing regeneration system. Finally by engine bench test, test the diesel exhaust particulate after-treatment device influence on power performance and fuel economy of diesel engine, the jet pressure, jet time and scavenging time on back and collection efficiency effect.

금속 DPF를 이용한 입자상물질의 저감효율에 관한 연구

After-treatment apparatus ceramic DPF (diesel particulate filter) have been applied to reduce harmful particulate matters(PM) among emissions from diesel engines so far, but they are easy to be fragile and weak in thermal shock. This research aims to investigate a metal type filter which is superior in mechanical strength and heat conduction rate and is beneficial economically in manufacturing. Basic performance of metal DPF such asloading test, temperature gradient test, thermal shock test, heat resistant test and back pressure was carried out. And then their experimental data provided key informations in designing and manufacturing such as detailed structures of metal mesh filter. Also diesel engine and vehicle of 2957cc displacement was tested under lug-down 3 mode and CVS-75 mode. PM reduction efficiency was 54.5% using metal DPF without loss of performance and fuel consumption.

Broadband ultra-low-loss mesh filters on flexible cyclic olefin copolymer films for terahertz applications

The cyclic olefin copolymer (COC) has recently demonstrated promising properties for THz applications due to its extremely high transparency in the THz region. Here, we prove that COC can be efficiently used as substrate material for free-space THz devices through the design, fabrication, and characterization of high-pass metal mesh filters. Measurements are in good agreement with calculations, and a transmittance higher than 75% has been measured between 1.5 THz and 2.5 THz for a single-layer filter. In addition, we prove that stacked meshes can be easily embedded to improve their rejection ratio in the stop-band, while preserving a high transparency in the pass-band. The broadband behavior of these filters should extend up to their diffraction limit estimated at around 6.3 THz for the single-layer filter.

Compact micromachined infrared bandpass filters for planetary spectroscopy

The future needs of space-based, observational planetary and astronomy missions include low mass and small volume radiometric instruments that can operate in high-radiation and low-temperature environments. Here, we focus on a central spectroscopic component, the bandpass filter. We model the bandpass response of the filters to target the wavelength of the resonance peaks at 20, 40, and 60 µm and report good agreement between the modeled and measured response. We present a technique of using standard micromachining processes for semiconductor fabrication to make compact, free-standing, resonant, metal mesh filter arrays with silicon support frames. The process can be customized to include multiple detector array architectures, and the silicon frame provides lightweight mechanical support with low form factor.

Cross-Shaped Terahertz Metal Mesh Filters: Historical Review and Results

Terahertz frequencies experiments has motivated the development of new sources, detectors and optical components. Here we will present a review of THz bandpass filters ranging from 0.4 to 10 THz. We also demonstrate our fabrication process, simulations and experimental results.

A simple Fourier transform spectrometer for terahertz applications

A simple Fourier transform spectrometer was designed and constructed for the measurement of detectors, sources, passive devices and materials in the terahertz (THz) range. It can be operated at frequencies between 0.3 and 1.5 THz, using a 50-μm-thick Mylar-film beam splitter. The spectral range can be changed by altering the thickness of the beam splitter. The highest frequency resolution is 750 MHz. We studied the properties of heterodyne detectors including superconductor mixers and semiconductor harmonic mixers, direct detectors including an InSb semiconductor bolometer, superconducting tunnel junctions and the Golay cell, and sources including Gunn oscillators and a microwave source with its multipliers, as well as various materials and passive devices including Si wafers and metal mesh filters.

A 570-630 GHz FREQUENCY DOMAIN TERAHERTZ SPECTROSCOPY SYSTEM BASED ON A BROADBAND QUASI-OPTICAL ZERO BIAS SCHOTTKY DIODE DETECTOR

We report a room temperature 570-630 GHz frequency domain terahertz (THz) spectroscopy system developed on the basis of a broadband quasi-optical zero bias Schottky diode detector. The detector is designed to cover the frequency range of 100 GHz to nearly 900 GHz. A responsivity of 300-1000 V/W has been measured, and the noise equivalent power (NEP) is estimated to be 5-20 pW/√Hz based on the measurements of similar detectors. For a prototype demonstration, the frequency domain THz spectroscopy system was operated within the region of 570-630 GHz using a VDI (Virginia Diodes, Inc.) frequency extension module (FEM) to provide the THz radiation. Mylar thin films with different thicknesses and THz metal mesh filters have been measured using this system, demonstrating a measurement accuracy of ~2%. This system has been applied to measure biomolecules in liquid-phase, and nano-material samples in solid-phase. Initial results and discussion are presented.

Band-pass filters for THz spectral range fabricated by laser ablation

The terahertz resonant metal-mesh filters were fabricated using the laser direct writing technique. UV picosecond laser was employed to cut matrixes of cross-shaped holes in stainless steel foil and molybdenum layer deposited on polyimide substrate. Different laser processing strategies were developed: holes were cut through in the metal foil and the molybdenum film was removed from the polyimide by laser ablation. Band-pass filters with a different center frequency were designed and fabricated. The regular shape, smoothness of edges and sharpness of corners of the cross-shaped holes in the metal were the main attributes for quality assessment for the laser ablation process. Spectral characteristics of the filters, determined by the mesh period, cross-arm length, and its width, were investigated by terahertz time-domain spectroscopy and conventional space-domain Fourier transform spectroscopy. Experimental data were supported by three-dimensional finite-difference time-domain simulations.