Monolithic Filters Research Articles

Carbon-cryogel hierarchical composites as effective and scalable filters for removal of trace organic pollutants from water

Effective technologies are required to remove organic micropollutants from large fluid volumes to overcome present and future challenges in water and effluent treatment. A novel hierarchical composite filter material for rapid and effective removal of polar organic contaminants from water was developed. The composite is fabricated from phenolic resin-derived carbon microbeads with controllable porous structure and specific surface area embedded in a monolithic, flow permeable, poly(vinyl alcohol) cryogel. The bead-embedded monolithic composite filter retains the bulk of the high adsorptive capacity of the carbon microbeads while improving pore diffusion rates of organic pollutants. Water spiked with organic contaminants, both at environmentally relevant concentrations and at high levels of contamination, was used to determine the purification limits of the filter. Flow through tests using water spiked with the pesticides atrazine (32 mg/L) and malathion (16 mg/L) indicated maximum adsorptive capacities of 641 and 591 mg pollutant/g carbon, respectively. Over 400 bed volumes of water contaminated with 32 mg atrazine/L, and over 27,400 bed volumes of water contaminated with 2 μg atrazine/L, were treated before pesticide guideline values of 0.1 μg/L were exceeded. High adsorptive capacity was maintained when using water with high total organic carbon (TOC) levels and high salinity. The toxicity of water filtrates was tested in vitro with human epithelial cells with no evidence of cytotoxicity after initial washing.

Miniaturized dielectric waveguide filters

ABSTRACTDesign techniques for a new class of integrated monolithic high-permittivity ceramic waveguide filters are presented. These filters enable a size reduction of 50% compared to air-filled transverse electromagnetic filters with the same unloaded Q-factor. Designs for Chebyshev and asymmetric generalised Chebyshev filter and a diplexer are presented with experimental results for an 1800 MHz Chebyshev filter and a 1700 MHz generalised Chebyshev filter showing excellent agreement with theory.

MEMS-Based UHF Monolithic Crystal Filters for Integrated RF Circuits

We report our work in developing microelectromechanical systems (MEMS)-based Ultra High Frequency (UHF) AT-cut quartz monolithic crystal filters operating between 350 and 400 MHz for integration with Si electronics for highly compact Radio Frequency (RF) front-end electronics. Our narrow bandwidth (0.2%) high $Q$ filters have measured insertion losses of −2 dB with temperature stability of roughly 50 ppm over a temperature range of 10°– 80°C. Wafer-level optical metrology and ion milling techniques have been developed to provide enhanced accuracy of the filter center frequency and resonator parameters for optimized performance and improved yields. [2015-0163]

An Intrinsically Switchable, Monolithic BAW Filter Using Ferroelectric BST

This letter presents an intrinsically switchable monolithic filter based on laterally acoustically coupled bulk acoustic wave resonators. The filter is based on a barium strontium titanate-on-silicon (BST-on-Si) composite structure which can be turned on and off by the application of a dc bias. In its off state, the filter provides an isolation of 40 dB. In its on state, the filter exhibits an insertion loss of 7.1 dB and greater than 30 dB of out-of-band rejection. The center frequency and bandwidth of the filter are 748 MHz and 13.8 MHz, respectively. The mechanical quality factor of the coupled resonators is calculated to be 99.

Monolithic Crystal Filter for Application in Viscosity Sensor

Monolithic crystal filter (MCF) on AT-cut quartz for application in viscosity sensor was developed. After proper matching, at a frequency of $\sim 3.6$ MHz, insertion loss in air of $\sim 1.6$ dB was obtained. The linear coefficient of frequency of about −5 ppm/°C and changes of the insertion loss of $\sim 0.5$ dB, in the temperature range of 10°–80°, were obtained. To eliminate errors caused by the longitudinal acoustic wave generation, MCF should be immersed in a measured liquid or proper amount of liquid should be inserted into the sensing window. Using water and glycerin solutions, insertion loss changes against dynamic viscosity of the MCF were measured. In a viscosity range from about 1 to 1000 $\textrm {mPa}\cdot \textrm {s}$ , an insertion loss change of $\sim 24$ dB was obtained.

Lamb Wave AlN Micromechanical Filters Integrated With On-chip Capacitors for RF Front-End Architectures

This paper reports on the implementation of an ultraminiature 140 MHz narrowband filter based on aluminum nitride Lamb wave resonators. Monolithically integrated with a pair of on-chip capacitors and cascaded with a pair of inductors, the filter is well matched to 50 ohm, showing a remarkably high performance. A low pass-band insertion loss of 2.78 dB and steep filter skirts are achieved. The form factor of the monolithic microelectromechanical systems filter is more than ten times smaller than its surface acoustic wave counterpart in the intermediate frequency band and it involves much simpler matching circuits.

Structured catalysts based on sepiolite with tailored porosity to remove diesel soot

Wall-flow monolithic filters are commonly made of silicon carbide or cordierite and present high porosity, but low surface area. Alternatively, wall-flow monoliths with high surface area can be employed as support for active phases that catalyze the elimination of the particles deposited in the pores. In this study, mesoporous monoliths with tailored macroporosity are obtained by extrusion using sepiolite clay and different pore generating agents. Cobalt, barium and potassium were incorporated as active phases during the kneading of the dough or by impregnation of the structured material to give the monoliths the capacity for catalytically burning soot under the conditions of diesel engine exhausts. The incorporated and impregnated catalytic monoliths were morphologically, mechanically and physical-chemically characterized at different preparation stages to study the influence of support porosity and the method of addition of active phases in the catalytic activity for diesel soot combustion. The most active catalyst was obtained impregnating the active components to a previously extruded monolith calcined at 850°C, and then calcining the assembly at 600°C, for which the temperature of maximum soot combustion rate was 385°C.

Monolithic Multi-Frequency Wideband RF Filters Using Two-Port Laterally Vibrating Lithium Niobate MEMS Resonators

This paper reports on monolithically integrated multifrequency wideband radio frequency (RF) filters based on two-port laterally vibrating lithium niobate microelectromechanical (MEMS) resonators (LVRs). Two-port MEMS resonators based on transferred lithium niobate thin film are designed and experimentally demonstrated. Self-coupled RF filters are implemented by cascading two identical two-port resonators. Modified Mason's models are used to predict the resonators and filters performance. A good agreement is attained between theory and experimental results. The fabricated two-port devices with center frequencies at 500 and 750 MHz exhibit electromechanical coupling coefficients (k t 2 ) of 8% and 14.6%, respectively. As a result, the self-coupled RF filters formed by these resonators are capable of low loss (4 dB) and wideband filtering. Fractional bandwidth of 2% and 3.9% have been achieved-the highest reported for MEMS LVRs. This paper shows that RF-MEMS filters based on LVRs can achieve sufficient bandwidth to cover most of the existing commercial standards.

Moiré volume Bragg grating filter with tunable bandwidth.

We propose a monolithic large-aperture narrowband optical filter based on a moiré volume Bragg grating formed by two sequentially recorded gratings with slightly different resonant wavelengths. Such recording creates a spatial modulation of refractive index with a slowly varying sinusoidal envelope. By cutting a specimen at a small angle, to a thickness of one-period of this envelope, the longitudinal envelope profile will shift from a sine profile to a cosine profile across the face of the device. The transmission peak of the filter has a tunable bandwidth while remaining at a fixed resonant wavelength by a transversal shift of incidence position. Analytical expressions for the tunable bandwidth of such a filter are calculated and experimental data from a filter operating at 1064 nm with bandwidth range 30-90 pm is demonstrated.

1–5 GHz monolithic multifrequency-variable band elimination filter utilizing fluid microelectromechanical system variable capacitors

At present, variable RF filters to vary the filter characteristic in a wide frequency range are strongly required. We have developed a variable band elimination filter (BEF) consisting of a variable capacitor and an inductor. The variable capacitor consists of eight capacitor cells, each of which changes the capacitance by filling the gap between two electrodes with pure water. This permittivity change due to filling water has the capacitance change ratio (CCR) of 80 in theory. A fabricated variable capacitor was measured to have a CCR of 31. The decrease from the theoretical value is caused by a parasitic capacitance. A fabricated BEF was also measured to vary the elimination center frequency from 4.52 to 0.92 GHz, as each capacitor cell was filled with water. This fact indicates that the filter frequency change ratio of 4.9 was successfully achieved. Such a large value of the CCR will be expected to expand MEMS filters in many mobile applications.

New opportunities in microwave electronics with ferromagnetic nanowires

A series of monolithic tunable microwave band-stop filters and phase shifters have been designed, fabricated, and characterized on arrays of ferromagnetic nanowires (FMNWs) constituted of Ni, Co, CoFeB, and NiFe alloy embedded in anodic alumina templates (AAO). The aim of the present investigation is to significantly boost the operating frequency of devices in very low applied magnetic field. The stop-band response can cover from 8 to 40 GHz with an applied magnetic field up to 5 kOe using these materials. In addition, we observed a substantial increase in frequency tunability (>110%) for Ni and NiFe alloy based filter. Frequency bandwidth/linewidth can be tuned with the proper choice of magnetic material, broad band for Co nanowires to narrow band for CoFeB nanowires. The amorphous nature of CoFeB reduces linewidth considerably and hence increases resonance absorption. It is also observed that the frequency linewidth (Δf) decreases with increasing applied magnetic field. The same filter can be used as a tunable phase shifter. For Ni nanowire based phase shifter, a maximum shift of 75°/cm at 4 kOe was observed.

Tunable Low-Pass MEMS Filter Using Defected Ground Structures (DGS)

In this paper, fully monolithic tunable millimeter-wave filters using defected ground structures (DGS) are proposed using the CPW-based periodic structures with novel multiple-contact MEMS switches. Millimeter-wave low-pass filters were designed, fabricated, and tested. The cascaded CPW-based periodic structures, with low-pass intrinsic filtering characteristics, are reconfigured into a self-similar single unit cell by the operation of the novel multiple-contact MEMS switches with single actuation. In the first order tuning, the 3-dB cut-off frequency changes from 8.2GHz to10.5GHz, and the second order tuning is 8.2GHz to 16.8GHz. The tested results show that the pass-band ripple is less than 1.2dB and the maximal out-of-band rejection is better than 27dB. The chip size of the low-pass filter is 2.5mm×1.2mm.

Modeling of Flow Through a Sandwiched Monolith Filter

The flow field and filtration efficiency was modeled and analyzed for a novel monolith filter, comprised of a series of layers of microchannels. In our simulations, we considered two scenarios: the fluid flowing tangentially across the filter face (cross flow) and fluid flowing normal to the filter face (normal flow). The aim of this article is to study the effect of having two or more layers of filters in series on particle capture efficiency. This will help in understanding the mechanisms of particle capture and provide inputs for studying particle segregation or selective filtration using monolith filters. The influences of particle size, number of filter layers and pressure drop on particle capture efficiency were also investigated.

CMOS Pixels Directly Sensitive to Both Visible and Near-Infrared Radiation

This paper proposes a pixel topology for the joint capture of visible (VIS) and near-infrared (NIR) signals in a monolithic CMOS sensor, with neither optical nor IR-blocking filters, in a single shot and with the same sensor resolution for the VIS and NIR channels. The topology exploits the radiation absorption depth dependence on the wavelength and is based on the principle of the Transverse Field Detector. The device principle, finite element simulation, and design are presented with validation of the working principle through experimental tests on a prototype with an overall four-band passive pixel width of 6.4 μm.

A monolithic layered nonwoven–woven geotextile for use with drainage geocomposites in coal combustion residual projects

A layered monolithic filter consisting of a nonwoven needlepunched and a woven monofilament geotextile is presented in this paper. The two geotextiles are mechanically bonded in a needlepunching process to produce a hybrid geotextile on a commercial scale. The fuzzy woven side of the geotextile, resulting from the needlepunching process, is ideally suited for lamination to a geonet, although a standalone filter application is also possible. Filter press tests on the geotextile against a fly ash slurry of 500% yielded a retention efficiency of 99.6%. Gradient ratio values of 1.0–1.5 and hydraulic conductivity ratio values of 0.5–1.0 were obtained against fly ash and FGD gypsum from four power plants. Four field basin tests were performed under the CCRs wherein effluent parameters of total suspended solids, total dissolved solids, turbidity, conductivity and pH were monitored with time. The field tests showed that the fly ash and FGD gypsum contained in the test basins were not migrating with time.

Submicron particle filtration in monolith filters – A modeling and experimental study

With over a million micron-sized channels per square centimeter arranged in a regular pattern on a thin film, monolith filters have significant potential for submicron aerosol particle filtration, even though the filtration process with this class of filters has not been well studied. In order to better understand the capture mechanisms and the main factors that affect the capture efficiency, so as to build predictive numerical models and to improve the design of monolith filters, the filtration process in monolith filters was investigated both experimentally and numerically. Using an electrostatic particle classifier (EPC) and a condensation particle counter (CPC), the experimental platform measured the capture efficiency of salt particles with diameters ranging from 50–300 nm on two monolith filter samples. Based on the filtration process and the repeating geometric structure, a single unit model was proposed. The drag force, electrostatic force, and Brownian motion are considered as the major forces affecting particle motion. Published theories underestimated the capture efficiency compared to the experimental results. The Brownian motion model and the capture criterion were then empirically modified to gain better agreement with the experiment.

Modeling of Cross-Flow Across an Electrostatically Charged Monolith Filter

The flow field and filtration efficiency of electrostatically charged micro-channel filters under cross-flow conditions were modeled. In our simulations, the fluid flows tangentially to the filter face (cross-flow). Particles with diameters larger than 2 μm were considered in this study, hence, the effects of Brownian motion were not included in the simulations. The influence of particle size, pressure drop, and electrostatic charge on the filtration efficiency was investigated. Measurements from performing electrostatic force microscopy (EFM) on the monolith sample confirmed the presence of charge and gave a qualitative measurement of the charge distribution. Results from the flow simulations indicate that the electrostatic forces increased the particle capture efficiency only at lower pressure drop. At higher pressure drops, electrostatic forces did not significantly increase the capture efficiency of the particles. Also, the capture efficiency of relatively small particles is found to be more dependent on the pressure drop across the filter than that of larger particles.

A 12–16 GHz microelectromechanical system-switchable bandpass filter

This paper describes a novel monolithic switchable filter covering a bandpass frequency of 12–16 GHz at the Ku-band on a silicon substrate. The filter structure is based on parallel-coupled half-wavelength resonator topologies and microelectromechanical system-tunable resonators designed by placing ohmic switches at the open ends of the microstrip resonators. A wideband coplanar waveguide is designed for microstrip transition without via holes during wafer testing. The measured results show a minimum insertion loss of 3.6 dB, a return loss better than 15 dB, a 10.2% fractional bandwidth and a 14.2% tuning range from 13 to 15 GHz. The fabricated filter has a chip area of 15.1 mm × 3 mm and has achieved skirt slopes of over 30 dB GHz−1.

Note: A monolithic filter cavity for experiments in quantum optics

By applying a high-reflectivity dielectric coating on both sides of a commercial plano-convex lens, we produce a stable monolithic Fabry-Perot cavity suitable for use as a narrow band filter in quantum optics experiments. The resonant frequency is selected by means of thermal expansion. Owing to the long term mechanical stability, no optical locking techniques are required. We characterize the cavity performance as an optical filter, obtaining a 45dB suppression of unwanted modes while maintaining a transmission of 60%.

Ultra-broad and sharp-transition bandpass terahertz filters by hybridizing multiple resonances mode in monolithic metamaterials

We present three monolithic metamaterial-based THz bandpass filters, the skewed circular slot rings, meandered slots and Jerusalem cross slots, to fit in the THz gap. These THz bandpass filters are comprised of a metal-dielectric-metal (MDM) structure that supports multiple resonances of electric dipole, magnetic dipole, and standing-wave-like modes. By exciting and further hybridizing these individual resonance modes, we demonstrate excellent performance of broad bandwidth and sharp band-edge transition beyond conventional bandpass filters. By further employing our ad hoc Genetic Algorithm (GA) and Periodic Method of Moments (PMM) to optimize our designs, we achieve an ultra-broad 3dB fractional bandwidth and sharp band-edge transition up to 82.2% and 58.3 dB/octave, respectively, benefiting the practical applications such as material recognition in security systems, imaging, and absorbers.