Switchable Filter Research Articles

Switchable filter compensating installation in AC traction network

In the AC traction network, the use of adjustable transverse capacitive compensation systems has become necessary primarily for normalizing the voltage at the current collector of the electric rolling stock. Currently, static reactive power generators are used at the sections of the traction network, which have proved their effectiveness in increasing and stabilizing the voltage level, as a result of which the railway capacity is increased. This article substantiates the necessity and expediency of the inclusion of adjustable transverse capacitive compensation installations at sectioning posts in AC traction networks to normalize the voltage at the current collector of electric rolling stock, and therefore, increase the throughput capacity of railway sections. It is shown that, in modern conditions, it is expedient and economically justified to modernize existing unregulated installations with transferring them to a controlled mode by introducing an additional subsequently connected second section of capacitors, which is automatically shunted by the switching device at high loads in the traction network. Modernized installation, proposed by the authors and called switchable, has been successfully operating on the Gorky Railway for more than 6 years. A description of the proposed installation is given and the results of a theoretical analysis of transients during shunting and unloading of the additional section are presented. An algorithm for switching the proposed installation is given. It is shown that the additional section should be shunted at a time when the voltage across the capacitors is zero. Theoretical and experimental oscillograms of switching processes are presented. Recommendations are given for choosing thyristors for a controlled key, as well as recommendations for improving the reliability of the proposed installation.

Autonomously Tunable Filters for Interference Mitigation: Advances in Autonomously Switchable/Tunable RF/Microwave Filters for Interference Mitigation Without Operator Intervention

In wireless communication, there is a strong demand for tunable filters in scenarios that require adaptively coping with multiband interference in RF front ends. Tuning devices, ferroelectric capacitors, ferromagnetic-material-based devices, microelectromechanical systems capacitors, and piezoelectric-material-based devices are commonly used for center frequency tuning or bandwidth adjustment in tunable filter realizations. Tunable or switchable filters are essential for this desired adaptability. However, each type has thus far demonstrated its particular disadvantages. Typically, continuously tunable filters are difficult to design or require intensive use of resources to control accurately, while switchable filter banks have significant insertion loss from switching networks. Tuning capability in tunable filters often requires human intervention to control tuning frequencies or bandwidths. In this article, we introduce autonomously tunable filters to adaptively protect or mitigate receiver systems from unwanted or unreferenced signals in RF front ends using an RF-power-dependent coupling without extra control signals or closed-loop feedback of digital processing of the spectrum through analog-to-digital and digital-to-analog converters.

Design of Beidou timing module

The Beidou timing module receives the Beidou Satellite Information, calculates the time and positioning information, transmits the time and timing information through various external interfaces, and has the function of short message forwarding. This paper presents a system design scheme for the Beidou time-keeping module, which uses adaptive filter switching technology to achieve accurate and stable time-keeping results, by automatically switching synchronous clock source (Beidou, IRIG-B (DC), internal high-stability crystal Oscillator) to complete time service, Beidou module with seamless switching, short-circuit protection, fault detection and diagnosis, health management and other functions.

Optimized Design for AC Filter and Switching Frequency of Parallel-Connected Inverters With Global Synchronous Pulsewidth Modulation

This article proposes a new optimized design method for AC filter and switching frequency of parallel-connected inverters with global synchronous pulse width modulation (GSPWM) to improve the efficiency or reduce the cost. Being different from the traditional design methods that only focus on the individual inverter itself, the quantity of parallel-connected inverters and the operational principles of GSPWM are involved as the key considerations for designing the proper ac filter values and switching frequencies. In specific, the general principles and the realization details are comprehensively elaborated. Experimental results are presented to verify the proposed theoretical findings.

Materials with switchable radiometric properties: Could they become the perfect greenhouse cover?

Greenhouses shelter the crop from unfavourable environmental conditions and the covering largely contributes to creating beneficial growing conditions inside. There is no perfect greenhouse cover for all combinations of crop and climatic regions. Usually a greenhouse cover has permanent optical properties determining the amount of solar radiation entering the greenhouse. Consequently during crop growth, the amount and quality (spectrum, direct/diffuse ratio) of the solar radiation is not ideal for the crop. Growers try to compensate for this by using different additional techniques such as temporary coatings, screens (mobile or fixed, etc.) and heating or cooling. New materials are currently being developed, whose optical properties can be (almost) instantaneously changed (materials with switchable properties). This will allow growers to gain real-time control on the quantity and quality of the light entering the greenhouse to match crop requirement. The present study uses advanced simulation models to predict the potential of covers with switchable properties to improve tomato yield and use of resources in different climatic regions (mild winter and tropical) and with different greenhouse types (artisan and industrial type). Results indicate that covers with switchable properties have advantages over permanent properties for most combinations of filter type/location. Only in very extreme tropical climates will covering materials with permanent filter properties have advantages. Furthermore, simulations models can play a major role in optimising the switchable filter design.

The influence of the closing phase angle of AC filter on the action of arrester in ±800 kV Nuozhadu DC transmission project

The power system is affected by different levels of transient shock caused by different switching angle when AC filter switching on. The shock causes frequent action and aging of lightning arrester. In this article, the causes of frequent action of lightning arrester in Nuozhadu DC project are analyzed by means of power systems computer aided design simulation. The overvoltage, current, and energy of AC filter switching on are also analyzed. The critical angle of the arrester action of AC filters is discussed. The results show that AC filter switching on can affect this group and other groups. When the closing phase angle reaches 12°, the arrester in this group lightnings. When the closing phase angle reaches 18, the arresters in other groups lightning. Finally, the influence of the three phases and the impact which varies with power are also discussed.

Switchable microwave photonic filter using a phase modulator and a silicon-on-insulator micro-ring resonator

A switchable microwave photonic filter (MPF) using a phase modulator (PM) and a silicon-on-insulator micro-ring resonator (MRR) is proposed and demonstrated. By adjusting the polarization controller between the PM and the MRR, the filtering function of the MPF can be switched between a band-stop filter and a band-pass filter. In a proof-of-concept experiment, an MPF with a rejection ratio of 30 dB (or 15 dB) for the band-stop (or band-pass) response and a frequency tuning range from 9.6 to 20.5 GHz is achieved.

A Novel Synthesis for Bandwidth Switchable Bandpass Filters Using Semi-Conductor Distributed Doped Areas

This paper presents a novel synthesis for bandwidth switchable bandpass filters using Semi-conductor Distributed Doped Areas (ScDDAs) as active elements. A co-design method is proposed with a global and simultaneous conception for the active and the passive parts of the switchable filters. The ScDDAs, integrated in the silicon substrate, are able to commute from half-wavelength open-ended stubs to quarter-wavelength short-circuited ones. This co-design method offers a great flexibility and allows to integrate the active elements directly in the substrate, therefore avoiding any soldering of components. The synthesis is developed for the two-states of the active elements and applied, as a proof of concept, to a four-pole bandwidth switchable bandpass filter. This filter operates at 5 GHz with a 50 % bandwidth in the OFF-state (when the stubs are terminated by an open-circuit) and with a 70 % bandwidth in the ON-state (when the stubs are short-circuited). For this filter, the synthesis is detailed in the two-states allowing to choose the two desired bandwidths. A good fitting is obtained for these results proving the viability of such an approach.

Smart greenhouse covers: a look into the future

In a greenhouse, the cover is the main element determining the amount and quality of entering and outgoing radiation, both short and longwave. The cover properties are therefore essential in determining inside climate and the amount of external resources (such as heating and water) required to maintain the greenhouse climate within the boundaries required for crop production. There is not a single “ideal” greenhouse cover for the entire world. Growers use different systems like different shading techniques and/or different types of thermal screens to optimize the radiative fluxes in the greenhouse on each season, but no system is optimum. Therefore, the development of new “smart” covering materials that would allow for the instantaneous modification of the radiometric properties of the cover, could potentially serve a large market worldwide. Some of these materials already exist in the market, such as the electrochromic glass or polymer dispersed liquid crystals, but they have not technically and economically been optimized for their use as greenhouse covers. So, companies operating in this sector have a need to identify which properties are useful in various conditions and to quantify the advantage of (some of) them being switchable. A number of theoretical covering materials with filters transmitting selectively certain ranges of wavelength (PAR, NIR, TIR) for which the effect on greenhouse microclimate and crop growth can be simulated, have been considered for analysis. The present work uses existing simulation models to quantify the benefit (in terms of production and reduced resource requirement) of improving the optical properties of the cover and the added value of making some of them switchable, for greenhouses typical of a mild winter region, represented by Agadir (Morocco), and a very popular crop, tomato. Results indicate an interesting potential for improvement of greenhouse microclimate and tomato yield, for the individual simulated switchable optical filters. However, the simulated yield increases are comparable to those obtained with existing technology, such as shading mobile screens in these regions, as reported in the literature. Therefore, newly developed smart covers will have to be competitive in price with the price of these types of screens to be competitive in these regions or they must lead to other benefits for crop production not simulated with the models (e.g., fruit quality, less risk of diseases).

Design of a Microstrip Three-State Switchable and Fully Tunable Bandpass Filter With an Extra-Wide Frequency Tuning Range

In this study, a new method and structure are proposed to design of a switchable and fully tunable microstrip bandpass filter (BPF). The central frequency and bandwidth (or the resonance frequency of the resonators, coupling coefficient between resonators, and external quality factor of the I/O resonator) of the proposed BPF can be efficiently controlled using varactor diodes as tuners. In addition, the proposed BPF is designed to have three operating states, each with a different frequency tuning range. The three operating states can be switched between independently by introducing three pairs of switching diodes in the input and output feeding structures. Because of the ability to switch among the three operating states, an extra-wide frequency tuning range can be achieved. For demonstration, a two-pole switchable and tunable BPF was designed and implemented using microstrip technology. The experimental and simulation results were consistent and indicate that a wide frequency tuning range from 0.54 to 2.4 GHz, corresponding to a fractional tuning range of 127%, and a nearly constant absolute bandwidth of 82 MHz are achieved. In addition, the proposed switchable and tunable BPF is small (0.24λ g × 0.15λ g ).

Differentiator-Based Output-Feedback Controller for Uncertain Nonautonomous Nonlinear Systems With Unknown Relative Degree

A novel output-feedback controller for uncertain nonautonomous nonlinear systems with unknown relative-degree is proposed in this study. With the assumption that the upper bound of the relative degree is known, the proposed control scheme is designed based on the input filter and higher-order switching differentiator(HOSD) with over dimension. Using the overestimated time-derivatives of tracking error by HOSD, the proposed controller compensates for the effects of uncertainties including an unknown relative degree in the controlled system. Assuming that the internal zero dynamics, if they exist, are stable, the asymptotic stability of the closed-loop system is guaranteed.

Intrinsically Switchable and Bandwidth Reconfigurable Ferroelectric Bulk Acoustic Wave Filters.

Reconfigurable bulk acoustic wave filters provide a number of advantages for wireless communication systems, including compact size, cost effectiveness, and less complexity. This article presents the design methodology of an intrinsically switchable and bandwidth reconfigurable film bulk acoustic resonator (FBAR) filter, employing the electrostriction in ferroelectric barium strontium titanate (BST). Two examples of ferroelectric BST-based filters are designed and fabricated as a proof of concept. Under the application of a dc bias voltage, the fabricated switchable filters exhibit a bandpass response with a fractional BW of 3%. By changing the state of the ferroelectric BST FBARs through applied dc bias voltages, the bandwidth of the filters is adjusted. Without any bias, the filters switch OFF to provide isolation between the input and output ports. BST-based bandwidth reconfigurable filters can potentially reduce the number of required filters and switches in future multiband RF front ends.

$Ku$ -Band Channel Aggregation Waveguide Filters by RF MEMS-Based Detuning

By switching high Q-factor 3-D waveguide bandpass filters with planar radio frequency micro-electromechanical system (RF MEMS)-based elements, a channel aggregation technique is developed in this article. These planar elements play the role of generating an effective phase shift when activated, detuning the resonant cavities of the bandpass filter, and contributing minimal insertion loss when deactivated. The proposed detuning system also has the advantage of not affecting the other operating filter channels connected to manifolds in a switchable waveguide filter bank. A two-channel prototype, based on the Australian satellite Ku-band, with 500-MHz bandwidth, at 14.25GHz (CH1) and 16.25-GHz (CH2) frequencies, is designed, fabricated, and measured demonstrating the channel aggregation operation. When using only two waveguide bandpass filters with no external switches, four different passband states are implemented, e.g., both channels disable (00), channel 2 enables only (01), channel 1 enables only (10), and both channels enable (11). The system provides excellent channel isolation of better than 35 dB over the disabled channels. For the enabled channels, the filters maintain a measured Q-factor of over 800, and better than 15 dB return loss. The measurements confirm that the detuning elements have a minimal impact on the manifolds and other channel filters, regardless of the operating states.

Marshaling Access: Four-Channel Switchable Filter Bank

Modern multistandard wireless systems require reconfigurability for mult iband operat ion; therefore, switchable or reconfigurable frontend filters are in high demand. This article introduces a four-channel switchable filter bank, which was awarded first place in the Four-Channel Switchable/Reconfigurable Filter Bank category of the Student Design Competition (SDC) sponsored by Technical Committee 8 at the 2019 IEEE Microwave Theory and Techniques Society International Microwave Symposium.

Wedge prism approach for simultaneous multichannel microscopy

Multichannel (multicolor) imaging has become a powerful technique in biology research for performing in vivo neuronal calcium imaging, colocalization of fluorescent labels, non-invasive pH measurement, and other procedures. We describe a novel add-on approach for simultaneous multichannel optical microscopy based on simple wedge prisms. Our device requires no alignment and is simple, robust, user-friendly, and less expensive than current commercial instruments based on switchable filters or dual-view strategies. Point spread function measurements and simulations in Zemax indicate a reduction in resolution in the direction orthogonal to the wedge interface and in the axial direction, without introducing aberration. These effects depend on the objective utilized and are most significant near the periphery of the field of view. We tested a two-channel device on C. elegans neurons in vivo and demonstrated comparable signals to a conventional dual-view instrument. We also tested a four-channel device on fixed chick embryo Brainbow samples and identified individual neurons by their spectra without extensive image postprocessing. Therefore, we believe that this technology has the potential for broad use in microscopy.

New Functional Capabilities of Microwave Interferometry When Using Metastructure as a Tunable Beam Splitter

It is experimentally shown that the microwave metainterferometer with a metastructure (metasurface or metaatom) as a tunable beam splitter possesses the unique possibility to specify selective magnetic and electric tuning of multiband filtration of electromagnetic waves. The investigation results are shown concerning the interferogram of a modified metainterferometer based upon the waveguide tee junctions in which the metastructure contains a ferrite plate or a structure made of conducting resonant elements compatible with the controlling elements or their combination with ferrite. The dependences of the shape, width, intensity, and frequency of the interference band on the value and sign of a magnetostatic field, on the relative position of ferromagnetic resonance and the band, and on the electric voltage on the varactors included in the discontinuities of elements. We have experimental results that open new methods and approaches in the design of switchable and tunable multiband microwave filters needed in multifunctional multichannel telecommunication systems.

Multichannel Active Noise Control Based on Filtered-x Affine Projection-Like and LMS Algorithms with Switching Filter Selection

Affine projection (AP) algorithms have been demonstrated to have faster convergence speeds than the conventional least mean square (LMS) algorithms. However, LMS algorithms exhibit smaller steady-state mean square errors (MSEs) when compared with affine projection (AP) algorithms. Recently, several authors have proposed alternative methods based on convex combinations to improve the steady-state MSE of AP algorithms, even with the increased computational cost from the simultaneous use of two filters. In this paper, we present an alternative method based on an affine projection-like (APL-I) algorithm and least mean square (LMS) algorithm to solve the ANC under stationary Gaussian noise environments. In particular, we propose a switching filter selection criteria to improve the steady-state MSE without increasing the computational cost when compared with existing models. Here, we validate the proposed strategy in a single and a multichannel system, with and without automatically adjusting the scaling factor of the APL-I algorithm. The results demonstrate that the proposed scheme exploits the best features of each filter (APL-I and LMS) to guarantee rapid convergence with a low steady-state MSE. Additionally, the proposed approach demands a low computational burden compared with existing convex combination approaches, which will potentially lead to the development of real-time ANC applications.

Complementary hybrid electrodes for high contrast electrochromic devices with fast response

Fast switching ‘transparent-to-black’ electrochromic devices are currently under investigation as potential candidates in modern applications like e-papers or with additional functionality as ultracompact iris or switchable neutral filter in camera systems. However, recent electrochromic devices show either a lack of contrast or slow response times. To overcome these deficiencies we focus on a careful material composition of the colouring hybrid electrodes in our device. We have established a nanoporous Sb-doped SnO{}_{2} electrode as supporting electrode for chemisorbed electrochromic tetraphenylbenzidine molecules due to its good conductivity in the redox potential range of the molecule. This hybrid electrode was combined with a modified nanoporous TiO{}_{2} / viologen electrode to realize a high performance, complementary electrochromic device. Fast switching time constants of 0.5 s and concurrently high change in optical density DeltaOD = 2.04 at 605 nm confirm our successful concept. The achieved colouration efficiency of 440 cm{}^{2} C{}^{-1} exceeds every high contrast device presented so far.

Center frequency and bandwidth switchable substrate integrated waveguide filters

AbstractThis paper presents center frequency and bandwidth switchable substrate integrated waveguide filters loaded with PIN diodes. The diodes are added in the slot on the surface of the resonators to switch the resonant frequencies and the coupling coefficients. Although the introduction of the slot causes extra radiation loss, it is small and acceptable. The proposed center frequency switchable filter has four center frequency switchable states of 1.78, 1.82, 1.88, and 1.91 GHz, while the bandwidth only changes ±0.64%. The bandwidth switchable filter has two states with 3 dB bandwidths of 70 and 103 MHz at a center frequency of 2.08/2.09 GHz. The measured performance of the fabricated filters shows good agreement with the simulation.

Dynamic Reactive Power Coordination Control Method for UHVDC Converter Station

In recent years, UHVDC transmission has developed rapidly. However, large-capacity DC converters generally use semi-controlled devices. The receiving converter station consumes a large amount of reactive power, which is easy to change when the AC bus voltage drops. The commutation failure happened, and more reactive power is absorbed from the AC system, which threatens the stability of the bus voltage. In order to study the dynamic reactive power coordination control strategy of UHVDC converter station, this paper compares the commonly used reactive power compensation equipment, and points out that synchronous condenser (SC) has significant advantages in reactive power regulation. This paper proposes a DC control system and SC coordination control scheme, and simulates the strategy through the electromagnetic transient simulation software PSCAD. The simulation shows that the synchronous condenser can provide continuously adjustable dynamic reactive power support during the change of the system switching filter, avoiding the risk of grid voltage drop exceeding the limit and improving the stability of the AC bus voltage.