Switchable Frequency Research Articles

Uniformity improvement of microwave heating with switchable frequency selective surface

Microwave heating has attracted interests in many industrial applications, yet heating inhomogeneity remains a critical issue. This study proposes a novel approach to enhance microwave heating uniformity employing a switchable frequency selective surface (FSS). The PIN diodes in each FSS unit cell can be toggled ON or OFF by controlling voltage biases, enabling the FSS to either reflect or transmit incident electromagnetic waves. Placing this switchable FSS in front of a heating cavity wall creates a dynamic reflecting boundary, which, through periodic alterations of the FSS and metallic wall, effectively improves the heating uniformity. To validate this method, we simulated the heating of a potato sample at 2450 MHz using COMSOL Multiphysics and conducted experimental tests. Both simulation and experimental results demonstrate that the proposed method significantly enhances microwave heating uniformity across various materials and sample sizes. This work provides a promising solution for designing microwave heating reactors.

Electronically Switchable Frequency and Pattern Reconfigurable Segmented Patch Antenna for Internet of Vehicles

Electronically Switchable Frequency and Pattern Reconfigurable Segmented Patch Antenna for Internet of Vehicles

Graphene-based magnetically tunable multi-band terahertz absorber with switchable frequency

Graphene-based magnetically tunable multi-band terahertz absorber with switchable frequency

Selective Metallization on 3D Substrates for MIMO Antennae

Multiple-input multiple-output (MIMO) antenna technology owes its low weight and energy-saving electronic applications to the use of polymer substrates. Applying metallization to obtain conductive substrates involves spraying untreated molds with a gel to form a temporary protective coating. The coating is then partially removed with a laser to expose areas for metallization. After that, the exposed areas are modified with a palladium-tin (Pd-Sn) colloidal catalyst to enhance the adhesion between the insulating surface and copper deposition. It’s with these three steps that the modified areas become selective to metallization. It’s observed that copper deposited incessantly at a high speed of 5 μm/hr after above treatment, and formed a dense layer with a low resistivity. The conductive patterns plated on the 3D substrate render the MIMO antenna system applicable to wireless local area network (WLAN) with two switchable frequencies, as evidenced by the simulation tests in which the antennae had ECC values below 0.2, a VSWR of 3 to 1, and a radiation efficiency around 50% at 2.4 GHz and 37% at 5.8 GHz. The electroless plating technology used above adds to a duplicable MIMO-antenna manufacturing process of low temperature and cost.

Miniaturized 3‐bit frequency‐reconfigurable monopole antenna with a meander line

AbstractA novel 3‐bit frequency‐reconfigurable antenna (FRA) with miniaturized dimensions is realized with a meander line. The frequency reconfiguration of the antenna is achieved by introducing N Radio Frequency (RF) PIN diodes into the meander line. The related parts of the meander line with different lengths are bypassed or included into the antenna by switching on or off the diodes, resulting in 2N switchable size lengths of the antenna and equally spaced operating frequencies. A 3‐bit reconfigurable meander‐line antenna (N = 3) is designed, and the simulated and measured results agree well. The antenna provides 8 (23) independent and switchable states, with the operating frequencies covering a wide switchable frequency range from 1.04 to 1.51 GHz and the working bandwidths varying from 80 to 150 MHz. The number of working bandwidth states is maximized, considering the number of switches used. Moreover, the results reveal an acceptable peak gain of 1.59 dBi in terms of the miniaturized total dimension of 0.17 λg × 0.07 λg (λg is the guided wavelength at the lowest working frequency), which is more compact than several published FRAs.

Switchable Frequency Response Based on Electropermanent Magnet Actuator for Wide-Range Operation of Electromagnetic Devices

This paper proposes a linear oscillatory actuator (LOA) that can switch its degree of freedom (DOF) for the purpose of improving its frequency response. Electropermanent magnet (EPM) is selected as an energy-saving solution to switch the DOF by absorbing and desorbing secondary mass with primary mass. First, motion equations for 1- and 2-DOF systems are derived and The corresponding frequency response curves are numerically obtained. Second, finite element analysis coupled with a numerical simulator reveals that transient absorption and desorption motions are successfully performed with a help of EPM. Finally, measurement using a prototype shows that the proposed switchable frequency response technique is experimentally realized and the measured result ares in good agreement with the numerical ones.

A Switchable Frequency Selective Rasorber with a Broad Transmission Window at the X-Band

This paper proposes a switchable polarization-insensitive frequency selective rasorber (FSR) within the X-band. The FSR comprises a lossy layer, a lossless layer, and an intermediate air layer. The lossy layer consists of metal patches, folded wires, and lumped resistors, while the lossless layer is formed with square and cross patches loaded with PIN diodes. An equivalent circuit model (ECM) has been developed to analyze and verify the working principle of the system. By altering the state of the PIN diodes, it is feasible to switch between absorbing and transmitting modes. In the rasorber mode, the switchable FSR attains a transmission window ranging from 10.13 to 12.27 GHz with a minimum insertion loss below 2 dB and a broad absorption band covering 5.79–15.37 GHz. When switched to absorber mode, the passband is negated, and the FSR exhibits a low transmission band from 10.68 to 18.00 GHz. This innovation can improve the omni-directional stealth capability and battlefield survivability of radar systems, possessing substantial research importance and practical applications.

Dynamic Mode Suppression and Frequency Tuning in S-Band GaN/YIG Magnetoelastic HBARs.

This work presents the detailed characterization and analysis of recently reported magnetoelastic high-overtone bulk acoustic resonators (ME-HBARs), which are multimode RF-acoustic (phononic) resonators operating in the S -band. These unique devices are fabricated by microtransfer printing (MTP) piezoelectric GaN transducers onto a ferrimagnetic yttrium iron garnet (YIG) substrate. The YIG substrate also supports spin waves (magnons) when biased with an external magnetic field. The resulting phonon-magnon hybridization can be used to suppress or tune the acoustic modes of the ME-HBAR. The experiment spans 66 distinct acoustic resonance modes from 2.4 to 3 GHz, each of which can be suppressed or tuned as much as ±6 MHz, with a bias magnetic field ≤ 0.21 T. The experimental ME-HBAR data show good agreement with analytical modeling of the magnetoelastic hybridization in YIG. Such ME-HBARs can be used as dynamically tunable or switchable resonators, oscillators, comb filters, or frequency selective limiters in RF signal processing subcomponents. By integrating incompatible materials (YIG, epitaxial GaN) and disparate functionalities (spin waves, acoustic waves) into one hybrid multidomain system, this work also demonstrates the power and broad scope of the MTP technique.

Active Frequency Selective Rasorber With Switchable Transmission Band and Tunable Absorption Band

This letter proposes a frequency selective rasorber (FSR), whose transmission and absorption bands can be controlled independently by the Schottky barrier diode (SBD) and stepper motor, respectively. The FSR is composed of a resistive sheet, a switchable bandpass frequency selective surface (FSS), and four stepper motors. The transmission band can be switched to the stopband with the SBD turned on. And the location of absorption bands can be adjusted by the stepper motors. Both the simulated and measured results show that the transmission band and the absorption band can be independently controlled and do not affect each other.

Active frequency selective surface-based 360° beam steering in two switchable frequency bands independently

ABSTRACT A reconfigurable antenna with frequency agility and pattern-switching ability is presented in this paper. The proposed design comprises a planar and compact frequency reconfigurable monopole antenna and an active frequency selective surface (AFSS) with reconfigurable transmission and reflection properties in dual bands. The AFSS screen is divided into four sections and each section is composed of four FSS elements with only one PIN diode in each unit cell. The monopole antenna, which is situated at the center of the box-shaped AFSS to illuminate , can reconfigure its resonating frequency between 2.5 and 3.6 GHz with the help of only one PIN diode. With the help of this transformation ability of AFSS behavior electronically, the pattern can be steered across the entire X–Z plane in eight steps at two different operating frequencies independently. This antenna can be very useful in various wireless applications such as drones, small base stations, etc.

Design and Experimental Validation of a Switchable Frequency Selective Surface with Incorporated Control Network.

Tunable/switchable devices are more and more required in modern communication systems. However, the realization of the tuning requires the presence of active devices, which in turn must be biased. The current paper comes up with a solution for designing and experimentally validating such a switchable Frequency Selective Surface. Two different metallic structures are simulated and measured, having incorporated the same topology control network (CN). In this scenario, the main innovation of this paper is the presence of the feeding part, namely the control network. In this work, the main FSS structure is flanked by three parallel CN microstrip lines and several via holes that allow biasing the active elements, namely PIN diodes. The switchability of the proposed structure is achieved through PIN diodes, whose bias determines the values of the elements in the equivalent circuit. At different biases, the response of the FSS changes accordingly. From all possible values of the bias, the extreme cases when the diodes act as (almost) short- and open-circuits are considered in the submitted manuscript for the sake of brevity. These cases are modeled by the main and cut-slot structures, respectively. The proposed structures have been evaluated using electromagnetic simulation and implemented on an FR4 substrate having a thickness of 1.58 mm. With the periodicity of the square-shaped unit cell of 18 mm edge length, different filtering bands are obtained below 12 GHz. Another novelty that has received very little consideration in the existing literature is the use of a finite array of unit cells instead of an infinite one. And finally, tests in an anechoic chamber have proved that there is a good agreement between practical and simulation results and also demonstrated the proper performance of the devices for wide angular incidence for both TE and TM polarizations.

A flexibly frequency switchable active mode-locking optoelectronic oscillator with supermode noise suppression

In this paper, we propose and experimentally demonstrate a flexibly frequency switchable active mode-locking optoelectronic oscillator (FSAML-OEO) in which a multi-passband microwave photonic filter (MPF) with two polarization-maintaining fibers (PMF) based Solc-Sagnac interferometer is used. Microwave frequency combs (MFCs) signals with four switchable central frequencies of 217 MHz, 453 MHz, 662 MHz and 1101 MHz are generated by controlling the polarization state of the Sagnac interferometer via rotating the polarization controller (PC). By cascading a dual-loop structure, MFCs signals with adjustable comb spacing of 1 MHz, 3 MHz, and 5 MHz are obtained with fundamental and harmonic FSAML-OEO, in which the supermode noise suppression ratios of the dominate modes and the super-modes are measured to be about 30 dB.

A multi-wavelength Brillouin fiber laser of switchable frequency spacing based on a bi-directional ring cavity

A multi-wavelength Brillouin fiber laser (MW-BFL) of switchable frequency spacing is proposed and experimentally demonstrated. This MW-BFL comprises a ring cavity that includes a piece of 20-km-long single-mode fiber as the gain medium for Brillouin amplification. The switchability of wavelength spacing is implemented by adjusting the Brillouin pump (BP) coupling ratio into the ring cavity of a bi-directional pumping scheme, as the outputs of single and double Brillouin shifts are achieved with either a 50/50 coupler or a 99/1 coupler, respectively. A total of 11 lasing Stokes lines with single Brillouin shifts and 9 lasing Stokes lines with double Brillouin shifts have been observed when the BP power is set at 0 dBm. Both Brillouin lasers are wavelength-tunable, and the tuning ranges are 16 and 10 nm for the single- and double-spaced outputs, respectively.

Switchable Polarization Insensitivity Radar Absorber/Reflector Based on Active Frequency Selective Surface

In this article, a switchable polarization-insensitive lower thickness active frequency selective surfaces (AFSSs) absorber/reflector is proposed. The proposed structure consists of the top AFSS layer, which contains four patches and four pairs of PIN diodes in parallel with resistors, the upper substrate I, a metal ground, the bottom substrate II, and a simple bias network behind the bottom substrates that effectively reduce unnecessary disturb. The PIN diodes are controlled by the bias networks through the metalized via holes to obtain the switchable properties. The polarization-insensitive performance is realized by symmetrical structure. The resistors in parallel with PIN diodes load between every two patches to enlarge the resonant bandwidth. One remarkable feature of the structure exists in it can be switched in a variety of operating states to control the visibility of the target in radar systems. When it operates as an absorber, it has a stable absorptivity, which is more than 85% in the frequency range of 12.6–25 GHz with a small radar cross section. The equivalent circuit model, surface loss density, and surface circuit distribution are provided to assist in understanding the physical property of the entire design. A configuration of the structure is fabricated and the measurement results demonstrate a reasonable agreement with the simulate ones, thus confirming the proposed concept.

The experimental study on pump influence of a multi-wavelength Brillouin fiber laser with switchable frequency spacing

An experimental study of the pump influence upon a multi-wavelength Brillouin fiber laser (MW-BFL) of switchable Brillouin Stokes generation is presented. The bi-directional ring cavity in the MW-BFL is comprised of a piece of 20-km single-mode fiber to provide the Brillouin gain. We investigate the major pump parameters including the Brillouin pump (BP) ratio into the ring cavity, the initial BP power, and the primary pump power for their effectiveness on the switchable-spaced Brillouin generation. The optical signal to noise discrepancy (OSNRD) between the adjacent odd and even Stokes lines is evaluated as the main indicator. The optimal BP coupling ratio is found as 90/10 for the proposed scheme. Four Brillouin lasing lines with single frequency shift of 10.75 GHz and one Brillouin lasing line with double Brillouin shift of 21.51 GHz have been observed when the input BP power is at −5 dBm and 4 dBm, respectively. An appreciable OSNRD is obtained accordingly, which is 0.6 dB for the single-spaced spectrum and 18.6 dB for the double-spaced spectrum.

A circularly polarised monopole antenna with switchable frequency, pattern and polarisation

ABSTRACT A compound reconfigurable monopole antenna (CRMA) having ability to change its frequency, polarisation and also pattern is presented in this paper. Only 6 PIN diodes are positioned on the monopole and ground to achieve reconfigurable operations and thus the antenna can operate over 8 different states. The radiation patterns of the proposed antenna can be tilted into two different directions. In each direction, the antenna can shift its operation in between two different frequency bands, and for each band, switching between two orthogonal circularly polarised (CP) radiation can be possible. A prototype is fabricated and measured. Based on various parametric analyses, a simple design guideline is also presented. By considering its overall simple configuration, low profile, and planar geometry, proposed antenna can be a useful candidate for future wireless applications like cognitive radio, 5 G devices, and so on.

Planar Frequency Selective Surface-Based Switchable Rasorber/Absorber for Airborne Application

In this letter, a switchable frequency selective surface is designed that can operate between rasorber and absorber having a wide passband characteristics. The structure has an extra advantage of being built on a single dielectric layer having lossy and lossless layer on the two opposite sides. The lossy layer comprises of lumped resistors, which assists in wideband absorption from 4.8 to 15 GHz. PIN diodes are mounted in the lossless layer to equip the structure with rasorber/absorber operation. Under the rasorber operation, a wide transmission bandwidth in between the absorption band from 9 to 11 GHz is obtained. The system is also simplified with the help of an equivalent circuit model. The structure is carefully designed so that it is immuned to polarization and angle sensitivity. Finally, the prototype is fabricated and measured, and the results are found to be in good agreement with the simulated ones. The proposed design is expected to find its application in all airborne technologies.

Design of a Broadband Switchable Active Frequency Selective Surfaces Based on Modified Diode Model

In this letter, a broadband switchable active frequency selective surfaces (AFSSs) is presented, and the proposed structure is comprised of three metallic layers and two Rogers RT5880 substrates. In order to realize broadband transmission, a second-order bandpass filter is constructed, and the multilayer coupling effect is utilized. A modified equivalent circuit model of the p-i-n diode is proposed to reduce the simulation error and improve the design accuracy. By controlling the bias voltage of the p-i-n diodes, two completely different functions are realized. At the function of dual-polarized shielding, the shielding bandwidth is 2–18 GHz, and the transmission bandwidth is 8.2–10.5 GHz with a fractional bandwidth of 24.6% at the function of dual-polarized transmission. A prototype has been fabricated and measured, and the measurement results are in good agreement with the simulation results, indicating that the AFSSs has good polarization stability for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -band radar applications.

Liquid-based transparent, wideband and reconfigurable absorber/reflector

In this paper, an optically transparent and wideband absorber/reflector with switchable states and tunable frequency spectrum is presented. The proposed structure consists of a Polydimethylsiloxane (PDMS) layer with microchannel structures and an Indium Tin Oxide (ITO) layer as the metal panel. The switching function is implemented by controlling the injection and discharge of pure water, and the switchable frequency band of the absorbing and reflecting states ranges from 7.9 to 34.4 GHz with a fractional bandwidth of 125.2%. The tunable properties are achieved by changing the concentration of the injected saline water. In addition, the distributions of the electric field, the magnetic field and the power loss density are used to further understand the physical mechanism of the structure. Moreover, it also performs well under different polarizations and incident angles. For validation, a transparent and wideband absorber/reflector is fabricated and tested, and the simulated and measured results are consistent with each other.

A Mechanically Controlled Switchable Wideband Frequency–Selective Rasorber/Absorber

A mechanically controlled switchable wideband frequency–selective rasorber/absorber, with the transmission window inside the absorption band, based on a frequency–selective surface and a rotatable metal plate, is presented in this paper. The absorption of the switchable rasorber/absorber is over 90%, from 3.9 GHz to 11.77 GHz, when the rotatable metal plate is parallel to the rest of the layers, and its transmission coefficient can reach up to 0.62 at 11.6 GHz, with the rotatable metal plate perpendicular to the rest of the layers. The mechanism of wideband absorption and transmission are explained by monitoring and analyzing the surface current distribution at the absorption and transmission frequencies. The control method is simple, reliable and accurate. It has application value in communication and radar stations.