Frequency Selectivity Research Articles

Design of a novel stripline diplexer using frequency‐dependent couplings

AbstractA novel stripline diplexer design using frequency‐dependent couplings (FDC) to achieve multiple transmission zeros is developed in this paper. The transmission zeros generated by FDCs are flexible and controllable; on the basis of the existing cross‐coupled, more transmission zeros are introduced to improve the frequency selection characteristics. Based on this characteristic, the authors synthesized and designed a 2.6‐GHz diplexer, its transmitting channel filter is five orders with three transmission zeros, and the receiving channel filter is four orders with three transmission zeros. The authors fabricated and measured it, in narrowband, the tested results, synthesis responses and simulation results are well matched with each other, which will provide more flexibility in the design of diplexers for wireless communication system.

5G wideband bandpass filtering power amplifiers based on a bandwidth-extended bandpass matching network

In this paper, a 5G wideband power amplifier (PA) with bandpass filtering response is synthesized using a bandwidth-extended bandpass filter as the matching network (MN). In this structure, the bandwidth (θ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</inf> ) is defined as a variable in the closed-form equations provided by the microstrip bandpass filter. It can be extended over a wide range only by changing the characteristic impedances of the structure. Different from the other wideband MNs, the extension of bandwidth does not increase the complexity of the structure (order n is fixed). In addition, based on the bandwidth-extended structure, the wideband design of bandpass filtering PA is not limited to the fixed bandwidth of the specific filter structure. The theoretical analysis of the MN and the design flow of the PA are provided in this design. The fabricated bandpass filtering PA can support almost one-octave bandwidth (2–3.8 GHz), covering the two 5G bands (n41 and n78). The drain efficiency of 47%–60% and output power higher than 40 dBm are measured. Good frequency selectivity in S-parameter measurements can be observed.

Automating Stimulation Frequency Selection for SSVEP-Based Brain-Computer Interfaces

Brain–computer interfaces (BCIs) based on steady-state visually evoked potentials (SSVEPs) are inexpensive and do not require user training. However, the highly personalized reaction to visual stimulation is an obstacle to the wider application of this technique, as it can be ineffective, tiring, or even harmful at certain frequencies. In our experimental study, we proposed a new approach to the selection of optimal frequencies of photostimulation. By using a custom photostimulation device, we covered a frequency range from 5 to 25 Hz with 1 Hz increments, recording the subjects’ brainwave activity (EEG) and analyzing the signal-to-noise ratio (SNR) changes at the corresponding frequencies. The proposed set of SNR-based coefficients and the discomfort index, determined by the ratio of theta and beta rhythms in the EEG signal, enables the automation of obtaining the recommended stimulation frequencies for use in SSVEP-based BCIs.

Effect of repetition of rTMS at different frequencies on the efficacy of swallowing disorders after stroke: A systematic review and meta-analysis.

To systematically evaluate the curative effect of repeated transcranial magnetic stimulation at different frequencies on swallowing disorders after stroke. A search was conducted for randomized controlled trials of repeated transcranial magnetic stimulation for stroke patients in CNKI, Wanfang, VIP, ProQuest, PubMed, Cochrane Library, Scopus, and Web of Science databases until December 2022. The 2 researchers strictly screened and checked the included documents, extracted relevant data, assessed the risk quality of the literature using the Cochrane manual, and conducted a network meta-analysis of the data using State16.0. Eighteen studies included 680 participants. The results of the reticular meta-analysis showed that in the leakage-aspiration scale (PAS) indicators, 1 Hz, 3 Hz, 5 Hz, and 10 Hz were all better treatment effects compared with the control group, and there was a statistically significant difference (P < .05). In the standard swallowing function assessment (SSA) index, 3 Hz, 5 Hz, and 10 Hz compared with the control group were statistically significant (P < .05); there was no difference between 1 Hz and the control group (P > .05). The cumulative probability ranking results showed that the intervention effect of 3 Hz was the best in the PAS index, much greater than that of other frequencies, and the intervention effects of 10 Hz and 5 Hz were similar. For the SSA index, the intervention effect was optimal at 10 Hz, followed by 5 Hz. Note that the treatment effect of 1 Hz ranked last, even lower than that of the control group. The results of the 5 Hz treatment site grouping analysis showed that the affected side was > bilateral > healthy in PAS and > bilateral > healthy in SSA. Based on the current study, the optimal frequency and site selection results of the 2 evaluation indicators are not uniform, but from the combination of the 2 evaluation indicators, the treatment effect of 10H is good, and the effect of bilateral stimulation for the selection of stimulation sites is good. The above conclusions need to be verified in high-quality studies.

Incoherent frequency-selective phase coded holography and axial overlap information stripping

In the paper, we proposed frequency-selective carrier coded aperture correlation holography (FSC-COACH). Incoherent frequency selection technique is introduced into coded aperture correlation holography for the first time, and mask scattering imaging of arbitrary branches is realized. This represents a novel form of non-visual imaging technology capable of effectively suppressing background noise and facilitating holographic separation and reconstruction beneath the obstruction of multiple opaque mediums. Experimental analysis explores the impact of virtual point spread function filter radius on the quality of reconstruction. Through the reconstruction of standard particles and the overlapping dual-path reconstruction of the USAF chart under mask obstruction, the feasibility of our technology is demonstrated. We are confident that the proposed approach will pioneer paradigm shifts in incoherent imaging, wavefront acquisition through scattering mediums, astronomical imaging, and rapid object recognition applications.

Behavioral characterization of the cochlear amplifier lesion due to loss of function of stereocilin (STRC) in human subjects

Loss of function of stereocilin (STRC) is the second most common cause of inherited hearing loss. The loss of the stereocilin protein, encoded by the STRC gene, induces the loss of connection between outer hair cells and tectorial membrane. This only affects the outer hair cells (OHCs) function, involving deficits of active cochlear frequency selectivity and amplifier functions despite preservation of normal inner hair cells. Better understanding of cochlear features associated with mutation of STRC will improve our knowledge of normal cochlear function, the pathophysiology of hearing impairment, and potentially enhance hearing aid and cochlear implant signal processing. Nine subjects with homozygous or compound heterozygous loss of function mutations in STRC were included, age 7–24 years. Temporal and spectral modulation perception were measured, characterized by spectral and temporal modulation transfer functions. Speech-in-noise perception was studied with spondee identification in adaptive steady-state noise and AzBio sentences with 0 and -5 dB SNR multitalker babble. Results were compared with normal hearing (NH) and cochlear implant (CI) listeners to place STRC−/− listeners’ hearing capacity in context. Spectral ripple discrimination thresholds in the STRC−/− subjects were poorer than in NH listeners (p < 0.0001) but remained better than for CI listeners (p < 0.0001). Frequency resolution appeared impaired in the STRC−/− group compared to NH listeners but did not reach statistical significance (p = 0.06). Compared to NH listeners, amplitude modulation detection thresholds in the STRC−/− group did not reach significance (p= 0.06) but were better than in CI subjects (p < 0.0001). Temporal resolution in STRC−/− subjects was similar to NH (p = 0.98) but better than in CI listeners (p = 0.04). The spondee reception threshold in the STRC−/− group was worse than NH listeners (p = 0.0008) but better than CI listeners (p = 0.0001). For AzBio sentences, performance at 0 dB SNR was similar between the STRC−/− group and the NH group, 88 % and 97 % respectively. For -5 dB SNR, the STRC−/− performance was significantly poorer than NH, 40 % and 85 % respectively, yet much better than with CI who performed at 54 % at +5 dB SNR in children and 53 % at + 10 dB SNR in adults. To our knowledge, this is the first study of the psychoacoustic performance of human subjects lacking cochlear amplification but with normal inner hair cell function. Our data demonstrate preservation of temporal resolution and a trend to impaired frequency resolution in this group without reaching statistical significance. Speech-in-noise perception compared to NH listeners was impaired as well. All measures were better than those in CI listeners. It remains to be seen if hearing aid modifications, customized for the spectral deficits in STRC−/− listeners can improve speech understanding in noise. Since cochlear implants are also limited by deficient spectral selectivity, STRC−/− hearing may provide an upper bound on what could be obtained with better temporal coding in electrical stimulation.

Continuous catalytic esterification using a solid acid activated carbon monolith: Comparison of granular and monolith forms with a commercial catalyst

2-hydroxyisobutyric acid (2-HIBA) is a significant platform chemical for the synthesis of various products and has been produced fermentatively. Recently, the esters of 2-HIBA have gained interest for applications in fragrances and as low-toxic solvents. In this study, solid acid (sulfonated) wood-based activated carbon granular (sGAC) and monolith (sACM) catalysts were employed for the continuous esterification of 2-hydroxyisobuytric acid with ethanol. The effect of reaction conditions, including pressure and feed flow rate (Ql) on ester (ethyl 2-hydroxyisobutyrate) space–time yield (STY), ester yield, and selectivity, were determined. A higher STY of 96 g Lcat-1h−1 (341 g kg cat-1h−1) and selectivity of 76 % was achieved with the sACM compared to the sGAC (87 g Lcat-1h−1, 60 %) at 150 °C, 300 psig, and 3 mL min−1 (18.5–20 min contact time). At optimum pressure (300 psig) and temperature (150 °C for sGAC and sACM; maximum of 120 °C for Amberlyst), and in time-on-stream studies, 2-HIBA turnover frequency and ester selectivity were higher for sGAC and sACM over Amberlyst-15. The solid acid carbon monolith is a promising catalyst for the continuous catalytic upgrading of biobased organic acids.

Resistance frequency selection surface framed reflector antenna for 5G OTA measurement

AbstractIndirect far field (IFF) over‐the‐air (OTA) test could be one of the most applicable test methods for 5G mmWave devices. The compact antenna test range (CATR) method has been introduced to the OTA test by 3GPP. Conventional metallic parabolic reflectors without edge treatment can lead to serious edge diffraction which results in high noise and low accuracy. The serrated reflector improves edge diffraction but performs poorly at low frequencies. Reflector antenna with a resistance frequency selection surface (RFSS) frame is proposed for 5G OTA CATR measurement at millimeter frequency, which collimates spherical incident waves into quasi‐plane waves in a relatively short distance, thus forming a quiet zone (QZ) in which large devices under test can be measured in small chamber. In this paper, the reflector with RFSS is investigated through the numerical and experimental methods, it is found that serrated RFSS frame with low edge diffraction could achieve the excellent QZ, which could be helpful in miniaturing CATR chambers for 5G OTA measurement.

A dynamically switchable multifunctional meta-device in terahertz based on vanadium dioxide and photosensitive silicon

In this study, we propose a dynamically switchable multifunctional device operating in the terahertz range. The device is designed by employing a multilayered planar structure that incorporates vanadium dioxide and photosensitive silicon films. We analyze the transmission characteristics and multifunctional attributes of the device. The device exhibits the capacity to transition among diverse functionalities, including linear polarization conversion, field intensity modulation, frequency selection, and wave absorption. The polarization conversion ratio exceeds 90%, and precise control over the amplitude ratio between cross-polarized and co-polarized fields is achievable. Field intensity modulation can be realized through any of three distinct methods. Upon activation of the frequency selection function, the device can effectively operate as a band-stop filter, yielding a -20dB bandwidth of 0.57 THz. Furthermore, in absorber mode, the device demonstrates a peak absorption efficiency of 90%.

Nonlinear control of topological corner and edge states in a loop resonator

The modulation and transformation of topological states play a crucial role in controlling light transport in optical communication system. Herein, we construct a Su-Schrieffer-Heeger (SSH) lattice beyond the linear optical regime. The SSH model has resulted in the topological edge states (TESs) and the topological corner states (TCSs). It is demonstrated that the second-harmonic generation (SHG) and third-harmonic generation (THG) can occur in a topological edge loop based on the frequency matching in all-dielectric photonic crystals. Different from previous studies in which the excitation of TESs and TCSs is achieved through the selection of frequencies, in this paper the excitation of TESs and TCSs has been achieved through the harmonic generations with different orders. More importantly, there is a transformation from the trapping of optical signal on the TCS to the releasing of optical signal on the TES. The mode transformation between TESs and TCSs has important applications in optical flow control, optical signal storing and releasing.

Neuromorphic Computing via Fission-based Broadband Frequency Generation.

The performance limitations of traditional computer architectures have led to the rise of brain-inspired hardware, with optical solutions gaining popularity due to the energy efficiency, high speed, and scalability of linear operations. However, the use of optics to emulate the synaptic activity of neurons has remained a challenge since the integration of nonlinear nodes is power-hungry and, thus, hard to scale. Neuromorphic wave computing offers a new paradigm for energy-efficient information processing, building upon transient and passively nonlinear interactions between optical modes in a waveguide. Here, an implementation of this concept is presented using broadband frequency conversion by coherent higher-order soliton fission in a single-mode fiber. It is shown that phase encoding on femtosecond pulses at the input, alongside frequency selection and weighting at the system output, makes transient spectro-temporal system states interpretable and allows for the energy-efficient emulation of various digital neural networks. The experiments in a compact, fully fiber-integrated setup substantiate an anticipated enhancement in computational performance with increasing system nonlinearity. The findings suggest that broadband frequency generation, accessible on-chip and in-fiber with off-the-shelf components, may challenge the traditional approach to node-based brain-inspired hardware design, ultimately leading to energy-efficient, scalable, and dependable computing with minimal optical hardware requirements.

A HYBRID STRUCTURE OF FREQUENCY SELECTIVE SURFACE AND MAGNETIC ABSORBING SALISBURY SCREEN FOR WIDEBAND RADAR CROSS SECTION REDUCTION

This article presents a novel hybrid physical mechanism that combines frequency selective surface (FSS) and Salisbury-type absorption to create a structure that can reduce the radar cross section (RCS) over a wide frequency range. The proposed design integrates a lossy sheet composed of a magnetic absorbing material (MAM) with a traditional Salisbury screen and a FSS of a T-ring resonator. The Salisbury screen effectively absorbs incoming waves when illuminated by a plane wave with normal incidence. Furthermore, the integration of a T-ring resonator generates high-order reflection beams, thereby enabling the selection of absorption band. Simulation results demonstrate that the proposed structure enables tunable RCS reduction between 2 and 18 GHz under various conditions with normal incidence. The combination of broadband absorption mechanism with frequency selective resonance allows to construct a perfect structure both in terms of bandwidth and frequency selection of absorption.

Model-Based Thompson Sampling for Frequency and Rate Selection in Underwater Acoustic Communications

Due to the harsh propagation environment, limited bandwidth, and constrained battery life, transmission efficiency is a crucial issue for underwater acoustic (UWA) communications. This paper studies the link adaptation problem of a single UWA link by jointly selecting the transmission frequency and data rate. Since the current UWA channel lacks a universal model, we formulate this joint selection problem as a model-based stochastic multi-armed bandit (SMAB) problem. Thereafter, we propose three algorithms to solve this model-based SMAB problem under the settings of the stationary channel, non-stationary channel, and large arm (i.e., frequency and rate pair) space. For the stationary channel, we propose a unimodal objective-based Thompson sampling (UO-TS) algorithm by exploiting the unimodal feature of the objective function. For the non-stationary channel, we put forth a hybrid change detection UO-TS (HCD-UO-TS) algorithm based on the features of the unimodal objective function and non-stationary channel. For the large arm space, we propose an iterative boundary-shrinking TS (IBS-TS) algorithm by using the logistic regression-based arm classification model. These algorithms are all data-driven and have low complexity and a fast convergence rate. In addition, we derive an upper regret bound for the UO-TS algorithm. Numerical results show that the proposed algorithms outperform the state-of-the-art bandit algorithms and are not sensitive to the arm space.

Design of Nonreciprocal Filtering Antenna Using Spatio-Temporal Modulated SIW Resonators

This article reports on, for the first time, the design of nonreciprocal filtering antennas using spatio-temporal modulated substrate integrated waveguide (SIW) resonators. It consists of two SIW cavities and a half-mode SIW (HMSIW) cavity, which is designed as the last-stage resonator and the radiator. By integrating time-modulated capacitors on the surface gaps of the three cavities, the nonreciprocal radiation patterns in transmission and reception modes are achieved at the same operating frequency. Three radiation nulls are generated due to the cross-coupling in the time-modulated network and source-load coupling. The theoretical analysis of the co-designed nonreciprocal SIW filtering antenna is detailed, along with methods for its co-simulations and measurements. For the proof-of-concept demonstration, a nonreciprocal SIW filtering antenna operating at 2.4 GHz is designed and fabricated. The measured 10-dB bandwidth and peak gain are 1.7% and 2.6 dBi, respectively. The measured realized gains at transmission and reception show that the reverse isolation is greater than 11 dB within a bandwidth of 30 MHz. The frequency selectivity values are 756 and 368 dB/GHz at the left and right sides of the passband, respectively.

OTA testing of near‐field and far‐field communication links

AbstractIn this work, near‐field and far‐field link measurement in metal enclosure environment is performed. The performance of near‐field and far‐field links are assessed using key performance indicators such as error vector magnitude, bit error rate, and signal‐to‐noise ratio. The metal enclosure is placed in an anechoic chamber, ensuring a stationary measurement environment. There are no external interference sources and the results are a function of near‐field and far‐field scenarios and hardware impairments. In measurements, software‐defined radios used for the transmission and reception of image data using the long‐term evolution‐advanced physical layer. Based on the results of the study, an optimum gain region can be determined where better key performance indicators are achieved. Furthermore, the frequency selectivity of the channel is reduced within the determined optimum gain region, leading to an improvement in the system's performance.

Performance improvement in computing the L-infinity norm of descriptor systems

"Efficient and realible algorithms for finding the L-infinity norm for both continuous- and discrete-time descriptor systems have been recently developed. These algorithms exploit the underlying Hamiltonian or symplectic structure of the computational problem. The solver incorporating these advances has been extensively tested on large sets of control applications. Numerical results and comparisons illustrated the good performance and effectiveness of this solver. However, further investigations have shown that the performance can still be improved. The refinements performed include a better selection of the test frequencies used to find a lower bound for the L-infinity norm and of the tolerances for detecting the poles lying on the boundary of the stability domain, a better use of the computer memory hierarchy, an optimal workspace for computations, etc. Such refinements allowed not only to reduce the computing time, but also to improve the accuracy and reliability of the results. "

Geothermal Water Exploration of the Maoyanhe Hot Spring Scenic Spot in Zhangjiajie Using the Natural Electric Field Frequency Selection Method

Natural electric field frequency selection method was proposed by Chinese scholars in the 1980s on the basis of imitating the field observation method of the magnetotelluric method (MT). It can only measure the magnetotelluric field components of one or several frequencies on the surface to determine the existence of underground geological bodies. This method has played an important role in shallow groundwater exploration. This paper mainly discusses the application of frequency selection method in the exploration of underground hot water in the Maoyanhe Scenic spot, Zhangjiajie City, Hunan Province, in order to illustrate the effectiveness of the frequency selection method in water exploration. According to the situation of the construction site, nearly 20 geophysical prospecting survey lines of varying lengths were laid flexibly within the red line of the Maoyan River Scenic Spot. Firstly, three-frequency (170 Hz, 67 Hz and 25 Hz) measurements were carried out on each survey line to preliminarily determine the possible horizontal location of underground hot water. Secondly, in the vicinity of the low potential anomaly of the three-frequency curve, the fine measurement by using multi-frequency bipolar profile method was further carried out. The specific distribution of underground hot water was determined based on the principle of frequency domain sounding and the static effect characteristics of the electromagnetic method so as to provide a scientific basis for the drilling layout. Finally, the reliability of the frequency selection method is verified by two verification boreholes. The results indicate that the frequency selection method is one of the effective geophysical exploration methods in groundwater exploration.

An integrated frequency assignment and fleet assignment model: A strategic application in the Brazilian regional aviation market

Airlines endeavour to implement substantial measures to ensure profitability and maintain a competitive edge in the market. This entails conducting extensive studies and engaging in strategic planning to make optimal decisions. A crucial element of this process involves addressing the Fleet Assignment Problem (FAP). Typically, aircraft operating within an established network are acquired before adopting this method, rather than being selected based on an optimal solution. Consequently, incumbent airlines frequently operate in Brazilian regional aviation with fleets that are not optimised for the specific routes they serve. This study aims to explore an integrated frequency assignment and fleet assignment model, which identifies the most suitable aircraft for a given network. Model parameters were estimated from historical data from multiple incumbent airlines and were applied to a fictitious airline operating from Goiania International Airport (Brazil) as the hub. The findings from multiple test runs ascertain optimal frequency and aircraft capacity selections, as well as recommended fleet sizes. Further analysis reveals, for instance, that the Embraer E190-E2 is the most suitable aircraft for a scenario constrained to a single type of fleet, demonstrating the potential for significant profitability on the routes in the simulated network.

Rechargeable Active Implantable Medical Devices (AIMDs)

Active Implantable Medical Devices (AIMDs) act as lifesaving devices. They provide electrical signals to tissues as well as perform data-logging operations. To perform these operations, they need power. The battery is the only source for such devices, as they are placed invasively inside the human body. Once the battery drains out, the patient wearing the device has to undergo medical surgery for the second time, where there are many chances of infections, and it could be life-threatening too. If the AIMDs, e.g., pacemakers are designed using rechargeable batteries, then the devices can be recharged regularly, which can increase the life of the device as well as reduce its size. Wireless charging of AIMDs such as ICDs or pacemakers is proposed in this paper using magnetic resonant coupling. The selection of frequency for power transfer is the most crucial part, as the basic restriction (BR) criteria proposed by ICNIRP guidelines and the IEEEC95.1 standard need to be followed, which ensures the safety of the patient. This is suggested by considering some basic restriction parameters, such as specific absorption rate (SAR) and current density, as suggested by guidelines. In this paper, experimentation using two frequencies is shown, i.e., 1.47 MHz (the high frequency) and 62 KHz (the low frequency). For experimentation, goat flesh and saline solution are used. Secondary coil and flesh are dipped in the saline solution. Battery recharging performed at a lower frequency took less time than with a frequency in the MHz range. All BR criteria are fulfilled for both frequencies, so the proposed methodology is safe to use.

Ga2O3-Pt dual-site functionally separated catalyst for efficient hydrogenation of furfural under hydrogen spillover

The selective hydrogenation of furfural (FFL) to furfuryl alcohol (FAL) is an interest topic in the conversion of biomass. Herein, we present a Ga2O3-Pt two-component spatially isolated catalyst to achieve enhanced catalytic activity and selectivity under hydrogen spillover. Specifically, Pt and Ga2O3 active sites are confined in the micropores and mesopores of TS-1@mesoporous-silica, respectively. The Pt sites within the micropores is responsible for the activation of hydrogen while the Ga2O3 sites in mesopores acts as the active center for FFL activation. This synergistic effect of double site exhibits a significant improvement in catalytic activity and selectivity, with the turnover frequency (TOF) and FAL selectivity up to 72.2 h−1 and 96.5%, respectively. This strategy provides an idea for the understanding of synergistic nature in bicomponent catalysts under hydrogen spillover.