Loop Resonator Research Articles

Circularly polarized D-shaped slot antenna for wireless applications

A multiband circularly polarized slot antenna for wireless local area networks (WLAN) and worldwide interoperability for microwave access (WiMAX) applications is designed, studied, and fabricated. Using modified ground plane structure, circular polarized characteristics are realized. An open rectangular loop is introduced on the ground plane to generate orthogonal modes at middle resonance frequency. At higher resonance frequency to improve axial ratio bandwidth, a D-shaped radiator is used. Thus, the cooperation of modified ground plane, open loop resonator, and D-shaped radiator improves performance of the antenna at all the required bands. The proposed microstrip antenna generates separate impedance bandwidths to cover frequency bands of WLAN and WiMAX applications. The realized antenna is relatively small in size 40 × 54 mm2 or 0.26_ × 0.36_ where _ is the free-space wavelength at the desired first resonant frequency 2.0 GHz and operates over frequency ranges 26% (2.0-2.6 GHz), 8.9% (3.21-3.51 GHz), and 50.6% (3.8-6.38 GHz). In addition, the antenna exhibits 5% (2.32-2.44 GHz), 5.8% (3.3-3.5 GHz), and 5.2% (5.61-5.91 GHz) Circular Polarization bandwidth, making it suitable for WLAN and WiMAX applications.

Optical characterization of different waist diameter on microfiber loop resonator humidity sensor

In this paper, the effect of different waist diameter on silica microfiber loop resonator (MLR) relative humidity (%RH) sensor is reported. The silica fiber was tapered to vary the waist diameter to 3 μm, 4 μm, 5 μm,7 μm, 8 μm and 10 μm using flame brushing technique. The MLR with a 300 μm diameter loop was formed by manually twisted the tapered fiber under an optical microscope into a self-touching loop. Initially, the effect of whispering gallery modes (WGMs) on the MLR was observed. Transmission mode spectra were observed to determine the number of resonated wavelength and quality factor (Q-factor). The Q-factor is observed to be >105 for all samples and MLR with 3 μm diameter achieve the highest Q-factor value. A significant response to %RH from 35% to 85% was observed due to the change of refractive index between the MLR and the surrounding medium resulting different light attenuation in the microfiber. The sensitivity increased by a factor of 12.2 for the MLR with diameter of 7 μm as compared to the smaller diameter MLRs and a factor of 13.7 as compared to straight microfiber (SmF). As for resolution, the MLR with waist diameter of 7 μm improve by a factor of 5 as compared to the smaller waist diameter and a factor of 6.5 as compared to SmF. The proposed humidity sensor employs the microfiber loop resonator without any sensitive material coated on it which reduced the complexity during the fabrication and manufacturing process. The reported results may contribute to the optimal waist diameter of microfiber loop resonators for humidity sensing application.

Miniaturized Planar Monopole UWB Antenna with Integrated RFID/GPS/GSM/WLAN Bands Using Capactively Loaded Loop Resonator (CLLRs)

Miniaturized Planar Monopole UWB Antenna with Integrated RFID/GPS/GSM/WLAN Bands Using Capactively Loaded Loop Resonator (CLLRs)

Tuning the Resonance Frequency and Miniaturization of a Novel Microstrip Bandpass Filter

In this paper, a compact microstrip bandpass filter is designed using two open loop resonators. In order to obtain a tunable bandpass response with low insertion loss, two stubs are loaded inside them. The design process is based on obtaining the input admittance. Then, using the input admittance, a method is presented to control the resonance frequency and miniaturization simultaneously. The obtained insertion loss and the return loss at the resonance frequency are 0.1 dB and 19.7 dB respectively. To verify the design method, the proposed filter is fabricated and measured. The measured results are in good agreement with the simulated results.

Tuning the Resonance Frequency and Miniaturization of a Novel Microstrip Bandpass Filter

In this paper, a compact microstrip bandpass filter is designed using two open loop resonators. In order to obtain a tunable bandpass response with low insertion loss, two stubs are loaded inside them. The design process is based on obtaining the input admittance. Then, using the input admittance, a method is presented to control the resonance frequency and miniaturization simultaneously. The obtained insertion loss and the return loss at the resonance frequency are 0.1 dB and 19.7 dB respectively. To verify the design method, the proposed filter is fabricated and measured. The measured results are in good agreement with the simulated results.

Compact filters with adjustable multi-band rejections based on spoof surface plasmon polaritons

Owing to the gorgeous features of planar design, strong field confinement, and compatibility with traditional microwave devices, spoof surface plasmon polaritons (SSPPs) have been developing at a rapid pace in modern microwave technologies. Band-rejection filters, especially multi-band rejection filters, are a significant ecosystem of SSPPs to be designed. Here, we firstly propose compact multi-band rejection filters, including dual-band and triple-band, through the addition of interdigital capacitance loaded loop resonators (IDCLLRs) into the grooves of the corrugated SSPP transmission line (TL). Compared to traditional metamaterial particles like split ring resonators (SRRs) and complementary SRRs (CSRRs) with the same size, IDCLLRs possess excellent merits of lower resonant frequency, larger dynamic range, and more tunable parameters, which enable the proposed device to be more compact and have more freedom for adjusting bandwidths. Both the simulated and experimental results demonstrate the high performance of two multi-band rejection filters, which can provide wide stop-bandwidth (a maximum relative bandwidth of up to 9.5% for the dual-band filter and 8.8% for the triple-band filter) and high isolation (the isolation of both filters can be less than −30 dB and the maximum isolation of up to −60 dB for the dual-band filter and −58 dB for the triple-band filter). The compact SSPP filters with adjustable multi-band rejections may greatly advance progress towards SSPP-based devices and integrated systems.

An effective way regarding to coupling reduction and pattern correction in base station design

AbstractAn effective method regarding to coupling reduction and pattern correction in base station antenna design is developed. Initially, a hybrid antenna with one lower band element, two middle band elements, two higher band elements, and a reflector is designed. It is found that a “C‐shaped” current loop is formed by the horizontal radiating arm of the middle band element, its vertical balun ground, and the horizontal reflector. Strong coupling between the lower and middle band elements occurs, making the lower band beamwidth nonconvergent. Hence, a middle band element with comparatively enclosed feeding structure is chosen to interrupt the resonant loop, thus weakening the coupling among those elements. Then, a π‐shaped metal plate and rectangle baffles are added to finely reshape the radiation pattern of these elements. As a result, the coupling between these elements are weakened and the HPBWs of the proposed antenna can keep an extremely stable value of 65° ± 5°. The discovery and analysis of coupling mechanism has great value for improving the radiation performance of the antenna array.

A Compact Wideband Monopole Antenna using Single Open Loop Resonator for Wireless Communication Applications

A novel single layer, microstrip line fed compact wideband monopole antenna using open loop resonator has been designed and analyzed. The proposed antenna occupies a compact size of only 30 36.5 1.6 mm3. A partial ground plane is employed to enhance the operating bandwidth and reflection coefficient of the proposed antenna. The variations in operating bandwidth of the proposed antenna can be easily controlled by properly adjusting the position of the gap in the open loop resonator.The antenna prototype is fabricated on FR4 substrate with a dielectric constant 4.2. In this design, the antenna exhibits 10dB wide impedance bandwidth of 61% from 2.0174 to 3.7903 GHz.The antenna can be easily fed using a 50 Ω microstrip feed line and it covers the bandwidth requirements of a number of modern wireless communication systems such as IEEE 502.11b WLAN band (2.4 2.5 GHz), extended UMTS (2.5 2.69 GHz), IMT (2.7 2.9 GHz), and IEEE 802.16 Wi MAX band (3.3 3.6 GHz) applications. The desired antenna is designed and simulated using Computer Simulation Technology (CST). An extensive analysis of the antenna parameters (reflection coefficient, radiation pattern, directivity, and VSWR) including surface current distributions is presented and discussed in this paper. Good agreement between simulated and measured result is obtained.

Resolution improvement for digital closed loop resonator micro-optic gyro based on tunable resonator

In the resonator micro-optic gyro (RMOG) frequency locking loop, digital-to-analog converter quantization error leads to low-accuracy laser tuning, causing frequency locking and rotation sensing dead zones. This paper proposes a planar waveguide resonator (PWR) frequency locking scheme with a piezoelectric (PZT) ring to tune the PWR resonant frequency to track and lock to the laser frequency. The proposed scheme achieved PZT-PWR Q = 4 × 107 and frequency tuning coefficient = 1.124 MHz / V. Direct comparison on an RMOG device experimentally verified the proposed scheme reduced frequency locking noise to 0.25 deg / s and improved gyro resolution from 1 to <0.05 deg / s.

Laser frequency noise measurement in a resonant fiber optic gyro

A resonant fiber optic gyro (RFOG) is a high-accuracy inertial rotation sensor based on the Sagnac effect. Knowledge of the laser frequency noise, especially the study of its transfer characteristics is critical to optimize the resonant frequency servo loop parameters in the RFOG. In this paper, a Mach–Zehnder interferometer (MZI) is used to measure the changes of the power spectral density (PSD) of the laser frequency noise. Three different observation points are set to investigate the transfer characteristics of the laser beam along the transmission loop of the RFOG. Through real-time observation and analysis of the PSDs of the laser frequency noise, we found that the effects of the laser frequency noise on the RFOG can be clearly determined, and the resonant frequency servo loop parameters can be optimized according to the required gyro bandwidth. We also demonstrate the significance of reducing the residual error at the lock-in frequency while ensuring a sufficient gyro bandwidth.

Synthesis, characterization, optical and magnetic properties of pure and Mn, Fe and Zn doped NiO nanoparticles

Pure and 2% Mn, Fe and Zn doped NiO nanoparticles were synthesized by co-precipitation method at calcination temperature 550 °C. They were characterized by X-ray powder diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, proton induced x-ray emission, Rutherford Back Scattering, Fourier transmission infrared spectroscopy, UV-vis spectroscopy, M-H loop and electron paramagnetic resonance. The obtained results indicate that the lattice parameter, crystalline size, direct energy gap and chemical functional group are significantly dependent on the kind of dopant element. Moreover, the dopant elements are not affected by the ferromagnetic nature of NiO nanoparticles while g-factor varies according to the kind of dopant elements.

Open Loop Resonator-Based Triple Passband Filter for 1.5 GHz, 2.45 GHz and 3.65 GHz Applications

In this paper, a dual mode mixed open loop resonator (OLR)-based metamaterial antenna is introduced for the design of a triple-passband filter for GPS, WLAN and WiMAX applications. The antenna is embedded into a 50-Ω microstrip framework. The Rogers RT-5880, which has a succinct structure, is used as the substrate in the proposed passband filter design, where the attainment of the antenna is explored both integrally and experimentally. A partial ground system is applied in the ground layer and stepwise analysis is performed on the proposed resonator, which can pursue the fundamental even-mode resonant frequency. Based on the proposed resonator, a bandpass filter is designed and fabricated to justify the perception, focusing on 1.5 GHz, 2.45 GHz, and 3.65 GHz. In addition, the filter is evaluated using the Nicolson–Ross–Weir approach at the filtering frequency. The effective electromagnetic parameters retrieved from the simulation of the S-parameters imply that the OLR metamaterial antenna exhibits negative refraction bands. With a favorable design and double-negative characteristics, this structure is suitable for a triple passband filter, particularly at 1.5 GHz, 2.45 GHz and 3.65 GHz, which cover GPS, WLAN, and WiMAX, respectively.

Labyrinth double split open loop resonator based bandpass filter design for S, C and X-band application

Nested circular shaped Labyrinth double split open loop resonators (OLRs) are introduced in this article to design a triple bandpass filter for 3.01 GHz, 7.39 GHz and 12.88 GHz applications. A Rogers RT-5880 is used as a substrate to design the proposed passband filter which has a succinct structure where the attainment of the resonator is explored both integrally and experimentally. The same structure is designed on both sides of the substrate and an analysis is made on the current distribution. Based on the proposed resonator, a bandpass filter is designed and fabricated to justify the perception focusing on 3.01 GHz, 7.39 GHz and 12.88 GHz. It has also been observed by the Nicolson–Ross–Weir approach at the filtering frequencies. The effective electromagnetic parameters retrieved from the simulation of the S-parameters imply that the OLR metamaterial filter shows negative refraction bands. Having an auspicious design and double negative characteristics, this structure is suitable for triple passband filters, particularly for S, C and X-band applications.

Catalyst degradation diagnostics of proton exchange membrane fuel cells using electrochemical impedance spectroscopy

A previously validated equivalent circuit model, in which two resonant circuits were inserted to represent the processes in the catalyst layers, is applied to fit the electrochemical impedance spectroscopy results of a single proton exchange membrane fuel cell exposed to accelerated stress test targeting catalyst degradation. The simulation results of the applied equivalent circuit model show very good agreement with the experimental data. The applied model is able to extract contributions of each of the model elements to the cell degradation. The obtained results indicate that the cathode catalyst layer resonant loop parameters, together with the cathode charge transfer resistance and cathode double-layer capacitance, change the most during the accelerated stress test. If each of the elements of the cathode resonant loop can be associated with physical processes inside the catalyst layer, the model may be used to give more insight into the degradation effects on functioning of the catalyst layer. From the conducted electrochemical impedance spectroscopy analysis, it seems that the low-frequency intercept in Nyquist plot shows the most significant change with degradation, so it may be used directly as a sufficient indicator of fuel cell performance degradation due to catalyst layer degradation.

Simple dual‐mode balanced bandpass filter with high selectivity and extended common‐mode noise suppression

A new miniaturised dual-mode balanced bandpass filter (BPF) is presented in this letter. To achieve the required differential-mode (DM) operation with common-mode (CM) suppression, an octagonal microstrip dual-mode loop resonator is employed. By symmetrically locating four high-low impedance sections inside the free area of the loop resonator, the proposed balanced BPF can realise compact size, wide stopband under DM operation, and extended CM suppression, simultaneously. Furthermore, a pair of coupled lines is introduced to readily achieve two transmission zeroes for realising high selectivity of DM response. For demonstration, a dual-mode balanced BPF with the passband centred at 2.39 GHz is designed and measured. Both the simulated and measured results are provided with good agreement.

Resonant–repetitive controller with phase correction applied to uninterruptible power supplies

This paper proposes a new control structure based on the parallel interconnection of a filtered repetitive controller and a resonant structure applied to uninterruptible power supplies — UPS. In particular, the filter in series with the repetitive controller adjusts the phase angle between resonant and repetitive loops, improving in this way the tracking performance. A particular filter structure is proposed, and an augmented state formulation is derived. Controller design is then carried out by the solution of an optimization problem with linear matrix inequalities constraints. Experimental results on a commercial 3.5kVA UPS illustrate the closed-loop performance.

Dual band pass filter with sharp transmission zeros for wireless applications

Band stop/pass filters using octagonal and rectangular-shaped open loop resonators are proposed for wireless applications. The filter has the advantage of low insertion loss in the passbands and high return loss in the stopbands. The main idea of the filter is to achieve transmission bands by utilizing rectangular shape open loop resonators which are coupled to the input and output ports. The open loop resonators are used to generate stopbands in the filter response. The filter has small size, good response and the simulated results agree with the measured results. The lower insertion loss, and higher rejection band levels are investigated which confirm the suitability of the proposed dual BPF for WLAN and WiMAX applications.

New compact low-pass filter (LPF) using cascaded square open loop resonator

This article introduces a new design technique of low-pass filter using cascaded square open loop resonator (SOLR) for the multi-wireless communication system. In the design procedure, a half-wavelength SOLR is realized with 6 GHz to meet the desired LPF cut off frequency. As the resonator is fed by a direct connection of 50-ohm input/output ports, the structure is directly transferred into a second-order low-pass filter with elliptic behavior. An equivalent circuit is extracted and its lumped elements are computed to support the proposed second-order LPF. Based on the equivalent circuit, highly selective third and fifth-order LPFs with wide rejection band are developed. To achieve this development several SOLR are cascaded by a direct connection. The designed filters are implemented on a grounded substrate which has relative permittivity of 6.15 and thickness of 0.508 mm. To verify the design concept, a third-order LPF using two cascaded SOLRs is designed, simulated, fabricated and measured. The filter responses obtained from theory, simulation, and measurement show good agreement. The filter has very small circuit area about 31 mm2 excluding the input/output feeding ports.

Phase-sensitive detection of acoustically stimulated electromagnetic response in steel

The signal amplitude and the phase of acoustically stimulated electromagnetic (ASEM) response have been investigated in steel. In the ASEM method, magnetization is temporally modulated with the radio frequency (rf) of irradiated ultrasonic waves through magnetomechanical coupling. The first-harmonic components of the induced rf dipolar magnetic fields are detected using a resonant loop antenna. The signal amplitude of ASEM waves is determined by the magnitude of local piezomagnetic coefficients on an acoustically excited spot. Here, we divided the ASEM waves into the “in-phase” and “quadrature” components by phase-sensitive detection (PSD). On the basis of the linear response theory, we provided the theoretical formalism of ASEM response by introducing local complex piezomagnetic coefficients, dloc = d′ + id′′. We investigated the magnetic field (H) dependence of the individual components on the different surface conditions of steel plates. The in-phase component [∝ d′(H)] shows a hysteresis loop on the machined surface of a steel plate, in which d′(H) switches sign at two finite field values, ±H0. The inversion of magnetization associated with the applied static fields is thus definitely observed in the PSD measurements. In addition, we measured the hysteresis behaviors on a steel surface with a thin mill scale (iron oxide layers). The hysteresis loop broadens and a significant contribution of the quadrature component [∝ d′′(H)] is found. We discuss the origin of the hysteresis behaviors of d′ and d′′ using the Debye relaxation model.

A Circuit Model-Based Analysis of Magnetically Coupled Resonant Loops in Wireless Power Transfer Systems

DOI: 10.26650/electrica.2018.55345 Magnetically coupled resonant loops can be represented by a lumped element circuit model. Each parameter in the lumped element model can be expressed as a function of loop geometry and the separation between the loops; therefore, the geometry can be systematically changed, and the power transfer efficiency of the coupled loops can be predicted. This paper presents a simulation-based efficiency analysis for wireless power transfer systems utilizing magnetically coupled resonant loops. The behavior of power transfer efficiency is studied for various loop geometry parameters, and the simulation results are presented in detail. These results clearly show that there is a trade-off between peak efficiency and critical coupling distance, both of which depend on the loop size, frequency of operation, and source-load impedances. To verify the accuracy model, two identical circular loops are fabricated and measured, and the measurement results agree well with the model.