Loop Resonator Research Articles

Efficient wideband filter using closed loop resonator with coupling lines

Efficient wideband filter using closed loop resonator with coupling lines

Efficient wideband filter using closed loop resonator with coupling lines

This paper is about a wideband filter using closed loop resonator with inter-digital coupling lines. The square resonator is used as closed loop structure integrated with inter-digital coupling on both sides which plays a major key role in this filter design. The proposed wideband filter can be employed in ultra-wideband (UWB) receivers since the operating band of UWB is matching with operating bandwidth of this filter. Design and EM simulation of the UWB filter's characteristics are discussed in this work. The proposed UWB filter produces tremendous bandwidth ranges from 2.3 GHz to 8 GHz. The filter evaluation parameters like return loss, insertion loss, phase and group delay are obtained, and their responses are analysed. The complete size measurement of the filter is achieved to be 39 mm × 3.2 mm × 1.6 mm on accounting the above features. The calculated bandwidth ratio with respect to centre frequency of the filter is obtained about 115%. The performance parameter results show the filter's return loss (S11) and insertion loss (S21) are −41 dB and −2 dB respectively. Both simulation and measured values the UWB-BPF are compared.

X-Band Microstrip Bandpass Filter Design using Square Loop Resonator and Defected Ground Structure

Filter is an important part in telecommunication system including in radar system. To get the better performance in selecting the signal, a ftlter must have a good Q-Factor. In this paper, an investigation of a ftlter design for synthetic radar has been successfully done. This ftlter has been designed to work at x-band using square loop resonator (SLR). A Defected Ground Structure (DGS) has been implemented to this work to increase the Q-factor of the ftlter. The result of measurement getting that the center frequency at 9.51 GHz with the bandwidth 610 MHz and PCB size of this ftlter is 22 mm x 16 mm.

Compact Bandpass Filters Using Folded Quad-Mode Stub-Loaded Loop Resonators

Folded quad-mode stub-loaded loop resonators (QMSLLRs) are proposed for realizing both bandpass and dual-band bandpass filters with compact dimensions. The QMSLLR is a folded square loop loaded with four short stubs, providing structure symmetry in both transversal and longitudinal directions. Determined by the lengths of the loaded stubs, the four resonant frequencies as analyzed with even-odd mode method can be either distributed in one passband with equal space, or in two passbands with a guard band in between, for realizing a single-band bandpass filter or a dual-band bandpass filter, respectively. For both the input and output couplings, two perpendicular feeding lines are parallel coupled to the QMSLLR at one corner. The measure results prove that the structure is suitable for the design of a medium band or even narrow band bandpass filters with compact dimensions.

An octagonal-shaped conductive HC12 & LIBERATOR-40 thread embroidered chipless RFID for general IoT applications

This paper presents the design, fabrication and testing of two embroidered chipless octagonal-shaped RFID tags on cotton fabric for wearable applications. The first tag is designed by using silver-coated polyamide conductive fibre (HC12) and the second tag is embroidered by using highly conductive Vectran (LIBERATOR 40) which is highly conductive multifilament yarn spun from Liquid Crystal Polymers (LCP), on cotton fabrics. In contrast to the traditional RFID tag, the chipless RFID tagging, the ID code is not saved in the memory, instead, it uses the physical features of the tag to send data. The proposed tag's design uses a Frequency Selective Surface (FSS) technique for the frequency range of 8–18 GHz. These tags are designed using CST studio and precisely fabricated by using commercial ZSK Technical Embroidery System JCZA (0109–550). The tag design is composed of six concentric octagonal loop resonators with one unitary element. The electromagnetic scattering waves behaviour and Singularity Expansion Method (SEM) based circuit modelling for the octagonal-shaped tag is performed, and the coupling coefficients are evaluated. The desired data bits are obtained by a series of comparative experiments for Radar Cross Section (RCS) in an anechoic chamber. The experimental results obtained show that the 4-bit data is accurately retrieved with the variation of distance by up to 1.8 m at 0 dB m. Moreover, the average transition from minimum ‘0’ to maximum 1’ is -27 dB for both designs. Furthermore, the experimental results for on-body RCS measurements and the bending effects on both tags down to 7 mm is observed. This octagonal embroidered Chipless RFID tag is a fully textile design which is compact and can be deployed commercially in various IoT applications.

Amplification of optical activity in a fiber loop resonator.

In this paper, we have theoretically studied an effective amplification of optical activity by a fiber loop resonator. We propose a scheme in which an optically active element is placed in the loop segment of the resonator. Assuming that the coupling in the resonator is polarization-independent, we have shown that initially small polarization plane rotation, which arises due to the optically active element, can be significantly amplified by tuning the resonator's closed-path phase. We have also studied the influence of losses on the amplification of optical activity. We have shown that the maximal amplification takes place under the condition of critical coupling, at which the attenuation parameter is equal to the resonator's effective reflection coefficient. We have also studied effective dichroism in such a system and shown the relevance of a critical coupling regime to that effect.

Wearable Magnetoinductive Waveguide for Low-Loss Wireless Body Area Networks

A novel approach of wearable magnetoinductive waveguide (MIW) is introduced for wireless body area network (WBAN) communications that brings forward significant advances over state-of-the-art. The MIW consists of series of electrically small resonant loops worn upon the human body to support magnetoinductive waves (MI waves) for low-loss/low-power WBANs. Compared to previous approaches, the proposed MIW exhibits 63 dB lower loss, translating conventional power levels of mW down to μW or nW. In this work, we introduce the operating principle of MIW WBAN through underlying theory and dispersion diagrams. The proof-of-concept numerical and experimental results are reported for frequency bands centered around 40.4 and 80.7 MHz for a cylindrical human limb and are found to be in excellent agreement. Design guidelines are extensively discussed to accommodate several possible scenarios (frequency selection, gap between the loops, number of loops, and loop radius) along with practical considerations including loop tilts, anatomical limbs, limb movements, unequal loop gaps, and loop failure. Specific absorption rate (SAR) calculations confirm that this technology is highly safe for human use. A bit error rate (BER) analysis further demonstrates that the MIW can form a high-quality communication channel for WBAN. Overall, the reported approach unveils a new possibility of low-loss and seamless WBANs.

A Novel 2.4-GHz Low-Profile Smart MIMO Antenna with Reconfigurable Frequency-Selective Reflectors

In this paper, a new low-profile smart multiple-input multiple-output (MIMO) antenna system is presented for WiFi IEEE 802.11a/b/g/n/ac/ax applications. The proposed compact 2.4-GHz antenna system employs two beam-switching antenna cells for MIMO operation. Each antenna cell is composed of four reconfigurable frequency-selective reflectors (RFSRs) and a one-to-four switching feeding network. The RFSRs are constructed using a one-wavelength metal loop resonator, which functions as a radiating antenna or a wave reflector to reflect beams along a specific direction, as controlled by the switching network. The feeding switching network utilizes PIN diodes to adjust the phase and impedance required for changing the operational status of each RFSR. The overall dimensions of the antenna system, including the metallic ground, are 120 mm ´ 120 mm ´ 9.5 mm. Moreover, the measured operational bandwidth of the 2.4-GHz antenna is approximately 100 MHz, and the radiation efficiency of each directed beam is 40%–70%.

Design of Real-Time Free Spectral Range Measurement Based on HOPLL Technique

A real-time free spectral range (FSR) measurement system based on heterodyne optical phase-locked loop (HOPLL) is proposed for the first time to test the FSR of a fiber resonator. In this system, HOPLL is used to lock phase between the master and slave lasers, so that the frequency difference between them reach one FSR. In addition, PDH technique is used to establish a resonant tracking loop. By setting the loop control parameters, the master and slave lasers are respectively locked on two adjacent resonance peaks of the cavity. If the ambient temperature changes, the cavity length of the resonant cavity will change accordingly. Then the real-time change of FSR of the resonant cavity can be measured by detecting feedback change of the loop. The experimental results show that the linewidth of beat signal of the master and slave lasers after phase-locking is less than 10Hz, and also the frequency noise of the 10Hz bandwidth is 0.0154Hz which is 60dB lower than that before phase-locking. The researchers find that the FSR coefficient of thermal expansion is −210.35 ± 0.15Hz/°C, which is consistent with theoretical results. The relative measurement accuracy of $1.5\times 10 ^{-9}$ is achieved in this loop. Therefore, the experimental results effectively verify the actual application performance of the real-time FSR measurement based on HOPLL technique.

Resonant frequency tracking mode on eddy current pulsed thermography non-destructive testing

Eddy current pulsed thermography (ECPT) has been widely used in the field of non-destructive testing due to its safety, non-contact detection, high spatial resolution and intuitive results. Inductive excitation source is an important component of ECPT and provides high-frequency alternating current to drive the excitation coil. However, a resonant frequency distortion phenomenon exists in the excitation source during the detection process, which seriously affects the output power of the excitation source and the sample detection effect. This paper presents a fast resonant frequency tracking loop for full bridge series resonant inverter which is used to search the resonance frequency in real time through direct digital synthesizer (DDS) and all-digital phase-locked loop. Theoretical analysis and simulation are presented to explain the working principle of the loop. Then, an experimental prototype is manufactured which serves as an excitation source for the ECPT experimental system. Compared with traditional excitation sources, the prototype does not need a water-cooled device and the tracking speed can be adjusted by modifying the parameters of DDS. Finally, experiments have been conducted on both artificial slot of 45# steel and natural cracks of rail and stainless steel to investigate the influence of resonant frequency tracking speed on the crack detection. The results revealed that reducing the resonant frequency tracking time can efficiently improve defect detectability and the manufactured prototype showed more application potential. This article is part of the theme issue 'Advanced electromagnetic non-destructive evaluation and smart monitoring'.

A Non-Invasive Flexible Glucose Monitoring Sensor Using a Broadband Reject Filter

In this paper, a novel, highly accurate, non-invasive glucose-monitoring sensor that is based on a flexible broadband reject filter is presented. The filter topology comprises a tapered feed line at a top layer that excites four open loop resonators on the bottom layer. The broadband reject response is achieved by relying on a modified log-periodic distribution of the open loop resonators. The embedded resonators are reduced in size and are designed to exhibit an enhanced sensitivity to track the variations of the glucose level across the 1.25-2.65 GHz frequency span. The proposed flexible filter is tested within in-vitro, ex-vivo and in-vivo setups. A high correlation between the scattering parameters of the proposed sensor and the variations in glucose levels is attained. Regression models are developed using experimental data obtained from healthy patients that are subjected to glucose tolerance tests. Results demonstrate less than 4% mean absolute relative difference between the reference and estimated glucose levels, and the predicted glucose levels lie 100% within the clinically acceptable zones as shown by the Clarke Error Grid analysis.

Design of tunable microstrip diplexer with reconfigurable filtering characteristics based on dual‐mode square loop resonators

A novel compact microstrip diplexer with tunable centre frequencies and reconfigurable filtering characteristics at both channels is presented. The designed diplexer is constructed by coupling two dual-mode square loop resonators (DMSLRs) having different electrical lengths. The DMSLRs are investigated by virtue of the coupled line analysis to evaluate the resonance frequencies, transmission zeros and out-band insertion loss level more conveniently. Centre frequencies of both channels can be independently tuned by the varactor diodes utilised instead of perturbation and reference capacitances. Depending on the specialised values of perturbation and reference capacitances, filtering characteristics of both channels can be reconfigured in terms of transmission zeros. The designed diplexer was fabricated and tested for the experimental studies and the measurements were obtained in a good agreement with the predicted results. Tuning ranges of the measured centre frequency in the first channel are between 1.23 and 1.43 and 1.35 and 1.64 GHz for the filtering characteristics with right- and left-side transmission zeros, respectively. In the second channel, they are 2.07–2.31 and 2.14–2.51 GHz for the filtering characteristics with real- and imaginary-axis transmission zeros, respectively. Isolation between two channels has been obtained better than 22 dB.

Design of a compact microstrip quadruplexer with closely spaced switchable and tunable channels based on asymmetrical dual-mode loop resonators

In this letter, a switchable microstrip quadruplexer based on asymmetrical dual-mode loop resonators (ADMLRs) is presented. Four ADMLRs at different electrical lengths for creating four channels are coupled to input/output (I/O) ports by means of thin film capacitors. Each resonator has two patch elements behaving as reference capacitors that are needed for switching process. In order to achieve the switching ability, varactor diodes are employed to provide variable capacitances at each resonator. Thus, all channels can be independently switched on/off by changing the capacitances of the varactor diodes. Moreover, all channels have fine bandwidth tuning mechanism depending on the capacitance changes. The designed quadruplexer was fabricated and the measurements were observed in a good agreement with the predicted results. Center frequencies of the proposed quadruplexer are adjusted to 1.8, 2.1, 2.4, and 2.7 GHz with the frequency ratios between the adjacent channels of 1.17, 1.14, and 1.13. Isolations between the outputs have been observed as better than 28 dB.

Multivariable generalised predictive control with measurement noise rejection and speed ripple mitigation for PMSM drives

Generalised predictive control (GPC) is known for its good dynamic performance and long prediction horizon, but the performance can be severely deteriorated when measurement noises exist due to the wide control bandwidth of GPC. Meanwhile, the unmodelled periodic disturbances can cause ripples to the output variables. In this study, a practical permanent magnet synchronous motor (PMSM) drive system with speed measurement noise and periodic disturbances is considered, for which a novel multivariable GPC method is proposed to achieve both good dynamic performance and speed ripple mitigation. The proposed method has a simple structure, since the traditional cascaded speed and current control loops are replaced by a non-cascaded one. To reject the measurement noise without jeopardising the system stability, an internal low-pass filter is embedded in the GPC. Meanwhile, external resonant loops are added to the GPC to mitigate the low-order speed ripples caused by the periodic disturbances. Furthermore, a deadbeat-based current constraint method is proposed to avoid overcurrent during transient processes. Theoretical stability analysis of the proposed method is presented. Experimental results show that the proposed method has good steady-state and dynamic performances, including measurement noise rejection and speed ripple mitigation.

Compact Frequency and Bandwidth Reconfigurable Microwave Filter

This paper details the construction and working of a compound reconfigurable filter capable of frequency and bandwidth reconfiguration in the frequency range from 2 to 3 GHz. The switching between frequency and bandwidth reconfiguration is inherited by two PIN diodes. Bandwidth tuning is facilitated by tuning two transmission zeros individually using varactor diodes, giving flexibility in reconfiguring the upper and lower pass edges. The two transmission zeros are obtained using simple concentric square loop resonators. The maximum bandwidth obtained is 1.5 times the minimum bandwidth offered by the filter. Hence the filter can be used for dynamic bandwidth allocation. This prototype is fabricated and validated in real-time. The simulated and measured results are analogous to each other.

Common‐ground non‐isolated high‐gain DC/DC converter for low powerdistributed generation photovoltaic systems

A high step-up/high-efficiency converter is one of the essential requirements of a low power grid-connected photovoltaic system that provides the maximum power point tracking ability and injects the low voltage extracted power to AC or DC distribution network. This study presents a common-ground non-isolated high-gain DC/DC converter whit a naturally wide range of soft-switching conditions. The proposed converter has two resonant loops, and a new simple structure consists of an active switch, three diodes, two inductors and two capacitors, work in two useful operation modes. In the optimum operation mode (OOM), the switch turns on/off in zero current switching (ZCS)/zero voltage switching condition, and at the sub-OOM, the switch turns on in ZCS condition and turns off in hard switching condition. The mathematical analysis and MATLAB/SIMULINK simulation results are described in detail. Also, a prototype 100 W converter is built and tested to validate the simulation analysis on a 100 W photovoltaic panel.

(INVITED) Fiber loop resonator sensor achieved by high-scattering MgO nanoparticle-doped fibers

A Sagnac loop-based fiber sensor has been built using a special MgO-based nanoparticle doped fiber. The fiber presents a backscattering of 39.5 dB higher with respect to a standard SMF-28 telecom fiber. The backscattering properties of the fiber, combined with a locally stable polarization pattern, have fostered a clear interferometer pattern in middle point of the loop, presenting a backscattering peak roughly 78 dB higher with respect to a standard SMF-28 telecom fiber. The interferometer spectrum, showing a noisy nature given by the presence of the NP-doped fiber element, is clearly detectable. The loop-based sensor has been investigated by changing temperature and strain. The interferometer spectrum shows a shift, detectable with peak tracking and/or correlation method, toward the longer wavelength when temperature and applied strain increase. The measured coefficient of temperature and strain are respectively 1.75 p.m./°C and 1.93 p.m./με. This system shows interesting perspective for combining different optical fiber devices, in order to achieve simultaneous detection and discrimination of temperature and strain.

Simultaneous measurement of temperature and refractive index using microfiber knot resonators in Hi-Bi fiber loop mirrors

Based on the large evanescent field of microfibers, a novel fiber sensor using a microfiber knot resonator embedded in a Hi-Bi fiber loop mirror is proposed for simultaneous measurement of the temperature and refractive index of solutions. Due to the different responses of the microfiber knot resonator and fiber loop mirror to temperature and refractive index variations, the fiber sensor can measure temperature and refractive index simultaneously by utilizing the sensitivity matrix. The experimental measurements show that the sensitivities of the microfiber knot resonator and the fiber loop mirror to temperature are 5.6 pm/°C and −464.1 pm/°C, respectively. The sensitivity of the microfiber knot resonator to the refractive index of dilute solutions is 116 nm/RIU. The sensor has a higher sensitivity to refractive index variations than LPGs and has potential for use in the field of biochemistry.

Compact and wideband microwave bandstop filter for wireless applications

Compact, tunable and wide band stop filter (BSF) for wireless application is presented. The proposed filter is composed of compact rectangular microstrip open loop resonator with stub loaded resonator as building blocks of the filter. First, two vertical lumped capacitors are inserted in the open loop resonator from top to bottom of the substrate at the place which has maximum electric field to decrease the resonance frequency which in turn miniaturize the filter size. The resonance frequency of the fundamental mode is shifted from 5.5 to 4.2 GHz when lumped capacitors of 0.2 pF are added. Second, the capacitance of the open-ended stub can be changed to control the second resonance mode of the filter. Also, by inserting another vertical capacitor at the end of the open-ended stub, the second resonance mode can be controlled and reduced. Finally, by properly selecting the capacitance of the third lumped capacitor, the second resonance mode can be designed to be close to the fundamental mode and hence wide band stop filter can be achieved. The proposed BSF has some appropriate features such as compact size (its size has more than 40% size reduction), wide stopband and most importantly tunability of stopband. The band stop filter has a center frequency of 6.2 GHz, a stop band from 3.5 to 9 GHz, insertion loss lower than − 30 dB, and a return loss higher than 0.4 dB is accomplished inside the stop band. The measured results have good matching with the simulated results.

Two-Phase Interleaved Boost Converter with ZVT Turn-On for Main Switches and ZCS Turn-Off for Auxiliary Switches Based on One Resonant Loop

A two-phase interleaved boost converter with soft switching is proposed herein. By means of only one auxiliary circuit with two auxiliary switches having zero-current switching (ZCS) turn-on, two main switches are switched on with zero-voltage transition (ZVT) to enhance the overall efficiency. Moreover, a current-balancing circuit with a no current-balancing bus is utilized to render the load current extracted from the two phases as even as possible, so that the system stability is upgraded. In such a study, this converter, having the input of 24 V ± 10 % and the rated output of 36V/6A, was employed to demonstrate the effectiveness of such a converter by experiment.