Planar Ring Resonator Research Articles

Switchable VO₂ Metamaterial Based on Planar and Vertical Split Ring Resonators for High-Performance Sensing

Switchable VO₂ Metamaterial Based on Planar and Vertical Split Ring Resonators for High-Performance Sensing

A Microwave Voyage into Swelling Phenomenon: Investigation of Polydimethylsiloxane and VOCs Interaction.

When exposed to specific gases, polymers undergo swelling, leading to physiochemical changes that can significantly affect their performance. Monitoring this swelling phenomenon requires innovative approaches. This study focuses on investigating the real-time resonant microwave behavior of two polydimethylsiloxane (PDMS) structures (solid and porous) in interaction with tetrahydrofuran (THF) and acetone, which are primary swelling agents. A microwave measurement method is proposed using an 8.63 GHz planar split ring resonator (SRR). The device's resonant frequency downshifts to 7.75 and 8.42 GHz when solid and porous PDMS blocks are placed on the split ring gap. Interaction of the solid PDMS and porous PDMS with target gases caused a change in PDMS structure resulting in alterations in the dielectric properties of the PDMS/gas system, as evidenced by the resonator's transmission amplitude and resonant frequency shifts. The magnitude of these shifts depends on the type and concentration of the solvent gas. The PDMS-integrated SRR exhibits a sensitivity of 25.3 MHz/1 ppt THF and 7 MHz/1 ppt acetone. Additionally, the solid block demonstrates response times of 6800 and 4200 s for swelling and deswelling, respectively, when in exposure to 25 ppt concentrations of THF and acetone. Overall, this study underscores the substantial potential of microwave resonators as versatile tools for investigating the physical changes in polymers during their interaction with gases, contributing to the understanding of polymer-gas interactions and opening avenues for further research and diverse applications.

Investigating the thickness-effect of free-standing high aspect-ratio TiO2 nanotube layers on microwave-photoresponse using planar microwave resonators

One-dimensional TiO2 nanotube (TNT) layers are a promising candidate for UV detection due to their distinctive anisotropic geometry which is effective for light harvesting and rapid carrier transport. Here, the photosensitivity efficiency of TNT layers with various thicknesses of 15, 50, 80, and 110 µm was utilized at a microwave frequency regime by modeling and experimentally. A planar microwave split ring resonator (PMSRR) was designed and fabricated to operate at ∼8 GHz to study TNT layers by monitoring the scattering parameter (S21) of the PMSRR under a constant UV irradiation power of ∼96.4 µW/cm2. According to the results, the 80 µm thick TNT layers demonstrated the highest resonant amplitude variation for the customized PMSRR. The change of the resonant amplitude was mainly attributed to the conductivity variation contributed by perturbation of trapped electron concentration, as the dominant factor under UV illumination, and their electromagnetic wave interaction. The main advantage of the proposed method of PMSRR for microwave photosensitivity monitoring over the conventional direct current (DC) conductivity measurements is to eliminate the effect of contact resistance between the TNT layers and metal electrodes utilizing the contactless aspect of wave interactions with the TNT layers at microwave regime to perform electrode-less measurements.

A New Varactor-Tuned 5.8 GHz Dielectric Resonator Band-Stop Filter for ITS and C-V2X Coexistence with Vehicular DSRC

In this paper, we introduce an electronically tuneable band-stop filter based on a dielectric resonator, along with its design principles and equivalent circuit model aimed at the coexistence of intelligent transport systems (ITS) and cellular vehicle-to-everything (C-V2X) communications operating at 5.9 GHz, with the widely spread vehicular dedicated short range communications (DSRC) at 5.8 GHz. The proposed architecture involves a dielectric resonator coupled via a microstrip transmission line to a planar ring resonator. The resonance is electronically tuned by varying the bias voltage of a varactor diode placed in the ring. This design is analyzed theoretically and experimentally. For validation, a filter operating at 5.8 GHz was designed. The prototype is capable of enhancing coexistence exhibiting to features. First, when inserted into the ITS transmitter chain, it reduces unwanted transmitter emissions in the out-of-band spectrum occupied by the DSRC carriers in the 5.8 GHz frequency band of at least 25 dB, with a minimal insertion loss at 5. 9 GHz of 1.6 dB; secondly, when inserted in the ITS receiver chain, it exhibits high linearity that prevents the generation of intermodulation products falling into the filter pass band. The prototype features more than 21 dBm of third-order input intercept points, and a tuning range of 26 MHz while maintaining a minimal loaded Q factor of 93. The prototype is discussed regarding the detailed equivalent circuit parameter extraction and their dependency upon the control voltage.

A Low-Cost Microwave Microfluidic Sensor based on Planar Ring Resonator

A Low-Cost Microwave Microfluidic Sensor based on Planar Ring Resonator

Planar Optofluidic Integration of Ring Resonator and Microfluidic Channels.

We report an optofluidic hybrid silicon-polymer planar ring resonator with integrated microfluidic channels for efficient liquid delivery. The device features a planar architecture of intersecting liquid-core waveguides and microfluidic channels. A low-loss integration of microfluidic channels is accomplished by exploiting the interference pattern created by the self-imaging effect in the multimode interference-based coupler waveguides. Numerical simulations have been performed in order to minimize the propagation losses along the ring loop caused by the integration of microfluidic channels. The device has been fabricated and optically characterized by measuring the quality factor, obtaining a value of 4 × 103. This result is comparable with the quality factor of an optofluidic ring with the same optical layout but without integrated microfluidic channels, thus, confirming the suitability of the proposed approach for microfluidics integration in planar optofluidic design.

Non-recovery moisture sensor for breach integrity using the degenerate mode of planar microwave ring resonator

A non-recovery moisture sensor (NMS) based on a planar-microwave resonator for breach integrity is presented. The NMS consists of a microwave ring transducer (MRT), a non-recovery hydrophilic film, and expected to be patterned in the infrastructures transporting the target content. Though PVA and PANI are organic polymers with switchable conductivity, they are incapable of withholding water indefinitely. As PVA conductivity permits switching between p-, n-type semiconductor states, and insulator; a certain concentration of PANI is infused. Because PANI exhibits an extra proton from an acid attached to the nitrogen group, the non-recovery change occurs as it accepts hydronium ions from water, and changes to a more conductive form. The concentration of the acidity results in the degree of permittivity variance. The MRT is configured to see the permittivity variance and convert it into electrical quantities.

Dual-band reflection polarization converter for circularly polarized waves based on a zigzag asymmetric split ring resonator

Polarization converters based on metasurfaces are one of the recently developed metadevices that can change the polarization state with designated modes, utilizing the sub-wavelength unit construction. In this paper, a kind of planar zigzag asymmetric split ring resonator (Z-ASRR) metasurface with dual bands is proposed to achieve nearly perfect polarization conversion for circularly polarized waves. Compared with the original prototype asymmetric resonant ring (ASRR), both magnitude and bandwidth have been remarkably improved for achieving a higher resonance, with the introduction of zigzag metallic wires. The reflection polarization conversion ratio possesses two peak values with 0.94 and 0.99 at 5.39 GHz and 9.65 GHz, respectively. It is also demonstrated that the introduction of extra gaps, which are closely linked with the multi-node standing wave characteristic, can control the number of resonant modes or modulate the relative bandwidth. Besides, an equivalent circuit model, the degree of zigzag bending, and the oblique incidence are further analyzed in detail. The experimental results agree well with the simulations, and this chiral metadevice could be applied for on-chip integration in an optical detection/laser, a chiral biosensor, and molecular spectroscopy.

Differential Microwave Resonator Sensor Reveals Glucose-Dependent Growth Profile of E. coli on Solid Agar

This letter presents a practical application of a differential microstrip microwave sensor for label-free and realtime monitoring of Escherichia coli (E. coli) growth under different nutritional conditions on solid agar media. Two planar microstrip ring resonators coupled with a one-port power divider form the core of the sensing system. The sensing resonator operates at 1.509 GHz with an amplitude of -10.21 dB and the reference resonator operates at 1.798 GHz with an amplitude of -11.75 dB. The growth profile of E. coli at each glucose concentration in Luria-Bertani (LB) agar was derived by measuring the resonant amplitude variations (AA) and is further supported by microscopic images. A complete inhibition of growth was observed at 10% glucose concentration. This research expands the application of microwave sensors to investigate the effect of nutritional parameters on bacterial growth.

Planar microwave resonator with electrodeposited ZnO thin film for ultraviolet detection

A ZnO thin film is electrodeposited on the conducting strips of a planar microwave ring resonator to enable the formation of a novel sensor for ultraviolet irradiation. The fabrication of the sensor involves a low-cost process that basically utilizes a printed circuit board and an aqueous precursor solution. The resonator with no ZnO coating operates with a resonant frequency of 6.2 GHz and a quality factor of 170. The time-resolved microwave photoresponse of the sensor to UV illumination, under ambient conditions, is assessed through measurements of the resonance profile of the S21 parameter. The resonance frequency exhibited a highly sensitive downshift of ∼6 MHz after a UV illumination time of ∼3 min. This downshift is mostly attributed to the change in the dielectric constant of the ZnO film caused largely by the additional creation of bound charges. The usually reported long-lived and persistent post-illumination effects were not observed. The measurements of the resonance amplitude carried out at 20% and 70% relative humidity levels revealed average excess carrier relaxation lifetimes of 213 s and 185 s, respectively. Concomitantly, the measured resonance frequency downshift increased with increased humidity. These results highlight the difference in the interaction mechanisms of photogenerated carriers with water and oxygen molecules on the surface and grain boundaries of the ZnO film. To our knowledge, this UV irradiation sensor is the first ZnO-based sensor device implemented with planar microwave circuit technology. In addition, the capabilities demonstrated by this simple photosensing method to determine induced carrier lifetimes make it a valuable technique for in-depth investigation of the material properties.

A Label-Free, Non-Intrusive, and Rapid Monitoring of Bacterial Growth on Solid Medium Using Microwave Biosensor.

Microwave resonator sensors are attractive for their contactless and label-free capability of monitoring bacterial growth in liquid media. This paper outlines a new label-free microwave biosensor based on a pair of planar split ring resonators for non-invasive monitoring of bacterial growth on a solid agar media. The sensor is comprised of two split ring resonators with slightly different resonant frequencies for differential operation. The transmission coefficient (S21) of the sensor is considered as the sensor's response with a designed and measured quality factor above 200 to ensure a high-resolution operation of the biosensor. Two resonant frequencies of 1.95 and 2.11 GHz represent the sensing signal and the reference signal, respectively. The developed sensor demonstrates high performance in monitoring the growth dynamics of Escherichia coli (E. coli) on Luria-Bertani (LB) agar with 4 mm thickness. The sensor's resonant amplitude response demonstrated 0.5 dB variation corresponding to the bacterial growth over 48 hours when bacteria were spread on LB agar starting with initial OD600 = 1.5. Moreover, 0.6 dB change in the sensor's response was observed over 96 hours of bacterial growth starting with an initial OD600 = 1.17 spotted on LB agar. The measured results fit well to the curves created using Richards' bacterial growth model, showing the strength of the sensor as a potential candidate for use in predictive food microbiology systems.

Miniaturised MIMO antenna array of two vertical monopoles embedded inside a planar decoupling network for the 2.4 GHz ISM band

This study introduces a fundamentally new approach to suppress mutual coupling among two closely-spaced vertical monopole elements of a multiple-input multiple-output antenna array. The 40 × 40 × 1.27 mm decoupling and matching element consists of a single planar ring resonator acting as a stop-band filter along with two tuning strips printed on an ungrounded substrate surrounding a two-element co-planar waveguide-fed monopoles separated by 8 mm ( λ 0 /16) at 2.45 GHz. Measurements reveal 14.2% bandwidth centred at 2.395 GHz over which the decoupling is below 20 dB, and -10-dB impedance bandwidth of 19.5% centred at 2.36 GHz. An improvement of 43 dB in isolation is observed at a frequency of 2.38 GHz. It is shown that the decoupled array provides a total realised gain of 1.69 dBi with excellent diversity performance as demonstrated by the low envelope correlation coefficient and improved link efficiency in highly-correlated channel environments due to the spatially orthogonal 3D radiation patterns. The capacity offered by the decoupled array is enhanced by 50, 22, 18 and 12% at signal-to-noise ratios of 5, 20, 30, and 50 dB, respectively, as compared to the coupled array in an urban micro-channel spatial model.

A Compact Microwave Device for Fracture Diagnosis of the Human Tibia

In this paper, a portable system for noninvasive detection of fractures in human bones is presented. A planar microwave ring resonator is used as the sensor. The proposed planar microwave sensor is designed using the finite integration-based CST Microwave Studio and tested on a human bone covered by porcine tissues. Fracture induced in the bone was detected by monitoring the transmission characteristics of the sensor as it scans the affected region. The resonant frequency of the ring resonator has been observed at every scan point, and the values are plotted using iterative curvature-based interpolation, improved new edge directed interpolation, and Lanczos imaging technique. The extent of fracture is then derived from the image. The average accuracy of the detected fracture for Lanczos method of resampling was 98.86%. The specific absorption rate was below the minimum level of 1.6 W/Kg at every point of scanning. Portable noninvasive monitoring of fractures in the tibial bone will help in immobilizing the affected part at an earlier stage, thereby reducing the recovery time for patients.

Determination of solid material permittivity using T-ring resonator for food industry

In this paper, we present a simple design of a T-ring resonator sensor for characterizing solid detection. The sensor is based on a planar microwave ring resonator and operating at 4.2 GHz frequency with a high-quality factor and sensitivity. An optimization of the T-ring geometry and materials were made to achieve high sensitivity for microwave material characterizations. This technique can determine the properties of solid materials from range of 2 GHz to 12 GHz frequencies. Techniques of current microwave resonator are usually measuring the properties of material at frequencies with a wide range; however, their accuracy is limited. Contrary to techniques that have a narrowband which is normally measuring the properties of materials to a high-accuracy with limitation to only a single frequency. This sensor has a capability of measuring the properties of materials at frequencies of wide range to a high-accuracy. A good agreement is achieved between the simulated results of the tested materials and the values of the manufacturer’s Data sheets. An empirical equation has been developed accordingly for the simulated results of the tested materials. Various standard materials have been tested for validation and verification of the sensor sensitivity. The proposed concept enables the detection and characterization of materials and it has miniaturized the size with low cost, reusable, reliable, and ease of design fabrication with using a small size of tested sample. It is inspiring a broader of interest in developing microwave planar sensors and improving their applications in food industry, quality control and biomedical materials.

Spoof Surface Plasmon Polariton-Based Reconfigurable Band-Pass Filter Using Planar Ring Resonator

In this paper, we report the design, analysis, and development of spoof surface plasmon polariton (SSPP)-based reconfigurable band-pass filter using a planar ring resonator. A transition from quasi-transverse electromagnetic (QTEM) mode of microstrip to SSPP mode was implemented which has been subsequently used to develop a reconfigurable band-pass filter. Trapezoidal shape periodically corrugated metallic grooves etched on the planar metallic surface have been used in the implementation of this transition. In the designed transition, impedance and mode matching between QTEM mode and SSPP mode have been achieved using gradient grooves. The developed transition has been used in the characterization of a ring resonator corrugated with the periodical array of the trapezoidal shape grooves. This SSPP ring resonator shows multiple passbands at different frequencies within the specified frequency range. Varactor diodes have been incorporated in the SSPP ring resonator to obtain tunable passband. Three types of varactor-tuned circuits have been experimentally implemented and characterized using SMV2019-079LF diode package. These circuits will pave the path for development of other front-end circuit elements using the concept of spoof SPP.

One-Way Rotating Photonic Crystal Ring Resonator With High Quality Factor

We propose a planar photonic crystal ring resonator consists of a looped single interface between a regular and a magneto-optical photonic crystal structure. The cavity modes are shown to possess the unidirectional rotation characteristics, and the rotating direction is determined by the direction of an externally applied magnetic field normal to the rotation plane. This unique unidirectional feature results in the realization of cavity with extremely high Q factor of 3.2 × 106, more than one order of magnitude higher than the previous report for cavity with the same ring size [Z. Qiang, W. Zhou, and R. A. Soref, “Optical add-drop filters based on photonic crystal ring resonators,” Opt. Exp ress , vol. 15, no. 4, pp. 1823–1831, Feb. 2007]. As an example of its applications, we present a unidirectional channel-drop filter design based on the one-way rotating photonic crystal ring resonator. Our simulation result shows that a 96.7% backward dropping efficiency can be achieved by this filter.

Miniaturization of Microwave Biosensor for Non-invasive Measurements of Materials and Biological Tissues

Non-invasive planar complementary split ring resonators (CSRRs) coupled to microstrip line for measuring the dielectric properties of materials and biological tissues are presented in this paper. The expectations of health professionals are increasingly turning to less invasive surgical procedures and treatments. In particular, the monitoring of vital parameters (sweat, water in the lungs, etc.) or the evolution of certain pathologies, such as cancer cells, could be observed regularly if suitable devices were developed and could especially replace traditional invasive method. Appropriate miniaturized RF or microwave devices could be an alternative for some medical diagnostic applications. These devices would make it possible to determine the dielectric characteristics of biological tissues, which represent their real pathological states. It would thus be possible, by means of dielectric contrast measurements, to follow the evolution of pathology as well as the vital parameters of a patient. The objective of this research is to produce a prototype biosensor that is suitable for measurements on biological tissues and that can be miniaturized to enhance its spatial sensitivity. This work focuses on the design, electromagnetic simulations and characterization of a new miniaturized biosensors operating between 1 and 10 GHz. The ex-vivo experimental results will be shown by measuring the S-parameters of various materials and animal biological tissues. The extraction of the dielectric parameters of these samples is obtained by the measurements of materials

Dual Active Resonator for Dispersion Coefficient Measurement of Asphaltene Nano-Particles

Dispersion and diffusion of Asphaltene particles in n-Heptane is measured to investigate the solution characteristics of different concentrations in wide range of 0.000625-0.625 (%wt). Planar split ring resonator (SRR) is armed with active circuitry (active resonator) to enhance the quality factor over 3 K to achieve ultra-high resolution sensing and track minute variations in microfluidic tube. Parallel SRRs as dual active resonator are performing independently, both in sensing and resolution, at 1.03 GHz (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> ) and 1.149 GHz (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> ) as the sensing tool in non-contact mode to monitor the spread of model oil (short pulse) in n-Heptane (continuous flow). With the frequency shifts (Δf <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> , Δf <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</sub> ), average flow rate, and the inner diameter of the tube, the molecular diffusion coefficient, and then the dispersion coefficient can be rapidly derived according to two-window solution of Taylor-Aris dispersion analysis. Samples with higher concentration of Asphaltene are shown to have faster spread and larger dispersion in the flow. Dispersion coefficients of the samples cover the range of 5.2-7 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-4</sup> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /s in great agreement with conventional methods.

Multi-band planar miniaturised negative-index metamaterials

In this paper, a miniaturised negative-index metamaterial (NIM) based on planar concentric split ring resonators was designed, simulated, fabricated and tested that can maintain NIM properties. The offered metamaterial structure showed miniaturisation factor compared with traditional metamaterial unit cells and conformed better effective medium ratio (EMR). Finite-difference time-domain method-based computer simulation technology for the numerical analyses and a vector network analyser (N5227A) was used for the measurements. The proposed metamaterial exhibited multi-band response in conjunction with the NIM property over the certain frequency bands in the microwave spectra and the EMR considerably improved compared to previously reported metamaterials. The measured results revealed good agreement with the simulated results. The distribution of surface current, electric field and equivalent circuit model were verified for the proposed structure. The size, scattering parameters and EMR parameters of the proposed miniaturised NIM is appropriate for multi-band applications.

Robust Ultra-High Resolution Microwave Planar Sensor Using Fuzzy Neural Network Approach

In this paper, we develop a robust and fault-tolerant approach to microwave-based sensitive measurements using fuzzy neural network (FNN). Microwave chemic-identification, recently, is employing active planar ring resonators to enhance the resolutions significantly. However, in practice, when the technology of resolution improves, the results become more prone to minor variations in the measurement setup and user error. In order to eliminate these unwanted and uncontrollable deviations from the final allocations, we propose a novel and robust approach that uses more than one parameter out of measurements and incorporates FNN as a machine learning architecture at the post processing stage of sensing to obtain fault-tolerant classification. We have compared different membership functions used in the FNN and shown improvement in assigning accuracy from 49% (single parameter-dependent) up to 81.5% (three parameters-dependent) on an average of four materials, such as isopropanol-2 (IPA), ethanol, acetone, and water.