Microwave Ring Resonator Research Articles

Valley Pseudospin Polarized Evanescent Coupling between Microwave Ring Resonator and Waveguide in Phononic Topological Insulators.

A coupled ring-waveguide structure is at the core of bosonic wave-based information processing systems, enabling advanced wave manipulations such as filtering, routing, and multiplexing. However, its miniaturization is challenging due to momentum conservation issues in rings with larger curvature that induce significant backscattering and radiation leakage and hampering stable operation. Here, we address it by taking an alternative approach of using topological technology in wavelength-scale and microwave ring-waveguide coupled systems built in nanoengineered phononic crystals. Our approach, which leverages pseudospin conservation in valley topological systems, eliminates phonon backscattering and achieves directional evanescent coupling. The resultant hypersonic waves in the tiny ring exhibit robust transport and resonant circulation. Furthermore, the ring-waveguide hybridization enables critical coupling, where valley-dependent ring-waveguide interference blocks the transmission. Our findings reveal the capability of topological phenomena for managing ultrahigh-frequency phonons in nano/microscale structures and pave the way for advanced phononic circuits in classical and quantum signal processing applications.

Use of transmission and reflection complex time delays to reveal scattering matrix poles and zeros: Example of the ring graph.

We identify the poles and zeros of the scattering matrix of a simple quantum graph by means of systematic measurement and analysis of Wigner, transmission, and reflection complex time delays. We examine the ring graph because it displays both shape and Feshbach resonances, the latter of which arises from an embedded eigenstate on the real frequency axis. Our analysis provides a unified understanding of the so-called shape, Feshbach, electromagnetically induced transparency, and Fano resonances on the basis of the distribution of poles and zeros of the scattering matrix in the complex frequency plane. It also provides a first-principles understanding of sharp resonant scattering features and associated large time delay in a variety of practical devices, including photonic microring resonators, microwave ring resonators, and mesoscopic ring-shaped conductor devices. Our analysis involves use of the reflection time difference, as well as a comprehensive use of complex time delay, to analyze experimental scattering data.

T-shaped double-strip spoof surface plasmon polariton transmission lines and application to microwave resonators

A microwave double-strip spoof surface plasmon polariton (DS SSPP) is proposed for high-speed interconnects and high-performance microwave circuits. Based on the dispersion analysis, a T-shaped double-strip structure is designed to provide strong surface- and slow-wave properties from very low to very high frequencies (~ 40 GHz). It allows the tight field confinement and greatly reduces the electromagnetic wave leakage. It exhibits broadband performance with reduced ripples in the insertion loss. It also shows more constant group delay and impedance than counterpart single-strip SSPP. The compact coaxial-to-microstrip-to-DS SSPP transition are designed using gradient grooves. The measurement shows that the DS SSPP lines can exhibit the lower coupling and lower insertion loss than the microstrip lines, so that the former is well-suited for the densely packed high-speed interconnects. The designed DS SSPP is utilized for high quality (Q)-factor microwave ring resonator. The measured unloaded Q-factor is 107.9 at the resonant frequency of 8.7 GHz, which is 1.3 times higher than the microstrip ring resonator. It is found to be caused by the reduction of the radiation loss, according to the loss analysis. The size is also reduced due to the short wavelength, occupying 56.8% of that of the microstrip ring resonator. Therefore, the proposed T-shaped DS SSPP can be also applied for high-performance miniaturized microwave circuits.

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.

A planar microwave resonator with odd resonance for calibration in permanent moisture sensing applications

A cylindrical dual-mode planar microwave ring resonator for a permanent moisture sensor is presented. The ring is design for TMn10 fundamental (odd-mode) resonance, and optimized to sustain stability (suitable for calibration reference against environmental interference) using Ansys high-frequency structure simulator. An even-mode resonance is perturbed by etching a step-impedance stub on the upper 0.5λ ring. The equations for the TMn10 mode resonance and its mode splitting are stated. The equivalent circuits of the ring, odd-, and even-modes are derived. The even-mode is set to capture the response of the permanent moisture withholding hydrophilic polyvinyl alcohol (PVA)–polyaniline (PANI) 0.26 mm-thick films. The in-lab made films are produced by infusing certain concentrations of PANI into pure PVA. On-spot measurements using a vector network analyzer (VNA) and time-based continuous data acquisitions using LabVIEW on NI PXIe–1075 VNA are done to confirm repeatability of the obtained results. A measured permanent moisture response of 180 MHz is confirmed for 50% PANI with a thickness (hfilm) of 0.55 mm. The sources of permanent moisture withholding capability of the films are investigated. Structural observation of the residue films, its permittivity changes, and morphological structural imagery confirmed the sources of permanent response.

Passive Microwave Biosensor for Real-Time Monitoring of Subsurface Bacterial Growth.

A real-time and label-free microstrip sensor capable of detecting and monitoring subsurface growth of Escherichia coli (E. coli) on solid growth media such as Luria-Bertani (LB) agar is presented. The microwave ring resonator was designed to operate at 1.76GHz to detect variations in the dielectric properties such as permittivity and loss tangent to monitor bacterial growth. The sensor demonstrated high efficiency in monitoring subsurface dynamics of E. coli growth between two layers of LB agar. The resonant amplitude variations (Δ Amplitude (dB)) were recorded for different volumes of E. coli (3μL and 9μL) and compared to control without E. coli for 36 hours. The control showed a maximum amplitude variation of 0.037dB, which was selected as a threshold to distinguish between the presence and absence of E. coli growth. The measured results by sensors were further supported by microscopic images. It is worth noticing that the amplitude variations fit well with the Gompertz growth model. The rate of amplitude change correlating bacteria growth rate was calculated as 0.08 and 0.13dB/hr. for 3μL and 9μL of E. coli, respectively. This work is a proof of concept to demonstrate the capability of microwave sensors to detect and monitor subsurface bacterial growth.

Enhancement of microwave ring resonator based on poly-lactic acid thermoplastic substrate

In this paper, the development of a single-port microwave ring resonator (MRR) sensor based on a thermoplastic material, which is poly-lactic acid (PLA), is presented. The open-ended coaxial probe method was applied to identify the dielectric properties of PLA in terms of dielectric constant (2.25) and loss tangent (0.0001). The PLA substrate was fabricated using a hot press machine and with the same thickness (1.6 mm) as FR4. Hence, to consider the PLA as microwave substrate, microwave ring resonator (MRR) operating at 1.1 GHz resonance frequency was designed, simulated, and measured. Based on the observation, the return loss of MRR for the simulation and the measurement of the conventional design are -5.37 dB and -5.02 dB, respectively. The quality factor (Q-factor) for both are 122.22 and 183.33, respectively. Then, the enhanced coupling gap method was applied to improve the performance of MRR sensitivity in terms of return loss and Q-factor. It is observed that the return loss of the enhanced design for the simulation and the measurement are -26.67 dB and -20.23 dB, respectively, and the Q-factor are 122.22 and 200, respectively. Thus, the performance of the MRR based on different designs were compared in order to validate the sensor’s sensitivity and PLA can be recognized as a substrate material for RF and microwave applications.

Aerosol Jet Printed, Microwave Microstrip Ring Resonators for System-In-Package Applications

This article presents the design, simulation, and fabrication of printed microstrip transmission line (TL) and microwave ring resonators using aerosol-jet printing for system-in-package applications. The printed TLs are 8 mm long and their S-parameters are measured over a wide bandwidth ranging from 1 to 26 GHz. Their insertion loss ranges between 0.02 dB/mm at 1 GHz and 0.56 dB/mm at 26 GHz. Ring resonators were designed and printed to operate at center frequencies of 15.5, 17.5, 19.5, and 21.5 GHz by tuning the size of the ring. Variability studies are carried out to evaluate the ability of the printing process to fabricate reproducible devices. The coupling gap is optimized in order to minimize the insertion loss in the ring resonators without compromising $Q$ -factor. The simulations show good agreement with the experimental results. The ability to print both conductors as well as dielectrics for the fabrication of microwave resonators demonstrate the potential for in-package integration of RF resonators for low-cost sensor applications.

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 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.

Amplitude and phase modulation in microwave ring resonators by doped CVD graphene

In this paper, we numerically and experimentally demonstrate how to modulate the amplitude and phase of a microwave ring resonator by means of few-layers chemical vapour deposition graphene. In particular, both numerical and experimental results show a modulation of about 10 dB and a 90 degrees-shift (quadrature phase shift) when the graphene sheet-resistance is varied. These findings prove once again that graphene could be efficiently exploited for the dynamically tuning and modulation of microwave devices fostering the realization of (i) innovative beam-steering and beam-forming systems and (ii) graphene-based sensors.

Improved microwave biosensor for non-invasive dielectric characterization of biological tissues

Microwave planar sensors have a great interest in the medical environment due to their ability to measure the bulk dielectric parameters of biological tissues through non-invasive and contact-less sensing properties. Changes of these parameters, which are frequency dependent, can be representative of the pathological state of biological tissues. In this work, an improved prototype of planar sensor based on a microwave ring resonator operating at 1 GHz for the fundamental mode is presented. The objective is to obtain a better sensitivity for measuring high complex permittivity values of materials such as biological tissues, and to obtain higher precision in parameters determination. The performances of two sensors optimized on two different substrates were measured in a frequency range 1–10 GHz; an accurate equivalent electrical model is proposed to reproduce the frequency dependence of the resonators. Characterization of liquids and ex-vivo animal tissues is achieved to evaluate the effectiveness and the performances of the resonator sensor, and results are compared with electromagnetic simulations.

A Microwave Ring Resonator Sensor for Early Detection of Breaches in Pipeline Coatings

A planar microwave resonator sensor is designed, customized, and fabricated to detect coating breaches in industrial steel pipelines. The sensor, which utilizes a ring-shaped resonator to maximize the sensitivity at its core, is tuned to 2.5 GHz with a quality factor of 280. In the setup, the sensor is grounded to a piece of steel pipeline with an Epoxy-100 coating, which provides the substrate beneath the microstrip structure. It is demonstrated that any change in the gap height between the substrate layer and the pipeline, from 0 to 3.5 mm, produces a significant resonant frequency variation and bandwidth change in the sensor's response. The sensor structure demonstrates sensitivity and selectivity to air and water penetration to the breach. The sensor structure described in this work is a compact, low-cost solution and has potential for further miniaturization in mobile applications which may serve as a method for pipeline breach detection.

Dielectric analysis of liquid solvents using microwave resonator sensor for high efficiency measurement

ABSTRACTA microwave ring resonator sensor has been practically applied as a micro‐volume sensor dedicated to solvent characterization with perspectives for chemical substances. The tested microliter range liquid solution is placed on capillary glass which is a compatible medium for planar sensor integration. The electrical response between electric field and solvent is converted into a predictable relationship between dielectric properties and the relative permittivity of the solution. A compact split ring resonator has been fabricated and tested with several common solvents on trace amount of volume. The result achieved recorded a very high Q factor of 525 making it practically suitable for beverages industry application. Good agreement has been achieved between the theoretical, simulation, and parameters measurement where the measurement errors of the complex permittivity is less than 0.5%, validating the concept of the accurate characterization theory using planar sensor. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:367–371, 2017

A Microwave Ring-Resonator Sensor for Non-Invasive Assessment of Meat Aging.

The assessment of moisture loss from meat during the aging period is a critical issue for the meat industry. In this article, a non-invasive microwave ring-resonator sensor is presented to evaluate the moisture content, or more precisely water holding capacity (WHC) of broiler meat over a four-week period. The developed sensor has shown significant changes in its resonance frequency and return loss due to reduction in WHC in the studied duration. The obtained results are also confirmed by physical measurements. Further, these results are evaluated using the Fricke model, which provides a good fit for electric circuit components in biological tissue. Significant changes were observed in membrane integrity, where the corresponding capacitance decreases 30% in the early aging (0D-7D) period. Similarly, the losses associated with intracellular and extracellular fluids exhibit changed up to 42% and 53%, respectively. Ultimately, empirical polynomial models are developed to predict the electrical component values for a better understanding of aging effects. The measured and calculated values are found to be in good agreement.

A Microwave Ring Resonator Based Glucose Sensor

A microwave ring resonator based glucose detecting biosensor incorporating glucose oxidase enzyme is presented. Sensor uses a split ring resonator as a transducer, where the sensing operation is done by the observation of shifts in its resonant frequency. Resonator was fabricated with basic fabrication techniques and the enzyme was immobilized via conductive polymer agent PEDOT:PSS. Experimentally observed redshift of resonant frequency of the sensor in response to different loading conditions are in agreement with simulation results and theoretical expectations. Sensor selectivity is confirmed with control experiments conducted with NaCl solutions. Experiments done with different glucose solution concentrations yielded a sensor sensitivity of 0.174MHz/mgml-1.

Time-Resolved Microwave Photoconductivity (TRMC) Using Planar Microwave Resonators: Application to the Study of Long-Lived Charge Pairs in Photoexcited Titania Nanotube Arrays

Steady-state (SRMC) and time-resolved microwave photoconductivity (TRMC) are key techniques used to perform the contact-less determination of carrier density, transport, trapping, and recombination parameters in charge transport materials such as organic semiconductors and dyes, inorganic semiconductors, and metal–insulator composites, which find use in conductive inks, thin film transistors, light-emitting diodes, photocatalysts, and photovoltaics. We present the theory, design, simulation, and fabrication of a planar microwave ring resonator operating at 5.25 GHz with a quality factor of 224, to perform SRMC and TRMC measurements. Our method consists of measuring the resonance frequency (f0) and Q-factor of the microwave resonator with the sample to be probed placed in a defined sensitive region of the resonator where the microwave field is highly concentrated. We also provide proof of concept measurements of the time-resolved microwave photoresponse of anatase-phase TiO2 nanotube array membranes (TNTAM...

Vector Finite Elements and the Step by Step Eigenvalue Perturbation Methods

The electromagnetic resonant structures and their perturbations have been found their way in many applications in microwave engineering. Analysis of these structures using finite element method results in a generalized eigenvalue problem, where the eigenvalues correspond to the resonant frequencies, and the eigenvectors correspond to the resonant modes. The perturbations of resonant structures yield perturbed eigenvalue problem and can be solved by eigenvalue perturbation methods, effectively. Combining finite element method with step by step eigenvalue perturbation method yields parametric history with respect to perturbation parameter. In this study perturbation of a microwave ring resonator placed in a metalic enclosure has been examined, combining the vector finite element and the step-by-step generalized eigenvalue perturbation methods.

Low-power photonic control of a microwave ring resonator using bulk illumination

We demonstrate the feasibility of bulk illumination technique for low-power photonic control of RF resonance.Using this technique, the transmitted RF power through a microstripline-ring filter on a junction-less silicon substrate is changed by 11 dB with less than 2 mW of interacting optical power. © 2013 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:1594–1599, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.27606