Planar Microwave Resonator Research Articles

Low-loss millimeter-wave resonators with an improved coupling structure

Millimeter-wave superconducting resonators are a useful tool for studying quantum device coherence in a new frequency domain. However, improving resonators is difficult without a robust and reliable method for coupling millimeter-wave signals to 2D structures. We develop and characterize a tapered transition structure coupling a rectangular waveguide to a planar slotline waveguide with better than 0.5 dB efficiency over 14 GHz, and use it to measure ground-shielded resonators in the W band (75–110 GHz). Having decoupled the resonators from radiative losses, we consistently achieve single-photon quality factors above 105, with a two-level-system loss limit above 106, and verify the effectiveness of oxide removal treatments to reduce loss. These values are 4–5 times higher than those previously reported in the W band, and much closer to typical planar microwave resonators. The improved losses demonstrated by these on-chip millimeter-wave devices shed new light on quantum decoherence in a different frequency regime, offer increased selectivity for high-frequency detectors, and enables new possibilities for hybrid quantum experiments integrating millimeter-wave frequencies.

MAGNETIC CORE APPLICATION IN A PLANAR RESONATOR WITH A YTTRIUM IRON GARNET FILM FOR ENHANCING STRONG PHOTON-MAGNON COUPLING

Subject and Purpose. This paper presents numerical simulation results on the transmission spectra of a split-ring resonator (SRR) loaded with a thin film of yttrium iron garnet (YIG). The application of a magnetic core in the SRR is proposed for increasing the photon-magnon (P-M) coupling strength. The anticrossing effect in the frequency dispersion behavior of the SRR modes and YIG film ferromagnetic resonance modes, namely SRR-YIG coupled modes, is identified. The dimensional parameters of the SRR with a magnetic core are calculated, taking care to preserve the design compactness and striving to obtain a maximum possible spin-number-normalized coupling strength for such a system. The work has been aimed at evaluating the efficiency of applying the magnetic core as a part of the planar microwave resonator to enhance the P-M coupling strength. Methods and Methodology. The transmission coefficient |S21| spectra of electromagnetic waves propagating through the planar resonator with the YIG film under the ferromagnetic resonance condition are numerically studied using the CST Studio Suite package in the frequency domain. The spatial distribution function of the magnetic field strength is calculated for the two scenarios of YIG film location: near the magnetic core (between the SRR and the feeding stripline) and inside the magnetic core (in the SRR center). Also, for each of these two scenarios, the transmission coefficient |S21| spectra of the wave propagation through the feeding stripline in the region of SRR-YIG coupled modes are simulated with and without the magnetic core. The dispersion curves of the SRR-YIG coupled modes are obtained in analytical terms. Results. It has been shown that the magnetic core application increases the P-M coupling strength 2.0 times in the scenario of YIG film location near the magnetic core (between the SRR and the feeding stripline). When the YIG film is inside the magnetic core (in the SRR center), the P-M coupling strength rises 2.3 times compared to similar cases without the magnetic core. Conclusions. The suggested magnetic core application can be used to increase the P-M coupling strength in the SRR — magnetic film resonant system, striving to develop effective microwave-to-optical converters and create efficient information exchange between quantum computers.

Design of novel highly sensitive sensors for crack detection in metal surfaces: theoretical foundation and experimental validation

The application of different types of microwave resonators for sensing cracks in metallic structures has been subject of many studies. While most studies have been focused on improving the sensitivity of planar crack sensors, the theoretical foundation of the topic has not been treated in much detail. The major objective of this study is to perform an exhaustive study of the principles and theoretical foundations for crack sensing based on planar microwave resonators, especially defective ground structures (DGS) including complementary split ring resonators (CSRRs). The analysis is carried out from the equivalent circuit model as well as the electromagnetic (EM) field perspectives, and guidelines for the design of crack sensors with high sensitivity are developed. Numerical and experimental validation of the provided theoretical analysis is another aim of this article. With this aim, the developed guidelines are used to design a crack sensor based on a single-ring CSRR. It is shown that the sensitivity of the proposed sensor is almost three times higher than the sensitivity of a conventional double-ring CSRR. Moreover, it is demonstrated that folded dumbbell-shape DGS resonators can be used to achieve even higher sensitivities. The CSRR-based crack sensors presented in this study and other studies available in the literature are only sensitive to cracks with a specific orientation. To address this limitation, a modified version of the DGS is proposed to sense cracks with arbitrary orientations at the cost of lower sensitivity. The performance of all the presented sensors is validated through EM simulation, equivalent circuit model extraction, and measurement of the fabricated prototypes.

Detection of impact damage in glass fibre-reinforced polymer composites using a microwave planar resonator sensor

ABSTRACT A novel non-destructive testing scheme was proposed for the detection of impact damage in glass fibre-reinforced polymer (GFRP) composites using a microwave planar resonator sensor. The sensor offers the advantages of small size, low cost and simple structure. It is an open-circuited λ/2 long microstrip line and the detection principle is material perturbation. Electromagnetic simulation verifies the sensor design. A GFRP specimen subjected to 5,10 and 20 J impact was examined. The 20 J impact damage was detected through line and two-dimensional scanning. The line scanning enabled accurate localisation of the damage, whereas the two-dimensional scanning facilitated more precise reconstruction of the surface damage features in addition to localisation. The sensor performance for detecting impact damage with lower energy levels was investigated by line scanning. It was found that the sensor could detect and locate 10 J impact damage. Principal component analysis was introduced to significantly reduce the false detection of the 5 J impact damage. It is well demonstrated that the proposed scheme could serve as an alternative method.

Review of scientific instruments: Evaluation of adulteration in honey using a microwave planar resonator sensor.

A microwave microstrip line resonator sensor is developed as an alternative tool for detecting adulteration in honey. A honey-filled tube is placed at the position with the maximum electric field intensity. When the honey is adulterated, its permittivity is changed, leading to a distinct resonance frequency shift and enabling detection. Compared with the existing microwave sensors, this sensor offers the advantages of low cost, compact size, and easy fabrication. Moreover, quantitative analysis of the adulteration could be achieved. Electromagnetic simulation is performed using a co-simulation with CST and MATLAB. The simulation results reveal that the resonance frequency of the resonator decreases as the added water content increases, following a quadratic polynomial relationship. In the experiments, the results demonstrate a successive decrease in the resonance frequency from the empty tube, honey-filled tube to water-filled tube cases. Furthermore, honey samples with varying water contents (up to 70%) are tested, and the resonance frequency decreases with increasing added water content, which agrees well with the simulation results. In addition, there is a quadratic relationship between the two parameters. Principal component analysis is conducted on the transmission coefficients, and the first principal component decreases with increasing water content. With the addition of the second principal component, the cases of different water contents in honey can be well classified.

Sensitivity–Enhanced detection of acetone gas using MXene-Immobilized planar microwave sensor

This work presents the noncontact immobilization of Ti3C2Tx MXene on a planar microwave resonator sensor via a polyimide film to enhance the gas detection sensitivity, enabling the characterization of the part per million-level of acetone gas. Sandwiching a polyimide (PI) film confined an intense electromagnetic field between the resonator’s interdigital capacitor structure and the MXene layer, maintaining a significant interaction between the acetone gas molecules and the resonator’s EM field via the MXene layer. Therefore, contactless immobilization of the MXene layer enhanced the acetone gas detection sensitivity by 110% compared to the resonator gas sensor with MXene deposited directly on the resonator surface. As a proof of concept, two sensor prototypes were implemented using resonators with layers of PI film and MXene and resonators with MXene only and were applied to detect a wide range of acetone gas concentrations. Immobilizing the layers of PI film and MXene on the microwave resonator achieved a linear correlation between the resonant frequency and acetone gas concentration with high sensitivity (17.85 kHz/ppm, a fast response time (60 s), and recovery time (85 s).

Polarization singularities in planar electromagnetic resonators with rotation and mirror symmetries

In this work, we apply the group representation theory to systematically study polarization singularities in the in-plane components of the electric fields supported by a planar electromagnetic (EM) resonator with generic rotation and reflection symmetries. We reveal the intrinsic connections between the symmetries and the topological features, i.e., the spatial configuration of the in-plane fields and the associated polarization singularities. The connections are substantiated by a simple relation that links the topological charges of the singularities and the symmetries of the resonator. To verify, a microwave planar resonator with the D8 group symmetries is designed and numerically simulated, which demonstrates the theoretical findings well. Our discussions can be applied to generic EM resonators working in a wide EM spectrum, such as circular antenna arrays, microring resonators, and photonic quasi-crystals, and provide a unique symmetry perspective on many effects in singular optics and topological photonics.

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.

Gigahertz-Based Visible Light Detection Enabled via CdS-Coated TiO2 Nanotube Layers

Detection of visible light is a key component in material characterization techniques and often a key component of quality or purity control analyses for health and safety applications. Here in this work, to enable visible light detection at gigahertz frequencies, a planar microwave resonator is integrated with high aspect ratio TiO2 nanotube (TNT) layer-sensitized CdS coating using the atomic layer deposition (ALD) technique. This unique method of visible light detection with microwave-based sensing improves integration of the light detection devices with digital technology. The designed planar microwave resonator sensor was implemented and tested with resonant frequency between 8.2 and 8.4 GHz and a resonant amplitude between -15 and -25 dB, depending on the wavelength of the illuminated light illumination on the nanotubes. The ALD CdS coating sensitized the nanotubes in visible light up to ∼650 nm wavelengths, as characterized by visible spectroscopy. Furthermore, CdS-coated TNT layer integration with the planar resonator sensor allowed for development of a robust microwave sensing platform with improved sensitivity to green and red light (60 and 1300%, respectively) compared to the blank TNT layers. Moreover, the CdS coating of the TNT layer enhanced the sensor's response to light exposure and resulted in shorter recovery times once the light source was removed. Despite having a CdS coating, the sensor was capable of detecting blue and UV light; however, refining the sensitizing layer could potentially enhance its sensitivity to specific wavelengths of light in certain applications.

Variable bandwidth, high efficiency microwave resonator for control of spin-qubits in nitrogen-vacancy centers.

Nitrogen-Vacancy (NV) centers in diamond are attractive tools for sensing and quantum information. Realization of this potential requires effective tools for controlling the spin degree of freedom by microwave (mw) magnetic fields. In this work, we present a planar microwave resonator optimized for microwave-optical double resonance experiments on single NV centers in diamond. It consists of a piece of wide microstrip line, which is symmetrically connected to two 50Ω microstrip feed lines. In the center of the resonator, an Ω-shaped loop focuses the current and the mw magnetic field. It generates a relatively homogeneous magnetic field over a volume of 0.07 × 0.1mm3. It can be operated at 2.9GHz in both transmission and reflection modes with bandwidths of 1000 and 400MHz, respectively. The high power-to-magnetic field conversion efficiency allows us to produce π-pulses with a duration of 50ns with only about 200 and 50 mW microwave power in transmission and reflection, respectively. The transmission mode also offers capability for efficient radio frequency excitation. The resonance frequency can be tuned between 1.3 and 6GHz by adjusting the length of the resonator. This will be useful for experiments on NV-centers at higher external magnetic fields and on different types of optically active spin centers.

On the Selectivity of Planar Microwave Glucose Sensors with Multicomponent Solutions

The development of glucose concentration sensors by means of microwave planar resonant technology is an active field attracting considerable attention from the scientific community. Although showing promising results, the current experimental sensors are facing some fundamental challenges. Among them, the most critical one seems to be the selectivity of glucose concentration against the variations of the concentrations of other components or parameters. In this article, we investigate the selectivity of microwave planar resonant sensors when measuring multicomponent solutions. Three sensors are involved, two of them having been designed looking for a more simplified system with a reduced size, and the third one has been specially developed to improve the sensitivity. The performance of these sensors is thoroughly assessed with a large set of measurements involving multicomponent solutions composed of pure water, NaCl, albumin at different concentrations and glucose at different concentrations. The impact of the simultaneous variations of the concentrations of glucose and albumin on the final measurements is analyzed, and the effective selectivity of the sensors is discussed. The results show a clear influence of the albumin concentration on the measurements of the glucose concentration, thereby pointing to a lack of selectivity for all sensors. This influence has been modeled, and strategies to manage this selectivity challenge are inferred.

Coherent spin dynamics of rare-earth doped crystals in the high-cooperativity regime

Rare-earth doped crystals have long coherence times and the potential to provide quantum interfaces between microwave and optical photons. Such applications benefit from a high cooperativity between the spin ensemble and a microwave cavity---this motivates an increase in the rare-earth ion concentration which in turn impacts the spin coherence lifetime. We measure spin dynamics of two rare-earth spin species, $^{145}\mathrm{Nd}$ and Yb, doped into ${\mathrm{Y}}_{\text{2}}{\mathrm{SiO}}_{\text{5}}$, coupled to a planar microwave resonator in the high-cooperativity regime, in the temperature range $1.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ to $14\phantom{\rule{0.16em}{0ex}}\mathrm{mK}$. We identify relevant decoherence mechanisms, including instantaneous diffusion arising from resonant spins and temperature-dependent spectral diffusion from impurity electron and nuclear spins in the environment. We explore two methods to mitigate the effects of spectral diffusion in the Yb system in the low-temperature limit, first, using magnetic fields of up to 1 T to suppress impurity spin dynamics and, second, using transitions with low effective $g$ factors to reduce sensitivity to such dynamics. Finally, we demonstrate how the ``clock transition'' present in the $^{171}\mathrm{Yb}$ system at zero field can be used to increase coherence times up to ${T}_{2}=6(1)\phantom{\rule{0.16em}{0ex}}\mathrm{ms}$.

Microwave Sensor Loaded With Complementary Curved Ring Resonator for Material Permittivity Detection

In the field of microwave measurement, how to miniaturize devices and improve measurement sensitivity is a major challenge. In this article, a planar microwave sensor loaded with a complementary curved ring resonator (CCRR) is proposed to measure the permittivity of substrate materials. The current forms a magnetic field along the path of the curved ring, which acts on the capacitance between the rings of the curved ring and makes the circuit resonate. At this time, the curved ring structure stores a huge amount of energy. When the substrate materials with different permittivity are loaded into the measurement area of the sensor, the resonant frequency of the sensor will change. By establishing a mathematical model between the permittivity and the resonant frequency and conducting a full-wave electromagnetic simulation, it can be seen that the CCRR combined with the substrate integrated waveguide (SIW) structure can effectively enhance the electric field intensity in the measured region. Compared with the conventional planar microwave resonator. The sensitivity, resolution, and size of the proposed sensor are 3.51%, 133 MHz, and 52 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 34 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula> 0.508 mm3, respectively. After optimizing the structural parameters of the sensor, the actual sensor was manufactured. Four kinds of substrate materials commonly used in microwave circuits are used as samples to test the sensor. The results show that the sensor has the characteristics of high sensitivity, high resolution, and high measurement accuracy, which confirms the promising application of the sensor in the field of permittivity measurement.

Non-Invasive Lactate Monitoring System Using Wearable Chipless Microwave Sensors With Enhanced Sensitivity and Zero Power Consumption.

Monitoring lactate levels is an established method for determining hyperlactatemia in critically ill patients and assessing aerobic fitness. It is a widely used gold-standard technique in both professional and serious amateur sports. Non-invasive real-time lactate monitoring offers significant advantages over the current technology of finger-prick blood sampling. Possible candidate technology for developing non-invasive real-time lactate monitoring should be highly sensitive, flexible, and capable of real-time monitoring of lactate levels in interstitial fluid or within specific working muscle groups depending on the type of sport. Herein we describe a planar, flexible, passive, chipless tag resonator that is electromagnetically coupled to a reader placed in proximity to the lactate sensor tag. The tag resonator is a thin metallic tracing that can be taped on the skin. The resonance frequency of the tag fluctuates proportionately with changing lactate concentrations in a solution mimicking human interstitial fluid with very high sensitivity. The spectrum of the tag is reflected in the spectrum of the reader, which is a planar microwave resonator designed at a different frequency. The reader could be embedded in a cellphone or an application-specific wearable device for data communication and processing. The tag can accurately and reproducibly measure lactate concentrations in the range of 1 to 10 mM, which is in the physiological range of lactate observed at rest and during intense physical activity. Furthermore, the chrematistics of this technology will allow monitoring of lactate in specific working muscle groups.

Smart low interfacial toughness coatings for on-demand de-icing without melting

Ice accretion causes problems in vital industries and has been addressed over the past decades with either passive or active de-icing systems. This work presents a smart, hybrid (passive and active) de-icing system through the combination of a low interfacial toughness coating, printed circuit board heaters, and an ice-detecting microwave sensor. The coating’s interfacial toughness with ice is found to be temperature dependent and can be modulated using the embedded heaters. Accordingly, de-icing is realized without melting the interface. The synergistic combination of the low interfacial toughness coating and periodic heaters results in a greater de-icing power density than a full-coverage heater system. The hybrid de-icing system also shows durability towards repeated icing/de-icing, mechanical abrasion, outdoor exposure, and chemical contamination. A non-contact planar microwave resonator sensor is additionally designed and implemented to precisely detect the presence or absence of water or ice on the surface while operating beneath the coating, further enhancing the system’s energy efficiency. Scalability of the smart coating is demonstrated using large (up to 1 m) iced interfaces. Overall, the smart hybrid system designed here offers a paradigm shift in de-icing that can efficiently render a surface ice-free without the need for energetically expensive interface melting.

High-Cooperativity Coupling of Rare-Earth Spins to a Planar Superconducting Resonator

In one branch of quantum information processing, high cooperativity between spins and a resonator is essential. Planar superconducting resonators present an opportunity for miniaturization and fully integrated circuitry, but unfortunately their cooperativity is a fraction of that of their bulk counterparts. This study designs a planar microwave resonator to achieve homogeneous magnetic field, and utilizes the anisotropic g-factor tensor of erbium spins in yttrium orthosilicate for maximum spin-photon coupling. Cooperativity on par with that of a three-dimensional cavity is achieved, marking an exciting step toward integrated circuits for spin quantum information processing.

Solid Characterization Utilizing Planar Microwave Resonator Sensor

This paper outlines the design and the implementation of a planar microwave resonator sensor for sensing application using the perturbation concept in which the dielectric characteristics of the resonator influence the quality factor (QF) and the resonance frequency. The designed sensor is fabricated using Roger 5880, and it is operating at 2.27 GHz in ranges of 1-3 GHz for testing solid materials. In addition, applying a specific experimental methodology, practical material is used as material samples such as those in Roger 5880, Roger 4350, and FR4. To investigate the microwave resonator sensor performance, an equivalent circuit model (ECM) is introduced. The proposed sensor has achieved a narrow bandwidth and high QF value of 240 at an operating frequency of 2.27GHz. Besides, the sensitivity and accuracy of the sensor is more than 80%, which makes this sensor an excellent solution to characterize the material, especially in discovering the material characteristics and quality.

TiO2 Nanotube Integrated Microwave Resonator UV Sensor

Ultraviolet (UV) irradiation is extensively utilized in numerous applications such as outer space communication, biological disinfection, memory storage, optoelectronic circuits, and biological analysis [1]. Excessive exposure to UV irradiation is deleterious and causes adverse health effects, for instance, premature aging and skin cancer. A rapid and highly sensitive device for the detection of UV is in great demand in various applications. Recently, planar microwave resonator sensors have demonstrated attractive and robust performance providing high sensitivity, real-time response, and low-cost fabrication process [2]. The planar microwave resonators can easily be integrated with nanostructured materials to make them sensitive to UV radiation via absorption and subsequent charge generation [3]. Among various wide bandgap metal oxides such as TiO2, ZnO, SnO2, one-dimensional TiO2 nanotubes (TNTs) are favorable in UV photodetectors as they possess, except intrinsic TiO2 properties high active surface area and their unique hollow geometry enables increased charge trapping and, a direct pathway for rapid transport of photogenerated carriers [4-6]. Therefore, the use of high aspect ratio (HAR) TNTs might offers superior sensing performance in the UV region.In this presentation, the impact of TNT thicknesses on the UV sensitivity of the planar microwave resonator’s response will be investigated. We will demonstrate the use of a high frequency microwave resonator integrated with different thicknesses (50, 80, 100 µm) of TNT membranes. The presented work will aid in selecting an optimized thickness of TNT membranes with a large active surface-to-volume ratio to provide the highest sensitivity to UV irradiation. We expect this investigation to act as basis for expanding the use of HAR TNTs to effectively develop low-cost, easy to use and robust microwave UV sensors in a wide range of applications. Experimental details and recent results will be presented and discussed.

Interdigitated Planar Microwave Sensor for Characterizing Single/Multilayers Magnetodielectric Material

Simultaneous characterization of permittivity and permeability of magnetodielectric materials using a single resonator-based microwave sensor is challenging due to their similar impacts on the sensor’s response. This work presents an interdigital structure-based planar microwave resonator sensor featuring high-intensity electric (E)-field zones and magnetic (M)-field zones to characterize permittivity and permeability. The proposed sensor’s sensing E-field and M-field zones were implemented using the interdigital fingers configured as a spur line structure and interdigital electrodes, respectively, generating a 5.9-GHz resonance frequency with a high Q-factor (1700). The resonance frequency of the designed sensor exhibited high sensitivities (324 MHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \varepsilon _{r}$ </tex-math></inline-formula> for permittivity and 825 MHz/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Delta \mu _{r}$ </tex-math></inline-formula> for permeability) for characterizing single/multilayers magnetodielectric materials with excellent resolutions (0.324 for permittivity and 0.825 for permeability). The demonstrated high sensitivity and resolution results validate the performance of the interdigital structure-based microwave resonator sensor for simultaneous characterization of multilayer magnetodielectric materials.

Microwave Spoof Surface Plasmon Sensor for Dielectric Material Characterization

A microwave planar resonator sensor design supporting spoof surface plasmon waves is used for wafer dielectric characterization. The proposed circuit guides the microwave as a surface wave across the metal signal line, from port to port of the device. The surface wave effectively interacts with the sample being measured, placed on top of the planar sensor. The proposed planar sensor is fabricated on an RF-35 substrate, resulting in a low-cost implementation. The sensor is used to discriminate between wafers with different dielectric permittivity and thickness. Quartz, borosilicate, BK7 glass, and Silicon wafers have been characterized using the proposed sensor. The sensor resonant frequency and losses change according to the permittivity and the thickness of the samples, with an achieved sensor sensitivity of 60.22 MHz/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ϵ_r</i> . Simulation and measurements demonstrate that the proposed spoof surface plasmon resonator sensor can be used to create a high sensitivity sensor for dielectric material characterization. The dielectric constant and loss tangent of the samples are inferred from a polynomial fit obtained from sample simulations and confirmed through measurements.