Spiral Resonators Research Articles

Application of Counter-wound Multi-arm Spirals in HTS Resonator Design.

Significant sensitivity improvements have been achieved by utilizing high temperature superconducting (HTS) resonators in nuclear magnetic resonance (NMR) probes. Many nuclei such as 13C benefit from strong excitation fields which cannot be produced by traditional HTS resonator designs. We investigate the use of double-sided, counter-wound multi-arm spiral HTS resonators with the aim of increasing the excitation field at the required nuclear Larmor frequency for 13C. When compared to double-sided, counter-wound spiral resonators with similar geometry, simulations indicate that the multi-arm spiral version develops a more uniform current distribution. Preliminary tests of a two-arm resonator indicate that it may produce a stronger excitation field.

A metamaterial sensor for detecting the location of a sub-wavelength object

A metamaterial sensor is proposed to detect the random location of a sub-wavelength metallic object. The sensor is composed of a transmission line (TL), which supports the propagation of spoof surface plasmon polaritons (SSPPs) with localized electromagnetic (EM) field, and a complementary spiral resonator (CSR) that resonates strongly at designed frequencies around 0.9 and 2.7 GHz. Based on the shift of the resonance frequencies, this sensor is able to detect the location of a sub-wavelength metallic object (whose diameter is smaller than 0.6 mm) randomly attached to the CSR. A prototype of the sensor is fabricated and tested. In practice, the CSR is excited through the EM coupling of the SSPP TL, and the location of the metallic object is obtained through the transmission coefficient (S21). To improve the accuracy, a retrieval curve for locating is generated and calibrated. It is proved that the random location of the sub-wavelength object can be accurately detected inside an area of 9π mm2 with a low error of 2‰.

Mangosteen Flesh Condition Detector Based on Microwave Non-destructive Technique Using Spiral Resonator Sensor’s

The mangosteen fruit has a characteristic thick skin, so it is difficult to know the condition of the flesh. Farmer can only know damage to the fruit flesh after the fruit skin had opened. Detection of the quality of the mangosteen flesh can be detected using a sensor capable of penetrating the thickness of the mangosteen rind. Flesh quality detection is carried out based on the S21 value (attenuation of mangosteen flesh value) using a portable device equipped with a sensor and capable of emitting microwaves. The S21 value of the fruit's flesh was measured using a spiral resonator that functioned as a sensor. The prototype device consists of an oscillator circuit, a power splitter, and a phase detector with 2507 MHz. Fruit flesh had divided into two conditions: damaged for fruit flesh with yellow sap or Translucent Flesh Disorder, and suitable condition for clean fruit flesh. The results showed that the fruit flesh had an average S21 value of 7.041 dB for damaged flesh and 6.007 dB for good flesh condition. The difference in the value of S21 had used as a reference for detecting the shape of the fruit flesh, with the detection threshold calculated by the Support Vector Machine, resulting in a threshold value of 6.712 dB.

Preliminary Analysis of Burn Degree Using Non-invasive Microwave Spiral Resonator Sensor for Clinical Applications.

The European “Senseburn” project aims to develop a smart, portable, non-invasive microwave early effective diagnostic tool to assess the depth(d) and degree of burn. The objective of the work is to design and develop a convenient non-invasive microwave sensor for the analysis of the burn degree on burnt human skin. The flexible and biocompatible microwave sensor is developed using a magnetically coupled loop probe with a spiral resonator (SR). The sensor is realized with precise knowledge of the lumped element characteristics (resistor (R), an inductor (L), and a capacitor (C) RLC parameters). The estimated electrical equivalent circuit technique relies on a rigorous method enabling a comprehensive characterization of the sensor (loop probe and SR). The microwave resonator sensor with high quality factor (Q) is simulated using a CST studio suite, AWR microwave office, and fabricated on the RO 3003 substrate with a standard thickness of 0.13 mm. The sensor is prepared based on the change in dielectric property variation in the burnt skin. The sensor can detect a range of permittivity variations (εr 3–38). The sensor is showing a good response in changing resonance frequency between 1.5 and 1.71 GHz for (εr 3 to 38). The sensor is encapsulated with PDMS for the biocompatible property. The dimension of the sensor element is length (L) = 39 mm, width (W) = 34 mm, and thickness (T) = 1.4 mm. The software algorithm is prepared to automate the process of burn analysis. The proposed electromagnetic (EM) resonator based sensor provides a non-invasive technique to assess burn degree by monitoring the changes in resonance frequency. Most of the results are based on numerical simulation. We propose the unique circuit set up and the sensor device based on the information generated from the simulation in this article. The clinical validation of the sensor will be in our future work, where we will understand closely the practical functioning of the sensor based on burn degrees. The senseburn system is designed to support doctors to gather vital info of the injuries wirelessly and hence provide efficient treatment for burn victims, thus saving lives.

Design Guidelines for Sensors Based on Spiral Resonators.

Wireless microwave sensors provide a practical alternative where traditional contact-based measurement techniques are not possible to implement or suffer from performance deterioration. Resonating elements are commonly used in these sensors as the sensing concept relies on the resonance properties of the employed structure. This work presents some simple guidelines for designing displacement sensors based on spiral resonator (SR) tags. The working principle of this sensor is based on the variation of the coupling strength between the SR tag and a probing microstrip loop with the distance between them. The performance of the sensor depends on the main design parameters, such as tag dimensions, filling factor, number of turns, and the size of probing loop. The guidelines provided herein can be used for the initial phase of the design process by helping to select a preliminary set of parameters according to the desired application requirements. The provided conclusions are supported using electromagnetic simulations and analytical expressions. Finally, a corrected equivalent circuit model that takes into account the phenomenon of the resonant frequency shift at small distances is provided. The findings are compared against experimental measurements to verify their validity.

Constant Absolute Bandwidth Tunable Symmetric and Asymmetric Bandpass Responses Based on Reconfigurable Transmission Zeros and Bandwidth

A two-pole reconfigurable and tunable bandpass filter (BPF) with constant absolute bandwidth (CABW) and tunable transmission zeros (TZs) is presented in this paper. The BPF consists of asymmetrical spiral resonators having open ends on one side and capacitor loaded on the other side. The varactor loaded coupled-feed scheme is used at input and output. The two coupling feed-lines are also coupled to each other. It is shown that the control over TZs using the coupling-capacitor loaded between the two resonators leads to two different symmetric frequency responses – first with one TZ on each side of the passband, second with no TZ on either side of the passband. Further, asymmetrical frequency responses having single TZ either on lower or upper side of the passband are achieved by varying the capacitors loaded to the end of coupling-line. CABW while tuning as well as tunable bandwidth (BW) are achieved in all type of responses by using the coupling-capacitor. While tuning, quality factor is maintained by varying the capacitor loaded at the end of the coupled-feed. For the demonstration of the concept, a two-pole tunable BPF is designed and fabricated. The fabricated BPF having size of 13.1 mm × 9.4 mm, shows four different responses based on the position of TZs. All four CABW responses of the BPF have a tuning range of 300 MHz. Also, a tunable bandwidth is achieved in every response of the BPF.

Bulk properties of honeycomb lattices of superconducting microwave resonators

We have realized different honeycomb lattices for microwave photons in the 4 to 8 GHz band using superconducting spiral resonators. Each lattice comprises a few hundred sites. Two designs have been studied, one leading to two bands touching at the Dirac points and one where a gap opens at the Dirac points. Using a scanning laser technique to image the eigenmodes of this new type of photonic lattices, we are able to reconstruct their band structure. The measured bands are in excellent agreement with ab initio models that combine numerical simulations of the electromagnetic properties of the spiral resonator and analytical calculations.

Phase-resolved visualization of radio-frequency standing waves in superconducting spiral resonator for metamaterial applications

Superconducting microcircuits and metamaterials are promising candidates for use in new generation cryogenic electronics. Their functionality is largely justified by the macroscopic distribution of electromagnetic fields in arranged unit cells, rather than by the microscopic properties of composite materials. We present a new method for visualizing the spatial structure of penetrating microwaves with microscopic resolution in planar superconducting macroscopic resonators as the most important circuit-forming elements of modern microelectronics. This method uses a low-temperature laser scanning microscope that examines the phase (i.e., direction) and amplitude of local radio-frequency currents versus the two-dimensional coordinates of the superconducting resonant structure under test. Phase-sensitive contrast is achieved by synchronizing the intensity-modulated laser radiation with the resonant harmonics of the microwave signal passing through the sample. In this case, the laser-beam-induced loss in the illuminated area will strongly depend on the local phase difference between the RF carrier signal and the spatially temporal structure of the focused laser oscillation. This approach eliminates the hardware limitations of the existing technique of radio-frequency microscopy and brings the phase-sensitive demodulation mode to the level necessary for studying the physics of superconducting metamaterials. The advantage of the presented method over the previous method of RF laser scanning micros-copy is demonstrated by the example of the formation of standing waves in a spiral superconducting Archimedean resonator up to the 38th eigenmode resonance.

Machine Learning Assisted Novel Microwave Sensor Design for Dielectric Parameter Characterization of Water–Ethanol Mixture

In this paper, a novel machine learning assisted microwave sensor is introduced for the dielectric parameter characterization of ethanol liquid samples with different ingredient concentrations. The proposed sensor is designed with structural geometry of two intercoupled spiral resonators on Rogers RO4003 substrate in band stop filter configuration. The fabricated prototype has overall physical size of 15 mm x 20 mm in 1.8 GHz frequency band. The quantitative sensing performance is numerically analyzed and experimentally verified with the result of good agreement in between. One design novelty in the proposed microwave sensor is that the middle part of main sensing unit is empty for a disposable 3D printed cap to be placed into. These results minor amount of liquid samples to be dropped without the requirement of whole microwave sensor circuit to be replaced for each sample measurement. The liquid samples dropped into the middle part of microwave sensor change the stop band frequency, which is the main parameter to be correlated to dielectric parameters of liquid samples. The proposed microwave sensor has technical potential to be utilized as quality benchmarking equipment for ethanol samples in a compact size with low cost, high sensitivity, reusable, easy fabrication, and machine learning assisted operability features.

Dual-Polarized Keratin-Based UWB Chipless RFID Relative Humidity Sensor

In this paper, we realize a non-invasive, bio-compatible, reliable and compact sensor to measure relative humidity (RH) levels by depositing keratin bio-polymer on a dual-polarized ultra wide band (UWB) chipless radio frequency identification (RFID) tag. The bio-compatible and hydrophilic properties of keratin make the proposed sensor an appropriate solution for monitoring RH level in different food and pharmaceutical industries, where non-toxic materials are in high demand. The proposed sensor comprises two main parts: a three-armed Fermat spiral resonator and the keratin bio-polymer mounted on the surface of the resonator. Keratin is extracted through the alkaline hydrolysis process and analyzed using X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FTIR) methods. The three-armed Fermat spiral resonator acts as a scatterer, generating both co- and cross-polarized resonant responses when interrogated by a signal in a UWB frequency range. Having a cross-polarized response increases the robustness of the proposed sensor in the presence of interference and helps enhance the reliability of the sensor by offering three additional parameters. Amplitude, quality factor, and resonant frequencies are three main parameters that have been extracted from the responses of the proposed RH sensor at both co- and cross-polarization by modelling its responses as a function of frequency. To examine the performance of the sensor, laboratory measurements are carried out in the Esky box. The results show that the proposed sensor can be used to monitor RH changes from 54% to 74% at 26° Celsius.

Metamaterials for Improving Efficiency of Magnetic Resonant Wireless Power Transfer Applications

In this article, we investigate a compact metamaterial structure for enhancing a magnetic resonant wireless power transfer (WPT) system operated at 6.5 MHz. A thin magnetic metamaterial (MM) slab placed between the transmitter (Tx) and receiver (Rx) coil can improve WPT efficiency. The metamaterial unit cell is designed by a ten-turn spiral resonator (10T-SR) loaded with an external capacitor. The resonant frequency of MM unit cells can be easily controlled by changing the capacitor value. By using the optimization approach, we achieve a significant WPT efficiency improvement at a mid-range distance. The results showed an enhancement of the magnetic field in the WPT system when MM slab was present. This demonstrates the ability to amplify the evanescent wave of MM slab, thereby improving the WPT efficiency. The transmission coefficients of WPT system at 60 cm increased from 0.5 to 0.76 with MM slab, which corresponds to a 46% improvement.

A Dual-Band Resonator Sensor for Low Permittivity Characterization

Low permittivity materials are widely used in many electronic systems. However, dielectric measurement on low permittivity material is challenging. To address this difficulty, a dual-band resonant sensor is developed. The proposed sensor is an improved design from the complementary square spiral resonator (CSSR). By adding a square patch on top of the resonant cell, the local field is significantly increased. Therefore, the interaction between field and material is strengthened, resulting in enhancement in measurement sensitivity. Owing to the increased sensitivity, low permittivity samples down to 1.19 can be measured with an accuracy of better than 3%. Such results demonstrate that this sensor is promising for low permittivity characterization. Moreover, this sensor is also capable of measuring samples with permittivity in the range of 2-10, with an accuracy of 5%. Furthermore, two resonances are created, enabling dual-band operation. The unloaded resonances take place at 2.00 GHz and 5.41 GHz. Particularly, the measurement can be conducted simultaneously in the two operation bands. Measured results demonstrate that the accuracy and sensitivity are satisfactorily high and comparatively superior to the designs in the literature for low permittivity measurement.

Design of broadband Helmholtz resonator arrays using the radiation impedance method.

This paper describes the design process of a low-frequency sound absorptive panel composed of differently tuned Helmholtz resonators (HRs), considering size and fabrication constraints relevant for applications in the building sector. The paper focuses on cylindrical and spiral resonators with embedded necks that are thin and can achieve high absorption. the mutual interaction between the resonators was modeled based on the radiation impedance method and it plays a key component in enhancing the absorption performance of the array. The differential evolution search algorithm was used to design the resonators and modify their mutual interaction to derive the absorption performance of multiple HR arrays for comparison. Optimizations to the resonator configuration and the neck resistance were implemented to produce a unit panel that has a broadband absorption performance with emphasis on the low to mid frequencies and is thin and light in weight. Unit panels with dimensions of 20 cm×20 cm, consisting of 29 cylindrical HRs designed to absorb in the 25-900 Hz frequency range, were constructed and tested in a custom-built impedance tube. The measured absorption performance of these panels is consistent with the theoretical predictions.

High-Sensitivity and Compact Time Domain Soil Moisture Sensor Using Dispersive Phase Shifter for Complex Permittivity Measurement

This article presents a time domain transmissometry soil moisture sensor (TDT-SMS) using a dispersive phase shifter (DPS), consisting of an interdigital capacitor that is loaded with a stacked four-turn complementary spiral resonator (S4-CSR). Soil moisture measurement technique of the proposed sensor is based on the complex permittivity sensing property of a DPS in time domain. Soil relative permittivity which varies with its moisture content is measured by burying the DPS under a soil mass and changing its phase difference while excited with a 114-MHz sine wave (single tone). DPS output phase and magnitude are compared with the reference signal and measured with a phase/loss detector. The proposed sensor exhibits accuracy better than ±1.2% at the highest volumetric water content (VWC = 30%) for sandy-type soil. Precise design guide is developed and simulations are performed to achieve a highly sensitive sensor. The measurement results validate the accuracy of theoretical analysis and design procedure. Owning the advantages of low profile, low power consumption, and high sensitivity makes the proposed TDT-SMS a good candidate for precision farming and internet of things (IoT) systems.

Highly Sensitive Differential Microwave Sensor for Soil Moisture Measurement

This paper presents a highly sensitive differential soil moisture sensor (DSMS) using a microstrip line loaded with triangular two-turn resonator (T2-SR) and complementary of the rectangular two-turn spiral resonator (CR2-SR), simultaneously. Volumetric Water Content (VWC) or permittivity sensing is conducted by loading the T2-SR side with dielectric samples. Two transmission notches are observed for identical loads relating to T2-SR and CR2-SR. The CR2-SR notch at 4.39 GHz is used as a reference for differential permittivity measurement method. Further, the resonance frequency of T2-SR is measured relative to the reference value. Based on this frequency difference, the permittivity of soil is calculated which is related to the soil VWC. Triangular two-turn resonator (T2-SR) resonance frequency changes from 4 to 2.38 GHz when VWC varies 0% to 30%. The sensor’s operation principle is described through circuit model analysis and simulations. To validate the differential sensing concept, prototype of the designed 3-cell DSMS is fabricated and measured. The proposed sensor exhibits frequency shift of 110 MHz for 1% change at the highest soil moisture content (30%) for sandy-type soil. This work proves the differential microwave sensing concept for precision agriculture.

A low-noise on-chip coherent microwave source

The scaleup of quantum computers operating in the microwave domain requires advanced control electronics, and the use of integrated components that operate at the temperature of the quantum devices is potentially beneficial. However, such an approach requires ultra-low power dissipation and high signal quality in order to ensure quantum-coherent operations. Here, we report an on-chip device that is based on a Josephson junction coupled to a spiral resonator and is capable of coherent continuous-wave microwave emission. We show that characteristics of the device accurately follow a theory based on a perturbative treatment of the capacitively shunted Josephson junction as a gain element. The infidelity of typical quantum gate operations due to the phase noise of this cryogenic 25-pW microwave source is less than 0.1% up to 10-ms evolution times, which is below the infidelity caused by dephasing in state-of-the-art superconducting qubits. Together with future cryogenic amplitude and phase modulation techniques, our approach may lead to scalable cryogenic control systems for quantum processors.

Design evaluation of microwave transmission properties of YBa2Cu3O7-based kinetic inductance detectors

We designed, fabricated, and characterized microwave transmission properties with rewound strip structures for YBa2Cu3O7 (YBCO)-based kinetic inductance detectors (KIDs). The superconducting rewound strip serves as a microwave resonator and as a broadband terahertz-wave antenna. To predict the microwave resonance characteristics before fabrication, the line-width (w) and space (s) dependence of the spiral resonators were analyzed using an electromagnetic simulator; the resonance frequency increased, and the quality factor decreased with increasing w and s from 10 to 40 μm. YBCO-based KID arrays with different w (10 and 40 μm) were fabricated on 10 mm-square MgO substrates, cooled to 3 K using a 4He refrigerator, and evaluated using a vector network analyzer to verify the result of the simulation experimentally. The measured resonance frequency ratio of 1.11 times (5.04 → 5.59 GHz) agreed with the simulated ones of 1.10 times (4.84 → 5.33 GHz) between w = 10 and 40 μm. The other resonance characteristics, such as transmission coefficient and quality factor, have a similar w dependence with the simulation.

SMALL-SIZE FILTER USING SPIRAL RESONATORS 
 WITH HIGH QUALITY FACTOR

The article shows the potential for use of integral spiral microwave resonators in the LTCC structure and filters based on them. It provides calculated ratios, developed 3D model of the spiral filter and obtained calculated S-parameters of the filter model.

High Sensitivity Sensor Loaded With Octagonal Spiral Resonators for Retrieval of Solid Material Permittivity

In this paper, a highly sensitive octagonal spiral sensor is presented that can be applied to measure the permittivity of solid materials with high accuracy. Compared with the traditional split-ring resonator (SRR)-based configuration, the confinement of the electric field in the gap of the polygon spiral resonator can be improved by increasing the number of polygon sides, which leads to higher measurement sensitivity. By compromising between ease of processing and sensitivity improvement, an octagonal spiral structure is finally obtained. To determine the measurement sensitivity, a differential measurement scheme loaded with dual octagonal spiral sensors is adopted, and the sensor is modeled under the unloaded condition to confirm its designed operating frequency of 2.48 GHz. Then, experiments and corresponding simulations are implemented on loading with two different kinds of reference materials. The equivalent circuit model is obtained, and its results are compared with those from the numerical simulation. The sensor is fabricated on a 0.5-mm-thick Teflon substrate. Two of standard solid dielectric samples are tested using the proposed scheme, and their permittivity values are retrieved. The measured data are in agreement with the corresponding reference values available in the literature, with typical errors of less than 2%.

Rapid Prototyping of Bio-Inspired Dielectric Resonator Antennas for Sub-6 GHz Applications.

Bio-inspired Dielectric Resonator Antennas (DRAs) are engaging more and more attention from the scientific community due to their exceptional wideband characteristic, which is especially desirable for the implementation of 5G communications. Nonetheless, since these antennas exhibit peculiar geometries in their micro-features, high dimensional accuracy must be accomplished via the selection of the most suitable fabrication process. In this study, the challenges to the manufacturing process presented by the wideband Spiral shell Dielectric Resonator Antenna (SsDRA), based on the Gielis superformula, are addressed. Three prototypes, made of three different photopolymer resins, were manufactured by bottom-up micro-Stereolithography (SLA). This process allows to cope with SsDRA’s fabrication criticalities, especially concerning the wavy features characterizing the thin spiral surface and the micro-features located in close proximity to the spiral origin. The assembly of the SsDRAs with a ground plane and feed probe was also accurately managed in order to guarantee reliable and repeatable measurements. The scattering parameter S11 trends were then measured by means of a Vector Network Analyzer, while the realized gains and 3D radiation diagrams were measured in the anechoic chamber. The experimental results show that all SsDRAs display relevant wideband behavior of 2 GHz at −10 dB in the sub-6 GHz range.