Spiral Resonators Research Articles

Numerical analysis on droplet mixing induced by microwave heating: Decoupling of influencing physical properties

Microwave resonator offers simultaneous sensing and heating of individual droplets in microchannels presenting unique advantages for applications requiring well-controlled reaction time. This study numerically investigates the effects of the temperature-dependent fluid properties including viscosity, density, diffusivity, and interfacial tension, on microwave heating induced mixing. A system consisting of a spiral resonator integrated with a microchannel with aqueous droplets moving with a carrier oil is considered. The electromagnetic field which provides heating to the droplets, and the flow and tracer concentration fields inside the droplet are obtained using commercial software, Ansys HFSS and Fluent, respectively. It is found that the mixing index can be increased from 0.4 to 0.84 within 320[ms] with microwave heating and it would be slightly increased to 0.47 when only the interfacial tension was made independent on temperature, which suggests that the temperature-dependent interfacial tension is the dominant factor for microwave heating induced mixing.

A Simple High-Resolution Near-Field Probe for Microwave Non-Destructive Test and Imaging

Non-destructive tests working at lower microwave frequencies have large advantages of dielectric material penetrability, lower equipment cost, and lower implementation complexity. However, the resolution will become worse as the work frequencies become lower. Relying on designing the structure of high field confinement, this study realizes a simple complementary spiral resonators (CSRs)-based near-field probe for microwave non-destructive testing (NDT) and imaging around 390 MHz (λ = 769 mm) whereby very high resolution (λ/308, 2.5 mm) is achieved. By applying an ingenious structure where a short microstrip is connected to a microstrip ring to feed the CSR, the probe, that is a single-port microwave planar circuit, does not need any extra matching circuits, which has more application potential in sensor arraying compared with other microwave probes. The variation of the electric field distribution with the standoff distance (SOD) between the material under test and the probe are analyzed to reveal the operation mechanisms behind the improved sensitivity and resolution of the proposed probe. Besides, the detection abilities of the tiny defects in metal and non-metal materials are demonstrated by the related experiments. The smallest detectable crack and via in the non-metal materials and the metal materials are of a λ/1538 (0.5 mm) width, a λ/513 (1.5 mm) diameter, a λ/3846 (0.2 mm) width and a λ/513 (1.5 mm) diameter, respectively. Moreover, to further evaluate the performance of the proposed probe, the defects under skin layer in the multilayer composite materials and the defects under corrosion in the carbon steel are inspected and imaged. Due to lower work frequency, high resolution, outstanding detection abilities of tiny defects, and large potentials in sensor arraying, the proposed probe would be a good candidate for microwave NDT and imaging.

Miniaturized Full-Metal Dual-Band Filter Using Dual-Mode Circular Spiral Resonators

A miniaturized full-metal dual-band bandpass filter using a dual-mode circular spiral resonator (CSR) in a single metal cavity is proposed. Two spirals are combined together to form a dual-mode resonator, and the transmission zero (TZ) produced by the source–load coupling can separate the two modes and achieve the desired dual-band property. Then, a second-order dual-band filter is designed based on the dual-mode resonator, and each band can be individually synthesized, designed, and tuned to achieve the desired filtering performances. In addition, each band has TZs on both sides of the passband to achieve high selectivity. The size of the second-order dual-band filter is only $0.073\lambda _{0} \times 0.055\lambda _{0} \times 0.015\lambda _{0}$ calculated at the center frequency of the lower band. Finally, the filter is fabricated and measured, and a good agreement is achieved between the measurement and simulation.

A silicon‐organic hybrid platform for quantum microwave-to-optical transduction

Low-loss fiber optic links have the potential to connect superconducting quantum processors together over long distances to form large scale quantum networks. A key component of these future networks is a quantum transducer that coherently and bidirectionally converts photons from microwave frequencies to optical frequencies. We present a platform for electro-optic photon conversion based on silicon‐organic hybrid photonics. Our device combines high quality factor microwave and optical resonators with an electro-optic polymer cladding to perform microwave-to-optical photon conversion from 6.7 GHz to 193 THz (1558 nm). The device achieves an electro-optic coupling rate of 590 Hz in a millikelvin dilution refrigerator environment. We use an optical heterodyne measurement technique to demonstrate the single-sideband nature of the conversion with a selectivity of approximately 10 dB. We analyze the effects of stray light in our device and suggest ways in which this can be mitigated. Finally, we present initial results on high-impedance spiral resonators designed to increase the electro-optic coupling.

Wireless Power Transfer System With High Misalignment Tolerance for Bio-Medical Implants

A hybrid array resonator structure for Wireless Power Transfer (WPT) is presented. The proposed structure exploits an array of four identical coils surrounded by a larger coil to generate uniform magnetic field. As a result, a nearly constant and high efficiency is achieved over a large misalignment region. The quasi-uniform magnetic field distribution of the proposed structure is analytically derived. For demonstration, one prototype operating at 40 MHz is designed for implantable medical devices (IMDs). According to experimental results, the developed WPT system exhibits an efficiency of 53% when the receiver and the transmitter are aligned, while the efficiency is 44% when they operate with a lateral misalignment of 10 mm. As per a conventional WPT system using a single spiral resonator as transmitter and receiver, the efficiency is 47.2% in aligned condition, while, it is 30.5% for a 10 mm lateral misalignment. The reported results demonstrate that the proposed design approach provides a high misalignment tolerance. This represents an attractive future for applications, such as the recharge of embedded devices, where the alignment between the transmitter and the receiver is difficult to guarantee.

Folded Spiral Resonator with Double-Layered Structure for Near-Field Wireless Power Transfer

In this paper, a folded spiral resonator with a double-layered structure for near-field wireless power transfer is proposed. In near-field wireless power transfer, conjugate impedance matching is important to achieve high transfer efficiency. To achieve maximum available efficiency, it is common to connect a matching circuit to the antenna. However, the loss increases if a matching circuit is used. A coupling inductor with a resonant capacitor has the capability to adjust an imaginary part of the input impedance, whereas the folded spiral resonator has the capability to adjust both the imaginary and real parts of the input impedance. This resonator can achieve the maximum available efficiency without a matching circuit. This paper shows that the folded spiral resonator with a double-layered structure realizes high transfer efficiency compared to conventional models.

Compact narrow band-pass filter based on alternate right–left handed transmission line concept

A new topology for the design of microwave narrow band-pass filters (NBPFs) based on the alternate right–left handed transmission line (TL) concept is proposed. The proposed NBPF is a three-stage structure which two LH stages and one RH stage are used. The proposed LH stage is implemented by a spiral complementary split ring resonator (spiral CSRRs) and an interdigital capacitor while for implementing the RH stage, the conventional TL shorted by via and the spiral CSRR are used. The spiral CSRRs have been etched in the ground plane. To improve frequency selectivity and out-of-band rejection, the proposed RH stage has been cascaded with two LH stages. Accordingly, a compact NBPF is designed which exhibits extremely sharp rejection skirts around the target passband. The equivalent circuit model and full-wave simulation results of the proposed NBPF are developed. To validate the design concept, the designed filter has been fabricated and tested. Experimental verification is provided and a good agreement has been found between the simulation and measurement. The proposed NBPF has a passband covering 2.3–2.45 GHz and its measured 3-dB fractional bandwidth is about 7.5%. The total size of the proposed NBPF is 0.18 × 0.15 λg2. Compared with some other reported NBPFs, the presented NBPF has significant improvements on size reduction and selectivity.

Optical vortex rotation and propagation from a spiral phase plate resonator with surface reflective coating.

A spiral phase plate resonator (SPPR) is created by depositing a reflective coating on the surfaces of a single conventional spiral phase plate (SPP) for the first time to the best of our knowledge. Optical transmission through the SPPR on the output plane of the device is measured to give sharp Fabry-Perot resonances as a function of beam roll angle. Similar measurements are performed for the reflected light emerging from the input plane of the SPPR device. Varying the light frequency going into the SPPR changes the orientation of the angular pattern (Fabry-Perot resonances) to give the rotational constant of the device, in agreement with theory. The optical mode profile is measured after the beam has propagated beyond the plane of the SPPR device while remaining in the diffraction near field, thus revealing new features in the transmitted optical beam. These new results have important implications for developing the SPPR for microscopy, imaging, angle measurement, rotational scanning, and LiDAR.

Long Array of Microwave Sensors for Real-Time Coating Defect Detection

A real-time, inexpensive, and easy-to-install resonator-based microwave sensor array for coating defect detection on metallic structures is presented. The sensor array is composed of 55 identical rectangular spiral resonators coupled to a 120-cm-long transmission line. The array was simulated, fabricated, and measured. A stopband was created at the fundamental resonant frequency of the resonators. The fabricated sensor array was implemented on the coating to monitor defects beneath the sensor. The proposed sensor array can be used to detect water ingress and coating delamination, which are causes for alarm in metallic structure corrosion and cracking. The proposed structure is a low-cost solution for real-time coating failure identification.

A Flexible Microwave Sensor Based on Complementary Spiral Resonator for Material Dielectric Characterization

In this paper, a flexible microwave sensor for material dielectric characterization is presented. The sensor is composed of a two-turn complementary spiral resonator (CSR) in coplanar waveguide (CPW) technology developed on a flexible polyethylene terephthalate (PET) substrate. The sensing principle is based on the measured transmission coefficient of the designed structure, where the resonant frequency and its magnitude are in function of the dielectric properties of loaded materials under test (MUTs). A prototype of the proposed sensor is fabricated and experimentally validated by extracting the dielectric constant and loss tangent of the reference samples loaded above the region of the CSR. Specially, due to the flexibility, the fabricated sensor can be conformally attached to the palm of a dexterous robotic hand to function as robotic electronic skin for material dielectric characterization, more specifically, to obtain dielectric properties of the objects grasped by the dexterous robotic hand. Moreover, the sensing functionality of the sensor structure under different bending levels is validated by calculating the dielectric property of loaded objects with non-planar surfaces.

Water Spiral Dielectric Resonator Antenna for Generating Multimode OAM

This letter presents a novel water spiral dielectric resonator antenna (DRA) to generate multimode orbital angular momentum (OAM) waves. The shell of the spiral DRA filled with distilled water is designed as a cylinder with a spiral paraboloid on one side produced by a 3-D printer, and fed with two orthogonal signals at the other (bottom) side to excite higher order modes. By changing the radius, height, and notch height of the spiral DRA, l = ±1 OAM modes can be generated at 4.8 and 5.6 GHz, and l = ±3 OAM modes can be generated at 5.11, 5.66, and 6.36 GHz, respectively. The measurement results show that the 10 dB frequency bandwidth of the spiral DRA from 5.07 to 5.14 GHz and isolation excess of 20 dB can be achieved. The proposed spiral DRA with low cost, compact construction, and easy processing has the potential in a short-range OAM wireless communication.

Calculation and analysis of near-field magnetic spiral metamaterials for MCR-WPT application

Mu-negative and mu-near-zero metamaterials have great potential for magnetically coupling resonant wireless power transfer (MCR-WPT) application. It is well known that square and circular spiral structures are often applied in MCR-WPT system. However, there is rarely comparative analysis in detail. Here we present the electrical Lorentzian-like model of square and circular spiral resonators to accurately predict the − 1 and 0 points of effective permeability. Combined with semi-empirical equations, analytical process is completely given out. Particularly, all losses of unit cell are calculated in detail. Higher losses are observed in self-resonance circular spiral resonator, resulting in lower quality factor (Q). Measurement and full-wave simulation verify the calculated accuracy of effective permeability. To further analyze two spiral metamaterials, their magnetic fields (Hz) are calculated. By the comprehensive comparison of lumped capacitor and self-resonance metamaterials, the near-field metamaterial with lumped capacitor possesses the better performance. This model can accelerate the design process of near-field metamaterials. These results have the guidance meaning in MCR-WPT application.

Design of Distributed Spiral Resonators for the Decoupling of MRI Double-Tuned RF Coils.

A systematic analytical approach to design Spiral Resonators (SRs), acting as distributed magnetic traps (DMTs), for the decoupling of concentric Double-Tuned (DT) RF coils suitable for Ultra-High Field (7 T) MRI is presented. The design is based on small planar SRs placed in between the two RF loops (used for signal detection of the two nuclei of interest). We developed a general framework based on a fully analytical approach to estimate the mutual coupling between the RF coils and to provide design guidelines for the geometry and number of SRs to be employed. Starting from the full-analytical estimations of the SRs geometry, electromagnetic simulations for improving and validating the performance can be carried out. We applied the method to a test case of a DT RF coil consisting of two concentric and coplanar loops used for 7 T MRI, tuned at the Larmor frequencies of the proton (1H, 298 MHz) and sodium (23Na, 79 MHz) nuclei, respectively. We performed numerical simulations and experimental measurements on fabricated prototypes, which both demonstrated the effectiveness of the proposed design procedure. The decoupling is achieved by printing the SRs on the same dielectric substrate of the RF coils thus allowing a drastic simplification of the fabrication procedure. It is worth noting that there are no physical connections between the decoupling SRs and the 1H/23Na RF coils, thus providing a mechanically robust experimental set-up, and improving the transceiver design with respect to other traditional decoupling techniques.

Polarization-insensitive electromagnetically-induced transparency in planar metamaterial based on coupling of ring and zigzag spiral resonators

A planar metamaterial (MM) mimicking electromagnetically-induced transparency (EIT) effect is demonstrated numerically and experimentally in the microwave region. The structure of MM is a periodicity of ring and zigzag spiral resonators, in which each resonator can be excited directly by the external field. By matching the characteristic resonance frequencies of two resonators, the coupling of two bright modes appears, leading to an EIT effect with a transparency peak at 4.86 GHz. Although the geometry of the structure is not perfectly symmetric, the proposed electromagnetically-induced transparency metamaterial (EIT-MM) is insensitive to the polarization of incoming wave. Furthermore, the EIT-MM exhibits a strong dispersion behavior, which leads to a high group index of 2785 and a group delay of 0.83 ns. Our work might be useful to potential applications using EIT-MM such as modulators, filters and sensors.

High Resolution and Polarization Independent Microwave Near-Field Imaging Using Planar Resonator Probes

Various near-field microwave imaging probes were developed previously for nondestructive testing of material structures. Sensitivity and resolution are key parameters for quantifying the efficacy of a given imaging probe. For polarized targets like cracks, the sensitivity of conventional aperture probes depends on the relative orientation between the probe's electric-field vector and the target. In practice, target orientation is typically unknown. Furthermore, the imaging resolution of conventional aperture probes is limited to aperture dimensions. Obtaining imaging resolution in the order of few millimeters using conventional aperture probes requires operation at high frequencies, (above 30 GHz). In contrast, planar probes consisting of loops loaded with spiral resonators could provide resolution in the order of few millimeters while working at relatively low frequencies (below 1 GHz). Unlike conventional aperture probes, the radiated near-fields of these probes are characterized by two significant components oriented along orthogonal axes. Therefore, the probe intrinsically provides a polarization-independent response. In this article, the near-field imaging resolution of the planar resonator probe is further enhanced, and its polarization-independent response is demonstrated for the first time. The response of three planar probe prototypes of different dimensions is analyzed based on numerical simulation and experimental results. The performance of the probes is extensively evaluated by acquiring line-scans and 2D-images of metal and dielectric samples. The near-field images of the metal sample obtained using the planar probes working below 1 GHz are compared to the images obtained using aperture probes working at 24 GHz, 33 GHz, and 70 GHz. Furthermore, the probe imaging performance for a polarized target (i.e., narrow cuts) is compared to dual-polarized circular probe working at 24 GHz and open-ended coaxial probe working at 10 GHz. Overall, the proposed probe yielded more than twofold increase in the image signal-to-noise ratio (SNR) compared to all the probes utilized herein.

PEEC Modeling of Planar Spiral Resonators

The partial element equivalent circuit (PEEC) method is applied to a frequency-sweep study for investigating the resonant modes of planar spiral resonators. A low-rank approximation algorithm, based on hierarchical matrices, is coupled to the method in order to reduce the computational effort due to the use of dense matrices. The partitioning of the matrices is carefully addressed in order to allow an efficient hierarchical off-diagonal low-rank structure of the system matrix.

Silicon photonic spiral shape resonator applied to the optoelectronic oscillator

We present here the implementation of an optoelectronic oscillator (OEO) that leverages the optical comb produced by a silicon add-drop ring resonator to directly convert signals from optical to microwave domain. The OEO comprises a CW laser, an intensity modulator, a silicon add-drop ring, a photodetector, and radiofrequency amplifier. By using millimeter-long silicon-on insulator micro-ring resonator, we generated an oscillation signal with a frequency determined by the free spectral range (FSR) of the ring. In this scheme, the sharp transmission peaks in the drop port of an add-drop silicon resonator are used as the optical comb. The optimised ring has a length of 5.8 mm with a measured FSR of 112 pm, an extinction ratio of 20 dB and an optical quality factor of 2.2 × 10 5 . The complete OEO loop yields a 14.12 GHz signal with a phase noise level of -100 dBc/Hz at an offset of 100 kHz from the carrier. This result shows that OEOs directly based on millimeters long silicon rings are a promising path for generating low-noise microwave signals.

Multiresonant Chipless RFID Array System for Coating Defect Detection and Corrosion Prediction

In this article, a fully passive, wireless solution for out-of-sight pipeline monitoring is presented. By predicting corrosion before its occurrence, a proactive response may be taken to mitigate the chance of an environmental disaster. The chipless radio-frequency identification system is a combination of a tag ID, consisting of an array of six rectangular spiral resonators, and a tag antenna consisting of two cross-polarized novel patch antennas etched on a skin-thin microwave laminate. The tags are grounded on a carbon steel pipeline coated with $\text{3 mm}$ Teflon (polyethylene-like electrical characteristics). The proposed system exhibits robust capability to create frequency signatures to detect and monitor defects underneath the pipeline coating owing to water ingress that could eventuate to corrode the pipeline. The reader antenna above the pipeline comprises two identically cross-polarized log periodic dipole antennas with the intent to remotely capture resonances of the tag ID in real-time for early detection and prediction of potential pipeline exposure to moisture. The proposed structure provides low-cost real-time solution.

Design of phase coded spiral resonator based Chipless RFID tag for tracking applications

RFID (Radio identification) is a technology which deals with the wireless identification of people and products. This chipless RFID tag design is on research to replace chipped RFID tags, which employs high cost silicon wafer to store unique identification code. The main challenge in the design of chipless RFID tag is how to encode the data without a chip. This challenge is overcome by the use of electromagnetic properties of the resonators, filters etc to encode the data bits. In this work RFID tag is designed based on multiresonators with each resonator representing a data bit. The proposed tag consists of the multiresonating circuit to store information bits and transmitting and receiving UWB antenna for wireless communication with the RFID reader for identification. The multiresonating circuit designed consists of 4-spiral resonators electromagnetically coupled to the microstip coupled line. Each spiral resonates at unique resonating frequency representing the unique data bit. The data encoding is carried out with the help of phase ripples at the resonating frequency of the spirals. Three variations are observed and corresponding 3-logic states (0, 1, 2) are encoded. The designed tag is simulated in Advanced Design System (ADS) using RO-4003 substrate with the dielectric constant 3.38 and thickness of 20 mil. From the proposed methodology, a total of 34=81 unique tags can be designed that can be employed in cheap item tracking. The Monopole disc antenna is designed which operates for wide band covering all resonating frequency of the spiral resonator.

High-order cylindrical vector beams with tunable topological charge up to 14 directly generated from a microchip laser with high beam quality and high efficiency

Large topological charge optical vortex beams carrying orbital angular momentum have potential applications on optical trapping, optical communication with high capacity, quantum information processing. However, the beam quality is degraded in vortex beams generated with spiral phase plates or resonator mirrors with defect spots and optical conversion efficiency in solid-state lasers is sacrificed by controlling the loss of resonator. It is a big challenge for generating high beam quality, high-order cylindrical vector beams with large topological charge in compact solid-state lasers. Here, high-order cylindrical vector beams [Laguerre-Gaussian (LG) modes with zero degree and order of l, LG0,l] with tunable topological charges up to 14 have been generated in an annular beam pumped Yb:YAG microchip laser by manipulating the pump power-dependent population inversion distribution. Efficient performance with optical efficiency of 17.5% has been achieved. The output power is 1.36 W for a vector-vortex laser with 14 topological charges. The pump power dependent wavelength tunable and dual-wavelength laser oscillation in vector-vortex beams has been observed by controlling the reabsorption loss at 1030 nm. Wavelength tunable, dual-wavelength (1030 and 1050 nm) laser oscillation has been achieved for vector-vortex beams with topological charges of 8, 9, and 10. The laser beam quality factor M2 close to the theoretical value (l + 1) has been achieved for LG0,l vector-vortex beams with tunable topological charges up to 14. This work provides a new effective method for generating large topological charge high-order cylindrical vector beams in solid-state microchip lasers with high efficiency and high beam quality.