Spiral Resonators Research Articles

Spiral Resonator Arrays for Misalignment Compensation in Wireless Power Transfer Systems

In this contribution, the authors focus on the use of a metasurface (physically implemented as a 2D array of spiral resonators) as an additional component of a two-coil Wireless Power Transfer (WPT) system, with the aim of increasing the robustness to misalignment between the transmitter and the receiver coils. Resonator arrays have been proven to have a positive effect on WPT systems’ performance since they produce a focusing effect on the magnetic field; at the same time, they contribute to the reduction of the electric near field. In addition, we herein demonstrate how proper control over the metasurface’s unit cells can contribute to making a WPT system more tolerant to misalignment. In particular, the comparison between metasurfaces of different sizes (keeping the same transmitting and receiving coils) and their optimization performed to improve misalignment robustness is proved by numerical simulations.

Wearable Textile-Based Sensor Tag for Breath Rate Measurement

Breath rate is an important vital sign for monitoring the well-being and detecting underlying illnesses related to the respiratory system. The spirometer is widely used for evaluating the health of the respiratory system by measuring lung capacity and respiration rate (RR). Although this test yields accurate results, however, it is significantly inconvenient and invasive, as the test subject must breathe through a tube inserted in the mouth. Therefore, this device is not suitable for continuous monitoring of respiration. In this article, a novel contactless wearable breath rate measurement system is presented. The proposed sensor is based on a spiral resonator (SR) tag printed on a thin flexible textile substrate. The sensor exploits the body expansion and contraction during respiration to provide an estimate of the breathing frequency. This movement is measured by a microstrip probing loop that acts as the antenna of the reader. The reader operates at one frequency; the resonant frequency of the tag, and the sensing principle relies on the near-field coupling between the probe and the resonating tag at this frequency. The proposed sensor is characterized with its simple and lightweight design, can be easily integrated in garments, and its capability of providing continuous monitoring of the breathing rate. The proposed sensor has been tested through experimental measurements, and the results matched measurements from a reference ground-truth breath rate sensor based on a nasal cannula equipped with a thermistor. The solution proposed in this work provides a novel contactless technique for RR estimation.

High-Sensitivity Sensor Loaded With Coupled Complementary Spiral Resonators for Simultaneous Permittivity and Thickness Measurement of Solid Dielectric Sheet

High-precision measurement of permittivity and thickness enables advanced quality control of microwave substrates. In this article, a subwavelength planar microwave sensor is proposed, which is composed of a single-microstrip transmission line with a pair of coupled circular complementary spiral resonators (CSRs). Thus, two robust band-stop notches in the transmission response are developed, which can be utilized for simultaneous thickness and permittivity measurements of a dielectric sheet. The mutual capacitance and inductance, which quantify the coupling effect between the two resonators, are added to the equivalent lumped circuit model. They enhance the frequency shifts, thus improving sensitivity. The results of full-wave simulations and measurements on five different types of samples verify the concept’s effectiveness.

REDUCING THE CROSS-POLARIZATION PATTERN IN A DUAL-POLARIZED ANTENNA USING SPIRAL AND SPLIT RING RESONATORS

This paper introduces the design of a new dual polarization rectangular microstrip patch antenna based on metamaterial structures at X-band. The work focuses on two distinct configurations of a microstrip patch antenna utilizing metamaterials. Pairs of spiral ring resonators are loaded into a rectangular patch antenna system in the first design. The second strategy involves inserting a split ring resonator at the end of microstrip feed lines. The utilization of metamaterial structures in the microstrip antenna system compensates for the patch antenna's asymmetric current distribution of the flow, resulting in symmetrical current distribution. The simulation results display an import cross-polarization cross-polarization discrimination (XPD) and good port decoupling. The antenna system has various characteristics, including a basic structure and metamaterial inclusions that take up a small amount of space, making the suggested metamaterial inclusions more beneficial for dual-linear polarized patch antenna construction. These prototypes are suitable to work for polarimetric radars.

A Flexible Near-Field Biosensor for Multisite Arterial Blood Flow Detection

Modern wearable devices show promising results in terms of detecting vital bodily signs from the wrist. However, there remains a considerable need for a device that can conform to the human body's variable geometry to accurately detect those vital signs and to understand health better. Flexible radio frequency (RF) resonators are well poised to address this need by providing conformable bio-interfaces suitable for different anatomical locations. In this work, we develop a compact wearable RF biosensor that detects multisite hemodynamic events due to pulsatile blood flow through noninvasive tissue-electromagnetic (EM) field interaction. The sensor consists of a skin patch spiral resonator and a wearable transceiver. During resonance, the resonator establishes a strong capacitive coupling with layered dielectric tissues due to impedance matching. Therefore, any variation in the dielectric properties within the near-field of the coupled system will result in field perturbation. This perturbation also results in RF carrier modulation, transduced via a demodulator in the transceiver unit. The main elements of the transceiver consist of a direct digital synthesizer for RF carrier generation and a demodulator unit comprised of a resistive bridge coupled with an envelope detector, a filter, and an amplifier. In this work, we build and study the sensor at the radial artery, thorax, carotid artery, and supraorbital locations of a healthy human subject, which hold clinical significance in evaluating cardiovascular health. The carrier frequency is tuned at the resonance of the spiral resonator, which is 34.5 ± 1.5 MHz. The resulting transient waveforms from the demodulator indicate the presence of hemodynamic events, i.e., systolic upstroke, systolic peak, dicrotic notch, and diastolic downstroke. The preliminary results also confirm the sensor's ability to detect multisite blood flow events noninvasively on a single wearable platform.

A Miniaturized Dual-Resonator-Based High-Capacity Chipless Radio Frequency Identification Tag Sensor

The chipless radio-frequency identification (RFID) sensor is a potential technology for future RFID-based sensing systems. A novel ultra-wideband and retransmission-method-based frequency-coded chipless RFID tag is presented in this letter. The footprint of the proposed RFID tag is reduced by incorporating spur-line spiral resonators along with the spiral resonators. These resonators are designed within and around the transmission line connecting two orthogonal ports of the dual-polarized monopole antenna operating in the transceiver mode. Initially, the patch antenna and the resonator circuits are optimized separately for the intended impedance bandwidth and frequency response, respectively, and are later integrated together to achieve the required performance. The operating range of the tag antenna is from 2 to 5.2 GHz. Furthermore, two prototypes of the proposed RFID tag with the 10-b code are fabricated and tested. The simulation and experimental results are found to be in good agreement, validating the proposed design.

Control of Quasibound Waves in Spiral Metasurfaces

Resonant light scattering by a subwavelength dielectric resonator array can show narrow, highly tunable resonant lineshapes from the interaction among multiple resonances. Several approaches have been introduced to control the spectral response of resonant light scattering, including optimization of the aspect ratio of cylindrical resonators, breaking in-plane inverse symmetry of coupled resonators, and operating periodic structures at the Γ point in reciprocal space. In this paper, we report the experimental demonstration of the control of resonant light scattering by subwavelength spiral resonator arrays. The fabricated metasurfaces support two types of resonances: the first one characterized by a Lorentzian peak with a long lifetime and the second type with a short lifetime supported by the lattice. By controlling the coupling strength between these two resonances through tailored broken symmetries, the resonant line shape of the spiral metasurface can be precisely tuned. The measured spectra show an ultrawide frequency tuning (over 16 THz) of the resonant mode by changing the spiral parameter at a fixed lattice constant. A temporal couple-mode theory combined with frequency-domain finite element method simulations was used to describe the measured transmission spectra of the fabricated metasurfaces.

Maximizing Archimedes spiral packing density area.

In this paper, we experimentally demonstrate a broadband Archimedes spiral delay line with high packing density on a silicon photonic platform. This high density is achieved by optimizing the gap between the adjacent waveguides (down to sub-micron scale) in the spiral configuration. However, care must be taken to avoid evanescent coupling, the presence of which will cause the spiral to behave as a novel type of distributed spiral resonator. To this end, an analytical model of the resonance phenomenon was developed for a simple spiral. Moreover, it is demonstrated that this distributed spiral resonator effect can be minimized by ensuring that adjacent waveguides in the spiral configuration have different propagation constants (β). Experimental validations were accomplished by fabricating and testing multiple spiral waveguides with varying lengths (i.e., 0.4, 0.8, and 1.4 mm) and separation gaps (i.e., 300 and 150 nm). Finally, a Linear Density Figure of Merit (LDFM) is introduced to evaluate the packing efficiency of various spiral designs in the literature. In this work, the optimum experimental design with mitigated resonance had a length of 1.4mm and occupied an area of 60 × 60µm, corresponding to an LDFM of 388km-1.

Design of frequency‐selective rasorber with multiple bands

In this letter, a novel dual-polarized frequency selective rasorber (FSR) with multiple absorption bands and multiple transmission bands is presented. The proposed FSR consists of a lossy layer and a lossless multi-bandpass frequency selective surface (FSS) layer, which are isolated by an air spacer. In the lossy layer, three parallel resonances can be generated by introducing rectangular spiral resonators on cross metal lines loaded with resistors. In order to achieve the same transmission frequency band as the top lossy layer, three square slots are designed at the bottom FSS layer. For demonstration, the proposed FSR is simulated, manufactured, and measured, and the measurement results are consistent with the simulation results.

Experimental Study of Effectiveness of Metasurface for Efficiency and Misalignment Enhancement of Near-Field WPT System

Unlikely for a far-field wireless power transfer (WPT) system, designing a metasurface is critical for a near-field WPT system. First, a robust near-field WPT system using open-loop spiral resonators and a metasurface are designed, and then, the effectiveness of the metasurface is investigated in improving the power transfer efficiency (PTE) and misalignment effects. Furthermore, a study of planar and angular misalignments is also executed experimentally to prove the WPT system immunity. The proposed WPT system offers a PTE of 30% when the Rx shifts by the lateral length of the Rx that means the Rx does not remain in front of the Tx. Moreover, the efficiency is almost unchanged due to the angular misalignment.

Hybrid frequency‐selective rasorber with wide passband based on spiral resonator

Hybrid frequency‐selective rasorber with wide passband based on spiral resonator

Single-coil Design Approach for Dual-band Near-field Coupled Resonators

With the adoption of single coil approach, printed spiral resonator design strategy for near-field wireless energy transfer is presented. A pair of symmetrical resonators operating at high frequency band specifically 6.78 MHz and 13.56 MHz is designed. Simulated power transfer efficiency (PTE) of over 88% are obtained for both frequencies when coupled spiral resonators separated at a distance of 25 mm is integrated with hybrid compensation network topology. The variance of PTE between both frequencies is about 0.04.

A metamaterial based microfluidic sensor for permittivity detection of liquid

The electromagnetic (EM) behavior of a microwave sensor has specific relationship with the physical properties of the materials to be detected, e.g. the concentration of solution and the permittivity of gas. The microwave sensor can detect changes of EM response in real time, and obtain the material properties with low sample consumption, high efficiency and dispersion characteristics. This work presents a microfluidic sensor using spiral resonators and plasmonic metamaterials with confined EM fields for intensive resonance. Two microfluidic chips with spiral channels engraved in polydimethylsiloxane are also adopted to enhance the interaction between the EM fields and the carried liquids at resonance frequencies. The permittivity of liquid samples can be detected through the shift of resonance frequency. A prototype of the sensor is fabricated and tested with several regular solutions and organic solvents, showing a good performance in terms of low liquid consumption (8 μl), good sensitivity (410 MHz frequency offset when ϵr changes from 1 to 36.7) and low cost.

Miniaturized Multilayer Surface-Mountable 5G Filter Based on Shielded Spiral Resonator

This brief presents a miniaturized bandpass filter (BPF) based on the shielded Archimedes spiral resonators using the multilayer printed circuit board (PCB) technology. The spiral resonators are incorporated inside a substrate integrated waveguide cavity, resulting in miniaturization by introducing additional coil-to-ground capacitance, and the enhancement of electromagnetic compatibility (EMC) due to the enclosed metal cavity. Detailed theoretical derivation for the resonator is presented to prove its miniaturized effect. A miniaturized 4 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sup> -order BPF for 5G N78 application is developed with the proposed resonators. Compactness is further realized by the multilayer geometrical arrangement, consisting of two types of inter-stage coupling. One is the horizontal edge coupling and the other is the vertical space coupling through the spiral slot. Transmission zeros (TZs) are generated on each side of the passband by source-to-load coupling. The proposed filter is featured with an extremely small volume, low loss, together with good surface-mountable characteristic.

Design of Spiral Resonator Based on Fractal Metamaterials and Its Improvement for MCR-WPT Performance

To further optimize the electromagnetic characteristics of square spiral resonator (SSR) in wireless power transfer (WPT) system, the SSR fractal finite element model is established in the high frequency structure simulator (HFSS) simulation software based on Koch curve and Hilbert curve. The mechanism of the effect of Koch and Hilbert fractal structure on frequency and permeability characteristics of SSR is analyzed in depth. The inductance of the resonant coil is calculated by the Maxwell software and then a magnetically coupling resonant WPT (MCR-WPT) system operating at 6.78 MHz is constructed in HFSS. The influence mechanism of the spiral metamaterial (MM) structure combined with the Koch/Hilbert fractal on the transfer performance of MCR-WPT system is analyzed. The simulation and experimental results show that the power transfer efficiency (PTE) of the system can be improved effectively when the negative permeability/hybrid MM slab (NMS/HMS) based on Koch/Hilbert/initial SSRs is inserted in the middle of the transfer distance. In the experiment, the PTE of the HMS based on Hilbert fractal can be improved by up to 21.62%.

Second-Order, Single-Band and Dual-Band Bandstop Frequency Selective Surfaces at Millimeter Wave Regime

This communication presents the miniaturized low-profile second-order (SO) bandstop frequency selective surfaces (FSSs) for single- and dual-band resonances. The unit cell comprises two identical first-order (FO) elements in a back-to-back configuration with the metal grid in between. Two thin dielectric substrates separate the three metal layers. The proposed FO unit cell consists of intercell-connected spiral resonators (SRs) with capacitively coupled cross loop dipole. The SO filter response of the proposed FSS exhibits a wide stopband ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$S_{21} &lt; -10$ </tex-math></inline-formula> dB) bandwidth (BW) of 27.6%. The unit cell has the periodicity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.162\lambda _{0}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> is the free space wavelength at the lower passband. The novelty of the proposed work is a miniaturized simple unit cell geometry, at the millimeter-waveband but not limited to it, with polarization insensitive and high angular stable filter response up to 60° with small variations in the BW. An unconventional four-unit cell element FSS is designed for dual-band SO stopband resonances with the BWs of 8.3% and 13.8%. Prototypes of both FSSs were fabricated and their measured results were found consistent with the simulated filter responses.

A Wideband Frequency-Selective Rasorber With Rectangular Spiral Resonators

This letter presents a frequency selective absorber (FSR) with a passband and two wide absorption bands. The structure is composed of a resistive layer and a bandpass frequency selective surface (FSS) layer. The resistive layer is a combination of metal lines with loaded resistors and rectangular spiral resonators, which generate parallel resonances. Square slots are designed in the bandpass FSS to produce parallel resonance inside the passband and perform as a metal plane outside the passband. A nearly transparent window can be obtained by adjusting the parallel resonant frequencies of two layers to be consistent. The simulation results show that the 3 dB transmission band ranges from 6.5 to 7.76 GHz, and the minimum insertion loss is 0.05 dB at 7.09 GHz. The dual-polarized FSR presents stable operating characteristics and realizes two absorption bands on both sides of the passband, and the fractional bandwidth of the reflection coefficient lower than −10 dB is up to 127%, which ranges from 2.69 to 12.04 GHz. In addition, the FSR is manufactured and measured, and the measurement results are consistent with the simulation results.

An ultra‐wide passband frequency‐selective rasorber with high transmission

Abstract A frequency‐selective rasorber (FSR) with an ultra‐wide transmission band and low‐insertion loss based on compound spiral resonator is presented. The structure consists of the top lossy layer and bottom lossless layer. The frequency‐selective surface is adopted as the lossless layer to obtain an ultra‐wide transmission window. The top lossy layer is made up of the compound spiral resonator and I‐shaped metallic strips with four lumped resistors in this design. The equivalent circuit model is constructed to expound the operating mechanism of this FSR. The 1 dB transmission bandwidth is achieved from 6.98 to 12.21 GHz (54.5%) with the minimum insertion loss of 0.13 dB at 10.40 GHz. Moreover, the bandwidth of S11 &lt; −10 dB is obtained in 4.64–12.21 GHz with a fractional bandwidth of 89.8%. Furthermore, the designed FSR has a good oblique incident angle of 30° and polarization stability. Finally, the simulation results are proved by the experimental results, which confirm the feasibility of the design.

High capacity chipless RFID tags for biomass tracking application

AbstractThe design of a low-cost, flexible, miniaturized, and a high code density chipless radio-frequency identification (RFID) tag is presented as a solution for tracking the transportation of biomass fuel pellets. The performance of the tag is presented and demonstrates the applicability of the design for different material systems, while maintaining a compact size of 5.06 cm2. The tag consists of nested concentric hexagonal elements and a central spiral resonator suitable for ID encoding. The tag presented demonstrates code density of 3.6-bits/cm2, possesses angular stability up to 60°, and high radar cross section (RCS). The tag performance was also observed for tracking 5 kg of fly-ash biomass. Additionally, as the tag mass mostly consists of FR4, PET, or Taconic TLX-0 with a minute mass of either copper, gold, or silver, the tag can be easily combusted and disposed of during biomass combustion. The novel features of this tag are the combination of hexagonal and spiral shape slots for maximum space utilization thereby achieving high RCS signatures along with high code density. All these properties of the proposed chipless RFID tag provide a pioneering pathway for a real-time biomass tracking application.

In-Situ permittivity measurement of liquids using immersible planar resonator

Accurate dielectric characterization of liquid materials is critical for a wide range of applications. In this paper, a permittivity measurement method featuring a planar immersible probe consisting of a small loop loaded with a spiral resonator is presented. The design of the probe is described herein, and its performance is demonstrated through measurements and benchmarking with a widely accepted commercial dielectric measurement solution. It is shown that the probe renders accurate permittivity values for various edible oils, crude oil and ethanol solutions with varying concentrations.