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Langmuir probe (LP) diagnostics is performed on an inductively coupled plasma (ICP) generated using a flat spiral antenna. The current–voltage (I - V) characteristics are measured using a radio frequency (RF) compensated LP to mitigate the effect of RF distortion in I - V measurements. All-important plasma parameters such as electron density (ne), electron temperature (Te), plasma potential (Vp), and electron energy distribution function (EEDF) are measured in a cylindrical-shaped ICP. The plasma is generated by feeding RF (13.56 MHz) current in the planer multiple spiral antennas. It is seen that the plasma is uniform over an area with 200 mm diameter, with an electron number density in the range from ~ 1011 to 1012 cm−3. Typically for plasma processing of materials, the required density fall in that region. Variation of plasma parameters is investigated as a function of applied RF power and operating pressure and the observed results are discussed. [ABSTRACT FROM AUTHOR]

A large circular transmitter (power pad) is often utilized for inductively wireless charging so that the power receiver can position itself freely within the power pad. However, the uneven magnetic field distribution leads to the impedance mismatch and the variable transferred power due to the misalignment between a receiving coil and a relatively large transmitter coil. In this paper, the effects of the turn numbers, trace spacing, and coil size on the uniformity of magnetic field distribution over a planar spiral coil (PSC) are investigated based on an analytical model. Then, the genetic algorithm is used to optimize the trace width and spacing of a ten-turn PSC with the fixed outer and inner diameters, whereas the magnetic field is numerically calculated by HFSS software. The geometrically optimal PSC is obtained with the trace width approximately equal to trace spacing for each turn by minimizing the coefficient of variation (COV) of magnetic field within an effective charging area over the coil. The results showed that the simulated and measured COVs of magnetic field were 0.130 and 0.121, respectively, which are obviously less than that of the uniformly spaced regular coil and show a little less than that of the optimally spaced coil with fixed trace width. Therefore, the trace spacing is a major consideration to achieve the uniform magnetic field, whereas the trace width variation is applied to refine the evenness of field. It is also expected that the proposed GA-based optimization is well applied to design other Txs with conformable shape in inductively WPT systems for stable power delivery regardless of the receiver positions. [ABSTRACT FROM AUTHOR]

Wireless power coils have found important use in implantable medical devices for safe and reliable wireless power transfer. Designing coils for each specific application is a complex process with many interdependent design variables; determining the most optimal design parameters for each pair is challenging and time-consuming. In this paper, we develop an automated design method for planar square-spiral coils that generates the idealized design parameters for maximum power transfer efficiency according to the input design requirements. Computational complexity is first reduced by isolating the inductive coupling coefficient, k, from other design parameters. A simplified but accurate equivalent circuit model is then developed, where skin effect, proximity effect, and parasitic capacitive coupling are iteratively considered. The proposed method is implemented in an open-source software which accounts for the input fabrication limitations and application specific requirements. The accuracy of the estimated power transfer efficiency is validated via finite element method simulation. Using the presented approach, the coil design process is fully automated and can be done in few minutes. [ABSTRACT FROM AUTHOR]

An implantable antenna appropriate for wireless medical telemetry services (WMTS) band (1.39–1.42 GHz) and ISM band (2.4–2.48 GHz) biotelemetry application is presented in this article. Meandered structure of varying width ended with spiral is employed for miniaturization. Antenna size is further reduced by a shorting pin with an overall dimension of 11 mm $\times11$ mm $\times1.28$ mm and coaxial fed. The proposed antenna is designed, simulated, and optimized with a layer of skin phantom model. The measured −10 dB bandwidth range from 1.395 to 1.44 GHz at WMTS band and 2.3905 to 2.4512 GHz at ISM band. The proposed antenna shows an $S_{11}$ of −25.78 and −39.95 dB at WMTS and ISM bands, respectively. The antenna has been simulated and found to radiate at ISM and WMTS bands in a free space scenario too. The proposed work is implemented using Rogers 3010 substrate, and the reflection coefficient of those modules was then measured using a network analyzer. [ABSTRACT FROM AUTHOR]

A dual-function solar cell antenna is presented for wideband communication and optical energy harvesting. In the proposed design, four solar cells have been adopted as antenna and energy harvesting array for both wireless communication and optical energy harvesting simultaneously. The radiation performances of the proposed solar cell antenna are measured and the optical experiment is conducted to verify its abilities of optical energy harvesting. To clarify the effects of solar cells on the antenna performance, another copper antenna with the same structure is fabricated for comparison. The proposed technology can integrate wireless communication and green battery components, makes it promising for green communication, clean energy, and environmental protection. [ABSTRACT FROM AUTHOR]

We study spiral waves in a mathematical model of a nonlinear optical system with a feedback loop. Starting from a delayed scalar diffusion equation in a thin annulus with oblique derivative boundary conditions, we shrink the annulus and derive the limiting equation on a circle. Based on the explicitly constructed normal form of the Hopf bifurcation for the one-dimensional delayed scalar diffusion equation, we make predictions about the existence and stability of two-dimensional spirals that we verify in direct numerical simulations, observing pulsating and rotating spiral waves. [ABSTRACT FROM AUTHOR]

Power transfer efficiency (PTE) is a key performance parameter in development work on resonant inductive power transfer (IPT) systems. Geometrically optimizing the transmitter (Tx) and receiver (Rx) coil pair is a way of improving the IPT system’s efficiency. In this article, a new figure-of-merit (FoM) is proposed to find an optimum coil geometry which maximizes the PTE. The employed FoM parameter, called the “strong coupling factor” (${P_{\text {scf}}}$), is defined such that its value indicates how strongly the Tx and Rx coils are linked together. Considering the IPT application and its physical size constraints, a proper selection method for identifying the numerical value of ${P_{\text {scf}}}$ is essential for optimal coil geometry design. This article presents an iterative algorithm to assist in the selection of the most favorable ${P_{\text {scf}}}$ value which provides maximized PTE for the designed optimum coil geometry. Design examples of two nominal IPT systems at frequencies of 415 and 0.1 MHz are used to investigate the design algorithm. Theoretical calculations show the optimum geometry designed for the IPT system operating at 415 MHz, with coupling coefficient ($K$) of 0.2, can achieve maximum PTE of 85.70%. Measurements presented from a practical Tx/Rx coil pair in the IPT link operating at 0.1 MHz, with $K=0.05$ , show a PTE of 83.10% against a calculated PTE of 84.11% validating the design process. [ABSTRACT FROM AUTHOR]

Acquisition and tracking systems form an important component of free-space optical communications due to directional nature of the optical signal. Acquisition subsystems are needed in order to search and locate the receiver terminal in an uncertainty/search region with very narrow laser beams. In this paper, we have proposed and analyzed two adaptive search schemes for acquisition systems that perform better—for the low probability of detection—than the spiral scanning approach. The first of these schemes, the adaptive spiral search, provides a better acquisition time performance by dividing the search region into a number of smaller subregions, and prioritizing search in regions of higher probability mass. The second technique—the shotgun approach—searches the region in a random manner by sampling the search region according to a Gaussian distribution. The adaptive spiral scheme outperforms the shotgun approach in terms of acquisition time, especially if the number of search subregions is large enough. However, a higher pointing accuracy is required by the adaptive spiral search in order to search the region precisely. On the other hand, the shotgun scanning approach does not require such stringent pointing accuracy. [ABSTRACT FROM AUTHOR]

For wideband frequency-agile radio frequency (RF) integrated circuits, tunable components are essential. It has been a great challenge in RF electronics to utilize a magnetic tunable inductor for ultrawideband applications. This letter demonstrates an electrically tunable RF inductor encompassing a broad range of frequencies from 4 to 20 GHz. This is achieved by integrating domain-patterned Permalloy of various thicknesses, such as 20, 60, and 92 nm. There is a performance boost of the inductor, and a tunable inductor is achieved by applying dc current. Experimental results show that amongst all the Permalloy patterns, $11\,\mu\text{m}\times 13\,\mu\text{m}$ provides the highest inductance tunability of 15.8% at 20 GHz for 60 nm patterns, 10.8% at 15.1 GHz for 92 nm, and 4.3% at 15.7 GHz for 20 nm. This is the highest inductance tunability obtained so far for spiral inductors integrated with 60 nm Permalloy patterns using the dc bias method. The 15.8%, 10.8%, and 4.3% inductance tunability provides 8%, 5.7%, and 2.1% frequency tuning correspondingly. [ABSTRACT FROM AUTHOR]

There are a large number and variety of microalgae in the ocean, which are important natural resources for extensive applications. However, how to identify and separate microalgae quickly and effectively remains a major challenge for investigation and utilization of microalgae resources. There are many methods for cell separation, while each of them has pros and cons. Therefore, it is difficult to meet the particular requirements of separating complex samples, such as microalgae, solely with a single method. Herein, a two-stage microfluidic separation chip was designed by combining inertial and dielectrophoretic (DEP) forces, which can achieve rapid and accurate separation of three common microalgae cells, including Platymonas, Closterium and Chlorella, with separation efficiency exceeding 90%. In the first-stage, high-throughput inertial separation technique was used to separate microalgae with their different equilibrium positions. Then, the DEP force was used to separate microalgae cells which were not separated in the first-stage through their dielectric properties. To the best of our knowledge, there is no prior reports of microalgae separation by combining DEP and inertial techniques. In addition, the DEP characteristics of microalgae cells under a non-uniform AC electric field were firstly reported in this study, and the DEP responses of each cell type were measured against AC electrical frequency changes. These findings may contribute to our understanding of the dielectric properties of microalgae, as well as the development of novel techniques for microalgae separation, detection, and marine environmental monitor and analysis. [ABSTRACT FROM AUTHOR]

We introduce a kernel low-rank algorithm to recover free-breathing and ungated dynamic MRI from spiral acquisitions without explicit k-space navigators. It is often challenging for low-rank methods to recover free-breathing and ungated images from undersampled measurements; extensive cardiac and respiratory motion often results in the Casorati matrix not being sufficiently low-rank. Therefore, we exploit the non-linear structure of the dynamic data, which gives the low-rank kernel matrix. Unlike prior work that rely on navigators to estimate the manifold structure, we propose a kernel low-rank matrix completion method to directly fill in the missing k-space data from variable density spiral acquisitions. We validate the proposed scheme using simulated data and in-vivo data. Our results show that the proposed scheme provides improved reconstructions compared to the classical methods such as low-rank and XD-GRASP. The comparison with breath-held cine data shows that the quantitative metrics agree, whereas the image quality is marginally lower. [ABSTRACT FROM AUTHOR]

We theoretically present the selective remote-excitation of the gap mode in the silver nanowire-nanoparticle (Ag NW-NP) system based on the excitation of the ±1-order chiral surface plasmonic polaritons (SPPs) modes, which have the crescent-shaped transverse intensity distributions and the helical propagation traces. When the gap mode at junction between the Ag-NW and the Ag-NP is excited via the +1-order chiral SPPs mode, the −1-order chiral SPP mode cannot effectively excite the gap mode, because the propagation traces of the ±1-order spiral SPPs modes have complementary intensity distributions. This selective remote-excitation method may be used in the nanowire photonics and nano-optical spectroscopy. [ABSTRACT FROM AUTHOR]

Fully integrated voltage regulation, while important for a number of applications, is challenging due to the limitations of on-chip passive components, particularly inductors. This work demonstrates a new direction in passive-component integration through the design and implementation of a silicon-integrated merged- $LC$ resonator, used in a resonant switched-capacitor voltage regulator. The merged- $LC$ resonator combines flying capacitance and inductance into a single structure to reduce ac resistive losses, achieving higher efficiency and power density. The voltage regulator is implemented in a 0.18- $\mu \text{m}$ CMOS process and achieves 85.5% efficiency at 0.47 W without off-chip passive components. Light-load efficiency is extended through the use of OFF-time modulation (OTM); the design achieves <40-mV under-/over-shoot during 2–50-mA/4- $\mu \text{s}$ load transients. [ABSTRACT FROM AUTHOR]

The establishment of laser communication relies on high probability acquisition and then stably track with a high precision. However, the limitation of laser divergence and the interference may lead to unstable acquisition and tracking. In this paper, we proposed a novel beaconless acquisition approach to achieve the coverage of a large uncertainty cone with a narrow communication beam, using a composite spiral scanning method based on fast steering mirror and servomechanism system. The modeling and an analytical expression of sub-regions searching in conjunction with spiral skip overlap are described to realize the effective coverage. A detailed analysis of optimal matching for acquisition parameter is presented to quantify the design result. For the tracking procedure, an experiment is presented to investigate the performance of servo system with the combination of coarse-fine tracking consideration, and iteration learning control scheme in additional to the traditional controller based on periodic external disturbance is introduced for dynamic target tracking system. The iterative control law is taken into account to adjust deviation value and further improve the tracking performance. The obtained tracking accuracy is within ±2µrad which demonstrates the effectiveness the control characteristic in the presence of laser fluctuation. [ABSTRACT FROM AUTHOR]

For real-time millimeter-wave (MMW) imaging applications, spatially 2-D sparse sampling is one of the most promising techniques to reduce the heavy cost of signal acquisition. Therefore, in this article, we develop a new MMW synthetic aperture radar (SAR) sparse imaging method by establishing a 2-D pseudorandom spiral-sampling pattern. The method consists of two phases: sparse sampling-pattern design and sparse-imaging processing. The sparse sampling-pattern design is modeled as an optimization programming problem, in which the initial sampling pattern is a classical Archimedes spiral, and then, the number of samples per cycle is adjusted by coming up with a modified sigmoid function. This function is employed to increase the angular aperiodicity and randomness over the whole planar aperture. For sparse-imaging processing, a singular value thresholding (SVT) algorithm is applied to reconstruct the complete echo from partial samples observed by sparse sampling, and then, the inversion can be performed via the traditional imaging algorithms. In particular, a performance-guarantee condition of SVT is introduced to control the minimum number of samples, which bridges the relationship between pattern optimization and reconstruction performance. Our motivation is to answer what the undersampling pattern is and to estimate the extent to which the number of samples can be reduced by the current sparse imaging method. Finally, simulations and experiments validate the feasibility and effectiveness of the proposed sampling pattern, and the imaging results further demonstrate that our method with partially observed samples can offer the performance comparable to dense sampling. [ABSTRACT FROM AUTHOR]

This brief presents a self-packaged spiral shape power divider (SSPD) using substrate integrated suspended line (SISL). The two output paths are designed to form mutually coupled spiral shape, and the isolation resistor is placed at the center of the spiral to reduce the circuit area. By properly increasing the coupling, short total electrical length can be obtained. SISL is adopted for low loss and self-packaging. The suspended substrate is patterned to further reduce the dielectric loss. The even-/odd- mode method is used to analyze this circuit, and the design equations are derived. A SISL SSPD with patterned substrate works at 2.5 GHz is implemented for verification. In a wide fractional bandwidth (FBW) of 55%, the measured return loss and two output ports isolation are both better than 15 dB, while the SSPD with patterned substrate achieves 0.06 dB insertion loss at the center frequency. [ABSTRACT FROM AUTHOR]

Abstract Embryo transfer (ET) is a decisive step in the in vitro fertilization process. In most cases, the embryo is transferred to the uterus after several days of in vitro culture. Although studies have identified the beneficial effects of ET on proper embryo development in the earlier stages, this strategy is compromised by the necessity to transfer early embryos (zygotes) back to the fallopian tube instead of the uterus, which requires a more invasive, laparoscopic procedure, termed zygote intrafallopian transfer (ZIFT). Magnetic micromotors offer the possibility to mitigate such surgical interventions, as they have the potential to transport and deliver cellular cargo such as zygotes through the uterus and fallopian tube noninvasively, actuated by an externally applied rotating magnetic field. This study presents the capture, transport, and release of bovine and murine zygotes using two types of magnetic micropropellers, helix and spiral. Although helices represent an established micromotor architecture, spirals surpass them in terms of motion performance and with their ability to reliably capture and secure the cargo during both motion and transfer between different environments. Herein, this is demonstrated with murine oocytes/zygotes as the cargo; this is the first step toward the application of noninvasive, magnetic micromotor‐assisted ZIFT.

Direction-of-Arrival (DOA) estimation capability of sensor arrays is greatly influenced by geometric configuration of arrays. We proposed a new type 2-D planar array, improved Archimedean spiral array (IASA), to arrange sensor elements and enhance the array performance through Archimedean curves. The 2-D MUSIC algorithm is used to estimate the spatial spectrum of signals. The analysis is complemented with numerical simulations. By comparing the root mean square error, the IASA has better 2-D DOA estimation results than circular array, rectangular array, and concentric ring array.

A low-profile spiral antenna backed by a circular high-impedance surface (HIS) reflector composed of homogeneous (CirHISRhomo) fan-shaped patch elements is investigated. The total antenna height from the bottom of the CirHISRhomo to the spiral antenna is very small: 0.09 wavelength at a lowest design frequency of 3 GHz. It is revealed that the CirHISRhomo contributes to a constant input impedance and a small axial ratio (AR) across the design frequency range of 3–10 GHz (the fractional bandwidth is approximately 108%). For comparison, the AR for the spiral antenna backed by a conventional perfect electric conducting reflector is also presented. The analysis results are verified by the measured results of the fabricated antenna. [ABSTRACT FROM AUTHOR]

A novel artificial magnetic conductor (AMC) ground plane with spherical curvature is proposed. The metallic patches used to form the high impedance surface (HIS) ground plane are of circular periodicity. A detailed description on the design procedure and reflection phase characterization of such ground planes is provided. The impact of the curvature on the reflection characteristics and the maximum curvature which can be applied to the flat HIS are also examined. Two curvilinear antenna elements (loop and spiral) are located above the designed ground plane, and their performances are compared when the two are placed on a flat HIS. Measurements are performed to validate the simulations. An excellent agreement is attained. [ABSTRACT FROM AUTHOR]

Objective: 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. Methods: 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. Results and Conclusion: 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. Significance: 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. [ABSTRACT FROM AUTHOR]

Electromagnetic manufacturing (EMMa) methods are being developed as an auxiliary to conventional manufacturing processes as it offers many potential advantages. Numerical methods are being employed to predict the plastic deformation of the workpiece. A multiphysics coupled study of transient electromagnetic, thermal, and mechanical fields is imperative to predict the dynamic deformation of the workpiece during the manufacturing process. The challenging feature of solving a multiphysics problem is the high degree of coupling between the partial differential equations involved. This article describes a fast and efficient method for analyzing a coupled transient electromagnetic and mechanical problem during the process of EMMa process. A 3-D model has been considered for the formulation of electromagnetic and mechanical field equations. The coupling is usually done using finite elements methods (FEMs) which is computationally demanding for solving Electromagnetic fields. Use of FEM for solving an EM problem requires extra fine meshing of the workpiece in order to capture the skin effect and it also needs to mesh the surrounding air domain which is of no interest. This article describes an analytical framework for computing the electromagnetic pressure distribution on the workpiece, and the results have been compared with those obtained using FEM techniques. The mechanical problem is solved using commercial available FEM tools. The effects of deformation in the geometry of the workpiece and its velocity are considered which provide more accurate results. [ABSTRACT FROM AUTHOR]

This letter introduces two concentric open-loop spiral resonators (OLSRs) that are used to improve magnetic field for nonradiative wireless power transfer (WPT) systems. OLSRs are fed through metal–insulator–metal (MIM) capacitive coupling using a 50- $\Omega $ microstrip transmission line. First, a single OLSR is designed and implemented for WPT, then two OLSRs are used instead of a single OLSR to emphasize the surface current on the spiral resonators. Therefore, it helps to intensify the electromagnetic field in order to get a high transmission distance or higher efficiency. The proposed WPT system operates at 438.5 MHz with a measured power transfer efficiency (PTE) of 70.8% at a transmission distance of 31 mm and a design area of 576 mm2. An equivalent circuit of the proposed WPT system is presented as a heuristic approach to show the electrical behavior of the WPT system. [ABSTRACT FROM AUTHOR]

This letter presents a novel distributed choking technique, the spiral choke, for scattering suppression in dual-band antenna arrays. The working principle and the scattering suppression capability of the choke are analyzed. The spiral chokes are implemented as low-band radiators in a colocated 4G and 5G dual-band array to suppress cross-band scattering while broadening the bandwidth of the choked element. The experimental results demonstrate that the cross-band scattering in the array is largely eliminated, and the realized dual-band array has very stable radiation performance in both well-matched bands. [ABSTRACT FROM AUTHOR]

Embryo transfer (ET) is a decisive step in the in vitro fertilization process. In most cases, the embryo is transferred to the uterus after several days of in vitro culture. Although studies have identified the beneficial effects of ET on proper embryo development in the earlier stages, this strategy is compromised by the necessity to transfer early embryos (zygotes) back to the fallopian tube instead of the uterus, which requires a more invasive, laparoscopic procedure, termed zygote intrafallopian transfer (ZIFT). Magnetic micromotors offer the possibility to mitigate such surgical interventions, as they have the potential to transport and deliver cellular cargo such as zygotes through the uterus and fallopian tube noninvasively, actuated by an externally applied rotating magnetic field. This study presents the capture, transport, and release of bovine and murine zygotes using two types of magnetic micropropellers, helix and spiral. Although helices represent an established micromotor architecture, spirals surpass them in terms of motion performance and with their ability to reliably capture and secure the cargo during both motion and transfer between different environments. Herein, this is demonstrated with murine oocytes/zygotes as the cargo; this is the first step toward the application of noninvasive, magnetic micromotor‐assisted ZIFT. [ABSTRACT FROM AUTHOR]

In this paper, we present the design and the validation of a new smart textile developed for real time monitoring of human breath. The smart textile is a wearable stretching T-shirt featuring an array of six contactless and non-invasive sensors placed on human’s thoraco-abdominal walls. The wireless sensors communicate quasi-simultaneously the data to a detection base station through Bluetooth protocol. The sensor is composed of a spiral shaped multi-material fiber antenna with a central frequency at 2.4 GHz connected to a compact Bluetooth transmitter. The sensors are integrated on the stretchable T-shirt without compromising the user’s comfort. The sensing mechanism of the system is based on the shift of the central frequency of the spiral fiber antenna induced by the deformation of the thorax and the abdomen during the breath. As a consequence, the breathing pattern is obtained through the received signal strength indicator recorded by a portable detection base station. With the sensor array integrated into a T-shirt, we demonstrate the feasibility assessment for monitoring breathing of seven volunteers in seating and standing positions. Using an array of sensors strategically placed on the T-shirt provides a more reliable approach to detect interpretable breathing patterns by sensing the movement of the abdomen and the thorax at the same time. Using a commercial spirometer as a standard reference, we assessed the validity of breathing parameters (ie; expiration and inspiration times, breathing period, and breathing rate) measured with the T-shirt. Based on Bland-Altman statistical analysis, a good agreement between textile-based sensors and the standard reference was obtained. We were able to show that the smart T-shirt could detect breathing patterns and pauses in breathing, which could be very useful to monitor sleep apnea and clinical monitoring of patients. [ABSTRACT FROM AUTHOR]

Up–down series stacked inductors (UDSSIs) are known to have higher self-resonant frequency (SRF) when compared to standard series stacked inductors (SSSIs). In this article, a physics-based distributed capacitance model is presented to accurately estimate the interlayer parasitic capacitance in both these configurations. Based on our analytical formulations, it is revealed that the total capacitance reduces substantially with increasing spiral turns in UDSSI, which is in turn responsible for increased SRF and inductor figure of merit (FOM). The importance of substrate resistivity and interlayer dielectric thickness in further improved inductor FOM with UDSSI configuration is also demonstrated. Prototype inductors using SSSI and UDSSI configurations are fabricated in 0.35-μm BiCMOS technology. The measured results showed a 70% improvement in SRF with UDSSI structure while achieving inductance, quality factor, and FOM values of 31.54 nH, 12.34, and 4.4, respectively. [ABSTRACT FROM AUTHOR]

The integrated passive device (IPD) technology has become a new research hotspot, and it depends on electrical characteristics of GaAs, NiCr, and Si3N4 to construct radio frequency (RF) components. RF elements constructed by the IPD technology have features of high quality and ultra-small size, especially for capacitors and inductors. In order to realize the miniaturization of RF circuits, dimensions become as small as possible. Consequently, the layout of a spiral coupled line (SCL) cannot be drawn freely, so that it has uncontrollable odd- and even-mode impedances and a large coupling coefficient, which may limit the design of the traditional Marchand balun negatively. This article solves this problem by designing a GaAs IPD Marchand balun with 1/8-wavelength coupled lines (CLs) and using a capacitor termination to replace the open end in the conventional Marchand balun. Meanwhile, a filter is added to realize a filtering function. The proposed bandpass filtering Marchand balun (BFMB) chip has a size of 1.49 mm $\times1.39$ mm, and measured results indicate that it has an operation band of 2.39–5.68 GHz with a phase imbalance of 5.26° and a magnitude imbalance of less than 0.35 dB. [ABSTRACT FROM AUTHOR]

We report the design and characterization of a high performance integrated arbitrary filter from 1450 to 1640 nm. The filter's target spectrum is chosen to suppress the night-sky OH emission lines, which is critical for ground-based astronomical telescopes. This type of filter is featured by its large spectral range, high rejection ratio, and narrow notch width. Traditionally it is only successfully accomplished with fiber Bragg gratings. The technique we demonstrate here is proven to be very efficient for on-chip platforms, which can bring many benefits for device footprint, performance, and cost. For the design part, two inverse scattering algorithms are compared, the frequency domain discrete layer-peeling (f-DLP) and the time domain discrete layer-peeling (t-DLP). f-DLP is found to be superior for the grating reconstruction in terms of accuracy and robustness. A method is proposed to resolve the non-uniformity issue caused by the non-zero layer size in the DLP algorithm. The designed 55-notch filter is 50-mm-long and implemented on a compact Si3N4/SiO2 spiral waveguide with a total length of 63 mm. Experimentally, we demonstrate that the device has a insertion loss as low as 2.5 dB, and that the waveguide propagation loss is as low as 0.10 dB/cm. We are also able to achieve uniform notch depths and 3-dB widths of about 28 dB and 0.22 nm, respectively. [ABSTRACT FROM AUTHOR]

The issue of asset tracking in dense environments where the performance of the global positioning system (GPS) becomes unavailable or unreliable is addressed. The proposed solution uses a low-profile array of antenna elements (sensors) mounted on a finite conducting ground. A compact-size sensor array of six electrically small dual-band omnidirectional spiral antenna elements was designed as a front end of a tracker to operate in the 402 and 837 MHz spectrum bands. For the lower band, a three-element superposition method is applied to support estimation of the angle of arrival (AOA), whereas all six sensors are employed for the higher band. A low complexity and accurate AOA determination algorithm is proposed, the projection vector (PV), and this is combined with the array mentioned. Orthogonal frequency division multiplexing (OFDM) is integrated with the PV technique to increase the estimation resolution. The system was found to be suitable for installation on the roof of vehicles to localize the position of assets. The proposed system was tested for the tracking of nonstationary sources, and then two scenarios were investigated using propagation modeling software: outdoor to outdoor and outdoor to indoor. The results confirm that the proposed tracking system works efficiently with a single snapshot. [ABSTRACT FROM AUTHOR]

This paper tested the behaviour of 32 high-strength concrete columns confined by high-strength spirals under concentric compression. The test parameters included unconfined concrete compressive strength, spiral yield strength, volumetric ratio, and spiral spacing. The results showed that bulging and shear sliding were the two characteristic types of failure patterns of the thirty-two confined columns, depending on spiral spacing and concrete strength. Moreover, the spiral in most specimens did not yield at the confined concrete compressive strength. An analytical confinement model for high-strength concrete columns confined by high-strength spirals was proposed. In this proposed model, the calculated value of the spiral stress at the confined concrete compressive strength was used to calculate the feature points of the stressstrain curve. The proposed model showed good correlations with available experimental results of 64 columns. [ABSTRACT FROM AUTHOR]

In this article, we demonstrate the near electric field reduction ability of spiral resonators arrays (SRAs) in resonant inductive wireless power transfer (WPT) applications. In particular, we show that a suitably designed planar SRA, placed in the proximity of the driver loop, can significantly decrease the electric field level at the operative frequency, thus reducing the potentially dangerous radiation (i.e., the specific absorption rate) in the case of human exposure. In addition, due to the thin structure of the SRAs, the system is able to enhance the performance with respect to a conventional simple driver–receiver system for a fixed working distance. A systematic study has been performed through electromagnetic simulations to evaluate the optimum number of array unit cells to eventually achieve a compromise between efficiency enhancement and electric field shielding on a two-coil system, selected as a test case. Finally, the numerical results have been confirmed through measurements conducted on fabricated prototypes of the proposed WPT configurations. The introduced solution can be remarkably useful in all the WPT applications requiring a close interaction with human operators where exposure is a concern, such as automotive applications, biomedical implants, and rechargeable devices. [ABSTRACT FROM AUTHOR]

In this article, a miniaturized 2.5-D frequency selective surface with the band-stop response at 900 MHz is presented. The proposed FSS unit cell comprises rectangular spiral elements printed on both sides of the dielectric substrate. These spirals are connected with plated through-hole vias to form a “2.5-D closed loop”. The large perimeter of the closed loop increases the effective inductance and causes a reduction in resonant frequency and size of the unit cell. The structure is designed to operate at 900 MHz for shielding the interference from other GSM sources. The size of the proposed unit cell is 0.021λ0 × 0.021λ0 which is very compact with a figure-of-merit λ0/p = 47.6, where ${{\boldsymbol{\lambda }}_0}$ is the free-space wavelength of resonant frequency and p is the periodicity of unit cell. Further, the effect of substrate parameters on resonance performance has been studied. The proposed structure is polarization-independent and angularly stable for both TE and TM polarizations. A prototype of the FSS is fabricated and measured, where the measured responses show good agreement with the simulated responses. [ABSTRACT FROM AUTHOR]

Cell-scale micro-magnetic stimulation is the process of stimulating neuronal tissues using a sub-millimeter coil. During the process, a time-varying current is fed to the micro-coil, and the micro-coil generates a dispersed magnetic field in the focal region of the tissue to create the effect of magnetic stimulation. The micro-magnetic coil has the drawbacks of small inductance, large power consumption, low-quality factor, and uneven distribution of magnetic induction. In this article, we designed an improved F/C structure, which was surrounded by a magnetic film/planar coil, and developed a method for determining the geometric parameters of the structure based on an investigation of how the pattern, thickness, spacing, and width of the magnetic shielding layer (MSL) affect the micro-coil inductance $L$ and the magnetic induction $B$. The experimental results show: when the magnetic permeability $\mu _{r}$ of the micro-magnetic coil with the improved F/C structure is 106 H/m, the inductance reaches 1149.3 nH, the maximum value of magnetic induction $B$ on the $Z = 800$ nm tangential surface reaches 11.33 mT, and the average value of $B$ is 5.5 mT (the $B$ value exceeds 4.28 mT in 92.6% of the area of the $100\,\,\mu \text{m}\,\,\times 100\,\,\mu \text{m}$ micro-coil); the range of action of magnetic induction is approximately $20~\mu \text{m}$ in the $Z$ -direction. It can be concluded that the micro-magnetic coil with the improved F/C structure is superior to the existing micro-coils in terms of magnetic field uniformity, action strength, and inductance value, and the increased inductance value improves the quality factor $Q$ of the coil and reduces the power consumption of the micro-magnetic coil. [ABSTRACT FROM AUTHOR]

Traditionally, optical vortices (OVs) were generated with diffractive optical elements (DOEs) such as spiral phase plate (SPP), fork grating, spatial light modulator (SLM), and liquid crystal display (LCD). Here, a method was proposed for generating OVs by employing all-dielectric polarization-insensitive metasurfaces with cylinder arrays, which have high transmission efficiency. The polarization insensitivity of the metasurfaces was illustrated with the incidence of two pairs of orthogonal polarization, both the phase and transmission efficiency were consistent for the cylinder unit cell, and similar OVs were generated with the cylinder array. The topological charges of the generated OVs can be adjusted through the design of the metasurfaces. OVs with additional characteristics as vector beams, focused beams and Bessel beams were further generated. This work has potential applications in beam shaping, optical tweezers, and optical communication. [ABSTRACT FROM AUTHOR]

In the past, a lot of research has focused on using spirals and rings to confine concrete. Yet, the effect of using spirals to confine square cross sections is not well investigated. It would appear from the above, therefore, that there is a need for a reappraisal of the material model used to describe the behaviour of concrete in the compressive zone of a beam. Its aim should be to improve the theoretical basis of the structural concrete design so as to be compatible with concrete behaviour in the experimental observation. This paper proposes an analytical confinement model that measures the stress–strain behaviour of rectangular concrete sections confined with spiral links. This research aims to provide an average equation to calculate the strength enhancement that results from confining rectangular beams with spiral links and hence this simplified model could be used for design purposes. The proposed model is capable of predicting the behaviour of normal-strength concrete as well as high-strength concrete and incorporates allowance strength variation. Comparisons are made between the proposed new model and the models of others in the literature. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Objective: A soft and stretchable inductive sensor is presented with the ability to wirelessly transmit large strain measurements without the need for directly connected circuitry. Methods: The sensor is fabricated using a scaffold-removal technique to create microfluidic channels within an elastomer sheet (0.07 MPa modulus), which are injected with a non-toxic liquid metal alloy electrode. An analytical model is derived to predict the static inductance of the sensor while being uniaxially stretched and experimental characterisation of the sensor’s dynamic response to axial and biaxial deformation is conducted, as well as wireless measurements within ex-vivo porcine tissue. Results: Experimental validation showed that the sensor’s inductance change is linear with uniaxial and biaxial strains up to twice its original length. Strain-rate dependent hysteresis was negligible during slow deformation ($ < {5} {s}^{-{1}}$) and below 10% during more rapid changes in length ($15\,\,{s}^{-{1}}$). For wireless strain sensing, the variation of inductance in the sensor induced an increase in the transmitting voltage from 3.1 V to 5.7 V for strains up to 83%. While implanted within different layers of porcine tissue, the transmitter voltage linearly increased by 750 mV on average under bending deformation. Conclusion: Large stretching (83%) and bending ($8\,\,{m}^{-{1}}$) deformations in the inherently soft sensor can be wirelessly captured, including through biological tissue. Significance: The wireless sensor’s simplified structure, where the antenna and sensor are integrated into a single soft spiral electrode with modulus comparable to biological tissue, means that this novel design shows significant potential for implantable and wearable biomedical devices to monitor dynamic deformation. [ABSTRACT FROM AUTHOR]

A plane spiral orbital angular momentum (PSOAM) mode-group (MG) based multiple-in-multiple-out (MIMO) communication system is proposed, and the performance is numerically analyzed in line-of-sight (LoS) channel. The simulated results show that the proposed scheme can increase the channel capacity, which means that PSOAM MGs superposed by several PSOAM waves can not only improve the signal-to-noise ratio (SNR) of system but also decrease the spatial correlation of sub-channels. Besides, combined with partial arc sampling receiving (PASR) method, the data streams can be recovered orthogonally with low complexity. The capacity gain and bit-error rate (BER) performance of the proposed scheme are evaluated. This technique may have potential in higher wireless capacity communications. [ABSTRACT FROM AUTHOR]

In this article, a novel approach to design low-profile miniaturized frequency-selective surfaces (FSSs) is proposed. The effective miniaturization of the FSS elements, based on square-ring-slot resonators, is accomplished by reactively loading the FSS unit cell with monolithically integrated components. The reactive components, such as capacitors and inductors embedded in the resonant unit cell, are fabricated using a multistep thin-film process based on benzocyclobutene (BCB) resin. The capacitors are built as planar metal-insulator-metal structures using an ultra-thin dielectric layer of BCB, while the multiturn inductors are fabricated as planar spiral structures with two metal layers and BCB as an interlevel dielectric for crossover. The advantages of the proposed approach are the capability to obtain large values of capacitances and inductances within small areas with low parasitics as well as the benefits in cost reduction and easy fabrication by using a planar microfabrication process. A component value variation analysis is performed to study the effect of fabrication tolerances in the reflection and transmission coefficients of the FSS when non-identical small cells are obtained. It has been experimentally validated that a 2.46 mm unit cell resonates at 4.175 GHz with transmission loss of 0.86 dB, achieving a miniaturization level of $\lambda $ /29. [ABSTRACT FROM AUTHOR]

In this article, a novel signal-transformation-based repetitive controller (STBRC) dedicated to the accurate and fast tracking of spiral trajectory with a time-variant amplitude is proposed and tested. To overcome the requirement of strictly periodic references of conventional repetitive controller, a mapping between spiral trajectory and constant amplitude sinusoid is developed to provide multiple lower gains at the fundamental frequency and its harmonics of the spiral trajectory to ensure zero steady-state errors. The stability of the control method and convergence of steady-state errors are analyzed with a lifted-system representation, respectively, for its time-variant property. Compared with internal model-based controllers for this trajectory, STBRC has the advantages of a simpler structure, fewer parameters, and better performance. The application to a piezoelectric nanopositioning stage verifies the effectiveness of the proposed control method on suppression of cross-coupling errors and improving the tracking performance of high-speed spiral trajectory in comparison with other controllers. [ABSTRACT FROM AUTHOR]

A neuro-fuzzy system is a learning machine that finds the parameters of a fuzzy system using approximate techniques of neural networks. Both neural network and fuzzy system have common features. These can solve problems that have no mathematical models. Adaptive neuro-fuzzy inference system (ANFIS) is an adaptive network that uses supervised learning on learning algorithm. To achieve effective results with ANFIS, selecting the optimization method in training is very important. Heuristics and metaheuristics algorithms attempt to find the best solution out of all possible solutions to an optimization problem. ANFIS training can be based on nonderivative algorithms. Heuristics and metaheuristics are nonderivative algorithms that can lead to better performance in ANFIS training. Most heuristic and metaheuristic algorithms are taken from the behavior of biological systems or physical systems in nature. The newly released emperor penguins colony (EPC) algorithm is a population-based and nature-inspired metaheuristic algorithm. This algorithm has much potential for solving various problems. In this article, an optimized ANFIS based on the new EPC algorithm is proposed. The optimized ANFIS is compared with other nonderivative algorithms on benchmark data sets. Eventually, the proposed algorithm is used to solve the classical inverted pendulum problem. The results show that the proposed ANFIS based on the EPC algorithm has less error and better performance than other state-of-the-art algorithms in both training and testing phase. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cylindrical whispering gallery mode (WGM) microresonators have achieved much attention in the sensing field due to high sensitivity, compatibility and integration. The excitation of spiral modes in such a resonator is unavoidable, causing the axial field distribution, and the injected analytes will undoubtedly interact with the axial mode field, resulting in unclear spectral responses. Here, these responses of the cylindrical WGM are investigated experimentally and theoretically for the first time. Using an optical fiber as the resonator, the experiment is performed by introducing the liquid into a part of the evanescent field along the axis. The perturbation is attributed to the modification of the resonator's profile, leading to an increase of the effective slope. We find the experimental demonstrations of the short-wavelength oscillations of spectral line shapes and the blue shifts of resonant wavelengths. Theoretical studies are consistent with the experimental phenomena. The research in the responses to the axial perturbation provides valuable insights into the effect of spiral modes on cylindrical WGMs and a potentially powerful tool for real-time biochemical analysis. [ABSTRACT FROM AUTHOR]

We propose an effective method to measure the orbital angular momentum of a perfect optical vortex (POV) beam with a hybrid angular gradient phase grating (HAG-PG), which is a gradient grating with angular changing distribution. The HAG-PG performs the transformation from the POV to the dark stripes of the diffraction intensity patterns. From the number and the orientation of dark stripes of far-field diffraction patterns formed by the HAG-PG, the modulus of TC and sign of the incident POV beam can be determined. The high scalability of this method for being unrestricted by the Fourier plane and its adaptation for measuring the POV beams with different states are demonstrated by loading the HAG-PG hologram on a spatial light modulator. And the detection sensitivity of the POV beam can be significantly improved. The experimental results agree well with the theoretical simulations. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hybrid secure method based on improved deoxyribonucleic acid (DNA) encoding encryption and spiral scrambling in chaotic OFDM-PON for enhancing the physical-layer security. In the improved DNA encoding encryption, the odd-even cross-bit DNA encoding, base scrambling and base-level substitution are determined by chaotic sequences. For each binary and base, the selected encoding rules and base scrambling methods are dynamically changing, which enhances the robustness against malicious attacks by attackers. In the spiral scrambling process, the QAM symbol matrix is divided into several blocks, and these blocks are scrambled. In the scrambling of the plural matrix, the position where the spiral starts and the orientation and direction of the traversal are also controlled by the chaotic sequences. By employing DNA encoding encryption and spiral scrambling, a key space of $\sim \!{10^{135}}$ can be achieved in the multi-fold encryption of the proposed scheme, which can improve the physical-layer security. The encrypted 16-QAM OFDM data are successfully transmitted over a 60-km SSMF in OFDM-PON. The simulation results demonstrate that it has better BER performance at the BER of ${10^{ - 3}}$ than other schemes. The proposed encryption method can effectively protect data from attacks by eavesdroppers or illegal users. [ABSTRACT FROM AUTHOR]

Based on the theory of transformation optics (TO), a new and simple method for generating multimodal orbital angular momentum (OAM) carrying beams in 3-D space is proposed in this letter. The proposed 3-D arbitrary-way multimodal OAM generator only requires an electric dipole as the source. It consists of a four-way plane waves converter and four multimodal OAM generators. Since this method only requires the operation of radial scaling map, different topological charge modes can be easily obtained by appropriately setting the sizes of the physical geometries. [ABSTRACT FROM AUTHOR]