Circular Array Research Articles

Analysis of the shear wave velocity structure of a soft-hard interlayered rock slope based on surface wave and microtremor survey

The information regarding the layered structure is pivotal to the stability analysis of soft-hard interlayered rock slopes. The variation in the shear wave velocity offers insights into the characteristics of the strata structure within a rock slope. In this study, a joint analysis method that combines the multichannel analysis of surface waves (MASW) and the microtremor surface method (MSM) was used to identify the layered structure of a soft-hard interlayered rock slope located in the Shandong Province, China. The survey lines were positioned on slope crests. For the MASW, the receivers were placed in line with an active seismic source. The MSM method uses a concentric circular array comprising seven receivers. Fundamental-mode dispersion data were extracted from the active and passive microtremor sources. The 1D velocity models were then inverted from the combined dispersion curves using a surrogate optimization algorithm. A 2D velocity profile of the investigated slope was constructed through linear interpolation, and it exhibited distinct characteristics of high- and low-velocity interlayers, consistent with the borehole data. Our results demonstrate that the joint analysis method provides a complementary approach to image velocity profiling of slopes, thus contributing to enhanced investigation depth and resolution in shallow layers owing to the wider frequency range of the dispersion curves.

Experimental Evaluation of an SDR-Based UAV Localization System.

UAV communications have seen a rapid rise in the last few years. The drone class of UAV has particularly become more widespread around the world, and illicit behavior using drones has become a problem. Therefore, localization, tracking, and even taking control of drones have also gained interest. Knowing the frequency of a target signal, its position can be determined (as the angle of arrival with respect to a fixed receiver point) using radio frequency-based localization techniques. One such technique is represented by the subspace-based algorithms that offer highly accurate results. This paper presents the implementation of the MUSIC algorithm on an SDR-based system using a uniform circular antenna array and its experimental evaluation in relevant outdoor environments for drone localization. The results show the capability of the system to indicate the AoA of the target signal. The results are compared with the actual direction computed from the log files of the drone application and validated with a professional direction-finding solution (i.e., Narda SignalShark equipped with the automatic direction-finding antenna).

Signal Processing Using a Circular Sensor Array to Measure the Torsional Angle of a Bolted Joint.

This study presents a new approach to determining the preload force of bolted joints. The concept involves measuring the torsional angle without contact. For this purpose, we present a circular magnetic sensor array integrated into the torque wrench. The torsional angle in bolted joints depends on the dimensions of the screw and the materials used and is typically less than four degrees. For this reason, one requirement is a high angular resolution so that a continuous recording of the torsion angle is feasible during the assembly process. This can be achieved using the circular sensor array and adapted signal processing methods. Two signal processing approaches are utilized. First, the direct method uses the discrete Fourier transformation to calculate the rotation angle from the signal phase. This approach is robust to signal distortion and does not depend on signal amplitude. Second, the method with a learning phase employs Gaussian process regression to minimize the angle error. In an experiment, both approaches were applied within a test bench and showed promising results. The direct method demonstrated a very good angular resolution without training and calibration. For mobile and less-complex applications where a reference system is unavailable, the direct method is preferable. However, in complex measurement systems where reference systems can be utilized initially, significant enhancements to an excellent resolution can be achieved through prior training.

Beampattern Synthesis and Optimization Method Based on Circular Frequency Diverse Array Engineering Model

The frequency diverse array (FDA) is capable of generating range-angle-dependent beampatterns by introducing a tiny frequency offset to the transmit carrier frequency of each array element. However, the beam-scanning potential of conventional linear FDA applications is limited, notably in their incapacity for 360° omnidirectional scanning. This paper introduces a method that leverages the geometric configuration of circular frequency diverse arrays (CFDAs) for synthesizing and optimizing beampatterns through a practical engineering approach. Initially, we compute the structural parameters and configurations of CFDA. Subsequently, the isophase plane is utilized to adjust the phase of each array element. Ultimately, the CFDA structure is used to optimize the non-uniform frequency offset, and the beampattern, which is capable of 360° omnidirectional scanning, is realized by low sidelobe optimization. Simulation results affirm that the CFDA antenna, as per the actual engineering model, possesses precise dot-shaped beampattern scanning abilities across both range and angle dimensions.

A Novel method for current measurement in an off-centered conductor of a circular array current probe

This paper introduces a yokeless and contactless circular array current probe specifically designed for measuring current in an off-centered conductor. Unlike conventional approaches that require the current-carrying conductor to be centered within the circular array for optimal accuracy, the proposed method utilizes four magnetic sensors strategically placed on the circumference of a circular PCB. This unique configuration allows for precise current measurement even with an off-centered conductor of a smaller radius. To eliminate errors due to the off-centered conductor, there is a need for more sensors on the circular array by using the averaging method. The proposed method is independent of the conductor’s position and diameter, ensuring accurate current measurements using only the circular array of four magnetic sensors. A functional prototype was constructed and subjected to laboratory testing, demonstrating the effectiveness of the proposed approach. In experimental setup, the proposed method’s circular array current probe exhibited a current measurement error below 1%, affirming its reliability and suitability for practical applications.

APC: Contactless healthy sitting posture monitoring with microphone array

The prevalence of poor sitting posture in daily work has become a growing concern among office workers and students due to the associated health problems. To address this issue, we design an acoustic sitting posture care system (termed, APC) based on a circular microphone array. Compared with classic posture recognition technologies such as visual perception and sensors, acoustic sensing naturally possesses advantages such as privacy protection and contactless capabilities. Concretely, our system leverages a customized and inaudible sound signal sent from a speaker to a user’s body, and an echo signal preprocessing method to sense the body posture. Our system comprises three modules: signal generation and collection, signal preprocessing, and posture classification. The signal generation and collection module is designed to create an appropriate signal waveform for transmitting the sound signal. We also develop a unique alignment method for received signals to implement background interference cancellation. In the signal preprocessing module, we propose a body profile extraction method based on the phase difference between received signals. In the posture classification module, we design an attention mechanism based classification network that can map the output of the previous module to different sitting posture categories. The experimental results show that our proposed method achieves an average accuracy of 98.4% for five common sitting postures. Furthermore, case studies conducted under different practical conditions have validated the robustness of our system.

Structural diversity of crustacean exoskeletons and its implications for biomimetics.

The crustacean cuticle is a biological composite material consisting of chitin-protein fibres in a mineralized matrix. Recent research has revealed a surprising range of fibre architectures and mineral compositions of crustacean skeletal structures adapted to various mechanical demands. It is becoming increasingly clear that the organic fibres in the cuticle may be organized in patterns differing from the standard twisted plywood model. Observed fibre architectures in protruding skeletal structures include longitudinal and circular parallel fibre arrays. Skeletal minerals often include calcium phosphates in addition to calcium carbonates. Furthermore, skeletal properties are affected by protein cross-linking, which replaces mineralization as a stiffening mechanism in some structures. Several common structural motifs, such as the stiffening of the outer skeletal layers, the incorporation of non-mineralized cuticle in exposed structures, and interchanging layers of parallel fibres and the twisted plywood structure, can be identified in skeletal elements with similar functions. These evolutionary solutions have the potential for biomimetic applications, particularly as manufacturing technologies advance. To make use of this potential, we need to understand the processes behind the formation of the crustacean exoskeleton and determine which features are truly adaptive and worth mimicking.

Development of an innovative wireless power transmission model for marine applications

The conventional wired charging system for ship-to-shore charging of underwater vehicles is prone to specific problems related to unreliable connection mechanisms and safety. The wireless charging system overcomes the danger of electrocution, as the power is transferred from the shore to the ship via electromagnetic induction instead of traditional ways of transferring AC power in the marine environment. This paper presents a novel system-level modeling and designing of wireless power transmission for marine applications. The proposed system comprises three main components: (a) a shore-side mobile transmitter (Shore-SMT), (b) an onboard static receiver, and (c) another ship-side mobile transmitter (Ship-SMT). The Shore-SMT and Ship-SMT, each consisting of a circular array of magnets, rotate in the vicinity of the receiver with a fixed circular variety of coils, resulting in voltage induction in the receiver coil. Consequently, the induced voltage in the receiver coil charges the onboard batteries. COMSOL® MULTIPHYSICS environment is used for the modeling and simulation of the proposed system using finite element method (FEM). The test cases simulate the individual and mutual rotation of the transmitters at several distances from the receiver coil. A prototype of the model is also developed. Experimental results from the developed prototype show promising performance as the percentage of transferred voltage increases from a single layer of x9 coil and x9 magnet bars to 70-75% and 80% in a double layer of x9 Ferro bars with x9 winding coils and double-sided x12 magnets and x9 winding coils respectively. It proves to be a better alternative to the conventional methods used for Ships and Vessel charging.

Plasmonic Properties of Self-Assembled Gold Nanocrescents: Implications for Chemical Sensing.

A bottom-up approach, the Langmuir-Blodgett technique, is used for the preparation of composite thin films of gold nanoparticles and polymers: poly(styrene-b-2-vinylpyridine), poly-2-vinylpyridine, and polystyrene. The self-assembly of poly(styrene-b-2-vinylpyridine) at the air-water interface leads to the formation of surface micelles, which serve as a template for the organization of gold nanoparticles into ring assemblies. By using poly-2-vinylpyridine in conjunction with low surface pressure, the distance between nanostructures can be increased, allowing for optical characterization of single nanostructures. Once deposited on a solid substrate, the preorganized gold nanoparticles are subjected to further growth by the reduction of additional gold, leading to a variety of nanostructures which can be divided into two categories: nanocrescents and circular arrays of nanoparticles. The optical properties of individual structures are investigated by optical dark-field spectroscopy and numerical calculations. The plasmonic behavior of the nanostructures is elucidated through the correlation of optical properties with structural features and the identification of dominant plasmon modes. Being based on a self-assembly approach, the reported method allows for the formation of interesting plasmonic materials under ambient conditions, at a relatively large scale, and at low cost. These attributes, in addition to the resonances located in the near-infrared region of the spectrum, make nanocrescents candidates for biological and chemical sensing.

Enabling More Users to Benefit From Near-Field Communications: From Linear to Circular Array

Enabling More Users to Benefit From Near-Field Communications: From Linear to Circular Array

A Structure-Shared Dual-Polarization Endfire MIMO Antenna Based on Uniform Circular Array for Positioning EMIS

A Structure-Shared Dual-Polarization Endfire MIMO Antenna Based on Uniform Circular Array for Positioning EMIS

Mode reconfigurable OAM helical array antenna for higher mode generation

AbstractIn this paper, an orbital angular momentum (OAM) mode reconfigurable antenna based on a uniform circular array (UCA) is presented. The phase superposition method is presented to overcome the limitation of the number of array units on the mode order in the conventional four‐element UCA antenna, which is limited to generating first‐order OAM beams. The unit phase is introduced by a bifilar helical antenna in this method, and the unit phase is superimposed with the feed phase of the UCA to enable the generation of 3rd‐order OAM beams from the four‐element UCA. At the same time, the DC signal‐controlled feed network assigns three distinct feed phases to the UCA, which realizes the reconfigurability of the three OAM beams. To achieve mode reconfigurability, 20 p‐i‐n diodes were integrated as switches in the feed network for controlling the ON/OFF status of p‐i‐n diodes in the feed network using DC signals. Finally, simulated and measured results show that three OAM beams (lz = −1, −2, and −3) have been generated in the frequency band from 10.6 to 11.8 GHz.

Novel baseline-free ultrasonic Lamb wave defect location method based on path amplitude matching

Ultrasonic Lamb wave detection technology constitutes a non-destructive evaluation approach extensively employed for the identification of flaws within plate-like structures. The conventional method for detecting and localizing defects in isotropic plate-like structures using ultrasonic Lamb waves relies on baseline signal data. However, the reliability of baseline data as a reference value is diminished due to varying working conditions of the structure. Therefore, to overcome the influence of mismatched baseline data, this paper proposes a novel non-baseline Lamb wave defect detection and localization method. Through simulation and experiment studies, it is discovered that defects at different positions have varied impacts on the amplitude of direct wave-packets under the same propagation path. By eliminating differences in the piezoelectric excitation characteristics of the sensing array (normalized through boundary reflect wave), the direct wave amplitude of multiple sensor pairs in the circular array can be compared and ranked. The paths closest to the location of the damage can be identified, enabling to obtain the defect location information. In this paper, the feasibility and effectiveness of this method has been verified by simulation and practical experiments. The experimental data and imaging results obtained over a four-month period demonstrate that, compared to the traditional baseline localization method, the baseline-free method proposed in this study exhibits a greater ability to resist interference caused by changes in environmental temperature. By increasing the number of sensors from 16 to 32, the positioning accuracy can be significantly improved, reducing the positioning deviation from 13 mm to 0.42 mm. This new non-baseline method based on path amplitude matching demonstrates enhanced practicality within the realm of engineering. Notably, this method holds the potential to be synergistically incorporated and applied in conjunction with various other measurement techniques.

Topology Optimization Design Method for Acoustic Imaging Array of Power Equipment.

Acoustic imaging technology has the advantages of non-contact and intuitive positioning. It is suitable for the rapid positioning of defects such as the mechanical loosening, discharge, and DC bias of power equipment. However, the existing research lacks the optimization design of microphone array topology. The acoustic frequency domain characteristics of typical power equipment are elaborately sorted out. After that, the cut-off frequencies of acoustic imaging instruments are determined, to meet the needs of the full bandwidth test requirements. Through a simulation calculation, the circular array is demonstrated to be the optimal shape. And the design parameters affect the imaging performance of the array to varying degrees, indicating that it is difficult to obtain the optimal array topology by an exhaustive method. Aimed at the complex working conditions of power equipment, a topology optimization design method of an acoustic imaging array for power equipment is proposed, and the global optimal solution of microphone array topology is obtained. Compared with the original array, the imaging performance of the improved LF and HF array is promoted by 54% and 49%, respectively. Combined with the simulation analysis and laboratory test, it is verified that the improved array can not only accurately locate the single sound source but also accurately identify the main sound source from the interference of the contiguous sound source.

An Integrated Approach to Control the Penetration Depth of 3D-Printed Hollow Microneedles

A variety of hollow microneedle (HMN) designs has emerged for minimally invasive therapies and monitoring systems. In this study, a design change limiting the indentation depth of the (3D) printed custom microneedle assembly (circular array of five conical frusta with and without a stopper, aspect ratio = 1.875) fabricated using stereolithography has been experimentally validated and modeled in silico. The micro-indentation profiles generated in confined compression on 1 mm ± 0.073 mm alginate films enabled the generation of a Prony series, where displacement ranged from 100 to 250 µm. These constants were used as intrinsic properties simulating experimental ramp/release profiles. Puncture occurred on two distinct hydrogel formulations at the design depth of 150 µm and indentation rate of 0.1 mm/s characterized by a peak force of 3.5 N (H = 31 kPa) and 8.3 N (H = 36.5 kPa), respectively. Experimental and theoretical alignments for peak force trends were obtained when the printing resolution was simulated. Higher puncture force and uniformity inferred by the stopper was confirmed via microscopy and profilometry. Meanwhile, poroviscoelasticity characterization is required to distinguish mass loss vs. redistribution post-indentation through pycnometry. Results from this paper highlight the feasibility of insertion-depth control within the epidermis thickness for the first time in solid HMN literature.

Bi-directional extraordinary absorption, transmission multifunctional metamaterial based on circular metal-VO2 composites

Multifunctional metamaterials play a crucial role in advancing terahertz technology. In this paper, a multifunctional metamaterial composed solely of circular metal-vanadium dioxide (VO2) is designed and numerically demonstrated. The device comprises a top layer of circular VO2 ring, two polyimide dielectric layers, with two metal layers etched and filled with VO2, and a bottom embedded silver (Ag) circular ring dielectric layer. The metamaterial serves as a broadband and narrowband absorptive or transmissive substrate, utilizing the phase transition of VO2 between its metal and dielectric states. When VO2 is in its metal phase, the top circular VO2 ring periodic array functions as a broadband absorber, exhibiting a relative absorption bandwidth of approximately 93%. Meanwhile, the bottom circular Ag ring periodic array functions as a narrowband absorber and exhibits high sensitivity. In contrast, when VO2 is in the insulating phase, the metamaterial acts as a broadband transmittance substrate, exhibiting a maximum transmittance greater than 85%. This proposed metamaterial holds tremendous potential for utilization across various applications within the terahertz band, spanning from terahertz stealth radar to tunable biosensors and photodetectors.

Exploring attentive listening in noise through the just-follow conversation task

Listening to a conversation demands comprehension, attention and prediction. To better understand the impact of these demands, as well as how hearing aids might alleviate them, a conversational listening test should be realistic, repeatable and relatable (i.e., have interpretable units). A test that potentially satisfies these needs is the just-follow conversation (JFC) task, where the listener adjusts the signal level to where they can understand, with effort, the gist of what is being said in a background of noise. Fifty-four participants sat in the centre of a circular loudspeaker array and adjusted the overall level of one monologue, one dialogue, two monologues or two dialogues presented in the front hemifield to where they could just follow the speech four times per trial. Signals were presented in surrounding fixed-level café and same-spectrum noise backgrounds. Bilateral hearing-aid users adjusted aided and unaided; non-users repeated each condition to evaluate reliability. Results showed an increase in JFC for dialogues re monologues. Individual JFC SNRs correlated with SSQ12 speech subscale scores as well as pure-tone threshold averages. JFC reliability was comparable to more objective speech understanding measures, but it may not be suitable to capture perceived conversational benefits for more subtle changes in hearing-aid processing. [Work supported by the UK Medical Research Council Grant No. MR/X003620/1 & WS Audiology.]

Low SLL Control of Two-Way Pattern in Shared Circular Planar Radar Arrays

Low SLL Control of Two-Way Pattern in Shared Circular Planar Radar Arrays

Performance analysis of the dual-band trapezoidal antenna array for ultra-wideband application

Designing a wireless transmission system with high data rates, high fidelity, and small size is a tough undertaking that has become more popular in the digital age. One of the most important components of wireless communication systems, such as wireless LANs, mobile WIMAX, and Bluetooth devices, is the design of an efficient antenna system. The new circular slot Trapezoidal patch antenna array, which operates in the ultra wide band frequency range of 3.1 GHz to 10.6 GHz, is introduced in this study. The FR4 substrate on which the antenna system is built has a dielectric constant of 4.4. The CST microwave studio suite is used to develop and analyze the performance of the compact structure patch antenna array. Antenna performance is examined in the frequency range of 2 GHz to 5 GHz. Antenna array resonance frequency is 3.1 GHz. By inserting a quarter wave line between the SMA connection and the micro stripline, 50 ohm impedance matching may be achieved. In comparison to previous studies, the intended antenna array has a minimum VSWR of 1.18, a maximum radiation efficiency of ?4.842 dB, and a directivity of 8.645 dBi. Using network analyzer, the test and simulation data were analyzed. The intended use of the antenna array system is for biomedical imaging and body area networks. Abbreviations: UWB: ultra wideband; EMI: electromagnetic interference; MIMO: multiple input multiple output; WLAN: wireless local area network; VSWR: voltage standing wave ratio; AVA: antipodal vivaldi antenna; DGS: defected ground structure; RF: radio frequency.

Optimization and analysis of air-to-ground wireless link parameters for UAV mounted adaptable Radar Antenna Array

Unmanned Aerial Vehicles (UAVs) are rapidly used in a variety of applications such as surveillance, search and rescue operation, delivery, etc. These operations strongly depend on the performance of the air-to-ground (A2G) communication link. This link communicates vital information between the UAV and the ground station (GS). However, due to the UAV’s unpredictable mobility, the A2G link becomes unreliable, which limits the quality of data transfer. An Adaptable Radar Antenna Array (ARAA) can be used to solve this problem by effectively handling transmitted data through altering the antenna pattern using the beamforming process. This work proposes a new algorithm for selecting antenna patterns with proper beamforming by considering the effect of wobbling and mutual coupling (MC). In addition, the proposed algorithm is used to reduce the maximum sidelobe level (SLL) and optimize the distance between the interelement of ARAA, which directly controls the MC effect in a time-varying channel. Also, an analysis is done for various antenna configurations, such as Uniform Linear Array (ULA), Uniform Rectangular Array (URA), and Uniform Circular Array (UCA), while varying different UAV parameters like altitude, speed, location error, and beamforming capacity.