Array Shape Research Articles

CABE: A Cloud-Based Acoustic Beamforming Emulator for FPGA-Based Sound Source Localization.

Microphone arrays are gaining in popularity thanks to the availability of low-cost microphones. Applications including sonar, binaural hearing aid devices, acoustic indoor localization techniques and speech recognition are proposed by several research groups and companies. In most of the available implementations, the microphones utilized are assumed to offer an ideal response in a given frequency domain. Several toolboxes and software can be used to obtain a theoretical response of a microphone array with a given beamforming algorithm. However, a tool facilitating the design of a microphone array taking into account the non-ideal characteristics could not be found. Moreover, generating packages facilitating the implementation on Field Programmable Gate Arrays has, to our knowledge, not been carried out yet. Visualizing the responses in 2D and 3D also poses an engineering challenge. To alleviate these shortcomings, a scalable Cloud-based Acoustic Beamforming Emulator (CABE) is proposed. The non-ideal characteristics of microphones are considered during the computations and results are validated with acoustic data captured from microphones. It is also possible to generate hardware description language packages containing delay tables facilitating the implementation of Delay-and-Sum beamformers in embedded hardware. Truncation error analysis can also be carried out for fixed-point signal processing. The effects of disabling a given group of microphones within the microphone array can also be calculated. Results and packages can be visualized with a dedicated client application. Users can create and configure several parameters of an emulation, including sound source placement, the shape of the microphone array and the required signal processing flow. Depending on the user configuration, 2D and 3D graphs showing the beamforming results, waterfall diagrams and performance metrics can be generated by the client application. The emulations are also validated with captured data from existing microphone arrays.

General space‐time clutter model for multi‐channel airborne radar

Ground clutter of looking-down airborne radar is spread in Doppler because of the platform motion, and thus the interested moving targets may be masked by the ground clutter. In order to enhance the performance of clutter suppression, the clutter characteristics should be analysed in detail. So here, a general clutter model which suits for the conventional-phased array radar, multiple-input-multiple-output (MIMO) radar, and hybrid MIMO-phased array radar, all with arbitrary array shape, whether in monostatic or bistatic applications, is developed. Clutter characteristics under two typical scenarios are presented by simulation examples, simultaneously; the effectiveness of the general clutter model is demonstrated.

COMPUTER SIMULATION RESEARCH AND ANALYSIS OF HEAT IN BRAKING PROCESS

Aiming at the problem of heat dissipation performance of disc brake, a computer simulation method is used to analyze the braking process. Taking ventilated brake disc as the research object, four geometric models of ventilated brake disc with different arrays and shapes were established. Considering typical braking conditions, the heat dissipation characteristics of ventilated brake discs were simulated by computational fluid dynamics (CFD). The influence of array mode and shape of rib heat dissipation structure on heat dissipation characteristics of ventilated brake disc is analyzed. The results show that the array mode of the rib plate heat dissipation structure in the radial ventilation duct has a great influence on the heat dissipation characteristics of the brake disc. In the ventilation duct of the triangular array ribbed heat dissipation structure, there is less air resistance, stronger turbulence, less flow separation, higher convective heat transfer coefficient and heat flux.

3D-Printed Multilayer Sensor Structure for Electrical Capacitance Tomography.

Presently, Electrical Capacitance Tomography (ECT) is positioned as a relatively mature and inexpensive tool for the diagnosis of non-conductive industrial processes. For most industrial applications, a hand-made approach for an ECT sensor and its 3D extended structure fabrication is used. Moreover, a hand-made procedure is often inaccurate, complicated, and time-consuming. Another drawback is that a hand-made ECT sensor’s geometrical parameters, mounting base profile thickness, and electrode array shape usually depends on the structure of industrial test objects, tanks, and containers available on the market. Most of the traditionally fabricated capacitance tomography sensors offer external measurements only with electrodes localized outside of the test object. Although internal measurement is possible, it is often difficult to implement. This leads to limited in-depth scanning abilities and poor sensitivity distribution of traditionally fabricated ECT sensors. In this work we propose, demonstrate, and validate experimentally a new 3D ECT sensor fabrication process. The proposed solution uses a computational workflow that incorporates both 3D computer modeling and 3D-printing techniques. Such a 3D-printed structure can be of any shape, and the electrode layout can be easily fitted to a broad range of industrial applications. A developed solution offers an internal measurement due to negligible thickness of sensor mount base profile. This paper analyses and compares measurement capabilities of a traditionally fabricated 3D ECT sensor with novel 3D-printed design. The authors compared two types of the 3D ECT sensors using experimental capacitance measurements for a set of low-contrast and high-contrast permittivity distribution phantoms. The comparison demonstrates advantages and benefits of using the new 3D-printed spatial capacitance sensor regarding the significant fabrication time reduction as well as the improvement of overall measurement accuracy and stability.

Joint calibration of array shape and sensor gain/phase for highly deformed arrays using wideband signals

A joint sensor position and gain/phase calibration method for highly deformed arrays is proposed. It applies to the case where the sensor gain is omnidirectional and frequency-invariant, and the sensor phase is directional and frequency-invariant. The method is initialized with the raw estimates of the sensor gains, which are simply obtained from the main diagonal elements of the sample covariance matrix. Then, it alternately updates either the sensor gain estimates or the sensor position and phase estimates while fixing the other. When the sensor gain estimates are available, the steering matrices for all the frequency bins are estimated using the constant modulus method. By combining all these steering matrices, the estimates of the sensor positions and the frequency-invariant sensor phases are straightforwardly derived. Then, the sensor gain estimates are refined for the next iteration by using the orthogonality of the subspaces. To resolve the phase ambiguities due to the large position mismatches of highly deformed arrays, the nominal intersensor distance and the array bending angle are used. The Cramer–Rao lower bounds (CRLBs) for the unknown sensor gain/phase and position are also derived. The performance of the proposed method is evaluated using simulation data and compared with the CRLBs.

Research on the directivity of transducer array based on typical array elements

In order to analyze the directivity of the array composed of different shape array elements, a line array is made up of the point source, circular, annular and rectangular piston sound source, and the directivity of the array is analyzed by simulation software. The results show that the directivity of line array is influenced by many factors, such as array element spacing, geometric dimensions, array shape, number of array elements, wave number or frequency, etc. When the condition is equivalent, the directivity of the transducer array composed of annular array element is relatively optimal.

Simulations of the electrostatic field, temperature, and tissue damage generated by multiple electrodes for electrochemical treatment

• Multiple pairs of electrodes for treating tumors simulated for first time. • Temperature and heat generated by multiple pairs of electrode covered whole tumor. • Multiple pairs of electrodes induced highest percentage of tissue damage. • Multiple pairs of electrodes can be employed for electrochemical therapy. Integrated analysis of the spatial distributions of the electric potential, electric field, temperature, and tissue damage generated by multiple arrays of straight needle electrodes inserted into tumors is highly significant for improving the effectiveness of electrochemical treatment. In this study, we simulated the spatial profiles generated by multiple electrodes inserted individually into a tumor and multiple pairs of straight needle electrodes inserted in a tumor surrounded by healthy tissue. Poisson nonlinear and Laplace equations were used to calculate the electric potential in the tumor and the surrounding healthy tissue, respectively. The stationary bioheat transfer equation of Pennes was used to calculate the temperature in both tissues. The percentage tissue damage was computed in each biological medium for each electrode array shape. Numerical simulations showed that the non-homogeneous spatial distributions of the temperature (above 40 °C) generated by different types of multiple pairs of straight needle electrodes covered the whole tumor volume. Spatial profiles of this physical magnitude were generated by multiple straight needle electrodes, which were individually inserted into the tumor and partially covered by its volume. In addition, the simulations showed that multiple pairs of electrodes led to tumor damage percentages above 80%. By contrast, multiple electrodes inserted individually in the tumor induced damage percentages below 25%. We conclude that multiple pairs of straight needle electrodes may be applied to deep-seated solid tumors in treatment with electrochemical therapy considering their theoretically calculated high tumor damage percentages.

A design for autonomous self-building blocks

The goal of this self-assembly blocks project is to demonstrate a proof of concept of self-configuring building block in potential dynamic structures application. Unlike regular masonry unit, a self-configuring block has latches, actuators and control system. Blocks translate themselves via expansion and retraction of its arm to push and pull other blocks in the system. Through the embedded control systems, these interactions and movements are coordinated to produce different geometric configurations based on user command. This paper presents our initial finding of this concept via the experiment we conducted on the interactions between two blocks. The mechanical design of the block is detailed and the rapid prototyping and molding technique used in manufacturing the parts is described. Novel circular Halbach magnetic array latches and shape memory alloy switches are shown. The coordination of the reconfiguration of the blocks by an Arduino UNO controller with motion sensors and H-bridges in the motor driving circuit is described. Finally, tests conducted on block action control, maximum motor and latch forces, and block interactions to accomplish a defined sequence action are discussed.

Binder Free Synthesis of Sulphur Doped Co3V2O8 Nanoarray for Hybrid Asymmetric Supercapacitor Application in Aqueous and Non-Aqueous Medium

Metal vanadate are the class of compound for high performance electrochemical charge storage application due to its multiple stable oxidation states, high electrical and ionic conductivity and high rate capability. Among all the metal vanadate, Co3V2O8 is one of the potential candidate due to low cost and environmentally benign nature of cobalt. However, the introduction of Sulfur in Co3V2O8 matrix substantially improves the electrochemical performance by improving the electrical conductivity. Herein, we report Sulfur doped Co3V2O8 (S-Co3V2O8) nanosheet arrays grown on Ni foam hydrothermally without using any binder. As synthesized Co3V2O8 attains nanosheet morphology with height of ~200 nm and thickness of ~10 nm. We note that the shape and size of S-Co3V2O8 nanosheet arrays remain unchanged after the doping of sulfur in Co3V2O8. Further, the thickness of nanosheet increases with increasing reaction time. We observed that the electrochemical performance of S-Co3V2O8 nanosheet array is ~25% better than the undoped Co3V2O8 nanosheet arrays. In aqueous alkaline electrolyte, S-Co3V2O8 nanosheet array exhibits a specific capacity of 1476 C/g (3690 F/g) at 2 A/g with enhanced rate capability and an excellent capacity retention of 94.2% at 5 A/g specific current after 4000 cycles. The doping of sulfur improves the electrochemical performance due to its low electronegativity and large size as compared to oxygen, which creates a robust structure, better transport properties and improved charge storage capacity. An asymmetric supercapacitor fabricated using S-Co3V2O8 nanosheet arrays as cathode and activate carbon (AC) as anode shows high specific capacity (or capacitance) of 174.5 C/g (or 116.33 F/g), energy density (36.4 Wh/kg) and power density (740 W/kg) at 2 A/g with 98.4% capacity retention after cycles. Further, Li-ion hybrid capacitor fabricated in the CR2032 coin cell exhibits specific capacity of 994 mAh/g with energy density of 695 W/kg at specific current of 1 A/g with good rate capability and 46.5% capacity retention after 100 cycles renders it as a potential candidate for future high energy storage system with long term durability.

Obtaining the Optimal Shape of Planar Antenna Arrays for Direction-of-Arrival Joint Estimation of One and Two Coordinates of Signal Sources on Azimuth

In this paper, an approach for obtaining optimal planar antenna arrays consisting of omnidirectional sensors for the direction-of-arrival estimation is proposed. Exact expressions of the Cramer-Rao lower bound are used. The obtained formulas describe the influence of the location of antenna elements on the accuracy of the direction-of-arrival non-joint estimation for one arriving signal and joint estimation with two signal sources. It has been shown that the accuracy of the direction-of-arrival non-joint estimation is determined as the sum of the squares of the differences between all the coordinates of omnidirectional elements along x- and y-axis if one signal arrives. If two signals arrive, the accuracy of the direction-of-arrival joint estimation depends on the sum of cosines having the argument with the difference between sensor coordinates and signals radius-vectors. The optimal locations of the antenna elements using the obtained expressions can be calculated very easily in order to reduce the direction-finding errors near particular sectors. In order to confirm the proposed methodology the optimal antenna arrays constructed after minimization of the new formulas are researched. It is found out that the new shapes of antenna arrays based on the analytical expressions have better direction-of-arrival accuracy in comparison with the circular ones.

Array auto-calibration using a generalized least-squares method

This paper introduces a new class of auto-calibration algorithms, based on a generalized least-squares (GLS) cost function. This class supports both gain-phase calibration and mutual coupling calibration and it is independent of array shape. The GLS cost function is minimized cyclically with respect to the direction of arrivals (DOA) and calibration parameters. These two minimization steps are repeated until convergence. In the DOA estimation step, minimization leads to the SPICE (SParse Iterative Covariance-based Estimation) DOA estimation algorithm. In fact, the innovation of this paper mainly lies in the calibration step. In the DOA estimation step, a generalized form of the SPICE algorithm should be used in the coherent sources case. Consequently, the proposed auto-calibration algorithm is able to support coherent source cases. Moreover, the proposed algorithm does not need multi-dimensional search. The necessary condition for the existence of a solution is studied as well. Using simulations, the performance of the proposed algorithm is compared with several other auto-calibration algorithms. Simulation results show that the proposed algorithm is more robust than the other algorithms and usually has better performance.

Impact of permeabilization and pH effects in the electrochemical treatment of tumors: Experiments and simulations

• Electrolysis products have a major role in electrochemical treatment of Tumors(EChT). • This work evidences that the extreme pH fronts affect the permeabilization of the tissue and consequently its destruction. • Modeled ions demonstrate the diffusive regime of ionic transport and show the low influence of the electric field on EChT. Electrochemical treatment is used in the local control of solid tumors in preclinical and clinical studies. We study pH fronts, permeabilization, electrical field and concentration of four chemical species in a tissue under electrochemical treatment by means of in vitro and in silico modeling. The in vitro model uses a piece of potato (solanum tuberosum L.) as analogy of tumor tissue, due to the characteristics of the potato tissue and the way in which it reacts against pH and potential. The in silico model solves the two-dimensional Nernst-Planck equations for ionic transport in a four-ion electrolyte. Modeled ions demonstrate the diffusive regime of ionic transport and show the little influence of the low electric field applied on this phenomenon. This work evidences that extreme pH fronts affect the permeabilization of the tissue and consequently its destruction. We also evaluate different shapes of electrode arrays by means of simulated and in vitro models. We concluded that the higher area of necrotic tissue was achieved for the greater separation between electrodes.

Design Considerations for Borehole Thermal Energy Storage (BTES): A Review with Emphasis on Convective Heat Transfer

Borehole thermal energy storage (BTES) exploits the high volumetric heat capacity of rock-forming minerals and pore water to store large quantities of heat (or cold) on a seasonal basis in the geological environment. The BTES is a volume of rock or sediment accessed via an array of borehole heat exchangers (BHE). Even well-designed BTES arrays will lose a significant quantity of heat to the adjacent and subjacent rocks/sediments and to the surface; both theoretical calculations and empirical observations suggest that seasonal thermal recovery factors in excess of 50% are difficult to obtain. Storage efficiency may be dramatically reduced in cases where (i) natural groundwater advection through the BTES removes stored heat, (ii) extensive free convection cells (thermosiphons) are allowed to form, and (iii) poor BTES design results in a high surface area/volume ratio of the array shape, allowing high conductive heat losses. The most efficient array shape will typically be a cylinder with similar dimensions of diameter and depth, preferably with an insulated top surface. Despite the potential for moderate thermal recovery, the sheer volume of thermal storage that the natural geological environment offers can still make BTES a very attractive strategy for seasonal thermal energy storage within a “smart” district heat network, especially when coupled with more efficient surficial engineered dynamic thermal energy stores (DTES).

Subarray Beam-space Adaptive Beamforming Combined with Array Shape Estimation based on Non-Acoustic Sensor

To address the issue of serious decline in performance of the array signal processing caused by the towed array shape distortion during maneuvering, this paper presents a new method of subarray beam-space adaptive beamforming combined with an array shape estimation method based on non-acoustic sensor. Firstly, the array shape through the approximate circular arc structure of the array segment between the adjacent sensor during maneuvering is preliminary calculated. Next, the final estimated array shape through a smooth processing method on the entire array shape by means of a calibration method using spline interpolation technique is achieved. This method is able to estimate the array shape in real time. The array steering vector based on the real-time estimation of the array shape is updated, using a subarray beam-space adaptive beamforming (SBABF) to reduce the demand of the number of the snapshots. And the beam-space covariance matrix converges fast within a few snapshots. The SBABF method combined with array shape estimation (AE-SBABF) was verified by simulation data and sea trial data processing results. During maneuvering, the AE-SBABF can not only improve the array processing gain of the target effectively, but also solve the left/right ambiguity problem well.

Tunable absorption enhancement in periodic elliptical hollow graphene arrays

In this contribution, a tunable plasmonic absorber consisting of periodical elliptical hollow graphene arrays deposited on SiO2 substrate is proposed in the far infrared and terahertz (THz). The simulation calculation results show that the structure supports a variety of effective tuning methods, such as changing the period, geometry parameters, Fermi level, relaxation time, incident angle, to achieve active and passive tuning. When the incident angle is set to 60°, the maximum absorption value (0.31) in our work can be achieved. Meanwhile, the red shift caused by period variations and blue shift phenomenon made of geometry parameters provides an exercisable way to select the resonance range. Therefore, these outcomes undoubtedlyoffer a unique source of inspiration for the diversity of graphene array shapes and the design and fabrication of absorption-related devices, such as filters, spatial light modulators, and sensors.

Lightweight and optimized sound source localization and tracking methods for open and closed microphone array configurations

Human–robot interaction in natural settings requires filtering out the different sources of sounds from the environment. Such ability usually involves the use of microphone arrays to localize, track and separate sound sources online. Multi-microphone signal processing techniques can improve robustness to noise but the processing cost increases with the number of microphones used, limiting response time and widespread use on different types of mobile robots. Since sound source localization methods are the most expensive in terms of computing resources as they involve scanning a large 3D space, minimizing the amount of computations required would facilitate their implementation and use on robots. The robot’s shape also brings constraints on the microphone array geometry and configurations. In addition, sound source localization methods usually return noisy features that need to be smoothed and filtered by tracking the sound sources. This paper presents a novel sound source localization method, called SRP-PHAT-HSDA, that scans space with coarse and fine resolution grids to reduce the number of memory lookups. A microphone directivity model is used to reduce the number of directions to scan and ignore non significant pairs of microphones. A configuration method is also introduced to automatically set parameters that are normally empirically tuned according to the shape of the microphone array. For sound source tracking, this paper presents a modified 3D Kalman (M3K) method capable of simultaneously tracking in 3D the directions of sound sources. Using a 16-microphone array and low cost hardware, results show that SRP-PHAT-HSDA and M3K perform at least as well as other sound source localization and tracking methods while using up to 4 and 30 times less computing resources respectively.

Integral Imaging With Full Parallax Based on Mini LED Display Unit

Integral imaging has been considered as the most applicable technology of true 3D display in the near future. In this paper, we propose the method to achieve full parallax and large-screen integral imaging display based on mini LED. Compared to the existing integral imaging systems based on the LED, the proposed method can present both horizontal and vertical parallaxes. We explore the optical parameter matching method between mini LED display unit and lenslet unit and design three different shapes of lenslet arrays. The imaging performance of lenslet arrays of circular-shape, square-shape, and hexagonal-shape is analyzed. The method of window interception is proposed to generate elemental images for the lenslet arrays with different apertures and arranging structures. The experimental results show that the true 3D display with full parallax and screen scalability has been realized using the proposed method and the display effect of lenslet array with hexagonal-shape is the best according to the evaluation of both subjective and objective merits.

Travel-time correction and preliminary results for ocean acoustic tomography in South China Sea

An acoustic tomography trial experiment was conducted in South China Sea during May to August in 2016. Two moorings are installed apart from about 56.94 km, while each consists of one low frequency source, 20 hydrophones deployed from the depth of about 400 m to 1600 m, total 32 depth sensors and 3 compass and tilt sensors. Due to internal waves and currents in this area, as a typical value, horizontal drift of a mooring can reach 300 m, thus moorings drift need to be considered to correct ray travel-time. In this paper, the shape of a mooring is estimated firstly and locations of all hydrophone array elements are then calculated and finally used to determine travel-time perturbation of acoustic arrivals. The mooring is modelled as 2 curves, while the end of the mooring is fixed at the cement anchor on the sea floor. Optimization is used to acquire hydrophone location inferential solution. The inferred shape of hydrophone array and element locations are used to correct the travel-times measured in the experiment. We find that corrected travel-times match the trend of the change of sound speed profile better in the sea. Finally, the corrected travel-times are used to tomography of sound speed profile. AR (Autoregressive) process is used to describe the dynamic evolution of sound speed profile and Kalman filter is applied in the sequential estimation. The performances of the time-independent method and the method using AR process and Kalman filter are compared, reasonably the latter is better than the former in particular with abundant measured data.

Accurate estimation of DOA and MAI mitigation in the presence of channel impairments at low SNR

Environmental effects may cause antenna array element positions to become disturbed, introducing array shape uncertainties. The presence of these uncertainties causes a rapid degradation in the detection, resolution and estimation performance of array processing algorithms. In this paper, the performance of the Multiple Signal Classification - Direction of Arrival (DOA) algorithm for estimating the direction of the incident angles of all the received signals impinging on the antenna array elements is analysed at low Signal to Noise Ratio (SNR). The investigation is achieved under different scenarios such as changing the number of antenna array elements at different values of SNR. The root mean square error of the estimated angles is computed and compared with the true angles of the desired user. The simulation results assure that in the presence of the reference signal, the DOA algorithm can identify the direction of the desired user with high accuracy and high resolution. Moreover, the Affine Projection Algorithm (APA) is implemented to enhance the accuracy of the estimated direction in order to generate a main beam towards the desired user and null towards interfering users.

Accurate estimation of DOA and MAI mitigation in the presence of channel impairments at low SNR

Environmental effects may cause antenna array element positions to become disturbed, introducing array shape uncertainties. The presence of these uncertainties causes a rapid degradation in the detection, resolution and estimation performance of array processing algorithms. In this paper, the performance of the Multiple Signal Classification - Direction of Arrival (DOA) algorithm for estimating the direction of the incident angles of all the received signals impinging on the antenna array elements is analysed at low Signal to Noise Ratio (SNR). The investigation is achieved under different scenarios such as changing the number of antenna array elements at different values of SNR. The root mean square error of the estimated angles is computed and compared with the true angles of the desired user. The simulation results assure that in the presence of the reference signal, the DOA algorithm can identify the direction of the desired user with high accuracy and high resolution. Moreover, the Affine Projection Algorithm (APA) is implemented to enhance the accuracy of the estimated direction in order to generate a main beam towards the desired user and null towards interfering users.