Array Beamforming Techniques Research Articles

A quantity to identify turbulence related sound generation on surfaces

This contribution addresses the problem of identifying sources of sound on aerodynamic surfaces subject to turbulent flow. A quantity is proposed, which identifies the location of the sound generation and serves as well to quantify these sources. The suggested concept reduces fluctuating surface pressure data to the part of the pressure which is actually relevant for sound generation (representing only a very small fraction of the former). The focus is put on the interpretation of surface pressures rather than prediction, i.e. data is assumed known, typically obtained from scale-resolving numerical simulations of the turbulent flow around the surfaces. The idea is to generate knowledge from this data, as a basis for designing more silent aero shapes. The localization of sources of sound generated aerodynamically is usually accomplished by phased microphone array (numerical) beamforming techniques in various variants involving acoustic propagation of source data to the acoustic farfield and subsequent data processing. This “detour” to the acoustic farfield indeed enables the separation of sound and aerodynamic (nearfield) data. The proposed approach explicitly uses nearfield information of the surface pressure field to identify and quantify aerodynamic sources of sound on surfaces without the need to introduce beamforming. The main hypothesis of this approach states that sound is generated where the mirror principle of flow quantities, ideally satisfied at plane hard surfaces, is violated. It turns out that the hypothesis is equivalent to the statement that aerosound is produced by diffraction of the pressure nearfield incident to a surface and as such intimately related to curvature. A physical quantity is proposed to quantify and thereby localize this source of sound. The method to determine the quantity is successfully validated for the cases of leading and trailing edge sound generation at an airfoil.

New Antenna Array Beamforming Techniques Based on Hybrid Convolution/Genetic Algorithm for 5G and Beyond Communications

New Antenna Array Beamforming Techniques Based on Hybrid Convolution/Genetic Algorithm for 5G and Beyond Communications

An Efficient Conformal Stacked Antenna Array Design and 3D-Beamforming for UAV and Space Vehicle Communications.

In this paper, a new conformal array structure and beamforming technique are proposed to provide efficient communication performance for unmanned aerial vehicles (UAVs) and space vehicles. The proposed array is formed by conformally stacking cylindrical, conical, and concentric circular (CSC4) arrays which are all coaxially aligned with the same axis of the conformed body and with uniform interelement spacing. The array elements are then fed by a weighting vector that has an adaptive cosine tapered profile where the maximum amplitude coefficient is oriented with the mainlobe direction to improve the scanning capabilities of the array and increase the array effective area. In addition, for very large, conformed body structures such as space vehicles, a frontal mainlobe-oriented partial CSC4 array beamforming technique is proposed to efficiently utilize the large CSC4 structure, reduce the processing requirements for mainlobe electronic steering, and to provide very low sidelobe levels with reduced backlobe levels. Simulation results show that the proposed CSC4 design can provide wide scanning angles of up to angular range in the -direction with only change in the beamwidth, without increasing array size and with achievable sidelobe level of −45 dB and backlobe levels less than −10 dB.

Iterative time-reversal for multi-frequency hyperthermia

Time-reversal (TR) is a known wideband array beam-forming technique that has been suggested as a treatment planning alternative in deep microwave hyperthermia for cancer treatment. While the aim in classic TR is to focus the energy at a specific point within the target, no assumptions are made on secondary lobes that might arise in the healthy tissues. These secondary lobes, together with tissue heterogeneity, may result in hot-spots (HSs), which are known to limit the efficiency of the thermal dose delivery to the tumor. This paper proposes a novel wideband TR focusing method that iteratively shifts the focus away from HSs and towards cold-spots from an initial TR solution, a procedure that improves tumor coverage and reduces HSs. We verify this method on two different applicator topologies and several target volume configurations. The algorithm is deterministic and runs within seconds, enabling its use for real-time applications. At the same time, it yields results comparable to those obtained with global stochastic optimizers such as Particle Swarm.

Anomalous azimuthal variations with 360° periodicity of Rayleigh phase velocities observed in Scandinavia

SUMMARY We use the recently deployed ScanArray network of broad-band stations covering most of Norway and Sweden as well as parts of Finland to analyse the propagation of Rayleigh waves in Scandinavia. Applying an array beamforming technique to teleseismic records from ScanArray and permanent stations in the study region, in total 159 stations with a typical station distance of about 70 km, we obtain phase velocities for three subregions, which collectively cover most of Scandinavia (excluding southern Norway). The average phase dispersion curves are similar for all three subregions. They resemble the dispersion previously observed for the South Baltic craton and are about 1 per cent slower than the North Baltic shield phase velocities for periods between 40 and 80 s. However, a remarkable sin(1θ) phase velocity variation with azimuth is observed for periods >35 s with a 5 per cent deviation between the maximum and minimum velocities, more than the overall lateral variation in average velocity. Such a variation, which is incompatible with seismic anisotropy, occurs in northern Scandinavia and southern Norway/Sweden but not in the central study area. The maximum and minimum velocities were measured for backazimuths of 120° and 300°, respectively. These directions are perpendicular to a step in the lithosphere–asthenosphere boundary (LAB) inferred by previous studies in southern Norway/Sweden, suggesting a relation to large lithospheric heterogeneity. In order to test this hypothesis, we carried out 2-D full-waveform modeling of Rayleigh wave propagation in synthetic models which incorporate a steep gradient in the LAB in combination with a pronounced reduction in the shear velocity below the LAB. This setup reproduces the observations qualitatively, and results in higher phase velocities for propagation in the direction of shallowing LAB, and lower ones for propagation in the direction of deepening LAB, probably due to the interference of forward scattered and reflected surface wave energy with the fundamental mode. Therefore, the reduction in lithospheric thickness towards southern Norway in the south, and towards the Atlantic ocean in the north provide a plausible explanation for the observed azimuthal variations.

Direction-independent and self-reconfigurable spherical-cap antenna array beamforming technique for massive 3D MIMO systems

Massive 3D MIMO beamforming is very important for 5G and beyond networks to improve the system performance and capacity. However, 3D beamforming capabilities are limited by the antenna array configuration. Therefore, in this paper, an efficient self-reconfigurable spherical-cap antenna array and 3D beamforming technique are proposed to provide direction-independent symmetrical beam patterns with low sidelobe and backlobe levels. The symmetric beam generation is achieved by forming electronically steerable spherical-cap array which is extracted from a uniform spherical antenna array and is continuously reconfigured so that its axis of symmetry is maintained the same as the mainlobe direction. On the other hand, the antenna elements in the spherical-cap array are further processed to minimize the sidelobe and backlobe levels by using an optimized exponential decaying feeding profile in the form of $$e^{{ - \alpha \left( \rho \right)^{\beta } }}$$ . Assuming isotropic antenna elements with negligible mutual coupling, the generated beam power patterns are examined where simulation results show that a sidelobe level of − 30 dB and backlobe level of less than − 16 dB relative to the mainlobe level can be achieved. Also, the variation in the 3 dB beamwidth with the mainlobe direction has been examined for 10,000 uniformly random generated mainlobe directions at different array sizes where it is found that the beamwidth is almost constant with less than 1% variation especially for large sized arrays.

The room impulse response in time, frequency, and space: Mapping spatial energy using spherical array beamforming techniques

The auditory perception of rooms is a multi-dimensional problem. Our hearing system interprets time, frequency, and spatial information from arriving room reflections, but traditionally, only the time and frequency domains are considered in room acoustic metric and objective sound field analyses. This work aims to develop spatial visualizations of the energy in a room impulse response (RIR). With a spherical microphone array, a room’s energy can be mapped in full three-dimensions. First, beamforming techniques are used to generate a set of directional RIRs from the spherical microphone array measurement. This set of directional RIRs is analogous to using a microphone with a directional beam pattern response, oriented individually at all points around a sphere. Then, these directional or beam RIRs are time windowed and band-pass filtered to create spatial energy maps of the room. Comparisons between a plane-wave beam pattern and a Dolph-Chebyshev beam pattern will be demonstrated in the context of RIR beamforming. As well, different strategies for normalizing peak energy amplitudes to either the direct sound or a spherical spreading condition will be compared. With these considerations, final results of these spatial energy visualizations and directional RIR animations will be demonstrated. [Work supported by NSF Award 1302741.]

An efficient traffic monitoring and control system using aerial platforms and vertical arrays

In this paper, a reliable traffic monitoring system is proposed based on aerial platform (AP) wireless sensor network with a new adaptive vertical linear array beamforming technique. This proposed beamforming technique improves the system performance compared with recent techniques using the same number of antenna elements which makes aerial platforms more feasible to establish wireless sensor network for traffic monitoring application. Four coverage scenarios of the proposed AP traffic monitoring system are examined at coverage diameters of 16 and 60 km and two bit rates of 38.4 and 250 kb/s. The simulation results depicts better performance of the proposed antenna technique in all the four examined coverage scenarios. At the worst case (60 km coverage diameter, 2400 MHz frequency and bit rate of 250 kb/s), the probability of bit-energy to noise-spectral-density (\(E_{b}/N_{o})\) to be less than 4 dB is zero for the proposed technique while it was 0.14 in the case of optimized concentric circular array technique and 0.76 for the conventional spot-beam antenna. Also, at the coverage diameter of 16 km and bit rate of 38.4 kb/s at 868 MHz, the results show that the probability of \(E_{b}/N_{o} < 34\) dB of the proposed technique is zero while it was 0.15 in the case of optimized concentric circular array and 0.72 for the conventional spot-beam antenna.

MmWave communications for 5G: implementation challenges and advances

The requirement of the fifth generation (5G) wireless communication for high throughput motivates the wireless industry to use the mmWave (millimeter wave) communications for its wide bandwidth advantage. To compensate the heavy path loss and increase the communications capacity, phased array beamforming and massive multiple-input multiple-output (MIMO) techniques are employed at both the user equipment (UE) and base stations (BS). Considering the commercial requirements, 5G mmWave large array systems should be implemented in an energy- and cost-efficient way with a small form factor. To address above issues and realize a reliable communications link, taking into account the particular characteristics of 5G mmWave systems, this paper firstly examines the design challenges and trade-offs in system implementations, then some of the design strategies are summarized. At last, recent advance in RF front-end circuits and receiver sub-systems is then highlighted.

Structural health monitoring of wind turbine blades using acoustic microphone array

This article proposes a non-contacting measurement technique based on acoustic monitoring to detect cracks or damage within a structure by observing sound radiation using a single microphone or a beamforming array. The technique works by mounting an audio speaker inside a hollow structure, such as a wind turbine blade, and observing the sound radiated from the blade to identify damage. The primary hypothesis for this structural damage detection technique is that the structural damage (cracks, edge splits, holes, etc.) on the surface results in changes in the sound radiation characteristics of the structure. Preliminary measurements to validate the methodology were carried out on a section of a wind turbine blade containing different sized holes and cracks. An acoustic microphone array with 62 microphones was used to measure the sound radiated from the structure when an audio speaker generating random noise was placed inside a cavity emulating a wind turbine blade. A phased array beamforming technique and CLEAN-based subtraction of point spread function from a reference were employed to locate the different damage types on the test structures. The same experiment was repeated using a commercially available 48-channel acoustic ring array to compare the test results. It was shown that both the acoustic beamforming and the CLEAN-based subtraction of point spread function from reference techniques can identify the damage in the test structures with sufficiently high fidelity.

Wind turbine blade health monitoring using acoustic beamforming techniques

Wind turbines operate autonomously and can possess reliability issues attributed to manufacturing defects, fatigue failure, or extreme weather events. In particular, wind turbine blades can suffer from leading and trailing edge splits, holes, or cracks that can lead to blade failure and loss of energy revenue generation. In order to help identify damage, several approaches have been used to detect cracks in wind turbine blades; however, most of these methods require transducers to be mounted on the turbine blades, are not effective, or require visual inspection. This paper will propose a new methodology of the wind turbine non-contact health monitoring using the acoustic beamforming techniques. By mounting an audio speaker inside of the wind turbine blade, it may be possible to detect cracks or damage within the structure by observing the sound radiated from the blade. Within this work, a phased array beamforming technique is used to process acoustic data for the purpose of damage detection. Several algorithms are evaluated including the CLEAN-based Subtraction of Point spread function from a Reference (CLSPR) on a composite panel and a section of a wind turbine blade in the laboratory.

Soil Moisture &amp; Snow Properties Determination with GNSS in Alpine Environments: Challenges, Status, and Perspectives

Moisture content in the soil and snow in the alpine environment is an important factor, not only for environmentally oriented research, but also for decision making in agriculture and hazard management. Current observation techniques quantifying soil moisture or characterizing a snow pack often require dedicated instrumentation that measures either at point scale or at very large (satellite pixel) scale. Given the heterogeneity of both snow cover and soil moisture in alpine terrain, observations of the spatial distribution of moisture and snow-cover are lacking at spatial scales relevant for alpine hydrometeorology. This paper provides an overview of the challenges and status of the determination of soil moisture and snow properties in alpine environments. Current measurement techniques and newly proposed ones, based on the reception of reflected Global Navigation Satellite Signals (i.e., GNSS Reflectometry or GNSS-R), or the use of laser scanning are reviewed, and the perspectives offered by these new techniques to fill the current gap in the instrumentation level are discussed. Some key enabling technologies including the availability of modernized GNSS signals and GNSS array beamforming techniques are also considered and discussed.

Broadband 3-D Sonar System Using a Sparse Array for Indoor Navigation

Array beamforming techniques allow for the generation of 3-D spatial filters which can be used to localize objects in a large field of view (FOV) without the need for mechanical scanning. By combining broadband beamforming with a sparse, random array of receivers, we have constructed a low-cost, yet powerful, in-air sonar system, which is suited for a wide range of robotic applications. Experimental results in unmodified office environments show the performance of the sonar sensor. In particular, we document the sensor's capacity to produce 3-D location measurements in the presence of multiple highly overlapping echoes. We show how this capability makes possible the combination of a wide FOV with accurate 3-D localization, allowing the sensor to operate under real-time constraints in realistic environments. To demonstrate the use of this sensor, we describe an odometry application that estimates egomotion of a mobile robot using acoustic flow.

Real-time full matrix capture + total focusing and other novel imaging options using general purpose PC-based array instrumentation

Data acquisition using full matrix capture (FMC) and image reconstruction by the total focusing method (TFM) offers many benefits over conventional ultrasonic array beamforming techniques. These include dynamic focus on both transmit and receive for enhanced resolution and the ability to alter the focus and steer angle without re-scanning. However, the technique has remained in the laboratory because of the costs associated with acquiring many channels in parallel and the absence of a real-time reconstruction capability. This paper describes a solution to these constraints. The paper reviews the issues limiting the current implementations and describes how they were overcome by using flexible and scalable PC-based hardware modules. This new architecture already achieves acquisition and processing at 20 Hz and higher, meeting the requirements for interactive scanning and so enabling these techniques to transfer from the laboratory into the field. Results from the first phase of a continuing investigation are presented. New application approaches, where these techniques offer particular benefits over conventional techniques, are discussed.

Photonic Beamforming Based on Programmable Phase Shifters With Amplitude and Phase Control

A new optically controlled phased array beamforming technique based on phase modulations of wavelength-division-multiplexed (WDM) single sideband modulated light with carrier using a two-dimensional array liquid crystal on silicon (LCoS) pixels device, is presented. It realizes multiple wideband photonic microwave phase shifters, operates over a wide frequency range, and simultaneously integrates the array phase taper and the array amplitude taper within a single unit. The beamforming is software programmable. Experimental results demonstrate multiple independent microwave phase shifters that operate simultaneously over a 10- to 20-GHz frequency range, and results demonstrate beamsteering in a four-element optically controlled beam steering array at 18 GHz.

Using Phased Array Beamforming to Identify Broadband Noise Sources in a Turbofan Engine

Fan broadband noise is a major component of the total noise emitted by turbofan engines, especially at lower shaft speeds. It is generated in the rotor/stator region, but the exact origin is not always known. This article discusses the application of phased array beamforming techniques for a better understanding of the source mechanisms of fan broadband noise. The Conventional Beamforming technique was applied, as well as the deconvolution technique CLEAN-SC and the beamforming technique ROSI for rotating sources. Beamforming was applied to acoustic data measured by two circular microphone arrays that were mounted in the intake and in the bypass of a Rolls-Royce fan rig. These arrays are normally used for the detection of azimuthal modes. The merits of beamforming are discussed by considering a number of typical low shaft speed cases. Using the intake array, in one of the cases forward radiating broadband noise sources were found that were coherent over a large area. These could have been due to a rotor instability. In an other case, the forward radiating broadband noise seemed to have its origin at the stator vanes. This could be made plausible with the help of the intake mode detection results. Using the bypass array, stator bound noise sources were found that seemed to be distributed along the span of the vanes. In other words, tip sources seemed to be of minor importance for aft radiating fan broadband noise. The bypass mode detection results seemed to indicate that the spanwise distributed noise sources were located at the trailing edges of the stator vanes.

Speech Enhancement and Recognition in Meetings With an Audio–Visual Sensor Array

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper addresses the problem of distant speech acquisition in multiparty meetings, using multiple microphones and cameras. Microphone array beamforming techniques present a potential alternative to close-talking microphones by providing speech enhancement through spatial filtering. Beamforming techniques, however, rely on knowledge of the speaker location. In this paper, we present an integrated approach, in which an audio– visual multiperson tracker is used to track active speakers with high accuracy. Speech enhancement is then achieved using microphone array beamforming followed by a novel postfiltering stage. Finally, speech recognition is performed to evaluate the quality of the enhanced speech signal. The approach is evaluated on data recorded in a real meeting room for stationary speaker, moving speaker, and overlapping speech scenarios. The results show that the speech enhancement and recognition performance achieved using our approach are significantly better than a single table-top microphone and are comparable to a lapel microphone for some of the scenarios. The results also indicate that the audio–visual-based system performs significantly better than audio-only system, both in terms of enhancement and recognition. This reveals that the accurate speaker tracking provided by the audio–visual sensor array proved beneficial to improve the recognition performance in a microphone array-based speech recognition system. </para>

Criterion for narrowband beamforming

A new criterion sensor narrowband equivalent efficiency (SNEE) is presented for array beamforming techniques. SNEE directly shows the performance when a band signal is processed with a narrowband model, and so it can be used to judge whether a band signal should be seen as narrowband.

Principles of space-time array processing for ultrawide-band impulse radar and radio communications

The emerging ultrawide-band (UWB) impulse technology has found numerous applications in the commercial as well as the military sector. The rapid technological advances have made it possible to implement (cost-effective, short-range) impulse radar and impulse-radio communication and localization systems. Array beamforming and space-time processing techniques promise further advancement in the operational capabilities of impulse radar and impulse-radio communications to achieve long-range coverage, high capacity and interference-free quality of reception. We introduce a realistic signal model for UWB impulse waveforms and develop the principles of space-time array processing based on the signal model. A space-time resolution function (STRF), a space-frequency distribution function (SFDF) and a monopulse-tracking signal are derived for impulse waveforms received by a self-steering array beamforming system. The directivity peak-power pattern and energy pattern of the beamformer are also derived. Computer plots of the STRF, SFDF and the beam patterns are obtained. The directivity beam patterns of impulse waveforms are sidelobe-free and, therefore, there is no need for sidelobe suppression via amplitude weighting of the array elements. Also, the resolution angle for the beam patterns is derived as a decreasing function of array size and frequency bandwidth. Electronic beamsteering based on slope processing of monopulse waveforms is described.

ACOUSTIC NOISE SOURCE MODELLING BASED ON MICROPHONE ARRAY MEASUREMENTS

A method will be presented which allows a construction of an acoustic source model based on the analysis of microphone array measurements during a train pass-by. The conventional array beam-forming technique is used as a kind of pre-processing or first order analysis to calculate in a second step the true source strengths by a back-projection method. The final equation to be solved connects the source power distribution on the vehicle surface with the measured microphone array amplitudes via a Green's function transfer matrix. By these means the side-lobe effects of the array characteristics as well as the Doppler frequency shift and amplitude augmentation of the sources are removed. The model is updated for consecutive time slices during the pass-by so that it is possible to study directional and time-dependent effects on the source characteristics. The method has been applied to measurements on the ICE-V train where three known artificial noise sources (loudspeakers) had been mounted on the outside of the sidewall. The source power distribution function gives a much better source separation than the conventional beam-forming result. The calculated source strengths show a good agreement with the true values.