Subarray Beamforming Research Articles

An Ultrasound Matrix Transducer for High-Frame-Rate 3-D Intra-cardiac Echocardiography

Described here is the development of an ultrasound matrix transducer prototype for high-frame-rate 3-D intra-cardiac echocardiography. The matrix array consists of 16×18 lead zirconate titanate elements with a pitch of 160 µm×160 µm built on top of an application-specific integrated circuit that generates transmission signals and digitizes the received signals. To reduce the number of cables in the catheter to a feasible number, we implement subarray beamforming and digitization in receive and use a combination of time-division multiplexing and pulse amplitude modulation data transmission, achieving an 18-fold reduction. The proposed imaging scheme employs seven fan-shaped diverging transmit beams operating at a pulse repetition frequency of 7.7 kHz to obtain a high frame rate. The performance of the prototype is characterized, and its functionality is fully verified. The transducer exhibits a transmit efficiency of 28 Pa/V at 5 cm per element and a bandwidth of 60% in transmission. In receive, a dynamic range of 80 dB is measured with a minimum detectable pressure of 10 Pa per element. The element yield of the prototype is 98%, indicating the efficacy of the manufacturing process. The transducer is capable of imaging at a frame rate of up to 1000 volumes/s and is intended to cover a volume of 70°×70°×10 cm. These advanced imaging capabilities have the potential to support complex interventional procedures and enable full-volumetric flow, tissue, and electromechanical wave tracking in the heart.

Passive source depth estimation using beam intensity striations of a horizontal linear array in deep water.

Source depth estimation is an important yet very difficult task for passive sonars, especially for horizontal linear arrays (HLAs). This paper proposes an efficient two-step depth estimation scheme using narrowband and broadband constructive and deconstructive striation patterns due to interference between the direct (D) and sea surface reflected (SR) arrivals at an HLA on the bottom of deep water. First, the horizontal source-array ranges are derived from triangulation results of solid angle estimates by subarray beamforming. The applicable areas of the method in deep water are investigated through Mento Carlo simulations, assuming different subarray partitioning ways of a given HLA aperture. Second, cost functions are built to match the measured beam intensity striations with modeled ones. To mitigate the spatial smoothing effect of the beam intensity striations during beamforming, a criterion of the largest subarray aperture is established, and a computationally efficient way is presented to model the replicas by the D-SR time delay templates at a single element of the array calculated by ray theory. The performance degradation due to limited source range spans, the distortion of the beam intensity striations, and range estimation errors has been analyzed. Two experimental datasets verify the effectiveness of the proposed method.

Compact beamforming network for producing multiple orthogonal beams in a limited field of view phased array antenna

AbstractDue to the advent of high-throughput communication satellites in a geostationary orbit, the development of multiple beam phased array antenna (MBPAA) technology has become a necessity. This paper presents the design and implementation of the constituent unit of a beamforming network (BFN), which feeds an MBPAA with interleaved sub-arrays. The proposed BFN generates multiple orthogonal sub-beams with a very tiny angular distance between adjacent sub-beams in a limited field of view. The BFN consists of sub-array beamforming networks (SABFNs) with unequal number of beam ports and antenna ports, which can feed both the arrays lateral elements and the interleaved core sub-arrays for pattern shaping and side-lobe level reduction. A microwave circuit for this SABFN has been designed and fabricated in C-band. The microstrip lines have been printed on the two sides of a suspended substrate. This technique leads to size reduction of the circuit by twice a value compared to a conventional microstrip circuit. Measurements have been compared to simulations, and good conformity has been observed. The insertion loss in the path of beam ports to the antenna ports is 3.5 dB for a relative bandwidth of 10%.

Fully Integrated Electronic-Photonic Ultrasound Receiver Array for Endoscopic Applications in a Zero-Change 45-nm CMOS-SOI Process

This article presents the first fully integrated 2-D array of electronic-photonic ultrasound sensors targeting low-power miniaturized ultrasound probes for endoscopic applications. Fabricated in a zero-change 45-nm CMOS-silicon-on-insulator (SOI) technology, this 5.53 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> 3.03 mm electronic-photonic system on chip (EPSoC) utilizes micro-ring resonators (MRRs) as ultrasound sensors instead of the traditional piezoelectric or capacitive micromachined transducers (PMUTs or CMUTs). The photonic nature of the sensor enables remoting of the power-hungry receive electronics outside the probe tip, thus lowering the power dissipation inside the human body. Moreover, it eliminates electrical cabling, replacing the bulky micro-coax cables with thinner optic fibers. This EPSoC also reduces fiber count by 8 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times$</tex-math> </inline-formula> with zero power and area overhead by performing wavelength division multiplexed interrogation of MRR sensors coupled onto the same waveguide in lieu of sub-array beamforming or in-pixel digitization. Leveraging the monolithic integration of photonic devices with CMOS circuitry, a complete receiver (RX) unit is built right next to the sensor MRRs, including a programmable gain transimpedance amplifier (TIA) and background current cancellation digital-to-analog converters ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I_{\text{DAC}}$</tex-math> </inline-formula> s), which allow for a sensor operating range of 74 dB. A 9-bit SAR ADC performs on-chip A/D conversion making for a self-contained endoscopic ultrasound receiver system. The photonic sensing element demonstrates 7.3 mV/kPa sensitivity while consuming 0.43 mW of power and occupying 0.01 mm of area. The functionality of the fabricated chip has been demonstrated in ultrasonic receiver beamforming experiments.

A Pitch-Matched Transceiver ASIC With Shared Hybrid Beamforming ADC for High-Frame-Rate 3-D Intracardiac Echocardiography

In this article, an application-specific integrated circuit (ASIC) for 3-D, high-frame-rate ultrasound imaging probes is presented. The design is the first to combine element-level, high-voltage (HV) transmitters and analog front-ends, subarray beamforming, and in-probe digitization in a scalable fashion for catheter-based probes. The integration challenge is met by a hybrid analog-to-digital converter (ADC), combining an efficient charge-sharing successive approximation register (SAR) first stage and a compact single-slope (SS) second stage. Application in large ultrasound imaging arrays is facilitated by directly interfacing the ADC with a charge-domain subarray beamformer, locally calibrating interstage gain errors and generating the SAR reference using a power-efficient local reference generator. Additional hardware-sharing between neighboring channels ultimately leads to the lowest reported area and power consumption across miniature ultrasound probe ADCs. A pitch-matched design is further enabled by an efficient split between the core circuitry and a periphery block, the latter including a datalink performing clock data recovery (CDR) and time-division multiplexing (TDM), which leads to a 12-fold total channel count reduction. A prototype of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8{\times }9$ </tex-math></inline-formula> elements was fabricated in a TSMC 0.18- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> HV BCD technology and a 2-D PZT transducer matrix with a pitch of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$160 \mu \text{m}$ </tex-math></inline-formula> , and a center frequency of 6 MHz was manufactured on the chip. The imaging device operates at up to 1000 volumes/s, generates 65-V transmit pulses, and has a receive power consumption of only 1.23 mW/element. The functionality has been demonstrated electrically as well as in acoustic and imaging experiments.

A low‐power and area‐efficient ultrasound receiver using beamforming successive approximation register analog‐to‐digital converter with capacitive digital‐to‐analog converter combined delay cell structure for 3‐D imaging systems

The authors present a low-power area-efficient subarray beamforming receiver (RX) structure for a miniaturized 3-D ultrasound imaging system. Given that the delay-and-sum (DAS) and digitization functions consume most of the area and power in the receiver, the beamforming successive approximation register (SAR) analog-to-digital converter (ADC) shares its capacitive digital-to-analog converter (CDAC) with the delay cells. As a result, the delay cells implemented with capacitors are embedded in the CDAC with significant area reduction, further eliminating the need for power-hungry ADC buffers. Furthermore, the dual reference 10-bit SAR ADC reduces the area of CDAC by 32 times, achieving a switching energy reduction of 98.3%, compared to the conventional SAR ADC. As a result, the proposed beamforming SAR ADC, simulated using a 0.18 μm CMOS process, consumes 230 μW per channel, significantly reducing the per channel capacitance.

Hybrid Waveguide Feed Network for Aperiodic Subarray Beamforming

In this letter, a hybrid waveguide feed network for an aperiodic subarray beamforming antenna is presented. The feed structure is divided into vertical and horizontal parts. Vertical parts have inclined slots with a reduced-height waveguide, and the horizontal part has unequal <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> -plane septum power dividers to achieve a compact feed network with acceptable electrical characteristics. The angle of each inclined slot and the position of each septum were designed for amplitude weighting and in-phase characteristics. For comparison, a simple resonant feed network without septum power dividers (i.e., with waveguides and inclined slots) was simulated to access the effectiveness of the proposed network. The proposed structure was fabricated using computer numerical control milling and diffusion bonding. The input reflection coefficient was less than −15 dB, and the transmission phase difference between 20 ports was less than 72° within a bandwidth of 2.4%. This feed network design has potential applications in electronically scanned arrays and subarray antennas for a limited field of view.

Robust Adaptive Beamforming Algorithm for Sparse Subarray Antenna Array Based on Hierarchical Weighting

Sparse antenna arrays based on subarrays have more and more broad application prospects for the limitation of array space, real-time algorithm and hardware costs. Aiming at the beamforming technology of sparse antenna arrays based on subarrays, this paper proposes a robust adaptive beamforming algorithm based on hierarchical weighting. The algorithm performs conventional beamforming to calculate the weights of each element in the subarray, then the synthetic signals output by each subarray are used as sparse array metadata. The Interference-plus-Noise Covariance Matrix (INCM) is reconstructed by integration in two-dimensional space, and a convex optimization model of a multi-constraint array containing the signal pointing error was established to estimate the real guide vector. Finally, using the reconstructed INCM and the estimation of the guide vector, we obtain a weighted vector between the subarrays and output signal for the whole array. The simulation results show that the proposed algorithm has better Signal-to-Interference-and-Noise Ratio (SINR) and robustness compared with other algorithms for sparse subarray antenna array beamforming.

Pruned Distributed and Parallel Subarray Beamforming for 3-D Underwater Imaging With Fine-Grid Sparse Arrays

The development of real-time 3-D underwater imaging systems with large planar arrays involves high hardware costs and great computational burden. This study proposes the concept of fine-grid sparse arrays and the pruned distributed and parallel subarray (P-DPS) beamforming algorithm to achieve 3-D narrowband underwater imaging systems with low complexity. Fine-grid sparse arrays refine traditional half-wavelength grids to improve the freedom of the sparse optimization process and reduce the number of active elements. However, grid refinement increases the computational load of conventional fast beamforming algorithms. To solve this problem, a new pruned fast Fourier transform is proposed to eliminate all the redundant operations in the P-DPS beamforming, which is suitable for fine-grid sparse arrays. The computational load of the P-DPS beamforming seldom increases with grid refinement. The validity of the proposed method is verified with a fine-grid sparse planar array designed in the study. The computational load is then analyzed and compared with those of other methods. Results show the notable improvements in array sparsity rate and computational efficiency relative to those in the literature.

Single-chip mixer-based subarray beamformer for sub-Nyquist sampling in ultrasound imaging

Compressed sensing (CS) has been proposed as a method of breaking the seemingly inherent tradeoff between sampling rate and resolution in a variety of applications, such as ultrasound imaging. Although various studies have demonstrated the effectiveness of using CS for sub-Nyquist sampling in ultrasound imaging, a dedicated integrated circuit (IC) has not yet been presented. This work introduces a single-chip mixer-based subarray beamformer, an important component for sub-Nyquist sampling in a CS ultrasound imaging system. The beamformer chip, which performs mixing, filtering, and summation of delayed signals within a subarray, is implemented using a single operational transconductance amplifier. We evaluated the performance of the proposed mixer-based subarray beamformer circuit fabricated using a 65 nm CMOS process with 0.4 mW ch−1 power consumption from a 1.2 V supply. Measurement results indicate that the prototype chip is suitable for subarray beamforming with a 5 ns resolution digital mixing sequence. The IC presented here is the first known implementation of a mixer-based subarray beamformer for sub-Nyquist sampling in ultrasonic applications and is expected to reduce sampling data requirements by a factor of 32.

A High Frame Rate Analog Front-End IC With Piezoelectric Micromachined Ultrasound Transducers Using Analog Multi-Line Acquisition for Ultrasound Imaging Systems

This paper proposes a high frame rate analog front-end (AFE) IC combined with a piezoelectric micromachined ultrasonic transducer (PMUT) for ultrasound imaging systems (UISs). The proposed AFE IC, which consists of 8-channel transceivers and a peripheral circuit, employs analog multi-line acquisition (AMLA) based on sub-array beamforming. This AMLA generates multiple scanlines during a scan time by simultaneously and precisely controlling the delay of the AFE IC, thus achieving the high frame rate of the AFE IC. The sensitivities of the PMUT for transmitting and receiving ultrasound waves are simulated to be 67.5 kPa/V and 1.2 mV/kPa, respectively, which are high enough to mitigate the needs of the high-voltage electronics for UISs. The proposed AFE IC was fabricated using a 0.18-μm silicon-on-insulator process and occupies an active area of 2.56 mm × 1.68 mm. The measurement results using the simulated PMUT parameters show that the proposed AFE IC with the AMLA precisely controls its delay up to 1 μs at a clock frequency of 40 MHz. It also acquires more than 9,000 scan/s even at a focal depth of 150 mm, which is at least twice greater than those of prior works, achieving a high frame rate of 93 Hz when 100 scanlines are used for a frame. In addition, a figure-of-merit, which considers the energy consumption per channel/scan and the energy loss, is achieved to be 20 nJ/scan/dB at a focal depth of 150 mm and a center frequency of 3.6 MHz; this is the best result compared to previously reported works. Therefore, the proposed AFE IC is suitable for UISs requiring a high frame rate.

Multiple Source Localization in a Shallow Water Waveguide Exploiting Subarray Beamforming and Deep Neural Networks.

Deep neural networks (DNNs) have been shown to be effective for single sound source localization in shallow water environments. However, multiple source localization is a more challenging task because of the interactions among multiple acoustic signals. This paper proposes a framework for multiple source localization on underwater horizontal arrays using deep neural networks. The two-stage DNNs are adopted to determine both the directions and ranges of multiple sources successively. A feed-forward neural network is trained for direction finding, while the long short term memory recurrent neural network is used for source ranging. Particularly, in the source ranging stage, we perform subarray beamforming to extract features of sources that are detected by the direction finding stage, because subarray beamforming can enhance the mixed signal to the desired direction while preserving the horizontal-longitudinal correlations of the acoustic field. In this way, a universal model trained in the single-source scenario can be applied to multi-source scenarios with arbitrary numbers of sources. Both simulations and experiments in a range-independent shallow water environment of SWellEx-96 Event S5 are given to demonstrate the effectiveness of the proposed method.

Design of Low-Complexity 3-D Underwater Imaging System With Sparse Planar Arrays

The development of a real-time 3-D underwater imaging system with a planar array is restricted by the huge hardware cost and computational burden associated with the large number of elements required. In this paper, a new design of low-complexity 3-D underwater imaging system is proposed, involving two key parts: a special sparse array with low hardware cost and an efficient beamforming with low computational burden. Especially, the simulated annealing algorithm is optimized based on distributed and parallel subarray (DPS) beamforming and results in fewer active elements than existing methods. To improve the computational efficiency especially for sparse arrays, an optimized DPS beamforming is presented with the pruning fast Fourier transform technology. To test the validity of the design, a real system based on the proposed methods was devised and employed in the lake and sea trials. The experiment results demonstrate that the low-complexity 3-D underwater imaging system can provide a satisfactory imaging quality.

Very-High-Frequency Single-Input–Multiple-Output Acoustic Communication in Shallow Water

Very-high-frequency (VHF) underwater acoustic communication is a relatively unexplored terrain, but its importance is expected to increase with the growing demands for larger bandwidths and higher data rates. Knowledge of VHF propagation channels is a prerequisite to achieve high data throughput. In this paper, we present time-variant angle-resolved impulse responses for a set of 250-kHz shallow-water channels. The measurements were performed at high resolution using 64 hydrophones arranged in a line array. The measured channels are characterized by delay spreads of several milliseconds, Doppler spreads of tens of hertz, and angular spreads up to 30 °. The angular spread is not separable from the delay-Doppler spread, and the impulse response depends heavily on the direction of arrival. Different beamforming and multichannel equalizer strategies are compared for a single-input-multiple-output configuration. A method combining subarray beamforming and multichannel equalization delivers in both noise- and interference-limited scenarios, transferring data at 78.125 kb/s over ranges up to 770 m.

Optimum Sparse Subarray Design for Multitask Receivers

The problem of optimum sparse array configuration to maximize the beamformer output signal-to-interference plus noise ratio (MaxSINR) in the presence of multiple sources of interest (SOI) has been recently addressed in the literature. In this paper, we consider a shared aperture system where optimum sparse subarrays are allocated to individual SOIs and collectively span the entire full array receiver aperture. Each subarray may have its own antenna type and can comprise a different number of antennas. The optimum joint sparse subarray design for shared aperture based on maximizing the sum of the subarray beamformer SINRs is considered with and without SINR threshold constraints. We utilize Taylor series approximation and sequential convex programming techniques to render the initial nonconvex optimization a convex problem. The simulation results validate the shared aperture design solutions for MaxSINR for both cases where the number of sparse subarray antennas is predefined or left to constitute an optimization variable.

Middle Subarray Interference Covariance Matrix Reconstruction Approach for Robust Adaptive Beamforming With Mutual Coupling

In this letter, a middle subarray interference-plus-noise covariance matrix (INCM) reconstruction approach is proposed to mitigate the mutual coupling problem in robust adaptive beamforming. In the proposed approach, the banded symmetric Toeplitz structure of mutual coupling matrix in the uniform linear array is employed. The INCM of middle subarray is first reconstructed by using the Capon spectrum of middle subarray to integrate over the possible interference region. Similarly, the desired signal covariance matrix of middle array is calculated over the desired signal region, and the desired signal steering vector of middle array is estimated. Finally, the proposed middle subarray beamformer weight vector is obtained. Simulation results validate the superiority and effectiveness of the proposed method.

A Pitch-Matched Front-End ASIC With Integrated Subarray Beamforming ADC for Miniature 3-D Ultrasound Probes

This paper presents a front-end application-specified integrated circuit (ASIC) integrated with a 2-D PZT matrix transducer that enables in-probe digitization with acceptable power dissipation for the next-generation endoscopic and catheter-based 3-D ultrasound imaging systems. To achieve power-efficient massively parallel analog-to-digital conversion (ADC) in a 2-D array, a 10-bit 30 MS/s beamforming ADC that merges the subarray beamforming and digitization functions in the charge domain is proposed. It eliminates the need for costly intermediate buffers, thus significantly reducing both power consumption and silicon area. Self-calibrated charge references are implemented in each subarray to further optimize the system-level power efficiency. High-speed datalinks are employed in combination with the subarray beamforming scheme to realize a 36-fold channel-count reduction and an aggregate output data rate of 6 Gb/s for a prototype receive array of $24 \times 6$ elements. The ASIC achieves a record power efficiency of 0.91 mW/element during receive. Its functionality has been demonstrated in both electrical and acoustic imaging experiments.

Localization of directional noise sources from high-performance military aircraft through subarray beamforming analysis

High-performance military aircraft noise is created by multiple sound generation mechanisms that need to be understood to guide noise reduction efforts and for adequate sound field predictions. Phased-array methods can be used to produce frequency-dependent equivalent acoustic source models. The Hybrid (beamforming) method [Padois et al., J. Sound Vib. 333 (2014)] is applied to an acoustical measurement along a 71-microphone ground-based array, spanning 32 m, placed in the vicinity of a high-performance military aircraft as the engine was operated at different powers. Application of the Hybrid method to the full-array creates an overall equivalent source model that is sufficient for predicting overall field radiation but fails to separate the different noise sources. Applying the Hybrid method to subarrays separates broadband shock-associated noise from the main radiation lobes of turbulent mixing noise. Results show that the subarray-based equivalent source distributions for the different types of noise originate from overlapping source locations. Further analysis of the subarray-based equivalent noise sources using coherence and directionality from the unwrapped phase of the cross-spectral source reconstructions identifies overlapping, frequency-dependent source regions with characteristics unique to broadband shock-associated noise and turbulent mixing noise. [Work supported by an Air Force Research Laboratory SBIR.]

High-resolution bottom detection algorithm for a multibeam echo-sounder system with a U-shaped array

High-resolution approaches such as multiple signal classification and estimation of signal parameters via rotational invariance techniques (ESPRIT) are currently employed widely in multibeam echo-sounder (MBES) systems for sea floor bathymetry, where a uniform line array is also required. However, due to the requirements in terms of the system coverage/resolution and installation space constraints, an MBES system usually employs a receiving array with a special shape, which means that high-resolution algorithms cannot be applied directly. In addition, the short-term stationary echo signals make it difficult to estimate the covariance matrix required by the high-resolution approaches, which further increases the complexity when applying the high-resolution algorithms in the MBES systems. The ESPRIT with multiple-angle subarray beamforming is employed to reduce the requirements in terms of the signal-to-noise ratio, number of snapshots, and computational effort. The simulations show that the new processing method can provide better fine-structure resolution. Then a highresolution bottom detection (HRBD) algorithm is developed by combining the new processing method with virtual array transformation. The application of the HRBD algorithm to a U-shaped array is also discuss. The computer simulations and experimental data processing results verify the effectiveness of the proposed algorithm.

DOA Estimation for UCAs Based on Virtual Subarray Beamforming Technique

Direction-of-arrival (DOA) estimation is always a hotspot research in the fields of radar, sonar, communication and so on. And uniform circular arrays (UCAs) are more attractive in the context of DOA estimation since their symmetrical structures have potential to provide two directions coverage. This paper proposed a new DOA estimation method for UCAs via virtual subarray beamforming technique. The method would provide an acceptable DOA estimate even if the number of sources is great than the number of array elements. Also, the performance of the proposed method would hold good when the snapshot length or the signal-to-noise ratio (SNR) is small. Simulations show that the proposed technique offers significantly improved estimation resolution, capacity, and accuracy relative to the existing techniques.