Design Of Linear Arrays Research Articles

Capacitive micromachined ultrasonic transducer (CMUT) arrays for medical imaging

Capacitive micromachined ultrasonic transducers (CMUTs) bring the fabrication technology of standard integrated circuits into the field of ultrasound medical imaging. This unique property, combined with the inherent advantages of CMUTs in terms of increased bandwidth and suitability for new imaging modalities and high frequency applications, have indicated these devices as new generation arrays for acoustic imaging. The advances in microfabrication have made possible to fabricate, in few years, silicon-based electrostatic transducers competing in performance with the piezoelectric transducers. This paper summarizes the fabrication, design, modeling, and characterization of 1D CMUT linear arrays for medical imaging, established in our laboratories during the past 3 years. Although the viability of our CMUT technology for applications in diagnostic echographic imaging is demonstrated, the whole process from silicon die to final probe is not fully mature yet for successful practical applications.

A Waveguide Broad-Wall Transverse Slot Linear Array with Reflection-Canceling Inductive Posts and Grating-Lobe Suppressing Parasitic Dipoles

A design of a linearly-polarized non-resonant waveguide broad-wall transverse slot linear array with suppressed grating lobes is presented. Each unit element in the array consists of a transverse slot, an inductive post and a parasitic dipole-pair at a height of half of the free space wavelength. It is designed as an isolated unit without considering mutual coupling by using the Method of Moments (MoM) for radiation suppression in grating beam direction and reflection cancellation at the input. The elements thus designed are used in a travelling wave array environment. It is predicted that the reflection is less than -20dB at 11.95 GHz while the grating lobes are suppressed by more than 15dB. The design and the characteristics of the array are confirmed by measurements.

Design and assembly of double-crossover linear arrays of micrometre length using rollingcircle replication

We demonstrate the use of rolling circle replication to template linear DNA arrays whosesizes bridge the gap between nanometre-scale self-assembly and top-down lithographicfabrication. Using rolling circle replication we have produced an oligonucleotidecontaining several hundred repeats of a short sequence motif. On this template wehave constructed, by self-assembly, an array consisting of two parallel duplexesperiodically linked by antiparallel Holliday junctions. We have observed arrays up to10 µm in length by atomic force microscopy.

A Design of a Leaky Waveguide Crossed-Slot Linear Array with a Matching Element by the Method of Moments with Numerical-Eigenmode Basis Functions

A waveguide crossed-slot linear array with a matching element is accurately analyzed and designed by the method of moments using numerical-eigenmode basis functions developed by the authors. The rounded ends of crossed-slots are accurately modeled in the analysis. The initial values of the slot parameters determined by a model with assumption of periodicity of field are modified and refined by the full-wave finite-array analysis for uniform excitation and small axial ratio. As an example, an 8-element linear array is designed at 11.85 GHz, which radiates a circularly polarized wave at a beam-tilting angle of 50 degrees. The radiation pattern, the frequency characteristics of the reflection and the axial ratio are compared between the analysis and the measurement and they agree very well. The calculated and measured axial ratio at the beam direction are 0.1 dB and 1.7dB, respectively. This method provides a basic and powerful design tool for slotted waveguide arrays.

Characterization of matched piezoelectric transducer bars

To aid the design of linear arrays, it is quite important to have a detailed understanding of the elementary transducer behavior. These transducer bars must be backed and matched. The aim of this work is to characterize and to optimize layers that are used to match such transducer bars. In order to show the influence of these layers, the acoustical (acoustical power, far-field directivity pattern), electrical (electrical impedance) and mechanical (displacement field) parameters of the transducer are computed using the finite element method. Numerical studies of several transducers with different ideal matching layers which satisfy the one-dimensional criterion are presented and carefully analyzed. These studies show the existence of parasitic modes in the desired operating band of the transducer, due to shear wave propagation in the matching layer. A simple choice criterion of the matching material suggesting no parasitic mode in the desired operating band of the transducer bar has been defined. This criterion is given by W<λS/2, where W is the width of the transducer and λS is the shear wavelength of the matching layer at the working frequency. Finally, experimental results of a matched transducer bar are successfully compared with numerical ones.

Dual-polarized linear series-fed microstrip arrays with very low losses and cross polarization

The design of a microstrip series-fed linear traveling-wave array is described in this paper. The array is composed of two symmetric subarrays formed by cascading an equal number of four-port aperture-coupled cross-patch elements and terminated on a two-port radiating matched load. Dual-linear and circular polarization can be achieved by appropriately exciting the array and by virtue of the symmetric arrangement of the antenna high polarization purity is obtained. A proof-of-concept linear array is developed and the corresponding numerical results performed through a full-wave approach based on the method of moments are presented.

Broadside linear array of resonant type leaky-wave antenna composed of image NRD guide

A broadside linear array of a resonant-type leaky-wave antenna with a new construction based on an image nonradiating dielectric (NRD) guide is proposed. Fundamental characteristics are investigated by performing both the finite-difference time-domain (FDTD) analysis and basic experiments. The proposed configuration makes it possible to improve the H-plane pattern beamwidth, which is much wider than that of the E-plane. First, a single-element resonant-type leaky-wave antenna fed by a longitudinal slot on the broad wall of a rectangular waveguide is analysed to obtain the data used for the design of the linear array. Next, based on the results obtained, a 2-element linear array employing the same feeding technique as that of the single-element case is designed and analysed. The H-plane beamwidth is found to be 34°, which is 36° narrower than that of the single-element antenna. Finally, measured results are also presented to confirm the effective performance of the proposed configuration.

Design of sparse linear arrays by Monte Carlo importance sampling

The formation of acoustic images in real-time requires an enormous computational burden. To reduce this demand the use of sparse arrays for beamforming is mandated. The design of these arrays for adequate mainlobe width and low sidelobe level is a difficult nonlinear optimization problem. A new approach to the joint optimization of sensor placement and shading weights is discussed. Based on the concept of importance sampling an optimization method is presented and some examples given to illustrate its effectiveness.

Characterizations of VO 2-based uncooled microbolometer linear array

Vanadium dioxide (VO 2) thin films are materials for uncooled microbolometer due to their high temperature coefficient of resistance (TCR) at room temperature. This paper describes the design and fabrication of eight-element uncooled microbolometer linear array using the films and micromachining technology. The characteristics of the array is investigated in the spectral region of 8–12 μm. The fabricated detectors exhibit responsivity of over 10 kV/W, detectivity of approximate 1.94×10 8 cm Hz 1/2/W, and thermal time constant of 11 ms, at 300 K and at a frequency of 30 Hz. Furthermore, the uncorrected response uniformity of the linear array bolometers is less than 20%.

Design of low-cost and high-throughput linear arrays for DFT computations: algorithms, architectures, and implementations

Recursive algorithms for discrete Fourier transform (DFT) computation are proposed, where the common entries of the decomposed matrices are factored out in order to reduce the number of multipliers during implementation. The derived algorithms are essentially band-matrix-vector multiplications with matrix bandwidth of 3 in the radix-2 case and bandwidth of 7 in the radix-4 case. Low cost architectures are derived using an efficient mapping technique for the corresponding heterogeneous dependence graphs of the decomposed band matrices. Only log/sub 2/ N(3 log/sub 4/ N) adders and log/sub 2/ N-1(log/sub 4/ N-1) multipliers are needed to compute the DFT of size N using the proposed radix-2 (radix-4) linear array architectures, a great saving in hardware cost compared to previous approaches. Due to the simplicity and regularity of the architectures, it is possible to reduce the power consumption of the DFT processors by temporarily disabling the multiplier units at proper time steps. VLSI implementations of an 8-point radix-2 DFT processor and a 64-point radix-4 DFT processor are also given.

General design method for diversity antenna arrays

Diversity reception is a widely used technique in radio communications to alleviate signal fading due to complex propagation environments such as downtown areas in large cities. This study concentrates on the design problem of an antenna array which can be used in a base station of a radio communication system to provide diversity. A design method for antenna arrays is introduced, which results in exactly the same power pattern but dissimilar phase patterns for the array. Radio signal reception using different phase pattern provides possibility to reduce destructive interference of incoming plane waves while the unchanging power pattern quarantees the fulfilment of original cell and network planning. The developed theory is rather general and can be applied for linear, planar and 3-dimensional array design. The well-known space diversity technique is shown to be a simple specific solution of the introduced method.

Design of a dual-polarization linear patch array via full-wave analysis

Design of a dual-polarization linear patch array via full-wave analysis

Design of a dual‐polarization linear patch array via full‐wave analysis

Design of a dual‐polarization linear patch array via full‐wave analysis

Ultrasonic imaging using a 5-MHz multilayer/single-layer hybrid array for increased signal-to-noise ratio

Conventional diagnostic ultrasound scanners are bulky and require significant amounts of electrical power during operation. Reducing the size, weight, and consumption of electrical power is made easier through the use of highly integrated compact transmit and receive electronics that may be incorporated in the transducer handle. This necessitates the use of low voltage transmitters and low power receive preamplifiers. Conventional scanners typically use approximately 100-V pulses during transmit; therefore, decreasing the transmit voltage to 15 V decreases the transmit sensitivity. Conventional receive electronics that are located at the scanner degrade the received signal-to-noise ratio (SNR) because the array element cannot efficiently drive the coaxial cable. Transmit sensitivity and received SNR can be radically improved using a multilayer/single-layer hybrid array making integration of electronics into the transducer handle more feasible. In this paper, we discuss the design, fabrication, and testing of a 5-MHz hybrid linear array. The hybrid array included 16 multilayer transmit elements (10 Omega impedance) and 24 single-layer receive elements at a half wavelength element pitch. Low voltage transmitters with an output resistance of 7 Omega and high impedance JFET preamplifiers using 15 V for biasing were located adjacent to the hybrid array in the transducer handle. The transmit sensitivity and received SNR of the hybrid array were compared with a conventional array using 50-Omega transmitters and receive preamplifiers at the scanner. The transmit sensitivity improved by 12.8 dB, and the received SNR improved by 7.8 dB, yielding an overall improvement of 20.6 dB, which compared well with predictions from the KLM model. Images of phantoms and in vivo images of the kidney obtained with the Siemens Model 1200 phased array system showed the increased SNR using the hybrid array. Estimates of penetration in tissue mimicking phantoms (alpha=0.5 dB/(cm MHz)) improved by 7 cm compared with the control.

Design and Development of Ultralow Sidelobe Antenna.

This paper describes the design and development of an airborne ultralow sidelobe level antenna, starting from the design of individual linear arrays and the power divider network. The antenna employs radiating slots on broadwall of rectangular waveguide and is of traveling wave type. The various stages involved in the design process are described briefly. The experimental results including the far-field patterns, voltage standing wave ratio, and power division ratios are discussed in detail.

A new approach for the design of linear systolic arrays for computing third-order cumulants

VLSI architectures for computing higher-order cumulants have gained considerable attention recently, as a consequence of the increasingly evident importance of using cumulant functions as an effective signal processing tool. This paper presents a new approach for designing linear systolic arrays for computing third-order cumulants. First, the estimation of third-order cumulants is formulated elegantly as a sequence of matrix multiplication operations. Then a special structure systolic array for this matrix multiplication is developed. The resulting structure is an efficient unidirectional array which not only is adequate for VLSI implementations but also is suitable for supporting fault-tolerance techniques.

Frequency‐independent features of self‐similar fractal antennas

A generalized approach to the study of frequency‐independent antennas is presented which relies on the recently developed theory of fractal geometry. It is demonstrated that this fractal geometric interpretation allows for the ability to characterize a much wider class of frequency‐independent antennas. This includes radiating structures which are self‐similar in the discrete sense, the smooth sense, and even the “rough” sense. The antenna configurations in this paper are all self‐similar and have been parameterized in terms of a common similarity factor of τ. Finally, it is shown how this new theory of self‐similar fractal radiators may be employed to develop a multiband linear array design methodology for which the directive gain is a log‐periodic function of frequency.

Optimizing the radiation pattern of sparse periodic two-dimensional arrays

A method for reducing the number of elements in a 2-D array while minimizing degradation of the beam forming properties is described. The method relies on selecting a different arrangement of elements when the array is transmitting energy and when the array is receiving energy. The transmit and receive aperture functions are chosen to minimize the difference between the effective aperture of the sparse array and the effective aperture of a desired dense array. In a companion paper [see ibid vol. 43, pp. 7-14, 1996], the design of sparse linear arrays using the effective aperture method was described. Here, we extend this method to the design of 2-D arrays. Comparisons of the radiation patterns of a dense 2-D array and sparse 2-D arrays with random and periodic element spacing are given. Using the effective aperture method, we show that the number of elements in a 64/spl times/64 2-D array can be reduced by more than six times, and the elements in a 128/spl times/128 array can be reduced by more than 12 times, with little effect on the beam forming properties of the arrays.

Closed-form mapping conditions for the synthesis of linear processor arrays

This paper addresses the problem of mapping algorithms with constant data dependences to linear processor arrays. The closed-form necessary and sufficient mapping conditions are derived to identify mappings without computational conflicts and data link collisions. These mapping conditions depend on the space-time mapping matrix and the problem size parameters only. Their correctness can be verified in constant time that is independent of problem size. The design of optimal linear processor arrays is formulated as a mathematic programming problem, which can be solved efficiently by a systematic enumeration of a polynomial search space.

Implementing division with field programmable gate arrays

This article presents a method to map digit-recurrence arithmetic algorithms to lookup-table based Field Programmable Gate Arrays (FPGAs). By reducing the number of binary inputs to combinational logic and merging algorithm steps, the strategy creates new simplified functions to decrease logic depth and area. To illustrate this method, a radix-2 digit-recurrence division algorithm is mapped to the Xilinx XC4010, a lookup-table based FPGA. The mapping develops a linear sequential array design that avoids the common problem of large fanout delay in the critical path. This approach has a cycle time independent of precision while requiring approximately the same number of logic blocks as a conventional design.