High-density flexible interconnect for two-dimensional ultrasound arrays

We present a method for fabricating flexible multilayer circuits for interconnection to 2-D array ultrasound transducers. In addition, we describe four 2-D arrays in which such flexible interconnect is implemented, including transthoracic arrays with 438 channels operating at up to 7 MHz and intracardiac catheter arrays with 70 channels operating at up to 7 MHz. We employ thin and thick film microfabrication techniques to batch produce the interconnect circuits with minimum dimensions of 12-mum lines, 40-mum vias, and 150-mum array pitch. The arrays show 50-Omega insertion loss of -60 to -84 dB and a fractional bandwidth of 27 to 67%. The arrays are used to obtain real time, in vivo volumetric scans.     

Fabrication and characterization of transducer elements in two-dimensional arrays for medical ultrasound imaging

Some of the problems of developing a two-dimensional (2-D) transducer array for medical imaging are examined. The fabrication of a 2-D array material consisting of lead zirconate titanate (PZT) elements separated by epoxy is discussed. Ultrasound pulses and transmitted radiation patterns from individual elements in the arrays are measured. A diffraction theory for the continuous wave pressure field of a 2-D array element is generalized to include both electrical and acoustical cross-coupling between elements. This theory can be fit to model the measured radiation patterns of 2-D array elements, giving an indication of the level of cross-coupling in the array, and the velocity of the acoustic cross-coupling wave. Improvements in bandwidth and cross-coupling resulting from the inclusion of a front acoustic matching layer are demonstrated, and the effects of including a lossy backing material on the array are discussed. A broadband electrical matching network is described, and pulse-echo waveforms and insertion loss from a 2-D array element are measured.     

The cross algorithm for phase-aberration correction in medical ultrasound images formed with two-dimensional arrays

Common-midpoint signals in the near-field signal-redundancy (NFSR) algorithm for one-dimensional arrays are acquired using three consecutive transducer elements. An all-row-plus-two-column algorithm has been proposed to implement the one-dimensional NFSR algorithm on two dimensional arrays. The disadvantage of this method is that its ambiguity profile is not linear and a timeconsuming iterative method has to be used to linearize the ambiguity profile. An all-row-plus-two-column-and-a-diagonal algorithm has also been proposed. Its ambiguity profile is linear, but it is very sensitive to noise and cannot be used. In this paper, a novel cross algorithm is proposed to implement the NFSR algorithm on two-dimensional arrays. In this algorithm, common-midpoint signals are acquired using four adjacent transducer elements, which is not available in one-dimensional arrays. Its advantage includes a linear ambiguity profile and a higher measurement signal-to-noise ratio. The performance of the cross algorithm is evaluated theoretically. The region of redundancy is analyzed. The procedure for deriving the phaseaberration profile from peak positions of cross-correlation functions between common-midpoint signals is discussed. This algorithm is tested with a simulated data set acquired with a two-dimensional array, and the result shows that the cross algorithm performs better than the all-row plus-twocolumn NFSR algorithm.     

双平行线阵的水下二维DOA估计算法

利用集群自主式水下航行器(Autonomous Underwater Vehicles,AUV)进行的水下协同作业的需求越来越多.对于水下集群作业来说,AUV的水下定位非常重要.目前,AUV通常采用声学定位的工作模式,利用长、短基线阵对水下目标的二维波达方向(Direction of Arrival,DOA)进行估计,...     

Damage-free top-down processes for fabricating two-dimensional arrays of 7 nm GaAs nanodiscs using bio-templates and neutral beam etching

The first damage-free top-down fabrication processes for a two-dimensional array of 7 nm GaAs nanodiscs was developed by using ferritin (a protein which includes a 7 nm diameter iron core) bio-templates and neutral beam etching. The photoluminescence of GaAs etched with a neutral beam clearly revealed that the processes could accomplish defect-free etching for GaAs. In the bio-template process, to remove the ferritin protein shell without thermal damage to the GaAs, we firstly developed an oxygen-radical treatment method with a low temperature of 280?°C. Then, the neutral beam etched the defect-free nanodisc structure of the GaAs using the iron core as an etching mask. As a result, a two-dimensional array of GaAs quantum dots with a diameter of ～ 7 nm, a height of ～ 10 nm, a high taper angle of 88° and a quantum dot density of more than 7 × 10(11) cm(-2) was successfully fabricated without causing any damage to the GaAs.     

Sample volume misregistration in linear array-based dual beam Doppler ultrasound systems

Large velocity estimation errors can occur in dual beam Doppler ultrasound velocity measurement systems when there is left/right sample volume misregistration, particularly when the interbeam angle is small. Such misregistration will occur when there is tissue inhomogeneity. This is investigated for a typical type of inhomogeneity-a layer of fat-by calculating the amount of both angle and translation misregistration occurring in such a system realized using a single linear array transducer. The complex sample volume sensitivity is calculated using a modified time domain approach, combining the spatial impulse response method with ray tracing. The effects on these misregistrations of altering the aperture sizes and their relative positions on the array is then investigated to derive an improved aperture configuration for dual beam velocity estimation. Arrangements with transmit apertures wider than the receive apertures are shown to be preferable in this context.     

Intracavitary ultrasound phased arrays for noninvasive prostatesurgery

The feasibility of using intracavitary ultrasound phased arrays for thermal surgery of the prostate was investigated. A simulation study was performed which demonstrated the ability of phased arrays to generate necrosed tissue volumes over anatomically appropriate ranges (2-6 cm deep and >6 cm axially) and investigated the effects of varying frequency, sonication time, maximum temperature, and blood perfusion on the necrosed tissue volume. An advantage that phased arrays have over geometrically focused transducers is that they are able to electronically scan a single focus over a specified range very quickly. This study demonstrated that the necrosed tissue volume may be increased by more than a factor of 100 by using electronic scanning. Scan parameters that were investigated included foci spacing, scan width, perfusion, maximum temperature, and unequal weighting of the foci. An optimization was performed to select the foci weighting parameters such that a uniform thermal dose was achieved at the focal depth, providing a more uniformly heated target volume. Finally, the ability of linear ultrasound phased arrays to create necrosed tissue lesions was demonstrated experimentally in fresh beef liver using a single stationary focus and single focus scans generated by an aperiodic 0.83-MHz 57-element linear ultrasound phased array     

Analysis and comparison of two-dimensional permanent-magnet arrays for planar motor

This paper investigates three kinds of permanent-magnet arrays used in planar motors with polarity centers distributed in the lattices of a matrix. The magnetic field of every kind of magnet array is analyzed by analytical methods. First, we give a Laplace equation of magnetic scalar potential and a series of boundary conditions. Then, we derive the analytical expressions of magnet field strength and magnet flux density in the air gap of each kind of magnet array by the method of separation of variables. Finally, we compare the three types of magnet arrays on the basis of the analytical solutions.     

Design and fabrication of annular arrays for high-frequency ultrasound

The design, fabrication, and performance of miniature high-frequency annular arrays are described. A 50-MHz, 2-mm-diameter, 7-element, equal-area annular array was fabricated and tested. The array elements were defined using photolithography and the electrical contacts were made using ultrasonic wire bonding. The resulting transducer produced pulses with a -6 dB bandwidth of 52% and an insertion loss of -16 dB. A radiation pattern was collected by scanning the transducer array above the tip of a glass fiber. A -6 dB two-way beam width of 75 microns was found at f/2. The radiation pattern decreased smoothly to less than -60 dB at a distance of 550 microns.     

Treatment planning for hyperthermia with ultrasound phased arrays

Treatment planning for ultrasound phased arrays suggests a strategy for hyperthermia therapy which satisfies therapeutic conditions at the target and spares other sensitive anatomical structures. To predict both desirable and harmful interactions between ultrasound and important structures such as the tumor, bones, and air pockets, a hyperthermia treatment planning system has been developed for ultrasound phased arrays. This collection of treatment planning routines consists of geometric and thermal optimization procedures specific to ultrasound phased arrays, where geometric treatment planning, combined with thermal treatment planning and three-dimensional visualization, provides essential information for the optimization of individual patient treatments. A patient image data set for cancer of the prostate, a difficult target situated in the midst of multiple pelvic bone obstructions, illustrates the geometric treatment planning algorithm and other tools for treatment analysis. The results indicate that the analysis of complex three-dimensional relationships between the applicator, anatomical structures, and incident fields provides an important means of predicting treatment limiting conditions, thereby allowing the hyperthermia applicator to electronically adapt to individual patients and specific sites     

Log-converting processor element for CCD linear imaging arrays

A photosensor element suitable for incorporation into charge-coupled device (CCD) imaging arrays in which the charge injected into the CCD is proportional to the logarithm of incident light intensity is presented. The photosensor element consists of a photodiode directly coupled to a two-stage MOSFET common source amplifier. This element occupies an area of 25 x 100 microm and is arranged so that it could be incorporated into a linear CCD imaging array having a period of 25 microm. A logarithmic response is measured over a 68.6-dB range of incident light intensity with a sensitivity of 55 mV/decade of light intensity.     

Band centers and track finding for large two-dimensional infrared spectroscopic arrays

An efficient two-dimensional (2D) peak-finding algorithm is proposed to find peak maps that specify the peak centers of all bands in two-dimensional arrays of time-series infrared spectral data. The algorithm combines the second-derivative method with the intrinsic characteristics of 2D infrared reaction spectral data. Initially, the second-derivative method is used to detect all possible peak center positions, and then three criteria drawn from characteristics of 2D continuous spectral data are employed to filter peak positions. Four 2D peak maps are generated in a sequential order, with better and better approximations to the peak center positions being obtained in each. The 2D peak-finding algorithm has been successfully applied to both simulated spectra (to initially evaluate the algorithm) and then real 2D experimental spectra. The resulting peak maps exhibit very good estimates of the peak center positions. An ordering from the most significant to the least significant bands is obtained. The final peak maps can be used as starting parameters for various applications including the computationally intensive curve-fitting of time-series data.     

Electrical transport properties and their reproducibility for linear porphyrin arrays

We present an investigation of electrical transport through fused and orthogonal dithiolated porphyrin arrays of different molecular lengths. Length dependence measurements show that conductance decreases much more slowly with molecular length than the exponential dependence expected from a simple theoretical model. From the temperature dependence of I_SD − V_SD curves, the thermal activation energy E_a is estimated to be about 0.35 eV at zero-bias voltage, independent of molecular conformation and length. At high-bias voltages, however, the decrease in E_a as a function of bias voltage is more significant for the longer porphyrin arrays. We have also studied the thermal cycling effects. After thermal cycling, dithiolated porphyrin arrays are found to aggregate into clusters between nanoelectrodes. This is probably due to the diffusion of porphyrin arrays on the SiO₂ substrate at low temperatures, which enhances the conductance.     

Efficient dynamic focus control for three-dimensional imaging using two-dimensional arrays

An efficient dynamic focus control scheme for a delay-and-sum-based beamformer is proposed. The scheme simplifies dynamic focus control by exploiting the range-dependent characteristics of the focusing delay. Specifically, the overall delay is divided into a range-independent steering term and a range-dependent focusing term. Because the focusing term is inversely proportional to range, approximation can be made to simplify dynamic focus control significantly at the price of minimal degradation in focusing quality at shallow depths. In addition, the aperture growth controlled by a constant f//sub number/ can also be utilized to devise a nonuniform quantization scheme for the focusing delay values. Efficacy of the proposed scheme is demonstrated using simulated beam plots of a fully sampled, two-dimensional array. Design procedures are also described in detail. One design example shows that, with the proposed dynamic focus control scheme, a 4096-element array only requires 227 independent controllers for the range-dependent focusing term. Moreover, only 28 non-uniform quantization levels are required to achieve the same focusing quality as that of a conventional scheme with 784 uniform quantization levels. The beam plots of a fully sampled array show that sidelobes are slightly increased below the -30 dB level for imaging depths less than 3 cm. At greater depths, there is no observable degradation.     

Microfabrication of electrode patterns for high-frequency ultrasound transducer arrays

High-frequency ultrasound is needed for medical imaging with high spatial resolution. A key issue in the development of ultrasound imaging arrays to operate at high frequencies (?30 MHz) is the need for photolithographic patterning of array electrodes. To achieve this directly on 1-3 piezocomposite, the material requires not only planar, parallel, and smooth surfaces, but also an epoxy composite filler that is resistant to chemicals, heat, and vacuum. This paper reports, first, on the surface finishing of 1-3 piezocomposite materials by lapping and polishing. Excellent surface flatness has been obtained, with an average surface roughness of materials as low as 3 nm and step heights between ceramic/polymer of ～80 nm. Subsequently, high-frequency array elements were patterned directly on top of these surfaces using a photolithography process. A 30-MHz linear array electrode pattern with 50-μm element pitch has been patterned on the lapped and polished surface of a high-frequency 1-3 piezocomposite. Excellent electrode edge definition and electrical contact to the composite were obtained. The composite has been lapped to a final thickness of ～55 μm. Good adhesion of electrodes on the piezocomposite has been achieved and electrical impedance measurements have demonstrated their basic functionality. The array was then packaged, and acoustic pulse-echo measurements were performed. These results demonstrate that direct patterning of electrodes by photolithography on 1-3 piezocomposite is feasible for fabrication of high-frequency ultrasound arrays. Furthermore, this method is more conducive to mass production than other reported array fabrication techniques.     

基于可控波束响应的球形传声器阵列定位方法研究

球形传声器阵列因其完全对称的结构,可在三维空间内实现有效的声源定位。文章重点关注基于球谐函数展开的可控波束响应算法,推导了算法的实现流程,并通过仿真验证了可控波束响应算法的性能。建立了包含8个传声器单元的实验系统,其中球形结构在8个单元的条件下可以视为立方结构,通过低阶球谐展开实验验证了可控波束算法的性能。在视听室的实验结果充分验证了定位算法的有效性,定位误差小于10°。     

Synthetic aperture-based beam compression for intravascular ultrasound imaging

In this paper, intravascular ultrasound (IVUS) images acquired with a 64-element array transducer using a multistatic acquisition scheme are presented. The images are reconstructed from a collection of pulse-echo measurements using a synthetic aperture array imaging technique. The main limitations of IVUS imaging are a poor lateral resolution and elevated grating lobes caused by the imaging geometry. We propose a Synthetic Aperture Focusing Technique (SAFT), which uses a limited number of A-scan signals. The focusing process, which is performed in the Fourier domain, requires far less computation time than conventional delay-and-sum methods. Two different reconstruction kernel functions have been derived and are compared for the processing of experimental data     

Plane waves in regular arrays of dipole scatterers and effective-medium modeling

A simple analytical theory for finding eigensolutions for plane electromagnetic waves propagating along an axis in infinite regular arrays of small dipole particles is presented. The spacing between dipoles in every plane is assumed to be smaller than the wavelength; separation between the planes is arbitrary. The influence of evanescent modes is taken into account. This theory gives a model for an effective propagation constant that can be applied in a wide frequency range from the quasi-static regime to the Bragg reflection (photonic bandgap) region.     

Feasibility of using ultrasound phased arrays for MRI monitorednoninvasive surgery

The purpose of this paper was to evaluate the in vivo feasibility of using phased arrays for MRI guided ultrasound surgery. Two different array concepts were investigated: a spherically curved concentric ring array to move the focus along the central axis and a spherically curved 16 square element array to make the focus larger. Rabbit thigh muscles were exposed in vivo in a 1.5 T MRI scanner to evaluate the array performance. The results showed that both of the arrays performed as expected, and the focus could be moved and enlarged. In addition, adequate power could be delivered from the arrays to necrose in vivo muscle tissue in 10 s. This study was the first implementation of phased arrays for MRI guided ultrasound surgery. The results demonstrate that phased arrays have significant potential for noninvasive tissue coagulation