Aperture Method Research Articles

Spatial and angular domain analysis of the near-field radiation of electrically large apertures with non-uniform field

According to the equivalence principle, the design of the compact range (CR) reflector can be transformed into the design of its aperture. Therefore the analysis of the CR performance variations caused by the mechanical and electrical defects can be transformed into the analysis of the aperture near-field in the spatial and angular domains. Based on a square aperture and a well-designed serrated-edge aperture, the near-field characteristics have been analysed when typical amplitude and phase non-uniformities have been induced in the aperture. The aperture field convolution method and plane wave spectrum method have been adopted. Simulation results have been presented and compared in detail. The width and height of the apertures are 150 wavelengths in free space. The amplitude and phase non-uniformities discussed include: amplitude taper, serrated edge, periodic amplitude, periodic phase, linear amplitude, linear phase, local amplitude mutation and local phase mutation. The conclusions provide references for CR design, testing, measurements and antenna tolerance analysis.

Optimization of the Multi-element Synthetic Transmit Aperture Method for Medical Ultrasound Imaging Applications

The paper presents the optimization problem for the multi-element synthetic transmit aperture method (MSTA) in ultrasound imaging applications. The optimal choice of the transmit aperture size is made as a trade-off between the lateral resolution, penetration depth and the frame rate. Results of the analysis obtained by a developed optimization algorithm are presented. The maximum penetration depth and lateral resolution at given depths are chosen as optimization criteria. The results of numerical experiments carried out in MATLABr using synthetic aperture data of point reflectors obtained by the FIELD II simulation program are presented. The visualization of experimental synthetic aperture data of a tissue mimicking phantom and in vitro measurements of the beef liver performed using the SonixTOUCH Research system are also shown.

Constructing the 2D radio images of objects with the use of multifrequency signals with coded carrier-frequency hopping (Costas signals)

An approach to constructing radial Doppler 2D radio images (RIs), in which the synthetic aperture method is applied to multifrequency signals with Costas-coded hopping of carrier frequencies, is investigated. The case of completely coherent signals and the case of their strong phase distortions have been discussed. Side lobe level suppression method based on multiplicative processing of 2D RIs constructed with the use of different frequency codes is proposed. Selection of code bases ensuring minimization of the side lobes level of the resulting 2D RI has been substantiated. The results simulation based on mathematical bright points are presented.

Golay Coded Sequences in Synthetic Aperture Imaging Systems

The paper presents the theoretical and experimental study of synthetic trans- mit aperture (STA) method combined with Golay coded transmission for medical ultrasound imaging applications. The transmission of long waveforms characterized by a particular autocorrelation function allows to increase the total energy of the transmitted signal without increasing the peak pressure. It can also improve signal- to-noise ratio and increase the visualization depth maintaining the ultrasound image resolution. In the work the 128-element linear transducer array with 0.3 mm pitch excited by the 8 and 16-bits Golay coded sequences as well as a one cycle at nominal frequencies 4 MHz were used. The comparison of 2D ultrasound images of the tissue mimicking phantoms is presented to demonstrate the benefits of coded transmission. The image reconstruction was performed using synthetic STA algorithm with transmit and receive signals correction based on a single element directivity function.

822 開口合成法による内部欠陥の可視化シミュレーション(GS21-3-3材料力学/材料加工,材料成形と評価(3))

822 開口合成法による内部欠陥の可視化シミュレーション(GS21-3-3材料力学/材料加工,材料成形と評価(3))

Two methods for measuring laser beam diameter

Two methods for measuring beam diameter are described with the derivation of the equations that make them valid. These methods are the aperture method and the knife edge technique. These methods have been used for decades; however, many do not have a firm grasp of the basic equations that make the methods valid and therefore cannot use and modify the methods with confidence to produce the desired results. The text derives the equations from basic science and mathematics to clarify the underlying concepts of the methods.

Effective ultrasonic virtual sources which can be positioned independently of physical aperture focus positions

Effective ultrasonic virtual sources which can be positioned independently of physical aperture focus positions Chikayoshi Sumi, Shinya UgaDepartment of Information and Communication Sciences, Faculty of Science and Technology, Sophia University, Tokyo, JapanAbstract: In this report, newly obtained ultrasonic virtual sources, VS1 and VS2, are described. That is, both virtual sources are obtained on the basis of the new viewpoint that the position of a virtual source can also be obtained regardless of the focus position of any physical aperture. VS1 is a virtual source that is a point acoustic source model set behind physical array elements and enables an increase in the transmitted ultrasound intensity using plural transmission ultrasound elements, and increases the size of the region of interest, that is, the same virtual source as that reported solo by other groups previously. As is well known, VS1 increases the echo signal-to-noise ratio; this yields a tissue displacement/strain measurement as well as B-mode imaging, and enables associated applications, eg, shear modulus reconstruction. Alternatively, VS2 uses an arbitrary position ahead of the physical array elements as a virtual source position with a synthetic aperture method. With VS2, random scattering media (material) such as point acoustic sources can be used as virtual sources. Preliminary experimental results are presented for a lateral modulation method. In the experiments described here using an ultrasound linear array type transducer (ultrasound element pitch, 0.2 mm; ultrasound frequency, 7.5 MHz), it was possible to use a depth range of ± 3 mm for virtual source positions. Remarkably, VS2 yielded higher lateral resolutions than the physical sources. That is, VS2 mitigates the physical and electrical limitations for using smaller ultrasound array elements and a smaller pitch, such that both a high lateral resolution and a high echo signal-to-noise ratio are obtained.Keywords: ultrasound, virtual source, lateral modulation, synthetic aperture, lateral resolution, displacement vector, strain tensor, shear modulus

High resolution digital holographic synthetic aperture applied to deformation measurement and extended depth of field method

This paper discusses the potential of the synthetic-aperture method in digital holography to increase the resolution, to perform high accuracy deformation measurement, and to obtain a three-dimensional topology map. The synthetic aperture method is realized by moving the camera with a motorized x-y stage. In this way a greater sensor area can be obtained resulting in a larger numerical aperture (NA). A larger NA enables a more detailed reconstruction combined with a smaller depth of field. The depth of field can be increased by applying the extended depth of field method, which yields an in-focus reconstruction of all longitudinal object regions. Moreover, a topology map of the object can be obtained.

Data Reduction Method for Synthetic Transmit Aperture Algorithm

Ultrasonic methods of human body internal structures imaging are being continuously enhanced. New algorithms are created to improve certain output parameters. A synthetic aperture method (SA) is an example which allows to display images at higher frame-rate than in case of conventional beam-forming method. Higher computational complexity is a limitation of SA method and it can prevent from obtaining a desired reconstruction time. This problem can be solved by neglecting a part of data. Obviously it implies a decrease of imaging quality, however a proper data reduction technique would minimize the image degradation. A proposed way of data reduction can be used with synthetic transmit aperture method (STA) and it bases on an assumption that a signal obtained from any pair of transducers is the same, no matter which transducer transmits and which receives. According to this postulate, nearly a half of the data can be ignored without image quality decrease. The presented results of simulations and measurements with use of wire and tissue phantom prove that the proposed data reduction technique reduces the amount of data to be processed by half, while maintaining resolution and allowing only a small decrease of SNR and contrast of resulting images.

长工作距离显微成像数字全息合成孔径方法

长工作距离显微成像数字全息合成孔径方法

MVDR-based coherence weighting for high-frame-rate adaptive imaging

Some success has been demonstrated in the extensive studies of adaptive imaging, but these approaches are generally not suitable for high-frame-rate (HFR) imaging where broad transmit beams are required. In this study, we propose an effective adaptive imaging method suitable for HFR imaging based on coherence-factor (CF) weighting and the minimum-variance-distortionless-response (MVDR) method. The CF is an index of focusing quality estimated from receive-channel data in which the amplitude of each image pixel is weighted by the corresponding CF so as to reduce the unwanted sidelobes. Direct implementation of CF weighting in HFR imaging does not provide satisfactory results because the broad transmit beams required for HFR imaging reduce the accuracy of CF calculations. In this study, we alleviated this problem by applying the MVDR method. We test the proposed method with the synthetic transmit aperture method where only 8 firings are required to form an image. Both simulations and clinical breast imaging data were used, and the proposed method enhanced the mean contrast by around 4.6 dB and the mean contrast-to-noise ratio by around 20%. The results demonstrate that the proposed method is effective at improving the image quality.

Aimed properties of parabolic aerial for satellite television

Using an aperture method, chosen irradiator orientation description, analytical expression which describes irradiator orientation description. Using Huygens’ element description as irradiator orientation description, found weeds parabolic aerial radiation.

A Demonstration of Optimal Apodization Determination for Proper Lateral Modulation

We have realized effective ultrasound (US) beamformings by the steering of plural beams and apodizations for B-mode imaging with a high lateral resolution and accurate measurement of tissue or blood displacement vector and/or strain tensor using the multidimensional cross-spectrum phase gradient method (MCSPGM), or multidimensional autocorrelation or Doppler methods (MAM and MDM) using multidimensional analytic signals. For instance, the coherent superposition of the steered beams performed in the lateral cosine modulation method (LCM) has a higher potential for realizing a more accurate measurement of a displacement vector than the synthesis of the displacement vector using the accurately measured axial displacements obtained by the multidimensional synthetic aperture method (MDSAM), multidirectional transmission method (MTM) or the use of plural US transducers. Originally, the apodization function to be used for realizing a designed point spread function (PSF) was obtained by the Fraunhofer approximation (FA). However, to obtain the best approximated, designed PSF in the least-squares sense, we proposed a linear optimization (LO) method. Furthermore, on the basis of the knowledge about the losts of US energy during the propagation, we have recently developed a nonlinear optimization (NLO) method, in which the feet of the main lobes in apodization function are properly truncated. Thus, NLO also allows the decrease in the number of channels or the confinement of the effective aperture. In this study, to gain insight into the ideal shape of the PSF, the accuracies of the two-dimensional (2D) displacement vector measurements were compared for typical PSFs with distinct lateral envelope shapes, particularly, in terms of full width at half maximum (FWHM) and the length of the feet, i.e., the Gaussian function, Hanning window and parabolic function. It was confirmed that a PSF having a wide FWHM and short feet was ideal. Such a PSF yielded an echo with a high signal-to-noise ratio (SNR), a large bandwidth and a large maximum spectrum of the center frequency. Moreover, for the three PSFs used, by calculating the PSFs using a typical transducer model and the apodization functions obtained by the respective LO and NLO methods and FA, we compare the approximation accuracies of the realized PSFs. NLO was effective for realizing such an ideal PSF. In addition, NLO allowed the significant decrease in the number of channels or the confinement of the effective aperture. Thus, in the comparisons of the three distinct PSFs, we obtain an appropriate apodization function. This study will assist the realization of the best lateral modulation.

Use of frequency-dynamic aperture method in ultrasonic diagnostic systems

Use of frequency-dynamic aperture method in ultrasonic diagnostic systems

Displacement vector measurement using instantaneous ultrasound signal phase-multidimensional autocorrelation and Doppler methods

Two new methods of measuring a multidimensional displacement vector using an instantaneous ultrasound signal phase are described, i.e., the multidimensional autocorrelation method (MAM) and multidimensional Doppler method (MDM). A high measurement accuracy is achieved by combining either method with the lateral Gaussian envelope cosine modulation method (LGECMM) or multidirectional synthetic aperture method (MDSAM). Measurement accuracy is evaluated using simulated noisy echo data. Both methods yield accurate measurements comparable to that of our previously developed cross-spectrum phase gradient method (MCSPGM); however, they require less computational time (the order, MDM < MAM approximate, equals MCSPGM) and would provide realtime measurements. Moreover, comparisons of LGECMM and MDSAM performed by geometrical evaluations clarifies that LGECMM has potentials to yield more accurate measurements with less computational time. Both MAM and MDM can be applied to the measurement of tissue strain, blood flow, sonar data, and other target motions.

Fusion Splicing of Ribbon-Shaped Optical Fibers with CO2 Laser Beams

The fusion splicing of ribbon-shaped eight optical fibers was carried out with CO2 laser beams. At first, laser beam of uniform power distribution, which was obtained by simple aperture method, was irradiated to every fiber. However, defective connections were frequently occurred at both edges of the ribbon fibers, because the heat inputs to these fibers were low and not enough to melt silica glass fibers. Two-dimensional heat conduction analysis indicated that the reason was the large heat transfer and radiation from these fibers to atmosphere. Therefore, higher laser power was necessary to be supplied to two edge fibers. Laser beams designed specially, which had about 20∼22 % higher power density at edge region, enabled the temperatures of all fibers to reach their softening point simultaneously. As a result, excellent connections with low splicing loss of 0.011dB on average values were achieved.

WE-E-L100J-03: Scatter Measurements and Simulations in X-Ray Cone Beam CT Breast Imaging

Purpose: To compare and validate Monte Carlo simulation using the GATE software with experimental measurements for scattered radiation in X‐ray cone beam CT breast imaging . In addition, to determine the scatter distribution for single‐order, and multiple‐order incoherent and coherent scatter using validated Monte Carlo simulation.Methods: This study used a bench‐top cone‐beam CT breast imagingsystem using a flat‐panel detector. A cylindrical phantom with equivalent composition of 50% fibro‐glandular and 50% adipose tissues was used. Scatter distributions were measured by beam stop and aperture methods. A lead strip was positioned between the X‐ray source and the breast phantom in the beam stop method. Its inverse version was used in the aperture method. We computed the scatter contribution in the breast phantom by subtracting background scatter. The background scatter fraction was measured without the phantom. The Geant4‐based simulation package GATE was used to model X‐ray photon interactions in the phantom and detector. Two implemented electromagnetic interactions packages, standard and low energy models, were compared for computing efficiency and physics ingredients. A structured breast phantom was used in GATE simulations to determine the characteristics of various scatter components which cannot be separated in measurements. Results: Measurements by the two methods are consistent within 5% after background subtraction, and agree with the low energy model simulations. A hybrid model in GATE, with photoelectric process from the standard model and Compton and Rayleigh scattering processes from the low energy model, is computationally efficient while maintaining physics accuracy. The GATE simulations in the Bakic phantom show that the multiple‐order scatter distribution, as well as single‐order Compton scatter, has predominantly low‐frequency characteristics. Single‐order Rayleigh scatter was observed to be the primary contribution to the spatially variant scatter component.

Density and geometry of single component plasmas

The density and geometry of p¯ and e+ plasmas in realistic trapping potentials are required to understand and optimize antihydrogen (H¯) formation. An aperture method and a quadrupole oscillation frequency method for characterizing such plasmas are compared for the first time, using electrons in a cylindrical Penning trap. Both methods are used in a way that makes it unnecessary to assume that the plasmas are spheroidal, and it is shown that they are not. Good agreement between the two methods illustrates the possibility to accurately determine plasma densities and geometries within non-idealized, realistic trapping potentials.

A Fast Algorithm for 3-Dimensional Imaging with UWB Pulse Radar Systems

SUMMARY Ultra-wideband pulse radars are promising candidates for 3-dimensional environment measurements by autonomous robots. Estimating 3-dimensional target shapes by scanning with an omni-directional antenna is an ill-posed inverse problem. Conventional algorithms such as the synthetic aperture method or parametric algorithms have a problem in terms of their calculation times. We have clarified the existence of a reversible transform between received data and target shapes for 3-dimensional systems. Calculation times are remarkably reduced by applying this transform because it directly estimates target shapes without iterations. We propose a new algorithm based on the transform and present an application example using numerical simulations. We confirm that the proposed algorithm has sufficient accuracy and a short calculation time.

Fiber-delivered Acoustic 3D Imaging System with Laser-induced Breakdown

This paper describes a fabrication scheme for integrating an optical fiber-delivered catheter for ultrasound (US) imaging. In this catheter, pulsed laser is focused and guided into a tapered optical fiber. The laser passes through the fiber and is refocused to generate laser-induced breakdown (LIB), which emits spherical pulsed US wave. The reflected US waves are received with a hydrophone array to reconstruct 3D images with synthetic aperture method. We examined the probability of LIB generation relative to pulsed energy level for stably producing US pulses and clarified a suitable specification for a laser delivering fiber. Proto-type catheter demonstrated real-time 3D imaging, in which LIB is continuously generated on the tip of the catheter and frontal situation is captured in 3D images in realtime process.