A generalized approach for computation of near field radiation pattern of an antenna

A generalized procedure in the form of an analytical formulation for the determination of radiation pattern of an antenna at any arbitrary distance which covers the near field as well as far field is presented in this paper. With the prior knowledge of either the current or field distribution on the radiating aperture, the proposed near field analysis is generic and can be applied for wide variety of antenna elements. The underlying principle of the generalized procedure is tantamount to considering the radiating aperture as an array of point electric and magnetic dipoles. The validity and novelty of the proposed new approach have been substantiated considering an open ended circular cylindrical waveguide and a conical horn as case studies and treating the far field as a special case of near field with pertinent distance criterion. The effect of change in the distance of observation ranging from reactive near field to far field on the radiation patterns of these antennas has also been discussed. The simulation studies reveal that the depicted normalized phase patterns of both the circular waveguide and conical horn follow the changes in the profile of the corresponding amplitude patterns

Sound field control with hemi-cylindrical loudspeaker arrays

An acoustical model for the sound field generated by hemi-cylindrical loudspeaker arrays is presented and a method for beamforming with said arrays is derived. The sound field model is obtained by introducing two independent boundary conditions for the sound field of a single impinging plane wave. The model for the radiation from a single loudspeaker in the array is then obtained from the reciprocity principle. Various beam patterns are presented and the theoretically predicted sound field is evaluated as a function of frequency. The results are discussed and an experimental array prototype is presented

Impact Of The Locations Of The Control Points On Optimal Solutions For Self-Bending Beamforming

Self-bending beamformers exhibit a sensitivity that bends over space in the nearfield of the array. They were derived from caustic wave fields and have been presented in the literature recently. It is fairly straightforward to obtain an analytic solution for the phase profile that has to be imposed onto the array elements. This approach is termed phase engineering. Deriving the corresponding gain profile is less straightforward. Solutions that have been proposed in the literature so far are educated guesses as well as numerically optimal solutions. The latter are the topic of the presented work. We use a convex approach. We show that the locations of both the (single) target control point in the bright zone as well as the (many) control points in the dark zone have a significant impact on the resulting beam. Particularly, the control point locations in the dark zone have to be chosen carefully so that the desired dark zone actually evolves. Choosing the target control point close to the caustic creates the largest beam gradient along the caustic. A remarkable observation is that prescribing a phase profile onto the elements of the array can also have a detrimental effect, and solving for the complex beamformer weights can yield a better result. Based on the observations we conclude that minimizing the norm of the beamformer weights does not seem to be the most favorable approach for the present problem

On the sparse beamformer design

In designing acoustic broadband beamformers, the complexity can grow significantly when the number of microphones and the filter length increase. It is advantageous if many of the filter coefficients are zeroes so that the implementation can be executed with less computation. Moreover, the size of the array can also be pruned to reduce complexity. These problems are addressed in this paper. A suitable optimization model is proposed. Both array pruning and filter thinning can be solved together as a two-stage optimization problem to yield the final sparse designs. Numerical results show that the complexity of the designed beamformers can be reduced significantly with minimal effect on performance

Binaural synthesis based on the spherical harmonic analysis with compact microphone arrays

Tohoku University鈴木陽

Near-field acoustic source localization based on beam space processing

The passive sonar systems estimate the target position using the radiated noise from ship such as machinery noise, cavitation noise, etc. In passive localization problem, various approaches have been investigated such as time difference of arrival (TDoA), the triangulation method and focused beamforming. However, when multiple targets exist, it can create problems with localization based on TDoA. It is difficult to obtain an accurate cross-correlation when other interference signals are present at the same time. Focused beamforming estimates the positions by measuring the spatial spectrum. Unlike localization based on TDoA and triangulation, this method has no classification problems. In this thesis, a focused array algorithm is proposed to reduce the computational complexity. The focused MVDR(minimum variance distortionless response) and MUSIC(multiple signal classification) algorithm is typically used to estimate location. It has high spatial resolution but it also has a high computational complexity. The main complexity load of the focused MVDR algorithm is in inverse matrix. And for the focused MUSIC algorithm it is in eigen-decomposition. The computational complexity of those depends on the dimensions of the correlation matrix. To reduce computational complexity, the dimensions of the correlation matrix using beam-space transformation are reduced. The beam-space signals are transformed from the originally received signal using the fact that the far-field beamformers have different direction. Simulation results are presented to evaluate the performance of the proposed method compared to the previous method. The computational complexity of the proposed method is lower than that of the previous focused beamforming, but it has a similar range resolution|수동형 소나는 선박의 기계 소음, 캐비테이션 소음 등의 방사 소음을 이용하여 표적의 위치를 추정한다. 수동형 위치 추정에는 도달 시간차, 삼각기법, 초점 빔 형성기 등을 이용한 다양한 연구가 있어 왔다. 그 중, 도달 시간차와 삼각기법 기반의 위치 추정은 수신된 신호들 사이의 상호 상관을 이용하여 추정한다. 이때 다수의 표적이 존재 한다면 관심 있는 표적 신호 이외의 표적 신호는 간섭 신호가 된다. 이 경우, 상호 상관을 이용하여 정확한 위치 정보를 구할 수 없게 된다. 또한 추정된 상호 상관 중 관심 표적 신호와 비 관심 표적 신호의 도달 시간차를 분류해야 한다. 초점 빔 형성기는 공간 스팩트럼을 추정하여 표적의 위치 추정을 하는 방법이다. 이때 초점 빔 형성기는 도달 시간차 및 삼각 기법과 같은 분류 문제가 발생하지 않는다. 본 학위 논문에서는 초점 빔 형성 알고리즘의 계산량을 줄이는 방법을 제안한다. 초점 MVDR(minimum variance distortionless response) 빔 형성과 MUSIC(multiple signal classification) 방법은 대표적인 위치 추정 알고리즘이다. 초점 MVDR 빔 형성과 MUSIC 방법은 높은 공간 분해능을 가지고 있으며, 많은 계산량을 가진다. 초점 MVDR 빔 형성 알고리즘에서 역행렬은 많은 계산량을 가지고, 초점 MUSIC 방법은 고유치 분해 과정이 많은 계산량을 가진다. 역행렬과 고유치 분해는 상관 행렬의 계산량은 행렬의 크기에 따라 달라지며, 계산량을 줄이기 위해 상관 행렬의 크기를 빔 영역으로 변환하여 줄인다. 이때 빔 영역 변환은 다른 방향으로 지향하는 원 거리 빔 형성기를 이용한다. 본 학위 논문에서 모의실험을 통해 제안된 방법을 비교 분석을 수행하였다. 제안된 방법은 기존의 방법보다 적은 계산량을 가지고 있으며 비슷한 위치 추정 성능을 가진다.List of Tables iii List of Figures iv Abstract v 제 1 장 서론 1 제 2 장 근접장 표적 거리 추정 2.1 근접장 신호 모델 4 2.2 도달 시간차 추정 기반 방법 5 2.3 초점 지연-합 빔 형성 7 2.4 초점 MVDR 빔 형성 10 2.5 초점 MUSIC 방법 11 제 3 장 빔 영역 근접장 표적 거리 추정 3.1 문제점 14 3.2 빔 영역 초점 MVDR 빔 형성 15 3.3 빔 영역 초점 MUSIC 방법 19 3.4 계산량 비교 22 제 4 장 모의실험 및 결과 분석 4.1 단일 표적 위치 추정 성능 24 4.2 근접 표적 위치 추정 성능 28 제 5 장 결론 33 참고문헌 35Maste

Spatial sound intensity vectors in spherical harmonic domain

Sound intensity is a fundamental quantity describing acoustic wave fields and it contains both energy and directivity information. It is used in a variety of applications such as source localization, reproduction, and power measurement. Until now, intensity is defined at a point in space, however given sound propagates over space, knowing its spatial distribution could be more powerful. This paper formulates spatial sound intensity vectors in spherical harmonic domain such that the vectors contain energy and directivity information over continuous spatial regions. These representations are derived with finite sets of closed form coefficients enabling ease of implementation

Lamb: a simulation tool for air-coupled lamb wave based ultrasonic NDE systems

La técnica de las ondas de Lamb acopladas por aire representa un importante avance en el área de los Ensayos No Destructivos (END) de materiales laminares.Sin embargo la compleja naturaleza de las vibraciones mecánicas encontradas en acústica, hacen que el análisis y el estudio de esta área del conocimiento sea un tema muy complejo. De allí que la posibilidad de contar con una herramienta de simulación de software que permita la evaluación y prueba de diferentes configuraciones de excitación y recepción acústica utilizando la flexibilidad de un modelo de computadora sea de una gran utilidad y ayuda.El objetivo de la presente tesis es proveer al área de los END con un software de simulación gratuito: The LAMB Matlab® toolbox basado en el modelo del software libre de la GNU.El software es capaz de simular el comportamiento de sistemas de END basados en ondas de Lamb acopladas por aire en láminas isótropas simples utilizando transductores tipo array.El programa se basa en un arreglo tipo C-scan de un sistema de END y está compuesto por tres bloques principales: 1) Excitación, 2) Propagación y 3) Recepción.La verificación individual del funcionamiento de dichos módulos se presenta a lo largo de la tesis mediante una serie de comparaciones entre simulaciones y datos experimentales provenientes de diferentes pruebas. Por otro lado, la validación del programa completo se llevo a cabo por medio de experimentos en láminas de cobre y aluminio; utilizando un sistema real de END por ondas de Lamb acopladas en aire mediante arrays cóncavos.La influencia negativa en el desempeño general de dicho sistema de END real basado en este tipo de transductores se comprobó efectivamente mediante el simulador desarrollado. Esto se debió fundamentalmente al efecto de directividad de los sensores individuales en los transductores y a la simetría cóncava de los arrays.Para emular este comportamiento la tesis presenta un modelo geométrico bidimensional simple de un filtro espacial, junto a las simulaciones de un nuevo tipo de array plano propuesto.El programa desarrollado comprobó así mismo la naturaleza coherente de los campos acústicos emitidos en aire por las láminas sujetas a vibraciones de Lamb. Esto se realizó mediante la implementación de un conformador de haz simple de suma y demora; constituyéndose así la etapa inicial de procesamiento de señal del bloque de recepción del programa.El objetivo principal del presente trabajo fue contribuir con un modelo operativo de simulación y prueba de nuevos diseños de arrays e implementación de estrategias de procesado de señal útiles en sistemas de END basados en ondas de Lamb acopladas por aire.Finalmente, si bien el objetivo de la calibración del programa no se pudo conseguir; si se logró efectivamente un notable grado de similitud con un sistema de END real.Air-coupled ultrasonic Lamb waves represent an important advance in Non- Destructive Testing and Evaluation (NDT & NDE) techniques of plate materials and structures. Examples of these advances are the characterization and quality assessment of laminate materials in manufacturing processes, the location of damaged parts in aircrafts and structure monitoring in the aerospace industry.However the rich and complex nature of mechanical vibrations encountered in acoustics make the subject of analysis and study of these systems a very complex task. Therefore a simulation tool that permits the evaluation and testing of different configuration scenarios using the flexibility of a computer model is an invaluable aid and advantage.The objective of this thesis is to provide the field of NDT with free open source software i.e. the LAMB Matlabrtoolbox. The toolbox is capable of simulating the behaviour of Lamb wave based NDE systems for single ideal isotropic laminates using air-coupled ultrasonic arrays. The programme usesa pitch-catch type of a Cscan NDE arrangement and is composed of three integrated sections each individually modelling a feature in the system: 1) Excitation, 2) Propagation, and 3) Reception.For assessment of the individual modules of the toolbox the thesis presents comparisons between each section simulations and the data obtained from different acoustic experiments. The validation of the complete simulator was carried out by evaluation tests on the copper and aluminium plates by use of a real hardware prototype of a Lamb wave based NDE system with aircoupled concave arrays.The negative impact on the performance of the real air-coupled NDE systembased on concave arrays was effectively confirmed by the programme. This was produced by the inherent directivity of the individual sensors as well as their concave arrangement. To emulate this behaviour the thesis introduces a simple two-dimensional geometric model for the inclusion of the spatial filtering effect of the sensors plus a group of simulations for a new proposed air-coupled plane array transducer.The software also verified the spatial coherent nature of the Lamb wave fields emitted by a plate in air. This was demonstrated by the implementation of a delay and sum beamformer to constitute an initial signal processing stage in the reception section