The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform

Thushara D. Abhayapala - One of the best experts on this subject based on the ideXlab platform.

  • theory and design of soundfield reproduction using continuous loudspeaker concept
    IEEE Transactions on Audio Speech and Language Processing, 2009
    Co-Authors: Thushara D. Abhayapala
    Abstract:

    Reproduction of a soundfield is a fundamental problem in acoustic signal processing. A common approach is to use an array of loudspeakers to reproduce the desired field where the least-squares method is used to calculate the loudspeaker weights. However, the least-squares method involves matrix inversion which may lead to errors if the matrix is poorly conditioned. In this paper, we use the concept of theoretical continuous loudspeaker on a circle to derive the discrete loudspeaker Aperture Functions by avoiding matrix inversion. In addition, the Aperture Function obtained through continuous loudspeaker method reveals the underlying structure of the solution as a Function of the desired soundfield, the loudspeaker positions, and the frequency. This concept can also be applied for the 3-D soundfield reproduction using spherical harmonics analysis with a spherical array. Results are verified through computer simulations.

  • ICASSP - Soundfield reproduction using theoretical continuous loudspeaker
    2008 IEEE International Conference on Acoustics Speech and Signal Processing, 2008
    Co-Authors: Thushara D. Abhayapala
    Abstract:

    Reproduction of a soundfield is a fundamental problem in acoustic signal processing. A common approach is to use an array of loudspeakers to reproduce the desired field where the least square method is used to calculate the loudspeaker weights. However, the least square method involves matrix inversion which may lead to errors if the matrix is poorly conditioned. In this paper, we derive a new theoretical continuous loudspeaker method to obtain the loudspeaker Aperture Function in order to avoid matrix inversion. In addition, the Aperture Function obtained through continuous loudspeaker method reveals the underlying structure of the solution as a Function of the desired soundfield, the loudspeaker positions and the frequency.

Daomu Zhao - One of the best experts on this subject based on the ideXlab platform.

  • Models for an Aperture Function and corresponding analytical propagation equations of a flattened Gaussian beam through an annular Apertured optical system
    Journal of Modern Optics, 2006
    Co-Authors: Zhangrong Mei, Daomu Zhao
    Abstract:

    Beam profiles that consist of a sum of complex-Gaussian Functions and a sum of polynomial-Gaussian Functions offset by some fixed amount are proposed as two types of models for a hard Aperture Function. By expanding an Aperture Function into two types of models, the approximate analytical expression of a flattened Gaussian beam through a paraxial ABCD optical system with an annular Aperture is derived. As special cases, the corresponding closed forms for the unAperture or circular Aperture or circular black screen cases are also obtained. The results provide a more convenient way of studying propagation and transformation than the usual method using diffraction integral formula directly. Numerical examples are given to illustrate the propagation properties of flattened Gaussian beams.

  • Analytical propagation expression of elliptical Gaussian beams through nonsymmetric systems with an elliptical Aperture
    Optik, 2006
    Co-Authors: Chongwei Zheng, Daomu Zhao
    Abstract:

    A tensor form for describing approximately the elliptical Aperture Function is defined that can be expanded into a finite sum of complex Gaussian Functions. An analytical propagation formula of elliptical Gaussian beams through nonsymmetric and paraxial optical systems with an elliptical Aperture is obtained by using tensor method. A simple numerical example is given to illustrate for its applications.

  • wigner distribution Function of hermite cosine gaussian beams through an Apertured optical system
    Journal of The Optical Society of America A-optics Image Science and Vision, 2005
    Co-Authors: Dong Sun, Daomu Zhao
    Abstract:

    By introducing the hard-Aperture Function into a finite sum of complex Gaussian Functions, the approximate analytical expressions of the Wigner distribution Function for Hermite–cosine-Gaussian beams passing through an Apertured paraxial ABCD optical system are obtained. The analytical results are compared with the numerically integrated ones, and the absolute errors are also given. It is shown that the analytical results are proper and that the calculation speed for them is much faster than for the numerical results.

  • Wigner distribution Function of Hermite–cosine-Gaussian beams through an Apertured optical system
    Journal of the Optical Society of America. A Optics image science and vision, 2005
    Co-Authors: Dong Sun, Daomu Zhao
    Abstract:

    By introducing the hard-Aperture Function into a finite sum of complex Gaussian Functions, the approximate analytical expressions of the Wigner distribution Function for Hermite–cosine-Gaussian beams passing through an Apertured paraxial ABCD optical system are obtained. The analytical results are compared with the numerically integrated ones, and the absolute errors are also given. It is shown that the analytical results are proper and that the calculation speed for them is much faster than for the numerical results.

  • different models for a hard Aperture Function and corresponding approximate analytical propagation equations of a gaussian beam through an Apertured optical system
    Journal of The Optical Society of America A-optics Image Science and Vision, 2005
    Co-Authors: Daomu Zhao
    Abstract:

    Beam profiles that consist of a sum of complex-Gaussian Functions, a sum of polynomial-Gaussian Functions and a sum of multi-Gaussian Functions offset by some fixed amount are proposed as three types of model for a hard-Aperture Function. By expanding an Aperture Function into these models, approximate analytical propagation equations for a Gaussian beam through an Apertured ABCD optical system are obtained. Comparison among these models themselves and among propagation characteristics of a Gaussian beam through these models are made. It is shown that the first and third types of model for a hard-Aperture Function are more suitable than the second type, in terms of calculation efficiency and simulation results, for application to such diffraction problems. Moreover, there are some differences in the applicability of the first and the third models.

Reinhard O. W. Franz - One of the best experts on this subject based on the ideXlab platform.

  • Band-Limited Signal Reconstruction From Irregular Samples With Variable Apertures
    IEEE Transactions on Geoscience and Remote Sensing, 2016
    Co-Authors: David G. Long, Reinhard O. W. Franz
    Abstract:

    Sampling plays a critical role in remote sensing and signal analysis. In conventional sampling theory, the signal is sampled at a uniform rate at a minimum of twice the signal bandwidth. Sampling with an Aperture Function requires a fixed-Aperture Function, which can be removed by deconvolution after signal reconstruction. However, in some cases, the signal samples are available only at irregular positions, and different samples use different Aperture Functions. In this paper, the theory of finite-length signal reconstruction with irregular samples and variable Apertures in one and two dimensions is considered. In the 1-D case, a band-limited discrete signal can be exactly reconstructed from a finite number of arbitrarily spaced samples with few restrictions on the Aperture Functions. Exact reconstruction in the 2-D case requires the sampling matrix be invertable, and is not always possible. Variable Aperture Functions, while complicating the process, can enable reconstruction for a broader range of sample locations. Practical issues are discussed, and numerical examples are provided. Variable Aperture reconstruction has application in a variety of remote sensing problems. In this paper, reconstruction from 2-D irregular sampling with variable Apertures is illustrated using Special Sensor Microwave/Imager radiometer observations.

Weiqing Pan - One of the best experts on this subject based on the ideXlab platform.

Chao Zuo - One of the best experts on this subject based on the ideXlab platform.

  • optimization method for the synthetic Apertures imaging system
    Advanced Optical Imaging Technologies III, 2020
    Co-Authors: Bowen Wang, Yan Zou, Chao Zuo
    Abstract:

    In the long-range imaging system, one of the main factors limiting the imaging resolution is the size of the imaging lens Aperture, which determines the diffraction limit of the optical system. In the actual Fourier ptychography imaging system, the system errors such as the aberrations of imaging devices and the noise of the detector will be introduced in the actual imaging, which is also one of the important factors to reduce the quality of the reconstructed image. In order to improve the reconstruction accuracy of the Fourier ptychography imaging algorithm, this paper mainly discusses some optimization algorithms in the process of the Fourier ptychography imaging algorithm to improve the high-resolution details of the restored image. The adaptive step size based optimization algorithm is used to update the spectrum and Aperture Function of the current sub-Aperture to obtain the high-resolution spectrum information of the measured target. The optimal spectrum overlap rate is discussed to reduce the number of image acquisition and calculation cost as much as possible. In the reconstruction process, the simulated annealing algorithm is used to correct the positioning error of the sub-Aperture, and the optimization algorithm is used to update the sub-Aperture, which greatly improves the accuracy of the reconstruction results and achieves the theoretical imaging resolution.