Showing papers by "A. J. Berkhout published in 1982"
TL;DR: In this paper, an unwrapped phase curve from the principal values of the phase can be computed in a simple way and the validity of the unwrapping procedure is tested by exploiting the phase information in the signal's first moment.
Abstract: An unwrapped phase curve from the principal values of the phase can be computed in a simple way. The validity of the unwrapping procedure is tested by exploiting the phase information in the signal's first moment. The significance of the unwrapped answer around notches in the amplitude spectrum is seriously degraded by noise.
The proposed method and the validity test are illustrated with examples.
26 citations
01 Jan 1982
TL;DR: In this article, the practical aspects of acoustic imaging were envisaged, based on the theoretical considerations given in the preceding paper (Part I), and the theoretical analysis was carried out.
Abstract: In this paper the practical aspects of acoustic imaging will be envisaged, based on the theoretical considerations given in the foregoing paper (Part I).
20 citations
01 Jan 1982
TL;DR: An approach to tissue characterization which was developed within this group is discussed, based on the minimization of the entropy of the synthetically focused image and a method of analysis based on two dimensional Fourier transformation of the r.f. data of part of the image.
Abstract: In this paper we will discuss an approach to tissue characterization which was developed within our group. First our approach will be outlined.One of the basic steps we use here is a high resolution Synthetic Focusing procedure (Berkhout et al.,1982). For this procedure, and also for tissue characterization itself, correct knowledge of the sound propagation velocity is essential. In the second part of this paper a method will be put forward to determine values of the sound propagation velocity with little prior knowledge of the medium.This method is based on the minimization of the entropy of the synthetically focused image. Now an optimally focused image can be produced,which may be analysed in detail.In the final part of this paper we will discuss a method of analysis,based on two dimensional Fourier transformation of the r.f.data of part of the image.
13 citations
01 Jan 1982
TL;DR: In this theoretical framework wave theory and systems theory have been combined, resulting in an accurate and concise description of the basic physical processes in acoustical echo experiments.
Abstract: Recently,the acoustics group of the Delft University has introduced a theoretical framework which significantly improves the insight in and understanding of fundamental problems in acoustical echo techniques.In this theoretical framework wave theory and systems theory have been combined,resulting in an accurate and concise description of the basic physical processes in acoustical echo experiments.
5 citations
01 Jan 1982
TL;DR: In this paper, the authors used a pulse-echo technique to acquire continuous recordings of sub-bottom density profiles and estimated the reflectivity function using a broad frequency spectrum for adequate depth-resolution, sufficient energy at low frequencies for a pre-specified depth-penetration and a narrow beamwidth to minimize the influence of scattering noise.
Abstract: Pulse-echo techniques may be well suited to acquire continuous recordings of sub-bottom density profiles. To obtain an accurate estimate of the sub-bottom reflectivity function, an acoustic system should have a broad frequency spectrum for adequate depth-resolution (a), sufficient energy at low frequencies for a pre-specified depth-penetration (b) and a narrow beamwidth to minimize the influence of scattering noise (c).
4 citations
2 citations
1 citations
01 Jan 1982
TL;DR: In this article, the main activity in the acoustics group of the Delft University of Technology is puls-echo techniques, which are the main activities of the group's research.
Abstract: Presently, puls-echo techniques present the main activity in the acoustics group of the Delft University of Technology.