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| 2. |
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| 3. |
- Grennberg, Anders, et al.
(författare)
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Estimation of subsample time delay differences in narrowband ultrasonic echoes using the Hilbert correlation
- 1994
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In many areas the time delay of arrival (TDOA) is desired. Conventional estimators usually have the property of breaking down for low SNR. In the case of narrowbanded signals we propose a fast and simple method to estimate the small time delays. The method is shown to have the same accuracy as conventional methods for small delays and high SNR while it performs better for low SNR. It is based on using the Hilbert transform in correlation between two signals. Apart from using it for better resolution in TDOA, it may also be used in applications with narrowbanded signals where the measurements are repeatable, such as ultrasonic imaging and ECG. In ultrasonic applications, due to fluctuations in the insonified media, a small random time shift may be present causing the signals to be misaligned in time. Averaging signals under these conditions will result in a distortion of the signal shape. We propose an averaging method to avoid this and to accomplish a higher SNR without the distortion. Simulations and experiments from ultrasonic applications are presented.
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| 4. |
- Grennberg, Anders, et al.
(författare)
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Estimation of subsample time delay differences in narrowband ultrasonic echoes using the Hilbert transform correlation
- 1994
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Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-3010 .- 1525-8955. ; 41:5, s. 588-595
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Tidskriftsartikel (refereegranskat)abstract
- In many areas the time delay of arrival (TDOA) is desired. In the case of narrowband signals we propose a fast and simple method to estimate small time delays. This method is shown to have the same or better accuracy as the cross correlation methods for small delays in the order of fractions of the sample interval. It is based on using the Hilbert transform in correlation between two signals and consists of only one scalar product, which makes it fast. It may also be used in applications with narrowband signals where the measurements are repeatable, such as ultrasonic imaging and nondestructive testing. In ultrasonic applications, due to fluctuations in the insonified media, a small random time shift may be present causing the signals to be misaligned in time. Averaging signals under these conditions will result in a distortion of the signal shape. We propose an averaging method to avoid this and to accomplish a higher SNR without the distortion. Simulations and experiments from ultrasonic applications are presented.
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| 5. |
- Grennberg, Anders, et al.
(författare)
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Experimental determination of the single point echo of an ultrasonic transducer using a tomographic approach
- 1992
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Ingår i: Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society. - Piscataway, NJ : IEEE Communications Society. ; , s. 2151-2152
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Konferensbidrag (refereegranskat)abstract
- The impulse response method is often used to study the ultrasonic field radiated by planar or gently curved transducers. This, however, requires one transmitting and one receiving transducer which has to be placed with great accuracy in the ultrasonic field. Here we propose a measuring method with only one transducer which acts both as transmitter and receiver. Echoes from sliding halfplanes are registered and by using tomographic methods, the echo from a single point in the same plane as the halfplanes can then be calculated. Beside the ultrasonic field, these calculations will yield us the transducer's characteristics. These can be used to extract further information from an echo of an arbitrary surface, such as the gradient of the surface
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| 6. |
- Grennberg, Anders, et al.
(författare)
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Experimental determination of the ultrasonic echo from a pointlike reflector using a tomographic approach
- 1992
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Ingår i: Proceedings. - Piscataway, NJ : IEEE Communications Society. - 0780305620 ; , s. 639-642
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Konferensbidrag (refereegranskat)abstract
- One important parameter for an ultrasonic transducer is the echo it yields from a pointlike reflector. It can be measured directly but there are however certain problems connected with this. This reflector must have such a size that it can be considered a point, which results in a very weak echo and consequently a low SNR. We propose an alternative method to calculate the echo from a pointlike reflector by measuring the echoes from sliding halfplanes. Using a tomographic way of reasoning, we can calculate the single point echo from these measurements. Our approach was to find basis functions that are suitable for the inversion of the measurements. These basis functions depend on which norm and weight function you choose. Numerical solutions are given for chosen weight functions and the inversion is shown for the measurements.
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| 7. |
- Grennberg, Anders
(författare)
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Measuring subsample time delay differences in narrowband ultrasonic echoes
- 1994
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Ingår i: Norsig 94. - Trondheim : Norsk forening for signalbehandling. - 8299315808 ; , s. 290-293
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Konferensbidrag (refereegranskat)abstract
- In many areas the time delay of arrival (TDOA) is desired. In the case of narrowband signals we us a new fast and simple method to estimate small time delays. This method has good accuracy for delays on the order of fractions of the sample interval. It is based on forming the scalar product of the signal and its Hilbert transform. The method can be applied to narrowband signals where the measurements are repeatable, such as ultrasonic imaging. In ultrasonic applications, due to fluctuations in the insonified media, especially in the air, a small random time shift may be present. By placing a wire at a fixed distance from the transducer, so small that it does not disturb the main echo from the surface but still gives a reference echo strong enough to use our method, we make corrections to the arrival time of the main echo.
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| 8. |
- Grennberg, Anders, et al.
(författare)
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Secondary sound classification for the assessment of focus positioning in shock-wave lithotripsy
- 1993
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Ingår i: IX Nordic Meeting on Medical and Biological Engineering. - Lund : Medicinsk Teknik.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A problem encountered when using acoustic shock-waves for kidney stone disintegration is that the positioning of the focus relative to a stone, for the best possible fragmenting effect, is crtitical. The standard methods for focus positioning are ultrasound or x-ray imaging. These methods are, however, not always sufficient and a better indication of a well positioned focus would be valuable. The secondary sound emitted as a result of each shock-wave has been found to contain valuable information. A skilled operator is able to hear from the timbre of these sound pulses when the positioning of the focus is adequate. A method for the automatic evaluation of secondary sounds, using a computer, is developed in this work.
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| 9. |
- Olsson, Lennart, et al.
(författare)
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Analysis and classification of secondary sounds from the disintegration of kidney-stones with acoustic shock waves
- 1991
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Ingår i: Ultrasound in Medicine and Biology. - 0301-5629 .- 1879-291X. ; 17:5, s. 491-495
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Tidskriftsartikel (refereegranskat)abstract
- Secondary sound emission, partly in the audible frequency range, from shock wave disintegration of kidney stones has been recorded during the treatment of two patients. A skilled operator can determine by listening if the stone is hit by the shock-wave or not. Spectral analysis of these recordings show differences between sounds which can be used to evaluate the fragmenting effect on the stone. Results are presented of a preliminary discriminating method based on parameters in an autoregressive signal model.
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| 10. |
- Sandell, Magnus, et al.
(författare)
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Estimation of ultrasonic point echoes
- 1993
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Ingår i: Radiovetenskaplig konferens på Lunds tekniska högskola 5-7 april 1993. - Lund : Lunds tekniska högskola. ; , s. 185-188
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Konferensbidrag (refereegranskat)abstract
- One important parameter for an ultrasonic transducer is the echo it yields from a pointlike reflector. It can be measured directly but there are however certain problems connected with this. We propose an alternative method to calculate the echo from a pointlike reflector by measuring the echoes from sliding halfplanes. Using a tomographic way of reasoning, we can calculate the point echoes from these measurements. Two methods to numerically perform this inversion are dealt with. The first one is a regularization technique used in conjunction with the analytical inversion formula. The other approach was to find basis functions that are suitable for the inversion of the measurements. These basis functions depend on which norm and weight function you choose. Numerical solutions are given for chosen weight functions and the inversion is shown for both methods.
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