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Ultrasonic pulse shaping with optimal lag filters

โœ Scribed by Max I. Fomitchev; Yuri E. Grigorashvily; Svyatoslav Volkov


Publisher
John Wiley and Sons
Year
1999
Tongue
English
Weight
115 KB
Volume
10
Category
Article
ISSN
0899-9457

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โœฆ Synopsis


Attempts to increase the resolution of ultrasound imaging apparata resulted in the desire for precise control over the shape of transmitted ultrasonic pulses. The shape of transmitted ultrasonic pulses can be controlled when a transducer is excited by a signal corresponding to a convolution filter. This article discusses a method of precise ultrasonic pulse shaping using lag filters. A lag filter f l (t) is a convolution filter calculated for a time-shifted desired output waveform w(t): w(t) 3 w(t ฯช l). An optimal lag filter is selected by trying all possible values of lag l and selecting a filter with the best performance. The filter coefficients can be calculated using a Fourier transform or least-squares criterion. The quality-limiting factors of the pulse shaping are the length of the filter and the accuracy of the actual excitation signal. The improvement of the pulse-shaping quality can be achieved by accounting for the amplifier transfer function or by accurate DAC-values-to-voltage mapping. The analysis of the experimental results indicates that the developed ultrasonic pulse-shaping technique provides a means for flexible control over the transmitted ultrasonic pulse waveform and frequency. The presented pulse-shaping technique is specially developed for cost effective ultrasound imaging devices utilizing a simplified beamformer composed of a single pair of input/output amplifiers.


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