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Regarding the operation of array transducers: a. To obtain a focused beam, the innermost element of the annular array is energized first b. Focusing in a linear array is achieved by first energizing the outermost elements of the active group c. The shorter the time delay between energizing the elements of the array, the shorter the focal distance d. In contrast to annular probes, array transducers do not give rise to grating lobes e. An ultrasound beam formed from a linear array may be steered from side to side by using the apodization technique |
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Answer» a. False. The outermost element is energized first and the innermost element last. b. True. c. False. A short focal distance is obtained by using a long delay between energizing the outer- and innermost elements of the active group. d. False. Grating lobes are weak replicas of the main ultrasound beam, which are unique to array transducers. They are caused by the regular, periodic spacing of the array elements, and arise when the size of the individual elements is larger than half the wavelength. Subdicing (dividing array elements into parts smaller than 0.5l) may be used to prevent their formation. e. False. Apodization is a technique used to prevent side lobe formation by applying less power to the outermost elements. Beam steering is achieved by energizing elements in succession beginning from one edge of the active group. |
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