At what time interval after the transmit pulse will an echo from an object at range 7 cm arrive back at the transducer array?

Consider a linear array of 100 flat, rectangular, 3.0 Mhz transducers, each 1.5 mm wide and 2.1 cm deep. Assume, for simplicity, that they are packed tightly together so that the array is 15 cm long by 2.1 cm deep. The transducer array is tested in a medium having a speed of sound of 1,500 m/s.

(a) If 14 consecutive transducers on the transducer array are electronically grouped on each transmit and receive, what depths (or ranges) are considered to be in the far field?

(b) At what time interval after the transmit pulse will an echo from an object at range 7 cm arrive back at the transducer array?

(c) A B-mode image is created by successively grouping 14 transducers on the array, sliding one transducer at a time down the length of the array. Suppose the depth of penetration is 20 cm. What is the frame rate for this linear array image?

(d) Describe two ways that the frame rate can be increased.

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