You are given a 1-D transducer with 16 elements that operates at 8 MHz.
The elements are lambda wide, 1 mm high, and the overall length of the
array is 20 mm. The focal point is at 3 cm; the transducer fractional BW
is 25%.
(a) What is the lateral and axial resolution
at the focal point (-6dB FWHM)?
(b) What is the position and level of the
first sidelobe?
(c) What is the position and level of the
first grating lobe?
The above transducer was sparsely populated. We now redo the same
transducer so that it has 64 elements, but all other parameters are the
same.
(a) What is the highest lateral spatial frequency in the K-space image
(use a 95% cutoff)? Based on this, what beam spacing should you use?
(This is lateral increment, or sampling).
(b) What is the % degradation of lateral and axial resolution 1 cm
beyond the focus?
Design an array that maintains a 500 micron resolution at the 3 cm focal
point. The available transducer BW is 50%, and the tissue attenuation
is 1 dB/cm*MHz. You are limited to 32 elements. Assume
that you can distinguish blood from tissue (these differ by 30 dB).
Choose the center frequency so that the overall dynamic range is 100dB,
and so that the blood/tissue distinction is maintained from the face of
the array to the focal point. Also, the design must provide grating
lobes that are > 40 dB down. Give all relevant specifications for
your design, and include relevant plots to demonstrate that your design
meets the requirements.
