Three Different Amplitude Values & Initial Pulse Amplitude, 7.5 MHz Ultrasound Beam of Intensity - Science & Maths Assignment Help

Assignment Task

Question 1

a) For a 7.5 MHz ultrasound beam of intensity 23.0 mW cm- 2 traveling in soft tissue, calculate: 

• The particle displacement amplitude. 
• The particle velocity amplitude.
• The acoustic pressure amplitude.

 
b)For the three different amplitude values you have found above, briefly state how these values compare, and whether this is what you would expect.

Question 2

a) An ultrasound pulse suffers a -35 dB change when passing through an 8 cm thickness of soft tissue. Find the following values if the original transmitted intensity into the tissue was 50 mWcm-2. 

• The final intensity.
• The ratio of the final pulse amplitude to the initial pulse amplitude.

b) An ultrasound pulse traveling in soft tissue has normal incidence on a layer of muscle.  

• Calculate the reflection and transmission coefficients
• Express the reflective loss in deciBels

Question 3

a)An ultrasound beam traveling in soft tissue is incident upon a layer of fat, striking the boundary at an angle of 70o to the boundary.  Calculate the change in direction between the incident beam and the transmitted beam.

b)Explain what is meant by the term Critical Angle and provide clear specifications of the critical angle for a soft tissue / fat interface.

Question 4  

A 5 MHz transducer is constructed with a crystal of diameter 11.0 mm, and has a curved surface to focus the beam at a depth of 55 mm.  Make the necessary calculations to complete the following:-  

a.Draw the effective beam profile for the focussed transducer, also showing the theoretical and effective beam profiles for the corresponding plane transducer for comparison.

b.Sketch a graph of the central axis intensity along the beam, indicating the estimated positions of maxima and minima.

c.Classify the focusing capability of the transducer.

Question 5  

A 5 MHz phased array transducer consists of fifteen 1.4 mm wide piezoelectric elements with a 0.1 mm gap between each element. Delay lines are used to both focus and steer the ultrasound beam in soft tissue. The elements are each 15 mm long and are mechanically focussed in the elevation direction.

a.Sketch the theoretical and effective lateral beam profiles if all elements are pulsed simultaneously, included calculated dimensions of the beam divergence and the near field length. 

b.Calculate the time delay between firing the central and outer elements if the effective radius of curvature of the ultrasound wavefront is 50 mm, and the beam is directed along the transducer axis or “un-steered” (ie perpendicular to the transducer face).

c Calculate the time delay between each end element and the central element if the beam is steered 10o away from the transducer axis and the focal depth is 45 mm, as measured along the axis of the transducer.

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