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CAIE A-Level Physics 24.1 Production and Use of Ultrasound

Practise analysing ultrasound generation, pulse-echo timing, acoustic impedance, reflection, transmission and attenuation for medical diagnosis.

Syllabus
2028–2030
Course
Physics 9702
Level
A2

Exam points

  • explain piezoelectric generation and detection of ultrasound using crystal deformation and induced e.m.f.
  • interpret reflected ultrasound timing and intensity to obtain internal-boundary depth and diagnostic information
  • calculate specific acoustic impedance from Z = ?c
  • calculate ultrasound intensity reflection or transmission at a boundary
  • calculate and interpret ultrasound attenuation using I = I?e??x

Covered syllabus points

24.1.1—A piezo-electric crystal changes shape when a p.d. is applied across it and24.1.2—Ultrasound waves are generated and detected by a piezoelectric transducer24.1.3—The reflection of pulses of ultrasound at boundaries between tissues can be24.1.4—The specific acoustic impedance of a medium as Z = ρc24.1.5—IR / I0 = (Z1 – Z2)2 / (Z1 + Z2)2 for the intensity reflection coefficient24.1.6—I = I0e–µx for the attenuation of ultrasound in matter

24.1 Production and use of ultrasound question 1

[Maximum number: 7]

Piezo-electric transducers are used for the generation of ultrasonic waves.

Question (a)

(a)

State one other use, apart from in ultrasound, of piezo-electric transducers.

[ 1 ]

Question (b)

(b)

Explain the main principles behind the use of ultrasound to obtain diagnostic information about internal body structures.

[ 6 ]

24.1 Production and use of ultrasound question 2

[Maximum number: 8]

Question (a)

(a)

Explain the principles of the generation of ultrasound waves for use in medical diagnosis.

[ 4 ]

Question (b)

(b)

The linear attenuation (absorption) coefficient for a parallel beam of ultrasound waves in air is 1.2 cm−11.2 \mathrm{~cm}^{-1}.

The parallel beam passes through a layer of air of thickness 3.5 cm .
Calculate the ratio, in dB,
intensity of beam after passing through the layer of air intensity of beam entering the layer of air
ratio = dB

[ 4 ]

24.1 Production and use of ultrasound question 3

[Maximum number: 7]

Question (a)

(a)

Explain how ultrasound pulses are used to obtain diagnostic information about internal body structures in medical diagnosis.

[ 3 ]

Question (b)

(b)

Define specific acoustic impedance.

[ 2 ]

Question (c)

(c)

Two media have specific acoustic impedances Z1Z_{1} and Z2Z_{2}.

State the approximate value of the intensity reflection coefficient at the boundary between the two media when:
- Z1\quad Z_{1} is almost equal to Z2Z_{2}

intensity reflection coefficient =

- Z1\quad Z_{1} is very different from Z2Z_{2}.
intensity reflection coefficient =

[ 2 ]
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