An ultrasound wave is normally incident from muscle onto bone. Their acoustic impedances are 1.710-4 and 6.110-4 kg m⁻² s⁻¹ respectively, as printed in the source. Find the reflected fraction of incident energy.

GATE 2026 BM – Question 45

Medical Imaging Systems · Ultrasound Imaging · 2 marks · Multiple choice

An ultrasound wave is normally incident from muscle onto bone. Their acoustic impedances are $1.7\times10^{-4}$ and $6.1\times10^{-4}$ kg m⁻² s⁻¹ respectively, as printed in the source. Find the reflected fraction of incident energy.

0.98
0.32
0.50
0.65

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Correct answer: (B) 0.32

Explanation

The energy reflection coefficient at normal incidence is $R=[(Z_2-Z_1)/(Z_2+Z_1)]^2$. The shared power of ten cancels: R=(4.4/7.8)²≈0.3182. Thus approximately 0.32, B. The numerical ratio is unaffected by the unusual absolute impedance scale printed in the source.

GATE 2026 BM – Question 45

Explanation

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