The impedance of PZT is about how many times greater than the impedance of skin?

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Multiple Choice

The impedance of PZT is about how many times greater than the impedance of skin?

Explanation:
Acoustic impedance tells us how much resistance a material offers to the passage of ultrasound, and it’s calculated as Z = ρc (density times sound speed). PZT is a dense, stiff ceramic, so its impedance is high—about 30 MRayl. Skin and surrounding soft tissue are much less dense and slower, around 1.5 MRayl. Dividing these values gives roughly a 20-to-1 difference. That means PZT’s impedance is about twenty times greater than skin’s, which is why energy would be largely reflected at the interface without a matching layer or coupling medium.

Acoustic impedance tells us how much resistance a material offers to the passage of ultrasound, and it’s calculated as Z = ρc (density times sound speed). PZT is a dense, stiff ceramic, so its impedance is high—about 30 MRayl. Skin and surrounding soft tissue are much less dense and slower, around 1.5 MRayl. Dividing these values gives roughly a 20-to-1 difference. That means PZT’s impedance is about twenty times greater than skin’s, which is why energy would be largely reflected at the interface without a matching layer or coupling medium.

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