An ultrasound system checks two adhesive bonds inside a laminated timber beam. In a second test, a greater proportion of the pulse energy is reflected at the first bond. The proportion absorbed there and all other conditions are unchanged.
Why is the echo from the second bond weaker in the second test?
The second echo takes longer to return, so the system records less pulse energy.
The pulse slows down after the first bond, so less pulse energy reaches the second bond.
Less pulse energy is transmitted through the first bond, so less reaches the second bond.
The frequency of the pulse falls at the first bond, so the second bond reflects less.