Fig. 1.

a Experimental setup for QUS measurement using a single-element transducer at a nominal 5-MHz center frequency (2.3 MHz actual center frequency). Bone specimens were placed on top of the transducer, and the wet surface provided an adequate acoustic coupling. b Schematics of the generated trigger pulse by the piezoelectric element (A0 amplitude) transmitting through the buffer and echoes reflected from the bone-buffer interface (A1 amplitude) and bone-air interface (A2 amplitude). Bone thickness and width are referred to as d and w, respectively. c A representative received an echo series in the time domain. The time of flight difference is referred to as Δt