Figure 3
Synchronization of the excitation tone burst and the detection pulses in RAR. (a) The pulse sequence for one RAR measurement shows that 20 imaging/detection pulses are applied at a pulse repetition frequency (PRF) of 10 kHz to obtain the baseline of the equilibrium position of the sample surface. Then a single ‘push’ pulse (tone burst) consisting of 100 cycles (shown within the blue box) is applied to induce a surface wave, followed by repeated applications of imaging pulses repeating every 100 µs (PRF 10 kHz) for 0.1 s to measure surface movement. (b) A representative backscattered signal received by a transducer, showing the echo signals from the two surfaces of the well plate as well as the echo from the top surface of the sample (air-sample interface). The time difference of these echoes reflect the thickness of the plate bottom and the spatial distance of the sample surface assuming constant sound velocity. The reflected signals received from the repeated pulse-echo detection within the 0.1 s window are used to determine the temporal shift of the echoes using cross-correlation to obtain the surface displacement.
