Two systems utilizing both a continuous wave (FMCW) and a pulsed (FMP) frequency modulation in an acoustic microscope are presented that are particularly suited to time-of-flight measurements, thus enabling the separation of topography from reflectivity as well as Rayleigh velocity measurements. The linear frequency modulation serves to map time-of-flight information onto the frequency domain, thus simplifying the signal processing. Whilst the FMCW system uses a voltage-controlled oscillator, the FMP system uses two standing acoustic wave devices for greater chirp linearity. Both systems have the advantages of pulse compression and allow all the signal processing to be carried out at low frequencies.
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