Differential Acoustic Spectroscopy (DARS)
Acoustical Resonance Spectroscopy (DARS) exploits the low frequency resonance (~1000 Hz) of a fluid column to measure the bulk acoustic properties of a small sample of rock and other material. First, we measure the resonant frequency spectrum of a fluid-filled but otherwise empty cavity. Next, we introduce a small sample of rock into the cavity and measure the changes in resonances, both frequency and Q. The changes are then inverted to estimate the modulus and Q of the sample. The first generation of DARS operates at atmospheric pressure. The drawing above shows a new generation of DARS that measures acoustic properties of a rock sample under high pressure.