We theoretically and experimentally investigated the frequency response of blobs in porous media to an oscillatory pressure difference. (The term blob refers to a connected liquid mass that occupies one or more pores.) To predict the frequency response analytically, we formulated a simple model pore system consisting of a blob in a capillary tube. This model accounts for the frequency-dependent viscous pressure drops in the blob and the surrounding liquid and for the dynamic capillary pressure that occurs due to contact line pinning. By using the planar laser-induced fluorescence technique, we visualized the dynamic response of blobs in porous media. As predicted by our theory, air and liquid blobs surrounded by an immiscible liquid exhibited resonance in a capillary tube. Furthermore, we showed, for the first time, that a liquid blob in a sphere-packing medium exhibits resonance.

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