Certain embodiments are directed to devices, systems and methods for determining a penetration depth of an induced oscillation in a porous medium. In certain examples, the devices, systems and methods are designed to detect a magnetic resonance signal in the presence of an induced oscillatory fluid flow in a porous medium to determine penetration depth of the induced oscillation in the porous medium. In some examples, the mobility of a fluid in the porous medium may be determined from the determined penetration depth.