I have earlier worked on detecting hand motion gesture using Ultrasonic sensors. Sound is absorbed by different objects. But is it possible to quantify absorption and determine the type of deflector?
One of the characteristic properties of ultrasound is that it travels at different velocities depending on the material where it is propagating. Then, yes, you will be able to determine different objects(materials) by measuring the ultrasound velocity usually by a pulse-echo technique.
Yes, it is definitely possible to detect the object. Generally, spherical object produces relatively smaller amount of reflect ultrasound. Remember the basic rule that the size of the object should be larger than wavelength. The detection capability basically depends on the sensitivity of the receiver, the frequency used. The motion of the object depends on the scanning rate and the software capabilities. For more details please explain the exact situation