In order to conduct a study, I need to place a rectangular plate freely placed (1 cm by 2cm) inside water and control it from outside (better wireless). I need to give oscillatory motion with specific frequency/amplitude. At present I used LEGO Next servo motors and I could not achieve it successfully due to mechanical instability and methods to control freq and amp. Also the gear assemblies used affected the results. May I ask people here to suggest a way to produce vibration motion of this plate with minimal interfering mechanical set up? I can choose any kind of plate (plastic or metal) I can employ magnetic or electric methods to produce vibration. any direction way forward will be appreciated.
get a loudspeaker and glue a tiny push rod to the center of the cone and to the plate. Then send an AC signal at the frequency of choice into the speaker. This will work for frequencies below the fundamental free-air resonance of the cone, for a 12" speaker this is usually about 1 to 2 kHz. for frequencies higher than that (up to 5kHz) you can use the driver unit off of a high-power horn type tweeter.
Professor Wiciak has done some similar researches using piezoelements to induce vibrations.