So i have a piezoelectric film deposited in the metal substrate and i want to determine the resonant frequency. Basically i can determine the resonant frequency base on the dimensions. But i need to proved it using experimental set-up. So i applied AC Voltage to the material then the material will vibrate and using oscilloscope i can determine the oscillations of the material. from that i can determine the frequency. The problem is, when i'm trying to vary the amplitude voltages the frequency that the oscilloscope detected is in not fixed (ranging from the 1KHz=1MHz). so it tried to vary the frequency of the AC voltage but the detected Amplitude voltage in the oscilloscope is constant as the frequency varies. So how i can determine the resonant frequency by applying different frequency of ac voltage?