Vibration sensor

A vibration sensor comprising:

• a sensor housing to vibrate together with a test object in synchronism with vibration of the test object;
• a piezoelectric substrate to vibrate together with the sensor housing in synchronism with vibration of the sensor housing, wherein a first interdigital electrode, a first terminal to input a signal into the first interdigital electrode, a second interdigital electrode, and a second terminal to output a signal from the second interdigital electrode are arranged on a first surface of the piezoelectric substrate, and the piezoelectric substrate is disposed inside the sensor housing to be fixed to the sensor housing;
• an amplifier to receive the signal output from the second terminal as an input signal, to amplify the received input signal, and to transmit the input signal after the amplification to the first terminal as an output signal;
• a deformable layer being elastic and having a first surface adhered to a second surface of the piezoelectric substrate;
• and
• a heavy object having a first surface adhered to a second surface of the deformable layer.