Development of velocity sensor with high frequency band using inverse notch filter

The vibration sensors are widely used in the field of vibration control and measurement. In applying the modern control theory to anti-vibration controlled objects, the state variables both the velocity and displacement become useful signals. Then, the velocity sensor in comparison with the acceleration sensor, which is in general used, is very useful. However, its frequency band is limited by high frequency resonance due to the electrical stiffness. If the velocity sensor having flat frequency band is developed, this sensor becomes easy to handle not only in the control field but also in the measurement filed. Then, this paper shows that the inverse notch filter, which is inserted in the closed loop, flattens out the frequency response originally having high frequency resonance. Firstly, the block diagram of the velocity sensor as a closed system is shown. Its sensitivity, the low break point frequency, and the high frequency resonance are formulated. Secondary, the gain and phase margins are calculated and we try to improve the frequency response based on these indices. Finally, it is shown that the frequency band can be flattened by inserting the inverse notch filter in the closed loop.