Investigation of frequency and step responses of pressure sensors with semi-closed structures based on numerical simulations and experiments

Abstract

We are developing a pressure sensor to detect very small pressure fluctuations produced during tsunami formation. For example, such a pressure fluctuation of± 50 Pa was actually observed in the 2011 Great East Japan Earthquake. The sensor has a semi-closed structure with a small hole which provides a unique high-pass filter function. Cutoff frequency of the high-pass characteristic is an important index to detect pressure fluctuations due to tsunami formation without interfering with normal atmospheric pressure change. Cutoff frequency can be evaluated from frequency response of the sensor. On the other hand, the step response of the sensor is also significant in providing a unique index, called the ‘duration time of induced pressure difference,’ which is defined as the time required for the pressure difference between the inside and outside of the semi-closed structure to disappear. If a connection between the cutoff frequency and the duration time can be established, the cutoff frequency could be estimated from the duration time obtained by a one-step simple measurement of the step response. In this study, this connection was considered based on the simulated results of frequency and step responses dependent on small-hole area, semi-closed-structure volume and pressure amplitude. Then, the connection was experimentally verified using a fabricated prototype of the semi-closed structure.