Design of air blast pressure sensors based on miniature silicon membrane and piezoresistive gauges

International audienceAvailable commercial piezoelectric pressure sensors are not able to accurately reproduce the ultra-fast transient pressure occurring during an air blast experiment. In this communication a new pressure sensor prototype based on a miniature silicon membrane and piezoresistive gauges is reported for significantly improving the performances in terms of time response. Simulation results indicate that it is possible to design a pressure transducer having a fundamental resonant frequency almost ten times greater than the commercial piezoelectric sensors one. 1. Introduction The typical pressure over time during an explosion is shown in Figure 1 [1-2]. First of all, the pressure increases abruptly (with a rise time between 10 ns and 100 ns) from atmospheric pressure to reach the overpressure peak Pmax (several tens of bar depending on the explosive load and the distance from the load). Then the pressure returns back to the atmospheric pressure during a positive phase in 500 µs followed by a negative phase. In order to validate the hydrocode, i.e. numerical simulations describing the shockwave discontinuity, an accurate measurement of the overpressure peak Pmax is required [3], involving the use of pressure sensors presenting a short time response ( 1000 °C) makes the real-time dynamic pressure measurement of the blast very challenging. The sensors used for the dynamic measurement of the pressure in harsh environment are usually piezoelectric pressure sensors (Table 1). Air blast experiments were performed at CEA-Gramat center using many piezoelectric sensors mounted on pencil probes to measure the incident pressure, ie with sensor surface parallel to the shock wave propagation (Figure 2). A typical example of the response of such sensors is illustrated in Figure 3. It can be observed that the time response is too long to provide an accurate estimation of the overpressure peak Pmax. The high cutoff frequency of such sensors is approximately 20 % of the resonant frequency. This bandwidth is also degraded by the large dimensions of the sensing part (between 78 mm² and 450 mm²). Moreover typical piezoelectric sensors have a low cutoff frequency (> 0.5 Hz at-5 %) which is too high to follow the overpressure decrease. The objective of this work is to achieve a device with a bandwidth at least ten times greater than the bandwidth of the available commercial piezoelectric sensors. In order to overcome the above-mentioned limitations of these sensors, we report here the design of a new piezoresistive pressure sensor based on a silicon membrane and silicon gauges. The piezoresitive detection has been chosen because it provides a better signal-to-noise ratio than their capacitive counterpart [4]