Abstract
An air-backed diaphragm is the key structure of most dynamic pressure sensors and plays a critical role in determining the sensor performance. Our previous analytical model investigated the influence of air cavity length on the sensitivity and bandwidth. The model found that as the cavity length decreases, the static sensitivity monotonically decreases, and the fundamental natural frequency shows a three-stage trend: increasing in the long-cavity-length range, reaching a plateau value in the medium-cavity-length range, and decreasing in the short-cavity-length range, which cannot be captured by the widely used lumped model. In this study, we conducted the first experimental measurements to validate these findings. Pressure sensors with a circular polyimide diaphragm and a backing air cavity with an adjustable length were designed, fabricated, and characterized, from which the static sensitivities and fundamental natural frequencies were obtained as a function of the cavity length. A further parametric study was conducted by changing the in-plane tension in the diaphragm. A finite element model was developed in COMSOL to investigate the effects of thermoviscous damping and provide validation for the experimental study. Along with the analytical model, this study provides a new understanding and important design guidelines for dynamic pressure sensors with air-backed diaphragms.
Highlights
For dynamic pressure sensors, the transduction method could be piezoelectric [1,2], piezoresistive [3], optical [4,5], or capacitive [6,7,8], but the key component of most sensors is a flexible diaphragm backed by an air cavity
To account for the effects of the air cavity, the most commonly used model is a lumped element model, where the diaphragm is described by a mass–spring–damper system and the backing air cavity acts as an effective spring [11]
To fully capture the acoustic–structural interaction, various analytical mechanics models have been developed, which are categorized in terms of how the cavity is modeled: i) using the Reynolds equation for thin viscous fluid films [12,13,14,15,16], or ii) using the sound wave equation where the viscous term is usually neglected [17,18,19,20,21,22,23,24,25,26]
Summary
The transduction method could be piezoelectric [1,2], piezoresistive [3], optical [4,5], or capacitive [6,7,8], but the key component of most sensors is a flexible diaphragm backed by an air cavity. Note that if the stiffness from the first mode and the effective mass from the second- and higher-order modes increase, diaphragm moves like a piston, only the first mode will be excited, and the closed air cavity as they scale with 1⁄l. A comprehensive experimental study is still lacking to systemically investigate the effects of changing air cavity length, in the context of dynamic pressure sensor development. As a follow-up study to the analytical model [27], the goal was to conduct the first experimental measurements to systemically validate the effects of the air cavity on SSc and fc when l continuously decreased, serving as a fundamental guideline for the design and development of dynamic pressure sensors. The experiment results were validated by comparing them with analytical and numerical simulations
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