Vibration mode investigation of a resonant silicon tube structure for use as a fluid density sensor

Abstract

We present a new sensor for on-line measurements of fluid density. The sensor consists of a tube system in single crystalline silicon which oscillates in mechanical resonance. The fluid is conveyed into and through two identical, serially and planarly arranged tube loops. A change in the density of the fluid in the tube changes the resonance frequency due to the change in the mass of the vibrating tube system. The sensor is fabricated using double-sided silicon KOH-etching and silicon fusion bonding. The silicon tube system (without the frame) is 8.6 by 17.7 mm with a thickness of 1 mm. The tubes have an inner diameter of approximately 0.8 mm and an outer diameter of approximately 1 mm. The micromachining process results in a total tube length of 61 mm and a sample volume of 0.035 ml. Fluid density measurements are presented and the vibration modes investigated.