FLUID DENSITY SENSOR-BASED ON RESONANCE VIBRATION

This paper presents the first silicon tube resonant fluid density sens or. The sensor is based on a tube system which is vibrated in a select ed balanced mixed torsion and bending mode. The resonant frequency cha nges with the density of the fluid in the tube due to the change of th e inertial mass of the vibrating tube system. A simplified analytical analysis shows that the resonance vibration frequency depends on the w eighted density, rho, as similar to 1/rho(1/2), where rho is the densi ty of the silicon and the fluid weighted in accordance to their area i n a cross section of the tube. The sensor was fabricated using double- sided silicon KOH etching and silicon fusion bonding. The silicon tube system (without the frame) is 8.6 x 17.7 mm with a thickness of 1 mm. The tube system was excited electrostatically into resonance vibratio n which was detected optically. The resonant frequency was measured fo r different mixtures of 2-propanol and water. The sensor shows very go od sensitivity,-200 ppm (kg m(-3))(-1) and a high mechanical Q-value, of the order of 1500. The sample volume is only 0.035 ml.