The development of batch-manufactured resonating silicon microtubes permits more accurate and more efficient measurement of the density and specific gravity of fluids by instruments that are much smaller, lighter, and potentially less expensive than the fluid-measuring instruments currently available.
Using a combination of plasma and wet-etch processing along with wafer bonding, Integrated Sensing Systems' silicon microtubes suit a wide range of sample-size and sensitivity measurement requirements. Yet they range in width from just 1000 µm down to 10 µm. The microtubes at the lower end of the width range are no wider than a human hair (Fig. 1).
The first instrument built with this technology is a handheld unit that weighs just 2.2 lb—a far cry from the approximately 60 lb many current desktop instruments weigh. It requires only microliters of fluid sample, compared to the milliliters normally needed by conventional instruments based on resonating glass or metal tubes (Fig. 2). The microtube is driven into resonance electrostatically by 0 to 5 V. Users can control the instrument through an alphanumeric keypad or an RS232 interface.
Because the density of most fluids varies sharply with temperature, accurate temperature control is normally required to ensure the best measurement of fluid density. On the same vacuum-packed MEMS chip, the microtube integrates a dynamic temperature controller that operates between 0°C and 90°C with an accuracy to within 0.01°C. Integrating the temperature controller in this way helped reduce the instrument's weight substantially.
For more information, call Doug Sparks at (734) 547-9896, ext. 119, or e-mail [email protected].