Miniature liquid/air interface sensor

摘要

Biomedical instrument systems often must determine whether a container or channel contains liquid or air. Many solutions to this problem have been proposed. Detectors that measure changes in capacitance, conductivity, pressure, ultrasonic coupling efficiency, and optical properties such as absorbance and index of refraction are routinely used. The ideal liquid/air interface detector would be small, inexpensive, reliable, immune to external influences, and chemically and physically compatible with the fluids being interrogated. We present a small liquid detector that uses failure of total internal reflection to indicate the transitions between air and liquid in a fluid conduit or container. The detector is manufactured with the same materials as the channels and chambers themselves, and as such is completely inert to the assay fluids it contacts. It is also relatively immune to external interference such as electromagnetic fields, ambient light, and physical variations in the fluids. It is tolerant of manufacturing variations, and would be inexpensive if manufactured even in moderate quantities. A few critical performance variables are analyzed and results from early testing of the sensor are discussed.