A high-precision gravity intravenous infusion rate meter using CMUT arrays

This paper describes the development of a compact, high-precision infusion rate meter, which makes use of ultrasound for finding polymer tube diameter and flow rate measurement with a pair of face-to-face CMUT (capacitive micromachined ultrasonic transducer) arrays. The CMUT arrays are embedded inside a chamber on a plastic clip. This CMUT flow meter is designed to be clipped on a polymer flow tube as a potable device. Ultrasound with a center frequency at 4.0 MHz is transmitted from one of the two linear CMUT arrays, traveling through the polymer flow tube, then being received by the other array. The flow tube diameter is measured through the time flight echo delays between near and far wall reflections. The infusion velocity is detected from the difference in time flight between the upstream and downstream using cross-correlation method. Combining the measurement of tube diameter and the fluid´s velocity, an accurate volumetric flow rate can be calculated. A flow rate resolution of 0.05 ml/min and a tube diameter resolution of 0.4 mm have been achieved.