Abstract: Doppler Ultrasound techniques have been used for many years to measure the flow rate of fluids. One of the challenges in using these techniques is to separate fluid flow signal from background noise. The present invention is directed to methods and apparatus for automatically distinguishing fluid flow signal from noise. It is found that noise in Doppler ultrasound techniques has characteristic of a white Gaussian spectral distribution and the mean noise can be characterized as a constant. The present invention involves measuring ultrasonic signals, generating sets of discrete spectral components from these signals, and statistically determining a maximum likelihood estimation from the spectral components. This estimation is used to calculate the fluid velocity.

Abstract: A strain gauge plethysmograph is provided comprising an elastic tubular member (2) filled with a non-mercury electrically conductive gallium-indium alloy which is fluid at room temperature. The tubular member (2) is attached to an inelastic strap member (1) at spaced points (5,6). The length of the strap (1) between the points of attachment (5,6) is limited to approximately 120% of the nominal length of the tubular member (2) for restricting stretching of the tubular member (2).