Liquid Flow Sensor Based on PVDF in its Beta Phase

This article describes a system for the measurement of liquid or gaseous fluids. The main innovation is that the device is of tubular form and is composed by a single part. It is manufactured from a piezoelectric polymer such as beta-PVDF, in which one electrode in the inside and three electrodes in the outer side are placed. One of the exterior electrodes is excited by an electric voltage, whose frequency, of the order of tens or hundreds of megahertz, produces mechanical oscillations in the area of the pipe in contact with it, producing an ultrasound with the same frequency. The areas of the pipe under the other two electrodes also work as ultrasound transducers, receiving the signal produced by the first one. There are two main methods of reading flows with ultrasound sensors: a method based on the Doppler effect and another method based in the transit time. In both of these methods, they are used the differences of frequency or phase between the emitted and the received signals in order to calculate the speed of the liquid or gas that passes through the pipe. The flow is then calculated by multiplying the speed of the fluid by the area of the section of the pipe. In this project, it was used the technique of the time of transit, where the flux is calculated from the difference between the time that ultrasounds need to travel in the direction of the flow and in the direction opposite to the flow. The main difference between this flow sensor and other ones available in the market is that this sensor is the pipe by itself, becoming simpler, more compact, more robust and cheaper.