High-precision Versatile Ultrasonic Flow Meters Based on Matrix Transducer Arrays

Ultrasonic flow meters are widely applied to measure flow in a variety of applications. The vast majority of ultrasonic flow meters are based on the measurement of the transit time of an acoustic pulse through the fluid. This can either be done in-line, by inserting a spool piece with ultrasonic transducers into the pipe carrying the fluid, or by clamping the transducers on an existing pipe. Clamp-on meters are attractive as they can be installed without cutting the pipe or shutting down the flow, but their stability is limited, and they are unable to measure flow profiles (in contrast with expensive multi-path in-line meters), which limits their linearity at low flow speeds. Moreover, their installation requires complex manual alignment of the transducers and input of a variety of setup parameters (e.g. pipe dimensions and material properties, speed of sound in the fluid) by the user. In this thesis, clamp-on meters based on matrix ultrasonic transducers are developed to address these drawbacks. These matrix transducers consist of a two-dimensional array of 100+ elements that enables beam steering in two directions by programming the timing of the electrical pulses applied to the elements. This allows to develop three innovative measurement techniques: (1) automatic beam alignment by adjusting the steering angles so as to optimize the signal-to-noise ratio and the path of the received pulse, thus simplifying installation and improving stability; (2) multi-path measurement by steering the beam at different angles, realizing the measurement of multiple paths through the fluid with a single pair of matrix transducers, and thus providing information about the flow profile; (3) self-calibration by using pulse-echo measurements between the elements of the matrix transducer to characterize the pipe wall and fluid, thus reducing the dependence on a-priori knowledge of their properties. The most significant steps to realize these kind of sensors were taken in this thesis. The mentioned measurement techniques were elaborated, and the relevant wave-propagation phenomena, beamforming schemes and transducer design were performed. Based on this, a prototype sensor was fabricated and successfully tested. Moreover, application-specific integrated circuits (ASICs) were developed with dedicated transmit and receive electronics to realize a cost-effective and accurate implementation of the beam forming and transit-time measurement.