Noise level analysis in buffer rod geometries for ultrasonic sensors

This work presents an ultrasonic sensor for on-line batter monitoring with low-noise design considerations. The density and the compressibility of the batter vary as a function of mixing time and are strongly related to the quality of the final product. Traditionally, a batter sample of a fixed volume is removed and weighted in order to determine its density. This is a time consuming process. Benefits to the industry of on-line measuring techniques include better control of product quality, improving processing efficiencies and reduction in wastage. In this paper low-noise design considerations are accounted for an ultrasonic sensor based on a piezoceramic disk mounted between two reference buffer rods of acrylic resin to measure the acoustic impedance of the batter. Measuring the acoustic impedance changes of the batter its compressibility and density can be monitored. Spurious echoes generated at different parts of the buffer rods boundary strongly affect accuracy and reliability of the measurements, and are considered as noise. The influence of buffer rods geometry on noise level is studied using simulations and afterwards justified experimentally. Design aspects such as buffer rods length and radius, piezoceramic disk frequency and radius are discussed and their influence on noise level is shown. Finally, strategies for optimum geometry design of the ultrasonic sensor are given. (c) 2006 Elsevier B. V. All rights reserved.