Backward-mode photoacoustic transducer for sensing optical scattering and ultrasonic attenuation: determining fraction consistencies in pulp suspensions

Abstract

An innovative backward-mode photoacoustic transducer was developed, consisting of an optical fibre, a composite absorber, piezoelectric film and high impedance preamplifier. By receiving scattering light from a turbid suspension, the transducer produces a photoacoustic source in it. This source emits two photoacoustic waves travelling in opposite directions. The waves' amplitudes relate to the optical scattering properties of the suspension, and the echo of a wave returning from the suspension carries information of acoustic attenuation. By assessing the optical scattering and acoustic attenuation, fraction consistencies in a two-fractional suspension can be determined if one fraction dominantly scatters light and the other mainly attenuates ultrasound. This technique is used in this paper to investigate paper pulp suspensions. Pulp consists of wood celluloses and wood fines (or extra-added fillers in some cases), where cellulose lengths range from a few sub-millimetres to millimetres and fines/filler sizes are a few tens of micrometres or smaller. Due to their different size and shape, celluloses and fines (or fillers) have different optical scattering and acoustic attenuation properties. Experimental results showed that the transducer can measure pulp consistency with good linearity at least in the range from 0.5% to 3%, and that it can distinguish pulp cellulose from fines or fillers (TiO 2 particles). Needless to say, this technique is also suitable for determining other suspensions in the food, pharmaceutical and mineral industries.

Photoacoustic spectroscopy for analytical measurements

“…A special way of PA spectroscopy and PA-induced ultrasound (US) was developed for the analysis of pulp in the process of paper manufacture [125]. The aim of the measurement in this case was not the optical absorption measurement, but the measurement of light scattering and acoustical attenuation.…”

Application of artificial bee colony algorithm for particle size distribution measurement of suspended sediment based on focused ultrasonic sensor

“…Ultrasound is the preferred alternative in the industry because of its advantages ease-of-use, low cost and robust-to-media characteristics (Wu et al, 2014). As the basic property of ultrasonic propagation, ultrasonic attenuation effect has been widely used in the measurement and application of multiphase flow (Su et al, 2017, Zhao et al, 2010) especially for the measurement of particle size distribution (Tran et al, 2016, Zou et al, 2014). This paper proposes a method system based on new focused ultrasonic transducer, which has the advantages of smaller scattering loss, greater energy concentration, higher sensitivity, and better symmetry.…”