A wideband ultrasonic test system for characterisation of particulate systems in the linear and non-linear regimes

Benny, C.G. and Gachagan, A. and Hayward, G. and Nordon, A. and Littlejohn, D. (2007) A wideband ultrasonic test system for characterisation of particulate systems in the linear and non-linear regimes. In: International Congress on Ultrasonics, 2007-04-09 - 2007-04-13.

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Abstract

This paper describes the development, characterisation and application of a versatile acoustic test cell for the derivation of through-transmission and backscattered ultrasonic signals from particulate suspensions. The test cell comprises a chamber for the mixture within a larger water tank, with fixtures for ultrasonic transducers at either end of the tank. The mixing chamber has wideband membrane hydrophones at the entrance and exit of the acoustic path. A range of broadband ultrasonic transmitters permits operation over the excitation frequency range 150 kHz – 10 MHz. Importantly, this configuration permits detection of the fundamental operating frequency and its sub- and superharmonics for both backscatter and through-transmission measurements from a single transducer excitation. The methodology employs coded excitation waveforms in the form of wideband chirps coupled with matched filtering of the received waveforms to enhance SNR and time resolution, and extract specific spectral information. For the linear analysis, through-transmission signal amplitudes provide a measure of attenuation and arrival times determine acoustic velocity. Spectral content of backscattered signals is used to identify non-linear characteristics, which are analysed for information related directly to the mixture properties. The particulate systems evaluated were glass beads, biomedical contrast agents and Avicel. Results have been achieved when operating in the linear regime, which compare well with published data, and with good scatterers in the non-linear regime, to which preliminary characterization of particle concentration has been applied.