Ultrasound/Acoustic Spectroscopy

Industrial Tomography Systems in  conjunction with the University of  Leeds have developed new  ultrasonic  tomography and spectroscopy measurements for the  m3000 platform. These modalities  can be used either separately or  together and can be combined with  the existing ERT and ECT modalities.

The use of Ultrasound imaging is well  known for non-invasive medical  diagnostics and non-destructive  testing, but has only recently been applied to process measurements. The use of spectroscopy with tomography add an extra dimension of material characteristics in addition to the identification of individual phases.

Ultrasound Spectroscopy (USS) is a technique which offers the possibility to overcome the obstacles to in-line analytics for a number of applications. 

USS has been developed over the last 20 years mainly for laboratory applications. However, recent developments in electronic systems and signal processing have increased the capabilities of the method to enable it to be viable on a wider range of applications which makes it a more suitable process sensor.

Ultrasound is the propagation of a mechanical wave through the molecular, microscopic and macroscopic structure of a material or materials. While most ultrasound methods use only one frequency to generate time of flight information, Ultrasonic Spectroscopy techniques measure a wide range of frequencies normally in the range 100kHz to 200MHz with standard instruments having typical ranges of 1MHz to 50MHz. From the individual frequency components the frequency dependant response (spectrum) of the materials mechanical properties are determined.

Ultrasonic Spectroscopy can measure the absolute frequency dependant velocity and attenuation of mainly liquids over a wide range of frequencies.

Typical spectra from a material exhibiting ultrasound dispersion such as a colloid

All Ultrasonic methods have a great advantage over optical methods in that they are not limited by the opacity of the material. Therefore they make ideal process sensor technologies as they are not affected by fouling of windows or sample opacity. Hence, there has been significant interest in the use of Ultrasonic Spectroscopy for the characterisation of concentrated materials (which is taken to mean concentrations of greater than 1% since laser diffraction is limited to <0.1% for most applications) in particular the:

• Measurement of density in solids and in pure/mixed liquids
• Determination of thermal properties of liquids
• Rheological characterisation of liquids and soft solids through phase velocity
• Particle Sizing of colloids using attenuation
• Relaxation phenomena in biomaterials and soft solids

What is Ultrasound?

Ultrasound is high frequency sound (above the audible range) which is taken to be greater 20kHz  

What is USS?

USS stands for Ultrasound Spectroscopy. USS measures the change in a ultrasound signal per unit distance as it propagates through a material.   The interaction of the ultrasound and the material causes a energy loss in the wave which is characteristic of the material.

What can USS be used for?

USS can be used to characterise the density and viscosity of the material. With additional analysis it can determine solids loading and particle size distribution.

What type of materials can be measured?

USS is currently only used on liquid and colloidal materials. Hence can be used on pure liquids, mixtures of liquids, emulsions, slurries and soft solids.

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