*4.6. Prospects for the Further Development of Ultrasound Methods and New Devices for Milk Analysis*

New promising directions for the development of milk characterization can become microfluidic concepts, phononic crystals concepts, and a combination of acoustic and optical approaches in one device.

Microfluidic technologies may be of interest for separating milk ingredients using acoustophoresis and other methods. Pre-separation of particles based on their differences in size and other physical properties allows for more accurate analysis at a later stage. Up to now, various microfluidic devices have been developed to separate and characterize suspensions and emulsions [112,129]. The acoustofluidic separation can become a powerful instrument for accurate milk analysis.

Improving existing and developing new microfluidic sensor devices involves the use of phononic crystals with liquid-filled cavities [146–148]. Phononic crystals can manipulate and tailor elastic and acoustic wave propagation, can create dynamically resonant metastructures. Phononic crystal designs can be scaled to meet given real object dimensions. Resonance frequency and bandwidth are highly sensitive to geometric and material parameters, specifically speed of sound and sound attenuation. High resolution requires high-Q resonators. Fabrication of phononic crystal and resonant sensor structures with high Q-factor is a challenging but realistic task. Recent studies [146–148] show that the use of phononic crystals can improve the resolution and isolation of responses from liquid resonances. The unique combination of the properties and concepts of phononic crystals, resonant sensors, ultrasonic measurement, and acoustofluidic methods can lead us to a new generation of high-sensitive and high-resolutive liquid sensor devices.



The development of liquid sensor devices that combine the advantages of optical and acoustic methods are carried out both on the basis of traditional methods (like ultrasonic interferometer include optical diffraction [141]) and using promising phononic-photonic crystals approaches [149].
