Non-Contact Sensing of Elastic Modulus of the UV Cured Furniture Coatings by the Transverse Acoustical Waves

Elastic modulus of the furniture coatings is an important parameter, which indicates the curing state of the composite resin curable by the ultraviolet radiation. Non-contact way of elastic modulus measurement by the transverse acoustical waves, propagating perpendicular to the surface of a 10-$\mu \text{m}$ thick polymer, is shown as a suitable principle of the curing state sensing during furniture production. Transverse waves were excited by the cone-shaped ultrasound transducer having its frequency band centered at 1 MHz and captured with a receive transducer within 10- to 30-mm distance away from the excitation point. This setup allows to measure the differences of the time of flight of the pulse of the transverse waves in respect of the curing state in a non-contact regime. Numerical simulation and experimental results have led to the function, which relates the time of flight with the elastic modulus of the polymer coating, which was identified to be less than 1.95 GPa for an insufficiently cured polymer up to a 2.25 GPa in the case when cured as specified by the manufacturer. These values were confirmed by the AFM force-separation curve measurement technique, used here as the reference measurement channel.