Method and apparatus for assessing material properties of sheet-like materials

Apparatus for producing an indication of a material property of a sheet-like material comprising:

• an excitation source for vibrating the sheet-like material to produce at least one traveling wave therein;
• a light source configured to produce an object wavefront and a reference wavefront, said light source directing the object wavefront toward the sheet-like material to produce a modulated object wavefront;
• a modulator operatively associated with the reference wavefront, said modulator modulating the reference wavefront in synchronization with the traveling wave on the sheet-like material to produce a modulated reference wavefront;
• a sensing medium positioned to receive the modulated object wavefront and the modulated reference wavefront, the sensing medium having a response range, the modulated reference wavefront being modulated by said modulator so that a difference frequency between the modulated object wavefront and the modulated reference wavefront is within the response range of said sensing medium, the modulated object wavefront and the modulated reference wavefront combining in said sensing medium to produce an output beam that contains an image of the traveling wave in said sheet-like material, the image of the traveling wave being related to a displacement amplitude of the traveling wave over a two-dimensional area of the vibrating sheet-like material;
• and
• a detector configured to detect the image of the traveling wave in said sheet-like material.

A method for assessing a material property of a sheet-like material, comprising:

• providing a sensing medium, said sensing medium having a response range;
• producing an object wavefront and a reference wavefront;
• vibrating the sheet-like material to produce at least one traveling wave therein;
• directing the object wavefront toward the vibrating sheet-like material so that said object wavefront is modulated by the vibrating sheet-like material to produce a modulated object wavefront;
• modulating the reference wavefront in synchronization with the vibrating sheet-like material to produce a modulated reference wavefront so that a difference frequency between the modulated object wavefront and the modulated reference wavefront is within the response range of the sensing medium;
• combining the modulated object wavefront and the modulated reference wavefront within the sensing medium to produce an output beam that contains an image of the traveling wave in the vibrating sheet-like material, the image of the traveling wave being related to a displacement amplitude of the traveling wave over a two-dimensional area of the vibrating sheet-like material;
• detecting an image of the traveling wave in the vibrating sheet-like material;
• and
• assessing the material property of the vibrating sheet-like material based on the detected image of the traveling wave.