Terahertz characterization of a multi-layered tire tread

A method for characterizing a multi-layered tire tread, the method comprising:

• producing a multi-layered tire tread comprising a first layer comprising a first rubber composition and a second layer comprising a second rubber composition, wherein the first rubber composition has a first refractive index and the second rubber composition has a second refractive index, and a difference between the first refractive index and the second refractive index is greater than, equal to, or lower than a threshold refractive index;
• irradiating the multi-layered tire tread with a THz electromagnetic radiation;
• and
• receiving radiation transmitted through the multi-layered tire tread and/or radiation reflected by the multi-layered tire tread,
• wherein the method further comprises adding a refractive index modifier to the first rubber composition and/or second rubber composition in case the comparison provides that the difference is greater than or lower than the threshold refractive index, and
• wherein an amount of the refractive index modifier is varied during the step of producing a multi-layered tire tread.