English to Italian Law/Patents Law: Patents, Trademarks, Copyright Sensore di torbidità

Nella descrizione di una figura relativa a sensori di misura della torbidità:

"In FIG. 1, L represents a light source to produce incident radiation with no divergence, E represents the direction of a excitation beam, S represents the direction of a scattered radiation, θ represents the measuring angle between the optical axis of the incident radiation and mat of the diffused radiation, and Ωθ represents the aperture angle in the water sample. The light source L produces an infrared beam with no divergence and convergence and not more than 1.5°. The measuring angle θ between the optical axis of the incident radiation and the mat of the diffused radiation should be 90 ± 2.5°. The aperture angle Ωθ in the water sample should be between 20° and 30°".

Qualcuno ha idea di cosa possa significare "mat"?
Mi piacerebbe allegare la figura, ma trattandosi di un brevetto temo di non poter inserire il link :(