Perhaps you should try some spelling variations:
acoustical materials » optical materials, critical materials, classical materials
acoustic materials » acoustic metamaterials, plastic materials, elastic materials
acoustic material » acoustic metamaterial, acoustic metamaterials, plastic material
optic materials » optical materials, basic materials, ionic materials

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: %((optic materials) OR (((((acoustical materials) OR (acoustic material))) OR (acoustic materials))))%22.
• The words AND, OR and NOT may confuse the search; try adding quotes: "%((optic materials) or (((((acoustical materials) OR (acoustic material))) or (acoustic materials))))%22".
• Adding a wildcard symbol may retrieve word variants: %((optic materials) or (((((acoustical materials) OR (acoustic material))) or (acoustic materials))))%22*.