Engineered aggregates for metamaterials

A structural metamaterial comprising:

• a matrix formed of a matrix material having a matrix density;
• and
• a plurality of engineered aggregates each formed of a geometric multilayer body disposed within the matrix material, each geometric multilayer body comprising at least an inner core surrounded by a compliant layer, wherein the inner core is formed of a core material having a core density, and wherein the compliant layer is formed of a compliant material having a compliant layer density that is lower than both the matrix density and the core density, and an elastic modulus adapted to induce a kinetic oscillation in the inner core when exposed to an energy wave that imparts mechanical energy to the geometric multilayer body within at least one target frequency range, such that the engineered aggregate exhibits a negative effective mass to trap at least a portion of the mechanical energy within the engineered aggregate such that the stress experienced by the surrounding matrix material is reduced.