Instytut Podstawowych Problemów Techniki

UMO-2020/39/B/ST8/03505

2021-07-28 / 2024-07-27

Jedyny wykonawca

NCN

OPUS

20

In this project we intend to exploit some peculiar properties of elastic metamaterials, i.e., their negative mass density and negative modulus of elasticity. Again, there is nothing magic in the concept of negative mass density and negative modulus of elasticity. To understand these notions we have to break some common sense tacit assumptions about the mass density and modulus of elasticity. In fact, in everyday life we consider mass density as always positive since we tacitly assume that all components of the material vibrates in unison. If we break this assumption, a negative effective mass density means that an elastic material accelerates out of phase with respect to a harmonic excitation (second Newton's law of dynamics). Similarly, materials with a negative effective bulk modulus, will compress upon dynamic elongation and stretch under dynamic compression (Hooke's law). The qualifier effective means here that we consider mass density and bulk modulus dynamically not statically, like in conventional definitions. In our project we need to have an elastic metamaterial in which the wave front (phase velocity) of the wave propagates in one direction but the energy of the wave propagates exactly in the opposite direction. Is it really possible? Of course, it is but the elastic metamaterial must display a negative bulk modulus. In our project we intend to combine together two different elastic metamaterials, i.e., one of finite thickness (surface layer) with the properties described above and the second one much thicker (substrate) in which the wave front and energy propagate in the same direction. Such a combination will form a metamaterial waveguide for elastic surface waves of the Love type, discovered by the Victorian era scientist A. E. H. Love in 1911. If loaded on top with a viscoelastic liquid, such a metamaterial waveguide will constitute a sensor for measurements of mass loading and/or other viscoelastic properties of liquids. Since energy of the Love wave in the surface layer and in the substrate propagates in opposite directions it may happen that for some combinations of the material constants in the surface layer and substrate, as well as frequency of the Love wave, the overall power (energy) flow P1 of the Love wave may cancel out, P1→0. Our preliminary analysis shows that in such waveguides, for which the overall power flow vanishes P1→0, the coefficient of sensitivity S of Love wave sensors should achieve extremely high values, in theory S → ∞. Achieving very high sensitivities of Love wave sensors is of paramount importance in diverse fields of science, technology and health care system, e.g., in medicine, biology, chemistry, environmental monitoring, etc.. In fact, many serious diseases, such as hepatitis B, human immunodeficiency virus (HIV) antibodies or E. coli bacteria infection, require constant monitoring at patient home (point of care). Similarly, in the environmental studies it is crucial to early detect tiny concentrations of harmful volatile substances, such CO, ammonia, pesticides, heavy metal particles, etc..