In this work, the experimental results of the creation of the second non-dispersive Zakharenko wave ($C_{ph} = C_{g} \neq 0$) in the negative roton branch (the so-called second sound) of the bulk elementary excitations (BEEs) energy spectra are introduced. Several BEE signals detected by a bolometer situated in the isotopically pure liquid helium-II at low temperatures $\sim 100$ mK are shown, which give evidence of negative roton creation in the liquid by helium atomic beams striking the liquid surface. The negative roton signals were clearly distinguished by the following ways: the negative roton signal created by helium atomic beams appeared earlier than the positive roton signal created by the beams, and presence of both positive and negative roton signals together. It is natural that the negative roton creation by the beams requires the ⁴He-atom energies $\sim 12$ K, while the positive roton creation by the atomic beams requires energies $\sim 35$ K. Therefore, successive increase in the heater power resulting in an increase in the ⁴He-atom energies gives solid evidence that the negative rotons are first created in the liquid by the helium atomic beams.

This report gives a discussion of a new wave characteristic as a material parameter for a composite with the magnetoelectric effect. The new parameter depends on the material constants of a piezoelectromagnetic composite. It can be implemented on : (A) mechanically free, electrically and magnetically open surface and (B) mechanically free, electrically and magnetically closed surface. These theoretical investigations are useful for researches in the firlds of acousto-optics, photonics and opto-acousto-electronics. Some sample calculations are carried out for BaTiO₃ - CoFe₂O₄ and PZT-5H-Terfenol-D composites of class $6 mm$. Also, the first and second derivatives of the new parameter with respect to the electromagnetic constant 𝛼 are graphically shown.

Fundamental modes of new dispersive shear-horizontal (SH) acoustic waves propagating in the (6 mm) piezoelectromagnetic plate are studied. These SH-waves can propagate when the following boundary conditions are exploited for both the upper and lower surfaces of the plate: (1) when the surfaces are mechanically free, electrically and magnetically closed and (2) when the surfaces are mechanically free, electrically and magnetically open. The SH-waves depend on the electromagnetic wave speed $V_{\text{EM}} = 1/\sqrt{(\varepsilon \mu)}$ and can only exist when the electromagnetic constant $\alpha \neq 0$. The calculations (first evidence) were performed for the PZT-5H–Terfenol-D which is a composite with a large value of $\alpha$. The limit cases of large values of $\alpha (\alpha^{2} = 0.5\varepsilon \mu, \alpha^{2} = 0.9\varepsilon \mu)$, and $\alpha^{2} = 0.99\varepsilon \mu$) are studied because they satisfy the limitation condition of $\alpha^{2} < \varepsilon \mu$.