We study the propagation of shear-horizontal waves near the surface of a piezoelectric semiconductor half-space of crystals of class 6 mm with the presence of a biasing electric field in the propagation direction. The three-dimensional equations of linear piezoelectric semiconductors are used. A transcendental equation that determines the dispersion relation is obtained and solved numerically. Results show that the semiconduction affects the wave speed and causes wave dispersion as well as attenuation, and that the waves can be amplified by the biasing electric field.

We study the interaction between mechanical fields and the motion of charge carriers in a composite beam of flexoelectric (nonpiezoelectric) and semiconductor layers. The macroscopic theory of flexoelectricity and the drift-diffusion theory of semiconduction are used. They are coupled by doping and mobile charges in Gauss's equation of electrostatics. A one-dimensional electromechanical model is established for the bending of the beam. Solutions from the model show that bending of the beam induces redistribution of charge carriers through the electric field produced by flexoelectric coupling. This provides a new means for constructing electromechanical semiconductor devices and extends piezotronic devices.

Point defect modes in a 2D phononic crystal with giant magnetostrictive material tuned by a magnetic field and compressive stress are investigated theoretically in this study. The 3D magnetostrictive constitutive model proposed by Liu and Zheng (2005 Acta Mech. Sin . 21 278–85) is adopted to develop effective elastic, piezomagnetic, and magnetic permeability constants. The finite element method, in combination with a supercell technique, is then applied to obtain the band structures and transmission spectra of the point defect modes in a 2D phononic crystal composed of Terfenol-D rods of circular cross section embedded in a polymethyl methacrylate matrix with a square lattice. The magnetic field not only enlarges the first band gap (FBG) but also opens up a new band gap of XY modes. New point defect modes are simultaneously trapped in the band gaps. The width of the FBG and the frequencies of the point defects of the Z mode decrease as the magnetic field increases.