We propose an intensity modulator utilizing two-dimensional plasmons (2DPs) in a dual-grating-gate high-electron-mobility transistor. The device primarily functions as a plasmon-resonant emitter in which the seeds of non-radiative longitudinal modes of 2DPs are efficiently converted into radiative transverse modes of terahertz (THz) electromagnetic waves. In this work, we numerically study the behavior of the mode conversion between 2DPs and THz electromagnetic waves as a function of the 2DP dispersion. The finite difference time domain analysis demonstrates that the coupling of THz electromagnetic waves and 2DPs changes with the electron drift velocity and with the sheet electron density in 2DPs. The analysis also reveals that the intensity of transmitted waves can be modulated over a wide THz range with an extinction ratio beyond 60% by optimizing the sheet electron density and the drift velocity under nominal area-factor condition (ratio of the 2DP area over the total active channel area) up to 0.6.

We consider a single spike of ferrofluid, arising in a small cylindrical container, when a vertically oriented magnetic field is applied. The height of the spike as well as the surface topography is measured experimentally by two different technologies and calculated numerically using the finite element method. As a consequence of the finite size of the container, the numerics uncovers an imperfect bifurcation to a single spike solution, which is forward. This is in contrast to the standard transcritical bifurcation to hexagons, common for rotational symmetric systems with broken up-down symmetry. The numerical findings are corroborated in the experiments. The small hysteresis observed is explained in terms of a hysteretic wetting of the side wall.

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