Optical transmission of ferrofluids exposed to a magnetic field: Analysis by electromagnetic wave propagation numerical methods

Absorption spectrum of magnetically structured emulsions in the centimeter range

“…With increasing magnetic field strength, there is a transition from individual chains to the formation of dense columnar structures of emulsion droplets. Such a transformation of the structure of magnetic suspensions was observed earlier in a number of works and led to a similar change in the character of macroscopic properties of the medium, in particular, optical properties [27,[34][35][36][37].…”

“…In the lateral parts of the cell, on the contrary, the chains are predominantly perpendicular to the electric field; this leads to a weakly noticeable but nevertheless occurring decrease in the absorption of electromagnetic energy. Note that such anisotropy of the interaction of electromagnetic radiation in the optical range with structured magnetic suspensions was previously demonstrated in [36,46]. The influence of the formation of chain structures on the macroscopic properties of the material has the character of saturation.…”

Numerical calculation of ferrofluid optical transmission evolution after magnetic field switch-on

“…Besides, once γ t has been determined, the time scale indicates that the simulation corresponds to the first seconds of the sample response. The effects associated to chain coalescence have been experimentally observed in this sample after several tens of seconds (sample#1 in [24]), when a trend inversion on the transmission evolution is detected. Therefore, figure 6 results are consistent with the fact that the program only accounts for the initial formation of individual chains of particles.…”

“…These models are typically quite complex and would require a high precision in the ferrofluid parameters to obtain adequate quantitative results. On the other hand, numerical software for calculating the propagation of an electromagnetic pulse, typically by means of finite integration methods, usually requires long computational times for just one particle distribution at a specific time step [24]. Therefore, determining the transmission evolution of the ferrofluid would take an unaffordable time.…”

“…Those which study the optical effects are based on calculating the area projected by the particles in the light direction to determine the optical attenuation through scattering models such as the Mie theory [22], or directly calculating the propagation of a plane wave [23]. Due to the limitations of these theories or the difficulty of specifying exactly the characteristics and conditions of the real ferrofluid, determining the correlation between the magnetic effect and the optical consequence is not an easy task, and sometimes only a qualitative study of trends related to the magnetic processes is possible [24]. It is remarkable that the main obstacle for any adequate calculation of light propagation through the sample by means of the typical numerical methods is the computational time which any kind of software would require.…”