Faculty Publications
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Item Dynamics of Chemical Excitation Waves Subjected to Subthreshold Electric Field in a Mathematical Model of the Belousov-Zhabotinsky Reaction(Springer Science and Business Media B.V., 2022) Sebastian, A.; Amrutha, S.V.; Punacha, S.; Shajahan, T.K.We present a numerical study of the dynamics of spiral waves in a weak external electric field, using the Oregonator model of the Belousov-Zhabotinky (BZ) reaction. Both free and pinned spiral waves are studied in two types of electric fields: unidirectional (DC) and Circularly Polarised Electric Field (CPEF). Both free spirals and pinned spiral waves rotate faster in the DC field. The CPEF can help a free spiral to be spatially confined. A pinned spiral period can be controlled by varying the period of the CPEF. Both DC and CPEF can unpin the pinned spiral wave, but the minimum electric field required to unpin is much less with CPEF compared to DC. Thus, CPEF is more energy efficient to unpin a pinned spiral wave. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Variations in the Scroll Ring Characteristics with the Excitability and the Size of the Pinning Obstacle in the BZ Reaction(Springer Science and Business Media B.V., 2022) Sibeesh, P.; Amrutha, S.V.; Shajahan, T.K.We report the experimental results of the effects of excitability on the wave characteristics of free rotating and pinned scroll rings in the Belousov-Zhabotinsky (BZ) reaction. The experiments show that the stability of the scroll ring depends on the excitability of the medium. At low excitability, the scroll ring becomes less stable and eventually breaks up. As we increase the excitability of the medium, the time period (T) and wavelength (λ ) of the excitation wave decrease while wave velocity (v) increases. Properties of both free and pinned scroll rings change in the same way. However, at a given excitability, both the λ and v of a pinned scroll ring increase with the size of the obstacle. For the range of parameters chosen in our experiments, the excitability changes brought by varying reactant concentrations have a higher impact on the scroll ring properties than those induced by the size of the pinning obstacle. © 2022, The Author(s), under exclusive license to Springer Nature Switzerland AG.Item Mechanism of Spiral Wave Unpinning in the Belousov-Zhabotinsky Reaction with a DC Electric Field(American Chemical Society, 2022) Amrutha, S.V.; Sebastian, A.; Sibeesh, P.; Punacha, S.; Shajahan, T.K.We study the mechanism of spiral wave unpinning in the Belousov-Zhabotinsky (BZ) reaction with a DC electric field. The unpinning is characterized by the phase of the spiral tip around the obstacle boundary at the time of unpinning. We systematically measure the unpinning phase as a function of the chirality of spiral rotation, the initial phase of the spiral, the size of the pinning obstacle, the direction, and the strength of the applied electric field. In both BZ experiments and simulations using the Oregonator model, we observe that the spiral wave always unpins at a fixed position with respect to the applied field. The wave unpins when the electric field component in the direction of the tip velocity of the spiral waves becomes equal to a threshold field strength. From these observations, we deduce a relation between the phase of unpinning, the size of the pinning obstacle, the strength, and the direction of the electric field, and it agrees with our observations. We conclude from our observations that a retarding 'electric force' on the chemical wave is responsible for the unpinning in the BZ medium. Our results indicate that the 'electric force' is more effective in unpinning when the wave moves away from the anode than when it is moving toward it. © 2022 American Chemical Society.Item Theory and experiments of spiral unpinning in the Belousov-Zhabotinsky reaction using a circularly polarized electric field(American Institute of Physics Inc., 2023) Amrutha, S.V.; Sebastian, A.; Sibeesh, P.; Punacha, S.; Shajahan, T.K.We present the first experimental study of unpinning an excitation wave using a circularly polarized electric field. The experiments are conducted using the excitable chemical medium, the Belousov-Zhabotinsky (BZ) reaction, which is modeled with the Oregenator model. The excitation wave in the chemical medium is charged so that it can directly interact with the electric field. This is a unique feature of the chemical excitation wave. The mechanism of wave unpinning in the BZ reaction with a circularly polarized electric field is investigated by varying the pacing ratio, the initial phase of the wave, and field strength. The chemical wave in the BZ reaction unpins when the electric force opposite the direction of the spiral is equal to or above a threshold. We developed an analytical relation of the unpinning phase with the initial phase, the pacing ratio, and the field strength. This is then verified in experiments and simulations. © 2023 Author(s).Item Effect of electric field chirality on the unpinning of chemical waves in the Belousov–Zhabotinsky reaction(Elsevier Ltd, 2024) Sebastian, A.; Sibeesh, P.; Amrutha, S.V.; Punacha, S.; Shajahan, T.K.We investigate the unpinning of chemical spiral waves attached to obstacles in the Belousov–Zhabotinsky (BZ) reaction using a Circularly Polarized Electric Field (CPEF). The unpinning is quantified by measuring the angle at which the spiral leaves the obstacle. Previously, we had found that the wave can unpin when the electric field along the direction of the spiral is above a threshold value. When we apply a DC field, this condition can be satisfied for a range of spiral phases, which we call the unpinning window (UW). With a CPEF, this UW moves either along the direction of the spiral (co-rotating) or against the spiral (counter-rotating). We find that when the field is co-rotating, it can take several rotations of the spiral to get unpinned. With a counter-rotating field, the spiral always unpins during the first rotation. We analyze how unpinning with CPEF depends on the electric field's relative speed, chirality, and strength using experiments and the Oregonator model. Our work helps to understand and control chemical waves. © 2024 Elsevier Ltd