Electromagnetic induction and autapse play important roles in regulating the electric activities, excitability, and bistable structure of neurons. The firing activities and global bifurcation patterns of a four-dimensional (4D) hybrid neuron model that combines the fast dynamic variables of the Wilson model and the slow feedback variables of the Hindmarsh–Rose (HR) model and magnetic flux are investigated based on the Matcont software and numerical calculation. The effect of electrical autapse on the dynamic evolution of the system is also discussed emphatically. Upon encountering electromagnetic induction, the hybrid neuron model exhibits complex global stability, Hopf bifurcation, and saddle-node bifurcation. Intriguingly, the system presents initial sensitivity and a bistable structure consisting of quiescent and period-1 spiking near the Hopf bifurcation point. It is worth noting that the feedback type of electrical autapse, including positive and negative feedback, has completely different effects on this bistable structure. Notably, the negative feedback autapse can expand and change the bistable region, so that the system generates a new bistable structure consisting of quiescent and periodic bursting states, and its bursting activities are also promoted. Moreover, extensive numerical results show that the system generally maintains a comb-shaped chaotic structure, abundant bifurcation patterns, and multistability. It should be noted that electrical autapse feedback types and time delays do not change the regular bifurcation structures but operate a complex regulatory mechanism for the coexistence of multiple attractors. These results will provide useful insights into the neuron’s dynamics under the atmosphere of electromagnetic induction and also electrical autapse.
In this work, a graphene loudspeaker is designed using laser scribing technology, and its theoretical model with AC and (AC + DC) excitation is established, which focuses on the effect of different excitations on the performance of graphene loudspeakers. The proposed theoretical model consists of a temperature gradient model and a sound pressure model. The application of (AC + DC) excitation helps to mitigate the frequency doubling effect caused by AC excitation. Sound pressure level (SPL) measurements with AC and (AC + DC) excitations are carried out to verify the theoretical model. The measured results show that the SPL is proportional to the input power and inversely proportional to the measurement distance. The highest SPL produced by the graphene loudspeaker is 53.3 dB with (5 V AC + 5 V DC ) excitation. The theoretical model of the graphene loudspeaker with different excitations has a certain reference value for further research on thermoacoustic effects and improving the efficiency of graphene loudspeakers.
In this work, the frequency doubling effect of thermoacoustic speakers is studied, and a method is analyzed to suppress the frequency doubling effect. Three cases were analyzed by superimposing the DC bias on the AC excitation: (1) DC is less than AC; (2) DC is equal to AC; (3) DC is greater than AC. We found that the frequency doubling effect can be well suppressed by superimposing a larger DC excitation on the AC excitation. The laser scribing technology was used to prepare graphene film in only one step, and the screen printing technology was used to prepare conductive electrodes. The microphone and B&K system was used to record the sound pressure level and study the suppression of frequency doubling effect. Finally, the sound pressure levels with the three different kinds of excitations were measured. The measured results show that they have a good agreement with the theoretical results. The suppression effect will be better when DC amplitude is greater than AC amplitude. Therefore, this work has certain reference significance for the further study and application of thermoacoustic speakers.
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