System-level graphene foam speaker and the simulation of the thermo-acoustic process

Recent studies have shown that microporous graphene foam (GF) exhibits photoacoustic effect when irradiated with modulated light. Inspired by this phenomenon, we fabricated a light emitting diode (LED)-induced system-level GF speaker that generates photoacoustic waves in a frequency range of 0.2-16 kHz or plays music with high fidelity when illuminated by modulated LED light. LED light modulation is realized by our specially designed driving circuit that combines the AC voltage corresponding to the audio signal (sinusoidal signal or music from a cell phone) and a DC bias. To reveal the effect of the microporous structure of GF on the photoacoustics, we simulated the thermo-acoustic process (the second process of the photoacoustic effect). We built a periodically heated model of micro-spherical air unit with a diameter of 42 μm to investigate the relationship between the heat flow absorbed by the air unit and the thermo-acoustic wave created by it. The simulated results show that in the frequency range of 0.2-16 kHz, the thermo-acoustic pressure correlates with the frequency of heat flow. Moreover, in the diameter range of 10 to 80 μm of the air unit, the thermo-acoustic pressure is directly proportional to the square of the diameter of the air unit, suggesting that the photoacoustic effect can be enhanced by increasing the size of the GF pores to a certain extent. This work demonstrates the light-induced speakers and provides theoretical support for the photoacoustic effect that occurs in materials with microporous structures.