Virtual Loudspeaker Effect of Graphene-Based Hybrid Material To Improve Low-Frequency Acoustic Performance

Synthesis of a zeolite@mesoporous silica composite to improve the low-frequency acoustic performance of a miniature loudspeaker system

Herein, a zeolite@mesoporous silica composite (Z@MS) with a hierarchical porous structure was synthesized and employed as the filling material in miniature loudspeakers. The material was synthesized via a simple surfactant-directed sol-gel process in which MFI zeolites with a high silica-alumina ratio (>1000) were encapsulated in mesoporous silica with worm-like pores templated by Brij 72 under acidic conditions. Pressure spray drying technology was adopted to reassemble the intermediate slurry into hierarchical porous microspheres with large particle sizes (∼200 μm). The resonance frequency of the miniature loudspeaker system decreased by 339.77 Hz upon loading Z@MS as the filling material. The excellent acoustic performance can be considered as the result of a synergy of respective energy transmission effects among hierarchical porous structures.

Vibroacoustic Characteristics of a Specific Patterned Polymer with Graphene for an Electrostatic Speaker

Graphene/polymer actuators were developed using bilayer graphene and various polymer substrates for use as transparent, flexible, and robust electrostatic speaker units. Additionally, a resonant frequency shift was induced using a polymer substrate on which various micropatterns were transferred to boost bass. The total sound pressure level (SPL) in the graphene/polymer actuator was measured by a sweep, and the frequency of the spectrum was confirmed to be one-third that of the octave band frequency. The change in the vibroacoustic characteristic with changes in Young's modulus and density was studied for the polymers of the same size and thickness. Particularly, the possibility of boosting bass was confirmed by inducing a resonant frequency shift and increasing the total SPL by adding micropatterns on a polymer substrate under the same conditions. The resonance frequency of 523 Hz and the SPL of 54 dBA in flat polymer film became 296 Hz and 69 dBA in a specific pattern, which produced a sound of >15 dB based on the same flat polymer. We expect that the design and information provided herein can provide the key parameters required to change the resonant frequency in small-size devices for the application of graphene/polymer thin-film actuators.

Graphene-Based Thermoacoustic Sound Source

Thermoacoustic (TA) effect has been discovered for more than 130 years. However, limited by the material characteristics, the performance of a TA sound source could not be compared with magnetoelectric and piezoelectric loudspeakers. Recently, graphene, a two-dimensional material with the lowest heat capacity per unit area, was discovered to have a good TA performance. Compared with a traditional sound source, graphene TA sound sources (GTASSs) have many advantages, such as small volume, no diaphragm vibration, wide frequency range, high transparency, good flexibility, and high sound pressure level (SPL). Therefore, graphene has a great potential as a next-generation sound source. Photoacoustic (PA) imaging can also be applied to the diagnosis and treatment of diseases using the photothermo-acoustic (PTA) effect. Therefore, in this review, we will introduce the history of TA devices. Then, the theory and simulation model of TA will be analyzed in detail. After that, we will talk about the graphene synthesis method. To improve the performance of GTASSs, many strategies such as lowering the thickness and using porous or suspended structures will be introduced. With a good PTA effect and large specific area, graphene PA imaging and drug delivery is a promising prospect in cancer treatment. Finally, the challenges and prospects of GTASSs will be discussed.