Exploration and Application Prospects of Diamond Acoustic Characteristics

Diamond has the highest sound propagation speed and extremely high Young's modulus, as well as excellent mechanical and chemical properties, and has broad application prospects in acoustics.

1.  Acoustic properties of diamond

The application of diamond in acoustics mainly utilizes its characteristics of high sound velocity, low density, high elastic modulus, mechanical strength, and thermal conductivity.

Longitudinal wave (VL) and transverse wave (VT) sound velocities along the [100] direction for various materials obtained from elastic constants

2.  Surface acoustic wave characteristics

Since Rayleigh discovered the surface acoustic wave (SAW) phenomenon on solid surfaces in 1885, related applications have also been developed, and SAW devices are one of them. The attenuation of SAW propagation along the solid surface is small, but it rapidly decays in the direction perpendicular to the surface. SAW mainly includes Rayleigh waves, Shear waves (SH waves), Q waves, Lamb waves, and SH-APM. The SAW filter widely used in the electronics industry currently utilizes the characteristics of Rayleigh waves.

3.  Diamond wafer acoustic applications

1.Diamond diaphragm

Compared with other diaphragm materials, diamond diaphragm has outstanding advantages, such as higher sound speed, highest Young's modulus, and lower density compared to metallic beryllium. The diaphragm used for the tweeters in the top tier series of B&W's 800 series floor standing speakers is fully crystalline diamond (CVD diamond).

B&W 803 D4

The frequency range of human hearing is generally between 16 and 20 kHz, and sound above 20 kHz is ultrasonic and cannot be heard by the human ear. However, as a sound playback device, its frequency response range should be greater than the actual auditory range. This is because sound is composed of low-frequency fundamental notes and high-frequency overtones, where fundamental notes determine melody and high notes determine timbre. As a high fidelity audio system, of course, it needs to reflect a realistic sound effect. Therefore, the richer the frequency of these overtones, the more realistic the timbre becomes. The frequency response of diamond tweeters has reached 60kHz, far beyond the auditory range of the human ear, but it plays a very important role in the integrity of the timbre .

Diamond diaphragm frequency response curve

2. SAW filter

SAW filters are indispensable in modern information devices (such as mobile phones, televisions, network terminals, etc.) and have a huge market capacity. The development of high-frequency SAW devices will greatly promote the development of high-speed and high-capacity communication systems. Sumitomo Electric has developed SAW devices based on silicon-based diamond films, including devices at 2.5 GHz, 3.1 GHz, and 5 GHz. Based on these devices, voltage controlled oscillators (VCSOs), narrowband filters (WCDMA pilot signals, harmonic filters, retiming filters, etc.), broadband filters (intermediate frequency filters and local oscillator devices for local multi-point distribution systems (LMDS) in 76G systems, etc.) can be fabricated.

3. Sound sensor

Acoustic sensors mainly measure changes in resonance response. There should be high sensitivity to changes in mechanical stress, temperature, damping, and mass load. Acoustic sensor applications can be divided into body wave (BAW) devices, surface wave (SAW) devices, and microcantilever beams.

CSMH is committed to the production and research and development of diamond materials, promoting the application of diamond in the field of acoustics. Its core products include diamond wafers, diamond heat sinks, diamond optical windows, diamond heterojunction integrated composite substrates, etc. Its products are applied in diamond resonators, SAW filters, and other fields.