Juho Rysti

Quasiparticle damping of surface waves in superfluid He-3 and He-4

Oscillations on free surfaces of superfluids at the inviscid limit are damped by quasiparticle scattering. We study this effect in both superfluid

Quartz Tuning Forks and Acoustic Phenomena: Application to Superfluid Helium

^{3}\mathrm{He}

Acoustic resonator providing fixed points of temperature between 0.1 and 2 K

and superfluid

Mode analysis for a quartz tuning fork coupled to acoustic resonances of fluid in a cylindrical cavity

^{4}\mathrm{He}

Melting pressure of saturated helium mixture at temperatures between 10 mK and 0.5 K

, deep below the respective critical temperatures. Surface oscillators offer several benefits over immersed mechanical oscillators traditionally used for similar purposes. Damping is modeled as specular scattering of ballistic quasiparticles from the moving free surface. The model is in reasonable agreement with our measurements for superfluid

Pressure dependent attenuation peaks for quartz tuning forks in superfluid 4He at mK temperatures

^{4}\mathrm{He}

Acoustic Resonances in Helium Fluids Excited by Quartz Tuning Forks

but significant deviation is found for

Effective3He interactions in dilute3He-4He mixtures

^{3}\mathrm{He}

Studies on Helium Liquids by Vibrating Wires and Quartz Tuning Forks

.

Excitation and Detection of Surface Waves on Normal and Superfluid 3 He

Immersed mechanical resonators are well suited for probing the properties of fluids, since the surrounding environment influences the resonant characteristics of such oscillators in several ways. Quartz tuning forks have gained much popularity in recent years as the resonators of choice for studies of liquid helium. They have many superior properties when compared to other oscillating bodies conventionally used for this purpose, such as vibrating wires. However, the intricate geometry of a tuning fork represents a challenge for analyzing their behavior in a fluid environment—analytical approaches do not carry very far. In this article the characteristics of immersed quartz tuning fork resonators are studied by numerical simulations. We account for the compressibility of the medium, that is acoustic phenomena, and neglect viscosity, with the aim to realistically model the oscillator response in superfluid helium. The significance of different tuning fork shapes is studied. Acoustic emission in infinite medium and acoustic resonances in confined volumes are investigated. The results can aid in choosing a quartz tuning fork with suitable properties for experiments, as well as interpreting measured data.