ON FLEXURAL VIBRATION OF HEMISPHERICAL SHELL

This paper makes detailed analyses tor the flexural vibration (frequency) of the hemispherical shell and presents the varying laws of frequency with the rarving boundary angles and the wall thickness of the above shell, It is an important value to develop the instrument, such as hemispherical resonator gyro (HRG), whose sensing component is a hemispherical shell.

A novel method of water bath heating assisted small ball-end magnetorheological polishing for hemispherical shell resonators

Hemispherical shell resonator(HSR)is the core component of hemispherical resonator gyro.It is aφ-shaped small-bore complex component with minimum curvature radius less than 3 mm.Thus,traditional polishing methods are difficult to polish it.Small ball-end magnetorheological polishing method can polish the small components with complicated three-dimensional surface and obtain non-destructive surface.Therefore,this method is suitable for polishing HSR.However,the material removal rate of the ordinary small ball-end magnetorheological polishing is low,leading to long polishing time and low output of HSR.To solve this problem,a water bath heating assisted small ball-end magnetorheological polishing method is proposed in this research.The influence rule of processing parameters on the material removal rate is studied experimentally.A set of optimal processing parameters is obtained to maximize the material removal rate.Compared with the ordinary method,the material removal rate of the new method can be improved by 143%.Subsequently,an HSR is polished by the new method.The results show that the polishing time can be reduced by 55%,and the polished surface roughness can reach 7.7 nm.The new method has the great potential to be used in actual production to improve the polishing efficiency of HSR.

Numerical Analysis of Material Properties in Deformation of Near Hemispherical Shells

In this paper,the effects of hardening exponent,yield strength and elastic modulus on the deformability of near hemispherical shells are investigated by means of finite element method and orthogonal experiment design.The largest eccentric angle during the deformation process and thickness reduction after the deformation are introduced to estimate the deformability quantitatively according to the deformation characteristics of near hemispherical shells.The results indicate that the hardening exponent is the most influential parameter,followed by elastic modulus and yield strength.The shell exhibits good deformability when the hardening exponent and elastic modulus are in the range of 0.1-0.125 and 70-108 GPa,respectively.

Thermoelastic Dissipation in Diamond Micro Hemispherical Shell Resonators

Maximizing quality factor (Q) is essential to improve the performance of micro hemispherical shell resonators (μHSRs) which can be used in microelectromechanical system (MEMS) gyroscopes to measure angular rotation.Several energy dissipation mechanisms limit Q,where thermoelastic dissipation (TED) is the major one and studied in this paper.Fully coupled thermo-mechanical equations for calculating TED are formulated,and then temperature distribution in a deformed μHSR and its quality factor related to TED (QTED) are obtained by solving the equations through a finite-element method (FEM).It has been found that different fabrication process conditions can obtain various geometrical parameters in our previous studies.In order to provide guidelines for the design and fabrication of μHSRs,the effects of their geometry on resonant frequency (f0) and QTED are studied.The change of anchor height and small enough anchor radius have no effect on both f0 and QTED,but the shell size including its radius,thickness and height has significant impact on f0 and QTED.It is found that whether a μHSR has lower f0 and higher QTED or higher f0 and higher QTED can be achieved by changing these geometrical parameters.The results presented in this paper can also be applied to other similar resonators.

Experimental demonstration of a three-dimensional omnidirectional and broadband acoustic concentrator using an anisotropic metamaterial

We report the theoretical design and experimental demonstration of a three-dimensional(3D)omnidirectional and broadband metamaterial-based concentrator for airborne sound.The proposed mechanism uses a homogeneous anisotropic acoustic metamaterial with an ellipsoidal equifrequency contour to efficiently redirect the acoustic energy impinging on its outer surface into the central region,regardless of the incident direction.A design of the metamaterial unit cell is proposed as a practical implementation of our strategy,which is simply realized by perforating a solid spherical shell with a linearly shrinking cross section in the radial direction.We analytically and numerically prove that the non-resonant anisotropic effective acoustic parameters required for building the concentrator are produced with such a design.Good agreement is observed between the theoretical predictions and experimental measurements.An effective concentration of the incident acoustic energy is observed within a broadband that ranges 1000-1600 Hz.The experimental realization of this 3D acoustic concentrator with a simple design,low energy loss,replaceable constituent material,and omnidirectional and broadband functionality offers new possibilities for acoustic manipulations and may have important applications in a plethora of scenarios ranging from energy harvesting to noise mitigation.