This work validates a method for increasing the radial restoring force on the voice coil in audio speakers containing ferrofluid. In addition, a study is made of factors influencing splash loss of the ferrofluid due to shock. Ferrohydrodynamic analysis is employed throughout to model behavior, and predictions are compared to experimental data.

SUMMARYThis paper proposes a novel evaluation method for dielectric characteristics of ceramic substrates made of high-permittivity material, (Ba, Sr)TiO 3 (BST), in the microwave region. The dielectric characteristics are obtained accurately and simply by measuring S-parameter and by full-wave analysis for coplanar waveguide (CPW) composed on the substrate. Only the measurement of S 21 response of the CPW is required for evaluation. The effective permittivity (ε eff ) and attenuation constant (α) are calculated from the S 21 data. Relative permittivity (ε r ) and tanδ of substrate material are estimated by relating the ε eff and α quantitatively with their simulated values calculated by the Extended Spectral Domain Approach (ESDA) taking the thickness effect of the conductor into consideration. Three kinds of BST substrates with different Ba to Sr ratios were measured as test samples. The estimated ε r 's of Ba 0.3 Sr 0.7 TiO 3 , Ba 0.5 Sr 0.5 TiO 3 , and Ba 0.7 Sr 0.3 TiO 3 were 662, 1650, and 4450, respectively. These ε r 's decrease slightly as the frequency increases. The estimated errors for the ε r 's are estimated to be less than 0.3%. This method is useful for the evaluation even of a small variation of dielectric constant in high-permittivity materials.

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The positioning accuracy of magnetic heads need to be improved to increase the recording capacity of hard disk drives. In our previous study, the experimental results confirmed that the head positioning error could be decreased by attaching linear protrusions on the leading edge of the carriage arms. However, the mechanism underlying the phenomenon has not been elucidated. In the current research, we evaluated the effect of leading-edge protrusions on the flow-induced carriage excitation force using the finite element (FE) method analysis and the Hilbert-Huang transform (HHT). We prepared two carriage-arm FE models, with and without linear protrusions, on the leading edges of the arm, and performed the FE analyses. Subsequently, we conducted a frequency analysis by applying the HHT to the simulated torque-disturbance time series of each FE model and the results were later compared. Our results show that the leading-edge protrusions were found to decrease the mean velocity between the arm and the disk, thereby decreasing the vorticity fluctuation in the arm hole, and to decrease the fluctuations in pressure on the outer sidewall of the carriage arm around the coil support.