Flow-induced vibration of a head gimbal assembly under various conditions
The flow-induced vibration of a head gimbal assembly (HGA), known as windage, is an obstacle to achieving higher track densities in hard disk drives (HDDs). We examine the characteristics of windage in this paper with the goal of enabling the development of smaller-windage HGAs. We used a 14.5-mm-length (from swage hole center to dimple) HGA in our study. The windage was measured by a laser Doppler vibrometer in a spin stand under various conditions, such as different slider radius locations (inner diameter, medium diameter, and outer diameter), disk-rotational speeds, Z heights (distance from arm to disk), and temperatures. With respect to the slider radius location, windage was much greater when the slider was on the outer diameter rather than at other positions. When the slider was positioned at a fixed location, the windage was proportional to the square of the disk rotational speed. At high temperatures, the resonant frequencies decreased and their amplitudes increased. For some resonance modes, there was an optimal Z height. These findings will be useful for evaluating HGAs and optimizing HGAs through experimental design.
Validation of the Finite Element Model and Vibration Characteristic of the Piezoelectric Head Gimbal Assembly
The dual-stage head gimbal assembly of the hard disk drive utilizes the piezoelectric actuator to supplement the voice coil motor for the precision head positioning. Vibration characteristic of the head gimbal assembly system is analyzed by using the finite element method. The modal characteristic of the piezoelectric head gimbal assembly is measured by the laser doppler vibrometer and compared with the finite element result to validate the finite element model. The natural frequencies and vibration mode shapes are determined via the frequency response functions by measuring the system response at the side of the head slider and the top of the load beam. The crucial vibration modes that may cause the off-track positioning of the read/write head are reported. The comparison of natural frequencies and mode shapes show agreement of the finite element model and experiment testing.
New Low-Profile Applicators for Local Heating of Tissues
A new type of low-profile applicator is described giving efficient power transfer to tissue with low leakage. It consists of a resonant element spaced from a ground plane by low-loss material having high relative permittivity and some relative permeability. This combination is covered by similar material which can be placed in direct contact with the tissue to be heated, or separated from it by a water bolus as required. Laboratory measurements using phantom materials show that these applicators are well matched and produce well defined and relatively uniform heating profiles. Applicators having maximum dimensions of 3-15 cm covering the frequency range 1000-100 MHz, respectively, are described. Penetration depths of at least 4 cm at 100-200 MHz are achieved. Tests on anesthetised pigs and some clinical assessment have confirmed the usefulness of this compact low-frequency type of applicator and have shown that performance compares favorably with that of other recently reported types. The design can be optimized for treatment of specific sites, and suitable choice of dimensions and electrical characteristics of the layer material allow the low-profile concept to be extended over a wide range of operating frequencies.