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.
Pressure Fluctuations and Flow-Induced Vibration Measurements in a Hard Disk Drive under Different Rotation Speeds
Flow-induced vibration (FIV) of a head gimbals assembly (HGA) in hard disk drives (HDDs) limits the positioning accuracy of magnetic head in the HGA for higher HDD magnetic recording density. The pressure fluctuations characterize turbulent fluctuations exciting the HGA off-track vibration (HGA-OTV). In this paper, experimental studies have been carried out to investigate the spectrum characteristics correspondence between pressure fluctuations around an HGA and the simultaneous HGA-OTV under different HDD rotation speeds. A practical and effective experimental setup has been implemented to enable the simultaneous measurements on both the pressure fluctuation and HGA-OTV signals, where pressure fluctuations are measured with a pressure transducer through a small hole on the HDD top cover and the direct HGA-OTV signals are detected through a laser Doppler vibrometer. Results under conditions of three different HDD rotation speeds of 7200, 9000, 10800 rpm have been investigated and compared. It is shown that the HGA off-track vibration spectra are highly associated with those of the pressure fluctuations in terms of principal peaks in four frequency bands around 1.8 kHz, 2.5-3.5 kHz, 7-7.5 kHz and 11.5-12.5 kHz. With increasing HDD rotation speed, it is shown that the spectrum magnitudes of both the pressure fluctuation and the HGA off-track vibration increase correspondingly, while the principal peak positions in spectra of either pressure fluctuation or the HGA off-track vibration always hold the line. This study demonstrates a causal nexus from the pressure fluctuation to the HGA off-track vibration and suggests the feasibility of controlling the HGA-OTV through suppression of pressure fluctuations around the HGA.
Microwave source with enhanced radiation power based on orbitron MASERs
We have proposed the design of high power microwave source in a vacuum tube based on the theory of negative mass instability. The proposed source does not operate based on a slow-wave structure but instead makes use of accelerated charged particles. In our structure, an electron emitter injects the charged particles into to the cavity. Emitted particles move around the anode, which leads to electron acceleration and emission of electromagnetic waves with a specific frequency. In this paper, we have enhanced the output power and frequency of microwave source by variation of particles initial energy and the number of anodes incorporating their specific arrangement and applied voltages. Working at room temperature, compactness, wide bandwidth, and tunability of output frequency are among the advantages of the proposed source.