HDD Micro-actuator Reliability Study

In vacuum devices such as vacuum interrupters (VIs), surface flashover events are one of the obstacles for developing their higher performance. It is believed that such a surface flashover in vacuum has a close relationship with a charging phenomenon on the insulator surface. Therefore, it is important to grasp the charging characteristics on the inner surface of the VI. In this study, we have measured the charge distribution characteristics inside a cylindrical type insulator employed as a model insulator of VI after the AC voltage (50 Hz) application. This cylindrical insulator has shield rings to relax the electric field at triple junction at both ends of the insulator. We investigate the charging characteristics for samples having different gaps between the shield and insulator. As a result, in the case of first AC voltage application to each sample, the vacuum side of the cylindrical insulators were charged to a certain value. As repeating the AC voltage application several times, the amount of electric charge on the insulator surface was gradually reduced in each sample. However the reduction rate of the sample with the narrow clearance is larger than wide one. In addition, the sample with the wide clearance was charged on a larger surface area than that of the narrow clearance.

Effect of AC electric fields on the stabilization of premixed bunsen flames

An accelerated life test (ALT) is often well planned to yield the most statistical information given limited test resources. Nevertheless, ALT planning requires rough estimates of the model parameters as an input, called planning values. The discrepancy between the planning values and the true values may result in insufficient or even no failures at the low-stress level, making the subsequent data analysis difficult. Motivated by the need in the ALTs of data acquisition devices used in smart grids, an adaptive ALT scheme is proposed. The key idea is based on the observation that, when the product reliability is underestimated during the ALT design phase, it is unlikely to observe failures at the early stage of the test. Therefore, the low-stress level should be elevated to protect against insufficient failures. Under this adaptive ALT framework, order statistics techniques are used to derive the likelihood function by assuming a general log-location-scale distribution for the product lifetime. Confidence intervals for the parameters are constructed based on the large-sample approximation as well as the accelerated bootstrap method. A simulation study is conducted to demonstrate the advantages of the adaptive ALT compared with the simple constant-stress ALT. Its application is illustrated using the motivating example from smart grids.

We review a new experimental implementation of Kelvin probe force microscopy (KPFM) in which the dissipation signal of frequency modulation atomic force microscopy (FM-AFM) is used for dc bias voltage feedback (D-KPFM). The dissipation arises from an oscillating electrostatic force that is coherent with the tip oscillation, which is caused by applying the ac voltage between the tip and sample. The magnitude of the externally induced dissipation is found to be proportional to the effective dc bias voltage, which is the difference between the applied dc voltage and the contact potential difference. Two different implementations of D-KPFM are presented. In the first implementation, the frequency of the applied ac voltage, \(f_\mathrm {el}\), is chosen to be the same as the tip oscillation (\(f_\mathrm {el} = f_\mathrm {m}\): \(1\omega \)D-KPFM). In the second one, the ac voltage frequency, \(f_\mathrm {el}\), is chosen to be twice the tip oscillation frequency (\(f_\mathrm {el}= 2 f_\mathrm {m}\): \(2\omega \)D-KPFM). In \(1\omega \)D-KPFM, the dissipation is proportional to the electrostatic force, which enables the use of a small ac voltage amplitude even down to \({\approx }10\) mV. In \(2\omega \)D-KPFM, the dissipation is proportional to the electrostatic force gradient, which results in the same potential contrast as that obtained by FM-KPFM. D-KPFM features a simple implementation with no lock-in amplifier and faster scanning as it requires no low frequency modulation. The use of a small ac voltage amplitude in \(1\omega \)D-KPFM is of great importance in characterizing of technically relevant materials in which their electrical properties can be disturbed by the applied electric field. \(2\omega \)D-KPFM is useful when more accurate potential measurement is required. The operations in \(1\omega \) and \(2\omega \)D-KPFM can be switched easily to take advantage of both features at the same location on a sample.

The paper describes an investigation into aging of medium voltage mica-based groundwall insulation when subjected to high frequency AC and steep-front pulse voltages. The test conditions adopted in this study involve 60 Hz, 3 kHz and 4 kHz AC frequencies, nanosecond rise time pulses with repetition rates up to 2000 pps, and at temperatures of 20 and 155 /spl deg/C. The experimental data of time-to-failure in the accelerated life tests are presented by Weibull distributions. The parameters of the life model are developed that link the failure time to the amplitude and temperature of the applied voltages. The test method and the data processing adopted in this study are useful to characterize groundwall insulation in terms of improved vacuum pressure impregnation (VPI) and for applications at higher temperatures and frequencies.

We present a detailed study of the optoelectronic mixing effect in metal–semiconductor–metal detectors. Both analytical and numerical results are presented and the anisotropic effect is included in the calculations. Under transient bias voltage, the device shows two transient current responses: a fast one related to the displacement current and a slow one related to removal of carriers from the device. The mixing efficiency of the device increases with an increase in applied ac voltage and decreases with an increase in ac frequency. For anisotropic devices, rectification current exists. This rectification current varies not only with the ac voltage and optical power, but also with the ac frequency. This variation in current results in a self-clutter signal being observed in the experiments.

For increasing areal density in hard disk drives (HDDs), the physical clearance between the read/write element and the surface of the disk has been continuously decreasing to 1 nm or below [1]. At such a low clearance, the contact between the head and the disk is inevitable to occur, so head wear is becoming a critical issue in the development of HDD. The contact between the head and the disk induces a frictional heating, which may generate an additional thermal protrusion in the contact area of the head, and causes more wear. On the other hand, the target clearance in a HDD is generally determined by pulling back a setting TFC power from the touchdown point, accurately identifying the touchdown point is very significant for the clearance control in hard disk drive. A thermal protrusion is caused by friction-heating in the status of touchdown. Therefore, it is very necessary to quantitatively understand on friction induced thermal protrusion and clearance loss.

In this paper, the air purification effect of positively and negatively charged ions generated by discharge plasma at atmospheric pressure is reported. We have developed a novel ion generation device which consists of a cylindrical glass tube and attached inner and outer mesh electrodes. With the application of AC voltage between the electrodes, positively charged ions and negatively charged ions have been generated at atmospheric pressure. The ion densities of 3.0×104–7.0×104 counts/cm3 have been obtained with the AC voltage of 1.8–2.3 kV (effective value). We have examined the air purification properties of this device. By the operation of this device, the initial oxygen nitride (NO) density of 10 ppm in 1 m3 (in cigarette smoke) was decreased to 1 ppm after 30 min. The number of suspended germs in air has been significantly reduced by the use of this type of ion generation device.

Increasing requirements on computational speed and graphically virtual reality for game console are pushing the processor units toward the denser the routing layout and the higher the output wattage. The thermal interconnect of Power supply-Fan-Heat sink-Thermal Interface Material-Processor Unit is the key element in the effectiveness of the thermal reliability system. In this study the thermal performance of the cooling fan is assessed through the measurement of volumetric airflow rate and pressure drop and then used as targets for statistic process control and management. Thermal degradation of the Thermal Interface Material (TIM) due to pump out is studied by measuring the junction to heatsink thermal resistance while the interconnect system is under thermal aging. The end seal integrity of integrated Heatsink and heatpipe heatpipe (IHSHP) is verified by checking the Lead-free SnBi Solder bond leakage and loss of thermal conductivity due to factors such as thermal stress and fin surface contamination and corrosion. Accelerated life testing is conducted on all devices with multiple stress conditions in order to derive acceleration factor (AF) and life prediction to the user environment for each individual device. For system life prediction, the governing parameters of distribution model and life & stress relationship are derived in the process first. Then, the reliability integration of the whole thermal system will be conducted by using Reliability Block Diagram (RBD) to derive the life of the thermal system. Finally reliability allocation and device quality improvement are rationalized by considering the technical feasibility and cost structure in the near future. On the Ongoing Reliability Test (ORT) basis, the derived AF and one of the stress conditions are used in the ALT to ensure the life and fundamental mechanism of the device is maintained under the management of quality control chart and statistic run rule. A methodology is derived to correlate field failure data to the distribution of DVT to improve the accuracy of the life prediction model.

The performance of spindle motor system is crucial to that of the hard disk drive (HDD). The spindle motor system faces tremendous challenges as the HDD industry keeps pushing up magnetic recording areal density. This paper analyzes several attributes of the spindle motor system which affect the recording density of the hard disk drive. Some of the attributes have not been highlighted and studied before. The present analysis shows that the performance of spindle motor system can be improved through the integration of optimal electromagnetic design, mechanical system enhancement and advanced power drive to meet the requirements of the next-generation hard disk drive with ultrahigh areal density.

SummaryThis article presents an electrically tunable dual‐beam ⵣ‐shaped microstrip leaky wave antenna (MLWA) based on liquid crystal (LC). A new ⵣ‐shaped microstrip component (Berber's alphabet: pronounced |z|) is proposed as a single unit‐cell to achieve a dual‐beam radiation pattern with adjustable dual‐beam angles controlled by the ⵣ‐shaped length‐to‐width ratio. The dual‐beam radiation pattern of ⵣ‐shaped microstrip is theoretically derived. The tunable dual‐beam scanning is achieved using a nematic liquid crystal (N‐LC). An AC voltage controls the permittivity of N‐LC applied on the inverted radiating metal. The orientation angle of the N‐LC molecules is also determined theoretically. Besides, the MLWA is rearranged due to the meandering configuration of its microstrip transmission lines, which reduces the antenna's size. As a result, this antenna has a symmetrical dual‐beam at a pointing angle of ±37° in the YZ‐plane. Furthermore, the proposed MLWA is tuned up to 25° at a fixed frequency in XZ‐plane directions by applied AC voltage from 0 to 20 V, which changes the permittivity of the N‐LC from 2.47 to 3.25, respectively. Meanwhile, the MLWA has a realized gain of up to 7.5 dB and a beam scanning range of 40° in the XZ‐plane for all operating frequencies. Finally, the proposed antenna can be suitable for satellite and radar communication systems.

This study aims to establish an insulation diagnosis technique using partial discharge (PD) detection for cast resin transformers (CRTr). In the previous paper, the frequency components of PD current in a PD test of a CRTr by applying AC voltage between lumped high voltage and low voltage terminals were identified and analyzed in EMTP using an equivalent circuit model. On the other hand, another PD test is the test with an inductive voltage application in which an AC voltage is applied to the low voltage side of the transformer and then a high voltage is applied between the high voltage terminals in a transformer. This paper presents investigation on dominant frequency of PD current detected with high frequency current transformer (CT) in the inductive PD test of a 6.6 kV cast resin voltage transformer 6.6 kV CRTr-VT. An attempt is also made to identify PD signal source, the signal propagation path of the PD current, as well as the dominant frequency components.

Microphysiological systems (MPSs) have emerged as promising platforms for drug discovery and in vitro pharmacological testing. MPSs aid to reproduce physiologically relevant microenvironments, in which controlled perfusion can play important role. In this study, an on-chip AC electrothermal (ACET) pump was developed for pulsatile perfusion in microfluidic cell culture systems. The proposed pump generates fluid motion through the interaction between an applied electric field and temperature-dependent gradients in the electrical properties of the fluid. Pulsatile perfusion was produced by periodic application of an AC voltage to the electrode array, and the pulsation cycle could be controlled electrically. The maximum flow velocity increased with the applied AC voltage, demonstrating tunable flow generation by the ACET pump. To evaluate the applicability of the developed system to cell culture, human mesenchymal stem cells (hMSCs) were cultured under pulsatile perfusion conditions for five days. The results showed that osteogenic differentiation under pulsatile perfusion was higher than that under static culture conditions. These findings demonstrate the potential of the proposed on-chip ACET pump as a simple and effective platform for generating physiologically relevant pulsatile perfusion in microphysiological systems.

We propose a quantum-mechanical model to calculate the current through a single molecular junction immersed in a solvent and surrounded by a thin shell of bound water under an applied ac voltage. The solvent plus hydration shell are captured by a dielectric continuum model for which the resulting spectral density is determined. Here the dielectric properties, e.g., the Debye relaxation time and the dielectric constant, of the bulk solvent and the hydration shell as well as the shell thickness directly enter. We determine the charge current through the molecular junction under an ac voltage in the sequential tunneling regime where we solve a quantum master equation by a real-time diagrammatic technique. Interestingly, the Fourier components of the charge current show an exponential-like decline when the hydration shell thickness increases. Finally, we apply our findings to binary solvent mixtures with varying volume fractions and find that the current is highly sensitive to both the hydration shell thickness as well as the volume fraction of the solvent mixture, giving rise to possible applications as shell and concentration sensors on the molecular scale.

Thin films of various thicknesses in the MIM structure have been prepared from the the powders of SnO2, Sb2O3 and (SnO2 + Sb2O3) of high purity by the thermal evaporation technique in a vacuum of 10−5 Torr. Dielectric properties of SnO2, Sb2O3, and their mixed thin films have been studied with ac and dc electric fields and frequency. Capacitance and loss tangent are almost independent on dc voltage upto 1.0 V for SnO2, 10.0 V for Sb2O3 and 2.5 V for mixed films. These capacitors become unstable at 1.0 V for SnO2 films and 2.5 V for mixed films. For higher film thicknesses the decay in these films starts at higher voltages. Capacitance and loss tangent increases with applied ac voltage in SnO2, Sb2O3, and their mixed films. A comparison of the capacitance values of SnO2, Sb2O3, and their mixed films showed that the capacitance values are less in Sb2O3 as compared to SnO2 films. In mixed films the capacitance is greater than the constituent films. These studies have shown that Sb2O3 films are found to be more stable compared to SnO2 and their mixed films for ac and dc voltages. The results thus obtained on SnO2, Sb2O3, and their films are presented and discussed.