An investigation of high-frequency bias-induced tape noise

Bias-induced tape noise remains a major limitation of the SNR in audio magnetic tape recording systems. Defined as the increment in system noise incurred when the bias oscillator is turned on, the noise can originate from a number of different causes; namely, bias oscillator harmonic distortion, magnetized heads, the earth's magnetic field, and an intrinsic noise source. The latter noise source is our primary concern here. Such record system parameters as head-to-tape spacing, gap length, bias current, and bias frequency were investigated with regard to their influence on this intrinsic bias noise source. Two models of the mechanism of intrinsic bias noise are examined. The first, the "amplitude modulation model." proposes that bias noise is generated by amplitude modulation of the recorded bias signal by the physical and magnetic variations of the head-tape system. In this model, bias noise is merely the lower AM sidebands of the recorded bias signal. The second model relates bias noise to the interaction fields in erased tape. This model proposes that these fields behave similarly to normal recording fields and can be "re-recorded" on the tape at an enhanced level. The two proposed mechanisms are examined in the light of the experimental data. The amplitude modulation model is shown to agree with all the observed data with the exception of the existence of bias noise at bias wavelengths smaller than the particle size. The second model, which does not incorporate a wavelength dependency of bias noise, is in qualitative agreement with the observed data. Methods are discussed for reducing the bias noise without materially affecting the system performance.     

A magnetic recording tape based on iron particles

Tapes based on acicular iron particles give an outstanding recording performance compared to γ-Fe2O3and CrO2tapes. Especially in the short wavelength region the signal to noise ratio is, respectively, 12 and 7 dB better, whereas the bias noise level is somewhat lower. The iron tapes have a high coercivity, between 80 and90 times 10^{3}A/m, and hence the required bias is about 9 dB higher than for γ-Fe2O3. The print through properties are excellent.     

Recommendation of a simple and universally applicable method for measuring the switching field distribution of magneting recording media

The most common methods for assessing the switching field distribution (SFD) of magnetic recording media are compared for samples of acicular magnetic particles made of different types of magnetic materials and having various degrees of particle orientation. It is shown that the method of using the maximum slopedM/dH = M_{R}/H_{c}(1-S*)atM = 0of the magnetic hysteresis loopM(H)can be used to characterize SFD of the irreversible magnetization processes which correlate to the recording performance. Thus, (1-S*) is recommended as the most easily accessible and universally applicable figure of merit for SFD.     

挤压油膜阻尼器支承的柔性转子的双稳态响应特性

分析了同心型挤压油膜阻尼器的流体惯性力对柔性转子的双稳态响应的影响。研究表明，雷诺数越大（即惯性力的影响越大），则挤压油膜阻尼器的刚度力越小，阻尼力越大，从而导致系统稳态响应的峰值转速降低，且在大多数转速区轴颈的振幅减小。盘心的振幅变化有类似的趋势。流体惯性力对系统在亚临界及超临界的双稳态响应具有明显的抑制作用，随惯性力增大，系统的双稳态响应特性得到改善。     

Visible-infrared spectral response of microcrystalline hydrogenated silicon hetero-junctions

Microcrystalline p–i–n devices with an increased infrared sensitivity infrared sensitivity are prepared by the closed-chamber cyclic technique.The spectral response for different applied bias, the current–voltage characteristics at different wavelengths and the photocurrent delivered by the device are analysed. The spectral response is extended far beyond the amorphous limit of about 750 nm and even at a wavelength of 1000 nm, the response is still at a level of about 5% of the maximum. The good near infrared sensitivity is considered to be a result of the large optical absorption ascribed to the crystalline phase. Under reverse bias, the spectral response is high and essentially unchanged, reflecting a good collection efficiency. Under increasing forward bias, up to values near the open-circuit voltage, it decreases continuously, but even at much higher bias (up to about 0.8 V), the device produces a photocurrent.A heterojunction model based on the growth mechanism of the device and supported by a numerical simulation is presented to explain this behaviour.     

The effect of remanence and coercivity on short wavelength recording

The effect of saturation remanence and coercivity on the short wavelength reproduce signal has been examined. For constant current unbiased sinewave recording on tapes of 4.5μm coating thickness, set to peak on each tape the shortest wavelength (λ=1.2μm), the data can be interpreted in terms of an effective spacing loss with an effective recording depth of 0.6μm or in terms of a loss line evaluation of the major hysteresis loop of the tapes. Within the range of remanence and coercivity under investigation, the reproduce signal can be approximated by MRⁿHc^mwhere n and m are 0.75 and 0.25 at 23.5μm, 0.4 and 0.6 at 5μm, and 0.08 and 0.92 at 1.2μm wavelength respectively, i.e. the influence of coercivity predominates at short wavelengths.     

Breakdown of Zero-Energy Quantum Hall State in Graphene in the Light of Current Fluctuations and Shot Noise

We have investigated the cross-over from Zener tunneling of single charge carriers to avalanche type of bunched electron transport in a suspended graphene Corbino disk in the zeroth Landau level. At low bias, we find a tunneling current that follows the gyrotropic Zener tunneling behavior. At larger bias, we find an avalanche type of transport that sets in at a smaller current the larger the magnetic field is. The low-frequency noise indicates strong bunching of the electrons in the avalanches. On the basis of the measured low-frequency switching noise power, we deduce the characteristic switching rates of the avalanche sequence. The simultaneous microwave shot noise measurement also reveals intrinsic correlations within the avalanche pulses and indicate a decrease in correlations with increasing bias.     

Principles of a three-dimensional recording model for short wavelength magnetic recording

Principles are provided for a method of evaluating the magnetization of a magnetic recording tape element running in front of a recording gap. The distributions of switching fields P(Hc) and magnetization axes P(θ, φ) used in the calculations are derived from simple experimental results. The output level is calculated by means of the reciprocity principle. The first application of the method concerns certain phenomenological aspects of magnetic recording. As a practical example, a qualitative explanation of the output level curve versus the recording current for short wavelength signals is given; the advantage of microgaps for recording are demonstrated and finally, the circular Bitter patterns discovered by S. Iwasaki are shown to be predicted by the model. This study is a first step toward a more general solution including the demagnetizing field.     

Relationship of surface roughness of video tape to its magnetic performance

The surface roughness, known to influence the recording and play-back properties of magnetic recording media, was interferometrically measured of a series of VHS video tapes. A strong correlation (r>.95) was found between both the signal outputs and noise of these tapes with rms surface roughness. The measured short waveloength rf output was shown to decrease with increasing surface roughness in a manner consistent with three theoretical models. A multiplier of 2.7 times the interferometrically measured rms surface roughness is equal to the calculated head-to-tape spacing of these tapes.     

SOA-based multi-wavelength source

A simple fiber laser configuration based on a semiconductor optical amplifier (SOA) is proposed for obtaining multi-wavelength oscillation at room temperature, in which a Sagnac loop mirror is used as the wavelength selective component. The SOA has a flat gain of approximately 23dB within a bandwidth of 12 nm at a small input signal power. The loop mirror was constructed using a 3dB coupler and polarization maintaining fiber (PMF). The output spectrum of the proposed laser can be adjusted by controlling the bias current of the SOA and is quite stable at room temperature. At a bias current of 150 mA, six lines are obtained with at least ?40 dBm output power and 25dB signal-to-noise ratio (SNR). The channel spacing and number of lines is determined by the length of polarization maintaining fiber (PMF) used in the loop mirror. The channel spacing of the proposed laser is 1.49 nm with a PMF 3 m. The multi-wavelength comb output can also be tuned by adjusting the operating temperature of the SOA. The multi-wavelength laser has the advantage of a simple configuration, stability at room temperature, a broad wavelength band, and no need for optical pump lasers.     

Laser-induced incandescence: detection issues

Theoretical predictions suggest that soot particle size and local gas temperature affect both the spectral intensity and the temporal evolution of laser-induced incandescence. A discussion of both the physical structure and the theoretical absorption models of soot aggregates is presented, suggesting that the soot particle size relevant to laser-induced incandescence (LII) is the primary particle size regardless of whether the primary particle exists individually or is assembled into an aggregate. Experimental results of LII measurements in a laminar gas-jet flame with different signal collection strategies for the LII are presented. These results suggest that (a) signal integration during the laser pulse is essential for minimizing particle size and local temperature bias in the LII signal, (b) signal integration times subsequent to the laser pulse produce a size and local gas-temperature-dependent bias in the LII signal with long integration times more sensitive to these effects, and (c) long wavelength detection produces less of a size and local gas-temperature-dependent bias than short wavelength detection.     

Simultaneous optical and electrochemical recording of single nanoparticle electrochemistry

Single nanoparticle collisions have become popular for studying the electrochemical activity of single nanoparticles by determining the transient current during stochastic collisions with the electrode surface.However,if only the electrochemical current is measured,it remains challenging to identify and characterize the individual particle that is responsible for a specific current peak in a collision event;this hampers the understanding of the structure-activity relationship.Herein,we report simultaneous optical and electrochemical recording of a single nanoparticle collision;the electrochemical signal corresponds with the activity of a single nanoparticle,and the optical signal reveals the size and location of the same nanoparticle.Consequently,the structure (optical signal)-activity (electrochemical signal) relationship can be elucidated at the single nanopartide level;this has implications for various applications induding batteries,electrocatalysts,and electrochemical sensors.In addition,our previous studies have suggested an optical-to-electrochemical conversion model to independently calculate the electron transfer rate of single nanoparticles from the optical signal.The simultaneous optical and electrochemical recording achieved in the present work enables direct and quantitative validation of the optical-to-electrochemical conversion model.     

Investigation on the Mean Field Assumptions for Switching Field Distribution Measurements

Since the transition of the research focus from longitudual to perpendicular recording system in early 2000, there has been significant progress in understanding and developing metrologies to characterize the switching field distribution (SFD). However, most of the metrologies developed for characterizing SFD have relied on mean field assumptions. In this paper, we investigate the mean field assumptions commonly used in the SFD metrologies. For micromagnetic simulation data without intergranular exchange interactions, we find that the interaction fields are independent of the local environment of the spins, which suggests that the mean field approximation is applicable. Moreover, the dependency between the interaction field and the magnetization is rather linear with and without thermal fluctuations. For the experimental data obtained from a sample with moderate intergranular exchange interactions, we find that the mean field approximation is reasonable in situations with thermal fluctuation. But for the case without thermal fluctuation, such approximation might be called into question.     

An experimental, multilevel, high density disk recording system

Communication technology has been applied to a magnetic disk recording channel to achieve up to a fourfold increase in linear bit density as compared to conventional binary recording. Among the techniques incorporated were digital data transmission by Class IV Partial-Response signaling (Interleaved NRZI), recording channel pre-emphasis, equalization and filtering, and periodic amplitude sampling of the data signal. The magnetic recording channel was linearized using very high frequency a.c. bias, which also served simultaneously to erase old data. This enabled multilevel recording and the addition of a pilot tone for timing recovery. System block diagrams are presented together with a discussion of the optimization procedure and attained system performance.     

Edge luminescence of single-crystal silicon modulated by voltage variation on the p-n junction

The output power and quantum efficiency of the room-temperature quasi-stationary edge photoluminescence (PL) in a single-crystal silicon structure cut from a high-efficiency solar cell have been studied as functions of the power of exciting laser radiation with a wavelength of 658 nm at variable direct current and reverse-bias voltage on the p-n junction. It was found that the direct current passage led to a significant increase in the output power and quantum efficiency of the quasi-stationary PL and a decrease in the threshold power of PL excitation. The application of a reverse bias voltage produced the opposite effects. Possible physical factors responsible for these phenomena are considered.     

Resolution analysis of incoherent triangular holography

We derived the point-spread function (PSF) including the recording and reconstruction systems of the modified triangular interferometer; the modified triangular interferometer forms incoherent holograms without bias and the conjugate image. We also derived and analyzed the resolution of the modified triangular interferometer and compared it with that of the conventional one for amplification factor, wavelength, and hologram size.     

High density recording with write current shaping

A digital magnetic recording system is described that doubles the linear data bit density of an existing head/medium interface. It uses the combination of the following three techniques: an efficient new run-length limited code (3PM), a special kind of ac-bias recording, and pulse slimming by write current shaping. The new code has the inherent potential of increasing linear data density over MFM by 50 percent. This potential can be fully utilized only if the analog waveshape is equalized to optimum spectral shaping. The present paper uses pulse slimming by double step write current shaping to achieve optimum equalization. Write current shaping requires linear operation. This is accomplished by ac-bias recording, assuring symmetrical single pulse shape that allows a large degree of pulse slimming. The parameters of ac-bias recording are chosen so that large signal amplitude is used. This, in conjunction with write current shaping, maximizes signal-to-noise ratio in the read channel, further increasing the bit density. An additional increase is realized by using a low inductance head that yields narrow PW50value. The combination of all these factors results in 8000 BPI density on the original 4000 BPI MFM system.     

Relationships between magnetic tape properties and magnetic oxide concentration

A series of tapes were coated in which the concentration of the magnetic ferric oxide was essentially the sole variable. Magnetic and electroacoustic properties were evaluated as a function of magnetic oxide concentration. The intrinsic coercivity was found to increase slightly with decreasing oxide concentration but not to the extent predicted by the simple packing factor law. Biasing current changed in approximately the same ratio as coercivity. The sensitivity was directly proportional to the remanent flux density but the saturation output was proportional to the remanent flux. The linear range of the recording process increased appreciably with increasing oxide concentration. Frequency response decreased very slightly. Signal-to-noise ratio increased with increasing magnetic oxide concentration. Particle interactions had a strong effect upon the signal-to-print-through ratio. A decrease in magnetic oxide concentration to 50 percent of normal increased this ratio by 4 dB although coercivity was increased only slightly more than 5 percent.     

Wear-resistant magnetic head using amorphous alloy material

An audio recording/playback head using an amorphous (Fe-Co-Ru-Cr) ₇₅(Si-B)₂₅ alloy was developed. Compared with a commercial Sendust head, three excellent features were observed. The wear of the amorphous alloy head when used with γ-Fe₂O ₃ is two-thirds that of the Sendust head. The output level at high-frequency (14 kHz) is 5 dB higher than that of the Sendust head. The bias current for the amorphous alloy head is half that of the Sendust head     

正对电极结构型碳化硅光导开关的制备与性能研究

采用钒掺杂半绝缘6H-SiC衬底,以Ni/Au为接触电极制备了一系列正对电极结构型光导开关,对SiC光导开关进行了不同外加电压、激发光强、激发光波长条件下的测试,着重研究了SiC光导开关的光电吸收效应和光电响应性能.实验结果表明,532 nm的激光激发的脉冲信号宽度远小于1064 nm的激光激发的脉冲信号宽度,半绝缘6H-SiC衬底对532 nm激光的吸收系数在0.601～0.692 mm–1之间;采用532 nm的激光激发光导开关,获得了纳秒量级的响应信号;流经开关的瞬态电流随着外加电压和激发光能量的增加而增大,随着衬底厚度的增加而减小.