Near-field Recording Research Articles

Nevada Seismological Laboratory Rapid Seismic Monitoring Deployment and Data Availability for the 2020 Mww 6.5 Monte Cristo Range, Nevada, Earthquake Sequence

Abstract The Nevada Seismological Laboratory (NSL) at the University of Nevada, Reno, installed eight temporary seismic stations following the 15 May 2020 Mww 6.5 Monte Cristo Range earthquake. The mainshock and resulting aftershock sequence occurred in an unpopulated and sparsely instrumented region of the Mina deflection in the central Walker Lane, approximately 55 km west of Tonopah, Nevada. The temporary stations supplement NSL’s permanent seismic network, providing azimuthal coverage and near-field recording of the aftershock sequence beginning 1–3 days after the mainshock. We expect the deployment to remain in the field until May 2021. NSL initially attempted to acquire the Monte Cristo Range deployment data in real time via cellular telemetry; however, unreliable cellular coverage forced NSL to convert to microwave telemetry within the first week of the sequence to achieve continuous real-time acquisition. Through 31 August 2020, the temporary deployment has captured near-field records of three aftershocks ML≥5 and 25 ML 4–4.9 events. Here, we present details regarding the Monte Cristo Range deployment, instrumentation, and waveform availability. We combine this information with waveform availability and data access details from NSL’s permanent seismic network and partner regional seismic networks to create a comprehensive summary of Monte Cristo Range sequence data. NSL’s Monte Cristo Range temporary and permanent station waveform data are available in near-real time via the Incorporated Research Institutions for Seismology Data Management Center. Derived earthquake products, including NSL’s earthquake catalog and phase picks, are available via the Advanced National Seismic System Comprehensive Earthquake Catalog. The temporary deployment improved catalog completeness and location quality for the Monte Cristo Range sequence. We expect these data to be useful for continued study of the Monte Cristo Range sequence and constraining crustal and seismogenic properties of the Mina deflection and central Walker Lane.

Round-tower plasmonic optical microfiber tip for nanofocusing with a high field enhancement

A round-tower (RT) plasmonic tip based on an optical microfiber for nanofocusing is proposed. Its operation principle is systematically analyzed by theoretical methods. Four operation regions of the theoretical model of the plasmonic tip are identified for the first time in this study. In addition, the near-field performances of the plasmonic optical microfiber tip are investigated by a finite-element simulation. The results reveal that the field enhancement at the tip apex can be improved by adjusting the slope angle of its surface plasmon polariton region. Remarkably, the proposed RT plasmonic tip can achieve a significantly enhanced field at the tip apex and simultaneously focus the optical spot to a few nanometers. The characteristics of superfocused optical spot and ultrahigh field enhancement are promising for applications in scanning near-field optical microscopy, optical recording, nanolithography, and biosensing.

Head and Media Design for Curvature Reduction in Heat-Assisted Magnetic Recording

Recording curvature in magnetic data-storage technology has long been one of the significant challenges impacting on recording performance. Despite curvature occurrence in the conventional recording techniques such as perpendicular magnetic recording (PMR), heat-assisted magnetic recording (HAMR) is demonstrated to induce much more severe curvature than PMR. HAMR curvature could cause poor bit error rate and limits the maximum areal density capacity. Here we have theoretically predicted and demonstrated various approaches for curvature reduction from the aspect of either altering the near-field transducer head design or recording medium design. Optical and thermal modeling have indicated that by utilizing a crown-shape peg to change the thermal source profile and compensate for thermal expansion and rounding effect, it could potentially improve curvature figure of merit (FOM) and achieve curvature reduction by ~45%. In terms of the recording media design, by altering the heat sink and internal layer media material or geometry, it could also achieve curvature cancellation of ~40% with increased thermal gradient. The combined approach from both HAMR head and media perspectives with balanced recording FOMs, could potentially realize significant curvature reduction to be of similar or better recording curvature level to PMR.

相変化記録材料に対する50 Gbit/inch^2超近接場光記録の検討(光記録及び一般)

相変化記録材料に対する50 Gbit/inch^2超近接場光記録の検討(光記録及び一般)

Design of a microphone array for near-field conferencing applications

Microphone arrays are becoming increasingly popular for conferencing applications and near-field speech recording. In this work, a 16-element cylindrical microphone array is designed for beamforming toward a nearby speaker, while reducing the influence of competing talkers. A two-stage approach is used to obtain the desired array directivity pattern, optimizing both microphone locations and filter weights. The positions of the microphones are optimized by using a hybrid optimization technique, taking into account the influence of the nearby acoustic environment (array shape and conferencing desk). FIR filter coefficients for each microphone are derived from a regularized least-squares (LSQR) solution, combined with null-steering. An implementation of the array is made with digital MEMS microphones and the performance of the design is evaluated experimentally and compared with a classically used goose-neck microphone.

High atrioventricular phase index on near-field intracardiac electrogram is associated with risk of ventricular arrhythmia

The purposes of this study were to characterize and quantify concordance between consecutive atrial and ventricular activation time points through analysis of phases and to explore its association with outcomes in patients with implantable cardioverter-defibrillator (ICD). Patients with structural heart disease and dual-chamber ICDs underwent 5min baseline right ventricular (V) near-field and atrial (A) electrogram (EGM) recording. The cross-dependencies of phase dynamics of the changes in consecutive A (AA′) and V (VV′) were quantified and the AV phase dependency index was determined. In Cox regression analysis, a high AV phase index (in the highest quartile, >0.259) was significantly associated with higher risk of ventricular tachyarrhythmias (HR 2.84; 95% CI 1.05–7.67; P=0.04). In conclusion, in ICD patients with structural heart disease, high sinus AV phase dependency index on EGM is associated with the risk of ventricular arrhythmia.

P54. New electrodes for routine intra-operative dual near-field (DNF) monitoring of the cochlear nerve

Purpose Intraoperative near-field recording of cochlear and brainstem auditory potentials (BAEP) can significantly reduce acquisition time ( Matthies and Samii, 1997 ; Moller et al., 1994 ). Over a period of 15 years we have designed and tested tympanic and brainstem electrodes to monitor the functional integrity of the lower auditory pathway (cochlea, cochlear nerve, brain stem) during surgery in the cerebello-pontine angle (CPA) and the internal auditory canal. Method For routine application, a ball-shaped design has proven to be most advantageous and was developed with a company (inomed Medizintechnik, Emmendingen, Germany). Currently, two stainless steel mini-ball electrodes are employed. One of them is connected to a stainless-steel spring reaching out of an insert earphone and attaches to the tympanic membrane (ECoG, Krieg et al., 2014 ). A second mini-ball electrode with a diameter of 1.6 mm can be placed on the cochlear nerve or at the dorsal cochlear nucleus of the brainstem to record a central auditory brainstem response (CABR). These electrodes were applied in more than 500 patients with lesions in the CPA and internal auditory canal during microsurgery. Near-field potentials have been compared to the far-field auditory brainstem response (ABR, Cz-A1/A2, band-pass 100–3000 Hz). Click stimuli were applied at 13.2 Hz. Data processing was carried out with a commercially available electrophysiological monitoring system (ISIS®, inomed). Results Electrode impedance was consistently lower than 5 kOhm at 1 kHz. Because of its ball shape, the intracranial electrode could easily be placed in the lateral recess of the fourth ventricle (dorsal cochlear nucleus, DCN) and on the cochlear nerve without having to pay attention to a specific contact area on its surface ( Fig. 1 ). If necessary, it was slid out just as easy. Waves I and II of the BAEP were best identified in recordings at the tympanic membrane, wave III to V were largest in recordings with the mini-ball electrodes at the brainstem or on the cochlear nerve. Compared to far-field ABR, amplitudes were 3–4 times larger for ECoG, and 2–20 times larger for CABR in patients with functional hearing ( Fig. 2 ). CABR was more variable than the ECoG, depending mostly on electrode location relative to the brainstem generators. With optimal placement of the electrodes, reliable BAEP averages were obtained within 40 s in far-field, and within less than 10 s in near-field recordings. Conclusions Electrodes developed for near-field recording on both ends of the cochlear nerve allow for an almost instantaneous feedback on the integrity of hearing. Dual near-field (DNF) recording is significantly superior to standard auditory far-field monitoring.

The roar of Yasur: Handheld audio recorder monitoring of Vanuatu volcanic vent activity

We describe how near-field audio recording using a pocket digital sound recorder can usefully document volcanic activity, demonstrating the approach at Yasur, Vanuatu in May 2014. Prominent emissions peak at 263Hz, interpreted as an organ-pipe mode. High-pass filtering was found to usefully discriminate volcano vent noise from wind noise, and autocorrelation of the high pass acoustic power reveals a prominent peak in exhalation intervals of ~2.5, 4 and 8s, with a number of larger explosive events at ~200s intervals. We suggest that this compact and inexpensive audio instrumentation can usefully supplement other field monitoring such as seismic or infrasound. A simple estimate of acoustic power interpreted with a dipole jet noise model yielded vent velocities too low to be compatible with pyroclast emission, suggesting difficulties with this approach at audio frequencies (perhaps due to acoustic absorption by volcanic gases).

Dynamic Head-Disk Interface Modeling and Adaptive Control of a Hybrid Actuator for Optical Data Storage Systems

In the near-field recording (NFR) system, the gap between the lens and disk will drop down to 100 nm. However, the disk vibration and force disturbance make it difficult to maintain the desired flying height during disk operation, and the lens-disk collision can easily occur. It is proposed in this article to design a hybrid actuator system which combines both advantages of the flying slider used in hard disk drives and the voice coil actuator used in optical disk drives. The dynamic head-disk interface model of the hybrid actuator is first developed, then an adaptive regulation approach is proposed to control the flying height at its desired value despite the unknown disturbances. Simulation and experimental results are presented to illustrate the effectiveness of the proposed flying height control approach.

Recording characteristics of high-density thin optical disk using near-field optical recording

We report on the recording characteristics of a near-field optical recording thin optical disk (NFR-TOD). We proposed a new cooling-less-type write strategy for recording, applied it to the NFR-TOD experimental system, and also applied a partial response maximum likelihood (PRML) signal processing, which was evaluated and optimized the PR coefficient for playback signals of the prototype NFR-TOD. The NFR-TOD has a track pitch of 160 nm and improved recording characteristics. The experimental results of the prototype NFR-TOD and the system indicate sufficiently low bit error rates (bERs) for recorded data at a fourfold higher recording density than the current Blu-ray disk.

Current Status and Future Prospects of Conventional Recording Technologies for Mass Storage Applications

The global digital data has increased at an unprecedented rate during the last decade due to the digitization service of every industry as well as the rapid development of information technology. It is therefore timely to enhance the areal density of the mainstream storage devices in order to meet the current storage demand. In this paper, the development history of three major families of storage devices that consist of magnetic hard disk, magnetic tape, and optical disc has been reviewed associated with their respective strength and weakness when utilized for mass storage applications. Several emerging technologies that are likely to expand the areal density of the conventional recording forms beyond the physical limits are subsequently discussed in each case. The perspectives of these three devices used as next generation data storage memory are also compared with each other in terms of the areal density roadmap. According to the comparison, hard disk that is dominating the current mass storage market will still be the favorite candidate for next-generation storage device due to its ultra-high capacity and low cost, particularly with the help of several advanced technologies such as heat assisted magnetic recording and bit patterned media. In spite of much lower capacity than hard disk today, magnetic tape has exhibited an ample margin for booming the storage capacity, and its high stability and flexible removability render it a promising contender for data backup application. The prospect of optical disc seems to be somewhat pessimistic because of the rather slow progress on its capacity and the fairly high cost per GB. It is likely that optical disc will be superseded by the mass storage devices provided that no more innovative technologies than near-field recording and holographic storage emerge in the future. However, the potential merits of optical disc like long life time and portability may offer optical disc a new application that stores important data securely for long term such as official document and government legislation. Keywords: Areal density, magnetic hard disk, mass storage, memory, optical disc, tape.

Near-field recording on phase-change nanoparticles and reflective reproduction from nanoantenna utilizing plasmonic resonance for high-density optical memory

For high-density optical memory system, near-field recording on a medium with phase-change nanoparticles and dual metal layers was proposed. A finite difference time domain (FDTD) analysis demonstrated that a combination of a nanoantenna with such a medium so as to enhance plasmonic resonance would enable effective recording with larger (~10 times) working distance (WD) than for a conventional medium. A reproduction method of detecting the intensity of the reflected wave from the nanoantenna was also proposed in the same setup as the recording. We found that plasmonic resonance induced in the nanoantenna was enhanced and the intensity of reflected light was also increased when the phase state of nanoparticle was crystalline. Since the sub-diffraction limited size of nanoantenna is larger than a nanoparticle, the detected signal intensity can be greatly improved. Calculated results showed that our proposed system and methods for recording and reproduction would have a potential to become effective solutions for terabyte-class optical memory system.

Near-Field Optical Recording Using Solid Immersion Lens for High-Density Flexible Optical Disks

We propose a near-field optical recording flexible optical disk (NFR-FOD) for high-density recording at a high data transfer rate. We built a prototype high-density NFR-FOD that had a track pitch of 0.16 µm and we stacked some recording layers on a thin substrate that was 0.1 mm thick. We rotated the NFR-FOD closing the mechanical stabilizer on a drive system with less than 10 µmp–p axial run-out and achieved precise gap servo operation at a high rotational speed. We demonstrated near-field optical recording with a solid immersion lens with a numerical aperture (NA) of 1.84 on the NFR-FOD. The NFR-FOD has a fourfold higher recording density than the current Blu-ray disc, corresponding to a capacity of 100 Gbytes per layer, and a high data transfer rate of 250 Mbps, while rotating at half the speed.

Adaptive Regulation of Tracking Servo for Next Generation Optical Data Storage Systems

The tracking servo control has played an important role in the data storage servo systems. In the next generation optical data storage systems, i.e. the near-field recording system, the tracking error of the servo system should be below 10 nanometers under various unknown situations. However, higher data transfer rate and higher data density make it difficult to maintain the desired tracking precision during normal disk operation. It is proposed in this paper to use an adaptive regulation approach to maintain the tracking error below its desired value, despite unknown track eccentricity and external force disturbance. The performance of the proposed control approach is analyzed and simulation results are presented to illustrate the capability of the proposed adaptive regulator to achieve and maintain the desired tracking precision.

Efficient excitation of a monopole optical transducer for near-field recording

An optical near-field transducer composed of a rectangular patch and a protruded peg has been numerically studied for heat-assisted magnetic recording. This transducer strongly interacts with a planar solid immersion focusing field and efficiently couples optical energy into a recording medium in a region determined by the peg cross-section. The transducer is excited through the electric field predominantly normal to its edges. The optimal size of the rectangular patch is found to be a half-wave optical antenna in height and between half-wave and full-wave in width.

High-Speed and Precise Gap Servo System for Near-Field Optical Recording

We propose a high-speed and precise gap servo control system that is based on the feed-forward control method that can reduce the harmonic disturbance (RHD-FFC) on a near-field optical recording system with a solid immersion lens. An optical disk of 1.2 mm thickness rotates with about 30 µmp–p of axial run-out. The axial run-out prevents a gap servo from performing precisely at high rotational speed. The RHD-FFC method can suppress harmonic disturbances of gap error signal and can perform at high speed while keeping less than 25 nm of gap length between an optical head and a rotational disk surface. We confirmed that the gap servo applying the RHD-FFC method performed precisely and achieved at high disk rotational speed of 11000 rpm with a 1.2-mm-thick optical disk with a track pitch of 0.16 µm, corresponding to a data capacity of 100 Gbyte.

High-Speed and Precise Gap Servo System for Near-Field Optical Recording

We propose a high-speed and precise gap servo control system that is based on the feed-forward control method that can reduce the harmonic disturbance (RHD-FFC) on a near-field optical recording system with a solid immersion lens. An optical disk of 1.2 mm thickness rotates with about 30 µmp–p of axial run-out. The axial run-out prevents a gap servo from performing precisely at high rotational speed. The RHD-FFC method can suppress harmonic disturbances of gap error signal and can perform at high speed while keeping less than 25 nm of gap length between an optical head and a rotational disk surface. We confirmed that the gap servo applying the RHD-FFC method performed precisely and achieved at high disk rotational speed of 11000 rpm with a 1.2-mm-thick optical disk with a track pitch of 0.16 µm, corresponding to a data capacity of 100 Gbyte.

Application of Solid Immersion Lens-Based Near-Field Recording Technology to High-Speed Plasmonic Nanolithography

In this paper, we proposed a high-speed and high-throughput plasmonic nanolithography technique that uses a fabricated sharp-ridged nanoaperture on a solid immersion lens (SIL) and a precise active nanogap control algorithm. This plasmonic lithography with high throughput can make an optical spot with a diameter of the order of 10 nm and can perform nanopatterning at sub-m/s speed. An optical high-throughput head was designed on a metallic aluminum aperture by optimizing the geometric parameters of a sharp-ridged antenna on the basis of the optical intensity and spot size. Using the evanescent field generated from the SIL, the plasmonic SIL could be maintained below 20 nm above a photoresist-coated Si-wafer and could move at a speed of greater than 200 mm/s without friction; the patterning of lines could be performed under this condition. We achieved patterning with a line width (full-width at half-magnitude, FWHM) of 130 nm.

Application of Solid Immersion Lens-Based Near-Field Recording Technology to High-Speed Plasmonic Nanolithography

Application of Solid Immersion Lens-Based Near-Field Recording Technology to High-Speed Plasmonic Nanolithography

Near-field optical recording with nanocomposite cover-layer for numerical aperture of 1.85

Near-field optical recording media with a nanocomposite cover-layer were prepared and tested using a gap servo, near-field recording system with an effective numerical aperture of 1.85. The refractive index of the nanocomposite cover-layer, which has a smooth surface, is 1.86, yielding a successful gap servo operation. However, the recording density cannot be maximized due to the refractive index of the cover-layer being lower than the required value for the effective numerical aperture. A recording density of 95 GB per disc can be achieved with a nanocomposite cover-layer having a refractive index of 1.86. The readout signal from 110 GB is not clear due to the reduced eventual numerical aperture in conjunction with the limited refractive index of the cover-layer.