We present a graphene-based wideband microphone and a related ultrasonic radio that can be used for wireless communication. It is shown that graphene-based acoustic transmitters and receivers have a wide bandwidth, from the audible region (20∼20 kHz) to the ultrasonic region (20 kHz to at least 0.5 MHz). Using the graphene-based components, we demonstrate efficient high-fidelity information transmission using an ultrasonic band centered at 0.3 MHz. The graphene-based microphone is also shown to be capable of directly receiving ultrasound signals generated by bats in the field, and the ultrasonic radio, coupled to electromagnetic (EM) radio, is shown to function as a high-accuracy rangefinder. The ultrasonic radio could serve as a useful addition to wireless communication technology where the propagation of EM waves is difficult.odern wireless communication is based on generating and receiving electromagnetic (EM) waves that span a wide frequency range, from hertz to terahertz, providing abundant band resources and high data transfer rates. There are drawbacks to EM communication, though, including high extinction coefficient for electrically conductive materials and antenna size. However, animals have effectively used acoustic waves for shortrange communication for millions of years. Acoustic wave-based communication, while embodying reduced band resources, can overcome some of the EM difficulties and complement existing wireless technologies. For example, acoustic waves propagate well in conductive materials, and have thus been explored for underwater communication by submarines (1, 2). Marine mammals such as whales and dolphins are known to communicate effectively via acoustic waves. In land-based acoustic wave communication, the audible band is often occupied by human conversations, whereas the subsonic band can be disturbed by moving vehicles and building construction. The ultrasonic band, though having a wide frequency span and often free of disturbance, is rarely exploited for high data rate communication purposes; one possible reason for this is the lack of wide bandwidth ultrasonic generators and receivers. Conventional piezoelectric-based transducers only operate near their resonance frequencies (3, 4), preventing use in communications where wider bandwidth is essential for embedding information streams.In a conventional acoustic transducer such as a microphone, air pressure variations from a sound wave induce motion of a suspended diaphragm; this motion is in turn converted to an electrical signal via Faraday induction (using a magnet and coil) or capacitively. The areal mass density of the diaphragm sets an upper limit on the frequency response (FR) of the microphone. In the human auditory system, the diaphragm (eardrum) is relatively thick (∼100 μm), limiting flat FR to ∼2 kHz and ultimate detection to ∼20 kHz (5, 6). In bats the eardrums are thinner, allowing them to hear reflected echolocation calls up to ∼200 kHz (7-9). Diaphragms in high-end commercial microphones can be engineered to provide fla...
A perfect impedance match from water-rich hydrogels to an oceanic background makes hydrogel microphones ideal for long-distance, underwater acoustic reception with zero reflection. A novel hydrogel-graphene transistor is thus designed to work under a gate-free mode, in which a sheet of graphene directly converts mechanical vibrations from a microstructured hydrogel into electrical current. This work shows that the quantum capacitance of graphene plays an important role in determining the shift of the Fermi level in graphene and subsequently the amplitude of the current signal. Once employed underwater, this device provides a response to sound waves with high stability, low noise, and high sensitivity in a much-needed low-frequency domain.
When the magnetic spacing in hard disk drives is reduced to sub-3 nm, contact between the slider and disk becomes inevitable. Stability analysis is used in this study to investigate the head-disk interface (HDI) stability of thermal fly-height control (TFC) sliders in light contact with the disk lubricant or solid roughness. We implement an improved DMT model with sub-boundary lubrication into the CML air bearing program and analyze the stability of equilibrium states of a TFC slider under different thermal actuations. It is found that stability is lost when the slider penetrates deeper into the lubricant layer, due to a fast growth in the adhesion force, and it is restored when the solid roughness contact develops. In addition, the critical point for the onset of this instability and the range of this instability region is found to vary with lubricant thickness and protrusion surface steepness, while keeping the air bearing design the same.
Thermal flying-height control (TFC) sliders have been recently used in commercial hard disk drives (HDDs) to increase the HDDs’ capacity. The design of this new class of sliders depends on the numerical prediction of their flying performance, which requires a model for heat flux on the surface of the slider facing the disk. The currently widely used heat flux model is based on a first order slip theory and is believed to lack sufficient accuracy due to its limitation of applicability. This paper implements an improved heat flux model and compares numerical predictions of a TFC slider’s flying performance based on these two models with experiments. It is found that the numerical prediction based on the currently used model has a relative error less than 10% for a state-of-the-art TFC slider. It is suggested that the currently used model might cause large errors for the sliders which do not have a pressure peak near the transducer.
Thermal flying-height control (TFC) is now a key technology used in hard disk drives (HDD) to push the magnetic spacing to sub-5nm. The precise control of the flying height (FH) actuation is a major consideration in improving the read/write capability as well as increasing the reliability. In this paper, we investigate the response of TFC sliders to altitude change with a focus on the actuation efficiency variation with altitude. Numerical and experimental results both indicated an increase in the actuation efficiency at higher altitudes. Simulations are conducted which disclose that increased protrusion and less pushback near the transducer contribute to the efficiency increase at higher altitudes. This study is of practical importance for improving the heater and ABS designs to reduce HDD sliders’ sensitivities to altitude changes.
This letter employs established approaches to calculate the physical properties of the air-helium gas mixtures and investigates the thermal flying-height control slider’s flying performance in these environments. It is found that at a fixed heater power, the slider’s flying height first increases and then decreases with the fraction of helium in the gas mixture due to the combined effects of changes in the mean free path, viscosity, and thermal conductivity of the gas mixture with helium content. These findings, together with the proposed approach, are useful for future designs of sliders in air-helium mixtures.
Filling hard disk drives with air-helium gas mixtures instead of pure helium can balance performance improvement, such as reduced power cost, increased capacity and improved reliability, against manufacturing cost increase. A consistent approach is proposed here to investigate the flying performance of thermal flying height control sliders flying in air-helium gas mixtures. It is found that the smallest power required for a designated flying height appears when the gas mixture is composed of about half helium and half air. The proposed numerical approach can also find application in investigating a slider's flying performance in a humid environment.Index Terms-Flyability, gas mixtures, head-disk interface (HDI), thermal flying-height control (TFC).
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