Dunaevskij Zhurchat Ruchji Noti

A simple and practical synthesis of soluble hexa- peri-hexabenzocoronene ( HBC) from readily available hexaphenylbenzene ( HPB) is described. In this simple procedure, the substitution of the free para positions of the propeller-shaped HPB with tert-butyl groups and the oxidative cyclodehydrogenation to planar HBC is achieved in a one-pot reaction using ferric chloride both as a Lewis acid catalyst and as an oxidant in excellent yields. The ready availability of HBC allows the isolation of its pure cation-radical salt using a variety of chemical oxidants such as antimony pentachloride and triethyloxonium and nitrosonium hexachloroantimonate salts.

I am looking for a circuit diagram for a high power ultrasonic amplifier.Needs to drive an underwater transducer rated at 50 watts.Currently using a single HexFet driving a 1:25 toroid to 1000vpp, but I need to increase the duty cycle past 1% for more output power. A piezo transducer behaves somewhat as a capacitor. As your driver transistor allows only a single polarity intermittent current to flow in the transducer (with or without D1) there is no oscillation as would be required for an ultrasonic output. The transducer's capacitance simply charges up to about the supply voltage. Ultrasonic transducer driver amplifier circuit. When connect ultrasonic transducer amplifiers in parallel, a small resistor in series is needed to isolated the driver amps from one other. It is recommended to use 0.3Ω to 1.0Ω series resistance. Use larger resistance for higher output voltage. 40Khz Ultrasound Transducer Driver uses Medium Power - This crystal controlled circuit drives a 40KHz piezo transducer with a 30v peak to peak signal... Hobby Circuit designed by David Johnson P.E.-January, 2006. A Cheap Ultrasonic Range Finder - Do you need to add a distance sensor to your embedded project? Build this simple ultrasonic.

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Graphene is an optical material of unusual characteristics because of its linearly dispersive conduction and valence bands and the strong interband transitions. It allows broadband light-matter interactions with ultrafast responses and can be readily pasted to surfaces of functional structures for photonic and optoelectronic applications. Recently, graphene-based optical modulators have been demonstrated with electrical tuning of the Fermi level of graphene. Their operation bandwidth, however, was limited to about 1 GHz by the response of the driving electrical circuit. Clearly, this can be improved by an all-optical approach. Here, we show that a graphene-clad microfiber all-optical modulator can achieve a modulation depth of 38% and a response time of ∼2.2 ps, limited only by the intrinsic carrier relaxation time of graphene. This modulator is compatible with current high-speed fiber-optic communication networks and may open the door to meet future demand of ultrafast optical signal processing.

Graphene is known to exhibit a variety of exceptional electronic and photonic properties. Because of its unique electronic structure, a graphene monolayer can have a constant absorption coefficient of 2.3% over a wide spectral range from the visible to the infrared with the low-frequency part tunable by external fields (e.g., electrical-bias tuning of the Fermi level or optical excitation of carriers leading to Pauli blocking of part of the interband transitions). The relaxation time of the photoexcited carriers is only a few picoseconds, dominated by electron–phonon interactions and cooling of hot phonons.

Compared to many other materials for ultrafast optics, graphene has the unique merit of possessing exceptionally high nonlinearity over a broad spectral range with ultrafast response. Being atomically thin, it is also highly flexible to be incorporated into other photonic structures. Recently, by electrically tuning the Fermi level of a graphene film, pasted onto a planar waveguide to modify the interband transitions of graphene, Liu et al. Have successfully demonstrated a high-speed graphene-based optical modulator. The modulation bandwidth was however limited to ∼1 GHz by the response time of the bias circuit. For future optical data processing, a modulation rate larger than 100 GHz is needed. Obviously, the “electrical bottleneck” on the modulation rate can be circumvented by an all-optical scheme but to date graphene-based ultrafast all-optical modulation (e.g., bandwidth >100 GHz) has not yet been reported.

Here, taking the advantage of the mature platform of fiber optics, we report a graphene-clad microfiber (GCM) all-optical modulator at ∼1.5 μm (the C-band of optical communication) with a response time of ∼2.2 ps (corresponding to a calculated bandwidth of ∼200 GHz for Gaussian pulses with a time-bandwidth product of 0.44) limited only by the intrinsic graphene response time. The modulation comes from the enhanced light-graphene interaction due to optical field confined to the wave guiding microfiber and can reach a modulation depth of 38%. Our GCM all-optical modulator is illustrated in Figure a. A thin layer of graphene is wrapped around a single-mode microfiber, which is a section with the ends tapered down from a standard telecom optical fiber.

Previously, GCM structures have been reported for fiber-based mode-locking lasers and 1 MHz optical modulators in which the diameter of the microfiber is around 10 μm. Here, we employ subwavelength-diameter (e.g., around 1 μm diameter for C-band of optical communication) microfiber for single-mode operation.