30 results about "Bragg resonance" patented technology

The invention discloses a method for extracting wave height from sea echo first-order Bragg harmonic peak of a high-frequency ground wave radar. The method comprises the steps of building a response curve of the Bragg wave spectrum value based on the wave height; calibrating the first-order peak power of a long-distance unit through the wave length subjected to second-order spectrum inversion and the first-order peak powder in a near distance unit of the radar, so as to calculate the wave height distribution in the long-distance unit. The method is mainly dependent on the unsaturation feature of the Bragg wave; the wave height is extracted from the first-order Bragg resonance peak; the first-order peak under the general ocean state is obviously more than that in the second-order spectrum, so that the wave height detection distance of the high-frequency ground wave radar can be greatly improved; meanwhile, the portable radar adopting a compact receiving antenna has the space resolution for obtaining the wave height; therefore, the development, popularization and application are greatly promoted.

The invention provides a composite waveguiding structure broadband unidirectional silencer. A cuboid wave guide is formed by upper and lower walls, and front and back walls; the upper and lower walls are of a rectangular concave-convex structure with a fixed cycle; the front and back walls are flat; the size of each concave-convex structure at the left and right sides of the upper and lower walls is given by a dispersion curve; the waveguides with different functions at the left and right sides of the waveguide are named as the wave guide 1 and the wave guide 2; the concave-convex structure of the upper and lower walls can be produced on the selected flat material by a digital controlled lathe according to the size; the concave-convex structure of the waveguide 2 is to be carved when the cycle of the waveguide 1 is carved; the combination of the two waveguides can realize unidirectional conduction of the sound wave; and when incidence of the sound wave occurs, the waveguide 2 generates a frequency domain band gap for Bragg resonance of fundamental modes, the interaction among horizontal standing wave modes occurs in the waveguide 1, a single higher-order mode is generated and will not be influenced by the band gap generated by the waveguide 2, and the higher-order mode can be penetrated. The composite waveguiding structure broadband unidirectional silencer of the invention has the advantages of being high in noise abatement rate, being simple in structure, being high in adaptability, being lower in cost, and being easy to realize.

The clamp-on ultrasonic fluid flow meter system is an apparatus that includes structures that filter out a pipe structure-borne ultrasonic wave component. The clamp-on ultrasonic fluid flow meter system provides pipes that are modified to rely on Bragg resonance to attenuate the pipe structure-borne ultrasonic wave component. In a first embodiment, the fluid flow pipe is modified with corrugations so that the periodicity of the corrugations defines a pipe wall corrugation wavelength that is one-half the wavelength of the structure-borne ultrasonic wave component, satisfying Bragg's condition and preventing propagation of structure-borne noise that might interfere with the ultrasonic fluid flow meter. In a second embodiment, a pipe clad material having periodic corrugations as described above is adhesively or magnetically attached to the fluid flow pipe. In a third embodiment, alternating materials at a periodic rate satisfying Bragg's condition are attached to the exterior of the fluid flow pipe.

The invention relates to a method for realizing simultaneous sensing of temperature, strain and refractive index through a single fiber bragg grating (FBG). A localized FBG is written in a few-mode fiber by using femtosecond laser. The FBG transmitted spectrum is provided with multiple bragg resonance peaks and multiple cladding mode resonance peaks. All the bragg resonance peaks have different responses to the temperature and the strain and are not sensitive to the external refractive index. All the cladding mode resonance peaks have different responses to the external refractive index and the strain and are not sensitive to the temperature. The amount of movement of two bragg resonance peaks selected in the FBG transmitted spectrum and the normalized area ( the specific value of the area formed by enclosing of the upper and lower envelop of the cladding mode resonance peaks to the initial area) of the cladding mode resonance peaks are measured so as to realize simultaneous sensing of the temperature, the strain and the refractive index through the single FBG. The beneficial effects of the method are that the method has high sensing sensitivity, the signals are easy to demodulate, the sensing head is easy to manufacture and the mechanical strength is high with no requirement for special packaging.

The invention relates to a method for compensating a Doppler center error of along-track interferometric SAR (Synthetic Aperture Radar) in flow velocity measurement, which comprises the steps of S1, calculating a sea echo power spectrum of the along-track interferometric SAR; S2, calculating all-order derivative term values of a sea echo autocorrelation function according to a Fourier transform pair relation between the sea echo autocorrelation function and the sea echo power spectrum; S3, calculating all-order derivative term values of the along-track interferometric phase through the all-order derivative term values of the sea echo autocorrelation function according to a relation that the along-track interferometric phase is approximately equal to the phase of the sea echo autocorrelation function; and S4, compensating the Doppler center error of the along-track interferometric SAR according to the all-order derivative term values of the along-track interferometric phase. According to the invention, the Doppler center error generated by a high-order velocity change caused by the Bragg resonance wave phase velocity, the wave track velocity and various modulations can be compensated under a condition that the imaging time delay is great, and the measurement accuracy of the surface flow field velocity is improved.

The invention discloses an efficient broadband muffler pipe structure based on non-Bragg resonance, which is characterized in that the pipe wall of a tubular muffler pipe changes in periodic fluctuation, the change of each periodic fluctuation means that the inner wall of the pipe consists of adjacent concave-convex annular fluctuations, the width of each change period is equivalent to the size of the average radius of the muffler pipe, the incident wave frequency of the change period is audio, and the mode and direction of the incident wave are random; and the muffler pipe comprises more than five periods. By changing the parameters of the periodic pipe wall such as the number of the periods, the size of the fluctuation and the like, the muffling volume of the muffler pipe can be controlled. By selecting the period of the pipe wall, the muffling frequency band can be changed according to actual engineering demand. In actual engineering application, other resistive muffling methods can be compounded synchronously to improve the sound absorption effect. Moreover, the structure also can be used as an acoustic filter.

The present invention proposes a design method of an ultra-transmissive waveguide based on polarization resonance and Bragg resonance, and applies the ultra-transmissive waveguide to a surface plasmon waveguide system in which the basic unit consists of nano-scale metal-dielectric-metal waveguides and cyclically aligned laterally coupled resonators. Thus, the chain resonator structure has guide wave and band gap characteristics similar to that of photonic crystals. In the excitation of the single-ended waveguide mode, the waveguide mode is coupled with the lateral coupling resonance mode to modulate the transmission characteristics. In particular, the operating frequency of the waveguide structure can be controlled by the intrinsic frequency of the lateral resonator. The waveguide as a whole can achieve filtering, transmission and super transmission to form a laser state. In addition, the design method utilizes the gain and loss of the resonator to modulate the waveguide transmission characteristics. The design method gives the dispersion relation of the super transmission waveguide based on the coupling mode theory and the Bragg theory, combined with the polarization resonance and the Bragg resonance interaction.

The invention provides a multi-parameter measuring device based on a double-clad optical fiber. The device comprises a light source 1, a single-mode optical fiber 2, a polarizer 3, a polarization controller 4, the double-clad optical fiber 5 with a tilted grating 6 and a signal demodulator 7 which are connected in sequence. The double-clad optical fiber is provided with an inner cladding and an outer cladding, and the tilted grating is engraved on a fiber core. Light emitted by the light source forms a comb-shaped transmission spectrum after passing through the tilted grating, and the transmission spectrum comprises a Bragg resonance peak, an inner cladding resonance peak and an outer cladding resonance peak. When the external environment of the tilted grating changes, the transmission spectrum of the tilted grating changes, and real-time detection of parameters such as temperature, bending, axial strain and refractive index is realized by monitoring the changes of the wavelength and intensity of the resonance peaks, which has the advantages of small size, quick response, high sensitivity and the like.

Provided is an optical waveguide with an inscribed Bragg grating, where the Bragg grating is stable at high temperature, has low scattering loss and high reflectivity. Also provided is a method for inscribing a Bragg grating in an optical waveguide, the method comprising irradiating the optical waveguide with electromagnetic radiation from an ultrashort pulse duration laser of sufficient intensity to cause a permanent change in an index of refraction within a core of the optical waveguide, where the irradiating step is terminated prior to erasure of a Bragg resonance, and heating the optical waveguide to a temperature and for a duration sufficient to substantially remove a non-permanent grating formed in the optical waveguide by the irradiating step.

A method for writing a Bragg grating in a glass optical waveguide is provided. Ultrafast optical pulses are generated, preferably in the femtosecond range and having a writing wavelength in the range of 300 nm to 700 nm and an intensity sufficient to induce a change of refractive index in the waveguide through densification. The optical pulses are diffracted using a phase mask, to generate an interference pattern having a pitch providing a fundamental Bragg resonance corresponding to the target wavelength to be reflected by the grating. The interference pattern is impinged on a region of the waveguide, which is heated to a temperature above a threshold and for a predetermined heating period. Advantageously, the heating step allows the reduction of photoinduced losses which would otherwise be present in the waveguiding properties of the waveguide. Optionally, gratings may be written through the polymer jacket of an optical fiber.

The invention discloses a navigation mark stability maintenance power generation base based on Bragg resonance. The navigation mark stability maintenance power generation base comprises a Bragg resonance module and a navigation mark stability module. The Bragg resonance modules are installed on the navigation mark stabilizing module in an annular array mode with the central axis of the navigation mark as the rotation center, the navigation mark stabilizing module is used for fixing the navigation mark, and the tail ends of the Bragg resonance modules are connected with the top end of the navigation mark in a bolted mode through iron chains and provided with Bragg resonance plates. The arrangement of the Bragg resonance plate is similar to the wavelength of the current sea surface wave to induce Bragg resonance when the surface water body is in contact with the plate body, so that the sea surface wave generates terrain resonance in the peripheral area of the navigation mark. According to the device, the navigation mark can be protected and prevented from being damaged, and meanwhile collected and captured wave energy can be multiplied. According to the device, the service life of the navigation mark is prolonged, and meanwhile, the power generation benefit of wave energy power generation equipment is enhanced through Bragg resonance.

The invention discloses a circularly polarized coaxial embedded circular waveguide mode exciter and belongs to the field of a mode exciter. The mode exciter is of a coaxial waveguide structure with aninner conductor in a circular waveguide form and comprises a cut-off section, a resonance section and a radiation section which are connected in sequence, in the resonance section, coupling gaps or coupling hole arrays which are periodically and spirally distributed and meet Bragg resonance conditions in the angular direction and the axial direction are arranged on a waveguide wall of the inner conductor in the axial direction. The mode exciter is advantaged in that the mode exciter is simple in structure, high in vector mode purity, large in coupling efficiency, high in purity bandwidth andsmall in stray mode number.