132 results about "Microwave absorber" patented technology

A radar level gauging system comprising a microwave unit for transmitting and receiving first microwaves having a first and second distinguishable characteristics, a microwave absorber adapted to be arranged in a bottom region of the tank and adapted to absorb electromagnetic energy of microwaves having one of the first and second characteristics, and processing circuitry adapted to determine the product level based on a relationship between transmitted and received microwaves. The system thus emits microwaves in two channels, and the absorber is arranged to absorb energy in only one of the channels. Using the absorbed channel, it is possible to obtain a measurement with very limited interference from the bottom, which thus will be accurate also for levels close to the bottom. Using the unabsorbed channel, it is possible to obtain a reference measurement of the distance to the reflecting part of the absorber, thus enabling verification of the of the system.

The invention provides a method for preparing carbon-coated LiFePO4 by microwaves, which comprises the following steps: respectively obtaining a lithium source compound, a ferrous iron source compound and a phosphorous source compound in a stoichiometric ratio of the LiFePO4 required to be prepared, and adding a microwave absorber, an organic carbon source and a liquid dispersant; performing ball milling on the obtained raw material and drying treatment; putting the dried product in a microwave heating reaction cavity, and introducing protective gas into the reaction cavity; and heating to the temperature of between 550 and 850DEG C with the microwaves, introducing carbon source gas, and performing pyrolysis on the carbon source gas at the temperature of between 550 and 850DEG C to prepare the carbon-coated LiFePO4. The invention also provides a carbon-coated LiFePO4 material prepared by the method. The preparation method adopts microwave heating, and the carbon source gas is subjected to pyrolysis, so that the carbon species are deposited on the surface of the LiFePO4 to obtain the complete, uniform and firm carbon-coated LiFePO4; and simultaneously, by the preparation method, the machining property and the electrochemical performance of the LiFePO4 material can be obviously improved.

The invention discloses a method for preparing a ferrite nano fiber. The method comprises the following steps of: dissolving metal salt which can form ferrite into glacial acetic acid, adding deionized water to obtain metal salt solution; weighing Fe(3+) salt and dissolving the Fe(3+) salt into the deionized water; evenly stirring to obtain Fe(3+) salt solution; weighing citric acid according to a certain ratio, dissolving the citric acid in the Fe(3+) salt solution, mixing the obtained solution with metal salt solution, and then evaporating the obtained solution to form collosol; weighing an organic complexing agent, and dissolving the organic complexing agent into absolute ethyl alcohol or deionized water, so as to obtain organic complexing agent solution; adding the obtained gel to the obtained organic complexing agent solution and evenly agitating, so as to obtain spinnable precursor solution; carrying out electrostatic spinning to prepare a precursor fiber; and then drying, and burning for 1-3 hours in air atmosphere at 700-1000 DEG C, so as to obtain the ferrite nano fiber. The ferrite nano fiber with high performance disclosed by the invention can be used as a magnetic recording material, an electromagnetic microwave absorber and a structural wave-absorbing material.

The invention provides an ultra wideband material microwave absorber loaded with a chip resistor. The ultra wideband material microwave absorber comprises a unit structure and a bottom plate, wherein the unit structure is positioned on the bottom plate; the unit structure comprises a medium substrate, a metal slotting ring structure, the chip resistor and a metal back plate; the metal slotting ring structure is respectively connected with the medium substrate and the chip resistor. The ultra wideband material microwave absorber has the advantages that the strong circuit resonance and impedance matching properties are produced by the slotting ring structure loaded with the chip resistor, so that the ultra wideband impedance matching effect is realized, and the ultra wideband microwave strong absorbing effect is realized; when the electromagnetic wave is irradiated to the absorber, a magnetic field loop is generated around the resonance structure, a metal sheet and the chip resistor can produce ohm loss by the magnetic field loop, the electromagnetic energy of the electromagnetic wave is converted into heat energy by loss, then the loss of the irradiated electromagnetic wave is absorbed, and the ultra wideband high-property absorbing is realized; the structure is simple and small, the cost is low, the preparation is convenient, and the like.

The invention provides a frequency-adjustable microwave absorber, which is formed by a plurality of wave absorbing units on the sub wave length dimension through regular arrangement in the orthogonal direction. The frequency-adjustable microwave absorber is characterized in that capacitance and inductance coupling units are processed on the upper surface of a medium base plate, variable capacitance diodes are used for welding the adjacent capacitance and inductance coupling units, the positive and negative electrodes of each variable capacitance diode are respectively connected with a direct current feed line arranged at the back side of the medium base plate through one metallization through hole, all feed lines are combined into a feed network, the feed network at the lower surface of the medium base plate is divided into two parts including a positive part and a negative part, the two parts are respectively connected with the negative electrodes and the positive electrodes of all of the variable capacitance diodes, and the reverse bias is exerted on all of the variable capacitance diodes arranged on the upper surface of the medium base plate, and the current voltage source voltage is regulated in a range not exceeding the breakthrough voltage value of the variable capacitance diodes for changing the equivalent parameters of the variable capacitance diodes. The frequency-adjustable microwave absorber has the adjustable characteristics, the absorption frequency points in the wider bandwidth range are continuously adjustable, in addition, the regulation is very convenient, and wide application prospects can be realized in the fields of invisibility, radiation meters and the like.

The invention discloses a transparent ultra-wideband microwave absorber based on a transparent conductive film. The transparent ultra-wideband microwave absorber comprises a transparent substrate andthe transparent conductive film which is coated on the two surfaces of the transparent substrate. Periodically distributed wave absorbing structures are etched on the corresponding film of the microwave incident surface. Impedance matching of the impedance of the wave absorbing structures and the impedance of electromagnetic waves in the free space can be realized under the electromagnetic waves of the unabsorbed frequency. The absorbing bandwidth of the wave absorber can be 23.4 GHz, the overall thickness is 1.1mm, the bandwidth is only 0.11 time of the corresponding wavelength of 32.5GHz center frequency and the microwave absorber is insensitive to the polarization angle.

The invention relates to a microwave absorber with broadband absorption characteristics, in particular to a broadband microwave absorber based on a folded dipole. According to the broadband microwave absorber, a folded dipole antenna serves as a design starting point, an antenna array with a broadband is designed based on a smith chart impedance adjustment method, furthermore, a feed source is replaced by a load resistor based on the reciprocity principle of the antenna, and therefore the microwave absorber with the broadband absorption characteristics is obtained. A dielectric layer of the absorber is of a double-layer structure, the upper layer is a common dielectric substrate, and the lower layer is common polystyrene foam materials (the dielectric constant is approximately 1.07). Although double-layer dielectric materials are adopted, a single-layer metal SMD circuit is adopted to be used in cooperation with a thin film SMD resistor. The broadband microwave absorber based on the folded dipole is simpler in structure, easier to process, low in cost and light in weight, and therefore mass production can be achieved.

Metal nano articles were incorporated into wood. Ionic liquids were used to expand the wood cell wall structure for nanoparticle incorporation into the cell wall structure. Nanoparticles of elemental gold or silver were found to be effective surface enhanced Raman spectroscopy (SERS) imaging contrast or sensing agents. Nanoparticles of elemental iron were found to be efficient microwave absorbers and caused localized heating for disrupting the integrity of the lignocellulosic matrix. Controls suggest that the localized beating around the iron nanoparticles reduces losses of cellulose in the form of water volatiles and CO₂. The ionic liquid is needed during the incorporation process at room temperature. The use of small amounts of ionic liquid combined with the absence of an ionic liquid purification step and a lower energy and water use are expected to reduce costs in an up-scaled pretreatment process.

The invention discloses an adjustable terahertz broadband microwave absorber. A plurality of periodic units are periodically arranged; the periodic unit has a multilayer structure including a patch layer, a dielectric layer and a vanadium dioxide thin film layer, the dielectric layer is located between the patch layer and the vanadium dioxide thin film layer, wherein a plurality of metal patches disposed on the dielectric layer form a patch layer. The adjustable terahertz broadband microwave absorber of the invention provides a microwave absorber structure based on vanadium dioxide, and can realize the broadband strong absorption of terahertz waves; by adopting the temperature control property of vanadium dioxide, the dynamic adjustment of absorbing property can be realized; the performance of microwave absorber is not sensitive to the position of metal patch, which reduces the requirement of processing and production and has stronger practicability, the structure is simple and can beapplied to absorb electromagnetic wave in other frequency bands such as far-infrared, middle-infrared and so on.

The invention relates to the field of microwave absorbing materials. A 3-band switchable metamaterial microwave absorb/reflector is composed of metamaterial unit crystal cladding continuously and periodically arranged, and each metamaterial unit crystal cladding comprise a metal base plate layer, a dielectric substrate layer and a metal pattern layer, wherein that metal pattern layer is composed of an open straight cross structure, an open windmill structure and an open square ring structure. Seven absorption effect and one total reflection effect can be realized in a certain microwave range by meticulously design that structure of the resonant unit and the feeding network and controlling the state of the diode at different positions.

A metamaterial-based unidirectional non-reflective non-reciprocal microwave absorber disclosed in the invention includes at least two pair of metamaterial structures perpendicular to each other, thattwo pairs of metamaterial structures bee asymmetrical in X, Y and Z directions. The invention does not need to introduce a nonlinear material, but constructs artificial second-order nonlinear materialby artificially constructing mutually perpendicular metamaterial units to destroy the spatio-temporal parity characteristic of the equivalent permeability. The unidirectional microwave absorber withthe structure can exhibit obvious non-reciprocity characteristic for waves coming in different directions. The unidirectional non-reflective non-reciprocal absorber can work in two working modes, andit can work independently and without interference, which improves the efficiency and stability of the absorber. It has a wide range of applications in filters, sensors and photonic devices. The invention has the characteristics of popular structure, simple process, flexible design, strong functionality and the like.

The present invention attains a microwave absorber attachment in a readily, rapidly and stable manner. According to the microwave absorber attaching method and structure of the present invention, a plurality of ferrite plates 4 are bonded to a shield plate 2 at an installation place such as the ceiling, a wall, the floor or the like; the base portion of a support rod 6 is connected to the ferrite plates 4, causing the support rod 6 to project therefrom; a microwave absorber 1 is placed with its base portion placed along the ferrite plates 4; the support rod 6 passes through a tip opening 11 of the microwave absorber 1, causing the support rod 6 to project therethrough; a covering tray 8 allows for the support rod 6 to pass therethrough to cover the microwave absorber 1; and a fastening member is fastened to a tip threaded portion 12 of the support rod 6, thus attaching the microwave absorber 1 to the installation place. The gaps between adjacent ferrite plates 4 are filled with a magnetic sealing agent.

The invention relates to a high power waveguide impedance transformer that comprises a main waveguide, a water load, a short-circuit piston part and a terminal short circuit piston block, wherein circular flow water is used as a microwave absorber in the water load. The working waveguide wavelength of the transformer is lambda g. The front end portion of the water load is in a cone shape as well as the rear end of the water load is in a cylindrical shape and is connected with the short-circuit piston part. There is smooth transition between the front end cone and the rear end cylinder. The length L of the cone is greater than or is equal to 1 lambda g and the cone angle of the cone is from 5 degrees to 15 degrees. The length Lb of the cylinder is in a range of from 1 lambda g to 1.5 lambda g. According to the invention, an input standing-wave ratio can be adjusted in a range of from 1.05 to 5.0 and a phase variance can be adjusted in a range of from 0 degree to 180 degrees; the fluctuation range of the standing-wave ratio is basically in a ranged of -5% to +5%; after a corresponded waveguide caliber size is changed, the transformer can work at different frequencies from 2.0 GHz to 12.4 GHz; therefore, the transformer can be conveniently applied to accurate measurement on a performance parameter of a high power microwave signal source and microwave leakage can be avoided.

The invention discloses a method for rapidly preparing graphite phase carbon nitride nanorods without a template. The method is characterized by comprising the following steps of firstly preparing melamine micro-nano rods by a self-assembly method using melamine powder as a precursor; then uniformly mixing the prepared micro-nano rods and a microwave absorber, and placing in a ceramic crucible; finally, placing the crucible in the center of a high-energy microwave oven resonant cavity, vacuuming, conducting high-energy microwave irradiation heating, and rapidly obtaining the graphite phase carbon nitride nanorods. The method can efficiently and rapidly prepare the graphite phase carbon nitride nanorods with a high specific surface area, a high purity and a high yield without the template,and the nanorods have a length to diameter ratio of 10-20, and can be applied to fields of photohydrolysis of water to produce hydrogen and photohydrolysis of organic pollutants, biochemical sensors and the like.

The invention provides a miniature waveguide mode circulator which comprises an upper shell, a lower shell, a Y-shaped junction waveguide and ferrite elements, wherein permanent magnets are arranged on the upper shell and the lower shell, a waveguide impedance transformer is arranged on a wide-edge plane of the Y-shaped junction waveguide, and the two ferrite elements are positioned on a center axle line of the waveguide impedance transformer and the permanent magnets; metal electromagnetic conductors are placed into the Y-shaped junction waveguide and connected with the corresponding edge of the Y-shaped junction waveguide, the width of a port of the Y-shaped junction waveguide is less than the half-wavelength of a working frequency, the metal electromagnetic conductors extend from a Y-shaped junction plane of the Y-shaped junction waveguide and are mutually isolated; and at least one microwave absorber element is arranged at two sides of each metal electromagnetic conductor and used for absorbing a reflection power of the port. The miniature waveguide mode circulator is in a structure of matching a waveguide thin stick with a terminal load, is suitable for miniature waveguide isolator elements, has the advantages of small total size, light weight and ideal isolation property, and is used for filtering a high-order mode by adopting a combination mode of a plurality of waveguide isolators.

The invention discloses a graphene-based dual-band terahertz (THz) microwave absorber, which belongs to microwave absorbers in the technical field of terahertz and utilizes the surface plasmon characteristics of graphene. The wave absorber is a two-dimensional periodic structure and has the following structural components: a metal strip (1) made of gold, an aluminum dioxide dielectric layer (2), agraphene absorber layer (3), a polymethylmethacrylate (PMMA) dielectric layer (4), a silicon dioxide substrate layer (5), and a bottom metal reflective layer (6). The absorption spectrum of the terahertz wave is simulated and calculated by a finite element method. The structure of the wave absorber is optimized and the ideal absorption effect is obtained. The wave absorber has the advantages of simple structure and easy processing; and because of the special optical property of graphene, the absorption peak position can be adjusted by doping.

The invention discloses a control and synthesis method for a graphene-like carbon nitride ultrathin nanosheet, which comprises the following preparation steps: weighing nitrogen-enriched organic matters such as melamine, cyanuric acid and dicyandiamide according to proportion to be used as material precursors, and weighing boric acid or boron oxide used as shape control agents according to proportion, heating to 70-80 DEG C in a water solution for dissolving and mixing, and after being dissolved to present uniformly milk white, separating out and compounding; then drying, thus obtaining the uniformly compounded midbody; uniformly mixing the midbody with a carbon fiber microwave absorber, and then putting into a crucible; putting the crucible to the central position in a microwave cavity, vacuumizing until the pressure in the microwave cavity is 5-35kPa, setting microwave power to be 2-10kW, quickly heating the material to 500-620 DEG C by microwave irradiation, and carrying out thermalreaction for 5-30min, thus obtaining the ultrathin carbon nitride nanosheet with a graphene-like structure. By adopting the method disclosed by the invention, the ultrathin carbon nitride nanosheet with the graphene-like structure can be simply, conveniently and rapidly synthesized with advantages.

A microwave absorber, especially for high temperature applications, has at least one resistive sheet and at least one dielectric layer. The resistive sheet has a material of construction that is a MAX phase material.

The invention discloses a THz ultra-wideband microwave absorber based on an unequal-spacing laminated structure, comprising a reflecting plate and a dielectric body above the reflecting plate, whereinthe dielectric body is tapered, and at least one layer of metal resonant units periodically arranged by structural units is arranged inside the dielectric body; The metal resonant unit is centrosymmetrical and consists of three metal patches, comprising a hexagonal ring structure of the outer layer, a ring structure of the middle layer and an X-shaped broken line structure of the inner layer. Theinvention is designed based on the principle that the absorption frequency band can be broadened by the multilayer structure, which breaks through the traditional design idea that the layer spacing is equal, and adopts a laminated structure with unequal spacing to widen the absorption frequency domain to realize the ultra-wideband absorption of the THz band.

The invention discloses a method for preparing graphene by taking coal as a raw material, and in particular relates to a method for preparing graphene by utilizing a microwave pyrolysis technology anda supercritical carbon dioxide technology. The method comprises the following steps: by taking low-rank coal as a raw material, matching with a certain proportion of a microwave absorber and a catalyst, drying after uniformly mixing, placing the mixture in a microwave pyrolysis reactor, carrying out two stages of reaction at a final temperature of 400-650 DEG C and a final temperature of 800-1000DEG C, then cleaning, mixing cleaned samples with a dispersant and then placing the mixture in a supercritical carbon dioxide medium for reaction, and cleaning after the completion of the reaction toobtain thin-layer graphene. According to the method, the production cost of graphene can be significantly reduced, the process is simple, in the product quality is high, sources of raw materials arewide, and the method has good economical and social benefits.

The invention discloses a Salisbury screen flexible Terahertz microwave absorber based on DAST and a preparation method thereof. The absorber comprises a surface-layer DAST organic material layer, anintermediate thin film layer and a base layer metal thin film layer. The surface-layer DAST organic material layer is one kind of a DAST organic single crystal or a DAST organic thin film. The DAST organic single crystal or the DAST organic thin film absorbs waves in the Terahertz waveband. The three layers meet the impedance matching condition of the Salisbury screen flexible Terahertz microwaveabsorber. By use of the Terahertz wave absorption of the DAST organic material layer, the absorber has quite high alternating current conductivity. By designing the whole structure size, impedance matching of the Salisbury screen flexible Terahertz microwave absorber and the free space is achieved; the reflection of the whole Salisbury screen flexible Terahertz microwave absorber structure is allowed to be smallest; and energy absorbed by the structure is converted into thermal energy in the surface-layer DAST organic material layer, so the Salisbury screen flexible Terahertz microwave absorber is allowed to acquire excellent Terahertz absorption performance.