16 results about "Very low frequency" patented technology

Embodiments described herein relate to a VLF data communication system and method that allows a VLF transmitter or receiver to operate underground and be powered by a co-located power source for a long period of time. Data to be transmitted is encapsulated in a single data packet for transmission, minimizing the on time of the transmitter and receiver. One or more receivers process the data packet to synchronize with the transmitter symbol timing clock and then demodulate the encapsulated data. Timing information can also be used by the receiver to control external devices. The method used can be implemented on a low power microcontroller unit (MCU) to further reduce power consumption.

The present application belongs to the field of radio wave propagation theory and electromagnetic field numerical calculation technology, and discloses a low-dispersion very low frequency radio wave propagation characteristic prediction method.The present application method aims at the defects of large numerical dispersion, low calculation efficiency and high resource occupation of the existing FDTD method in long-distance, complex layered medium scene, and realizes high-precision and high-efficiency prediction of the very low frequency radio wave propagation characteristic in seawater-air-ionosphere medium by combining HIE-FDTD method and M(2,4)FDTD method through three-layer processing of the whole calculation area.The present application method solves the contradiction between reducing numerical dispersion error and reducing computer consumption of the traditional FDTD method, can greatly reduce computer memory resource occupation and improve calculation speed while ensuring prediction accuracy, is suitable for electromagnetic propagation simulation of large-size, complex medium and terrain, and has obvious advantages in phase delay prediction of very low frequency ground wave propagation.

The application discloses a kind of deep sea direct sound zone near seabed very low frequency line spectrum target ranging method, belong to deep sea signal processing and underwater target positioning field.The method steps include: based on target sea area environmental parameter establishment sound propagation model, through near seabed vertical direct receiving array obtains depth-intensity interference fringe;Copy sound field calculation model is constructed using virtual source method, and three main propagation paths are retained to generate copy interference fringe;To measured and copy stripe are standardized, with cross-correlation coefficient as matching index, realize target distance estimation by peak search.The application realizes the estimation of target sound source distance by matching the depth-intensity interference fringe formed by the near seabed vertical array at a single frequency, with the depth-intensity one-dimensional interference fringe as the matching object, the array aperture is small, the feature dimension is lower, the calculation amount of copy field generated by virtual source method is smaller, and due to the equivalent assumption of virtual source method, the method is not sensitive to environmental mismatch, and has good robustness.

The present application belongs to the field of radio wave propagation theory and electromagnetic field numerical calculation technology, and discloses a low-dispersion very low frequency radio wave propagation characteristic prediction method.The present application method aims at the defects of large numerical dispersion, low calculation efficiency and high resource occupation of the existing FDTD method in long-distance, complex layered medium scene, and realizes high-precision and high-efficiency prediction of the very low frequency radio wave propagation characteristic in seawater-air-ionosphere medium by combining HIE-FDTD method and M(2,4)FDTD method through three-layer processing of the whole calculation area.The present application method solves the contradiction between reducing numerical dispersion error and reducing computer consumption of the traditional FDTD method, can greatly reduce computer memory resource occupation and improve calculation speed while ensuring prediction accuracy, is suitable for electromagnetic propagation simulation of large-size, complex medium and terrain, and has obvious advantages in phase delay prediction of very low frequency ground wave propagation.

This utility model discloses a VLF broadband antenna, belonging to the field of very low frequency electromagnetic field monitoring. It includes a first PCB board and a second PCB board arranged vertically opposite each other, with several conductive support components disposed between them. One of the PCB boards has an output port. Each conductive support component includes a bracket vertically disposed between the first and second PCB boards. Multiple sets of coils are disposed inside the bracket. The coils employ a double-shielded structure, and the coils used for detecting electric fields and those used for detecting magnetic fields are arranged perpendicularly to each other. The double-shielded structure includes a copper foil shielding layer and a metal bracket shielding layer. The coils use single-strand silver-plated ribbon cables. This VLF broadband antenna, by employing high-Q, low-loss coils combined with high-Q materials, can more accurately capture electromagnetic field signals, providing more effective data for backend data processing and meeting the requirements of high-precision monitoring.

This invention proposes a composite rod-type magneto-electro-mechanical antenna and its fabrication method, belonging to the field of mechanical antenna technology. It solves the problems of low power capacity, weak radiation capability, and short communication distance commonly found in existing magneto-electro-mechanical antennas. It comprises a magnetostrictive layer, two transition layers, two sets of driving layers, and two sets of tail mass blocks. The magnetostrictive layer is located at the center, with the transition layer, driving layer, and tail mass blocks arranged sequentially from the center to both ends on either side. Each driving layer is composed of multiple piezoelectric ceramic rings and multiple electrode sheets stacked alternately. Each tail mass block consists of mass block one, a disc spring, and mass block two connected sequentially. The length of this composite rod-type magneto-electro-mechanical antenna is comparable to that of a traditional three-layer magneto-electro-electric antenna. When the antenna adopts the first-order longitudinal mode, it can operate in the very low frequency band. Depending on different application requirements, the composite rod-type magneto-electro-mechanical antenna of this invention can adopt the second-order longitudinal mode or operate in other frequency bands.

This invention belongs to the field of underwater sound source radiation characteristic measurement technology, and relates to a method and system for measuring the very low frequency radiated sound power of an omnidirectional sound source in a reverberant pool. The method includes: determining the first-order resonant frequency based on the structural parameters and water level of the reverberant pool; placing a standard sound source at the center of the pool and arranging multiple hydrophones at intervals on one side of the sound source; exciting the standard sound source with a single-frequency continuous sinusoidal signal lower than the first-order resonant frequency; establishing a fitting model of the standard sound source's radiated sound pressure field based on the radiated sound pressure amplitude collected by the hydrophones, and calculating the exponential function adjustment factor and the standard sound source intensity factor; replacing the standard sound source with the sound source to be measured, exciting the sound source to be measured with the same single-frequency continuous sinusoidal signal, establishing a fitting model of the sound source's radiated sound pressure field based on the radiated sound pressure amplitude collected by the hydrophones, and calculating the sound source intensity factor; and calculating the radiated sound power of the sound source to be measured. This invention achieves rapid and accurate acquisition of the very low frequency radiated sound power of the sound source to be measured.

The application discloses a lightning VLF electromagnetic wave signal compression method based on importance perception and belongs to the technical field of signal processing. The method comprises the following steps: firstly, acquiring an original lightning VLF electromagnetic wave time sequence signal and performing normalization processing; then, inputting the normalized signal into an importance prediction model, the model comprising a shared feature encoder, a time sequence-frequency domain double-channel attention module and a double-branch decoding structure, and outputting an importance score of each time slice; finally, according to the score, adopting an adaptive hierarchical compression strategy, performing non-uniform weighted sampling on key slices, uniform sampling on transition slices and sparse sampling on redundant slices, and obtaining a compressed signal. The application can adaptively distinguish lightning pulses from noises, accurately retains key waveform details such as rising edges, peak values and falling edges of the pulses under a high compression ratio, has small pulse peak value and arrival time error, has high waveform correlation coefficient, and is highly compatible with existing lightning monitoring and fault positioning processes.

The utility model relates to a kind of very low frequency broadband signal amplification circuit, belong to electronic circuit technical field. Very low frequency broadband signal amplification circuit includes two-stage filter circuit and three-stage amplifier circuit. First-stage filter circuit connects signal input end, for the filtering processing of very low frequency signal, and the very low frequency signal is the underwater acoustic signal of frequency as low as 0.001 hertz;The input end of first-stage amplifier circuit is connected with the output end of first-stage filter circuit;The input end of second-stage amplifier circuit is connected with the output end of first-stage amplifier circuit;Second-stage filter circuit connects the output end of second-stage amplifier circuit;The input end of third-stage amplifier circuit is connected with the output end of second-stage filter circuit;Negative feedback low-pass filter circuit is connected to the input end of first-stage amplifier circuit through the output end of third-stage amplifier circuit;The output end of third-stage amplifier circuit is as the output end of very low frequency broadband signal amplification circuit.

The application provides a full frequency domain ultra-wideband Doppler direction finding method. The technical core is based on the wavelength-independent double baseline difference positioning theory, combined with the equidistant linear array and the uniform motion characteristics of the platform, the mapping relationship from the frequency domain observation to the space domain geometry is established by approximating the radial velocity difference, and the mean correction mechanism is introduced to suppress the system deviation. The key breakthrough is to use the second-order dynamic frequency shift information to invert the v / lambda ratio, thereby completely eliminating the wavelength dependence in the direction finding equation, realizing the physical mapping without frequency priori. The method overturns the traditional direction finding mode, covers the full frequency band from very low frequency to terahertz, and is suitable for concealed target detection, electromagnetic spectrum battlefield perception and 6G+ terahertz imaging joint positioning and other frontier scenes. The frequency domain decoupling architecture lays the algorithm foundation for building a "space-environment-target" global perception system, promotes the direction finding technology from narrowband fixed point to broadband global, and is an important paradigm innovation in the field of intelligent electromagnetic perception.

This invention discloses a scalable power very low frequency (VLF) transmitter device and its control method. It consists of multiple individual cabinets, with multiple units sharing a single main control system, facilitating expansion and allowing for power level adjustments, improved waveform quality, and reduced output waveform harmonics. The input terminals of multiple individual power cabinets can be connected in parallel to DC or AC power supplies, and the output terminals are connected in series to the load. Each cabinet includes a switching module, a voltage conversion module, an adjustable voltage module, multiple switching signal modules, multiple multi-tap high-frequency transformers, and a corresponding number of bypass switches. The unique design of the switching signal modules facilitates online expansion and replacement. The high-frequency transformers are multi-tap high-frequency transformers; adjusting the tap positions allows for graded adjustable output voltage after multiple units are connected in parallel. The main control system includes a command control unit, a stepped waveform generation and expansion unit, a storage unit, and a communication unit. The main control system can multiply the comparison value and pulse quantity based on the individual unit comparison value using interpolation methods to provide pulse signals to the switching signal modules.

The application discloses a kind of electrochemical vector hydrophone of sound transmission type, belong to underwater acoustic technical field, including sound transmission membrane, electrolyte, sound transmission channel, sensitive electrode, circuit and sealing shell;Sound transmission membrane is placed in the both sides of sound transmission channel;Electrolyte is used to provide the medium of electrochemical reaction, and sound wave can propagate in electrolyte;Sound transmission channel is filled with electrolyte inside, and sensitive electrode is embedded in the middle;Sensitive electrode includes a plurality of anode and a plurality of cathode, and electrolyte occurs electrochemical reaction in anode and cathode to generate current, and a plurality of flow holes are formed on electrode to make electrolyte pass smoothly;Circuit includes current-voltage conversion circuit and differential amplification circuit;Sealing shell, wrap inside structure and circuit of hydrophone, only expose sound transmission membrane, and internal gap is filled with insulating liquid.Sound wave signal is transmitted through sound transmission membrane, through sound transmission channel, acts on electrolyte near sensitive electrode, and causes the particle vibration of electrolyte near sensitive electrode.The application of very low frequency band is more reliable, and smaller in size.

The invention belongs to the technical field of electromagnetic detection, and particularly relates to a ground-air very-low-frequency electromagnetic detection coil vibration attitude measuring device and method.The ground-air very-low-frequency electromagnetic detection coil vibration attitude measuring device comprises an unmanned aerial vehicle and a mission load system, and the mission load system comprises a three-component electromagnetic induction coil sensor used for measuring very-low-frequency electromagnetic signals; the two-degree-of-freedom active suspension system is connected between the unmanned aerial vehicle and the task load system, and the multi-mode sensing system is used for monitoring the attitude angle and the vibration state of the three-component electromagnetic induction coil sensor in real time; and the airborne computing unit runs a vision-attitude fusion algorithm and a three-component decoupling algorithm, and performs vibration compensation and noise removal on the received signals. The attitude change caused by maneuvering and airflow disturbance of the unmanned aerial vehicle can be effectively resisted, and the three-component electromagnetic induction coil sensor is dynamically stabilized in a state close to the horizontal state.