65 results about "Electromagnetic field" patented technology

A right-hand circularly-polarized patch antenna comprising a ground plane and a patch connected to each other with one or more wires for which the wire shape and location of the end points are selected such that they do not cause an antenna mismatch, and the electrical current carried in the wires produces an extra electromagnetic field subtracted from the patch field in the nadir direction.

The invention discloses an intelligent power grid optimization scheduling method based on digital twinning, and relates to the technical field of power grid optimization scheduling, and the method comprises the steps: building a dynamic power grid mirror image model according to a standardized power grid data matrix, and generating an evolution trajectory prediction report through a quantum magnetic coupling mechanism; establishing a variable association network based on the evolution trajectory prediction report, and generating an optimization scheduling instruction set in combination with the standardized data matrix; executing an optimization scheduling instruction set to obtain magnetic potential gradient distribution, and generating a topology reconstruction scheme by identifying a magnetic potential change trend; and inputting the topology reconstruction scheme into the dynamic power grid mirror image model to generate an electromagnetic field evolution trajectory, and generating a safety scheduling report in combination with magnetic potential energy gradient distribution. According to the method, the power grid magnetic field data is coded into an evolution trajectory prediction report through a quantum-magnetic coupling mechanism, and high-precision risk pre-judgment is realized; a topology reconstruction scheme is dynamically generated according to the electromagnetic energy gathering trend, and the power grid optimization scheduling efficiency is improved.

The invention relates to the technical field of chromatographic detection and material characteristic analysis, and discloses a multiphase chromatographic analysis system and method.The multiphase chromatographic analysis system comprises a multiphase sample injection module, a multi-field cooperative regulation and control separation column module and a plurality of separation chromatographic columns which are sequentially connected, and the separation chromatographic columns comprise partitions and are installed in a column box in an end-to-end connection mode; a temperature gradient field, an electric field gradient field, a controllable electromagnetic field and a fluid power field; and a multi-modal detection module, a data acquisition and control module and an auxiliary module. Through the brand-new multi-phase sample injection module, the multi-field coordinated regulation and control separation column module and the multi-mode detection module, direct input of detected objects in different phase states can be met, and phase state conversion is carried out according to needs, so that the phase state compatibility of the analysis system to the detected objects is obviously enhanced; and different components can be obviously separated according to different boiling points, migration speeds and magnetic susceptibilities by combining multi-field synergistic separation, so that the chromatogram is more accurate.

The method is based on a core idea of unifying a field theory and an interference field theory, is devoted to exploration and expansion of an artificial field frontier technology, and covers an artificial field plus quality technology, an artificial field interference technology and an artificial field control space-time technology. In the research process, mutual verification of experiments and theories is paid attention to. Theoretically, internal correlation among Planck mass, electron mass, gravitational force, electric field force, magnetic field force and fine structure constants is deeply analyzed, a conclusion that the gravitational force, the electric field force and the magnetic field force are equal when a substance reaches a light velocity is obtained, and a unique quantum effect is presented. In the aspect of experiments, a simple verification method is adopted, and substances are placed in a positive electrode area and a negative electrode area respectively. Along with the enhancement of the electric field intensity and the action time, the substance mass in the positive electrode area is gradually reduced, and the substance mass in the negative electrode area is correspondingly increased. The phenomenon can be explained as that the space where the positive charges are located has divergence characteristics and the space where the negative charges are located has convergence characteristics, so that the masses of the substances in the positive and negative electrode areas are changed alternately.

The invention belongs to the technical field of transformer substation engineering monitoring, and relates to a transformer substation engineering monitoring method based on intelligent perception, which dynamically generates a hoisting track envelope space containing a specified crane boom body and a hoisting object based on historical action inertia characteristics, current operation target constraints and real-time position feedback. Associating hoisting track envelope spaces of other cranes on a substation site, calibrating an envelope space intersection domain as a tangible collision risk domain, synchronously monitoring electromagnetic field intensity space distribution of an electric field source of the substation, and dynamically calculating a safety spacing margin threshold value between the tail end of a specified crane suspension arm and the nearest electric field source based on a field intensity gradient change rate and suspension arm pose parameters; and the nearest electric field source space coverage domain smaller than the margin threshold value is calibrated as an invisible collision risk domain, and when the specified crane enters the tangible collision risk domain or the invisible collision risk domain, a graded early warning signal is triggered, so that the application degree and precision of hoisting collision monitoring of the crane of the transformer substation are remarkably improved.

An alternating-current electromagnetic field stress measurement system, comprising: an excitation signal generation module, an alternating-current electromagnetic field stress measurement stress probe, a signal amplification circuit, an A / D conversion circuit and a processor, wherein the excitation signal generation module is used for loading a sinusoidal alternating-current signal to an excitation coil of the alternating-current electromagnetic field stress measurement stress probe, such that a periodically changing electric field is generated on a measured magnetic object; the alternating-current electromagnetic field stress measurement stress probe is used for sequentially routing a stress characterization signal, which is detected from the measured magnetic object, through the signal amplification circuit and the A / D conversion circuit, and then sending the stress characterization signal to the processor; and the processor is used for processing the received stress characterization signal by using an optimized J-A model in which an implicit equation originally characterizing a change in the magnetization intensity or magnetic induction intensity along with stress is made explicit, so as to calculate the stress of the measured magnetic object. The alternating-current electromagnetic field stress measurement system can monitor the stress increase trend in real time, and notice potential dangers in time. Further comprised is an alternating-current electromagnetic field stress measurement method and a computer program for executing the alternating-current electromagnetic field stress measurement method.

Provided are a method and device for driving movement of a target object by a gravitational field generated by a varying electromagnetic field which relate to the technical field of physics. The method includes: generating, by a variable electromagnetic field generator, a time-varying electromagnetic field in space where a target is located; adjusting a frequency, amplitude and phase of the time-varying electromagnetic field so as to generate an effect of a varying magnetic field in the space; and based on the time-varying electromagnetic field, generating an acting force on the target object to drive the target object to move along a predetermined trajectory or direction. The present invention breaks through limitation that the traditional electromagnetic mechanics can only drive metal materials, utilizes the varying characteristics of the electromagnetic field to drive and realize accurate control of movement of all objects comprising a non-magnetic substance and a non-conductive substance.

The invention discloses an underwater vehicle wireless electric energy transmission system with an omnidirectional anti-offset function. The transmission system comprises a magnetic coupler receiving assembly and a magnetic coupler sending assembly. The sending assembly is used for providing a charging magnetic field for the receiving assembly. The magnetic coupler transmitting assembly comprises a stepped coil and an anti-series coil, and the stepped coil is located in the anti-series coil; the magnetic coupler receiving assembly comprises a plurality of receiving coils, magnetic cores are arranged in the receiving coils, and the receiving coils are of solenoid structures and are wound around the magnetic cores; the number of the receiving coils is five, one receiving coil is arranged in the middle of the H shape, and the other four receiving coils are fixed to the ends of the H shape. According to the invention, the magnetic field intensity of the surrounding area of the wireless electric energy transmission system is improved, and the mutual inductance between the transmitting coil and the receiving coil is ensured to be stable when the omnidirectional position offset of the aircraft occurs.

The invention provides a deep and far sea wind power plant area lightning dynamic parameter inversion method and device, and relates to the technical field of lightning protection, and the method comprises the steps: building a fan return stroke model based on current reflection caused by the wave impedance discontinuity of a fan top, a return stroke channel and a fan bottom grounding position, obtaining an initial propagation model of the electromagnetic field along the sea-land mixed path by combining the surface equivalent impedance of the sea surface and the land of the observation point zone; correcting the initial propagation model through electromagnetic field influence parameters to obtain a target propagation model; inputting a radiation source signal received by an array into the target propagation model for waveform time sequence inversion processing to obtain a corresponding time reversal signal; the time reversal signals in different directions are superposed and focused to obtain the peak azimuth, and the three-dimensional positioning of the lightning radiation source is carried out in combination with the positioning result of the double stations, so that the lightning development spatial-temporal distribution law is determined, and the measurement precision of the lightning leader development speed is remarkably improved.

The present application discloses a fault identification and early warning method and system for a power transmission line, the method comprising: receiving a fault flashover signal, determining the occurrence area of the fault flashover signal, and obtaining a target image; determining whether there is abnormal discharge in the transmission line in the occurrence area; if so, performing image recognition to obtain a fault source to be tested; obtaining the inclination of the tower in the occurrence area and the electromagnetic field and radar changes; determining the movement path of the current fault source, determining the fault source category through image capture, and determining the target fault source; obtaining meteorological data through micro-meteorological sensors and network meteorological weather, and obtaining the future and real-time dancing amplitude and dancing frequency of the transmission line; combining the dancing amplitude, dancing frequency, tree obstacles, super-high engineering vehicles, floating objects, and lightning strikes, which are greater than the warning value, starting image capture to determine the target probability and image of the target fault source causing a secondary fault on the transmission line, determining the high-risk interval segment, and sending the warning picture and video to the background in real time.

The invention discloses a Helmholtz coil material lightning magnetic field shielding performance measuring device, which comprises a magnetic field generation device, a shielding test box is arranged in a magnetic field coverage range of the magnetic field generation device, an open hole is formed in the shielding test box, and the open hole enables a magnetic line of force of the magnetic field generation device to transversely penetrate through the shielding test box. The shielding test box is internally provided with the signal measurement unit, the signal measurement unit measures the magnetic field in the shielding test box, the lightning stroke magnetic field environment is accurately simulated, and the repeatability and accuracy of the shielding performance test are improved. The invention further discloses a method for measuring the lightning magnetic field shielding performance of the Helmholtz coil material, the lightning magnetic field shielding performance of the measured shielding material is measured by applying the device for measuring the lightning magnetic field shielding performance of the Helmholtz coil material, and the problem that traditional measurement is poor in accuracy is effectively solved.

The utility model relates to copper wire production technical field, concretely relates to a kind of copper wire production and processing's stretching device, including lubricating bucket and the conveying part for being immersed into the copper wire in lubricating bucket;Electromagnetic rod is located in lubricating bucket, it includes the sealing sleeve coaxially fixed in lubricating bucket and the electromagnetic coil coaxially located in sealing sleeve, for generating strong magnetic field and drive copper powder to the arc-shaped inner wall of lubricating bucket, fishing part is located in lubricating bucket, it includes the fishing ring coaxially slidingly located in lubricating bucket, the outer edge of the fishing ring contacts the inner wall of lubricating bucket.The utility model generates strong electromagnetic field by electromagnetic rod, since copper powder belongs to inverse magnetic material, it generates induced eddy current in alternating magnetic field, and then generates reverse magnetic field, forms repulsion with magnetic field source Lorentz magnetic force and is pushed to low magnetic field area by magnetic repulsion, copper powder can be pushed to the arc-shaped inner wall of lubricating bucket and gathered in real time, greatly extend the period of lubricating liquid cleaning or replacement, reduce its cleaning or replacement frequency.

A method and system for evaluating a cement bond. The method may include disposing a logging tool in a wellbore. The logging tool may include an electromagnetic (EM) sub and an acoustic sub. The method may further comprise transmitting an EM field from the EM sub into one or more tubulars to energize the one or more tubulars with the EM field and measuring a secondary EM field in the one or more tubulars with a EM receive. The method may further comprise transmitting a shaped acoustic signal from the acoustic sub into one or more tubulars and formation, measuring a result signal with the acoustic sub to form one or more acoustic measurements, estimating one or more pipe parameters from the eddy current, and evaluating a cement bond based at least in part on the one or more pipe parameters and the one or more acoustic measurements.

This invention belongs to the field of nondestructive testing technology, and particularly relates to a visual detection method for ferromagnetic material defects based on AC / DC composite excitation. This method overcomes the problem of existing AC electromagnetic field detection methods failing to obtain complete visualization of complex defect morphologies in ferromagnetic materials due to mutual interference between current disturbances and leakage magnetic field disturbances, thus providing more detailed and reliable data support for structural safety assessments of offshore oil platforms and offshore wind power platforms. The visual detection method for ferromagnetic material defects based on AC / DC composite excitation includes the following steps: scanning to obtain a magnetic field signal SBz; extracting the DC component SBz from the magnetic field signal SBz. z and communication component SBz j And form a surface matrix; calculate matrix Bz z Matrix Bz j The difference is used to obtain matrix Bz. By performing operations such as curl calculation, gradient calculation, grayscale conversion and binarization on the array of matrix Bz and the image, the defect contour, disturbance current density and disturbance current line image are obtained.

The invention discloses a high-selectivity broadband optical transparent energy selective surface and a control method. The high-selectivity broadband optical transparent energy selective surface comprises a single-layer optical transparent substrate and a parallel circuit structure, the LC series resonance branch is used for forming a fixed stop band in a conventional working state and can form a double-stop-band coupling structure with the field nonlinear device series branch after impedance change under strong electromagnetic attack so as to expand the protection bandwidth, and stable and efficient shielding in the whole target protection frequency band is achieved; and the field-induced nonlinear device series branch is used for performing main shielding and passband adaptive adjustment under strong electromagnetic attack through state switching of the field-induced nonlinear device, that is, the field-induced nonlinear device series branch can change the impedance characteristic under strong electromagnetic field excitation. The LC series branch and the field nonlinear device series branch are integrated on the single-layer light transparent base material, broadband protection performance and low insertion loss which are equivalent to those of a multi-layer or cascade structure are obtained, and meanwhile an extremely small section and a compact structure are achieved.

The invention discloses a nuclear magnetic resonance passive shimming module design method and device based on Gaussian splashing, and relates to the technical field of precision electromagnetic field optimizing.The nuclear magnetic resonance passive shimming module design method comprises the steps that initialization is conducted in a design domain of a passive shimming module, and an initial parameter set of all Gaussian splashing particles is obtained; constructing a mapping relation between the equivalent magnetic moment and the magnetization weight factor of each Gaussian splashing particle and between the intrinsic magnetization intensity and the scaling vector of the magnetic material, and constructing a magnetic field intensity calculation model; inputting the initial parameter set of all Gaussian splashing particles and the real magnetic field intensity into a Gaussian splashing particle parameter set iterative optimization algorithm, and calculating and predicting the magnetic field intensity through a magnetic field intensity calculation model; and based on the predicted magnetic field intensity, the real magnetic field intensity, the magnetization weight factor vector and the center position vector, constructing a multi-objective loss function and performing iterative optimization to obtain an optimized parameter set and manufacture a passive shimming module. The method solves the problem of low precision and efficiency of compensating a magnetic field with a complex shape.

The application belongs to the technical field of radio frequency electromagnetic field measurement, and particularly discloses a quantum field intensity measurement method and system of offset electric field regulation, which comprises the following steps: selecting a Rydberg atomic energy level close to resonance according to the microwave frequency of a measured signal; determining a coupling light wavelength according to the Rydberg atomic energy level, preparing a Rydberg atom, simultaneously obtaining a difference value between the microwave frequency of the measured signal and a resonance transition frequency, and obtaining an energy level offset value according to the difference value; obtaining a polarizability of the Rydberg atomic energy level, obtaining an offset electric field value to be applied according to the energy level offset value and the polarizability; and starting the offset electric field according to the offset electric field value, so that the relevant energy level of the Rydberg atom produces a movement in the offset electric field; when the energy difference between the offset Rydberg energy level and the adjacent energy level resonates with the microwave frequency of the measured signal, the offset sub-energy level forms an energy level splitting, and a frequency splitting is generated, and the electric field of the measured signal is measured according to the interval between the frequency splittings.

The present application relates to a kind of wave frequency energy emission devices, the device includes: electromagnetic modulation layer, for modulating preset frequency and power electric signal pulse, and change magnetic field is generated according to the electric signal pulse;Energy conversion layer is arranged in the magnetic field range of the change magnetic field, and the energy conversion layer is used to convert the magnetic field energy of the change magnetic field into vibration energy wave;The energy conversion layer is composed of one or two kinds of strain materials, and the expansion rate and response time of each strain material are different;The vibration energy wave is used to cause the resonance inside target object, to change the state of the target object.The present application utilizes the characteristics that the energy conversion layer generates expansion with the change of electromagnetic field, causes vibration, thereby converts into high-frequency vibration wave, thereby improves the efficiency and effect of energy output.

The present invention relates to the field of electromagnetic detection and provides a method for detecting wake electromagnetic field enhancement based on a circulating water flume. The method comprises: constructing a wake electromagnetic field test device based on a circulating water flume, fixing a model to be tested in the flow channel of the circulating water flume; placing a Helmholtz coil outside the circulating water flume to generate an enhanced background magnetic field; periodically changing the rotational speed of a drive device, thereby periodically changing the water flow velocity in the circulating water flume; measuring the electric and magnetic fields in the target area; and processing and analyzing the obtained signals.

According to the active terahertz polarization conversion and detection method based on the gap regulation metasurface, any completely polarized light can be decomposed into two orthogonal polarization components, the two components have a certain phase difference and amplitude ratio, and target polarization response can be obtained by changing the phase difference or the amplitude ratio. Therefore, in order to obtain the required polarized light, any phase retarder, namely a wave plate, is used for changing the phase difference between two orthogonal components of the incident polarized light, so that a target polarization state is obtained; the detection method is based on the reciprocity principle of an electromagnetic field, a device with a polarization conversion function can be reconfigured into a polarization detection system under time reversal symmetry, different polarization states are switched according to a time sequence through the conversion relation between a Jones matrix and a Muller matrix, and the detection accuracy is improved. And the light intensity with different polarization components is measured in sequence to realize full Stokes polarization detection of incident polarized light.

The present invention belongs to the technical field of substation engineering monitoring, and relates to a substation engineering monitoring method based on intelligent perception. The method dynamically generates a lifting trajectory envelope space including a specified crane boom body and a lifting object based on historical motion inertia characteristics, current operation target constraints, and real-time position feedback, associates the lifting trajectory envelope spaces of other cranes on the substation site, calibrates the intersection domain of the envelope space as a tangible collision risk domain, synchronously monitors the spatial distribution of the electromagnetic field strength of the substation electric field source, dynamically calculates the safety distance margin threshold between the end of the specified crane boom and the nearest electric field source based on the field strength gradient change rate and the boom posture parameters, calibrates the spatial coverage domain of the nearest electric field source that is less than the margin threshold as an intangible collision risk domain, and triggers a graded warning signal when the specified crane enters the tangible collision risk domain or the intangible collision risk domain, thereby significantly improving the application and accuracy of substation crane lifting collision monitoring.

An object of the present disclosure is to provide a detection system capable of detecting attachment position information relating to an attachment position of an environment control device. A detection system (1) includes an environment control device (10), an energy release unit (20), an acquisition section (32), and a detector (33). The environment control device (10) is to be mounted on a ceiling surface of a room (100) and is configured to control an environment in an interior space of the room (100). The energy release unit (20) is capable of outputting electromagnetic wave energy including at least one of light and heat in a predetermined direction from an attachment position of the environment control device (10). The acquisition unit (32) is configured to acquire distribution information including at least one of first distribution information relating to an electromagnetic field strength distribution on a ceiling surface of the room (100) and second distribution information relating to an electromagnetic field strength distribution on a floor surface of the room (100). The detector (33) is configured to detect attachment position information relating to an attachment position of the environment control device (10) on the ceiling surface on the basis of the distribution information acquired by the acquisition unit (32).

The invention provides an electromagnetic field visualization measurement method and device and electronic equipment, and the method comprises the steps: controlling an electromagnetic field measurement probe to move on a to-be-measured plane at a preset distance from a to-be-measured object in a preset track, and detecting the real-time electromagnetic field data; acquiring images of the to-be-measured object and the electromagnetic field measuring probe through a camera; identifying image features of the electromagnetic field measurement probe in the image; determining position data of the electromagnetic field measuring probe in the image according to image features of the electromagnetic field measuring probe; determining a target color corresponding to the real-time electromagnetic field data according to a mapping relationship between the real-time electromagnetic field data and a preset color; and overlapping the real-time electromagnetic field data and the pixel color blocks with target colors and transparency on the image according to the target position data of the electromagnetic field measurement probe corresponding to the real-time electromagnetic field data for displaying. According to the method, efficient cooperation of electromagnetic field measurement and display is realized, the measurement efficiency is remarkably improved, and the method supports flexible adaptation to different scene requirements.

The invention discloses a micron-scale focus temperature measurement method, which comprises the following steps of: exciting a rare earth doped film by using 980nm laser to generate dual-wavelength fluorescence corresponding to a thermal coupling energy level; submicron focusing and collection of fluorescence signals are realized through a microscope objective; a dual-wavelength fluorescence signal is separated by using a narrow-band optical filter group and is converted into an electric signal through a photoelectric detector; the dual-wavelength fluorescence intensity ratio is calculated, and the focus temperature is calculated in real time according to a pre-calibrated temperature-fluorescence intensity ratio curve; two-dimensional temperature distribution scanning is achieved through the three-dimensional displacement platform, a temperature distribution diagram with micron-level spatial resolution is generated, and interference of a traditional contact type temperature measurement method on a micro-scale system is avoided, such as measurement errors caused by heat conduction and damage to the surface of a sample. The method is suitable for temperature measurement in extreme environments such as high temperature, high pressure and strong electromagnetic field, and has wide applicability.

This invention discloses a wireless power transmission system for underwater vehicles with omnidirectional anti-drift capability. The system includes a magnetic coupler receiving component and a magnetic coupler transmitting component. The transmitting component provides a charging magnetic field to the receiving component. The magnetic coupler transmitting component includes a stepped coil and an anti-series coil, with the stepped coil located inside the anti-series coil. The magnetic coupler receiving component includes several receiving coils, each containing a magnetic core. The receiving coils employ a solenoid structure and are wound around the magnetic core. There are five receiving coils, with one located in the middle of an H-shape and the other four fixed at the ends of the H-shape. The wireless power transmission system of this invention maintains a stable magnetic field strength around the area and ensures stable mutual inductance between the transmitting and receiving coils when the vehicle experiences omnidirectional positional drift.

The present application discloses a system, method, device and electronic equipment for detecting the appearance of an object, which belongs to the field of radar detection technology. The system includes: a reflector, a radar, an electromagnetic field detector and a computing device, wherein the reflector can reflect part of the electromagnetic waves emitted by the radar, and the radar can receive the echo of the first electromagnetic wave reflected by the reflector and the second electromagnetic wave not reflected after detecting the object, and the electromagnetic field detector can measure the magnetic field information at different positions in the magnetic field formed by the interference of the echoes of the first electromagnetic wave and the second electromagnetic wave. Then, the computing device reads the magnetic field information at different positions measured by the electromagnetic field detector, and determines the electromagnetic wave transmittance corresponding to the magnetic field information at each position based on the established mapping relationship between the magnetic field information and the electromagnetic wave transmittance. Based on the electromagnetic wave transmittance corresponding to each position, a virtual medium is constructed to simulate the diffraction process of the electromagnetic wave when passing through the virtual medium, and obtain and output the three-dimensional appearance data of the object.

This invention relates to the field of magnetic pole topology design, and more particularly to a method for designing the magnetic pole topology of a finite-angle torque electromagnetic drive. The method includes: meshing the rotor back iron, air gap, and stator domain of a finite-angle torque motor; defining permanent magnet material variables and soft magnetic material variables; based on the material variables, performing filtering, projection, and constitutive equation electromagnetic field mapping through an electromagnetic field finite element model to generate mapped material variables and torque variables; constructing constraints and an objective function; and solving the magnetic field strength characterization variables of the objective function using an optimization solver to determine the optimal combination of the corresponding permanent magnet material variables and soft magnetic material variables. This invention transforms the distribution problem of permanent magnets and soft magnetic materials in the rotor back iron into a topology optimization problem, achieving a high-performance combination of permanent and soft magnetic materials, improving the material utilization rate and torque density of both permanent and soft magnets, and realizing high material utilization of the rotor back iron of a finite-angle torque motor.

The invention discloses an enhanced Smith-Perot terahertz radiation device and method based on a metasurface, and belongs to terahertz radiation. According to the enhanced Smith-Perot terahertz radiation device based on the metasurface provided by the invention, the penetrating composite hole digging unit is arranged on the metasurface structure, the cross section of the hole digging unit is of the cross structure formed by vertically intersecting the first rectangle and the second rectangle, and the center of the cross structure is the center of a circle, so that the specific hole digging structure can improve the radiation efficiency of the terahertz radiation device. Through cooperation with periodic arrangement of the whole metasurface in a two-dimensional array mode, the local field enhancement characteristic of the metasurface can be more effectively utilized, specifically, vertically-intersected rectangles form a hollow channel, charges are gathered due to the fact that no medium exists at the edge, and a high-strength electromagnetic field is formed in a cross area in combination with an evanescent field generated by electron beam glancing. The center of a circle coincides with the center of the cross structure, the electric field distribution symmetry is optimized, the scattering loss is reduced, the energy is further focused, and the radiation intensity is improved.

Head-mounted augmented reality (AR) devices can track pose of a wearer's head to provide a three-dimensional virtual representation of objects in the wearer's environment. An electromagnetic (EM) tracking system can track head or body pose. A handheld user input device can include an EM emitter that generates an EM field, and the head-mounted AR device can include an EM sensor that senses the EM field. EM information from the sensor can be analyzed to determine location and / or orientation of the sensor and thereby the wearer's pose. The EM emitter and sensor may utilize time division multiplexing (TDM) or dynamic frequency tuning to operate at multiple frequencies. Voltage gain control may be implemented in the transmitter, rather than the sensor, allowing smaller and lighter weight sensor designs. The EM sensor can implement noise cancellation to reduce the level of EM interference generated by nearby audio speakers.