# US 12,178,564 B2 · Electromagnetic tracking and position measurement system having interference reduction from nearby instrumentation by filtering time-division multiplexed signal via step function > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,178,564 B2 - Document ID: US12178564B2 - Status: Granted - Kind: B2 - Application number: 17/686,112 - Filed: 2022-03-03 - Published: 2022-09-08 - Granted: 2024-12-31 - Earliest claimed: 2021-03-04 - Assignees: Northern Digital Inc. - Applicants: Northern Digital Inc. - Inventors: Westley S. Ashe; William Petrow - Web page: https://patentgrep.com/patent/US12178564B2 ## CPC - A61B 5/062: {using magnetic field} - A61B 34/20: Surgical navigation systems; Devices for tracking or guiding surgical instruments, e.g. for frameless stereotaxis - A61B 5/7203: {for noise prevention, reduction or removal} - A61B 2034/2051: {Electromagnetic tracking systems} - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract An electromagnetic tracking (EMT) system is configured for determining a frequency for generating at least a portion of a magnetic field signal using a transmitter coil of a plurality of transmitter coils. The EMT system configures a time-division multiplexed (TDM) control signal configured to cause the transmitter coil to transmit bursts of the magnetic field signal at the frequency. The EMT system configures a filter for filtering the TDM control signal, the filter configured to shape each burst to reduce or eliminate a harmonic artifact of the bursts. The EMT system causes the transmitter coil to generate the shaped bursts of the magnetic field signal. The EMT system receives, from a sensor, a sensor signal that corresponds to the magnetic field signal, the sensor including the output response indicative of the location of the sensor relative to the transmitter. ## Claims ### Claim 1 A system comprising: a transmitter that includes a plurality of coils, the transmitter configured to generate magnetic field signals; a sensor that includes a receiver coil, the sensor configured to provide sensor signals that correspond to the magnetic field signals generated by the transmitter, wherein the sensor signal is configured to produce an output response indicative of a location of the sensor relative to the transmitter based on the magnetic field signals generated by the transmitter; and a computing device in communication with the transmitter and the sensor, the computing device configured to: determine a frequency for generating at least a portion of a magnetic field signal using a transmitter coil of the plurality; configure a time-division multiplexed (TDM) control signal for controlling transmissions of the magnetic field signal from the transmitter coil, the TDM control signal configured to cause the transmitter coil to periodically transmit bursts of the magnetic field signal at the frequency at a part of a TDM cycle different from other parts of the TDM cycle for one or more other transmitter coils of the plurality; configure a filter for filtering the TDM control signal, the filter configured to shape each burst by filtering a step function to reduce or prevent a harmonic artifact of the bursts, at the receiver coil, resulting from causing the transmitter coil to transmit the bursts of the magnetic signal periodically based on the TDM cycle; cause the transmitter coil to generate the shaped bursts of the magnetic field signal, the generation being periodic based on the TDM cycle, wherein the magnetic field signal comprises a TDM alternating current (TDM-AC) signal; and receive, from the sensor, a sensor signal that corresponds to the magnetic field signal, the sensor signal including the output response indicative of the location of the sensor relative to the transmitter. ### Claim 2 (depends on 1) The system of claim 1, wherein the computing device is further configured to: multiply the magnetic field signal with the step function to shape the bursts. ### Claim 3 (depends on 1) The system of claim 1, wherein the receiver coil comprises a core that has a relative magnetic permeability value greater than 1. ### Claim 4 (depends on 3) The system of claim 3, wherein the core comprises one of a ferrite material or a permalloy material. ### Claim 5 (depends on 1) The system of claim 1, wherein each coil of the plurality of coils in the transmitter is configured to generate a respective magnetic field signal at a respective frequency value that is different from other coils of the plurality. ### Claim 6 (depends on 5) The system of claim 5, wherein each burst is shaped by a filter signal to prevent interference of the magnetic field signal of a coil with adjacent measurement modalities of the other coils of the plurality. ### Claim 7 (depends on 1) The system of claim 1, wherein the sensor signal comprises a voltage that is generated based on interaction between the sensor and the magnetic field signal generated by the transmitter. ### Claim 8 (depends on 7) The system of claim 7, wherein a value of the voltage is indicative of at least one of an orientation and a position of the sensor relative to the transmitter. ### Claim 9 (depends on 1) The system of claim 1, wherein the filter is configured to reduce the harmonic artifact received at another electronic device in an environment to below a threshold level specified for the electronic device. ### Claim 10 (depends on 1) The system of claim 1, wherein the sensor is selected from a group comprising: a hall-effect sensor, a magnetoresistive sensor, a magneto-optical sensor, and a fluxgate magnetometer. ### Claim 11 A method for reducing interference caused by a magnetic tracking system, the method comprising: determining, by a computing device, a frequency for generating at least a portion of a magnetic field signal using a transmitter coil of a plurality of transmitter coils of a transmitter; configuring, by the computing device, a time-division multiplexed (TDM) control signal for controlling transmissions of the magnetic field signal from the transmitter coil, the TDM control signal configured to cause the transmitter coil to periodically transmit bursts of the magnetic field signal at the frequency at a part of a TDM cycle different from other parts of the TDM cycle for one or more other transmitter coils of the plurality; obtaining, by the computing device, threshold data indicating a threshold interference level for one or more devices in an environment of the magnetic tracking system; configuring, by the computing device, a filter for filtering the TDM control signal, the filter configured to shape each burst by filtering a step function to reduce or prevent a harmonic artifact of the bursts, at a receiver coil, resulting from causing the transmitter coil to transmit the bursts of the magnetic signal periodically based on the TDM cycle, below the threshold interference level of the threshold data; causing, by the computing device, the transmitter coil to generate the shaped bursts of the magnetic field signal, the generation being periodic based on the TDM cycle, wherein the magnetic field signal comprises a TDM alternating current (TDM-AC) signal; and receiving, from a sensor including a receiver coil, a sensor signal that corresponds to the magnetic field signal, the sensor including an output response indicative of a location of the sensor relative to the transmitter. ### Claim 12 (depends on 11) The method of claim 11, wherein the threshold data are obtained from one or more other devices after a first transmission of the magnetic tracking system, and, in response to obtaining the threshold data, the filter is configured to shape each burst for a second transmission. ### Claim 13 A method comprising: determining, by a computing device, a frequency for generating at least a portion of a magnetic field signal using a transmitter coil of a transmitter of a magnetic tracking system; configuring, by the computing device, a time-division multiplexed (TDM) control signal for controlling transmissions of the magnetic field signal from the transmitter coil, the TDM control signal configured to cause the transmitter coil to periodically transmit bursts of the magnetic field signal at the frequency at a part of a TDM cycle different from other parts of the TDM cycle for one or more other transmitter coils of the plurality; configuring, by the computing device, a filter for filtering the TDM control signal, the filter configured to shape each burst by filtering a step function to reduce or prevent a harmonic artifact of the bursts, at a receiver coil, resulting from causing the transmitter coil to transmit the bursts of the magnetic signal periodically based on the TDM cycle, wherein the magnetic field signal comprises a TDM alternating current (TDM-AC) signal; wherein the filter is configured to reduce the harmonic artifact received at another electronic device in an environment to below a threshold level specified for the electronic device; causing, by the computing device, the transmitter coil to generate the shaped bursts of the magnetic field signal, the generation being periodic based on the TDM cycle; and receiving, from a sensor of the magnetic tracking system, a sensor signal that corresponds to the magnetic field signal, the sensor signal including an output response indicative of a location of the sensor relative to the transmitter. ### Claim 14 (depends on 13) The method of claim 13, wherein the method further comprises multiplying the magnetic field signal with the step function to shape the bursts. ### Claim 15 (depends on 13) The method of claim 13, wherein a receiver coil of the sensor comprises a core that has a relative magnetic permeability value greater than 1. ### Claim 16 (depends on 15) The method of claim 15, wherein the core comprises one of a ferrite material or a permalloy material. ### Claim 17 (depends on 13) The method of claim 13, wherein the sensor is selected from a group comprising: a hall-effect sensor, a magnetoresistive sensor, a magneto-optical sensor, and a fluxgate magnetometer. ### Claim 18 (depends on 1) The system of claim 1, wherein the computing device is further configured to: determine a parameter value representing a magnetic property of a receiver core of a receiver coil; and configure the filter for filtering the TDM control signal based on the parameter value for the receiver core of the receiver coil. ### Claim 19 (depends on 1) The system of claim 1, wherein configuring the filter for filtering the TDM control signal comprises adjusting a size of a signal envelope based on a determined threshold or a signal strength of a harmonic artifact for the magnetic field signal transmitted by the transmitter coil. ### Claim 20 (depends on 13) The method of claim 13, wherein the computing device is further configured to: determine a parameter value representing a magnetic property of a receiver core of a receiver coil; and configure the filter for filtering the TDM control signal based on the parameter value for the receiver core of the receiver coil. ### Claim 21 (depends on 13) The method of claim 13, wherein configuring the filter for filtering the TDM control signal comprises adjusting a size of a signal envelope based on a determined threshold or a signal strength of a harmonic artifact for the magnetic field signal transmitted by the transmitter coil.