Location determination device and location determination method

Abstract

A method for determining the position and orientation of a localization device, the localization device having a magnet attached to a vibrating element. The method includes exciting the magnet with either an external force or a torque to produce a complex oscillatory motion of the magnet. The complex oscillatory motion includes translational motion and rotational motion of a magnetic moment of the magnet about an axis of rotation, the axis of rotation being located at an offset distance relative to the center of the magnetic moment of the magnet. The method includes sensing a magnetic field generated by the magnet using at least one sensor. The method includes determining the position and orientation of the localization device from the sensing.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to DE 102022120495 A, filed August 12, 2022. The entire disclosure content of German Patent Application No. 102022120495(A) is incorporated herein by reference. [Technical Field]

[0002] The present invention relates to a system and method for determining the position and orientation of a location device. [Background technology]

[0003] Successful in-vivo surgery and diagnostics require localization and tracking of medical robots or tools. In particular, methods and devices that can be used without particular concern for noise interference or signal absorption by biological tissue are the focus of current research.

[0004] Wireless biomedical devices, such as endoscopic capsules and tissue markers, require reliable localization and tracking using trackers with high spatial and temporal resolution to improve the success of medical procedures and diagnoses.

[0005] Over the years, many location methods have been developed. However, these location methods have many drawbacks. For example, X-rays and computed tomography (CT), which emit harmful radiation, and magnetic resonance imaging (MRI), which is easily disrupted, are established localization technologies for medical robots and tools, despite their drawbacks. However, they cannot be used during normal surgical procedures because they require special rooms, large machines, and careful preparation. Millimeter-sized electromagnetic (EM) trackers, for example, can be implanted into diseased tissue under local image guidance and tracked in three dimensions for more efficient radiation therapy. Other trackers, such as those with embedded sensors, can provide high spatial resolution but are generally too large for use on the human body.

[0006] Robots from millimeter to nanometer scale have attracted significant attention over the past few decades due to sophisticated manufacturing techniques, the incorporation of multifunctional materials, and design approaches. These robots are used in medical applications. Current research targets multifunctionality, miniaturization, device autonomy, energy efficiency and biocompatibility. While highly advanced miniaturized devices such as endoscopes and catheters are routinely used in clinical practice, wireless millimeter- to nanometer-scale devices are treated with caution due to poor position feedback and imprecise control.

[0007] Ultrasound (US) systems have also proven effective in locating small devices. Using such US systems inside the body is challenging because different biological materials (bone, organs, muscle, etc.) distort the ultrasound due to non-uniform wave propagation properties, preventing full spatial information from being obtained, and implementing an ultrasound source in a millimeter-scale device is challenging.

[0008] Low frequency electromagnetic (EM) waves and radio frequency (RF) waves in the range of a few kHz to a few GHz are suitable for use as trackers on the human body because they are very little attenuated in biological materials and have no harmful effects. A spatial resolution of less than 2 mm and a temporal resolution of 10 Hz have been achieved using multiple implanted coils with a relatively large size of 8 mm in length. The highly sophisticated design of the chip results in an on-board embedded sensor circuit that measures 3D magnetic field gradients at 10 Hz with sub-millimeter resolution. However, despite its large penetration depth and high accuracy, the RF method is susceptible to the influence of magnetic objects near the tracker. Currently, the permanent magnets embedded in trackers are relatively large (>6 mm) to generate measurable magnetic fields in deep biological tissue. 3 ) but using such permanent magnets is ideal for magnetic operation.

[0009] Magnetic resonance imaging (MRI), widely used in medicine, is a localization technique that allows for three-dimensional scanning of tissues in vivo. However, MRI has poor temporal resolution above 1 Hz and limited spatial resolution, making it unsuitable for tracking sub-millimeter markers.

[0010] Plotkin and Paperno, in Non-Patent Document 1, investigated sensors in magnetic fields. The authors report the development of a magnetic sensor that measures the magnetic field generated by an external electromagnetic coil. This magnetic device requires a wired connection to supply or receive energy and is easily disrupted by medical equipment and ferromagnetic materials.

[0011] Atuegwu and Galloway described a magnetic tracking system in [2]. Magnetic tracking systems are used in image-guided procedures. The magnetic tracking system includes a magnetic field generator and a coil sensor. The magnetic field generator includes a coil that generates an electromagnetic field. The coil sensor measures the voltage induced by the magnetic field generated by the coil. This induced voltage is then used to calculate the position and orientation of the coil sensor. The coil sensor requires a wired connection for energy supply. Coils are easily disrupted by medical devices and ferromagnetic materials.

[0012] Sharma et al., in Non-Patent Document 3, disclose a wireless tracking system using magnetic field gradients. The wireless tracking system then operates inside the human body during surgical and diagnostic procedures. The wireless tracking system includes a microchip, a magnetic sensor, and an inductor coil. The wireless tracking system is sensitive to ambient magnetic fields, and the implanted microchip is large.

[0013] A sensitive magnetic field generator is described by Fernandez et al. in Non-Patent Document 4. The authors disclose a magnetic tracking system based on a simplified position estimation algorithm. The magnetic tracking system includes a fixed magnetic field generating module that generates a known static magnetic field. The magnetic tracking system further includes a movable receiver module that senses the generated magnetic field, processes coordinate values ​​of the generated magnetic field, and transmits an estimated position and orientation of the marker point. This magnetic tracking system is based on a wired system.

[0014] Patent Document 1 discloses a detection, positioning and magnetic tracking system by rotating two magnet bars with a microprocessor, including two magnet bars, a magnet bar excitation circuit, a rotating device, a magnetoresistive sensor, a signal conditioning circuit, an ADC sampling circuit and a control processing unit. The magnetic bar then contains an electromagnetic coil. The magnet bar excitation circuit generates a magnetic field that excites the electromagnetic coil. The rotation device also includes a horizontal rotation stepping motor and a vertical rotation stepping motor, and the two groups of the rotation device respectively control the two magnet bars so that the two magnet bars can freely rotate in the horizontal and vertical directions, respectively.

[0015] Much research has been done on systems that have permanent magnets and determine the position and orientation of a location device. Son et al., in Non-Patent Document 5, disclose a system based on detecting static magnetic fields to determine the position of a tracker. The system includes a large permanent magnet that generates a magnetic field. The magnet used in operation has three box-shaped quadrature coils and a soft iron core. The system further includes a sensor array board having 64 Hall effect sensors that measure magnetic fields in a direction perpendicular to the sensor array.

[0016] Nicolae et al., in Non-Patent Document 6, describe a handheld probe that can detect the position and distance of a magnetic marker. The method for locating the magnetic marker then involves implanting the magnetic marker in the breast lesion and sensing the persistent magnetic field with a handheld probe.

[0017] Passive transponder-based methods have also been used to determine the position and orientation of a locating device. The passive transponder then includes an implantable electromagnetic (EM) coil that operates at radio frequencies. The method involves recording the magnitude of the magnetic moment of an electromagnetic circuit and calculating the phase difference between the emitted and received signals. Willoughby et al. disclose the use of a passive transponder in Non-Patent Document 7, and Hekimian-Williams et al. similarly disclose the use of a passive transponder in Non-Patent Document 8.

[0018] Mechanically resonating magnetic structures are known as magnetic field sensors. US Pat. No. 5,649,499 discloses a magnetic field sensor including a substrate on which a diaphragm is formed. Additionally, the magnetic field sensor includes a ferromagnetic thin film on the diaphragm. Patent Document 2 discloses a magnetic field sensor including an excitation device for exciting a diaphragm and a detection device for detecting the resonance frequency of the diaphragm, which depends on an external magnetic field.

[0019] US Pat. No. 5,629,999 discloses a system for determining magnetic proximity. The determination system includes a substrate and a contact supported by the substrate. A movable element having two separate ends is then attached to the substrate. A first permanent magnet is disposed near a first end of the moving element and generates a first magnetic attractive force and a first torque on the moving element. A second movable magnet is disposed near a second end of the movable element and generates a second magnetic attractive force and a second torque about the axis of rotation.

[0020] US Pat. No. 5,629,999 discloses a method for tracking a marker or location device. The marker device includes a magnetic object that rotates and vibrates, and a restoring torque unit that returns the magnetic object to its equilibrium position when the magnetic object is rotated from the equilibrium position by an external magnetic field. The disclosed method includes generating a magnetic field that causes a magnetic object to rotate and oscillate from an equilibrium position. Rotational vibration of the magnetic object generates an induced signal. This induced signal is sensed, allowing the position and orientation of the marker device to be determined.

[0021] Patent document 5 relates to a method and system for determining the location of an object. In the method according to Patent Document 5, a magnetic field is generated by emitting a magnetic field using a uniaxial source located on one side of a magnetic device, which then generates the magnetic field. The method further includes measuring the magnetic field generated by the magnetic device. By subtracting the emitted magnetic field from the magnetic field generated by the magnetic device, the object's location can be determined. A method for determining the position and orientation of a medical instrument is disclosed in US Pat. No. 6,233,999. The medical device includes a location device having an antenna and circuitry connected to the antenna. The method of Patent Document 6 uses a transmitting unit to emit electromagnetic radiation, so that the circuitry of the location device generates the electromagnetic radiation. A receiving unit senses the generated electromagnetic radiation and is able to determine the position and orientation of the medical device.

[0022] US Pat. No. 6,299,499 describes a tracking system for tracking a marker or location device. The marker device includes a housing having a magnetic object disposed therein. A magnetic object vibrates about its axis of rotation when an external magnetic or electromagnetic excitation acts on the magnetic object. A method for tracking this marker device is also described in US Pat. No. 5,649,399. The method includes generating a magnetic or electromagnetic excitation field that induces mechanical vibration of a magnetic object, simultaneously converting the magnetic or electromagnetic field generated by the induced mechanical vibration of the magnetic object into an electrical response signal, and determining the position of the marker device based on the electrical response signal. US Patent No. 6,299,949 describes a tracking system for tracking the position of a marker device for a medical procedure on a patient's body. The marker device has a sensing unit that includes a magnetic object that provides a permanent magnetic moment. The magnetic object is attached to one end of a mounting part such as a filament, the other end of which is attached to the casing. Additionally, a magnetic object can be rotated from its equilibrium orientation by an external magnetic torque generated by an external magnetic or electromagnetic field acting on the magnetic object. The rotation of the magnetic object is performed around an imaginary axis of rotation that crosses the center of the magnetic object, and the magnetic object is rotationally symmetric about the imaginary axis of rotation. The sensing unit further includes a restoring torque unit. The restoring torque unit then provides a restoring torque to return the magnetic object to its equilibrium orientation when the magnetic object is rotated from its equilibrium orientation by an external magnetic or electromagnetic field. The tracking system includes a plurality of coils configured to generate a magnetic or electromagnetic excitation field that induces mechanical vibrations in the magnetic object. Additionally, the plurality of coils are configured to convert magnetic or electromagnetic fields generated by the induced mechanical vibration of the magnetic object into a plurality of electrical response signals. Additionally, the tracking system includes a plurality of transceivers configured to be connected to the plurality of coils. Additionally, the tracking system includes a processor configured to determine a corresponding position of the marker device based on the one or more electrical response signals. [Prior art documents] [Patent documents]

[0023] [Patent Document 1] Chinese Patent Application Publication No. 102274024 [Patent Document 2] Japanese Patent Application No. 2005201775 [Patent Document 3] U.S. Patent No. 8,519,810 [Patent Document 4] European Patent Application Publication No. 3583896 [Patent Document 5] European Patent No. 2378305 [Patent Document 6] European Patent No. 2034879 [Patent Document 7] U.S. Patent Application Publication No. 2020 / 0397510 [Patent Document 8] US Patent Application Publication No. 2022 / 0257138 [Non-patent literature]

[0024] [Non-Patent Document 1] "3-D Magnetic Tracking of a Single Subminiature Coil with a Large 2-D Array of Uniaxial Transmitters," IEEE Transactions on Magnetics, September 2003, Issue 5, page 3295 [Non-patent document 2] “Volumetric characterization of the Aurora magnetic tracker system for image-guided transorbital endoscopic procedures”, Physics in Medicine & Biology, 2008, issue 53, pages 4355-4368 [Non-patent document 3] “Wireless 3D Surgical Navigation and Tracking System With 100μm Accuracy Using Magnetic-Field Gradient-Based Localization” IEEE Transactions on Medical Imaging, August 2021, Issue 40(8), Pages 2066-2078 [Non-patent document 4] "High-Accuracy Wireless 6DOF Magnetic Tracking System Based on FEM Modeling," IEEE International Conference on Electronics, Circuits and Systems (ICECS), 2018, No. 25, pp. 413-416 [Non-patent document 5] “A 5-D Localization Method for a Magnetically Manipulated Untethered Robot Using a 2-D Array of Hall-Effect Sensors,” EEE / ASME Transactions on Mechatronics, 2016, Issue 21(2), Pages 708-716 [Non-patent document 6] “Evaluation of a Ferromagnetic Marker Technology for Intraoperative Localization of Nonpalpable Breast Lesions,” American Journal of Roentgenology, April 2019, pages 727-733 [Non-Patent Document 7] “Target localization and real-time tracking using the calypso 4d localization system in patients with localized prostate cancer,” International Journal of Radiation Oncology Biology / Physics, 2006, No. 65(2), pp. 528-534. [Non-patent document 8] "Accurate Localization of RFID Tags Using Phase Difference," IEEE RFID, 2010, pp. 89-96 Summary of the Invention [Problem to be solved by the invention]

[0025] This specification discloses a miniature magnetic vibration localization (SMOL) method and apparatus capable of wirelessly localizing trackers, such as millimeter-scale trackers. Using the present method and apparatus, the tracker can locate in all six degrees of freedom (6DoF) even over long distances in viscoelastic environments, such as biological materials, without using radiation or RF signals. The device is a mechanically resonant structure in the form of a magnet that utilizes a single, finite magnetic moment. The magnet is then attached to a tiny cantilever and oscillated at a designed frequency around a rotation axis perpendicular to the single finite magnetic moment, breaking the magnet's rotational symmetry. This mechanical resonant structure is excited by an excitation coil, and the magnetic signal it emits after excitation can be sensed by an external sensor unit, which, by evaluating this external sensor unit, can achieve full six-degree-of-freedom positioning with sub-millimeter accuracy and very high angular accuracy with a single sub-millimeter-sized magnet.

[0026] This mechanically resonant structure may be excited by providing linear mechanical motion (in the form of a longitudinal or transverse wave) in a direction substantially perpendicular to the long axis of the microcantilever and in the plane of vibration of the microcantilever. This linear mechanical motion creates relative motion between the housing and the magnet, exciting the magnet on the tiny cantilever. The connection between the housing and the magnet is non-rigid, i.e., elastic, and has a finite length (corresponding to the cantilever length of the microcantilever), and relative motion inputs kinetic energy into the microcantilever, which is converted into elastic (potential) energy within the microcantilever by deflection of the microcantilever.

[0027] The microcantilever has a resonant frequency, and naturally, when the microcantilever is mechanically excited at this resonant frequency, the vibration amplitude increases with each movement of the housing. Because mechanical excitation does not require a magnetic field to excite the resonant structure, this type of mechanical excitation does not interfere with the magnetic signal resulting from the oscillating magnetic moment. Unlike the prior art, no torsional motion is required to excite pure torsional motion of the resonant structure of the device.

[0028] The use of magnets means the device is compatible with common magnetic motion methods and can be used to track robots. The SMOL device combines the frequency encoding properties of an EM device with the miniaturization of magnets. The alternating magnetic field generated by the vibrating micromagnet is measured at multiple locations and fitted to a magnetic field model using a weighted Levenberg-Marquardt optimization algorithm to accurately determine all three translational and three rotational degrees of freedom of the device. The SMOL device can be easily integrated into a spiral millirobot, and the micromagnets can be used for both localization and movement under various magnetic field excitations. The millirobot will be tested in a biological gel phantom that mimics human brain tissue and a real pig brain. As a result, full six-degree-of-freedom tracking of the millirobot was achieved with sub-millimeter resolution for three translational degrees of freedom, sub-1 degree for two rotational axes perpendicular to the cantilever, and a very high spatial resolution of approximately 4° for the cantilever axis. The SMOL method requires simple instrumentation and maintains a high signal-to-noise ratio (SNR) in magnetically noisy environments by leveraging the device's unique frequency response. One possible field use is to localize small robots deep inside the human body in actual clinical situations. [Means for solving the problem]

[0029] Described herein are methods for determining the position and orientation of a location device, such as a tracker. First, the localization device has a magnet attached to a vibrating element located within the tracker. The magnet is excited using an external force or torque, such as an excitation magnetic field or a mechanical wave, which causes a complex oscillatory motion of the magnet, generating a varying magnetic field from the magnet itself. This complex oscillatory motion involves translational motion and rotational motion of the magnetic moment of the magnet. The complex oscillatory motion is a rotational motion of the magnet about an axis of rotation, the axis of rotation being located at an offset distance relative to the center of the magnetic moment of the magnet. As highlighted above, the inventors have discovered that this offset distance allows excitation of the magnet with mechanical waves. The magnetic field generated by the magnet is sensed using at least one sensor, and from this sensing the position and orientation of the locating device may be calculated.

[0030] The mechanical waves may vibrate in the longitudinal and / or shear direction of the vibrating element.

[0031] The axis of rotation and the magnetic moment vector emanating from the magnet are not parallel, and in one embodiment are substantially perpendicular to each other.

[0032] The vibrating element is disposed within a rigid or semi-rigid housing to protect it from surrounding biological tissue.

[0033] To avoid saturation of the sensor, sensing is performed with the excitation field turned off.

[0034] The vibration element includes a restoring force unit consisting of at least one cantilever beam or similar unit having an elastic restoring force.

[0035] The excitation, sensing, position and orientation determination of the localization device may be repeated (continuously) or may be performed non-continuously.

[0036] The excitation frequency of the magnet is approximately equal to the resonant frequency of the oscillator.

[0037] The method may be used to determine the local viscoelastic properties of a material.

[0038] After sensing the magnetic field generated by the magnet, the local viscoelastic properties of the material may be determined. The determined local viscoelastic properties of the material may further be used to determine the position and orientation of the localization device.

[0039] Also described herein is an apparatus for determining the position and orientation of a location device. The location device has a housing, and the magnet attached to the vibrating element is disposed within the housing. The localization device also includes an excitation unit that excites the magnet using either an external force or a torque, thereby creating a complex oscillatory motion of the magnet. This complex oscillatory motion involves translational motion and rotational motion of the magnet's magnetic moment about an axis of rotation that is located at an offset distance relative to the center of the magnet's magnetic moment. Furthermore, the localization device comprises a data acquisition unit that senses the magnetic field B generated by the oscillating magnet using a sensor.

[0040] The magnets include permanent magnets made of a magnetic material, preferably a ferromagnetic material.

[0041] The vibrating element includes a restoring force unit, in one aspect a cantilever.

[0042] The localization device is used to locate a medical implant in an animal or human body selected from one or more of a catheter, a stent, a guidewire, an endoscope, a capsule endoscope, a drug delivery device, or a miniature robot, or to locate an anatomical structure selected from one or more of a tumor, a blood vessel, a thrombus, a polyp, or a nerve. [Brief explanation of the drawings]

[0043] [Figure 1A] 1 shows an overview of a system with magnetic field excitation.

[0044] [Figure 1B] 1 shows an overview of a system with mechanical excitation.

[0045] [Figure 2] The device is shown with the cantilever in rest and deflected positions.

[0046] [Figure 3A] The time sequence of F, θ, and B is shown.

[0047] [Figure 3B] The timeline of the actual data time signals of F, θ, and B is shown.

[0048] [Figure 4] 4A-4D show schematic diagrams summarizing four methods for determining the position and orientation of a localization device.

[0049] [Figure 5] 5A to 5C show the sensing results of the location device within the housing.

[0050] [Figure 6] 1 shows a location device incorporated into a device that includes interconnected components.

[0051] [Figure 7] 1 shows a data evaluation flow chart for determining the position and orientation of a localization device.

[0052] [Figure 8] 10 shows a surface mesh of the tracker's measurement signal amplitude in the x-direction.

[0053] [Figure 9A] The localization accuracy along the x-axis and z-axis is shown for a 50 mm and 25 mm translation of the tracker along each axis.

[0054] [Figure 9B] 9A and 9B show experimental and simulation results showing the angular accuracy of the tracker's rotation around its native Z and Y axes.

[0055] [Figure 10]Simulations of absolute depth error are shown for increasing depth with varying noise and magnet conditions.

[0056] [Figure 11] The signal-to-noise ratio of the B-field signal measured in the x-direction at different distances from the sensor is shown.

[0057] [Figure 12] 10 shows the maximum localization depth of the localization device across resonant frequencies.

[0058] [Figure 13] 1 shows a view of the housing of a location device.

[0059] [Figure 14] 1 illustrates an embodiment in which the tracker is integrated into a millirobot.

[0060] [Figure 15] 1 shows the position and angular errors of a localization device integrated into a millirobot.

[0061] [Figure 16] 1 shows an embodiment in which a tracker within a millirobot is inserted into the cerebral gray matter of a pig's brain.

[0062] [Figure 17] The tracker inside the millirobot is inserted into brain tissue and localized using ultrasound, showing images.

[0063] [Figure 18] The results of the magnetic field amplitude difference when the tracker is rotated around the Z axis are shown.

[0064] [Figure 19] 1 shows a Maxwell diagram of a tracker in a viscoelastic medium.

[0065] [Figure 20]1 shows the attenuation coefficient of the magnetic signal of the localization device inside the gelatin.

[0066] [Figure 21] 1 shows the attenuation coefficient of the magnetic signal of a localization device in ex vivo animal tissue.

[0067] [Figure 22] 1 shows an example of the shape of a cavity in a localization device.

[0068] [Figure 23] 1 shows a flowchart for determining the position and orientation of a localization device. DETAILED DESCRIPTION OF THE INVENTION

[0069] The present invention will be described with reference to the drawings. The embodiments and aspects of the present invention are merely examples and do not in any way limit the scope of protection claimed. The invention is defined by the claims and their equivalents. Features of one aspect or embodiment of the invention may be combined with features of other aspects and / or embodiments of the invention.

[0070] FIG. 1A shows an overview of a system for detecting a localization device or tracker 10 within (soft) biological tissue 20 using an excitation coil 30 that is supplied with current to generate an excitation field, and a sensor unit 40 that measures orthogonal components of the time-varying magnetic fields Bx, By, Bz from the tracker 10. FIG. 1B shows an overview of a system for detecting a localization device or tracker 10 within (soft) biological tissue 20 using a mechanical excitation source 31 in physical contact via connecting pieces 32 to generate mechanical waves, and a sensor unit 40 that measures orthogonal components of the time-varying magnetic fields Bx, By, Bz from the tracker 10. As mentioned above, the SMOL method is based on the principle of mechanical resonance of a cantilever structure, as shown in FIG. 2, to which is attached a magnet 220 that generates a finite magnetic moment m. Tracker 10 includes a housing 200 having a cavity 210. In one non-limiting example, the cavity 210 is rectangular prism shaped. The cantilever structure includes a cantilever 230 (or beam) with a magnet 220 disposed at a first end 235 of the cantilever 230 .

[0071] The magnet 220 is made of a permanent magnet such as a ferromagnetic material, and functions as a device for transmitting the mechanical force of the excitation force F to the cantilever 230 and as a device for emitting a varying magnetic field for sensing. In the following description, the magnetic flux density B of the varying magnetic field is referred to as the B field or the magnetic field, and its orientation is represented by an external Euler rotation sequence zxy from the initial orientation (0°, 0°, 0°) of the cantilever 230 in its rest position (solid line) shown in Figure 2.

[0072] FIG. 22 shows a further example of the shape of the cavity 210. The inventors have discovered that optimizing the shape of the cavity 210 allows the deflection angle θ of the magnet 220 to be increased. The larger the deflection angle θ, the stronger the signal of the magnetic field B and the more accurate the localization of the localization device 10 becomes. In a non-limiting example, simulations have confirmed that the localization depth at which the localization error is less than 1 mm increases by 20% by increasing the deflection angle from 10° to 20°. Since the localization depth depends directly on the localization error, increasing the deflection angle provides higher accuracy at the same distance. When the deflection angle exceeds 30°, the rate of increase in localization depth with increasing deflection angle decreases significantly.

[0073] When cavity 210 is shaped as shown in FIG. 22, the deflection angle θ of magnet 220 can be increased compared to cavity 210 shaped as a rectangular parallelepiped as shown in FIG. 2, assuming that the internal volume of cavity 210 is the same. Optimization of the shape of the cavity 210 then depends on the size and deformation shape of the cantilever 230, the size and shape of the magnet 220, the path of travel 240 of the magnet 220, and the field of application. Certain shapes of cavity 210 are advantageous over others.

[0074] It has also been found that the “optimized” shape of cavity 210 needs to be wider so that magnet 220 has more freedom to rotate and translate within cavity 210 . However, there is a trade-off between the size of the housing 200 and the strength of the signal. This trade-off must be made and is dependent on the requirements of the application. For tracking a medical instrument outside the human body, such as a scalpel, the small tracker 10 is substantially unnecessary. Larger trackers 10 can be used where the cavity 210 is an optimized shape. A smaller tracker 10 is advantageous in intracorporeal, minimally invasive applications for tracking medical instruments from outside the body. However, the smaller tracker 10 comes at the cost of lower signal strength. The shape of the cavity 210 is designed based on, for example, optical recording of the movement path 240 of the magnet 220 of the cantilever 230 . The movement path 240 is then evaluated by a physical model such as beam theory or physical estimation.

[0075] The magnetic field B generated by the magnetic moment m of the magnet 220 is approximated by an ideal dipole model. TIFF2025528179000002.tif8170

[0076] JPEG2025528179000003.jpg10170JPEG2025528179000004.jpg11170 For a point in space (in this case sensor 40), the distance to the dipole center 225 of an arbitrarily oriented cantilever 230 can be expressed as: TIFF2025528179000005.tif6169

[0077] JPEG2025528179000006.jpg46170 TIFF2025528179000007.tif5169

[0078] JPEG2025528179000008.jpg14170 The time-dependent equation 1 is completed when the magnetic moment at rest is oriented positively in the x direction. TIFF2025528179000009.tif9170

[0079] matrix R y represents the rotation around the y-axis of the deflection angle θ in the right-handed coordinate system, and B r is the remanent field of the magnet and V is the magnetic volume. Therefore, by rotating around the vertical axis, the time-dependent oscillating dipole magnetic field is no longer rotationally symmetric around the axis of the static dipole magnetic moment, as expressed in equations (3) and (4). This gives the respective position r and rotation matrix R q For, we obtain a unique solution to equation (1). Thus, all six degrees of freedom of tracker 10 can be determined.

[0080] External magnetic field B perpendicular to the magnetic moment m of magnet 220 ext Assuming that, torque τ is applied to magnet 220, and the magnetic moment m of magnet 220 is changed to B ext Match it with TIFF2025528179000010.tif5170

[0081] A torque τ is transmitted to the cantilever 230, resulting in a restoring torque (bending moment) and an angular deflection θ. Due to the physical limitations of the available vibration volume within cavity 210, the movement of cantilever 230 with magnet 220 is limited to a maximum angle θ max is limited to.

[0082] A schematic time sequence of measurements at a single point with a single sensor 40 using magnetic excitation is shown in FIG. 3A. The measurement can be divided into an excitation phase (S100) and an evaluation phase (S110). In the first phase, the coil current I coil passes through excitation coil 30, generating an excitation field and inputting energy into the system, moving cantilever 230 at its resonant frequency and gradually increasing the deflection angle θ. The magnitude of the excitation magnetic field F exceeds the measurement range of the sensor 40, causing the sensor 40 to periodically saturate. In the second phase, the excitation field F is off (S105), and the energy stored in the cantilever 230 is released in an underdamped oscillatory motion, as shown in the second row of FIG. 3A. The position of magnet 220 moves in space as shown in FIG. 2 (dashed line) and described by Equations 2-4. Movement of magnet 220 emits a magnetic field that varies according to equation (1).

[0083] Vibration of tracker 10 will now be explained using the example of FIG. 3B. The values ​​are not limiting but are used only to illustrate the invention. The cantilever 230 shown in FIG. 2 was magnetically excited at a resonant frequency of 187 Hz by 10 square wave pulses of the excitation coil 30 and recorded with a high-speed camera. Magnetic signal B at one of the sensors 40 in the x direction x (i.e., the x-component of the changing magnetic field resulting from the magnet 220 oscillating on the beam) and the current I in the excitation coil coil and was measured for 0.3 seconds. In Figure 3B, I coil the value of , the angular deflection θ, and the magnetic signal B x The corresponding values ​​of are compared. At the start of the measurement, the magnetometer in the sensor 40 is saturated by the external excitation magnetic field F, and the saturation magnetic field is ±3.5 μT. Image analysis shows a direct increase in the deflection angle θ, visually assessed at 5000 frames / s. The excitation occurs at time t off When stopped at , an exponential decay of the deflection angle θ is observed. This can be described mathematically as a damped harmonic oscillator with frequency f and damping coefficient η. TIFF2025528179000011.tif5170

[0084] Similarly, the magnetic signal in direction i and position j can be written as: TIFF2025528179000012.tif5170 JPEG2025528179000013.jpg5170 This offset C is a constant value that does not change and depends on several factors, including the geometry of the system. JPEG2025528179000014.jpg14170

[0085] 4A through 4D show schematic diagrams summarizing four methods for determining the position H and orientation T of tracker 10. All four methods involve three main steps. The three main steps are an excitation step S100, in which an external force or torque F is used to excite magnet 220, thereby causing a complex oscillatory motion of magnet 220; a sensing step S110, in which the changing magnetic field B generated by magnet 220 is sensed; and a determination step S120, in which the position H and orientation T of tracker 10 are derived.

[0086] As shown in FIG. 4A, in an excitation step S100, the magnet 220 can be continuously excited, i.e., the magnet 220 vibrates continuously, and at a certain moment the magnetic field B is sensed (sensing step S110) and the position H and orientation T are determined. As shown in FIG. 4B, sensing of the magnetic field B in a sensing step S110 can be repeated during successive excitations in an excitation step S100, and the position H and orientation T can be repeatedly determined in a determining step S120. The sensing of the magnetic field B in the sensing step S110 may be repeated after the position H and orientation T are determined in the determining step S120.

[0087] The excitation step S100 may be discontinuous, meaning that the excitation stops at step S105 and the complex oscillations of the magnet 220 decay over time. As shown in FIG. 4C, in a sensing step S110, the magnetic field B is sensed and the position H and orientation T are determined. As shown in FIG. 4D, the excitation step S100 is repeated after the sensing step S110 because excitation was stopped in step S105, or after the determining step S120 of determining the position H and orientation T of tracker 10.

[0088] Then, by repeating this excitation step S100, either continuous (FIG. 4B) or discontinuous (FIG. 4D), followed by a sensing step S110 and a determination step S120 of the position H and orientation T of the tracker 10, the position H and orientation T of the tracker 10 can be determined over time. The non-sequential excitation step S100 and subsequent steps S105, sensing step S110 and decision step S120 can be performed, for example, in periodic time steps or as needed.

[0089] 5A-5C show the results of sensing step S110 of tracker 10 within housing 200. The magnetic signal B was recorded in the soft and hard gelatin-agarose hydrogels for 60 ms. Figure 5A shows the excitation (t shifted 5A and 5B show the Bx component of the fluctuating magnetic field B measured after the ion beam irradiation (=0) in the time domain, and in FIG. 5C in the frequency domain.

[0090] Between the end of excitation and the start of evaluation, a short buffer of 3 ms is used to allow cooling of the excitation coil. It can be seen that the raw signal exhibits low frequency noise, which is also confirmed by the discrete Fourier transform (DFT) in Figure 5C. A high pass filter was used at the (higher) resonant frequency and is shown as the filtered signal.

[0091] This signal can then be fitted with equation (7) using the Levenberg-Marquardt algorithm to extract the decaying sinusoidal features (solid lines in Figures 5A and 5B). Due to the damping behavior, the DFT peaks (Fig. 5C) are broadened and the frequency resolution is very low at 17 Hz, leading to an inaccurate analysis of the frequency spectrum. Figure 5C also shows a 10-second recording of the noisy magnetic environment in which all tests were performed. The strongest noise amplitudes of up to 56 nT were measured at 16.7 Hz, 28 Hz, and 50 Hz. The dominant frequency in the range above 100 Hz is about 2.5 nT, which limits the localization distance.

[0092] Tracker 10 can be incorporated into a device 5 that includes interconnected components as shown in FIG. For purposes of illustration, excitation using a magnetic excitation field is shown here. Repetitive instrument control and data processing were performed in MATLAB.

[0093] The sensor unit 40 includes three fluxgate sensors mounted on a two-dimensional positioning stage 45, aligned orthogonally to the 3D printed customized element. The positioning stage 45 is mounted on a 75 cm long rod to reduce magnetic influences from the electric motor that drives the positioning stage 45 . The sensor 40 moves in a grid pattern in the xy plane. At each position, the estimated resonant frequency f res A predetermined excitation signal of is sent to the current amplifier 35, which further generates a current I coil to the excitation coil 30. An alternating current (AC) induced in excitation coil 30 generates an AC magnetic field that can excite (S100) the mechanical resonant structure of tracker 10 with an excitation force F as described above.

[0094] An exemplary signal evaluation procedure step S120 is shown in FIG. The sensor signal recorded by the sensor 40 includes the excitation signal from the excitation coil 30 and therefore first cuts off the evaluable signal at the cut-off time. This cut-off time depends on the behavior of the excitation coil 30 and the individual configuration of the sensor 40 . f exct A moving average of a time window length that depends on is calculated and acts as a low pass filter S121. The moving average is subtracted from the raw magnetic signal B to obtain a high-pass signal containing the resonant frequency signal of the cantilever 230.

[0095] The Levenberg-Marquardt algorithm is developed to fit equation (7) to this high-pass signal to obtain the relevant free parameters of equation (7) (step S122). The signal amplitude obtained in step S122 can be further filtered in step S123 using parameters such as frequency, damping coefficient, and coefficient of determination. The threshold value of the physically unreasonable values ​​filtered in steps S122 and S123 may be, for example, a predefined fixed value.

[0096] The amplitude A obtained through steps S121 to S123 has its x-direction component illustrated in the surface mesh of FIG. 8, and is used as input for the final position identification step S124. JPEG2025528179000015.jpg16170TIFF2025528179000016.tif7170 JPEG2025528179000017.jpg13170TIFF2025528179000018.tif9170Here, p is a vector of optimization parameters including the positions x, y, z, the orientations q0, q1, q2, q3 given as quaternions, and the deflection angle θ. The parameters are randomized within physically reasonable ranges and the optimization algorithm is iterated a fixed number of times to avoid outliers. Once the optimal parameters p are automatically selected, the position H and orientation T of the tracker 10 are obtained.

[0097] To demonstrate the localization accuracy, both actual experiments and simulations using Model M were conducted. Because it is difficult to visually determine the actual value on the measurement surface to an accuracy of less than 1 mm, differential measurements were made.

[0098] FIG. 9A shows the localization accuracy along the x-axis and z-axis for translations of 50 mm and 25 mm along each axis. The localization values ​​along the x-axis are in perfect agreement with the actual values ​​over the entire 50 mm range, which is half of the total 100 mm x 100 mm scan surface, with an average accuracy of 0.6 mm ± 0.6 mm, and a maximum difference from the actual values ​​of 0.6 mm at the edge of the scan area. Since the scanned area is symmetrical along each of the x and y axes, the errors in the -x, -y, and +y directions are expected to be similar to +x. On average in the z-axis, the accuracy of the z-distance between 50mm and 75mm is 0.7mm±0.9mm. According to equation (1), the magnetic field attenuates as the cube of the distance, so the accuracy decreases as the distance increases. For distances less than 65 mm, the accuracy is 0.5 mm ± 0.6 mm. Overall, the movement accuracy in all directions was significantly less than 1 mm, demonstrating the high accuracy of the SMOL method.

[0099] FIG. 9B shows the angular accuracy of rotation about the z-axis and y-axis (of FIG. 2) inherent to the localization device 10, respectively. To determine the angular deviation, an axis perpendicular to the axis of rotation is used as the reference and the standard deviation is calculated using circular statistics. For rotation around the cantilever axis, i.e., the z-axis (Fig. 2), the accuracy is 3.4°±3.7°, whereas for rotation around the y-axis, the accuracy is significantly improved to 0.7°±0.8°. Due to the orthogonality of the rotation axes, similar accuracy can be expected for rotation around the magnetic moment axis (x-axis). Overall, the cantilever axis exhibits larger variations compared to the other two axes perpendicular to the cantilever, but all rotational localization accuracies are significantly lower than 5°.

[0100] Simulation results are also shown in Figures 9A and 9B and are in excellent agreement with the experimental results in all accuracy measures. The numerical model clearly demonstrates the important features of the SMOL method, since it takes into account magnetic noise in all directions. The agreement between simulation and experiment demonstrates the validity of the numerical model, thus providing a valuable method for predicting and optimizing the performance of compact, extended-range trackers 10.

[0101] To understand the performance of the SMOL method under various magnetic noise conditions, we measured the absolute depth error z as the depth z increased under different noise and magnet conditions. err Simulate the following. As shown in FIG. 10, the reference curve (black) represents a system where the noise factor (NF) and magnetic moment factor (MF) are both equal to one. This means that the noise and magnetic moment used in the simulation are the same as in the experimental setup. The effect of halving the noise (NF=0.5, MF=1) or halving the magnetic moment (NF=1, MF=0.5) is shown. It can be seen that for all curves, the localization error remains at a very low (sub-millimeter) level at close distances, but increases significantly above a certain threshold. The maximum localization distance is defined as the distance at which the localization error first reaches 0.5 mm (dashed horizontal line). Simulation results show that a tracker with half the magnetic moment can accurately locate up to a distance of 65 mm, and by attenuating the magnetic noise by half, the distance can be increased to 90 mm. In a magnetically shielded room (which only considers the electronic noise of the magnetic sensor), a theoretical detection distance of up to 110 mm can be achieved. Overall, operating in a magnetically shielded or low-noise environment and using more sensitive magnetometers (40) can significantly increase the localization depth beyond 100 mm, making the SMOL method suitable for real-world clinical localization applications, e.g., for miniature robots deep inside the human body.

[0102] FIG. 11 shows the signal-to-noise ratio (SNR) of the B-field signal measured in the x direction at different distances from the sensor z. The damped sinusoidal signal has a high pass filter S121 applied to it so that pure noise is processed as well. Without filtering frequencies below 270 Hz, the tracker's resonant frequency, the standard deviation of the noise is 20.9 nT, but after filtering, this drops to 1.7 nT. The latter value is used for evaluation, and the amplitude A is the maximum measured amplitude after filtering. As shown in Figure 11, the SNR of the simulation was over 170 at a distance of 45 mm and over 25 at a distance of 80 mm, and this trend is in good agreement with the third-order attenuation model of the magnetic field based on distance. The good fit with the experimental data indicates that the physical processes in the simulations are correctly modeled.

[0103] Therefore, the simulation reflects the real system with high accuracy; in other words, the real system behaves ideally enough to be numerically simulated, and further characterization of the tracker 10 is performed numerically.

[0104] The frequency scalability of the SMOL method is shown in Figure 12. Simulations were performed in the frequency range from 100 Hz to 1 kHz using the recorded noise, with the maximum localization distance (black) being the value at which the localization error was 0.5 mm (horizontal dashed line in Figure 10) (Figure 5C). It can be seen that as the frequency increases, the localization depth increases significantly. For example, for a 100 Hz tracker 10, the maximum location distance is approximately 60 mm, and for an 800 Hz device, the distance nearly doubles to 120 mm. The main reason is magnetic noise (from the environment and sensing electronics). N (gray) amplitude decreases across frequencies. What is noteworthy is that there are strong noise amplitudes (shown as grey boxes) at certain frequencies such as 250Hz, 350Hz, and 450Hz. At these frequencies, strong noise significantly impedes localization distances (black squares). Therefore, the optimum operating frequency for the SMOL method must be selected so that the environmental noise and the noise inherent in the sensor are minimized.

[0105] Increasing the resonant frequency not only increases the maximum localization distance, but also enables tracker 10 to be made even more compact. A spatially constrained two-dimensional geometric model of the cantilever 230 (Figure 2) was used to create a cantilever with a total volume of 1 mm 3 A miniaturized and optimized tracker 10 is designed and simulated. The results are shown in Figure 12 as black stars. The magnetic volume is 0.4 mm 3(1 mm x 0.8 mm x 0.5 mm), the maximum deflection angle is θ=17°, and the length of the cantilever 230 is 0.5 mm. To obtain a resonant frequency of 800 Hz with such a device, a steel cantilever approximately 5 μm thick and 1 mm wide is required. Using MEMS fabrication techniques, it is possible to fabricate devices that allow full six-degrees-of-freedom positioning with sub-millimeter accuracy over distances 100 times the size of the tracker. The SMOL method therefore opens up unprecedented possibilities for localizing and tracking sub-millimeter-scale implants, including miniature robots, deep within the human body.

[0106] The method described herein uses magnets 220 that can also be used for magnetic actuation of small robots. During actuation, a magnetic torque (Equation 5) about the cantilever axis is exerted on the micro-magnet 220, and the cantilever 230 can transmit a twist to the housing 200, which causes the tracker 10 to rotate.

[0107] In one embodiment of the method and apparatus of the present invention, the housing 200 has a helical or screw-like surface 201, as shown in FIG. 13, that allows it to combine rotational and translational motions to navigate through the soft viscoelastic material. In the design of robot R, special care was taken to avoid damaging the thin cantilever 230. If the magnet 220 were to rotate freely without angular constraints, the strong magnetic torque would continue to twist the cantilever 230 , exceeding the strength limit of the cantilever material and leading to permanent plastic deformation and breakage of the beam 230 . A geometric constraint (see FIG. 13) is added inside the housing 200, and the cantilever 230 directly contacts the housing 200, thereby transmitting torque to the housing 200.

[0108] In one embodiment, the tracker 10 is incorporated into a millirobot R that moves on a path P, as shown in FIG. The screw-shaped robot R was powered by a rotating permanent magnet with two rotation axes. When moving forward, the axis of motion must be aligned with the cantilever axis. To rotate the robot R, the operating magnet must be rotated about the steering axis. Since the SMOL method currently does not allow simultaneous movement and localization, measurements were performed in stages (HT1 to HT9), i.e. the vessel was cycled through movement and localization steps.

[0109] Detailed analysis shows that the planar position error (x, y in Figure 15) obtained at a distance of 40 and 50 mm from the sensor is on average 0.2 mm ± 0.1 mm compared to the visual actual values. The z position is stable around an average value of 50.3 mm ± 0.6 mm. The angular measurement of the planar angle ψ is averaged over all measurement points with a standard deviation of 1.5°, resulting in a mean error of 4.7°±3.6°. These results show that the presented method is capable of accurate localization and further demonstrate that the same magnetic moment m on a small robot R can be used for both motion and localization purposes. In one embodiment, the tracker 10 or robot R is insertable into biological tissue such as the brain, which is known to be one of the softest tissues in the human body. Since mechanical vibration behavior is strongly damped in brain tissue, it is expected that the function of the mechanical vibration element will be hindered, making it more difficult for the tracker 10 to obtain a sustained vibration signal for accurate localization.

[0110] Therefore, brain tissue was chosen as a realistic and demanding testing environment for the presented method. The results of the method of the present invention performed on an ex vivo pig brain are shown in FIG. Shows half of a pig's brain and tracker 10 in robot R inserted into the cerebral gray matter. Ultrasound imaging is used to obtain planar information of the position H of the tracker 10 relative to the fixed boundary of the vessel.

[0111] As shown in FIG. 17, the overall ultrasound imaging resolution and contrast is poor due to multiple reflections and scattering of the ultrasound beam in the heterogeneous brain tissue. Robot R (circled area) at a distance of 40 mm from the ultrasound probe is barely distinguishable from the background noise. In contrast to ultrasound imaging, the SMOL method accurately detects the position H and orientation T of the robot R within the brain. As shown in Figure 6C, the localization information of the position H and orientation T of the robot R within the brain is superimposed on the ultrasound image, showing very good correlation between the two localization methods. Ten independent measurements at a Z distance of 45 mm from the magnetic sensor 40 yield a standard deviation of 0.9 mm in the x direction and 0.7 mm in the y direction. This demonstrates the high reproducibility of the presented method in biological soft tissues. The white arrow indicates the detected orientation H of the robot R's main axis, which is in excellent agreement with the orientation estimated by ultrasound imaging. There is a deviation of about 3 mm in the Y direction. This systematic error may be caused by soft tissue deformation due to compression of the US probe. This is because the probe must be in close contact with the brain tissue via ultrasound gel during imaging. This shows that the method of the present invention has another important advantage over ultrasound imaging. The method of the present invention is a wireless localization method that does not require mechanical contact with biological tissue, which is an important aspect for protecting delicate soft organs such as the brain in actual clinical applications.

[0112] The method of the present invention provides a completely wireless localization technique that does not require external devices 30 and 40 to physically contact the soft biological tissue 20, which is useful in minimally invasive and robotic surgeries where direct contact of imaging probes with internal organs is often not possible. The minimal incision required to insert tracker 10 into the body is very small and can be easily introduced via a needle, catheter, or endoscope. The Tracker 10 has a small footprint and does not require an on-board power source, making it easy to incorporate into wireless medical devices such as capsule endoscopes and implants. In addition to miniaturization (Fig. 12), the high SNR (Fig. 11) and high accuracy over long distances (Fig. 10) exceed the capabilities of other wireless tracking methods, such as those based on static permanent magnets. The unique tunable frequency response of tracker 10 facilitates isolation from DC and low frequency magnetic noise (i.e., magnetic surgical tools).

[0113] In one embodiment, the unique frequency response of tracker 10 can be used to distinguish between multiple trackers 10 in this frequency space for simultaneous six-degree-of-freedom localization of multiple targets.

[0114] The method of the present invention breaks the rotational symmetry of the magnetostatic dipole by oscillating the magnetic moment about an axis perpendicular to the magnetic moment axis. JPEG2025528179000019.jpg16170 This mathematical consideration means that only five degrees of freedom can be determined, the same as the five degrees of freedom of a magnetostatic dipole.

[0115] JPEG2025528179000020.jpg16170 The difference between these two cases is shown in FIG. 18 with cantilever 230 (solid line) and without cantilever 230 (dashed line). The tracker 10 can detect amplitude differences in the oscillating magnetic field in the nanotesla range only in the presence of a cantilever 230 (FIG. 2) that rotates about the z-axis and cancels the oscillating magnetic moment m, whereas without the cantilever 230 the amplitude difference is close to or equal to zero. The high asymmetry of the amplitude for all rotations from 0° to 180° reveals that the method of the present invention is characterized by its ability to determine six degrees of freedom from the amplitude.

[0116] DC magnetic fields are noisy and such small devices cannot reliably detect DC magnetic fields from long distances, so measurements only consider the amplitude difference as useful information, not the absolute DC magnetic field.

[0117] Another way to determine the six degrees of freedom is to capture the double frequency component of the oscillating B-field. Due to the high spatial nonlinearity of the dynamic B field component of the magnetic dipole, the amplitude field of the oscillating dipole has zero crossings. When the sensor position is near such a zero crossing, the B-field signal exhibits a frequency component at twice the resonant frequency. However, these features can only be reliably measured if the B-field is closely scanned. In comparison, the presented method involving the cantilever 230 provides a uniquely more convenient way to sense all six degrees of freedom with far fewer magnetic sensors 40 and without relying on such features.

[0118] Because a single excitation coil 30 is used, not all orientations of the tracker 10 can be sufficiently excited to achieve large deflection amplitudes. If the magnetic torque τ (Equation 5) applied to the cantilever 230 via the external excitation magnetic field F (FIG. 3) is oriented close to or equal to zero, the deflection amplitude will not be large. This is true when the external magnetic field is parallel to the magnetic moment axis. Between perpendicular and parallel, the magnetic torque τ gradually decreases, so that the maximum deflection is not always achieved. To cover all orientations, a total of three orthogonally arranged excitation coils 30 are required, with the direction of the superimposed B field preferably parallel to the orientation T of the cantilever 230 detected previously. An omni magnet may be suitable for this application.

[0119] The system of the present invention (FIG. 6) is a two-dimensional scanning system that covers 25 points within a square with a side length of 10 cm in the xy plane. The range of the fluxgate sensor 40 is approximately ±3.5 μT, so the sensor will easily saturate if a strong ferromagnetic object is brought close to the scan region. A manual B-field correction function embedded in the sensor 40 is used once at the center of the scan region to correct for external B-fields. If the B field gradient along the scan plane is greater than a specified range, this process will not be able to detect a signal. In the future, automatic DC field correction can be performed at each location or a static sensor array 40 can be used.

[0120] Tracker 10 is a mechanical system and, as such, its characteristics may change over time and with use. The material used for cantilever 230 (C1095) has a very low chromium content and is particularly susceptible to corrosion. Since a decrease in resonance frequency over time has been observed in many prototypes, it is expected that oxidation weakens the cantilever 230. However, all cantilevers 230 were hermetically encapsulated, and the device, which was rarely used, showed little decrease in resonant frequency with age. JPEG2025528179000021.jpg16170

[0121] The determination of the position H and orientation T of the localization device 10 in step S120 can be performed, for example, by performing a Fourier analysis of the signal of the magnetic field B in step S200 and obtaining the amplitude A of the magnetic field B in the frequency domain in step S210. The position H and orientation T are determined from the magnitude of the amplitude A of the magnetic field B between the sensors 40 .

[0122] The determination of the position H and orientation T of the localization device 10 in the determination step S120 is then carried out, in another example, by using a physical model of the vibration of the magnet 220 in step S300. FIG. 23 shows that the determining step S120 includes directly evaluating the signal of the magnetic field B in the time domain in step S300. The physical model, in step S310, uses the known or calibrated values ​​of the magnetic moment m of magnet 220 and the offset distance between the center of magnet 220 and the center of rotation required in step S300. Unlike the prior art, the magnet 220 does not rotate about its own axis, so the dipole center 225 is not the center of rotation of the magnet 220 . The center of rotation of this magnet 220 is most likely its center of mass. The physical model further uses the maximum deflection angle θ, the signal attenuation ratio, the number and position j of sensors 40 in step S300. Furthermore, physical parameters such as air resistance, moment of inertia, and elastic modulus of the beam can be added to improve the physical model.

[0123] Using a physical model rather than a Fourier solution can reduce the signal recording time required for localization of the localization device 10 . This will be explained below. Determining the spectral content of the signal in the frequency domain requires a large number of periods, such as 10 or 40 periods, to provide sufficient signal peak sharpness to accurately locate the locating device 10 . Using a physical model, the required signal recording time can be reduced to an integer multiple of the half-period N of the vibration, or even to a fractional multiple of the half-period N of the vibration. Using a physical model, the vibration motion and the resulting recorded signal are well-defined for any position H and any orientation T.

[0124] In step S300, a physical model is fitted to the time domain signal to obtain optimized parameters for position H and orientation T. The time domain signal consists of N half periods. In step S300, the error between the physical model of the signal and the recorded magnetic signal B is minimized by an algorithm such as the least squares method. The error for the optimized parameters is minimized, thereby obtaining the accurate position H and orientation T of the localization device 10. The localization accuracy of the localization device 10 is further improved by increasing the number of half periods N by averaging out random noise from the environment.

[0125] The time domain signal is further illustratively divided into a desired number of half periods N_seg. The desired number of half periods N_seg depends on the degree of accuracy required. Therefore, a single excitation is sufficient to locate the locating device 10 multiple times.

[0126] For example, a localization device 10 with a resonant frequency f=100 Hz can locate at twice the rate of the resonant frequency, i.e., 200 Hz, if each half-cycle N is evaluated independently (N_seg=1). If two half-cycles N are evaluated per segment (N_seg=2), the localization rate will be 100 Hz. If four half-cycles N are evaluated per segment (N_seg=4), the localization rate will be 50 Hz. As the number of half periods N_seg increases, the maximum achievable location speed decreases to a value of 2*f / N_seg. This segment method allows the localization device 10 to measure the path of movement P at very high speeds (eg, >200 mm / s) or with great accuracy. The signal decays over time, reducing signal strength and location accuracy, and requiring the location device 10 to be re-activated. Since continuous or weakly damped vibration of the magnet 220 results in a continuous or weakly damped signal, it is desirable to use a discontinuous or strongly damped signal to avoid pauses for re-excitation due to an inability to determine the location of the localization device 10.

[0127] The localization device 10, i.e., the tracker, can be localized during excitation if the magnetic field from the excitation coil does not saturate the sensor 40. The localization device 10, i.e., the tracker, can be further localized during excitation when the magnetic field emanating from the excitation coil is zero or very low at the sensor 40.

[0128] And, a further method of determining the location of the locating device 10 is to mechanically excite the locating device 10 . The mechanical excitation does not interfere with the sensor 40, and continuous excitation of the locating device 10 without pausing allows for continuous locating, i.e., tracking. [Example]

[0129] Location system device. Iterative system control and data processing were performed in MATLAB (R2020b, TheMathWorks, USA). A data acquisition board (USB-6343, NI, USA) with an input range of ±11 V and a resolution of 16 bits (corresponding to a resolution of 0.33 mV) was used for signal emission and analog signal conversion. A weak magnetic field was measured with three fluxgate sensors (Fluxmaster, StefanMayerInstruments, Germany) positioned orthogonally in a customized holder fabricated with a 3D printer. These sensors feature manual offset compensation and have a sensitivity level of 1V / µT, a range of approximately ±3.5µT, a resolution of 0.1nT, and a frequency response of 20pTHz at 1Hz. -1 / 2 It has inherent noise. The sensor holder is mounted on a two-dimensional robotic positioning stage (M-414.2PD, 0.1 µm step size, PI, Germany) on a 75 cm long non-magnetic rod (polymethyl methacrylate) to reduce magnetic influences from the electric motor. Using this positioning stage, 25 locations in a 5 × 5 position grid pattern in the xy plane were scanned. To excite the tracker 10, a customized electromagnetic coil 30 (0.56 mm diameter enamelled copper wire, wrapped 150 times around a 60 mm × 50 mm × 15 mm 3D-printed mandrel) was constructed to generate a nearly uniform magnetic field (1 mT at a distance of 30 mm) around the electromagnetic coil 30. The magnetic field was driven by a current amplifier 35 (A1110-05-E, HUBERT, Germany) with a gain of 1 V and 5 A. The current amplifier is essential for fast and accurate cooling of the electromagnetic coil 30 because it allows the electrical components to be controlled by current rather than voltage. A short buffer time of 3 ms was applied between the end of the excitation phase S100 and the start of the evaluation phase S110 to avoid interference of the magnetic signal due to cooling of the coil.

[0130] Noise data for the fluxgate sensor 30 in a shielded room for the simulations in this study was provided by the manufacturer (Stefan Mayer Instruments). For spatial and angular precision measurements, a manual linear stage with a resolution of 10 μm (PT1, ThorLabs, Germany) and a manual rotation stage with a resolution of 0.1° (XRR1, ThorLabs) were used to precisely translate and rotate the tracker 10. Translational movements along the x-axis were measured in steps of 10 mm in the range of 0 mm to 50 mm. Translational movements along the $z$-axis were measured at distances of 50 mm to 75 mm from the sensor origin. For the values ​​presented, increasing positive values ​​of z define moving away from the sensor plane. The rotation of the system around the x-axis was measured in steps of 30° from 0° to 90°, and the rotation of the system around the y-axis was measured in steps of 15° from -45° to 45°. Each measurement was independently repeated 10 times. The mean and standard deviation were calculated and compared with the difference between the actual values ​​for each of the two locations. Statistical analyses were performed in MATLAB.

[0131] Even if the cantilever material is the same, due to imprecision in manual manufacturing, each tracker 10 may have a unique frequency response, so the individual resonant frequencies must first be determined after manufacturing. As a result, the amplitude filter parameters (S123) for each tracker 10 need to be adapted for each tracker 10. For the frequency filter, a threshold of ±5\% of the excitation frequency is selected, but the damping coefficient threshold needs to be adjusted for each embedding material. The tolerance is 5 s for the hydrogels used in precision measurements. -1 From the 1930s -1 For tracking demonstration, the time is set to 30 seconds. -1 From the 70s -1 It is set between. These ranges were found to be optimal for each material. A generous margin was chosen because factors such as proximity to the container wall and wetting of the tracker 10 surface due to the influence of the environment 20 have a direct effect on the attenuation coefficient.

[0132] To avoid such outliers, we restrict the location H to the area under the sensor array within a volume of 10 cm × 10 cm × 10 cm and calculate the individual quaternions q i Boundary conditions for the algorithm were adopted that limited the to ±1 and the deflection angle θ between 0° and 20°. The starting value is randomized within the aforementioned range, and the complete algorithm is repeated 10 times, from which R 2The one with the highest value is selected as the best fit. Relaxing this parameter restriction makes the algorithm very robust to variations, but requires special attention to amplitude filtering to provide sufficient and accurate information to the optimization algorithm.

[0133] After fitting the B field signal (S121), the entry A, called the amplitude filter, i,j A further filtering step (S123) is applied to the matrix using The main purpose of amplitude filtering S123 is to detect physically irrational and highly distorted results from the previous fitting step S121 and adjust the amplitudes accordingly. Amplitude distortions or outliers are of great importance as they directly affect the efficiency and quality of the subsequent optimization S124. Here, the frequency filter, the attenuation coefficient filter, and the weighting matrix W are derived from R 2 Filters Three main filters are used: Outliers can be detected automatically using thresholds around physically reasonable values ​​such as excitation frequency. The attenuation coefficient depends on the embedding material of the tracker, so the threshold needs to be adjusted accordingly. R 2 For , a looser cutoff value can be chosen due to the redundancy of the physical frequency and attenuation filters. If any value is outside the aforementioned threshold, its corresponding amplitude is A=0 and R 2 =1, so they are not completely excluded from the evaluation. Since undetectable vibrations mean that the amplitude is close to zero, this procedure increases the amount of information passed on to the subsequent optimization S124. The remaining values ​​within the threshold are then calculated using the amplitude matrix and R 2 matrices are simply passed to the matrix and both matrices are used for the final location S124.

[0134] The wireless tracker 10 includes two main parts: a screw-shaped housing 200 and a mechanical resonant structure to which a micro-magnet is attached. The housing 200 was designed with computer-aided design (CAD) software (Inventor Professional 2021, Autodesk, USA) and fabricated using a stereolithography 3D printer (3L, Formlabs, USA) with a resolution of 50 μm and translucent resin (Clear V4, Formlabs). Inside the housing 200, a cavity 210 was designed that provides sufficient space for the cantilever to be mounted and operate. The vibration frequency can be adjusted by selecting the dimensions and material of the cantilever 230, and frequencies in the range of 50 Hz to 1000 Hz can be achieved. In this experiment, a 3.5 mm x 0.5 mm x 30 μm piece of spring steel (C1095 spring steel, PrecisionBrand, USA) was cut with a laser (MPS Advanced, Coherent, USA) to form a cantilever 230, and two axially magnetized cylindrical NdFeB magnets 220 (N52, Guys Magnets, UK) measuring 1 mm x 0.5 mm (diameter x length) were attached to the end of the cantilever 230 using cyanoacrylate adhesive (Loctite401, Henkel, Germany).

[0135] The theoretical total magnetic moment is 0.89 mAm 2 is. A cantilever 230 with a fixed magnet 220 is inserted into a cavity 210 in the housing 200 and closed with a cover manufactured by a 3D printer. Overall, the size of the screw-type prototype tracker 10 is 3mm x 7mm (diameter x length).

[0136] The theoretical total magnetic moment is 0.89 mAm 2 is. Cyanoacrylate adhesive was used to prevent the parts from separating. The cantilever 230 with the magnet 220 is 10 mm 3 The cavity 210 was manually inserted into the cavity and closed with a suitable part manufactured by a 3D printer. Overall, the screw-type prototype tracker measures 3mm x 6.5mm. Many materials are suitable for the cantilever 230, such as spring steel, nitinol, or biaxial polyethylene terephthalate (PET). The resonant frequency increases as the elastic modulus of the material increases, but the thickness and width of the cantilever 230 are parameters to consider.

[0137] Filling material. To mimic the viscoelastic properties of biological tissues, this experiment used a gelatin-agarose mixture as a tissue model to mimic brain tissue, as previously reported. A hydrogel containing 6 wt% gelatin (type A powder from pigskin, Sigma-Aldrich, Germany) and 3 wt% agarose (Sigma-Aldrich) was used. Both components were stirred in double-distilled water at 80 °C for 30 min, filled into plastic containers, and cooled at 22 °C for at least 4 h before use. A rectangular container measuring 50 mm x 60 mm x 15 mm and a cylindrical container measuring 30 mm x 90 mm were used. To demonstrate the locomotion propulsion of the millirobot, a hydrogel containing 3 wt% gelatin and 0.2 wt% agarose was used. All experiments were carried out at room temperature (22°C).

[0138] simulation. A damped harmonic oscillator model with an initial angular deflection θ = 12° was used to simulate the B field signal of the SMOL device after excitation. The corresponding differential equation was solved for the deflection angle θ using Simulink (MATLAB), which was used as a time-varying input parameter of the vibration. First, the system-dependent variables, such as the cantilever length, magnetic moment, position H, and orientation T, were defined, and the motion of the magnetic moment in space was calculated by equations (1) to (4). An accurate representation of the actual measurement was obtained by calculating the time-dependent equation (1) from the cantilever movement at the same position of the sensor 40 and adding the recorded noise (FIG. 5C) to the magnetic signal B. Because magnetic noise is strongly direction-dependent, three different noise signals (one for each direction) were applied to each B-field signal, and a random phase shift of the noise was added to reflect any noise phase in the actual measurements. Analog to digital conversion is also simulated by breaking down the data into bits according to the data collection characteristics. Furthermore, data evaluation and localization optimization S120 was performed based on the actual measurement setup. Numerical simulations were carried out by customized codes in MATLAB.

[0139] Mechanical excitation. As shown in FIG. 1B, tracker 10 can also be excited by a mechanical force F transmitted from actuator 31 through connecting piece 32 to embedding material 20 of tracker 10. And if the actuator 31 and the connecting part 32 are non-magnetic, the sensor 40 can record the magnetic signal B (sensing step S110) during the excitation step S100 as shown in Figures 4A and 4B without any additional stops (S105 in Figures 4C and 4D). This allows the position H and orientation T of tracker 10 to be determined more frequently.

[0140] Simultaneous excitation and localization. If the excitation field does not interfere with the sensor 40, excitation and localization can occur simultaneously.

[0141] The first and second methods allow simultaneous excitation and localization for each excitation field.

[0142] The first method uses a precisely known, predefined excitation field. This predefined excitation field value can be digitally or analogically subtracted from the sensor 40 signal data, assuming no sensor saturation, to produce a residual signal. The remaining signal is the tracking device 10 signal. This first method means that the excitation can be performed continuously and localization can be performed during the excitation as required.

[0143] The second method uses a second excitation unit. This second excitation unit generates contrasting magnetic fields at each sensor 40 in the sensor array. The magnetic fields resulting from excitation at each sensor 40 cancel each other out and no significant signal is generated during excitation. The lack of a significant signal can be achieved, for example, by mirroring excitation coils with opposite polarity on opposite sides of the sensor array.

[0144] The first method can be implemented together with the second method, and can reduce the leakage magnetic field caused by slight differences in the arrangement of the excitation units on the mirrors. A prerequisite for the first and second methods is that the excitation and sensing units are independent. The reason is that the excitation unit and the sensing unit need to operate simultaneously.

[0145] If the mechanical excitation unit does not generate a magnetic field for generating the mechanical field, then simultaneous excitation and localization can occur. The mechanical waves can excite the localization device 10, i.e., the tracker. Simultaneous sensing and localization can be performed at any point during excitation.

[0146] Multiple device tracking. The localization device 10 operates at a tunable resonant frequency, defined, for example, by the dimensions and material of the cantilever 230 . Then, by using the frequency response unique to the position determining device 10, multiple position determining devices 10 can be distinguished and their positions determined. The steps of exciting S100, sensing S110, and determining S120 the position H and orientation T of the localization device 10 can be performed simultaneously or sequentially. Multiple location devices 10 can be used to track the relative movement of the location devices 10 . For example, it is possible to track the shape and deformation of medical devices and soft robots.

[0147] Fluxgate sensor array. By sensing S110 the magnetic field B using multiple sensors 40, such as a fluxgate magnetometer array, more spatial information about the magnetic field B is obtained from this sensing S110. The individual sensors 40 in the sensor array are spatially arranged in at least one dimension, and preferably two dimensions, and the sensor array measures the magnetic field B in at least one direction, preferably two orthogonal directions, and more preferably three orthogonal directions.

[0148] Tumor localization. Using medical imaging modalities such as MRI and computed tomography CT, the three-dimensional location and shape of the tumor can be determined and reconstructed in three dimensions. Under the guidance of ultrasound imaging, one or more tracking devices 10 are injected into tissue. The tracking device 10 can be placed inside or outside the tumor, but is preferably placed on the tumor border. The position H and orientation T of the localization device 10 are imaged by non-magnetic medical imaging such as CT, and based on these non-magnetic medical images the relative spatial positions and orientations of the tumor and the tracking device are calculated. In situations where large-scale medical imaging is not possible, such as in an operating room, the tracker is localized by the methods described herein, and based on the localization information of the localization device 10, the real-time position and orientation and shape of the tumor are calculated. Such information is displayed as an image superimposed on the patient's body during surgery, for example, via a screen, projector, or augmented reality glasses. This method allows near-precise real-time localization of tumors, regardless of soft tissue deformation, providing an accurate method for surgical tumor removal. The implanted localization device 10 is removed from the body along with the tumor after treatment. This method is generally also capable of tracking other important anatomical structures such as blood vessels, thrombi, polyps, nerves, etc. This procedure is not limited to tumor surgery, but also applies to other medical procedures requiring localization, such as radiation therapy, targeted chemotherapy, and selective embolization.

[0149] Operating system. An external rotating magnetic field was used to operate MilliRobot R. A cubic NdFeB magnet (side length 50.8 mm, N40, Supermagnete, Germany) was mechanically fixed to a stepper motor (23HS30-2804S, Stepperonline, USA) so that the magnetic axis was perpendicular to the rotation axis of the motor. This assembly was placed on a rotation stage (GFV5G50, Orientalmotor, Japan), and the rotation axis of the magnet was steered in a two-dimensional plane. The movement of the MilliRobot R was restricted to in-plane movement within the gel with a 6 mm gap between the PMMA plate and the bottom of the container, and the movement path was predefined within the gel. The speed of 0.25 Hz and the direction of the rotating magnetic field were controlled by an Arduino board (Ardunio Uno Rev3 SMD, Arduino), and the direction of the rotation axis was steered manually. The movement was stopped eight times to localize position H and orientation T. At each stop, the sample box (in which the robot R was statically embedded) was removed from the operating environment and placed in the localization environment. The movement then continued in the operational environment. An LED light source was used for illumination, and migration was imaged from above using a camera system (Canon EOS RP RF24-105mm F4 with RF35mm F1.8 lens at 25 fps, Canon, Japan). The eight videos were linked and analyzed using customized code (MATLAB), which recognized the center point and orientation of the robot in each frame (HT1 to HT9 in Figure 14) to plot a trajectory and overlay it on the original video.

[0150] Complementary ultrasound imaging. Pig brains were obtained from a local butcher, transported on ice, and stored in a refrigerator at 4°C. All experiments were performed within 12 hours after the animals were sacrificed. Samples were hydrated with phosphate-buffered saline (PBS, Sigma-Aldrich) and placed in 60 mm × 50 mm × 25 mm containers for measurements at room temperature. For ultrasound imaging, a handheld ultrasound device (iQ+, Butterfly Network, USA) was used with a frequency of 1 MHz–10 MHz and “MSK-Soft Tissue” settings, with a soft tissue thermal index (TIS) of 0.01 and mechanical index (MI) of 0.28. The ultrasound probe was brought into contact with the pig brain using ultrasound contact gel (Aquasonic 100, Parker Laboratories, USA).

[0151] Mechanical property testing of viscoelastic media, such as soft biological tissues, is crucial for understanding and characterizing complex, composite soft materials. In medicine, elastic properties are examined by palpation, a process that measures the elastic response of tissue by direct contact. Such mechanical testing is performed by quasi-static or dynamic indentation testing using external loads, flow measurements, or mechanical wave propagation. The results of such tests are used to model or estimate the material behavior of viscoelastic tissues. However, in vitro testing may not reflect in vivo physiological conditions and the surface structure of materials (such as skin), which typically exhibit properties that differ significantly from the bulk material. As another example, the brain is surrounded by a thin protective layer, the pia mater, which has a high modulus of elasticity compared to the bulk brain material. This discrepancy affects bulk material testing with externally applied forces, which do not represent true bulk properties.

[0152] A more general approach to characterizing bulk materials is to combine imaging with mechanical wave propagation. One such approach to mechanical sensing of biological tissues is magnetic resonance elastography (MRE), which can be used to directly image elastic properties by assessing the propagation of mechanical waves. However, it requires very large and complex magnetic MR equipment, making it unsuitable for long-term measurement and monitoring of elasticity development. Mechanically resonant structures have been proposed for materials sensing, such as magnetic MEMS devices for pressure sensing and fixed piezoelectrically driven cantilevers for viscoelastic characterization.

[0153] The localization device 10 can be used to wirelessly determine S115 the local viscoelastic properties of the soft biological material. The localization device 10 can then be directly embedded in the embedding material 20 . Through the mechanical resonant frequency and damping response of the localization device 10, material properties can be determined wirelessly without the use of expensive equipment (step S115). The localization device (10) can be used in minimally invasive procedures and can be used to monitor changes in the mechanical properties of soft biological materials over time.

[0154] To mimic soft biological tissue and verify the functionality of the localization device 10, an artificial hydrogel made of gelatin was prepared. Gelatin hydrogels (type A from pigskin, Sigma-Aldrich) at 2 wt % to 4 wt % were prepared by stirring gelatin powder in distilled water at 80 °C for 30 min. The mixture was poured into a 60 mm x 50 mm container and allowed to cool to room temperature for at least 12 hours before use. The container was covered with a lid to prevent dehydration. Ex vivo tissue specimens, i.e., turkey breast, pork liver and brain, were obtained from a local butcher and experiments were performed within 12 hours after slaughter of the animals. During testing at room temperature, samples were hydrated with phosphate-buffered saline (PBS, Sigma-Aldrich) and placed in a 60 mm × 50 mm container for measurement.

[0155] The localization device 10 includes an elastic spring element 230 with internal damping η1 and spring constant k1. Spring element 230 is coupled to two masses, m1 and m2. m1 is the magnet 220 attached to the free end 235 of the spring element 230, and m2 is the effective mass consisting of the housing 200 and the potting material 20. The potting material 20 may be a viscoelastic material. In one embodiment, the buried material 20 can be modeled as a Maxwell or Kelvin-Voigt linear model, shown in FIG. 19 by the dashed line.

[0156] The two localization devices 10 have a resonant frequency f res = 90.33Hz and f res = 100.73 Hz and was manually assembled using two 1 mm × 0.5 mm cylindrical N52 NdFeB magnets (glued to a 20 μm thick, 200 μm wide, 2.5 mm long steel cantilever, all encased in a 3D printed housing 200). For measurements on soft materials such as biological materials, the localization device 10 was embedded in the sample 20 at a distance of at least 10 mm from any hard boundaries.

[0157] The rigid boundary reference was measured by fixing the localization device 10 in a housing that was rigidly attached to a frame. Assuming an ideal damped mass-spring system with a quasi-infinite mass m2 (see Figure 19), the spring constant k1 can be calculated as follows: TIFF2025528179000022.tif11170

[0158] where f=f res and m1 is the mass of the magnet 220. η1=η r is the damping coefficient for the fixed boundary condition measured from the decaying magnetic field (Eq. (1)). Here, m1 = (7.9 ± 0.1) × 10 -6 kg, f res,1 =(90.33±0.04)Hz, η r =(4.2±0.1)s -1 In this case, k1 is (2.54±0.03)Nm -1 becomes. The spring constant can also be determined using the cantilever equation, taking into account the material and dimensions. TIFF2025528179000023.tif8170

[0159] JPEG2025528179000024.jpg15170 This gives the estimated spring constant k * is 1.2~2.54Nm -1 The range is as follows: The errors arise from manufacturing uncertainties. k1 is the estimated spring constant k * , confirming the assumption of a simple mass-spring system.

[0160] As mentioned above, the internal damping η1 of the localization device 10 can be obtained by equation (7). This value can be compared to a system in which m2 is softly bound to a viscoelastic environment 20, as shown for three concentrations of gelatin hydrogel in Figure 20. ηr is a lower bound on the possible damping, so the total damping of the system is the sum of the stiffness and viscoelastic contributions η=η r +η V This can be explained as follows. η increases significantly when the localization device (10) is inserted into the gelatin or when the gelatin content is reduced. This phenomenon is expected to be due to the fact that the gelatin matrix becomes harder with increasing gelatin content due to physical bonds caused by molecular entanglement. The literature reports that gelatin stiffness increases with increasing gelatin concentration, which is consistent with the current observations of the damping coefficient determined by a localization device (10).

[0161] Additionally, the damping behavior of various ex vivo tissues was measured and is shown in Figure 21 . The position determination device 10 used in these experiments had a spring constant k1 = (3.17 ± 0.04) Nm -1 It is composed of: The damping coefficient is (9.2±0.9)s at the rigid boundary. -1 and (24.2±1.6)s for pig brain. -1 was decided between η significantly increased between turkey breast, pork liver, and pork brain, which is in good agreement with the decrease in stiffness of these biological tissues. In the literature, the stiffness between muscle fibers and brain tissue in turkey breast has been reported to differ by two orders of magnitude, but η only varies by a factor of about 1.7. This indicates a nonlinear dependency between the damping coefficient and the stiffness of the material. [Explanation of symbols]

[0162] 5...device 10. Locating Devices / Trackers 20 Soft tissue / implantable materials 30 Magnetic field excitation coil 31 Mechanical excitation source 32 Connection parts 35. Current amplifier 40 Sensor 45 Positioning stage 50···Data Acquisition and Calculation Unit 200···Housing 210...Cavity 220 Magnet 225···Dipole center 230···Vibrator / Cantilever 235 First end 237 Rotating shaft 240....Movement path character explanation

[0163] F excitation magnetic field θ...deflection angle B...Magnetic field H: Position of the location identification device 10 T: Orientation of the location determination device 10 R...Robot with localization device 10 P: Robot R's motion path

Claims

1. A method for determining the position (H) and orientation (T) of a location device (10) having a magnet (220) attached to a vibrating element (230), comprising: an excitation step (S100) of exciting the magnet (220) using either an external force or a torque (F) to cause a complex oscillatory motion of the magnet (220), the complex oscillatory motion including a translational motion and a rotational motion of the magnetic moment of the magnet (220) about an axis of rotation (237), the axis of rotation (237) being located at an offset distance relative to the center of the magnetic moment of the magnet (220); a sensing step (S110) of sensing the magnetic field (B) generated by the magnet (220) using at least one sensor (40); a determining step (S120) of determining the position (H) and the orientation (T) of the location identification device (10) from the sensing step (S110); A method for determining the position (H) and orientation (T) of a locating device (10), comprising:

2. 2. The method for determining the position (H) and orientation (T) of a localization device (10) as described in claim 1, wherein the excitation step (S100) using either the external force or the torque (F) is performed by either an external excitation magnetic field or mechanical excitation.

3. 3. The method for determining the position (H) and orientation (T) of a localization device (10) as described in claim 2, wherein the mechanical excitation is one of a pulse and a wave that vibrates in at least one of the longitudinal and shear directions of the vibration element (230).

4. 4. A method for determining the position (H) and orientation (T) of a localization device (10) according to any one of claims 1 to 3, wherein the offset distance between the axis of rotation (237) and the magnetic moment of the magnet (220) is at least 5%, preferably 25%, more preferably greater than 100% of the maximum dimension of the magnet (220).

5. 5. A method for determining the position (H) and orientation (T) of a localization device (10) according to any one of claims 1 to 4, wherein the axis of rotation (237) and the vector of the magnetic moment arising from the magnet (220) are not parallel, but preferably substantially perpendicular.

6. 6. A method for determining the position (H) and orientation (T) of a localization device (10) according to any one of claims 1 to 5, wherein the vibration element (230) is arranged within a rigid housing (200), more preferably within a sealed and evacuated rigid housing (200).

7. 7. The method for determining the position (H) and orientation (T) of a localization device (10) according to any one of claims 1 to 6, wherein at least one of the sensing step (S110) or the determining step (S120) of the position (H) and the orientation (T) of the localization device (10) is performed when at least one of the excitation steps (S100) of the magnet (220) is stopped (S105) or is performed continuously during the excitation step (S100) of the magnet (220).

8. 8. A method for determining the position (H) and orientation (T) of a localization device (10) as described in any one of claims 1 to 7, wherein the vibration element (230) comprises at least one restoring force unit of a cantilever beam or similar unit having an elastic restoring force.

9. 9. A method for determining the position (H) and orientation (T) of a localization device (10) according to any one of claims 1 to 8, wherein the sensing step (S110) and the determining step (S120) of the position (H) and orientation (T) of the localization device (10) are repeated.

10. 10. A method for determining the position (H) and orientation (T) of a localization device (10) according to any one of claims 6 to 9, characterized in that the excitation frequency of the magnet (220) is approximately equal to the resonant frequency of the vibration element (230).

11. 11. A method for determining the position (H) and orientation (T) of a localization device (10) according to any one of claims 1 to 10, wherein the step (S120) of determining the position (H) and orientation (T) of the localization device (10) comprises using a physical model of the complex vibrational motion in the time domain.

12. 12. A method for determining the position (H) and orientation (T) of a localization device (10) according to any one of claims 1 to 11, wherein the step of sensing (S110) the magnetic field (B) generated by the magnet (220) is followed by determining (S115) the local viscoelastic properties of the material.

13. 12. The method for determining the position (H) and orientation (T) of a localization device (10) of claim 11, further comprising: determining the position (H) and orientation (T) of the localization device (10) by using the determined local viscoelastic properties of the material.

14. 1. A device (5) for determining the position (H) and orientation (T) of a location-identifying device (10), comprising a housing (200) and a magnet (220) attached to a vibration element (230) disposed within the housing (200), an excitation unit (30) for exciting (S100) the magnet (220) using either an external force or a torque (F) to generate a complex oscillatory motion of the magnet (220), the complex oscillatory motion including translational and rotational motion of the magnetic moment of the magnet (220) about an axis of rotation (237) located at an offset distance relative to the center of the magnetic moment of the magnet (220); a location determination device (10) having a housing (200), wherein the magnet (220) is attached to the vibration element (230) within the housing (200); a data collection unit that senses (S110) the magnetic field B generated by the magnet (220) using a sensor (40); A device (5) for determining the position (H) and orientation (T) of a localization device (10), comprising:

15. 15. The device (5) for determining the position (H) and orientation (T) of a localization device (10) according to claim 14, wherein the magnet (220) comprises a permanent magnet made of a magnetic material, preferably a ferromagnetic material.

16. A device (5) for determining the position (H) and orientation (T) of a localization device (10) according to claim 14 or claim 15, wherein the vibration element (230) comprises a restoring force unit, preferably a cantilever.

17. 17. Use of the device (5) according to any one of claims 14 to 16 for locating a medical implant in an animal or human body selected from one or more of a catheter, a stent, a guidewire, an endoscope, a capsule endoscope, a drug delivery device or a miniature robot, or for locating an anatomical structure selected from one or more of a tumor, a blood vessel, a thrombus, a polyp or a nerve.

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