Abstract
The invention relates to a medical microdevice (100) for insertion into a human body, wherein the microdevice allows for measuring at least one of a localization of the microdevice in a space and/or a physical parameter in the environment of the microdevice, wherein the microdevice comprises a casing (111) and within the casing a magneto mechanical rotator (110), wherein the magneto mechanical rotator comprises a magnetic object (113) providing a permanent magnetic moment and a rotary bearing (112) that is adapted to stabilize a rotational motion of the magnetic object, wherein the magneto mechanical rotator is adapted to transduce an external magnetic or electromagnetic excitation field into a mechanical rotation of the magnetic object relative to the rotary bearing such that a periodically changing magnetic response field is generated. The microdevice thus allows for an improved signal transmission and for a further miniaturization.
Claims
1. A medical microdevice for insertion into a human body, wherein the microdevice allows for measuring at least one of a location of the microdevice in space and/or a physical parameter in the environment of the microdevice, wherein the microdevice comprises a casing and within the casing magneto mechanical rotator, wherein the magneto mechanical rotator comprises a magnetic object providing a permanent magnetic moment and a rotary bearing that is adapted to stabilize a rotational motion of the magnetic object, wherein the magneto mechanical rotator is adapted to transduce an external magnetic or electromagnetic excitation field into a mechanical rotation of the magnetic object relative to the rotary bearing such that a periodically changing magnetic response field is generated.
2. The medical microdevice according to claim 1, wherein the rotary bearing comprises a retaining magnetic field generator to provide a saddle point, wherein the magnetic object is positioned substantially at the saddle point, and wherein the saddle point is defined such that, for a spatial plane predefined with respect to the rotary bearing, when the magnetic object is moved away from the saddle point within the spatial plane, the magnetic object is subjected to a magnetic restoring force provided by the retaining magnetic field forcing the magnetic object back into a direction to the saddle point.
3. The medical microdevice according to claim 2, wherein the rotary bearing comprises a retaining surface in a spatial direction perpendicular to the predefined spatial plane such that a movement of the magnetic object in the perpendicular spatial direction is restricted.
4. The medical microdevice according to claim 2, wherein the retaining magnetic field generator comprises two retaining permanent magnetic objects arranged on opposite sides of the magnetic object such that the saddle point is provided between the retaining permanent magnetic objects.
5. The medical microdevice according to claim 4, wherein retaining magnetic field generator additionally comprises two soft magnetic objects, wherein the two soft magnetic objects are arranged on the opposite sides of the magnetic object at which the retaining permanent magnetic objects are arranged, wherein the two retaining permanent magnetic objects are arranged further away from the magnetic object than the soft magnetic objects.
6. The medical microdevice according to claim 4, wherein more than one retaining permanent magnetic object is arranged on each side of the magnetic object.
7. The medical microdevice according to claim 1, wherein the medical microdevice comprises an additional magnetic object provided with a similar rotary bearing as the magnetic object, wherein the additional magnetic object is similar to the magnetic object and wherein the magnetic objects are arranged at a distance to each other such that the rotation axes of the two magnetic objects are parallel.
8. The medical microdevice according to claim 1, wherein the medical microdevice further comprises a signal modulator, wherein the signal modulator that modulates a response magnetic field generated by the magneto mechanical rotator when excited, wherein the modulated magnetic field allows for a localization of the medical microdevice.
9. The medical microdevice according to claim 8, wherein the signal modulator is adapted such that changes of a physical parameter in the environment of the medical microdevice introduce changes of the modulation of the response magnetic field that allow a determination of the changes of the physical parameter from a measurement of the modulated magnetic field.
10. The medical microdevice according to claim 9, wherein the signal modulator is adapted such that changes of the physical parameter lead to changes of the internal structure of the signal modulator such that the changes of the internal structure of the signal modulator introduce changes of the modulation of the response magnetic field.
11. The medical microdevice according to claim 10, wherein the signal modulator comprises a mechanical resonator, wherein the mechanical resonator can be excited by the response magnetic field generated by the rotational movement of the magnetic object, wherein the mechanical resonator is adapted such that changes of the physical parameter lead to a change of the resonance frequency of the mechanical resonator such that the excitation of the mechanical resonator by the generated response magnetic field introduces changes of the modulation of the response magnetic field in dependency of the physical parameter.
12. A reading system for wirelessly reading out the medical microdevice as defined by claim 1, wherein the reading system comprises: a field generator for generating a magnetic or electromagnetic excitation field for inducing a mechanical rotation of a magnetic object of a magneto mechanical rotator of the medical microdevice, wherein the rotation of the magnetic object generates a periodically changing response magnetic field, a transducer for sensing and transducing the response magnetic field into electrical response signals, a processor for processing the electrical response signals.
13. The reading system according to claim 12, wherein the processor is adapted to determine a location and/or a physical parameter and/or a change of a physical parameter in an environment of the medical microdevice based on the electrical response signals.
14. The reading system according to claim 12, wherein the field generator comprises at least one air-core coil that is adapted to generate an excitation field between 2 kHz and 200 kHz, wherein the transducer is adapted to sense and transduce a magnetic signal of up to more than twice the frequency of the excitation field.
15. A method for localizing a medical microdevice according to claim 1 and/or for determining a physical parameter in the environment of such a medical microdevice, wherein the method comprises: generating an excitation field for inducing a mechanical rotation of a magnetic object of a magneto mechanical rotator of the microdevice, wherein the rotation of the magnetic object generates a periodically changing response magnetic field, sensing and transducing the response magnetic field into electrical response signals, processing the electrical response signals to determine a location and/or a physical parameter and/or a change of a physical parameter in an environment of the medical microdevice based on the electrical response signals.
16. A non-transitory computer readable medium comprising program code for causing a reading system to carry out the steps of the localization method and/or the measurement method as defined by claim 15, respectively, when the program code is run on a computer controlling the reading system.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0058] FIG. 1 shows schematically and exemplarily an embodiment of a medical microdevice comprising a magneto mechanical rotator,
[0059] FIG. 2 shows schematically and exemplarily a model for calculating lubrication in the medical microdevice,
[0060] FIG. 3 to FIG. 15 show schematically and exemplarily different advantageous embodiments of the medical microdevice, and
[0061] FIG. 16 shows schematically and exemplarily a flowchart of a method for measuring a magnetic signal of the medical microdevice.
DETAILED DESCRIPTION OF EMBODIMENTS
[0062] FIG. 1 shows schematically and exemplarily an embodiment of a medical microdevice comprising a magneto mechanical rotator. The medical microdevice 100 comprises a casing 111 and within the casing the magneto mechanical rotator 110. The magneto mechanical rotator 110 is arranged within the casing 111, for instance, by providing the magneto mechanical rotator within an individual encasing structure that can also be a structural part of the casing 111 as indicated by the dashed line in FIG. 1. However, the magneto mechanical rotator 110 can also be arranged in the casing 111 by providing an attachment structure that allows to attach and stabilize the rotary bearing 112 in a stable position within the casing 111. The attachment structure can comprise an adhesive for gluing the rotary bearing 112 and/or other components of the magneto mechanical rotator 110 to the casing. Alternatively, the casing can comprise attachment structures that function as clamps for clamping the rotary bearing 112 and/or other components into place. The magneto mechanical rotator 110 comprises a permanent magnetic object 113 and the rotary bearing 112 that is adapted to stabilize the rotational motion of the magnetic object 113. In the embodiment shown in FIG. 1, the permanent magnetic object 113 provides a permanent magnetic moment indicated in FIG. 1 and in the following by the arrow within the magnetic object 113. Moreover, in this embodiment the magnetic object 113 is depicted as a sphere. However, also other shapes of the magnetic object 113 can be utilized advantageously. For example, prolate or oblate spheroids can also be employed. It is particularly preferred that the magnetic object 113 is adapted such that it provides the maximal moment of inertia around its rotation axis. This can be achieved, for instance, by choosing a corresponding shape or by adapting a mass distribution within the magnetic object accordingly.
[0063] The rotary bearing 112 in this embodiment comprises two magnetic discs that are arranged on opposite sides of the magnetic object 113 such that the magnetic moment of the magnetic object 113 can arrange itself in particular parallel to the surface that is provided by the magnetic discs. This kind of rotary bearing 112 is only one possibility for stabilizing the magnetic object 113 during its rotational motion while at the same time allowing for a rotational motion relative to the rotary bearing 112.
[0064] Generally, it is preferred that the rotary bearing 112 comprises a retaining magnetic field generator which in the example shown in FIG. 1 is formed by the two soft magnetic discs arranged around the magnetic object 113. The retaining magnetic field generator is adapted to generate a retaining magnetic field that provides a saddle point for the degrees of motional freedom of the magnetic object 113. Such a saddle point is defined such that it impedes the translational movement of the magnetic object 113 in two dimensions away from the saddle point when the magnetic object 113 is placed substantially at the saddle point. In particular, a magnetic restoring force is provided by the retaining magnetic field generator, in this example, the two soft magnetic discs, when the magnetic object 130 moves away from the saddle point in one of these dimensions, i.e. in a spatial plane pre-defined with respect to the rotary bearing 112. Thus, the magnetic field providing the saddle point is chosen such that it stabilizes the position of the magnetic object 113 in at least two dimensions. However, in the third dimension and thus in the third degree of translational freedom of the magnetic object 113 the magnetic field providing the saddle point might not provide a stabilizing, i.e. magnetic restoring force.
[0065] Thus, it is preferred for embodiments comprising a retaining magnetic field generator providing a magnetic field, as described above, that further a retaining surface is provided that retains the movement of the magnetic object 113 according to the third degree of translational freedom of the magnetic object 113, i.e. in a spatial direction perpendicular to the predefined spatial plane and thus perpendicular to the directions in which the movement of the magnetic object 113 is impeded. Generally, it is preferred that the retaining magnetic field generator, as shown in the exemplary embodiment of FIG. 1, also provides the retaining surface which can be in direct contact with the magnetic object 113.
[0066] The rotary bearing 112 shown in FIG. 1 is, as already discussed above, realized by two soft magnetic discs. Due to shape anisotropy, the soft magnetic discs prefer to be magnetized in the disc plane. This allows for a good alignment of the magnetic object 113 with the disc surfaces. In particular, if the saddle point is provided in the middle of the device, the magnetic alignment is as shown in FIG. 1. But, for this embodiment the true stable position is slightly off-center and the orientation not perfectly parallel nor perpendicular to the soft magnetic discs. However, if an external magnetic field 120 is provided, for instance, an external excitation field that is used for exciting, i.e. rotating, the magnetic object 113, the center position and alignment are stabilized. Once the magnetic object 113 rotates sufficiently fast, the center position becomes the stable position.
[0067] Generally, also for all following described embodiments of the rotary bearing comprising a retaining magnetic field generator, the retaining magnetic field and the saddle point can be calibrated as follows. For example, if the retaining magnetic field generator is realized in form of soft or permanent magnetic objects, the soft or permanent magnetic objects can be provided together with the magnetic object in a casing, for example, a tube, in accordance with the desired design. To manipulate a magnetization of one of the objects, for example, a laser or a heat generator, can then be utilized to adapt a distance and magnetic field characteristic of the magnetic system formed by the three or more magnetic objects. Alternatively, the soft or permanent magnetic objects of the arrangement can be mechanically manipulated, for instance, sanded in order to manipulate the magnetization and general magnetic field provided by the magnetic object. After having reached a desired configuration, the magnetic objects can be fixed in this configuration, for instance, by gluing them to the casing, and the casing can be closed after optionally having been filled with a lubrication fluid. Alternatively, a generally suitable configuration can be provided with one or more additional magnets outside the casing, for instance, glued or otherwise attached to the casing from the outside. Such additional magnets outside the casing allow for a correction and/or calibration of the magnetic field generated by the magnetic objects within the casing based on the location and orientation of the additional magnets outside the casing. Since this possibility can be used for calibrating the medical microdevice after having already provided a generally functional magneto mechanical rotator, it is much easier to perform.
[0068] Generally, for the calibration process a parameter is selected that can be measured and that should be optimized by the calibration process. Typically, the parameter refers to an oscillation frequency, if the magnetic object performs an oscillatory rotation, and/or to a quality factor of the rotation or oscillation. Based on the measurements of these parameters the above described methods can be used to manipulate the configuration of all magnetic components such that a desired parameter or parameter range is reached. The such found configuration can then be fixed, for instance, by gluing the components to the casing. The exact configuration can then be used for producing similar magneto mechanical rotators. Moreover, numerical simulations of the configurations of the magnetic components can be utilized for supporting and accelerating the calibration process.
[0069] FIG. 1 shows further a reading system 130 for wirelessly reading out the medical microdevice 100. The reading system 130 comprises at least a field generator 131 for generating the magnetic or electromagnetic excitation field 120 that can be used to excite the magneto mechanical rotator 110. Further, the reading system 130 comprises one or more transducers 132 that can measure the generated response magnetic field of the magneto mechanical rotator and transduce the generated response magnetic field into an electrical response signal. In some embodiments, the field generator 131 can also be utilized as transducer in addition or alternatively to the transducers 132 shown in FIG. 1. The transducers 132 can be realized as coils transducing the response magnetic field generated by the medical microdevice 100 into an electrical response signal. The electrical response signal can then be provided to a processor 133 that is adapted to process the electrical response signals, for instance, for localizing the medical microdevice or for determining a physical parameter measured by the medical microdevice in its environment. In particular, the processor 133 can be adapted to compare the response signal of different transducers and based on this comparison use a triangulation algorithm to determine the location of the medical microdevice. Moreover, the processor 133 can be adapted to analyze a frequency spectrum of the response signal and to compare the frequency spectrum to a frequency spectrum that is stored already, for instance, from a previous time span or from a calibration measurement. Based on this comparison the processor 133 can then determine a physical parameter or a change in a physical parameter in the environment of the medical microdevice. However, also other methods can be utilized for localizing the medical microdevice and/or for determining a physical parameter based on the response signals. It is generally preferred for all embodiments of the medical microdevice that the minimal system Q-factor for the rotating magnetic object 113 is higher than 100. Since for embodiments provided with a retaining magnetic field generator, like the embodiment shown in FIG. 1, the position of the magnetic object 113 is mainly stabilized by magnetic forces, the only source of friction that might impact the system Q-factor is the contact between the retaining surface and the magnetic object 113. Thus, by optimizing this contact, for instance, by minimizing forces acting on this contact point and/or the friction at this contact point, the system Q-factor can be advantageously improved further.
[0070] Some general considerations for decreasing the friction at the contact point between the magnetic object and the retaining surface will be discussed in the following. Generally, the friction depends on a contact area between the magnetic object and the retaining surface. Thus, it is preferred that the contact area is kept near the physically smallest possible contact area. A physically smallest possible contact area for a magnetic object realized as a sphere can be determined, for instance, according to the following derivation. A normal force with respect to the contact surface resulting from magnetic forces can be determined by F.sub.m= 4/3r.sup.3gn, wherein r is the radius of the magnetic object being in this case a sphere, is the density of the magnetic object, g is the gravitational acceleration, and n is the ratio between the normal force of the magnetic object and the weight of the magnetic object. The normal force resulting from the counter pressure in the material is given by F.sub.p=PA=PR.sup.2, wherein P refers to the material hardness, A is the physically smallest possible contact area, and R is the physically smallest possible contact radius for a spherical magnetic object. Since both forces will equal each other, for the physically smallest possible contact radius it can be determined that
[00001]
For example, for a contact surface comprising diamond-like carbon (DLC) with P=100 GPa, a magnetic object comprising a density of =7500 kg/m.sup.3, and a radius of r=250 m, the physical physically smallest possible contact radius refers to R=39 nm. For a contact surface comprising steel or glass with approximately P=10 GPa, the physically smallest possible contact radius refers to R=124 nm. A realistically possible and suitable contact area refers to about 100 times, preferably 10 times, the physically smallest possible contact area. The torque acting on the rotating magnetic object caused by the friction, if a constant pressure is assumed on the contact surface, can be determined by T=.sub.0.sup.R(2Px.sup.2) dx=PR.sup.3, wherein is the friction coefficient. Moreover, T is also given as T=I.Math., wherein I refers to the moment of inertia and co to the angular velocity of the magnetic object. From this, also the friction for the respective contact area can be determined Based on these principles a physically possible decay time of the rotation of the magnetic object of about 20 s for a retaining surface comprising DCL and about 6 s for glass can be calculated. Realistic decay times of about 0.5 s are possible for glass without taking further measures for decreasing the friction.
[0071] Moreover, as will be discussed with respect to FIG. 2, a lubricant oil can be provided as part of the rotary bearing 112, in particular, in the area of the contact point between the magnetic object 113 and the retaining surface, but preferably also in other regions in which a contact of the rotating magnetic object 113 and some surface might occur. In the following an approximation based on a simplified lubrication model will be provided that shows that providing such a lubricant oil has an advantageous influence on the friction between the magnetic object 113 and the retaining surface. In this simplified model it is assumed that viscosity drag acts only in columns, i.e. rings, without any lateral interaction. The magnetic object, being assumed to be spherical, is further described in this model by:
[00002]
[0072] wherein h refers to the height of the magnetic object above the retaining surface at a distance x from the contact point, and r to the radius of the magnetic object. The force by one ring can then be regarded as:
[00003]
[0073] with being the viscosity, the rotation angular frequency, =x the ring velocity and A=2xx the ring surface. The torque can then be described as the force times the distance, and hence as:
[00004]
[0074] An integration of this equation gives the total torque for an oil drop with radius x:
T=2rx.sup.2.
The torque provided by the magnetic forces acting on the magnetic object can be regarded as:
[00005]
[0075] with in being the magnetic dipole moment, M the magnetization of the sphere, and B the external flux density. Therefore, the maximum possible rotation frequency where T=T.sub.m, is given by:
[00006]
with
[00007]
the relative size of me oil droplet. Typical values for the parameters in this equation are, for instance, =3 mPas, M=1 T, B=1 mT. Based on these values a frequency of f=42 kHz .sup.2 can be calculated. A useful lubrication oil comprises, for instance, a relative droplet size of <0.1, which means that for typical sphere diameters of 0.5 mm, the lubrication does not hinder fast rotation and is in the order of damping due to the air in the device. Generally, if the magnetic object referring to a sphere rotates very fast, the lubricant oil will be expelled by centrifugal forces. However, this has the advantage that the system is automatically left with the right amount of lubrication provided that the surface wettability is chosen right. Preferably, the lubricant oil is a ferrofluid. This can lead to a distance between the magnetic sphere and the retaining surface. Due to this distance, the friction can be reduced further. Moreover, all components that comprise potential contact areas, like the magnetic object and the retaining surface, can be provided with additional layers that are configured to further reduce a friction between the components.
[0076] In the following, some exemplary embodiments will be shown and discussed in detail for a further reduction of the normal force acting on the contact point, for instance, by improving the stability of the position of the magnetic object 113 relative to the rotary bearing 112. Also other advantages might be provided by the respective embodiments.
[0077] FIG. 3 shows a set-up similar to the set-up already discussed with respect to FIG. 1, wherein in this case a supplemental soft magnetic ring 114 is added as part of the rotary bearing 112. The supplemental soft magnetic ring 114 is preferably arranged between the soft magnetic discs 112 and in a plane parallel to the plane provided by the planar surfaces of the soft magnetic discs 112. Thus, the supplemental soft magnetic ring 114 is arranged around a rotational equator of the magnetic object 113. The supplemental magnetic ring 114 has a further stabilizing effect on the orientation and position of the magnetic object 113 with respect to the soft magnetic discs 112.
[0078] A further advantageous embodiment is shown in FIG. 4. In this embodiment, additional soft magnetic sheets 115 are added above and below the retaining magnetic discs 112. Preferably, the additional soft magnetic sheets 115 also have the form of soft magnetic discs. However, they can also have any other two-dimensional form in the plane parallel to the surfaces of soft magnetic discs 112. Also these additional soft magnetic sheets 115 can provide an additional stabilization of the orientation and position of the magnetic object 113.
[0079] FIG. 5 shows a preferred modification that can be combined with any of the above already described embodiments. In this embodiment, the medical microdevice is provided with an additional magnetic object 113 comprising its own rotary bearing 112 that is similar to the rotary bearing 112 provided for the first magnetic object 113. In particular, in this embodiment it can be regarded that the medical microdevice is provided with an additional magneto mechanical rotator. Preferably, each of the magneto mechanical rotators is provided with its own casing structure to avoid a direct touching of the magneto mechanical rotators. However, also other structures can be provided that prevent a touching of the two magneto mechanical rotators, for instance, structures can be attached to the rotary bearings 112, 112 that allow to determine the position of the rotary bearings 112, 112 and thus also the position of the magnetic objects 113, 113. This embodiment allows for a very good stabilization of the rotational orientation and position of the rotating magnetic objects 113, 113. Generally, this set-up allows for a rotational oscillation of the two magnetic objects 113, 113, wherein the oscillation frequency of the rotational oscillation strongly depends on the distance between the two magnetic objects 113, 113. Thus, this embodiment can be advantageously utilized for generating a periodically changing response magnetic field that not only allows a localization of the medical microdevice, but further allows to encode information, for instance, on physical parameters in the environment of the medical microdevice or an identification information, into the generated response magnetic field. For example, at least one of the magneto mechanical rotators can be provided with an attachment, for instance, a bellows, that allows for a change of the distance between the two magneto mechanical rotators in dependency of a change of a physical parameter in the environment of the medical microdevice. In an example, the attachment can be sensitive to a temperature and/or pressure change in the environment and react to such a change with an elongation or contraction leading to a distance change and thus an oscillation frequency change of the magneto mechanical rotators. Such a change in the frequency of the generated response magnetic field of the two magneto mechanical rotators can be easily detected, for instance, based on calibration measurements or simulations associated with a respective change in the physical parameter. Based on calibration measurements performed with a medical microdevice in an accurately defined environment, and comparisons between actual measurements of the generated response magnetic field and the measurements made during the calibration, even absolute values of physical parameters in the environment of the medical microdevice can be determined. To facilitate such measurements and to avoid the problem that the energy between the two magneto mechanical rotators is transferred in this embodiment to a silent oscillation mode with a zero first order magnetization change, it can be advantageous to provide the two magnetic objects 113, 113 with different sizes.
[0080] FIG. 6 shows an embodiment of the magneto mechanical rotator in which the retaining magnetic field generator comprises as two retaining permanent magnetic objects two permanent magnetic spheres 210. Also in this embodiment the retaining surface is provided by the two retaining permanent magnetic spheres 210. The magnetic object 113 in this embodiment performs a rotational oscillation between the two permanent magnetic spheres 210 providing a magnetic moment that is stable relative to the casing at least on time scales that are comparable to the rotational motion of the magnetic object 113. The advantage of this embodiment is that the normal forces and the friction at the contact point between the magnetic object 113 and the retaining surface provided by the retaining permanent spheres 210 can be further decreased leading to a further improvement of the quality factor of the magneto mechanical rotator. To further reduce the normal forces acting on the contact points between the magnetic object 113 and the two retaining permanent magnetic spheres 210, it is preferred in this embodiment to provide the two retaining permanent magnetic spheres 210 with a greater diameter than the magnetic object 113. Moreover, providing the two retaining permanent magnetic spheres 210 with a greater diameter than the magnetic object 113 has the advantage that a higher oscillation frequency compared with an embodiment with equally sized magnetic objects can be reached. Generally, a higher oscillation frequency leads to a better signal.
[0081] The embodiment discussed with respect to FIG. 6 can be further modified as shown in FIG. 7. In this embodiment, an additional rotating magnetic object 113 is provided between the two retaining permanent magnetic objects 210. This leads to a torque balanced set-up for a rotational oscillation of the two rotating magnetic objects, 113, 113. Preferably, to increase the stability of this system the permanent magnetic objects 210 are provided larger than the rotating magnetic objects 113, 113, for instance, in case of spheres with larger diameters. It is further preferred that holding structures are provided to avoid the tendency of the magnetic objects 113, 113 to stick together. Such holding structures can be realized by providing a simple dividing wall between the two rotating magnetic objects, 113, 113 or by providing a bellows between the two rotating magnetic objects that still allows for the rotational oscillation and optionally for distance changes between the rotating magnetic objects 113, 113, but prevents a direct contact between the rotating magnetic objects 113, 113. A distance variation naturally changes a magnetic interaction of this system and thus can be utilized to encode a change of a physical parameter in the environment of the medical microdevice in the generated response magnetic signal. The influence of the physical parameter can be provided, for instance, by attaching at least one of the rotating magnetic objects 113, 113 to a bellow structure that reacts with a distance change to changes of the physical parameter in the environment.
[0082] The above described embodiment can be further advantageously modified by adding as part of the retaining magnetic field generator further soft magnetic discs 212, 212 to each of the rotating magnetic objects 113, 113 as shown in FIG. 8. The additional soft magnetic discs 212, 212 can be provided according to the principles already described above, for instance, with respect to the embodiment shown in FIG. 1. Preferably, the additional soft magnetic discs 212, 212 can be provided as part of a holding structure for stabilizing the two rotating magnetic objects, 113, 113. It is further preferred in this embodiment that the two retaining magnetic discs 212, 212 on the opposite sides of one of the rotating magnetic objects 113, 113 do not comprise the same size, i.e. do not have the same diameter. In particular, it is preferred in order to increase the stability of the set-up that the retaining soft magnetic discs 212, 212 facing each other directly have a smaller diameter than the two retaining soft magnetic discs 212, 212 between the rotating magnetic object and the retaining permanent magnetic objects 210. The additionally provided soft magnetic discs 212, 212 allow to advantageously modulate the normal forces on the contact points between the magnetic objects 113, 113 and the retaining surfaces formed here, as already described above, by the soft magnetic discs 212, 212 and at the same time further allows to reduce the size of the two retaining permanent magnetic objects 210 in relation to the magnetic objects 113, 113. In particular, in this embodiment it can be even advantageous to provide the two retaining permanent magnetic objects 210 with a size, for instance, a diameter, smaller than the size of the rotating magnetic objects 113, 113. Such a modification allows for a complete rotational movement of the rotating magnetic objects 113, 113. For this case, a distance between the rotating magnetic objects 113, 113 is not encoded in the oscillation frequency of the magnetic objects 113, 113 but in the shape, i.e. harmonic spectrum, of the generated response magnetic field. This allows for an even more accurate determination of the distance and thus of possible physical parameters influencing the distance between the rotating magnetic objects 113, 113.
[0083] A further advantageous modification of the above described embodiment is shown in FIG. 9. This embodiment provides a torque-balanced set-up with the addition of soft magnetic disks 212, 212 and pseudo-soft magnetic permanent magnet sphere assemblies 220, 220 instead of the retaining permanent magnetic objects. The pseudo soft magnetic permanent magnet sphere assemblies 220, 220 comprise at least two permanent magnetic objects 221, 221 that are arranged such that they can move with respect to each other, in particular, can adjust the orientation of their magnetic moments with respect to each other. Other movements can be impeded by encasing the at least two permanent magnetic objects 221, 221 with respect to casing structures 223, 223 that substantially fix a positional arrangement of the least two permanent magnetic objects 221, 221 without hindering a rotational motion of the least two permanent magnetic objects 221, 221 and thus an adjustment of the magnetic moments. However, instead of an encasing structure 223, 223, also other structures can be provided that provide a fixation of the positional arrangement without impeding a rotational motion. The advantage of this assembly is that it is not destroyed if a strong magnetic field is applied and thus allows for an MRI compatibility of the medical microdevice. The advantage over providing a soft magnetic material as retaining magnetic field generator is that these assemblies 220, 220 retain a permanent magnetization. In this arrangement, it is preferred that a very high viscosity fluid 222 is provided between the permanent magnetic objects 221, 221 that serves as a lubricant, but at the same time keeps the spheres fixed on the time scale of the rotational motion of the rotating magnetic objects 113, 113, thereby avoiding energy dissipation. The simplest set-up is a two sphere assembly 220 as shown on the left, but more complicated assemblies 220 consisting of curved chains may also be utilized as shown on the right.
[0084] FIG. 10 shows a preferred embodiment of the medical microdevice comprising, in addition to the magneto mechanical rotator, a signal modulator 310. A signal modulator 310 or any of its modifications described with respect to the following figures can be combined with any of the already described embodiments of a magneto mechanical rotator. However, it is particularly preferred to provide a signal modulator 310 in embodiments of the medical microdevice comprising magneto mechanical rotators which are adapted such that the magnetic object 113 transduces the excitation field into a complete rotational motion. In embodiments with a magneto mechanical rotator which is arranged such that the external excitation field is transduced in a rotational oscillation, a signal modulator 310 can also be provided, but is less advantageous than in the embodiments with the complete rotational motion.
[0085] Generally, the signal modulator 310 can refer to any arrangement that allows to modulate the response magnetic field generated by the rotating magnetic object 113. A simple embodiment of the signal modulator 310 is shown in FIG. 10. In this embodiment, the signal modulator comprises a soft magnetic element 311 and a bellows 312 that allows to change a distance between the soft magnetic element 311 and the magneto mechanical rotator. In this arrangement, the signal modulator 310 is preferably arranged along a rotation axis of the magnetic object 113. This allows to keep lateral forces that influence an orientation of the rotating magnetic object small. However, also other arrangements of the signal modulator 310 with respect to the magnetic object 113 are generally possible, and can be advantageous for some applications. In particular, in embodiments comprising a magneto mechanical rotator with a magnetic object 113 providing a complete rotational motion, a modulation of the generated response magnetic field allows to encode information, like a physical parameter or an identity of the medical microdevice, in the generated response magnetic field. For instance, the signal modulator 310 can produce harmonics or can incorporate a resonance into the generated response magnetic field as modulation. Preferably, the signal modulator 310 comprises a magnetization change comparable to the response magnetic field change caused by the rotating magnetic object 113 in order to generate a substantial signal modulation. Preferably, the signal modulator 310 is adapted to modulate the signal generated by the rotating magnetic object 113 such that at least 1%, more preferably 10%, of the signal received, for instance, by the transducer, is caused by the signal modulator 310. If the signal frequency should be similar to the rotation frequency of the magnetic object 113, the signal modulator 310 preferably has a similar size as the rotating magnetic object 113. If the signal modulator 310 should generate higher harmonics in the generated response magnetic field, the signal modulator 310 on the other hand is preferably smaller than the rotating magnetic object 113.
[0086] The advantage of the use of the rotating magnetic object together with the signal modulator is two-fold. First, it allows to operate the medical microdevice in a magnetic field with lower strength. For example, within the medical microdevice, i.e. between the rotating magnetic object and the field modulator, local operation field strengths of 50 mT are easily obtained, while an external magnetic field of more than 2 mT is barely tolerable for the patient. Second, it is easier to measure a modulated signal and the measured modulated signal allows to easily single out the signal indicative of a physical parameter or an identity of the medical microdevice. In particular, it is preferred that the signal modulator is coupled to a physical parameter in the environment of the medical microdevice. The physical parameter can, for instance, be translated to a movement of the signal modulator. The simplest coupling to the signal modulator is realized by changing a distance of the signal modulator to the rotating magnetic object. However, also other couplings are possible that can even be more effective. For instance, an internal structure of the signal modulator can be mechanically changed based on the physical parameter. Especially for temperature measurements, the signal modulator may react directly to the physical quantity, for instance, by changing a value of the saturation magnetization.
[0087] In a preferred modification of the above described embodiment the soft magnetic element 311 of the modified signal modulator 310 refers to a soft magnetic foil 311 as shown in FIG. 11. Preferably, the soft magnetic foil 311 comprises an asymmetric shape. Due to shape anisotropy the foil resists magnetization, wherein the resistance is higher in the shorter direction than in the longer direction. So if the foil is close to the rotating magnetic object 113, it is in saturation in all orientations and no harmonics are generated. If the distance increases, it is no more saturated when the magnetic sphere dipole is aligned with the short sides of the foil. Therefore, harmonics are generated in the generated response magnetic field. The exact shape of the harmonics spectrum sensitively depends on the material and the shape of the foil 311 and can be tailored to the desired application.
[0088] FIG. 12 shows a further modification of the above simple embodiment of the signal modulator 310, wherein in this further modification the signal modulator 310 comprises additionally a flux concentrator 313. The flux concentrator 313 preferably refers to a rigid structure of soft magnetic material that amplifies the response magnetic field generated by the magnetic object 113 and also the magnetic field gradient of the response magnetic field generated by the magnetic object 113. The addition of the flux concentrator 313 has the advantage that already very small movements of the signal modulator 311, i.e. very small distance changes, produce a signal change that can be measured. Thus, a signal modulator 310 comprising a flux concentrator 313 allows for a higher sensitivity for measuring changes of a physical parameter in the environment of the medical microdevice when compared with a medical microdevice comprising a signal modulator without a flux concentrator.
[0089] A further embodiment of the signal modulator is shown in FIG. 13, wherein the signal modulator 410 refers to a mechanical resonator that can be excited by the response magnetic field generated by the magneto mechanical rotator. In a preferred embodiment, as shown in FIG. 13, the mechanical resonator 410 comprises a) a magnetic component comprising an L-shaped permanent or soft magnetic element 412 and a flux concentrator 411, and b) a bellows 413. In the here shown exemplary embodiment, the bellows 413 connects the flux concentrator 411 comprising preferably a soft magnetic material and the magnetic element 412 to each other such that the flux concentrator 411 and the magnetic element 412 can change a distance to each other and thus an equilibrium position with respect to each other. Moreover, the restoring force provided by the bellows 413 acting against the change of the distance between the flux concentrator 411 and the magnetic element 412 leads in case of a resonant excitation of the mechanical resonator by the response magnetic field generated by the rotating magnetic object 113 to an oscillation around the equilibrium position of the magnetic element 412 and the flux concentrator 411. In particular, the mechanical resonator 410 can be arranged and adapted such that a change in the physical parameter in the environment of the medical microdevice leads to a change of the internal structure of the mechanical resonator 410, for this exemplary embodiment, to a contraction or elongation of the bellows 413 and thus a change of the equilibrium point of the magnetic element 412 and the flux concentrator 411. This change and the state of the bellows 413 then leads to a change of the resonance frequency of the mechanical resonator 410.
[0090] As a resonance frequency determination is highly desirable for an accurate parameter determination, this embodiment allows for a transformation of the signal to a higher frequency oscillation. The rotating magnetic object 113 provides a high frequency and high strength response magnetic field. By using preferably a high aspect ratio soft magnetic material, saturation can be reached and with this, high harmonics are produced. These high harmonics can then excite the mechanical resonator 410. The resonance frequency can be changed by a geometrical change of the bellows 413. The quantity to measure, i.e. the physical parameter, is in this case encoded in the phase difference between the excitation field and the harmonics in the generated response magnetic field. The rotating magnetic object 113 has here the additional benefit that both signals are fairly easy to measure simultaneously. It is possible to generate a 20.sup.th harmonics from a 100 kHz signal, and therefore the dynamic magnetic dipole of the mechanical resonator 410 can be provided small compared to the one of the rotating magnetic object 113 and still be detectable.
[0091] A more sophisticated embodiment that is also based on the principles described with respect to FIG. 13 is shown in FIG. 14. In this embodiment, the bellows 413 is provided, for instance, in form of a pressure can, i.e. a structure that reacts with a compression or elongation in one direction when subjected to changes in pressure in the environment. Within the bellow structure 413 in this embodiment the mechanical resonator 410 comprises as magnetic component at least one soft magnetic element comprising the form of an at least two pronged tuning fork. It is noted here the term tuning fork is only used for describing the geometrical form of the magnetic element, but not for describing its function. In the preferred embodiment shown in FIG. 14 the tuning fork comprises four prongs, however, also a two or three pronged tuning fork or a tuning fork with more than four prongs could be utilized. In this embodiment, also the flux concentrator 411 can be regarded as magnetic element and comprises the same form as the magnetic element 411, wherein the two magnetic elements, i.e. the magnetic element 412 and the flux concentrator 411, are arranged such that the prongs of the tuning forks face each other. Generally, also the principles of a mechanical resonator utilized as signal modulator in a medical microdevice as described above can be applied to this embodiment. The magnetic elements in form of a tuning fork are preferably made partially out of very thin and/or flexible material, so that a resonance frequency is low. Where the two tuning forks almost touch, they are split into a multitude of poles, which makes the attractive forces relatively large and significantly increases the resonance frequency of the whole assembly in the magnetized state. As the forces are only high if the poles are close to each other, the resonance frequency strongly depends on the distance, which is changed due to, for instance, a pressure applied to the pressure can. During the oscillation, the effective gap changes its width. If the external magnetic excitation field is sufficiently low, this changes the magnetization of the soft magnetic material and therefore the magnetic dipole moment. The tuning forks are preferably a little misaligned so that the changing field produces an exciting force. Harmonics are generated by the same soft material of the tuning forks and the right conditions for magnetization change are periodically met by the strong field change of the rotating magnetic object.
[0092] FIG. 15 shows another embodiment of a rotary bearing of a magneto mechanical rotator, wherein in this case the rotary bearing 510 does not comprise a saddle point. In this embodiment, the magneto mechanical rotator is provided with the rotary bearing 510 comprising a contact surface 512 which can comprise similar characteristics as the contact surfaces described above and which is in contact with the magnetic object 113. To hold the magnetic object 113 under the contact surface 512, the rotary bearing 510 is further provided with a permanent or soft magnetic foil 511 arranged beneath the contact surface 512. Preferably, the magnetic foil 511 is arranged parallel to the contact surface 512. The magnetic object 113 will then substantially arrange itself such that the magnetic moment of the magnetic object 113 is parallel to the contact surface 412 and the rotation axis is substantially perpendicular to the contact surface 512. Generally, although embodiments that do not comprise a retaining magnetic field generator adapted for generating a retaining magnetic field such that it is provided with a saddle point provide less stability, they can be easier produced and for some applications still be useful. To stabilize the rotating magnetic object 113 in this embodiment and to decrease a normal force on the contact surface 512, the contact surface 512 can comprise at least partly a concave shape encompassing at least a part of the magnetic object 113. In this case, the magnetic forces holding the magnetic object 113 at the contact surface 512 can be reduced, leading to a reduction of the normal force. Moreover, a lateral stability of the magnetic object 113 is increased.
[0093] Generally, the main idea of the invention refers to a magneto mechanical rotator comprising as first component a fast rotating permanent magnetic object. For this, the rotating magnetic object, possibly a sphere, is provided with some sort of rotary bearing. The rotary bearing can be realized advantageously in a plurality of ways, as already described above. One of the easiest ways is that the magnetic object is held in place on a flat contact surface by a magnetic foil. The magnetization of the magnetic foil is preferably perpendicular to the rotation axis. An oscillating or rotating external magnetic field can then spin the rotation of the magnetic object up by using, for instance, a suitable sweep from low to high frequencies, i.e. a chirped magnetic field. The maximal rotation speed of the rotating magnetic object is limited by its material strength to approximately 100 m/s at the rim. For a magnetic object realized as a 0.5 mm sphere, this approximation gives a maximal rotation speed of at least 64 kHz. To allow for an accurate detection of the signal provided by the rotating magnetic object, it is preferred that the friction is low enough that the signal can be recorded after the excitation. So, for instance, for several rotations the high speed needs to be maintained. The detailed embodiments described with respect to the figures provide examples on how to achieve such a low friction and accurate detection of the signal.
[0094] Generally, a simple and efficient rotary bearing for the fast rotating magnetic object can comprise a soft magnetic material that is brought close to the rotating magnetic object. The material can then reach magnetic saturation, wherein this saturation can generate harmonics in the generated response magnetic field, in particular, if a suitable anisotropy is maintained. The simplest embodiment can refer to providing a magnetic needle symmetrical at, but perpendicular to the rotation axis of the rotating magnetic object. If close enough, the needle gets in saturation and the resulting generated response magnetic field contains harmonics. These harmonics can then be evaluated, for instance, to decode a physical parameter or for an identification of the medical microdevice. Technically it is not even necessary to reach magnetic saturation. In such a case, the medical microdevice's generated rotationally symmetric response magnetic field just gets distorted to a more elliptical magnetic field. Such distortions can also be recorded using, for example, more than one transducer for transducing the response magnetic field to an electric response signal from more than one direction. To have a high signal strength, the saturation magnetic dipole moment of the needle is preferably close to the rotating permanent magnetic object's dipole moment. This allows the maximum possible signal in the harmonics.
[0095] The generation of harmonics by introduction of a soft magnetic material also enables detection of the medical microdevice during the excitation by the excitation magnetic field. For example, during the measurement the excitation frequency band can be suppressed in the receive path by adequate filtering and only the spectrum of higher harmonics can be used for detection and localization.
[0096] With the set-up described so far, it is possible to construct an efficient marker, i.e. a medical microdevice, that can be localized very accurately. The markers can even have some unique structure encoded in the generated signal, which allows the distinction of several thousand types of medical microdevices. To convert the medical microdevice into a sensor, the harmonics spectrum can be altered by an external physical parameter. For example, to measure a temperature the soft magnetic needle is provided with a Curie temperature close to the desired measurement temperature. Then the generated harmonics will be indicative of the temperature. For measuring pressure, the easiest way is to move the needle closer to the rotating magnetic object by a bellows. Changes in distance alter the local field and hence the harmonics spectrum. However, for a higher sensitivity it is preferred to move a second soft magnetic needle relative to the first one and thus change the harmonics spectrum. These objects can be much closer to each other than to the magnetic object such that smaller movements can be detected. A further possibility is to move a hard magnetic object relative to the soft magnetic needle and thereby modulate the harmonics spectrum.
[0097] FIG. 16 shows schematically and exemplarily a method for localizing a medical microdevice and/or for determining a physical parameter in the environment of the medical microdevice. The method 600 comprises a first step 610 of generating a magnetic or electromagnetic excitation field for inducing a mechanical rotation of a magnetic object of a magneto mechanical rotator as discussed, for instance, in the embodiments above. The rotation of the magnetic object of the magneto mechanical rotator then generates a periodically changing response magnetic field. In a next step 620, the periodically changing response magnetic field is transduced into electrical response signals. In step 630 the electrical response signals are then processed, for instance, by a processor, to determine a location and/or a physical parameter and/or a change of a physical parameter in an environment of the medical microdevice based on the electrical response signals.
[0098] Although in the above embodiments the magnetic object was depicted as a permanent magnetic sphere, in other embodiments the magnetic object can also comprise other shapes, like prolate or oblate spheroidal shapes, cylindrical shapes, etc. Moreover, although in the above embodiments soft magnetic discs and/or permanent magnetic spheres were shown as rotating magnetic field generator, in other embodiment also soft magnetic cylinders, permanent magnetic discs or cylinders, permanent magnetic cuboids, differently shaped spheroids, etc., can be utilized for providing the retaining magnetic field.
[0099] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.
[0100] In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality.
[0101] A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.
[0102] Determinations like the determination of the position of the microdevice, the change of a physical parameter, or the physical parameter itself based on the generated magnetic field, etc., performed by one or several units or devices can also be performed by any other number of units or devices. These processes can be implemented as program code of a computer program and/or as dedicated hardware.
[0103] A computer program may be stored/distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.
[0104] Any reference signs in the claims should not be construed as limiting the scope.
[0105] The invention relates to a medical microdevice for insertion into a human body, wherein the microdevice allows for measuring at least one of a localization of the microdevice in a space and/or a physical parameter in the environment of the microdevice, wherein the microdevice comprises a casing and within the casing a magneto mechanical rotator, wherein the magneto mechanical rotator comprises a magnetic object providing a permanent magnetic moment and a rotary bearing that is adapted to stabilize a rotational motion of the magnetic object, wherein the magneto mechanical rotator is adapted to transduce an external magnetic or electromagnetic excitation field into a mechanical rotation of the magnetic object relative to the rotary bearing such that a periodically changing magnetic response field is generated. The microdevice thus allows for an improved signal transmission and for a further miniaturization.
