PASSIVE TRANSPONDER SYSTEM AND PRESSURE WAVE MEASURING DEVICE

Description

[0001] The invention relates to a passive transponder system with a first or second conductor loop structure and a first and a second capacitive pressure sensor. Each conductor loop structure is coupled to one of the capacitive pressure sensors to form a resonant circuit. The first conductor loop structure is at a non-zero angle to the second conductor loop structure. The resonant frequencies of the resonant circuits are selected such that they do not overlap. The invention also relates to a pressure wave measuring device with such a passive transponder system and a readout unit.

[0002] For various applications, devices are used that utilize inductively coupled communication between a transponder or a passive resonant circuit and a reader. The transponder or passive resonant circuit is supplied with power via inductive coupling. At the same time, signal transmission, and thus information transfer, takes place via this coupling.

[0003] Such devices are used in medicine, for example, to obtain information about blood flow in blood vessels. The transponder can be designed as a coil that encircles the blood vessel in question.

[0004] The problem is that such coils have a pronounced figure-eight directional characteristic. This means that the coupling between the readout coil and the transponder coil depends crucially on the orientation of the transponder coil relative to the readout coil. When the transponder coil is maximally penetrated by the field generated by the readout coil, a maximum signal can be achieved. However, if the sensor coil is not penetrated at all by the field of the readout coil, e.g., if the two are positioned at a 90° angle to each other, no coupling is achieved, and reading becomes impossible.

[0005] One possible design of the transponder coil is a saddle-shaped winding in which the conductor tracks of the coil follow a cylindrical surface and the coil axis is perpendicular to the cylinder axis of this cylindrical surface.

[0006] When the transponder coil is implanted, it is impossible or very difficult to determine how the saddle coil is oriented around the corresponding blood vessel. If the axis of the saddle coil is parallel to the axis of the readout coil, the coupling is maximum. If the coil axes are perpendicular to each other, no coupling is achieved.

[0007] WO02 / 098296 A1 describes an endovascular implant or endograft comprising a tubular sleeve with integral inner and outer layers. A pressure sensor is embedded between and covered by the two layers. The sleeve is flexible at the pressure sensor to allow pressure transmission through the sleeve for detection by the pressure sensor used.

[0008] WO2012 / 100959 A1 relates to a cylindrical device for the flow of fluid, which has at least two pressure sensors with which a pressure of the fluid inside the device can be measured.

[0009] WO 2006 / 096685 A1 discloses a radio-frequency antenna arrangement for a medical device, for example, a device that can be implanted in a patient. The antenna assembly comprises multiple antennas, each oriented to receive a radio-frequency signal propagating in a different direction. The individual electrical signals generated in each antenna are additively combined into a single signal that has a greater strength than each of the individual electrical signals.

[0010] The object of the present invention is to provide a passive transponder that enables reliable and controllable coupling with a readout coil. It is also the object to provide a pressure wave measuring device that enables good and controllable signal readout.

[0011] This object is achieved by the passive transponder system according to claim 1 and the pressure wave measuring device according to claim 10. The respective dependent claims specify advantageous developments of the passive transponder system according to claim 1 and the pressure wave measuring device according to claim 10.

[0012] According to the invention, a passive transponder system is provided that has a first conductor loop structure with at least one turn and a second conductor loop structure with at least one turn. A conductor loop structure can be understood as a structure created from an electrical conductor that has at least one turn of the conductor. The conductor is preferably itself elongated, for example, as a wire or a conductor track, and is formed along its longitudinal direction into at least one turn.

[0013] The passive transponder system also includes a first capacitive pressure sensor and a second capacitive pressure sensor. A capacitive pressure sensor is defined as a capacitance, i.e., a capacitor, whose value depends on the pressure applied to the sensor. In a simple example, such a capacitive pressure sensor can be configured as a closed volume with a capacitor plate arranged on each of its opposite surfaces. If pressure is applied to such a structure, the distance between the capacitor plates changes, and thus the capacitance of the capacitor formed by the capacitor plates changes. The capacitance can therefore be used as a measure of the applied pressure.

[0014] According to the invention, the first capacitive pressure sensor is coupled to the first conductor loop structure to form a first resonant circuit. This first resonant circuit has a resonant frequency, which shall be referred to below as the "first resonant frequency." Furthermore, the second capacitive pressure sensor is electrically coupled to the second conductor loop structure to form a second resonant circuit, whose resonant frequency shall be referred to as the "second resonant frequency."

[0015] The turns of the conductor loop structures are each wound around at least one winding axis. Thus, at least one turn of the first conductor loop structure is wound around at least one first winding axis, and at least one turn of the second conductor loop structure is wound around at least a second winding axis. The winding axis is understood to be a straight line that is perpendicular to a surface in which the corresponding turn runs. The winding axis should preferably be perpendicular to a center point of the area of this surface enclosed by the corresponding turn. The center point can be considered to be the point with respect to which the corresponding turn is point-symmetrical. The fact that the turn is point-symmetrical is optional. The point symmetry is preferably present in projection onto a plane to which the winding axis is perpendicular.The coil axis preferably passes through this plane at a center point of the coil's projection onto this plane. A snail-shell-shaped coil, i.e., a coil that has a slightly larger or smaller radius after orbiting the coil axis than at its opposite end, should also be considered point-symmetric in this sense.

[0016] According to the invention, the at least one first winding axis and the at least one second winding axis are at a non-zero angle to each other. The angle is therefore greater than zero and less than 180°. The angle should not be 0° or 180°. Preferably, the angle is 90°. According to the invention, the winding axes do not need to intersect. In this case, the angle between projections of the winding axes in the direction perpendicular to one or both of the winding axes is measured on a common plane.

[0017] The passive transponder system of the invention can also be referred to as a passive transponder. The first resonant circuit and the second resonant circuit can advantageously be structurally connected to each other, but it is also possible to implement the two resonant circuits without being structurally connected to each other.

[0018] As is known, the resonant frequency of a resonant circuit can be adjusted by selecting the capacitance and inductance of the conductor loop structure. Preferably, the first resonant frequency and the second resonant frequency are at least sufficiently different that they do not overlap in a floating manner. The first resonant frequency and the second resonant frequency are therefore preferably selected such that, when superimposed, they do not create a floating pattern. This allows the signals generated by the individual resonant circuits to be separated particularly well.

[0019] It has proven advantageous if the resonant frequencies of the first and second resonant circuits differ by at least twice the bandwidth of the first or second resonant circuit. Advantageously, the resonant frequencies of the first and second resonant circuits differ by at least twice the bandwidth of the one of these two resonant circuits with the larger bandwidth. Advantageously, the bandwidth is the so-called 3 dB bandwidth, which is the difference between the upper -3 dB cutoff frequency f 2 and the lower -3 dB cutoff frequency f 1. The cutoff frequencies are those frequencies at which the resonance curve intersects the value -3 dB. The bandwidth B can also be defined as B = f 2 - f 1 = f 0 / Q, where f 0 = √(f 1 f 2 ) and Q is the quality factor of the resonant circuit. For common sensor resonant circuits, the minimum separation could therefore be 2 MHz, for example.

[0020] In an advantageous embodiment, the first and second conductor loop structures can be designed as flat coils arranged on surfaces of a support structure. If the conductor loop structures have more than one turn, these turns can each run on a common surface, with adjacent turns each having a slightly larger diameter so that adjacent turns enclose each other. In this way, coils can be produced that are flat and have any number of turns. In this embodiment, the surface of the flat coils, i.e., the surface in which the turns run, can be the surface of the support structure.

[0021] Particularly advantageously, the first conductor loop structure can be arranged on an inner surface of the support structure and the second conductor loop structure on an outer surface. However, it is also possible for both conductor loop structures to be arranged on the same surface of the support structure, in which case insulation of the conductor loop structures from one another is advantageously provided. For this purpose, for example, the conductor tracks of the conductor loop structures can be sheathed with an insulator. It is also possible to first apply one of the conductor loop structures, then coat this entire surface of the support structure with an insulating material and then apply the other conductor loop structure. In this way, any number of conductor loop structures can be arranged on the same surface of the support structure.However, it is also possible that the conductor track of one of the conductor loop structures only extends to the other surface of the carrier structure where it crosses a conductor track of the other conductor loop structure.

[0022] Advantageously, the support structure can have the shape of a partial cylinder, a cylinder, a partial hose, a hose, a partial pipe, or a pipe. A cylinder can be understood here as a surface that is the same distance from a common line at all points. This line is referred to here as the cylinder axis. The line can be curved or straight. Preferably, the surface is closed around the said line. Particularly preferably, a base area of the cylinder is circular, but other base shapes are also possible. A cylinder with a circular base area can also be referred to as a hose or a pipe, whereby in the case of a hose the said line can be curved, and in the case of a pipe the said line can be straight.A partial cylinder can be understood here as a shape whose points are entirely part of a cylindrical surface, but which does not form a complete cylindrical surface. Similarly, a partial tube or partial tube can be understood as a surface whose points are entirely part of a tube or tube, but do not completely fill it. The support structure can then, for example, have the shape of a three-quarters closed tube or tube. For use in blood vessels, the tube shape and the tube shape are preferred because they are adapted to the geometry of the blood vessel.

[0023] In this embodiment, the angle between the winding axes of the first and second conductor loop structures can be freely selected within the scope of the invention. If the conductor loop structures are arranged on surfaces of a tubular or hose-shaped structure, they can be saddle-shaped. Particularly advantageously, they can be designed such that the conductor loops or windings each have two straight sections in which they run parallel to a cylindrical axis of the support structure, wherein the straight sections are each connected to one another by circular arc-shaped sections in which the corresponding winding runs in a circular arc around the cylindrical axis of the support structure.The pressure sensors can also be arranged on the surfaces of the support structure, wherein preferably the first capacitive pressure sensor is arranged on that surface of the support structure on which the first conductor loop structure is also arranged and the second capacitive pressure sensor is arranged on that surface of the support structure on which the second conductor loop structure is also arranged.

[0024] The circular arc sections of the windings preferably have a length of 180°, which means that the two straight sections of the windings are exactly opposite each other with respect to the cylinder axis. This maximizes the area encircled by the winding and thus maximizes the coupling.

[0025] A plastic tube or hose is particularly suitable as a support structure. The two conductor loop structures are then electrically insulated from each other by the plastic tube or hose. The support structure can be made of polyimide, for example.

[0026] Preferably, the coil axes are perpendicular to each other in the sense described above, thereby minimizing mutual interference and achieving a directional characteristic that best matches a circular shape. During use, the cylindrical axis of the support structure can be coaxial with the longitudinal axis of a blood vessel on which the support structure is arranged. Since the blood vessels in the human body largely run parallel to the longest dimension of the body due to their anatomy, the aforementioned directional characteristic is preferably approximated to a circular shape in a plane that is perpendicular to the cylindrical axis or longitudinal axis of the support structure.The directional dependence is particularly advantageous in this radial direction because a correction by moving the readout coil around the vessel without signal loss would only be possible if the vessel were located exactly in the center of the cylindrical body part, which is actually only the case in a few exceptional cases. In all other cases, the vessel will be located closer to the surface of the body part in one direction, and it is precisely at this point that the coupling with the transponder coil should be as good as possible. While an axial displacement of the readout coil relative to the sensor coil is possible, it can be corrected by simply moving the readout coil along the body part.

[0027] Said flat coil can advantageously have a round, oval, square, or rectangular circumference, with the corresponding shapes being curved with the corresponding surface of the support structure. Preferably, the average width of the coil in the unbent, i.e., flat, state is equal to three-quarters of the circumference of the support structure.

[0028] According to the invention, the first conductor loop structure comprises a plurality of groups of turns arranged side by side in the direction of a main axis. Each group comprises at least one turn. Therefore, even a single turn can be considered a group in this sense.

[0029] Each of the groups of turns of the first conductor loop structure is wound around its own first winding axis, with the first winding axes of different groups preferably being parallel to one another and spaced apart from one another by a non-zero distance. These distances are preferably the same for all adjacent groups of turns of the first loop structures. Turns of the same group of turns are wound around the same winding axis. The winding axes of different groups are different, i.e., not coaxial, and spaced apart from one another.

[0030] Accordingly, the second conductor loop structure has a plurality of groups of turns arranged next to one another in the direction of the main axis. Each group has at least one turn. A single turn can therefore also be understood as a group in this sense. Each of the groups of turns of the second conductor loop structure is then wound around its own second winding axes, wherein the second winding axes are preferably parallel to one another and spaced from one another by a non-zero distance. Here, too, these distances are preferably the same for all adjacent second winding axes. Turns of the same group of turns are in turn wound around the same winding axis. The winding axes of different groups can be different, i.e. not coaxial, and spaced from one another.

[0031] The fact that turns are arranged next to each other primarily means that the winding axes are arranged next to each other. Turns of adjacent groups of the same conductor loop structure that are arranged next to each other can overlap, be directly adjacent to each other, or be spaced apart.

[0032] If each group has only one turn, the first conductor loop structure can have a plurality of turns arranged next to one another in the direction of a main axis, wherein each of the turns of the first conductor loop structure is wound around its own winding axis, wherein the first winding axes are spaced apart from one another by a non-zero distance. Accordingly, the second conductor loop structure can have a plurality of turns arranged next to one another in the direction of the main axis, wherein each of the turns of the second conductor loop structure is wound around its own second winding axis, wherein the second winding axes are spaced apart from one another by a non-zero distance.

[0033] Preferably, the winding axes of adjacently arranged windings or of groups of windings of the same conductor loop structure are parallel to each other.

[0034] Furthermore, the distances by which the second winding axes are spaced from one another are particularly preferably equal to the distances by which the first winding axes are spaced from one another. This configuration allows a directional characteristic that is as close as possible to a circular shape to be achieved in a plane perpendicular to the direction in which the winding axes are arranged next to one another. Furthermore, a homogeneous directional characteristic can be achieved over the entire length in the direction of the adjacent arrangement of the winding axes. Such a conductor loop structure can be significantly longer than the diameter.

[0035] In this embodiment of the invention, the first and second conductor loop structures can each be produced using a wire. Particularly advantageously, a wire forming the first conductor loop structure can be guided through turns of the wire forming the second conductor loop structure. In this way, the first and second conductor loop structures are advantageously interwoven and can thus form a stable structure. Such a structure can serve, for example, as a stent for a blood vessel. In a corresponding manner, the wire forming the second conductor loop structure can also be guided through the turns of the first conductor loop structure.

[0036] In an advantageous embodiment of the invention, the windings of the first conductor loop structure can extend in two surfaces opposite the main axis, with the first winding axes advantageously being perpendicular to these opposite surfaces. Advantageously, the windings of the second conductor loop structure can also extend in two surfaces opposite the main axis, to which the second winding axes are then each perpendicular. The fact that the two surfaces are opposite each other with respect to the main axis means that these surfaces are both perpendicular to a straight line that intersects the main axis, with the main axis being arranged between these two opposite surfaces.This design can be used advantageously both in the saddle-shaped design of the conductor loop structures described above and in the design with windings arranged next to one another.

[0037] If the first and second conductor loop structures have a plurality of turns arranged side by side in the direction of the main axis, these turns can extend correspondingly in two surfaces opposite each other with respect to the main axis. Particularly advantageously, the turns of the first conductor loop structure can each extend through the turns of the second conductor loop structure, so that the first and second conductor loop structures are interwoven. Along the circumference, one turn of the first conductor loop structure can then each extend through a turn of the second conductor loop structure, with this turn of the second conductor loop structure extending through a turn of the first conductor loop structure on its side facing away from said first turn.This last-mentioned turn of the first conductor loop structure can run on the surface opposite the surface in which the first-mentioned turn of the first conductor loop structure runs. The last-mentioned turn of the first conductor loop structure can then interlock with another turn of the second conductor loop structure, which in turn interlocks with the first-mentioned turn of the first conductor loop structure. In this way, the turns of the first and second conductor loop structures can form a fabric that completely surrounds the main axis, in which turns of the first conductor loop structure and the turns of the second conductor loop structure are opposite each other. The turns of the first conductor loop structure and the second conductor loop structure each interlock.In an advantageous embodiment of the invention, the first winding axes of the first conductor loop structure can be located between the second winding axes of the second conductor loop structure in the direction along the main axis. In this way, it can be achieved that a magnetic field generated by the windings of the first conductor loop structure penetrates the windings of the second conductor loop structure as little as possible, and a magnetic field generated by the windings of the second conductor loop structure penetrates the windings of the first conductor loop structure as little as possible. This improves the directional characteristic in the radial direction.

[0038] To enable the first and second conductor loop structures to be interwoven as described above, it is advantageous if the wire from which the first and second conductor loop structures are formed is coated with electrical insulation. For example, DFT wire with a core made of Au or Ag and coated with NiTi can be used.

[0039] The described interweaving of the first and second conductor loop structures corresponds, in terms of electrical and electromagnetic behavior, to two or more coils twisted relative to each other at the desired angle. Due to this interweaving, the coil has regions that represent the actual coils as well as intersection points where these coils can be mechanically combined into a cylindrical structure and fixed relative to each other. Such a configuration can function equally well as a coil and as a vascular support, e.g., a stent. It can be made of material that can have electrical, mechanical, and biocompatible properties. Because the coil axes are at a non-zero angle to each other, the described good coupling can be achieved regardless of the angle.

[0040] In an advantageous embodiment of the invention, the capacitive pressure sensors can be located with their pressure-measuring surface in one of the areas in which the conductor loop structure of the corresponding resonant circuit extends. Thus, the first capacitive pressure sensor can advantageously be arranged with its pressure-measuring surface in one of the areas in which the first conductor loop structure extends, and the second capacitive pressure sensor can advantageously be arranged with its pressure-measuring surface in one of the areas in which the second conductor loop structure extends.

[0041] Preferably, the first conductor loop structure and / or the second conductor loop structure can each be formed from a single wire. This wire can be bent to form all turns of the corresponding conductor loop structure. Advantageously, adjacent turns of the first and second conductor structures in the circumferential direction around the main axis can also be connected to one another in a manner other than interlocking. For example, these turns can be glued together. However, a design with interlocking conductor structures is particularly advantageous because no further production steps are required for the connection, thus simplifying manufacturing.

[0042] Advantageously, the first resonant frequency can be greater than or equal to 5 MHz, preferably greater than or equal to 10 MHz, particularly preferably greater than or equal to 15 MHz and / or less than or equal to 40 MHz, preferably less than or equal to 30 MHz, particularly preferably less than or equal to 20 MHz.

[0043] According to the invention, a pressure wave measuring device is also provided, which, on the one hand, has a passive transponder system, as described above, and, in addition, a readout unit. The readout unit has at least one readout coil, which can be arranged relative to the passive transponder system such that a magnetic field generated by it permeates at least one of the conductor loop structures of the transponder system. The pressure wave measuring device according to the invention also has evaluation electronics, with which the readout coil can be subjected to a signal that excites the resonant circuits of the passive transponder system. The signal is understood here to be an alternating electromagnetic field that can permeate the conductor loop structures of the passive transponder system if it is arranged at a suitable distance and with a suitable orientation relative to the passive transponder system.According to the invention, the evaluation electronics can also evaluate a signal received by the readout coil. The signal received by the readout coil is a temporal current waveform generated by the readout coil being permeated by an electromagnetic field generated by the resonant circuits of the passive transponder system.

[0044] In an advantageous embodiment of the invention, the pressure wave measuring device can comprise a signal source with which a signal, i.e., an alternating current waveform, can be generated at the resonant frequencies of the oscillating circuits. Advantageously, the pressure wave measuring device also comprises a directional coupler, to whose output the signal source is electrically coupled and to whose input the readout coil is coupled.

[0045] Advantageously, the signal can have the form a sin (ω at) + b sin (ω bt).

[0046] In a further advantageous embodiment of the invention, the pressure wave measuring device can have a first mixer into which a signal received by the readout coil can be introduced. A first low-pass filter can be provided downstream of the first mixer, into which a signal output by the mixer can be introduced. With the first mixer, a signal received by the readout coil from the transponder system at the first resonant frequency can be downmixed. The pressure wave measuring device of the invention can also have a further second mixer into which a signal received by the readout coil can be introduced. Downstream of this further mixer, a second low-pass filter can be provided into which a signal output by the second mixer can be introduced. In turn, the second mixer can downmix a signal of the second resonant frequency received by the readout coil from the transponder system.

[0047] Preferably, the pressure wave measuring device is configured such that the signal received at the first resonant frequency can be constructively added to the signal received at the second resonant frequency. If, as described above, a mixer and a low-pass filter are provided, the signal output by the first low-pass filter can advantageously be constructively added to the signal output by the second low-pass filter. This constructive addition can be achieved by, on the one hand, dividing the signal output by the first low-pass filter into absolute value or amplitude and phase, and, on the other hand, dividing the signal output by the second low-pass filter into amplitude or absolute value and phase. The absolute values or amplitudes can then be added together, and the phases can be added together, resulting in a total amplitude and a total phase.

[0048] The measuring principle can correspond to a lock-in amplifier. The first oscillating circuit and the second oscillating circuit provide an X component and a Y component, which are received by the readout coil. If ω a and ω b are the resonance frequencies of the two oscillating circuits of the passive transponder system at a specific trigger pressure pt, the signal can be specified as described above and coupled into the coils of the passive transponder system. Resonance frequencies can, for example, be in a range from 1 to 100 MHz, whereby the frequency components of the applied pressure can be, for example, between 0.1 and 50 Hz. When used on a blood vessel, the main component can, for example, be a heartbeat repeating periodically at approximately 1 Hz.

[0049] The signal source can then emit a signal with the two frequencies of interest, ω a and ω b, and send it to the output of the directional coupler. The directional coupler can transfer the signal to its input and forward it to the readout coil. Due to the directional coupler, direct transmission of the signal from the signal source to the mixer does not occur (or, for real directional couplers, only to a very limited extent, with an isolation parameter greater than 25 dB). However, what can normally reach the mixers from the readout coil are signals reflected from the coil due to the deviation from the system impedance (e.g., 50 ohms).

[0050] If the sensors of the passive transponder system change their resonance frequencies ω a and ω b due to variations in the pressure applied to the capacitive pressure sensors, this can be measured in the reflected signal, as this causes a change in the impedance of the readout coil and thus in the reflective signal.

[0051] Downconverting the signal and filtering it with a low-pass filter at the observed resonance frequencies ω a and ω b is advantageous because, for a wide measurement bandwidth, the noise level can also typically assume large values, and the change in the reflected signal can then be relatively weak for sensors located far away, for example, those embedded in body tissue. The information obtained in this way is then available directly in the baseband.

[0052] The separation of the amplitude and phase of the two signals is advantageous because they can be added together without canceling each other out at certain angles.

[0053] The mixer can advantageously multiply the measurement signal by the reference signal generated by the signal source, thus causing a frequency shift of the measurement signal's spectrum around the reference frequency. The frequency component of the measurement signal at the reference frequency can thus be mixed down to zero. Subsequent low-pass filtering can advantageously remove further mixing products and reduce noise.

[0054] A method for producing a passive transponder as described above is also specified. The first and / or second conductor loop structure is produced as follows. First, a plurality of support elements are lined up on a rod. Each of these support elements has a cylindrical outer surface in which a recess is made. This recess has a surface which, in turn, is a section of a cylindrical surface. This cylindrical surface advantageously has the same curvature as the outer surface of the support element. Furthermore, the cylindrical axis of this cylindrical surface of the recess is advantageously perpendicular to the cylindrical axis of the outer surface of the support element. In this way, a plurality of support elements can be lined up on the rod, wherein the cylindrical axes of the cylindrical outer surfaces of adjacent support elements are perpendicular to one another.

[0055] A first wire is then wound around a first group of support elements as the first conductor loop structure. The first group of support elements is characterized by the fact that the cylinder axes of their outer surfaces are all parallel to each other.

[0056] Furthermore, a second wire is wound around a second group of support elements as a second conductor loop structure. This second group, in turn, contains those support elements whose cylindrical axes are parallel to each other but perpendicular to the cylindrical axes of the support elements of the first group. In this way, the first and second conductor loop structures can be wound with mutually perpendicular winding axes.

[0057] Following winding, the rod can be pulled out of all the support elements so that they become freely movable and can be pushed out of the windings. Only the wound conductor loop structures remain. Advantageously, the first and the second wire can each be wound in such a way that they first run completely around a support element of the corresponding group at least once and then continue to the adjacent support element of the same group. They can then run completely around this element and then continue to the next support element of the same group. In this way, conductor loop structures with a large number of turns arranged next to one another can be created. The use of the support elements makes it possible in particular to wind in such a way that the first and the second windings each run in two opposite surfaces.Furthermore, it is readily possible to guide the wire of the first conductor loop structure through the turns of the second conductor loop structure and to guide the wire of the second conductor loop structure through the turns of the first conductor loop structure, resulting in a stable braided structure. It should be noted that the cylindrical axis of the outer surfaces of the support elements can correspond to the winding axes of the winding wound around this support element, and that the longitudinal axis of the rod corresponds to the main axis of the passive transponder system.

[0058] The invention will be explained below using a few examples. Like reference numerals correspond to like or corresponding features. The features shown in the examples can also be implemented independently of the corresponding example and can be combined between the examples.

[0059] It shows Figure 1 shows a measuring arrangement for determining a directional characteristic of a transponder, Figure 2 shows a directional characteristic of a transponder with two coils, Figure 3 shows a printed circuit for producing a transponder system, Figure 4 shows a side view of this transponder system, Figure 5 shows an axial view of this transponder system, Figure 6 shows an example of a transponder system according to the invention, Figure 7 shows a perspective view of the Figure 6 shown transponder system, Figure 8 a detailed view of the Figures 6 and 7 shown transponder system, Figure 9 an axial view of the Figures 6 to 8 shown inventive transponder system, Figure 10 an example of a pressure wave measuring device according to the invention, Figure 11 an exemplary circuit of two oscillating circuits tuned to the same frequency, Figure 12 the resonance shift of the in Figure 11 shown resonant circuits, and Figure 13 an example of a manufacturing process.

[0060] Figure 1 shows a measuring arrangement for measuring the directional characteristic of a transponder 1. The transponder 1 is arranged opposite a readout coil 2 with variable orientation. The measuring device has an optional angle scale 3 with which the orientation of the transponder can be measured. The readout coil 2 is a cylindrical coil which is Figure 1can be seen from the side. The transponder 1 is arranged opposite the readout coil 2 in such a way that an axis of symmetry 4 of the readout coil 2 intersects a cylindrical axis of the transponder 1, wherein the axis of symmetry 4 is perpendicular to both the readout coil 2 and the cylindrical axis of the transponder 1. The transponder 1 here has saddle-shaped coils which are arranged on cylindrical surfaces of the transponder 1 in such a way that the coil axes are perpendicular to the longitudinal axis of the transponder 1 and intersect the axis of symmetry 4 or are coaxial with it. The coil axes also intersect the cylindrical axis of the transponder 1, in this case the axis of rotation.

[0061] Figure 2 shows a directional characteristic as it is for a transponder with the Figure 1 shown measuring arrangement when the transponder has 2 cylindrical coils whose coil axes are perpendicular to each other and intersect each other. Figure 2 shows the X-component of the voltage induced in the readout coil and the Y-component of the voltage induced in the readout coil, whereby the coil axis of one coil of the transponder runs in the X-direction and the coil axis of the other coil of the transponder runs in the Y-direction.

[0062] The dotted line 5 (squares) in Figure 2shows the directional characteristic of the transponder coil whose coil axis is oriented in the Y direction. The small dashed line 6 (dots) shows the directional characteristic of the transponder coil whose coil axis is oriented in the X direction. It can be seen that the two individual coils of transponder 1 have a pronounced 8-shaped directional characteristic, with the directional characteristics of the two coils rotated by 90° relative to each other, since the coils are also rotated by 90° relative to each other. If the two coils of transponder 1 are simply connected in series, the result is the large dashed directional characteristic 7 (triangles), which is also 8-shaped and rotated by 45° relative to the directional characteristics of the two individual coils. The solid line (circles) shows the directional characteristic of a transponder according to the present invention.Because the signals from the two individual coils are distinguishable from one another due to their different resonant frequencies, they can be added constructively. This results in the nearly circular directional pattern marked with 8. The direction of the readout in the XY plane is irrelevant. Good coupling between the transponder and the readout coil is always achieved.

[0063] The Figures 3 to 5 show an example of a passive transponder not according to the invention. Figure 3 a printed circuit from which the transponder can be manufactured, Figure 4 shows two side views of the transponder produced in this way and Figure 5 an axial view of the transponder thus manufactured.

[0064] Figure 3shows a printed circuit 33 with a first conductor loop structure 31 and a second conductor loop structure. The conductor loop structure 31 is on a front side, in the Figure 3 facing the viewer, of a substrate 34 and the second conductor loop structure on a back side of the substrate 34 facing away from the viewer. The substrate 34 thus electrically insulates the first conductor loop structure 31 and the second conductor loop structure 32 from one another.

[0065] In the example shown, the conductor loop structures 31 and 32 each have three turns. Each of the conductor loop structures 31 and 32 has two straight regions that are parallel to one another and are connected to one another via two circularly curved regions. In the straight regions, the conductor tracks run parallel to one another and straight, and in the circularly curved regions, the conductor tracks run along a circular line and parallel to one another for all turns of the same conductor loop structure. A first capacitive pressure sensor 35 is coupled to the first conductor loop structure 31. The capacitive pressure sensor 35 is coupled between the two ends of the conductor loop structure 31. Accordingly, the conductor loop structure 32 has a second capacitive pressure sensor 36, which in turn is arranged between the two ends of the conductor loop structure 32.The first capacitive pressure sensor 35 forms a first resonant circuit with a first resonant frequency with the first conductor loop structure 31. The second capacitive pressure sensor 36 forms a second resonant circuit with a second resonant frequency with the second conductor loop structure 32.

[0066] The first conductor loop structure 31 is wound around a winding axis, wherein the winding axis here passes through the center of the conductor tracks of the conductor loop structure 31 and is perpendicular to the substrate 34. Similarly, the conductor tracks of the second conductor loop structure 32 are wound around a second coil axis, which in turn passes through the center of the conductor track of the second conductor loop structure 32 and is perpendicular to the substrate 34.

[0067] From the Figure 3 shown structure can be as in Figure 4shown non-inventive passive transponder can be produced by bending the substrate 34 about an axis which runs parallel to the long sides of the substrate 34, which are parallel to the straight sections of the conductor loop structures 31 and 32. This direction will be referred to below as the Z direction.

[0068] Figure 4A shows this embodiment of the transponder in a first direction, which is perpendicular to the Z-direction and at an angle of 45° to the X-axis and the Y-axis. Partial Figure 4B shows the transponder viewed in the X-axis direction.

[0069] The conductor loop structures 31 and 32 can advantageously be dimensioned such that, when the substrate 34 is bent in the manner described, the straight regions of the conductor loop structures are diametrically opposed to each other with respect to the axis around which the substrate 34 was bent. The substrate 34 is preferably bent into a circular shape such that the coil axes of the first conductor loop structure and the second conductor loop structure 32 are at the desired angle to each other, preferably perpendicular to each other.

[0070] Figure 5 shows the Figure 4 The design of the transponder shown in the direction of view in the Z-axis. Figure 4A The view shown is obtained by considering the Figure 5 shown view from the right and the one in Figure 4B The view shown is taken from the top right corner.

[0071] It can be seen that the substrate has been bent into a circular shape. The first conductor loop structure 31 lies on an inner surface of the resulting cylindrical substrate, and the second conductor loop structure 32 lies on its outer surface. The longitudinal regions 31a, 31b, and 31c of the first conductor loop structure 31 are located opposite one another, with respect to which the straight sections 31a, 31b, 31c of the same turn of the first conductor loop structure 31 are equally spaced. Similarly, the straight sections 32a, 32b, 32c are located opposite one another with respect to the YZ plane, with respect to which the straight sections 32a, 32b, 32c of the same turn are equally spaced.

[0072] The Figures 6 to 9 show another example of a passive transponder according to the invention. Figure 6 a side view in the direction perpendicular to the Z-axis, which corresponds to the longitudinal axis or main axis of the transponder, Figure 7a perspective view and Figure 8 a detailed view. Figure 9 shows a view in the direction of the Z-axis.

[0073] In this embodiment of the invention, a first wire 61 is bent into a first conductor loop structure 61, and a second wire 62 is bent into a second conductor structure 62. The first conductor loop structure 61 has a plurality of turns 61a, 61b, 61c arranged next to one another in the direction of a main axis, which here is the longitudinal axis, i.e., the Z-direction of the transponder, with each of the turns of the first conductor loop structure 61 being wound around its own winding axis. The first winding axes are parallel to one another and spaced apart from one another by a non-zero distance. The embodiment shown also has a second conductor loop structure 62 with a plurality of turns 62a, 62b, 62c arranged next to one another in a direction of the main axis, with each of the turns 62a, 62b, 62c of the second conductor loop structure 62 being wound around its own second winding axis.The second winding axes are again parallel to each other and spaced apart by a non-zero distance. In the example shown, the winding axes of the first windings 61a, 61b, 61c are also perpendicular to the winding axes of the second windings 62a, 62b, 62c. In the example shown, the conductor loop structure 61 also has two windings on each of the winding axes, which are opposite each other with respect to the Z axis. Furthermore, the second conductor loop structure 62 also has two windings for each of the winding axes, which are opposite each other with respect to the Z axis.

[0074] As in Figure 8As can be seen in detail, the turns 61a, 61b, 61c of the first conductor loop structure 61 are interwoven with the turns 62a, 62b of the second conductor loop structure 62. For this purpose, the wire of the first conductor loop structure 61 is first bent into a substantially circular turn, wherein the turn is closed by winding the wire around the wire of the second conductor loop structure 62 where it runs between two turns 62a and 62b of the second conductor loop structure. Accordingly, the wire of the second conductor loop structure 62 is bent into a turn 62a, which is closed by winding the wire around the wire of the first conductor loop structure 61 where it runs between two adjacent turns 61a and 61b of the first conductor loop structure.In this way, for each of the conductor loop structures 61 and 62, the wire is bent into a turn, then guided along a straight section parallel to the cylinder axis of the transponder to the adjacent turn of the same conductor loop structure, there again bent into a turn, and further guided in a straight section to the adjacent turn of the same conductor loop structure, which is repeated for the number of turns in the same area of the corresponding conductor loop structure. The second conductor loop structure is wound accordingly into turns 62a, 62b, which in turn are guided over straight sections parallel to the longitudinal axis of the transponder. The turns of the second conductor loop structure 62 are each wound around the straight section of the first conductor loop structure 61 in a partial section of the turns.Accordingly, the windings 61a, 61b, 61c of the first conductor loop structure 61 are wound around the straight region of the adjacent second conductor loop structure in the region of the winding.

[0075] It should be noted that the winding configuration shown here is merely an advantageous example that provides good mechanical stability. However, numerous other winding configurations are conceivable, resulting in a similar arrangement of the turns of the conductor loop structures 61 and 62 relative to one another. It is also possible for the conductors of the conductor loop structures 61 and 62 to be connected to one another in other ways, for example, by gluing or binding.

[0076] Figure 9 shows a view of the Figures 6 to 8The example of the transponder according to the invention shown is viewed in the direction of the longitudinal axis of the transponder, i.e., in the direction of the Z-axis. It can be seen that the conductor loop structures 61 and 62 describe an approximately circular circumference, so that the entire transponder approximately describes a cylindrical shape.

[0077] Here, too, the first conductor loop structure 62 is coupled at its ends to a first capacitive pressure sensor 63 and the second conductor loop structure 62 to a second capacitive pressure sensor 64.

[0078] Figure 10shows an exemplary circuit diagram of a pressure wave measuring device according to the invention. The pressure wave measuring device according to the invention has a passive transponder as described above, which is represented here by a first oscillating circuit 101 and a second oscillating circuit 102. The first oscillating circuit 101 has a first capacitive pressure sensor 103 and the second oscillating circuit 102 has a second capacitive pressure sensor 104, which in Figure 10 are represented as capacitances. Furthermore, the first resonant circuit 101 has a first conductor loop structure 105, and the second resonant circuit has a second conductor loop structure 107.

[0079] The Figure 10The measuring device shown also has a readout unit 108 with which the resonant circuits 101 and 102 can be read out. The readout unit 108 has a readout coil 2. By means of a signal source 109, a signal, i.e. a current signal, with two superimposed frequencies ω a and ω b can be generated, wherein the component with the frequency ω a is generated with an amplitude a and the component with the frequency ω b with an amplitude b. The result is therefore the signal form a · sin(ω at) + b · sin(ω bt). The signal thus generated is fed into the readout coil 2 via a directional coupler 110. The directional coupler is coupled to a first mixer 111 and a second mixer 112, into which a signal received by the directional coupler 110 from the readout coil 2 can be fed. In the first mixer 111, the signal obtained from the readout coil is mixed with the reference signal a · sin(ω at) and in the second mixer 112 with the reference signal b · sin(ω bt).

[0080] The signal output by the first mixer 111 is then fed to a low-pass filter 113. The signal output by the second mixer 112 is fed to a low-pass filter 114. The first low-pass filter 113 is then divided by the readout unit 108 into an absolute value or amplitude 115 and a phase 116. The signal output by the second low-pass filter 114 is also divided into an amplitude 117 and a phase 118. By means of an addition 119, the absolute values 115 and 117 of the first and second signals are added to obtain a sum 121. The phases 116 and 118 of the first and second signals are added by a further adder 120 to obtain a sum 122. The signal 121 and 122 obtained in this way then has a circular directional characteristic, as shown in Figure 2 shown with the solid line (circles).

[0081] It should be noted that mixers 111, 112 and low-pass filters 113, 114 serve to enhance the signal. They are therefore optional.

[0082] Figure 11shows a circuit in which two resonant circuits 1101 and 1102 tuned to the same frequency are coupled to one another via two coils L1 and L2 with a coupling factor K1. Their interaction is shown as a function of K1. The larger K1, the greater the interaction between the coils L1 and L2 and the greater the resulting detuning. The first resonant circuit has, in addition to the coil L1, which in the example shown has an inductance of 3 µH, a capacitance C1 of 10 pF and a resistor R1 with a value of 0.1 Ω. The second resonant circuit 1102 has the second coil L2, a second capacitance C2 and a second resistor R2 with the same values as in the first resonant circuit 1101, so that the two resonant circuits 1101 and 1102 have the same resonant frequency. A voltage V1 is applied to the first oscillating circuit 1101, with which it can be excited to oscillate.

[0083] Figure 12shows the impedance UIN / IIn measured in the first resonant circuit as a function of the frequency f / f 0 for various coupling factors K1. The value f 0 is the resonant frequency of the two resonant circuits 1101 and 1102 in the uncoupled state. The various curves show different values of the coupling factor K1. It can be seen that with a very small coupling of K1 = 0.001 (solid line), the resonant frequency does not shift. However, if the coupling is increased, it can be seen that the resonant frequencies of the two resonant circuits diverge.

[0084] Figure 13shows a pictorial manufacturing method for producing a passive transponder according to the invention. In a first step, a plurality of carrier elements 132 are lined up on a rod 131. Each carrier element 132 has a cylindrical outer surface into which a cylindrical recess 133 is formed. The carrier elements 132 are lined up on the rod such that the cylinder axes of their cylindrical outer surfaces are perpendicular to a longitudinal direction of the rod 131, and that, in addition, one of the carrier elements 132 lies in the cylindrical recess 133 of an adjacent carrier element 132. This state is shown in Figure 13B to recognize.

[0085] Support structures can also be used, as in the Figures 13C and 13D shown, whereby the variant produced in 13D can result from the process shown in sub-figures A and B.

[0086] The support elements 132 are then, as shown in Figure 13B indicated by dotted lines, a first wire is wound as the first conductor loop structure and a second wire 135 as the second conductor loop structure 135. The winding can be carried out in such a way that, for example, a structure as in the Figures 6 to 9 After winding is complete, the elements 132 can be removed, leaving only the conductor loop structures. For this purpose, Figures 13A and 13B For example, the rod 131 can be removed. Preferably, the wires 134 and 135 are each wound at least once around each of the support elements 132, resulting in one turn each.

Claims

1. Passive transponder system comprising a first conductor loop structure (61), wherein the first conductor loop structure (61) has a plurality of groups of turns, the groups arranged next to one another in the direction of a main axis of the transponder system, each group of turns comprising at least one turn (61a, 61b, 61c), wherein each of the turns of the same group of the first conductor loop structure (61) is wound around a common first turn axis, wherein the first turn axes of different groups are in each case spaced apart from one another by a non-vanishing distance, a second conductor loop structure (62), wherein the second conductor loop structure (62) has a plurality of groups of turns, the groups arranged next to one another in the direction of the main axis, each group comprising at least one turn (62a, 62b, 62c), wherein each of the turns of the same group of the second conductor loop structure (62) is wound around a common second turn axis, wherein the second turn axes of different groups are spaced apart from one another by a non-vanishing distance, a first capacitive pressure sensor (63), a second capacitive pressure sensor (64), wherein the first capacitive pressure sensor (63) is electrically coupled to the first conductor loop structure (61) to form a first resonant circuit with a first resonant frequency, wherein the second capacitive pressure sensor (64) is electrically coupled to the second conductor loop structure (62) to form a second resonant circuit with a second resonant frequency, wherein the first turn axes and the second turn axes are at a non-vanishing angle to one another, wherein the non-vanishing angle is greater than zero and less than 180°.

2. Passive transponder system according to the preceding claim, wherein the first resonant frequency and the second resonant frequency differ from one another at least to such an extent that they do not superpose one another in such a way as to produce a beat.

3. Passive transponder system according to one of the preceding claims, wherein the first conductor loop structure (61) and the second conductor loop structure (62) are designed as flat coils which are arranged on surfaces of a carrier structure (34).

4. Passive transponder system according to the preceding claim, wherein the carrier structure (34) is shaped as part of a cylinder or as a cylinder or as part of a hose or as part of a tube or as a hose or as a tube, wherein preferably the carrier structure (34) has or is a plastic tube.

5. Passive transponder system according to one of the two preceding claims 3 or 4, wherein the first conductor loop structure (61) is arranged on an inner surface of the carrier structure (34) and the second conductor loop structure (62) is arranged on an outer surface of the carrier structure (34).

6. Passive transponder system according to one of the preceding claims, wherein the first turn axes and / or the second turn axes are parallel to one another.

7. Passive transponder system according to the preceding claim, wherein the turns (61a, 61b, 61c) of the first conductor loop structure (61) extend in two surfaces located opposite one another in relation to the main axis, the first turn axes being perpendicular to said surfaces, and wherein the turns (62a, 62b, 62c) of the second conductor loop structure (62) extend in two surfaces located opposite one another in relation to the main axis, the second turn axes being perpendicular to said surfaces, wherein preferably the first turn axes are located between the second turn axes in the direction along the main axis.

8. Passive transponder system according to claim 7, wherein the capacitive pressure sensors (63, 64) are located with their pressure-measuring surfaces in each case in one of the opposing surfaces in which the conductor loop (61, 62) structure of the corresponding resonant circuit extends.

9. Passive transponder system according to one of the preceding claims, wherein the first and the second conductor loop structure (61, 62) form a vessel support for a blood vessel or a stent.

10. Pressure wave measuring device comprising a passive transponder system according to one of the preceding claims, and a reader unit (108), wherein the reader unit (108) has a reader coil (2) which can be arranged relative to the passive transponder system in such a way that a magnetic field generated by said reader coil passes through at least one of the conductor loop structures (61, 62) of the transponder system, further comprising evaluation electronics, by means of which a signal that excites the resonant circuits can be applied to the reader coil (2) and a signal received from the reader coil can be evaluated.

11. Pressure wave measuring device according to the preceding claim, comprising a signal source (109), by means of which a signal can be generated with the resonant frequencies of the resonant circuits, and further comprising a directional coupler (110), to the output of which the signal source (109) is electrically coupled and to the input of which the reader coil (2) is coupled.

12. Pressure wave measuring device according to one of the two preceding claims, further comprising a first mixer (111) and a first low-pass filter (113) arranged behind it, wherein a signal with the first resonant frequency that is received by the reader coil from the transponder system can be downmixed by means of the first mixer (111), and further comprising a further mixer (112) and a second low-pass filter (114) arranged behind it, wherein a signal with the second resonant frequency that is received by the reader coil (2) from the transponder system can be downmixed by means of the further mixer (112).

13. Pressure wave measuring device according to one of claims 10 to 12, wherein the pressure wave measuring device is designed to constructively add the signal output from the first low-pass filter (113) to the signal output from the second low-pass filter (114).

14. Pressure wave measuring device according to one of claims 10 to 13, wherein the pressure wave measuring device is configured to separate the signal generated by the first low-pass filter (113) into amplitude and phase and to separate the signal output from the second low-pass filter (114) into amplitude and phase, and is further configured to add the amplitude separated from the signal generated by the first low-pass filter (113) to the amplitude separated from the signal generated by the second low-pass filter (114), and preferably is additionally configured to add the phase separated from the signal generated by the first low-pass filter (113) to the phase separated from the signal generated by the second low-pass filter (114).