Pressure sensing unit, system and method for remote pressure sensing

Abstract

To provide a pressure sensing device using a remote and passive bioimplantable pressure sensor.SOLUTION: A wireless pressure sensing unit 20 comprises a membrane forming an outer wall portion of a cavity and two permanent magnets in the cavity. One magnet is coupled to the membrane and at least one of the magnets freely oscillates by a rotational movement. The at least one freely oscillates by a rotational movement. The oscillation occurs at a resonant frequency that is a function of the pressure being sensed, and the pressure affects the space between the two permanent magnets. This oscillation frequency can be sensed remotely by measuring the magnetic field changed by the oscillation. The wireless pressure sensing unit is provided on a catheter 21 or a guide wire.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to pressure sensing, and more particularly to pressure sensing using remote, passive pressure sensors, for example, implantable pressure sensors. [Background technology]

[0002] The measurement of blood pressure is important in medicine.

[0003] In recent decades, wire-based coronary artery blood pressure measurements have become an important tool for assessing the severity of stenosis, for example, in fractional flow reserve (FFR) procedures. This involves catheterization of the coronary arteries, during which a catheter is inserted into the femoral (groin) or radial (wrist) artery using a sheath and guidewire. FFR uses tiny sensors at the tip of the wire to measure pressure, temperature, and flow to determine the exact severity of the lesion. This is done during maximum blood flow (hyperemia), which can be induced by injecting appropriate medications.

[0004] An implantable pulmonary artery pressure sensor has also been proposed and commercialized to measure right ventricular pressure.

[0005] A major problem with FFR procedures is the lack of a completely wireless solution that facilitates rapid workflow. In addition, it is desirable to have more than one sensor on the guidewire, and it would be beneficial if precise location of the sensors were possible.

[0006] For other applications, such as pressure monitoring in aneurysms, there is also still no small enough wireless solution.

[0007] One wireless approach involves providing an inductive coil as part of the implanted sensor to establish communication with an external controller. These coils need to have a diameter of about 1 mm, which makes them too large for some delivery types and implantation sites.

[0008] Ultrasound-based sensors have also been proposed, but these do not work in all locations on the body (e.g., the lungs) and require direct contact with the skin for readout, which is often impractical.

[0009] The article "Design, Fabrication, and Implementation of a Wireless Passive Implantable Pressure Sensor Based on Magnetic Higher-Order Harmonic Fields" by Ee Lim Tan et al., Biosensors 2011, 1, 134-152, ISSN 2079-6374, discloses a pressure sensor that uses a magnetically soft material and a permanent magnet strip to produce a magnetic signature that depends on the separation distance between the two elements. The separation distance varies with the pressure being sensed. This produces a weak signal (as a result of the demagnetization factor) and therefore is not easily miniaturizable. Summary of the Invention [Problem to be solved by the invention]

[0010] There is a need for a compact, wireless solution for remote, passive pressure measurement. [Means for solving the problem]

[0011] The invention is defined by the claims.

[0012] According to an embodiment of the present invention, there is provided a wireless pressure sensing unit, the wireless pressure sensing unit comprising: a closed cavity comprising at least one membrane forming an outer wall portion of the closed cavity; a first permanent magnet within the closed cavity coupled to the at least one membrane; a second permanent magnet in the closed cavity; Equipped with At least one of the first and second permanent magnets is capable of rotational motion about an axis of rotation, with at least a portion of the magnetic moment oriented perpendicular to the axis of rotation.

[0013] The pressure sensing unit comprises two permanent magnets, at least one of which is movable to achieve rotation. The separation between the two permanent magnets is a function of external pressure (i.e., outside the cavity) because this deforms the membrane, which causes the two permanent magnets to move relative to each other. There may be only one membrane to which the first permanent magnet is coupled, but alternatively there may be two membranes, each coupled to a respective permanent magnet.

[0014] In all cases, the separation distance changes with membrane deflection, which affects how their magnetic fields interact and therefore the magnetodynamic resonance frequency. Pressure can therefore be sensed based on the resonant frequency component in the sensed magnetic field, specifically caused by the rotational oscillatory motion of the unfixed permanent magnet.

[0015] Such a sensing approach, based on rotational vibrations, provides sensitive operation and allows the unit to be miniaturized for use as, for example, an implantable sensor with remote readout capability.

[0016] In one configuration, one of the first and second permanent magnets may undergo rotational motion while the other of the first and second permanent magnets is fixed. This means that there is only one moving part. However, both permanent magnets may be movable, and the resulting effect on the generated magnetic field may still be detectable.

[0017] For example, two permanent magnets are arranged with their magnetic poles facing in opposite directions, i.e., in a stable state, and then disturbed by an external field, which means that the two magnets are attracted to each other.

[0018] The movable permanent magnet undergoes rotational oscillation within the magnetic field of other permanent magnets, the local magnetic field depending on the proximity of the magnets, which determines the resonant frequency of the oscillation.

[0019] Note that this pressure sensing unit is only the remote part of the overall system: excitation and readout of the resonance is accomplished by a separate remote unit.

[0020] At least one membrane is made, for example, from an elastomer or a patterned metal sheet, which deforms in response to external pressure, thereby changing the separation distance.

[0021] The closed cavity may be a cylinder and the membrane may form one end of the cylinder, or there may be a membrane at each end of the cylinder.

[0022] The cylinder is particularly suitable for miniature sensors to be passed along a conduit such as a blood vessel.

[0023] At least one of the first and second permanent magnets has a rotationally symmetric shape, such as a sphere or a cylinder, so that rotation does not induce physical vibrations. Both permanent magnets may have the same shape or different shapes. Spherical magnets are preferred because they are easier to manufacture to the desired size and tolerances.

[0024] At least one of the first and second permanent magnets is fitted into the cylinder with a circumferential gap so that it oscillates in space without frictional surface contact. At least one of the first and second permanent magnets is constrained to rotate as a result of the attractive force between the two magnets. Therefore, the movement of the permanent magnet does not require any additional space-occupying unit.

[0025] The second permanent magnet is coupled to the cavity, for example, by a fixed coupling, and the first permanent magnet is coupled to the at least one membrane by a wire or thread.

[0026] The wire or thread is held taut by, for example, the magnetic force of attraction between the two permanent magnets. This force is, for example, an order of magnitude greater than gravity. Therefore, the sensor unit can operate in any orientation. The wire or thread is held under extensional load by the magnetic forces. These forces also serve to center at least one of the first and second permanent magnets, thus ensuring rotation about a fixed axis.

[0027] A first permanent magnet may be glued within the cylinder, for example, while a second permanent magnet is suspended by a wire or thread. The wire or thread is held taut, providing a fixed distance between the membrane and the second permanent magnet, but is able to twist to allow for resonant vibration. Note that in an alternative configuration, the permanent magnet associated with the membrane may be fixed, while the permanent magnet associated with the cavity may be free to rotate.

[0028] The unit has an outer shape such that it fits into a cylinder of, for example, 1 mm diameter, for example 0.5 mm diameter, for example 0.3 mm diameter.

[0029] These levels of miniaturization make the device particularly suitable for implantation in the body.

[0030] The present invention also provides a pressure sensing system, the pressure sensing system comprising: a pressure sensing unit as defined above; an excitation coil arrangement for generating a magnetic field to wirelessly induce resonant rotational vibration of at least one of the first and second permanent magnets; Equipped with.

[0031] The overall system includes an external excitation system, which may be a coil surrounding the pressure sensing unit (e.g., surrounding the part of the subject's body in which the pressure sensing unit is implanted), or simply placed against the body, or multiple coils placed on either side of the pressure sensing unit. The location of the implanted pressure sensing unit may be determined, for example, by X-ray, but may alternatively be determined based on the sensing itself.

[0032] An external coil (or multiple external coils) generates a low intensity oscillating magnetic field to excite rotating mechanical vibrations.

[0033] The pressure sensing system controlling the excitation coil arrangement to induce and maintain resonant oscillation in the other of the first and second permanent magnets; Measuring the magnetic field changed by the resonant vibration The device further comprises a controller adapted to:

[0034] Thus, resonant vibrations can be detected and their frequencies correlated with the pressure being sensed.

[0035] The controller is adapted to control the excitation coil arrangement to induce and maintain resonant oscillations by applying a discontinuous external magnetic field.

[0036] In this way, the resonant vibration is maintained, overcoming frictional and other losses that would otherwise dampen the vibration.

[0037] The controller is adapted to measure the magnetic field between active periods of the discontinuous external magnetic field, or during active periods of the discontinuous external magnetic field, or during periods of the continuous external magnetic field, such that there is a repeating sequence of excitation and measurement, or alternatively there is a sequence of simultaneous excitation and measurement.

[0038] The excitation coil arrangement comprises at least three non-collinear coils for inducing and maintaining resonant oscillations and at least three non-collinear coils for measuring the magnetic field. The use of such multiple coils ensures that any orientation of the pressure sensing unit relative to the excitation field can be tolerated.

[0039] The controller may be adapted to use the same coil or coils to induce resonant oscillations as those used to measure the magnetic field, providing a low-cost set of hardware; of course, separate coils may be used if desired.

[0040] The pressure sensing system comprises a plurality of pressure sensing units, each having a different resonant frequency.

[0041] These are used to measure pressure at multiple locations, and different locations can be identified based on the known range of resonant frequencies they produce.

[0042] The present invention also provides a catheter or guidewire system, the catheter or guidewire system comprising: a catheter or guidewire; The pressure sensing system, wherein the pressure sensor unit is provided along a catheter or a guidewire; Equipped with.

[0043] There may be one pressure sensing unit at the tip, or multiple pressure sensing units along the length of the catheter or guidewire.

[0044] The present invention also provides a pressure sensing method, the pressure sensing method comprising: wirelessly exciting the pressure sensing unit to resonant vibration using an excitation coil arrangement; measuring the magnetic field changed by the resonant vibration; determining the pressure from the frequency of the measured magnetic field change; and The pressure sensing unit a closed cavity comprising at least one membrane forming an outer wall portion of the closed cavity; a first permanent magnet within the closed cavity coupled to the at least one membrane; and a second permanent magnet within the closed cavity, wherein at least one of the first and second permanent magnets is capable of rotational motion about an axis of rotation, with at least a portion of the magnetic moment oriented perpendicular to the axis of rotation, and at least one of the permanent magnets is excited to vibrate resonantly.

[0045] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0046] For a better understanding of the present invention, and to show more clearly how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings in which: [Brief explanation of the drawings]

[0047] [Figure 1] 1 illustrates a pressure sensing system. [Figure 2] 1 illustrates the pressure sensing unit in more detail. [Figure 3] 1 illustrates a combined apparatus including an excitation coil arrangement, an X-ray system, and a patient bench. [Figure 4] 1 illustrates a first example of a possible excitation coil configuration. [Figure 5] 1 illustrates a second example of a possible excitation coil configuration. [Figure 6] 10 illustrates a third example of a possible excitation coil configuration. [Figure 7] 1 illustrates a pressure sensing method. DETAILED DESCRIPTION OF THE INVENTION

[0048] The present invention will now be described with reference to the drawings.

[0049] It should be understood that the detailed description and specific examples, while indicating exemplary embodiments of the devices, systems, and methods, are intended for purposes of illustration only and are not intended to limit the scope of the invention. These and other features, aspects, and advantages of the devices, systems, and methods of the present invention will become better understood from the following description, appended claims, and accompanying drawings. It should be understood that the drawings are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the drawings to refer to the same or similar parts.

[0050] The present invention provides a wireless pressure sensing unit comprising two permanent magnets, at least one of which is free to vibrate by rotational motion. The vibration occurs at a resonant frequency that is a function of the pressure to be sensed, which affects the spacing between the two permanent magnets. This vibration frequency can be remotely sensed.

[0051] FIG. 1 illustrates a pressure sensing system 10 including a pressure sensing unit 20 that senses localized pressure. The pressure sensing unit 20 is wireless and does not require an on-board power source. It modulates a generated magnetic field based on the sensed pressure. In particular, it can be induced by an external electromagnetic field into a state of mechanical resonant vibration, which can be detected by the effect it has on the magnetic field generated by the sensing unit 20 itself. In this embodiment, the pressure sensing unit 20 is at the end of a medical intervention shaft 21, i.e., a catheter or guidewire. This could be anywhere along the shaft, or there could in fact be multiple pressure sensing units along the shaft. The pressure sensing unit could alternatively be part of a permanently implanted device, such as a stent or medical coil.

[0052] The system 10 includes an excitation coil arrangement 30 for wirelessly inducing magnetically induced mechanical resonance.

[0053] The excitation coil arrangement may be a single coil (which means one or more individual turns, but all parallel to each other and about a common axis), or it may be multiple coils, with or without parallel orientation.

[0054] FIG. 1 illustrates in schematic form an excitation coil arrangement 30 beside the pressure sensing unit 20. This may alternatively surround the pressure sensing unit (e.g., surround the body part of the subject in which the pressure sensing unit is implanted). There may be more than one coil, but all the coils are arranged and wound in the same plane to form an array. This coil array is placed below the patient (e.g., the patient is lying on a flat structure). However, there are many ways to arrange the excitation coil arrangement. Another example is to use coils wound around soft magnetic (ferrite) rods placed at the patient's sides.

[0055] The size required for the external coils depends on the technology used. The overall diameter of a flat coil array, for example, is comparable to the maximum measurement distance. Smaller coils require more power and possibly amplifiers with less noise reception. Coils utilizing cores of soft magnetic material can be even smaller in diameter. For example, each coil may have a diameter around one-tenth of the maximum distance.

[0056] A controller 40 is used to drive the excitation coil arrangement 30 to generate the alternating electromagnetic field, and in addition, the controller analyzes the sensed magnetic field and in particular senses the mechanical resonant frequency of the pressure sensing unit, which depends on the local pressure being sensed.

[0057] In a typical use (but not the only possible use), the pressure sensing unit 20 is implanted within a blood vessel 22 or organ of a subject. This location is identified and tracked by an imaging system, such as an X-ray, to place the pressure sensing unit at the desired location. An excitation coil arrangement can be positioned at the appropriate location. Alternatively, the pressure sensing unit can be brought to the desired location based on detection by the external coil 30 of the location of the magnetic field generated by the pressure sensing unit 20.

[0058] The controller 40 uses one external coil 30 (or multiple coils) to generate a low-intensity oscillating field to not only excite resonance but also sustain the resonant oscillation. In the embodiment of Figure 1, the same excitation coil arrangement is used to measure the magnetic field changed by the resonant oscillation. Alternatively, a separate coil or coils may be used for sensing the changing magnetic field generated by the oscillation.

[0059] The controller induces and maintains resonant oscillation by applying a pulsed alternating field and measures the magnetic field between pulses, so there is an excitation and measurement sequence.

[0060] FIG. 2 illustrates an embodiment of the pressure sensing unit 20 in more detail.

[0061] The pressure sensing unit 20 comprises a closed cavity 24 formed by a metal or polymer casing. A deformable membrane 25 forms the outer wall of the cavity. The membrane 25 is, for example, an elastomer or a structured metal foil. The cavity is filled with a gas (e.g., air) or is evacuated.

[0062] In the embodiment shown, the cavity is cylindrical and membrane 25 forms one end wall. In an alternative embodiment, both end walls are formed by membranes, and the two membranes move inward toward each other in response to an increase in external pressure.

[0063] The outer diameter of the cylinder, and therefore the sensing unit, may be less than 0.3 mm, for example as little as 0.2 mm, more typically less than 1 mm, and preferably less than 0.5 mm. More typically (and regardless of the particular shape), the pressure sensing unit will fit within a cylinder of the inner diameter listed above. The pressure sensing unit may then be integrated into a permanent implant, such as a stent or aneurysm coil, or a temporary implant, such as a guidewire or catheter, or may be delivered separately, such as via the bloodstream into the lungs.

[0064] The pressure sensing unit has a length in the range of, for example, 1 mm to 5 mm.

[0065] A first permanent magnet 26 is coupled to the membrane by an elongated structure 27 (e.g., a wire or thread). A second permanent magnet 28 is coupled to the interior of the cavity, specifically to the opposite closed end of the membrane 25. The second permanent magnet is attached, for example, by adhesive 29. Thus, in this particular embodiment, the second permanent magnet is stationary (relative to the fixed part of the cavity).

[0066] The permanent magnets are spheres, with at least a first permanent magnet 26 fitting into the cavity with spaced apart all around. A fixed second permanent magnet 28, together with an elongated structure 27, automatically centers the rotating first permanent magnet 26 within the device. In this way, the rotating magnet never touches the inside of the casing. This allows for high quality factor vibration.

[0067] The axis of rotation corresponds to the elongated axis of a wire or thread extending along the length of the cavity. At least a portion of the magnetic moment of the movable permanent magnet 26 is oriented perpendicular to the axis of rotation. Thus, the magnetic force experienced by the magnet 26 induces a rotational torque about the axis of rotation. In the illustrated embodiment, the permanent magnets are dipole magnets, with their magnetic moments perfectly perpendicular to the axis of rotation. The magnetic force aligns the magnets along the axis of rotation, with their magnetic moments in opposite directions as shown. The attractive force between the permanent magnets keeps the elongated structure 27 taut; therefore, the elongated structure is a wire or thread made of a flexible material.

[0068] Other magnet shapes may be used, such as cylindrical magnets or other shapes entirely. The movable first magnet preferably has a rotationally symmetric shape about the axis of rotation so that it is rotationally balanced. An advantage of the spherical magnets shown is that they can be easily manufactured with high precision and are therefore readily available.

[0069] The two permanent magnets do not have to be the same size, shape, or type. Essentially, a fixed permanent magnet is used to generate a static field, and the field of the moving permanent magnet interacts with this static field. The moving permanent magnet is used to generate a rotational vibration, and thus the rotational field interacts with the static field of the fixed permanent magnet.

[0070] The two permanent magnets are aligned in opposite directions, i.e., with the north-south and south-north pole pairs adjacent to each other. The rotational stiffness of the elongated structure (wire or thread) can be chosen to be low compared to the twisting caused by the magnetic field. Because there is a strong attractive force between the two magnets, a directional stress is applied to the wire or thread. The magnetic force is typically several hundred times greater than the force of gravity. Therefore, the wire or thread does not need to be significantly stiff and can be, for example, a very thin UHMWPE (ultra-high molecular weight polyethylene) thread. This also means that the sensor unit can be operated in any orientation, since the effect of gravity on the sensor readout is negligible.

[0071] In the illustrated embodiment, the second permanent magnet 28 is coupled to a fixed, stationary angular position, and the first permanent magnet 26 is coupled to an elongated structure (e.g., a wire or thread) that has flexibility to allow angular rotational movement.

[0072] The separation distance between the two magnets is a function of external pressure (i.e., outside the cavity) because this deforms the membrane 25, which causes the two permanent magnets to move relative to each other. The distance between the permanent magnet 26 and the membrane 25 is kept constant by an elongated structure (wire or thread) held taut by the magnetic attraction between the two magnets.

[0073] The permanent magnet 26 is rotatable, in particular about an axis defined by the wire or thread 27. The wire or thread is thin enough that the torque on the permanent magnet 26 due to twisting of the wire or thread is smaller than the torque experienced by the magnetic force. However, this is not necessary. A stiffer wire or thread will shift the resonant frequency of the vibration to a higher value, and therefore the recorded signal will be at a higher frequency, which is easier to process. However, a higher frequency signal will result in a lower frequency change per unit pressure change.

[0074] The resonant frequency is roughly inversely proportional to the linear dimension of the resonator, so for a 1 mm diameter device the resonant frequency is around 500 Hz, and for a 0.2 mm device the frequency is around 2.5 kHz.

[0075] The resonant rotational oscillation is initiated by a suitable electromagnetic impulse generated by the excitation coil arrangement 30 .

[0076] An excitation signal is used with a selected frequency that depends on the resonant frequency, if known approximately in advance. Alternatively, vibrations can be initiated with a single short excitation pulse. This initiates a recordable vibration. The resonant frequency can then be measured, and the next pulse is then timed to increase the amplitude of the vibration.

[0077] An alternative approach is to use a long train of pulses with a narrow frequency spectrum to initiate the oscillation. The center frequency is then changed until the resonance is well enough matched to receive a signal from the sensor. The frequency can then be tracked. By changing the length of the pulse train, the spectral selectivity can be changed. The advantage of a long (spectrally selective) pulse train is that a lower magnetic field amplitude is required to set the sensor at resonance. Therefore, less engineering effort is required in the transmit / receive system and / or the sensor can be located at a greater distance from the coil.

[0078] A drawback of using spectrally selective pulses is that it takes longer, on average, to find the sensor.

[0079] Therefore, a series of pulses is used to sustain the resonant vibration. This series of pulses then induces and sustains the resonant vibration with a discontinuous external magnetic field. The pulses used to sustain the vibration have a duration of at least 1 / 8 the vibration period in length, for example, 0.25 ms for a 1 mm sphere (500 Hz) and 0.05 ms for a 0.2 mm sphere (2.5 kHz). The pulses can be further shortened by increasing the amplitude.

[0080] The duration of the oscillations is on the order of a few seconds, for example 2 seconds. The maximum interval between excitation pulses is therefore approximately 1 second. In principle, the duration could be much longer, even tens or even hundreds of seconds, and the gap between excitation pulses would be adapted accordingly, with a maximum gap on the order of half the oscillation duration. However, in order to maintain a resonant response of substantially constant amplitude, it is preferable to perform many excitations per second.

[0081] As an example, it may be desirable to measure pressure approximately 10 times per second, so using a 10 excitation train per second is appropriate. For example, to make 50 or more measurements per second, a smaller device may be desirable, and it may be preferable to provide more excitations per second. There may be an excitation for each signal readout, and the readouts may be performed at the same point in the vibration lifetime, although this is not required. There may be any ratio between the period between excitations and the period between signal readouts.

[0082] The use of a discontinuous excitation signal allows for time-sequential excitation and readout. In this way, once the rotational oscillation of the first permanent magnet 26 is initiated, subsequent field pulses are timed to intensify the oscillation. Between the excitation pulses sent, the oscillating magnetic field produced by the sensor unit is measured.

[0083] However, simultaneous excitation and readout is also possible, in which case a continuous excitation signal is used, which requires a more complex receiver system.

[0084] In particular, to facilitate simultaneous signal measurement while providing excitation, the signal generated at the receiver in response to the excitation signal itself must be minimized. This can be achieved by a combination of analog subtraction of the transmitted (transmitted) signal at the receiver (e.g., by using a transformer in front of the receiver to which a portion of the transmitted signal is fed) and digital subtraction. In the digital subtraction step, the remaining transmitted signal at the receiver is first characterized and then digitally subtracted from the digitized received signal.

[0085] Thus, there are various ways to set the sensor in a resonant vibration state.

[0086] Measurement of the resonant frequency in the magnetic field generated by the magnet pair relies on mechanical rotation of the movable magnet (or, if both magnets are movable, rotation of both magnets as a rotating system), but this can also be performed in a variety of ways. The measurement can be performed by the same excitation coil arrangement as described above, or by a separate receiving system. The receiving system can utilize magnetic field sensors other than simple coils, such as flux-gate magnetometers, although coils may already provide the required sensitivity.

[0087] The separation distance between the two permanent magnets affects the mechanical response of the movable permanent magnet to an external field, as explained above. In particular, the closer the movable permanent magnet is to the fixed permanent magnet, the greater the force provided by the magnetic field of the fixed permanent magnet to align the movable permanent magnet. This force results in a higher resonant frequency of the mechanical resonance.

[0088] The interaction between the two magnetic fields is detectable and, since there is a dependence on the mechanical movement of the movable permanent magnet, the resonant frequency can be detected.

[0089] 3 illustrates a combined apparatus comprising an excitation coil arrangement 30, an imaging system 40 (e.g., an X-ray C-arm), and a patient bench 42. The pressure sensing unit is a sensor implanted in a patient lying on the bench. An imaging system, in this case an X-ray C-arm, is used to mount the pressure sensing unit.

[0090] The excitation coil arrangement 30 comprises an array of overlapping, generally planar coils 44 forming a planar coil array that is integrated into the patient bench 42. The coils are made, for example, from aluminum with a total thickness in the mm range, for example less than 2 mm thick. X-ray absorption from the X-ray system is low.

[0091] The coils may comprise a single loop or a flat spiral cut from a metal sheet. As mentioned above, the size of the individual coils and the overall coil configuration is designed taking into account the required magnetic field at the sensor unit and the maximum distance to the sensor unit.

[0092] Figure 4 illustrates a first example of a possible excitation coil configuration, which more clearly shows the configuration illustrated in Figure 3. It comprises an array of flat coils 44.

[0093] 5 illustrates a second example of a possible excitation coil configuration, comprising an array of cylindrical coils 46. These may comprise air-core coils or coils with ferrite cores.

[0094] 6 illustrates a third example of a possible excitation coil configuration, having three non-collinear coils 48. In the example shown, the magnetic moments of the three coils are perpendicular to each other, which provides greater freedom for any orientation of the pressure sensing unit relative to the excitation coil configuration.

[0095] Both the excitation system and the receiving system have at least three non-collinear field generators and receivers, however for many applications, e.g., implanted sensors that are only read occasionally, a uniaxial system is sufficient, especially if it can be freely oriented.

[0096] Thus, it can be seen that there are many possible designs for the excitation coil arrangement, which will be apparent to those skilled in the art.

[0097] The system can be expanded to include multiple sensor units, allowing sensing at multiple locations and also providing a way to reconstruct the position of the sensor unit using the relative amplitude in the receiving system or the relative amplitude in the excitation system required to sustain a constant vibration amplitude.

[0098] Multiple sensors can be operated in parallel if they are tuned to different resonant frequencies, for example using different distances between the permanent magnets or different magnetic properties in the sensors.

[0099] A shared coil system may be used, for example ensuring that the timing and / or shape of the excitation pulses are such that all sensors have increased energy content, with ideally the ranges of possible resonant frequencies for the different sensor units not overlapping so that a receiving system with excitation and receiving coils placed at different locations can distinguish between the sensors.

[0100] In the above example, the membrane is attached to a movable permanent magnet. Of course, the permanent magnet associated with the membrane may instead be fixed relative to the membrane, while the permanent magnet associated with the cavity is free to rotate. As mentioned above, there may be two membranes, each coupled to one of the permanent magnets, such that in the presence of external pressure, they both move towards each other. Only one of the two permanent magnets may be coupled to its respective membrane in a manner that allows for rotational movement, or alternatively, both may be coupled in a manner that allows for rotational movement, i.e., both may be connected to their respective membranes by elongated structures (wires or threads).

[0101] The change in resonant frequency as a function of the overall pressure range for which the sensor is designed corresponds to a frequency change by, for example, a factor of 2. The wire or thread also contributes to the torque generated during vibration, and the frequency response becomes more pronounced depending on the design of the wire or thread.

[0102] A desirable pressure range is, for example, from about 800 mBar (80 kPa, absolute pressure) to about 1300 mBar (0.13 MPa, absolute pressure). For example, the lower end corresponds to low blood pressure at high altitudes (e.g., Mexico City). If desired, there may be two (or more) product designs, one for standard altitudes and one for high altitudes, narrowing the pressure range and thus increasing sensitivity.

[0103] The pressure sensing unit may be applied to a catheter or guidewire, or may be used in other applications such as a pulmonary artery pressure sensor, a sensor in an implanted valve, a pressure sensor in a stent or medical coil.

[0104] FIG. 7 illustrates a pressure sensing method, which includes: At step 50, using an excitation coil arrangement to wirelessly excite the pressure sensing unit described above into resonant vibration; measuring the magnetic field changed by the resonant vibration in step 52; In step 54, determining the pressure from the frequency of the measured magnetic field change; It has.

[0105] Modifications 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. In the claims, the word "comprises" does not exclude other elements or steps, and the singular does not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain means are recited in mutually different dependent claims does not indicate that a combination of these means cannot be used to advantage. A computer program can be stored / distributed on a suitable medium, such as an optical or solid-state storage medium, together with or provided as part of other hardware, but can also be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A pressure sensing unit for sensing pressure within a body, the pressure sensing unit comprising a closed cavity with an outer wall, at least a portion of the outer wall of the closed cavity being made from an elastomer or a patterned metal sheet so as to be deformable, the pressure sensing unit comprising: a first permanent magnet within the closed cavity coupled to the outer wall; a second permanent magnet within the closed cavity coupled to at least a portion of the outer wall, the coupling being via an elongated structure that allows rotational movement of the second permanent magnet; The pressure sensing unit, wherein the first permanent magnet is coupled to the outer wall through a fixed coupling.

2. A pressure sensing unit for sensing pressure within a body, the pressure sensing unit comprising a closed cavity with an outer wall, at least a portion of the outer wall of the closed cavity being made from an elastomer or a patterned metal sheet so as to be deformable, the pressure sensing unit comprising: a first permanent magnet within the closed cavity coupled to the outer wall; a second permanent magnet within the closed cavity coupled to at least a portion of the outer wall, the coupling being via an elongated structure that allows rotational movement of the second permanent magnet; The pressure sensing unit, wherein the first permanent magnet is coupled to the outer wall through a thread or wire.

3. The pressure sensing unit of claim 2 , wherein the first permanent magnet and the second permanent magnet are each coupled by an elongated structure.

4. 4. A pressure sensing unit according to claim 1, wherein the closed cavity comprises a membrane forming an outer wall portion of the closed cavity.

5. The pressure sensing unit according to claim 4 , wherein the membrane is made of an elastomer or a structured metal foil.

6. 6. The pressure sensing unit of claim 1, wherein the separation distance between the first permanent magnet and the second permanent magnet is a function of external pressure.

7. The pressure sensing unit according to claim 1 , wherein the rotational movement is a rotational vibration.

8. A pressure sensing unit for sensing pressure within a body, said pressure sensing unit comprising a closed cavity with an outer wall, at least a portion of said outer wall of said closed cavity being made from an elastomer or a patterned metal sheet so as to be deformable, said pressure sensing unit comprising: a first permanent magnet within the closed cavity coupled to the outer wall; a second permanent magnet within the closed cavity coupled to at least a portion of the outer wall, the coupling being via an elongated structure that allows rotational movement of the second permanent magnet; A pressure sensing unit, wherein at least one of the first permanent magnet and the second permanent magnet is constrained to provide rotational movement as a result of an attractive force between the two magnets.

9. The pressure sensing unit according to claim 1 , wherein the pressure sensing unit has a diameter of 1.0 mm or less.

10. 10. A pressure sensing unit according to any one of claims 1 to 9, which is integrated into a permanent implant, integrated into a temporary implant, or delivered separately.

11. A pressure sensing unit assembly including at least two pressure sensing units that sense pressure within a body, Each of the at least two pressure sensing units comprises: a closed cavity having an outer wall, at least a portion of the outer wall of the closed cavity being made from an elastomer or a patterned metal sheet so as to be deformable; a first permanent magnet within the closed cavity coupled to the outer wall; a second permanent magnet within the closed cavity coupled to at least a portion of the outer wall, the coupling being via an elongated structure that allows rotational movement of the second permanent magnet; A pressure sensing unit assembly, wherein at least some of the at least two pressure sensing units have different frequencies.

12. A pressure sensing unit according to any one of claims 1 to 10; an excitation coil arrangement for generating a magnetic field to wirelessly induce resonant rotational vibration of at least one of the first permanent magnet and the second permanent magnet; and further comprising a controller controlling the excitation coil arrangement to induce and maintain the resonant rotational oscillation of the at least one of the first permanent magnet and the second permanent magnet.

13. A step in which a controller controls an excitation coil component to wirelessly excite the pressure sensing unit described in any one of claims 1 to 10 to cause it to resonate; the controller measuring a magnetic field changed by the resonant vibration; and wherein the controller determines the pressure from the measured frequency of the change in the magnetic field.

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