ARRANGEMENT

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of United States Provisional Application Serial Number 62/635,978, the entirety of which is hereby incorporated by reference.

FIELD

[0002] The present disclosure is directed to magnetostrictive sensors,

BACKGROUND

[0003] Ultrasonic wave converters are commonly used in magnetostrictive sensors and can be generally subdivided into axially and radially (or transversally) arranged systems. This depends on how the ultrasonic wave converter is positioned and implemented along a

Waveguide .

[0004] An axial system is illustrated in Figure 3 and includes a coil 32 which is oriented at the open end along or around the waveguide 33. Usually the wire turns of the coil 32 are accommodated on a bobbin for mechanical support of the conducting wire. Despite hundreds of turns of wire the coil 32 provides typically relative low signal amplitudes for a controller discussed below. In addition the bobbin is bulky due to its length of approximately 5 to 10 mm.

[0005] The transversal system is illustrated in Figure 4 and includes the waveguide 33 and one or two tapes 31 of magnetostrictive material attached to the waveguide 33.

[0006] The function of the transversal system is well known. In essence the tape 31 guides an acoustic ultrasonic wave into coil 32 where the electrical signal is detected for further processing in the controller.

[0007] The transversal system has a higher signal amplitude at the coil 32. This is achieved by utilizing a constructive interference of two incident waves on the tapes 31. One part of the acoustic ultrasonic wave propagates directly into the tape whereas the second part travels further to the end of the waveguide where the wave is reflected before it also propagates back to the tape where it interferes with the other part of the acoustic ultrasonic wave.

[0008] In order to achieve an optimal constructive interference in the coil 32, great care must be taken in the dimensioning of this setup. The end of the waveguide 34 to tape 31 distance, the length of the tape 31 and the location of the coil 32 along the tape 31 have to be carefully chosen and assembled. For example, in many systems, the coil 32 is disposed ¼ of the wavelength of the acoustic ultrasonic wave 5. In order to reflect part of the acoustic ultrasonic wave 5 efficiently from the open end of the waveguide 33 it is held in a metal clamp (anchor 9 as shown in Figure 2), which holds the waveguide 33 mechanically in place.

[0009] As should be evident from the above described configuration, the disadvantage of such a system is the high degree of mechanical accuracy and complexity involved. The tape 31 also has to be well centered in the coil 32, and the assembly process usually involves a kind of welding process to firmly attach tape 31 to waveguide 33.

[0010] Mechanical deviations can immediately cause a deterioration of the constructive signal interference by signal distortion or a reduced signal to noise ratio (SNR) of the electrical signal before it even reaches the controller.

[0011] In other systems, the signal is dampened with a damping element after passing the pick-up coil’s aperture so that the reflected signal’s amplitude is reduced to a level where no disturbance is expected. This damping element uses a certain spatial extent to ensure sufficient attenuation, so that additional sensor length is required that does not contribute to the

measurement length.

[0012] Mechanically the transversal system requires the tape 31 to be mounted perpendicular to the waveguide 33. This implies additional space requirements which can be restricting when very compact sensor designs are required. For fastening the tape in the exact position, which is a point of constructive interference as known from the axial system, the same precision as for the axial systems is required.

[0013] Another typical challenge is that the above systems suffer limitations due to dead- or null-zones. The dead- or null-zones are a limiting factor as they determine at which distance away from the coil 32 the sensor is able to measure within expected limits of accuracy. This dead- or null-zones usually stretches several tens of millimeters, which is not an issue for sensors where the ultrasonic wave converter 7 can be placed well inside a larger housing. SUMMARY

[0014] One general aspect includes a waveguide assembly for a magneto strictive sensor. The waveguide assembly includes a waveguide and a coil including a support located at an end of the waveguide, or at a position <1/4 wavelength of an acoustic pulse carried by the waveguide where constructive interference is expected, and a conductor having plurality of conductor turns secured to the support.

[0015] Another general aspect includes a waveguide assembly for a magnetostrictive sensor. The waveguide assembly a waveguide supported so as to have a free end. A coil is mounted to the free end of the waveguide.

[0016] Implementations may include one or more of the following features. The waveguide assembly where the coil is connected to an extension that is connected to the waveguide in a transverse manner. The waveguide assembly where the turns are held in a common plane in a spaced apart fixed relationship relative to each other. The waveguide assembly where the end of the waveguide is secured to a side of the support having the plurality of conductor turns. The waveguide assembly where the waveguide extends through the support and the end of the waveguide or extension is secured to a side of the support. The waveguide assembly 9 where and an endcap is provided over the end of the waveguide or extension. The waveguide assembly and a securing ring on the support to which the end of the waveguide or extension is secured. The waveguide assembly and a ferromagnetic layer on one or more sides of the support such as on a side that is opposite the plurality of conductor turns, on the same side as the plurality of conductor turns, and/or on one or more surfaces such as lateral surfaces that extend between the afore-mentioned sides. The waveguide assembly where the ferromagnetic layer is a soft magnetic foil, e.g., mu-metal. The waveguide assembly where the end of the waveguide or extension is attached to the ferromagnetic layer. The waveguide assembly and a second planar coil including a second support and a second conductor having a second plurality of conductor turns secured to the support where the turns are held in a second common plane in a spaced apart fixed relationship relative to each other. The waveguide assembly where the coil includes a support and a conductor having plurality of conductor turns is secured to the support where the turns are held in a common plane in a spaced apart fixed relationship relative to each other. The waveguide assembly where the waveguide is secured to the support where the conductor turns are disposed about a central axis of the waveguide. The waveguide assembly where an end of the waveguide is secured to the support.

[0017] Yet another general aspect includes a detection assembly for a magnetostrictive sensor. The detection assembly includes a waveguide having a longitudinal axis, a coil having turns oriented orthogonal to the longitudinal axis, and a return wire connected to a remote end of the waveguide and having a portion extending over at least a portion of the turns of the coil so as to induce a voltage in the coil with a polarity opposite the polarity of a voltage induced by current through the waveguide.

[0018] Another general aspect includes a waveguide assembly for a magnetostrictive sensor. The waveguide assembly includes a waveguide supported so as to have a free end. A support is mounted to the free end of the waveguide, where the support includes an aperture through which the waveguide extends, and where the support includes a plurality of coils mounted on the support, the plurality of coils arranged in a configuration about the aperture.

[0019] Implementations may include one or more of the following features. The waveguide assembly where a center axis of each of the coils of the plurality of coils is perpendicular to the waveguide. The waveguide assembly where a center axis of each of the coils of the plurality of coils is parallel to the waveguide. The waveguide assembly where a center axis of each of the coils of the plurality of coils is askew to the waveguide.

[0020] This summary is not intended to describe each disclosed embodiment or every implementation. Many other novel advantages, features, and relationships will become apparent as this description proceeds. The figures and the description that follow more particularly exemplify illustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a perspective view of an ultrasonic wave converter according to an embodiment of the present disclosure. [0022] Figure 2 is a schematic view of a magnetostrictive system on which embodiments of the present disclosure may be practiced.

[0023] Figure 3 is a perspective view of a portion of a typical axial magnetostrictive system.

[0024] Figure 4 is a perspective view of a portion of a typical transversal magnetostrictive system.

[0025] Figure 5 is view of a portion of a half round solderable via substrate.

[0026] Figure 6 is a view of a portion of a BGA-typ solderable pad substrate.

[0027] Figure 6A is a view of alternate assemblies on which embodiments of the present disclosure may be practiced.

[0028] Figure 7 is a view of an assembled embodiment of the present disclosure.

[0029] Figure 8 is an exploded view of the embodiment of Figure 7.

[0030] Figure 9 is a side view of another embodiment of the present disclosure.

[0031] Figure 10 is a side view of another embodiment of the present disclosure.

[0032] Figure 11 is a side view of another embodiment of the present disclosure.

[0033] Figure 12 is a side view of another embodiment of the present disclosure.

[0034] Figures 13A-13D are views of arrangements of coils about an aperture in a support according to additional embodiments of the present disclosure.

[0035] Figure 14 is a view of a flat wire-wound coil.

[0036] Figure 15 is a view of a multilayer chip inductor component.

[0037] Figure 16 is a view of a wire wound chip inductor.

[0038] Figure 17 is a view of another embodiment of the present disclosure.

[0039] Figure 18 is a side view of a placement of a coil according to another embodiment of the present disclosure.

DETAILED DESCRIPTION

[0040] This disclosure contains a novel design for an ultrasonic wave converter 7 shown in Figure 1 as it is typically used in magnetostrictive sensors as depicted in Figure 2. The ultrasonic wave converter 7 allows the conversion of an acoustic ultrasonic wave 5 propagating along a waveguide 1 into an electrical signal which is further processed inside a controller 18.

[0041] The controller 18 contains both analog circuitry for filtering, amplification of the analog electrical signal, but also digital or further analog circuits to enable a time of flight (ToF) evaluation between a start- and stop-signal event. In a wire with magnetoelastics properties, called the waveguide 1, an electric current pulse 2 is induced by controller 18 having an electric pulse generator commonly used in magneto strictive sensors, and thus not further elaborated herein. When the pulse 2 is sent, a clock of the controller 18 is started. The pulse 2 is transferred through the magnetoelastic material (the waveguide 1) and an electric circuit is closed using a return wire 3 connected to the end of the waveguide 1. Through the electric pulse 2, which basically happens instantaneously, a magnetic field is generated in the waveguide 1. When this magnetic field interacts with a position magnet 4, an acoustic ultrasonic wave 5 is generated in the waveguide 1, because magnetostrictive materials undergo a change of their physical dimensions when subjected to a magnetic field. This acoustic ultrasonic wave 5 travels from both sides of the position magnet 4 into the waveguide 1. In particular, the acoustic ultrasonic wave 5 propagates along the left hand side of the waveguide 1 in Figure 2 to a damper 6 and along the right hand side into the ultrasonic wave converter 7. When the Acoustic ultrasonic wave 5 reaches the ultrasonic wave converter 7, an electrical signal is generated through an inductive coil 8 in the ultrasonic wave converter 7. This electrical signal is provided to the controller 18, which triggers the above mentioned clock to stop. As the speed at which the acoustic ultrasonic wave 5 moves through the waveguide 1 is known, one can determine the geometrical distance between the position magnet 4 and the ultrasonic wave converter 7 from the clocked time of the ToF from the start signal to the stop signal. The ToF is used by the controller 18 to provide a suitable output signal 19 indicative of the position of the position magnet 4. Such processing is well known in magnetostrictive sensors.

[0042] The various embodiments of the novel ultrasonic wave converter 7 as shown in Figures 7-10 includes a support such as a printed circuit board (PCB) substrate 21 that supports a planar coil 22 having a number of conductor turns. As used herein, a planar coil 22 has a support that holds a conductor having at least one set of a plurality of conductor turns in a common plane such that the conductor turns are circumferentially or spirally arranged relative to each other where a perimeter of an outer conductor turn is greater than a perimeter of a conductor turn disposed closer to a center of the circumferentially or spirally arranged conductor turns. In further embodiments, discussed below, a wire-wound air coil (Figure 14), particularly, such a coil that has a minimal axial length, or an SMD (surface mount device) coil may be used. [0043] In one embodiment, a coil 22 is located at the actual end of the waveguide 33 and is disposed about a central axis of the waveguide 33. However, in comparison to the transversal or axial systems, the end 34 of the waveguide 33 where the coil is located is anchorless or free in one embodiment, or fixedly secured to a supporting structure, such as a PCB board, in another embodiment.

[0044] The conductor turns of the coil 22 may be provided on a single layered PCB substrate 21, but the turns may also be realized on two or more layers of a multi layered PCB substrate 21. By using a multi layered PCB, a high degree of flexibility is obtained with respect to mechanical and signal requirements. Generally a larger number of conductor turns tend to provide larger signal amplitudes.

[0045] As there are also limitations in the maximum number of layers which can be realized on a PCB substrate 21, if desired, the two or more multi layered PCB substrates 21 are in one embodiment disposed adjacent, preferably connected to, each other (i.e. stacked) by soldering the PCB substrates 21 together. Assembling interconnected multi layered PCB substrates 21 can be easily achieved by having either half round solderable vias on the side walls of each coil 22 as shown in the example of Figure 5, or may be soldered together like it is practiced for ball grid arrays (BGAs) as shown in the example of Figure 6.

[0046] In yet another embodiment shown in Fig. 6A, the coil 22 may be formed using a flexible PCB substrate 21 A where a plurality of planar sections 21B, for example, are joined to adjacent sections on opposed edges in an accordion manner. Each section includes one or more conductor turns on at least one and preferably on each opposed surface. The planar sections 21B may then be stacked upon each other as shown to provide a compact assembly 21C.

[0047] A planar coil 22 also offers increased flexibility in the way of integrating it into a sensor design. The planar coil 22 may be either directly integrated as part of another PCB substrate 21 or it may be placed onto another PCB by using it as an individual substrate similar to the implementation shown in Figure 5. The assembly then becomes suitable for a“Pick and Place” process, which is generally applied for surface mount device (SMD) manufacturing for PCBs.

[0048] Figures 7-8 illustrate an exemplary embodiment of the planar coil 22. Figure 7 shows the planar coil 22 assembled, and Figure 8 shows the planar coil 22 in an exploded view. The planar coil 22 in this embodiment includes a ferromagnetic layer 25 that acts as an anchor to hold and keep the waveguide 23 in a mechanically stable position. The ferromagnetic layer 25, preferably having high magnetic permeability (e.g., in the p _r of 80,000-140,000 or higher), also concentrates the magnetic field inside (substantially in the same geometric plane) the planar coil 22, thus significantly increasing an amplitude level of the electrical signal provided by coil 22. The ferromagnetic layer 25 may be located on a side of the substrate 21 on a side opposite the conductor turns as shown in Figures 7 and 8. However in the exemplary embodiment of Figures 7 and 8, multiple PCB substrates 21 are provided.

[0049] The planar coil 22 on PCB substrate 21 is fixedly secured or attached to the waveguide 23. Preferably a free end of the waveguide 23 is attached to the planar coil 22. The acoustic wave’s wavelength is much larger than the PCB thickness or the layer spacing. The “spot” is the location at or near the actual end of the waveguide where no superposition of the incident wave and the reflected wave occurs. Stated another way, this location or“spot” is less than 1/4 of the acoustic pulse wavelength where constructive interference is expected. Known pickups have wire- wound coils with an axial extent of several millimeters (ca. 8-l2mm). In one embodiment of the planar coil 22 of this disclosure, the support or PCB based inductor has an axial length when connected to the waveguide 33 of less than 2mm.

[0050] In one embodiment, the waveguide 23 is guided through an aperture 26 provided at least partially and preferably through the PCB substrate 21. It should be noted the waveguide 23 may extend freely through the aperture 26 being spaced apart from an inner surface of the aperture, or may be mechanically connected to the planar coil 22. For example, the waveguide 23 may be mechanically connected (e.g. soldered, glued or crimped) to the planar coil 22, i.e. to the substrate 21 or a conductor thereon. In a further embodiment, a rivet 24 (for example made of copper, as shown in Figures 11-12) may be provided on the waveguide 23 and used to make a mechanical connection between waveguide 33, PCB substrate 21 and/or mu-metal foil 25. It should be noted that in another embodiment, the waveguide 23 may also be directly soldered to a solder point on either side of the PCB substrate 21, which can be a through hole via, a ring, or a terminal connector on the PCB substrate 21.

[0051] The planar coil 22 may be laid out to provide a rotationally symmetric sensor element design, with the waveguide 23 guided through a hole in the supporting material 21 bearing the described coil structure. Since the PCB substrate 21 securely holds the conductors in a fixed position, a conductor turn may be disposed on the edge of the substrate 21 very close to the aperture through which the waveguide 23 extends. This can help increase the strength of the signal from the Coil 22.

[0052] As mentioned above, the waveguide 23 may be connected with help of a rivet or endcap 24 to either the mu-metal foil 25 or planar coil 22. Techniques to connect those parts may be realized by soldering, gluing or crimping those parts together.

[0053] The capability of soldering the waveguide 23 to the PCB substrate 21 avoids the use of clamping elements (e.g., such as with an anchor) as typically used for transversal systems which then also needs very accurate mechanical alignment.

[0054] An embodiment of the PCB substrate 21 shown in Figure 9 contains a circular shaped solderable pad 29. In such a configuration, the connection between waveguide 23 and the PCB substrate 21 may be implemented as a low resistive, conductive connection 29. This eliminates welding techniques being used to attach additional connection tapes or pins to the waveguide 23.

[0055] The embodiment of Figure 10 shows another implementation of a waveguide 23 being soldered to the mu-metal foil 25, which then can be used to supply the current pulse to the waveguide.

[0056] Figure 11 illustrates an embodiment using a rivet 24 secured to the end of the waveguide 23. The rivet 24 extends into the aperture or through hole provided in the PCB substrate 21. If desired, the rivet 24 may be fixedly secured to the PCB substrate 21 by being press fitted into the aperture (with or without use of the ring 29). In the embodiment of Figure 12, the rivet 24 is soldered to ring 28 forming a conductive connection.

[0057] It should also be noted in any of the embodiments where a gap exists between the waveguide 23 and the inner surface of the aperture of the substrate 21, this gap may be filled with a damping material (not shown), such as an elastomeric material, for example silicon. If desired, the damping material can be in the shape of a preformed tubular element to allow assembly and its proper location in the aperture. The damping material acts as a front end damping element contributing to echo attenuation for increased measurement frequency, and can aid in keeping the waveguide 23 centered in the aperture, particularly if the damping material is in the shape of a preformed tube.

[0058] An electrical connection is made to, in one embodiment, an end of the waveguide 23 with a conductor connected directly to the end (particularly, if the waveguide 23 is spaced apart from the inner surface of the aperture or is otherwise electrically isolated from for example a ring 28 provided on the substrate). If, however, a ring 28 is used to secure the waveguide 23 to the substrate, the electrical conductor may be connected to the ring 28.

[0059] Figures 13A-13D schematically illustrate embodiments of pick-up coil(s) that may be SMD mounted components containing either a flat wire-wound air coil (Figure 14), a multilayer chip inductor (MLCI) component (Figure 15) having a coil pattern 151, outer electrode 152, and non-magnetic ceramic 153, or a wire wound chip inductor (Figure 16). Like the planner coil 22 described above, these types of coils may be mounted on a support 40, such as a PCB (using any of the techniques described above), having an aperture 42 in the middle of the coil windings 44 so that the waveguide 23 may extend through this aperture 42. In this design the coil’s center axis 46 may be arranged perpendicular to the waveguide 23 (Figure 13A), askew to the waveguide 23 (Figure 13B) or parallel to the waveguide 23 (Figures 13C and 13D). Although a plurality of coils are arranged circularly or in a matrix about the aperture 42 as illustrated in Figures 13A-13D, if desired, a single coil may also be used. A suitable detection circuit can be connected to one or more coils.

[0060] Operation

[0061] Embodiments of the disclosure operate as follows. Referring to Figure 2 for the general operation of the system, the acoustic ultrasonic wave 5 travels from the position magnet 4 towards any of the planar coils 22 of Figures 7-12 or the coils of Figures 13A-13D

(collectively“coils herein disclosed”. The coils herein disclosed detect the acoustic ultrasonic wave 5 exactly at or close to the end of the waveguide 34. Signal detection at a position at the actual end of the waveguide leads to the effect that the incident wave and its reflection coincide in a spatial and temporal manner, so that the reflection is diverging from the coil and is not detected by the coil. The shape of the detected signal matches the shape of the incident signal coming from the magnet.

[0062] The fact that the waveguide is directly connected to the coil’s supporting structure makes the setup described insensitive to production tolerances. The disclosed coil designs allow the possibility of omitting an anchor component and therefor reducing the number of components which reduces the sensitivity for component tolerances.

[0063] As indicated above, the ferromagnetic (e.g., mu-metal) layer 25 with a relative high magnetic permeability concentrates the magnetic flux in the same geometric plane as the planar coil 22 which leads to a relatively large signal. However, it should be understood that more than one ferromagnetic layer may be present in the coil assembly. In particular, it may be advantageous to include one or more ferromagnetic layers in addition to or in the alternative to the ferromagnetic layer 25. For instance, a ferromagnetic layer may be provided on a planar side that is parallel to ferromagnetic layer 25 such as the planar side that faces in the opposite direction. It may also be helpful to have one or more ferromagnetic layers on the edge or lateral portions of the support 21, that is, sides that lie in a plane (or have a curved shape if the support is not in the shape of a rectangular block) that intersects with ferromagnetic layer 25.

[0064] Based on the inverse magnetostrictive effect, the acoustic ultrasonic wave 5 is transformed into an electrical signal which can be detected at the contacts of the coils herein disclosed.. In embodiments where the coil is a planar coil, it should be noted that by locating the planar coil at the actual end of the waveguide and the fact that it is a flat coil and not a wire wound coil on a bobbin that is spatially large in axial direction, the signal obtained is a true function of the ultrasonic wave from the magnet, because the reflection from the waveguide’s anchored end as found in the transversal system or axial system is not detected. However, it should also be noted that although the planar coil 22 disposed at a free end of the waveguide 23 has its advantages, if desired, in another embodiment, a bobbin coil could be disposed at the free end of the waveguide 23. The advantage of the bobbin coil is its relatively high number of conductor turns can produce a signal with greater strength. However, it may be particularly advantageous if an axial length of the bobbin be as small as possible so that it can be disposed at the end of the waveguide 23 like as discussed with the planner coil 22.

[0065] The detected signal described above can be assumed to be a first voltage portion that is induced into any of the coils described above. With reference to Figure 17, as another aspect of the present invention, the return wire 50 may be located across the coil 52 (herein illustrated as a planar coil although any of the coils described above may be used) so as to generate a voltage to reduce an unwanted voltage that occurs in the coil 52. In particular, when a current pulse is fired into the waveguide, the current pulse travels through coil 52. The current pulse induces a voltage into the coil 52, which is commonly known in the art as“ringing”. For purposes of understanding, this voltage will be referred to as a first portion of voltage. However, it has been found that for location of a portion 50 of the return wire across the coil 52 the current pulse being substantially instantaneous is also present in the portion 50 of the return wire, which will thereby induce a second portion of voltage in the coil 52 due to orientation and proximity of the portion 50 with respect to coil 52. The second portion of voltage may be inverted with respect to the first portion of voltage so as to reduce it.

[0066] Although particularly described above with the coils such as coil 22 connected to the end of the waveguide 23, it should be noted the coil(s) may also be incorporated in the sensor in the manner of the transversal system as schematically illustrated in Figure 18. As illustrated by way of example using the planar coil 22, the planar coil 22 (having any of the features described above) is connected to an end of a transverse extension 31 (e.g., tape portion) where the end opposite the planar coil 22 is joined to the waveguide 23 (similar to Figure 2). The end of the waveguide 23 would be anchored as in a transversal system of Figure 2. The features described above with respect to the coils and the manner in which they are connected to the end of the waveguide 23 applies to joining the coils to an end of the transverse extension 31.

[0067] Advantages:

[0068] Without limitation some advantages or novel features of the embodiments described herein include:

[0069] Compact coils located at the waveguide’s end which reduces the mechanical size leading to housings with lower height and/or smaller diameter.

[0070] Low part count and no filigree parts provide a mechanical simple and stable assembly which provides less possibilities for errors or faulty parts.

[0071] Coils may be either integrated directly onto an existing PCB substrate design or may also be placed on a small separate substrate which may be easily placed onto another PCB and soldered like it is done for conventional SMD component on PCB boards.

[0072] Fixing the waveguide to the pickup coil’s supporting structure creates a clearly defined reference point, that is directly linked to the pick-up coil so that the whole system is less error-prone to component and production tolerances.

[0073] The coils allow rotational symmetric compact sensor element designs.

[0074] Reduced ringing and therefore resulting in a shorter null zone.

[0075] Omitting troublesome parts like anchor, current feed pin, bobbins and tapes.

[0076] Tape welding process is omitted which reduces complexity and possibilities for errors. [0001] If additional shielding against external influences, e.g., electric or magnetic fields, is required, this can be easily implemented to surround the compact ultrasonic wave converter 7 due to small sized enclosures and simple geometry.

[0077] Some electrical advantages include:

[0078] Reduced complexity and optimized signal generation at the actual end of the waveguide lead to an improved sensor performance which is less sensitive to external interferers.

[0079] New sensor designs which require a very compact and small sized sensing element may be without noticeable null zones as the very short dead zone may be completely shifted inside the sensor electronics head.

[0080] The new sensor element results in a measured signal that is insensitive to

manufacturing tolerances.

[0081] As the new sensor element does not utilize constructive signal interference with tape and anchor there is no influence resulting in reduced or distorted signal due to misalignment of those mechanical parts.

[0082] Thermal behavior is improved as less mechanical influences are present

[0083] Reduction / cancellation of ringing

[0084] Some other improvements include:

[0085] Higher resilience against shock and vibration as for instance the tape and

mechanically bulky bobbins have been eliminated. The design contains fewer parts which are contained in a mechanically tight ensemble which provides a higher resilience against shock and vibration.

[0086] The actual signal detection concentrates at a single spot (small axial length if for example a stacked coil is used) at the end of the waveguide where the signal amplitude is at maximum without any additional interference from other signal reflections.

[0087] No bulky bobbins are required which contain several hundreds of turns wire windings.

[0088] No tape within a bobbin which eases assembly and both mechanical and electrical influences.

[0089] Simplified signal detection due to directly fixing the waveguide to the pick-up coil, so that disturbing influences from signal reflections are eliminated. [0090] Using a planar coil 22 which may be either single or multilayered accommodated on a PCB substrate 21.

[0091] Using the planar coil 22 in conjunction with a mu-metal foil 25 as a flux concentrator to boost the signal amplitude of the ultrasonic wave converter 7.

[0092] Soldered connection of waveguide to PCB substrate 21 that may be used as current feed for the attached waveguide 23.

[0093] Using novel ultrasonic wave converter 7 based on a planar coil 22 which may be integrated on another single or multilayered PCB.

[0094] The waveguide 23 may be equipped with a soldered, glued or crimped rivet 24 which allows connecting it by soldering, gluing or crimping to the mu-metal foil 25 or the planar coil 22.

[0095] A circular shaped solderable ring or pad 28 on the PCB substrate 21 allows the connection between waveguide 23 and PCB substrate 21. It provides a conductive low resistive connection 29 which avoids another welded connection between a pin and waveguide 23 which allows feeding the current pulse 2 into the waveguide 23.

[0096] The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present disclosure is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.