WO2026017482A1

WO2026017482A1 - System for object detection

Info

Publication number: WO2026017482A1
Application number: PCT/EP2025/069388
Authority: WO
Inventors: Thomas Stifter; Norbert HERSCHBACH; Andreas OLK; Martin BOGUSLAWSKI; Matthias Massing
Original assignee: IEE International Electronics and Engineering SA
Current assignee: IEE International Electronics and Engineering SA
Priority date: 2024-07-16
Filing date: 2025-07-08
Publication date: 2026-01-22
Anticipated expiration: 2027-01-16

Abstract

A system (1) for object detection by time-domain reflectometry comprises a sensor arrangement (10) with at least one signal line (12, 17, 18, 24), which is disposed within a detection area (A), comprises at least one conductor (13) and is adapted to propagate an electromagnetic signal (S, R), wherein a local impedance of the signal line (12, 17, 18, 24) is influenceable by an object (50) in at least one detection region (D1-D4) associated with the signal line (12, 17, 18, 24), and wherein the sensor arrangement (10) comprises, for at least one signal line (12, 17, 18, 24), at least one impedance discontinuity corresponding to a local impedance change; and a control device (30) that is operatively coupled to the at least one signal line (12, 17, 18, 24). The control device (30) is adapted to: - apply (100) a time-dependent detection signal (S) to each signal line (12) and receive a reflection signal (R) from the signal line (12); - identify (110) at least one characteristic feature (C1-C4) in the reflection signal (R) and determine a measured timing of the characteristic feature (C1-C4) wherein the characteristic feature (C1-C4) is associated with a reflection by an impedance discontinuity of the signal line (12, 17, 18, 24), - determine (120), for each characteristic feature (C1-C4), a time shift between the measured timing and a reference timing of the characteristic feature (C1-C4); and - detect (130) an object (50) in at least one detection region (D1-D4) based on the at least one time shift.

Description

System for Object Detection

Technical field

[0001 ] The invention relates to a system for object detection, and to a method for object detection.

Background of the Invention

[0002] In modem vehicles there can be various sensors for detecting the presence and/or position of an occupant or a body part of an occupant. For instance, there are sensors for occupancy detection of vehicle seats or hands-off-detection sensors for the steering wheel. These and other sensors, which can be referred to as “bodydetection sensors”, can be required due to a variety of reasons, oftentimes for safety reasons. For example, depending on the occupancy of a seat, seat belt reminders can be triggered, or the air bag function can be adapted. Similarly, if sensor signals indicate that the driver has removed his hands from the steering wheel, a warning signal can be output, or some safety measure can be initiated.

[0003] There are various types of sensors known in the art. Among these are, e.g., foil-based sensors, which are adapted for detecting pressure exerted by a human body, or capacitive sensors, which use electromagnetic fields for body detection. Such sensors, which use the influence of the human body on the electromagnetic field for detection, can be more sensitive. The aforementioned sensor types only allow for detecting the presence of an object or body part near the sensor. If the position is to be detected, these sensor types require a plurality of sensors to be provided for each of several detection regions. Another type of sensor employs Time Domain Reflectometry (TDR) to detect an object. In these sensors, a signal propagates along a signal line, is reflected, and the reflected signal is analyzed. Since a nearby object influences the local impedance of the signal line, it gives rise to a reflection. By analyzing the timing of the reflection, it is not only possible to detect the presence, but also the position of the object. However, these TDR based sensors may require sophisticated signal processing to reliably identify the reflection and deduce the object position. If the signal-to-noise ratio of the reflected signal gets worse, it may even be impossible to detect an object, or its position. [0004] US 2012/0001647 A1 discloses a sensor device for detection of an approach of an object in an observation area supervised by the sensor device, having a server circuit with an LC-oscillating circuit with a signal transducer circuit for generating an electric field, an electrode device coupled with the LC-oscillating circuit, whereby the capacitance of the electrode device is a component of the oscillator circuit capacitance and whereby the electric field generated by the LC- oscillating circuit on the electrode device is adapted to be radiated into the observation area, and an evaluating device. The approach of an object in the observation area of the electrode device causes a change of the capacitive environment of the electrode device, which is detectable by the evaluating device.

[0005] US 2014/0312962 A1 discloses a capacitive switch, comprising a drive circuit configured to output a drive signal, at least one detection circuit configured to detect a touch according to a capacitance variation, output a first signal according to the drive signal when the touch is not detected and output a second signal according to the drive signal when the touch is detected, a reference circuit configured to output the first signal according to the drive signal, wherein the reference circuit is a replica of the detection circuit, and an identification unit configured to output an identified signal according to a phase shift between the second signal of the detection circuit and the first signal of the reference circuit.

[0006] WO 2019/086388 A1 discloses a system for hand detection on a steering wheel, comprising a signal line extending from a first point to a second point and being disposed along at least a portion of a surface of the steering wheel, and a detection unit coupled to the first point, wherein the detection unit is configured to send a time-dependent detection signal traveling along the signal line, receive a reflected signal traveling along the signal line and detect the presence of a hand on the surface based on the reflected signal.

[0007] US 2020/0412003 A1 discloses a proximity sensor, comprising a transceiver unit and a leaky coaxial cable operably coupled to the transceiver unit. The proximity sensor may comprise a load operably coupled to the transceiver unit via the leaky coaxial cable. Also, the leaky coaxial cable may comprise at least one shielding layer having an opening formed therein, the opening in the at least one shielding layer allowing for energy leakage from the leaky coaxial cable. Object of the invention

[0008] It is thus an object of the present invention to provide efficient means for object detection.

[0009] This problem is solved by a system according to claim 1 .

General Description of the Invention

[0010] The invention relates to a system for object detection. The system could be used for different applications, e.g., in a portable device, or it could be installed in a building. In particular, it can be installed in a vehicle. The vehicle may be a road vehicle like a car, but could also be a train, a water vehicle, or an aircraft. The term “object detection” refers to detecting at least the presence of an object, and preferably also its position. The term “object” in this context explicitly includes a body part of a living being, in particular a human being. Object detection by the system is performed by time-domain ref lectom etry. In other words, it is based on analyzing a reflected signal in time-domain representation. However, the inventive system employs a variant of TDR that differs from previously known TDR implementations.

[0011 ] The system comprises a sensor arrangement with at least one signal line, which is disposed within a detection area, comprises at least one conductor and is adapted to propagate an electromagnetic signal. The sensor arrangement can be a single, coherent component or assembly. Preferably, it comprises a carrier, like a dielectric carrier, on which the at least one signal line is disposed. However, the sensor arrangement could also comprise a plurality of components that are not directly connected. The sensor arrangement may comprise a single signal line or a plurality of signal lines. Each signal line is disposed within an area which is referred to as the “detection area”. The detection area may correspond to a surface of an object, although in operational state, and any conductive component of the sensor arrangement is preferably covered by a non-conductive material to avoid direct contact by an object, as well as for aesthetical reasons.

[0012] The at least one signal line does not have to cover the detection area completely, although it is preferred that no point within the detection area is further away from the signal line than a certain maximum distance, which may be e.g. a few cm or mm. As suggested by the name “line”, the signal line may have a generally linear or “one-dimensional” shape, although there are embodiments in which its shape is rather planar or “two-dimensional”. In order to provide a better coverage of the detection area, the signal line may have a curvy shape, especially a meandering shape. The signal line comprises at least one conductor, and is therefore at least partially made of conductive material, preferably metal. However, its structure may comprise other materials. In any case, the signal line is adapted to propagate an electromagnetic signal. Such an electromagnetic signal may comprise electric field components as well as magnetic field components. It may coincide with an electric current along the signal line. The signal line is adapted so that the electromagnetic signal can propagate, spread, or move along the signal line. It will be understood that this may depend on the frequency of the signal. Some signals may propagate better than others, while some signals may not be able to propagate at all, e.g., due to a cut-off frequency of the signal line.

[0013] A local impedance of the signal line is influenceable by an object in at least one detection region associated with the signal line. The detection region is associated with (at least) one signal line and preferably has a fixed position and extent with respect to the signal line. There may be only one or preferably a plurality of detection regions. Preferably, each detection region is coherent. The detection region is normally a three-dimensional region, although it may be possible to define a two-dimensional detection region, depending on the embodiment. The detection region can at least partially be disposed above or below the detection area. Depending on the embodiment, a maximum dimension of the detection region may correspond to, e.g., between 1 % and 50% of a maximum dimension of the detection area, but smaller or larger percentages are also possible. An object in the detection region and the signal line may interact with each other through electric and/or magnetic fields. This interaction can be referred to as an “electromagnetic coupling”, one could also say a capacitive and/or inductive coupling. An electromagnetic field between the signal line and the object may extend into a space outside of the sensor arrangement, specifically above the detection area. The effective extent of the electromagnetic field may define the detection region. By the influence of the object on the electromagnetic field, the impedance of the signal line is influenced locally. “Locally” refers to a region or portion of the signal line, while other portions are unaffected. The extent of the influence depends on the size, material and proximity of the object. The presence of the object can introduce an impedance perturbation. This does not mean, however, that the signal line as such (i.e. without the presence of an object) has a constant impedance along its length. As will be explained later, the signal line may have “built-in” or “intrinsic” impedance-changing features, that is to say, the signal line contains characteristic changes of the characteristic impedance at specifically defined locations in its layout.

[0014] The sensor arrangement comprises, for at least one signal line, at least one impedance discontinuity corresponding to a local impedance change. In other words, apart from possible changes of the local impedance due to the presence of an object, the sensor arrangement as such is adapted to provide one or several impedance discontinuities for a signal line. Preferably, there is at least one impedance discontinuity for each signal line. The impedance discontinuity corresponds to a change of the local impedance. Such an impedance discontinuity, i.e., a change of local impedance, may be located within the signal line or at an end thereof. Specifically, the impedance discontinuity may be a change in the local impedance of the signal line. However, it could also be a change in the local impedance at a transition from one end of the signal line to a neighboring element or neighboring space.

[0015] The system also comprises a control device that is operatively coupled to the at least one signal line. The control device can be disposed on the same carrier as the sensor arrangement, but may also be disposed on a separate carrier, in a separate housing, or the like. It may perform various functions, some of which will be explained below. Specifically, the control device may comprise at least one signal generator, possibly a plurality of signal generators, and at least one receiver unit, possibly a plurality of receiver units. Also, the control device may comprise a processing unit, which may be adapted for signal processing. Other optional components include a filter and an analogue-digital-converter. Although the control device comprises at least one hardware component, some of its aspects may be software-implemented. It is operatively coupled to the at least one signal line. This may refer to an electrically conductive coupling, i.e., an electric connection. However, it may also refer to a non-conductive coupling, e.g., a capacitive and/or inductive coupling. As a rule, the operative coupling allows for a bi-directional signal transfer between the control device and the respective signal line. The control device can be connected to the sensor arrangement via a connection interface. The connection interface may enable a detachable connection, e.g., a socket-and-plug connection.

[0016] The control device is adapted to perform at least the following steps. These steps are preferably performed in the sequence in which they are mentioned but could also be performed in a different order and/or simultaneously. The steps may collectively be referred to as a detection process.

[0017] In one step of the process, the control device applies a time-dependent detection signal to each signal line and receives a reflection signal from the signal line. The detection signal is an electromagnetic signal which is applied to the signal line. In case of several signal lines, it is possible that different detection signals are applied to different signal lines, but it could also be the same detection signal for each signal line. Also, the detection signal could be applied simultaneously to each signal line or could be applied sequentially to the signal lines. This may help to avoid any cross-coupling between the signal lines. The signal is time-dependent, i.e., it changes over time. The detection signal is preferably a pulse signal. The pulse length and the pulse interval can be selected so that any reflection from one pulse reaches the control device after the pulse has left the control device but before the next pulse is generated. However, at least one detection signal can have another waveform. E.g., it can be a modulated signal, a frequency-swept signal, a pseudo random phase-shift keyed signal or a pseudo random signal. The detection signal propagates along the signal line and gives rise to the reflection signal, which propagates in the opposite direction back to the control device. Here and in the following, the travel direction of the detection signal (to the end of the signal line) is referred to as the “distal” direction, while the travel direction of the reflection signal (back to the control device) is referred to as the “proximal” direction. Also, the end of the signal line opposite the control device is referred to as the distal end. It will be understood that the two abovementioned signals overlap within the signal line. Depending on the characteristics of the detection signal and the reflection characteristics of the signal line, the signals may even overlap within the control device. However, it is preferred that the detection signal can be transmitted into the signal line before the reflection signal arrives at the control device. It will be understood that any impedance discontinuities lead to significant reflections. Such discontinuities can be due to an object in the proximity of the signal line but also due to the structure of the signal line itself. The reflection signal, or a relevant part thereof, can be stored in a memory of the control device for further reference.

[0018] In another step, the control device identifies at least one characteristic feature in the reflection signal and determines a measured timing of the characteristic feature, wherein the characteristic feature is associated with a reflection by an impedance discontinuity of the signal line. It will be understood that the reflection signal is used in time-domain representation for this step. The characteristic feature can be any clearly distinguishable structure within the reflection signal. Specifically, the characteristic feature may be distinguishable from other parts of the reflection signal by the amplitude and/or the slope (i.e. the first derivative). The characteristic feature is associated with reflection by an impedance discontinuity of the signal line. The impedance discontinuity leads to a characteristic reflection, which is identifiable by the characteristic feature in the reflection signal. In other words, the characteristic feature results from a reflection by an impedance discontinuity.. The control device identifies the characteristic feature, i.e., it determines that the characteristic feature is present. Also, it determines a measured timing of the characteristic feature. The measured timing is a position of the characteristic feature in the time domain. There may be various definitions for the measured timing, since the characteristic feature may extend over a non-negligible time interval. For instance, the measured timing may correspond to the beginning of the characteristic feature, the end of the characteristic feature, or a center of the characteristic feature.

[0019] Further, the control device determines, for each characteristic feature, a time shift between the measured timing and a reference timing of the characteristic feature. The control device has access to a reference timing for each characteristic feature. The reference timing can be stored in the control device or in a memory that is accessible by the control device. As a rule, the reference timing will be different for each characteristic feature, but it would be possible to use the same reference timing for all characteristic features. The control device then compares the measured timing with the reference timing, i.e., it calculates the difference between these timings. This difference is herein referred to as the time shift. The time shift could be zero, but generally has a non-zero value. In case of several characteristic features, the time shift is calculated individually for each characteristic feature. [0020] In another step, the control device detects an object in at least one detection region based on the at least one time shift. “An object” includes the possibility of several objects being detected. The object that is detected is disposed in at least one of the abovementioned detection regions. Therefore, it influences the impedance of the signal line. On the one hand, this leads to a contribution to the reflection signal, as is commonly known for TDR sensors. However, there is another effect that pertains to the transmitted part of the detection signal, i.e. , the part that is not reflected at the object but propagates further to the distal end of the signal line. Due to the presence of the object, this part is also influenced, specifically its speed. This, in turn, influences the timing of a characteristic feature, if this characteristic feature is associated with any reflection distally of the object. Specifically, if the influence of the object delays the transmitted part, this will also delay the characteristic feature associated with any distally-occurring reflection. Any change in timing can be detected by analyzing the time shift. Therefore, the presence of the object can be detected even without analyzing the reflection caused by the object itself.

[0021 ] The inventive system employs a variant of TDR that has several advantages over the TDR commonly used in prior art sensor systems. Since the object detection does not rely on detecting the reflection by the object itself, the object can be reliably detected even under circumstances in which such a reflection is not easily distinguishable. This is particularly true when the reflection signal has a low signal- to-noise ratio. It has been found that a characteristic feature, and its timing, can be safely detected even under such conditions. Also, the signal processing required for identifying the characteristic feature and determining the measurement timing can be simpler than for conventional TDR. Therefore, the inventive system may be not only more reliable but also simpler.

[0022] In general, the reference timing may correspond to any kind of known situation to which the current measurement can be compared. Preferably, the reference timing corresponds to a calibration measurement without an object in any detection region, and it is preferentially represented by a set of time delay values. In other words, the reference timing is the timing of the characteristic feature if no object is present in any detection region. In this case, the measured timing should either (at least approximately) be equal to the reference timing or it should be greater, corresponding to a delay of the characteristic feature. The reference timing could also be referred to as an undelayed timing.

[0023] Depending partially on the complexity and the setup of the control device, it could be adapted to identify various types of characteristic features. According to one embodiment, the control device is adapted to identify at least one characteristic feature by identifying a flank of the reflection signal, wherein the measured timing preferably corresponds to a timing of the flank. One could say that in this embodiment the flank of the reflection signal is a characteristic feature. The term “flank” refers to a sudden increase or decrease of the reflection signal. It will be understood that there can be more or less strict criteria for what is identified as a flank. These criteria may specifically include the “height” of the flank, i.e. the amount of increase or decrease represented by the flank. Alternatively, the control device could be adapted to identify a spike in the reflection signal, i.e., a short-time increase or decrease, which is followed by a decrease or increase. In this case, the timing of the peak of the spike could be the measured timing.

[0024] Preferably, at least one conductor of a signal line is disposed on a dielectric carrier. More preferably, a plurality of conductors or even all conductors of the sensor arrangement are disposed on a common dielectric carrier. The carrier can preferably be a flexible dielectric carrier, which may also be referred to as a dielectric carrier foil. The at least one signal line, and other elements, can be applied to the carrier by flex circuit technologies. This refers to, e.g. , screen printing, inkjet printing, flex PCB or etched aluminum laminates on polymer foil. However, the dielectric carrier could also be a fabric, textile or foam, to which the conductors could be connected by gluing, stitching, or the like. In other embodiments, the dielectric carrier may only have a limited flexibility. It is also preferred that the at least one conductor is covered by a dielectric cover. The dielectric cover could be made of the same material as the dielectric carrier. In some embodiments, the carrier and the cover may be indistinguishable since they are formed together by a process like casting, molding or 3D printing. In some embodiments, the conductor(s) may be embedded in a dielectric material that serves as a carrier and a cover.

[0025] As already mentioned, it is possible that a plurality of signal lines is connected to the control device. Thus, the control device can apply a detection signal to more than one signal line. The control device may be adapted to apply the same detection signal or different detection signals to the different signal lines. All signal lines may be disposed in the detection area. In some embodiments, they may partially overlap. In such a case, a dielectric isolation layer can be interposed between the overlapping portions. Alternatively or additionally, at least one signal line may comprise a plurality of conductors. Preferably, a signal line may comprise exactly two conductors or a pair of conductors. These conductors may at least partially be disposed parallel to each other, i.e., their relative distance can be constant, at least along a major part of their length. More specifically, the two- conductor signal line may be preferentially operated as differential transmission lines, where the common mode is irrelevant for the present sensor operation. Alternatively, at least one signal line may comprise a microstrip line, a coplanar waveguide, a strip line, and/or a slot line. In further alternative applications, signal lines may be formed using substrate-integrated waveguide technology or based on dielectric rod technology.

[0026] In some embodiments, the control device can be conductively coupled to one or several conductors of a signal line. Alternatively, the control device may be coupled to at least one conductor of a signal line via a capacitor. Although such a capacitive coupling influences the signal transmission between the control device and the respective conductor, it does not significantly impair the transmission. However, if the capacitor separates the conductor from the control device, it is possible to use the conductor for an additional function. For example, the conductor may be used as a heating element if the heating uses a DC current or an AC current of lower frequency outside of the frequency band used for the sensor function. The respective heating current will not affect the control device. The electric circuit providing the heating current is preferably connected to the conductor of the signal line with inductance elements or coils of an inductance large enough to prevent the transmission of the detection signal and the reflection signal in order to decouple the electric circuit providing the heating current.

[0027] In one embodiment of the invention, at least one characteristic feature is associated with a reflection by an impedance discontinuity at a distal end of the signal line. Without suitable termination of the signal line, the impedance changes at the distal end of the signal line, thus causing a characteristic reflection that represents a characteristic feature. Specifically, the characteristic feature could be a flank of the reflection signal that is due to a reflection at the distal end of the signal line.

[0028] At least one signal line may be open terminated, short terminated, or terminated with an impedance element. As will be understood, in an open terminated signal line the distal ends of the two conductors are electrically isolated from each other. In a short-terminated signal line, the distal ends are short-circuited. If the signal line is terminated with an impedance element, the distal ends are connected with an impedance element, e.g. a resistor, that has a defined impedance. As a rule, this impedance is designed to minimize any reflections by the distal ends. While such minimization can be advantageous in some embodiments, it may be more desirable in other embodiments to allow for significant reflections at the distal end of the signal line, since this leads to a characteristic feature that can be used for object detection.

[0029] In another embodiment, the sensor arrangement comprises at least one impedance-changing feature that represents a local impedance change in the signal line and that is associated with a characteristic feature of the reflection signal, wherein each impedance-changing feature separates two detection regions of the signal line. The impedance-changing feature may be a physical element, a portion of an element, a property of an element, or the like. Various types of impedancechanging features will be discussed below. The impedance-changing feature represents a local measurable impedance change in a signal line. One could also say that it represents, or gives rise to, a well-defined impedance variation, i.e. an impedance discontinuity. Such a deliberate impedance change leads to a portion of the detection signal being reflected. This contributes to the reflection signal. Specifically, the reflected portion can be identified by a characteristic feature of the reflection signal. Therefore, each impedance-changing feature corresponds to a characteristic feature. Each impedance-changing feature separates two detection regions of the signal line. One could also say that it defines a separation or a transition between two detection regions. One detection region is disposed proximally from the impedance-changing feature, while the other one is disposed distally from the impedance-changing feature. It will be understood that the sensor arrangement comprises a plurality of impedance-changing features, thus defining a plurality of detection regions (like n+1 detection regions being defined by n impedance-changing features). The reflection signal may comprise, apart from the characteristic features associated with the impedance-changing features, an additional characteristic feature associated with the distal end of the signal line.

[0030] Preferably, the control device is adapted to detect a plurality of characteristic features, and to determine a detection region in which the object is disposed based on the time shifts of the characteristic features. If an object is present, the time shifts of the characteristic features will generally be different depending on the position of the object. More specifically, if a characteristic feature is associated with an impedance-changing feature that is disposed distally from the position of the object, this characteristic feature experiences a significant time shift. On the other hand, if a characteristic feature is associated with an impedance-changing feature that is disposed proximally from the position of the object, this characteristic feature experiences no or only a negligible time shift. Therefore, it can be determined which impedance changing features are disposed proximally and distally from the object. Therefore, since each impedance-changing feature separates two detection regions, the detection region with the object can be determined.

[0031 ] According to one embodiment, at least one impedance-changing feature is a change of a cross-section of a conductor of a signal line. The cross-section of the respective conductor changes. This could refer to a changing shape of the crosssection, like a circular cross-section changing to a square cross-section. Also, it may refer to an increase or decrease of the cross-section, i.e. the area of the crosssection. It will be understood that there can be a plurality of such impedancechanging features, i.e. the cross-section could change several times along the length of the signal line. Alternatively or additionally, at least one impedancechanging feature can be a change of a distance between two conductors of a signal line which comprises a plurality of conductors, preferably two conductors. In other words, the distance between the two conductors increases or decreases. Optionally, this could be combined with a change in cross-section. It should be noted that either of these changes should be local in order to give rise to a clearly distinguishable characteristic feature. For example, the distance and the cross-section should remain constant over a certain length of the signal line, then at least one of these parameters changes within a relatively small length, whereafter both parameters remain constant again over a certain length. [0032] One embodiment provides that at least one impedance-changing feature is a local variation of a distance between two signal lines. It will be understood that the distance between two signal lines has an impact on the electromagnetic coupling between these two lines. When the signal lines are closer together, the coupling is stronger, which in turn has an influence on the local impedance. As a rule, there will always be some degree of variation of the distance between the signal lines. However, some types of variation, e.g. a local reduction of the distance, may have a more significant impact on the impedance. Thus, the “local variation” may specifically refer to a local reduction. However, it could also refer to a local increase. It will be understood that this may represent a pair of impedance-changing features, namely one for each single line. Also, at least one impedance-changing feature can be a local variation of a distance between two portions of a signal line. This embodiment works similar to the previous one and depends on the electromagnetic coupling between the two portions. Again, the local variation may in particular be a local reduction, or a local increase, of the distance. This variation also may lead to a pair of impedance-changing features, namely one for each region.

[0033] According to another embodiment, at least one impedance-changing feature is a conductive object disposed in proximity to a signal line. The conductive object and the signal line may interact with each other through an electromagnetic coupling. Since the conductive object is only disposed locally in proximity to a portion of the signal line, this leads to a local impedance change. The conductive object may be made of metal. Specifically, it can be made of the same material as the signal line. It is disposed in proximity to the signal line, but not in contact therewith. A suitable distance and size of the conductive object may vary for different embodiments. Both parameters have to be chosen so that the electromagnetic coupling with the signal line is non-negligible. Typically, the distance corresponds to less than 10% of a maximum dimension of the detection area. According to another embodiment, at least one impedance-changing feature is a dielectric object disposed at least in proximity to a signal line. In contrast to the conductive object, the dielectric object is an electrical isolator and can be in contact with the signal line. Alternatively, it can be disposed in proximity to the signal line but spaced therefrom. The dielectric object can be disposed on the signal line, thereby forming a portion of the above-mentioned dielectric cover. In order to achieve the impedance- changing effect, the dielectric object can have a different relative permittivity than other portions of the cover.

[0034] One embodiment provides that a plurality of signal lines is connected in parallel to the connection interface. The connection interface is connected detachably or non-detachably to the control device. In such an embodiment, the detection signal can be applied simultaneously to a plurality of signal lines. However, each signal line corresponds to a different detection region or group of detection regions, wherefore the position of the object can be determined with increased accuracy and/or within a larger detection area. Alternatively, or additionally, a plurality of signal lines can be connected in series to the connection interface. In this case, at least two conductors are connected to the connection interface.

[0035] The inventive system can be used for a variety of applications. In particular, it can be used in a vehicle, e.g. for occupancy detection or hands-off-detection. In such an embodiment, the sensor arrangement is disposed in a vehicle interior component and the detection area corresponds to a surface of the vehicle interior component. The vehicle interior component can be, e.g., a steering wheel, a trim panel, a door handle, a vehicle seat, an armrest, the foot space etc. However, other applications are also within the scope of the invention. The inventive system can be used as a touch sensor or touch switch for any type of machine or in a domestic installation, e.g. to control lighting in a house. The sensor arrangement can be realized as a thin, sheet-like structure that can be integrated into any type of surface, e.g., shoe insoles, wallpaper, floor coating, mat, or covering, hospital bed mattress or topper.

[0036] Another embodiment of the inventive system provides that a shell arrangement of a vehicle comprises the sensor arrangement, which shell arrangement has an external side and an opposite internal side on which a protection space is located that is protected by the shell arrangement. The shell arrangement in its entirety may be regarded as part of the system. It may at least in some embodiments also be referred to as a housing arrangement, a casing arrangement, or a wall arrangement. It is designed to protect a protection space and in particular a component of the vehicle that is disposed in the protection space. The shell arrangement preferably has a closed surface, but in order to provide mechanical protection, an open-work structure like grid or a mesh would also be possible. One side of the shell arrangement, on which the protection space is located, is herein referred to as the internal side. The opposite side is referred to as the external side. During operation of the vehicle, the shell arrangement is intended to keep potentially harmful influences on the external side away from the protection space. It may protect the protection space from impacting objects like stones, from dirt and/or from moisture. Specifically, the external side of the shell arrangement may be an external side of the vehicle. The sensor arrangement is part of the shell arrangement, one could also say that it is integrated into the shell arrangement. One application of such a system is to detect a foreign object in the vicinity of the shell arrangement, in particular a foreign object that could potentially damage the shell arrangement and/or a component in the protection space.

[0037] Alternatively or additionally to detecting a foreign object, the system may preferably be adapted to detect an object that is a deformed portion of the shell arrangement. The deformed portion is deformed with respect to an undeformed state of the shell arrangement. Such deformation may be an elastic deformation, which is normally only temporary, or it may be a plastic deformation, which is normally permanent. Even elastic deformation may be detected, which may be relevant since such deformation could indicate possible damage to a vehicle component in the protection space. Detection of such elastic deformation may be particularly advantageous since the deformation may not be visible during a later inspection. A plastic, i.e., permanent deformation may indicate that the shell arrangement has been permanently damaged and may need repair or replacement. If a deformation is detected, an inspection of the shell arrangement may be performed to assess any potential damage. The detection of the deformation may be based on the fact that the local impedance of the at least one signal line depends on the exact shape of the signal line and the shape and position of other parts of the shell arrangement in the vicinity of the signal line. Both may be changed when the shell arrangement is deformed.

[0038] According to one embodiment, the shell arrangement comprises an inner wall element disposed on the internal side relative to the sensor arrangement and an outer wall element disposed on the external side relative to the sensor arrangement, wherein the system is adapted to detect a deformed portion of the outer wall element. In this embodiment, the shell arrangement has a layered structure with the inner wall element, the outer wall element, and the sensor arrangement in between. The inner wall element is disposed internally of the sensor arrangement and the outer wall element is disposed externally of the sensor arrangement. The inner wall element may be the thickest and mechanically most stable component, while the outer wall element may be less thick and/or less stable. Thus, and because the outer wall element is disposed towards the external side, any deformation of the outer wall element does not necessarily imply a deformation of the inner wall element. However, the sensor arrangement is adapted to detect a deformed portion of the outer wall element, wherefore even minor damage is likely to be detected.

[0039] The sensor arrangement may be in direct contact with the inner wall element and/or the outer wall element. One embodiment provides that the outer wall element, in an undeformed state, is spaced from the sensor arrangement at least in a part of the shell arrangement. For stability reasons, the outer wall element may be locally connected to the sensor arrangement. However, in other parts of the shell arrangement, it is spaced from the sensor arrangement, i.e. , externally spaced. This refers to the undeformed, undamaged state of the outer wall element. If, for example, a portion of the outer wall element is deformed by a foreign object, it moves closer to the sensor arrangement and possibly even into contact therewith. This may lead to a change in the local impedance of a signal line. On the other hand, the spacing between the outer wall element and the sensor arrangement may prevent minor deformations of the outer wall element from damaging the sensor arrangement.

[0040] The shell arrangement may be disposed on a bottom of the vehicle to protect the protection space from below. It is understood that in particular for a road vehicle, the bottom is the part that is most likely to be damaged by foreign objects like stones, speed bumps or curb stones, while it is also the part that is most difficult to inspect visually. This problem can be effectively alleviated by a shell arrangement with a sensor arrangement as described above. In this context, the internal side corresponds to an upper side while the external side corresponds to a lower side. The shell arrangement may protect various vehicle components from below. In particular, it may be used to protect a battery element, i.e., the protection space is preferably adapted to receive a battery element. The battery element may be a battery pack, which is commonly installed on the lower side of the vehicle. Mechanical damage to the battery element could not only impair the function of the battery itself but could also endanger other components of the vehicle or the vehicle in its entirety. However, the shell arrangement could also be used to protect other critical components, like a fuel tank, hydraulic, pneumatic or electric lines etc.

[0041 ] It should be noted that while the inventive system detects an object based on the time shift of the characteristic feature, it may optionally also employ conventional TDR techniques, if the signal-to-noise ratio of the reflected signal allows for this. In other words, a location of an object may be determined by analyzing a timing of a reflection caused by the respective object.

[0042] The invention further relates to a method for object detection by timedomain reflectometry, using: a sensor arrangement with at least one signal line, which is disposed within a detection area, comprises at least one conductor and is adapted to propagate an electromagnetic signal, wherein a local impedance of the signal line is influenceable by an object in at least one detection region associated with the signal line; and a control device that is operatively coupled to the at least one signal line, wherein the control device: applies a time-dependent detection signal to each signal line and receives a reflection signal from the signal line; identifies at least one characteristic feature in the reflection signal and determines a measured timing of the characteristic feature, wherein the characteristic feature is associated with a reflection by an impedance discontinuity of the signal line; determines, for each characteristic feature, a time shift between the measured timing and a reference timing of the characteristic feature; and detects an object in at least one detection region based on the at least one time shift.

[0043] All these terms have been explained above with reference to the inventive system and therefore will not be explained again. Preferred embodiments of the inventive method correspond to those of the inventive system. Brief Description of the Drawings

[0044] Further details and advantages of the present invention will be apparent from the following detailed description of not limiting embodiments with reference to the attached drawing, wherein:

Fig.1 is a schematic top view of an inventive system with a first embodiment of a sensor arrangement;

Fig. 2 is a schematic side view of a steering wheel with the system from fig.1 ;

Fig. 3A-3F are sectional views of a portion of a sensor arrangement for an inventive system;

Fig. 4A-4C are top views of the distal part of a signal line;

Fig. 5A-5C are top views of a second embodiment of a sensor arrangement;

Fig. 6A-6C are diagrams illustrating a reflection signal;

Fig. 7A-7C are top views of a third embodiment of a sensor arrangement;

Fig. 8A-8B are diagrams illustrating a reflection signal;

Fig. 9 is a flow chart of an inventive method;

Fig. 10 is a top view of a fourth embodiment of a sensor arrangement;

Fig. 11 is a top view of a fifth embodiment of a sensor arrangement;

Fig. 12 is a top view of a sixth embodiment of a sensor arrangement;

Fig. 13 is a schematic top view of a fifth embodiment of a sensor arrangement;

Fig. 14 is a schematic top view of a part of a sixth embodiment of a sensor arrangement;

Fig. 15 is a schematic top view of a part of a seventh embodiment of a sensor arrangement;

Fig. 16 is a diagram illustrating a reflection signal;

Fig. 17-18 are top views of impedance-changing features in signal lines;

Fig. 19-24 are schematic top views of parallel and in-series connections of multiple signal lines; Fig.25 is an exploded view of a battery and a shell arrangement with an eighth embodiment of a sensor arrangement;

Fig.26 is a schematic top view of the sensor arrangement of fig.25;

Figs.27-29 are detail views of signal lines;

Fig.30A-30D are side views of the battery and the shell arrangement from fig.25 with an impacting object;

Fig.31A-31 D are diagrams illustrating reflection signals;

Fig. 32 is a schematic top view of a part of a ninth embodiment of a sensor arrangement; and

Fig. 33 is a diagram illustrating a reflection signal.

Description of Preferred Embodiments

[0045] Fig.1 is a schematic view of a system 1 for object detection. The system 1 comprises a sensor arrangement 10 with a signal line 12, which is disposed within a detection area A on a flexible dielectric carrier 11 . The signal line 12 can be printed onto the carrier 11 . The signal line 12 in this embodiment has a meandering shape and may be comparatively long, e.g., 1 - 10 m. Therefore, it can cover a large detection area A in that no point of this detection area A is further away from the signal line 12 than, e.g., a few millimeters or centimeters. The signal line 12 is designed as a two-conductor transmission line with two parallel conductors 13. The signal line 12 is preferentially operated in differential, or odd, mode. The system 1 also comprises a connection interface 25 by which the sensor arrangement 10 is connected to a control device 30, which could also be referred to as a control module. In this embodiment, a detection region D1 extends over the entire detection area A. The control device 30 is adapted to apply an electromagnetic detection signal S to the signal line 12, which then propagates along the signal line 12. The impedance of the signal line 12 can be locally influenced or perturbed by an object 50, like a hand 51 of a person, in the detection region D1. The detection signal S propagates from a proximal end 12.1 to a distal end 12.2 of the signal line 12, where the signal S is reflected. It gives rise to a reflection signal R that is received by the control device 30. [0046] The sensor arrangement 10 can be integrated into various components. Fig. 2 shows a steering wheel 60 with the sensor arrangement 10 integrated into the surface 60.1 of the rim, while the control device 30 and the interface 25 are integrated into the center of the steering wheel 60. The steering wheel 60 comprises a rigid metallic frame, several layers of foam spacer and a leather trim. The foilbased sensor arrangement 10 is wrapped around the steering wheel and is folded so that it covers most of the areas around the rim of the steering wheel 60, just underneath the leather trim. Thus, the signal line 12 is relatively close to a hand 51 to be detected. The surface 60.1 corresponds to the detection area A. In this embodiment, the vertical length of the sensor arrangement 10 in Fig. 1 corresponds to the circumference of the steering wheel 60.

[0047] Figs.3A-3E show cross-sectional views of various possibilities for realizing the structure of the signal line 12 with two conductors 13 within the sensor arrangement 10. Fig.3A shows two conductors 13 with circular cross-section that are embedded in the carrier 11. Fig.3B is a similar embodiment in which each conductor 13 is surrounded by a lining 14. This lining may have a different permittivity than the carrier 11 , e.g., a higher permittivity. Fig.3C is another similar embodiment in which the conductors 13 are disposed on top of the carrier 11 , and an additional cover layer or cover 15 is disposed on top of the conductors 13 and the carrier 11 . The cover 15 may be made of the same material as the carrier 11 or a different material. Fig.3D shows an embodiment that is similar to the one of Fig.3A, but in this case, the conductors 13 have a rectangular cross-section. Fig.3E shows an embodiment with rectangular cross-section conductors 13. In this case, the conductors 13 are disposed on top of the carrier 11 and are embedded in an intermediate layer 16. Additionally, a cover 15 is disposed on top of the conductors 13 and the intermediate layer 16. Fig.3F shows an embodiment of a signal line using microstrip technology in which one of the two conductors 13 is formed as a strip of thin rectangular cross section on top of the carrier 11 and embedded in an intermediate 16. An additional cover layer 15 is deposited on top of the strip-shaped conductor 13 and the intermediate layer. The second conductor 13 is disposed as broad conductive layer covering the back surface of the carrier 11 .

[0048] Figs.4A-4C show different possible layouts for the distal end 12.2 of the signal line 12. According to Fig.4A, the signal line 12 can be open terminated, i.e. , the signal line is abruptly terminated in space at the distal end 12.2. Alternatively, the signal line 12 can be short terminated as shown in Fig.4B, i.e. , the conductors 13 can be short-circuited at the distal end 12.2. In yet another embodiment according to Fig.4C, the conductors 13 are connected by an impedance element 19 with a specific load impedance, e.g., a resistor.

[0049] Figs.5A-5C show another embodiment of a sensor arrangement 10, in which the shape of the signal line 12 is somewhat simpler than in the first embodiment. Fig.5A shows a situation in which no object is present. Fig.6A shows the corresponding reflection signal R as a solid curve in time-domain representation. The signal strength is almost constant for some time until it sharply decreases in a falling flank that starts at a time t_ri. The falling flank is caused by the reflection of the detection signal at the signal line termination 12.2. The flank represents a (first) characteristic feature C1 , and the time t_ri is a (first) reference timing of this characteristic feature C1. It can be stored in a memory of the control device 30. Fig.5B shows a situation in which a hand 51 is disposed in proximity to the signal line 12, close to the proximal end 12.1. Fig.6A shows the corresponding reflection signal R as a dashed line. The first difference is that the local perturbation of the impedance caused by the presence of the hand 51 leads to a reflection feature P. Another difference is that the characteristic feature C1 is delayed so that it starts at a (first) measured timing t_mi. Fig.5C shows a situation in which a hand 51 is disposed in proximity to the signal line 12, approximately halfway between the proximal end 12.1 and the distal end 12.2. Fig.6B shows the corresponding reflection signal R as a dashed line. Again, the presence of the hand 51 leads to a reflection feature P, which occurs at a different time than in Fig.6A. The characteristic feature C1 is also delayed and starts at a measured timing t_mi that is approximately the same as in Fig.6A. Fig.6C also represents the situation shown in Fig.5B, but this time the reflection signal R has a worse signal-to-noise ratio. Accordingly, the reflection feature P is hardly distinguishable from the noise, while the characteristic feature C1 can be clearly distinguished. It will be noted that in Fig 6A t_ri appears to be the start of the flank. Alternatively, t_ri can be defined as when the signal undergoes a certain threshold, e.g., any value between 10% and 90%. Any other definitions are possible. [0050] Figs.7A-7C show another embodiment of a sensor arrangement 10 that is similar to the embodiment shown in Figs. 5A to 5C. In this case, however, there are two dielectric elements 20 disposed locally over the signal line 12. The dielectric elements 20 may have a comparably large permittivity, e.g., e_r=12, which may be significantly higher than that of the carrier 11 (which may be, e.g., e_r=3), and of the cover 15, if present. These dielectric elements 20 represent two impedancechanging features F1 , F2, by which three detection regions D1 , D2, D3 are defined. Fig. 7B shows a situation in which a hand 51 is disposed in the third detection region D3, while Fig. 7C shows a situation in which the hand 51 is disposed in the second detection region D2. Fig. 8A shows the reflection signal R for Fig. 7A as a solid line and the reflection signal R for Fig. 7B is a dashed line. Again, a falling flank as a first characteristic feature C1 begins at a first reference timing t_ri. Additionally, a second characteristic feature C2 associated with the first impedance-changing feature F1 starts at a second reference timing t_r2, and a third characteristic feature C3 associated with the second impedance-changing feature F2 starts at a third reference timing t_r3. With the presence of the hand 51 in the third detection region D3, all characteristic features C1 -C3 are delayed to measured timings t_ri, t_r2, t_r3- Also, a reflection feature P can be identified. In Fig. 8B, the first and second characteristic feature C1 , C2 are delayed as in Fig. 7B. The third characteristic feature C3, however, is not delayed, i.e. , the third measured timing t_m3 is equal to the third reference timing t_r3.

[0051 ] Fig. 9 is a flow chart illustrating an inventive method for object detection, which can be realized with a system 1 using e.g. the sensor arrangement 10 of Figs.7A to 7C. After the start, the control device 30 applies in a first step 100, the detection signal S to the signal line 12 and receives the reflection signal R from the signal line 12. Then, in a second step 110, the control device 30 identifies the characteristic features C1 -C3 and determines their measured timings t_mi, t_m2, tm3. In another step, at 120, a time shift is determined for each characteristic feature C1- C3 as the difference between the measured timing t_mi, t_m2, tm3 and the reference timing t_ri , t_r2, te. These reference timings originate from a calibration measurement 200 which is performed separately upfront, without test object. The calibration measurement 200 is evaluated in the same way (step 100 and 110) yielding reference timings t_ri, t_r2 and t_r3. Then, in a block 130, the hand 51 and its position are detected. At 140, all detection regions D1 -D3 are initialized as unoccupied, and the first characteristic feature C1 is selected. Then, at 150, it is determined whether there is a non-negligible time shift for the selected characteristic feature C1-C3. If there is a time shift, detection region D1-D3 which corresponds to the selected characteristic feature C1 -C3 is selected at step 160 as a possible position of the hand 51 . In case of the first characteristic feature C1 , this is the first detection region D1. Then, the following characteristic feature is selected at 170 before the method returns to step 150. If there is also a time shift for the second characteristic feature C2, the second detection region D2 is selected at step 160 as the possible position of the hand 51 , while the first detection region D1 is discarded. This loop continues until the last characteristic feature (in this example the third characteristic feature C3) has been reached or until no time shift can be detected. At step 180, detection region D1 -D3 that is currently selected as the possible position is determined as the actual position of the hand 51 .

[0052] The control device can be configured to make further quantitative evaluations of the time shift determined for each characteristic feature C1 -C3 as the difference between the measured time t_mi, t_m2, tm3 and the reference timing t_ri, t_r2, tr3. In these further quantitative evaluations of the time shift it can be determined whether a single object or multiple objects are present, and within which of the detection regions D1 , D2, D3 associated with the characteristic feature C1 , C2, C3 each of a single or multiple objects is positioned. For example, if two objects 50 are present, at least one time shift associated with the characteristic feature C1 -C3 can be expected to be approximately twice as large as a time shift obtained when only one object 50 is present. If the time shift for the characteristic features C1 and C2 are both about twice the time shift typically obtained for one object and no time shift for the characteristic feature C3 is determined, for example, the two objects are both in the detection region D2. When also a time shift for the characteristic feature C3 is obtained and it is about half the time shift determined for the characteristic features C1 and C2, one object can be identified as positioned in the detection region D3 and a second object as localized in detection region D2.

[0053] While the embodiment of Fig.1 shows an even distribution of the bents of the signal line 12 and a symmetric layout, this does not have to be so in other embodiments. An example of a layout of the signal line 12 in which the bends in the signal line 12 are not evenly or homogeneously distributed is shown in Fig.10. Fig.11 shows an example for a layout of the path of the signal line 12 that is not symmetrical and wherein the bends are not evenly distributed over the length of the signal line 12.

[0054] While in Figs.7A-7C the impedance-changing features F1 , F2 are dielectric elements 20, Fig.12 shows an embodiment in which the impedance-changing features F1 , F2 are variations of the distance between the conductors 13 of the signal line 12. Specifically, the distance is locally reduced. In the embodiment of Fig.13, the impedance-changing features F1 , F2 are conductive elements 21 which are disposed in proximity to the signal line 12 on the carrier 11. These conductive elements can be made of the same material as the conductors 13 or of a different conductive material. Alternatively, the conductive elements 21 can as well be replaced by non-conductive elements made of a dielectric material with a large permittivity, with which similar impedance-changing features F1 , F2 can be realized, Furthermore, instead of the conductive elements 21 voids can be cut into the carrier 11 and/or intermediate layer 16 and/or cover 15 to realize impedance changing features F1 , F2. Fig.14 shows an embodiment in which the impedance-changing feature F1 is a variation of the distance between two portions of the signal line 12. In this case, the two portions are locally closer together.

[0055] The previous embodiments show a sensor arrangement 10 with only a single signal line 12. Fig.15, on the other hand, is an embodiment with three signal lines 12, 17, 18. Each of the signal lines 12, 17, 18 represents a detection region D1 -D3. The signal lines 12, 17, 18 can be connected to the control device 30 either in parallel or in series. If they are connected in parallel, the resulting reflection signal R may look like in Fig.16. Due to its limited length, each of the signal lines 12, 17, 18 gives rise to a flank as a characteristic feature C1 -C3. In Fig.15, a hand 51 is disposed in the first detection region D1 , wherefore only the first characteristic feature C1 has a significant time shift.

[0056] Fig.17 is an embodiment in which the impedance-changing features are changes in the cross-section of the conductors 13. In a first conductor portion 13.1 , which corresponds to a first detection region D1 , the cross-section is comparatively small. In a second conductor portion 13.2, which corresponds to a second detection region D2, the cross-section is somewhat larger. In a third conductor portion 13.3, which corresponds to a third detection region D3, the cross-section is even larger. Fig.18 is an embodiment in which the impedance-changing features are changes in the distance between the conductors 13. In a first conductor portion 13.1 , which corresponds to a first detection region D1 , the distance is comparatively large. In a second conductor portion 13.2, which corresponds to a second detection region D2, the distance is somewhat smaller. In a third conductor portion 13.3, which corresponds to a third detection region D3, the distance is even smaller.

[0057] As already mentioned with respect to Fig.15, several signal lines 12, 17, 18 can be connected to the control device 30 either in parallel or in series. Fig.19 shows a sensor arrangement with two signal lines 12, 17 that are connected in parallel to the interface 25. The routing of the individual conductors 13 is chosen to avoid any contact between them. Fig.20 is an embodiment with three signal lines 12, 17, 18 connected in parallel. In this case, it is not possible to avoid any overlap between the conductors 13. Therefore, a dielectric spacer 22 is interposed between the conductors 13 of the second signal line 17 and one conductor 13 of the first signal line 12 that overlaps with them.

[0058] Figs.21 and 22 show embodiments in which two signal lines 12, 17 or three signal lines 12, 17, 18, respectively, are connected in series to the interface 25. Figs. 23 and 24 show similar embodiments. In this case, however, the connections between the two signal lines 12, 17 or three signal lines 12, 17, 18, respectively, as well as the connections to the interface 25 are each made with interposed capacitors 23. The capacitance of the capacitors 23 can be chosen large enough that their impedance in the frequency range relevant for the detection and reflection signals S and R is negligibly small compared to the characteristic impedance of the signal lines 12, 17 or 12, 17, 18 respectively. For example, choosing a capacitance larger than 1 ,6nF results in impedance values for the capacitors 23 smaller than 10hm for frequencies larger than 0.1 GHz. Thus, the capacitors 23 allow for the lossless transmission of the detection signal S from the control device 30 via the interface 25 to the signal lines 12, 17 or 12, 17, 18, respectively, as well as of the reflection signal R from the signal lines to the control device, while hampering the transmission of any low frequency or direct current signals. In this way, the conductors 13 can optionally be used for an additional purpose that makes use of low frequency or direct current signals. For instance, they could be used as heating wires. For using the conductors for an additional purpose they should preferentially be connected to the respectively configured electronic circuit for that additional purpose with additional inductance elements interposed that hamper the transmission of the larger frequency signals S and R to that additional electronic circuit.

[0059] Instead of combining multiple signal lines 12, 17, 18 using direct serial or parallel connections of signal lines 12, 17, 18 as shown in Figs. 19 - 24, circuit elements as known in the art, e.g., power splitters, signal combiners, possibly in conjunction with circulators, directional couplers and similar, can be used to feed the detection signal S to multiple signal lines 12, 17, 18 from the control device 30 and also combine the reflection signals R from multiple signal lines 12, 17, 18 or alternatively receive the reflection signal R from each of the multiple signal lines (12, 17, 18) separately.

[0060] Fig.25 is an exploded view of a shell arrangement 70 with an eighth embodiment of a sensor arrangement 10. The sensor arrangement 10 is shown individually in Fig.26. It comprises a carrier 11 on which a connection interface 25 and a single signal line 12 are disposed. The signal line 12 defines a detection region D1 . For sake of simplicity, the signal line 12 is shown with a single conductor 13, but it could also comprise a pair of conductors 13 as shown in the previous embodiments. In Fig.26, the signal line 12 is shown to have a meandering layout with straight portions that are connected by curved portions. Fig.27 shows an enlarged detail of a straight portion that is outlined in Fig.26 by the oval dashed line. However, the signal line 12 could also have a “fine structure” wherein the straight portions are modified as a zigzag shape as in Fig.28 or with a meandering, sinusoidal shape as in Fig. 29.

[0061 ] The shell arrangement 70 is adapted to protect a protection space 75 on an internal side I of the shell arrangement 70, i.e. the shell arrangement 70 is disposed on an external side E of the protection space 75. In this case, a battery element 74 of a vehicle is received in the protection space 75, and the shell arrangement 70 protects the battery element 74 from below. Therefore, the external side E corresponds to the lower side and the internal side I corresponds to the upper side. As can be seen in the side views of Figs.30A-30D, the sensor arrangement 10 is disposed in close proximity of the inner wall element 71 or even in contact therewith. The outer wall element 72, on the other hand, is spaced from the sensor arrangement 10, at least in its undeformed state that is shown in Fig.30A.

[0062] Figs.30A-30C illustrate different stages of an impact process by a foreign object 55 like a stone. Fig.30A shows a situation before the impact as the foreign object 55 approaches the shell arrangement 70 from below, i.e. , from the external side E. Fig.31A shows a corresponding reflection signal R with a single characteristic feature C1. Since the influence of the foreign object 55 on the local impedance of the signal line 12 is negligible at this time, the measured timing t_mi of the characteristic feature C1 is identical to its reference timing t_ri. Fig.30B shows a situation as the foreign object 55 hits the outer wall element 72, which leads to a deformation of the outer wall element 72. A deformed region 72.1 , which touches the sensor arrangement 10, leads to a significant change of the local impedance. To some extent, the change may also be caused by the foreign object 55 itself. It gives rise to a delay of the measured timing t_mi with respect to the reference timing t_ri, as is shown in Fig.31 B. Therefore, the impact can be detected and may be recorded in an error memory of the vehicle. Also, a reflection feature P is shown, which may however not be detected reliably, depending on the signal-to-noise ratio. Fig.30C shows a situation after the impact, as the foreign object 55 moves away from the outer wall element 72. The deformation has disappeared since it was only an elastic deformation. Accordingly, the reflection signal shown in Fig.31 C is largely identical to the one before the impact and does not show any difference between the measured timing t_mi and the reference timing t_ri. However, by accessing the error memory, one can find out that the impact has occurred even if the outer wall element 72 has no visible damage. Fig.30D shows a situation after the impact in case of a plastic deformation of the outer wall element 72. The deformed portion 72.1 is still visible after the impact, and is also detectable by a time shift in the reflection signal R shown in Fig.31 D.

[0063] Fig.32 shows another embodiment of a sensor arrangement 10 that could also be used in a shell arrangement 70. In this case, a total of four signal lines 12, 17, 18, 24 are connected to the connection interface 25. Each signal line 12, 17, 18, 24 extends over a roughly rectangular portion of the carrier 11 and defines a detection region D1 -D4. This embodiment, similar to the embodiment shown in Fig.15, allows for a localization of an object 50, i.e., the deformed portion 72.1. Specifically, it can be determined in which detection region D1 -D4 an impact has occurred. Fig.33 shows a diagram with a reflection signal R for a situation without an impact as a solid line and a reflection signal R during an impact as a dashed line. Both curves show a series of falling flanks representing a first, second, third, and fourth characteristic feature C1 -C4. During the impact, the measured timing t_mi of the first characteristic feature C1 is delayed with respect to the corresponding reference timing t_ri. The second, third and fourth characteristic feature C2-C4 do not show any such time shift. Accordingly, the detection region D1-D4 in which the impact occurs can be identified.

[0064] It should be noted that the sensor arrangements 10 shown in Figs. 26 and 32 could be modified in various ways. Specifically, one or more impedancechanging features could be added, which would increase the number of detection regions D1-D4 and would allow for a more precise localization of the impact.

List of Reference Symbols

1 system 10 sensor arrangement 11 carrier

12,17,18,24 signal line

12.1 proximal end

12.2 distal end

13 conductor

13.1-13.3 conductor portion

14 lining

15 cover

16 intermediate layer

19 impedance element

20 dielectric element

21 conductive element

22 spacer

23 capacitor

25 connection interface

30 control device 50 object 51 hand 55 foreign object

60 steering wheel

60.1 surface

70 shell arrangement 71 inner wall element 72 cover element 72.1 deformed portion

74 battery element

75 protection space

A detection area C1-C4 characteristic feature D1-D4 detection region E external side F 1 -F3 impedance-changing feature

I internal side

P reflection feature

R reflection signal

S detection signal

Claims

1 . A system (1 ) for object detection by time-domain ref lectom etry, the system (1 ) comprising:

- a sensor arrangement (10) with at least one signal line (12, 17, 18, 24), which is disposed within a detection area (A), comprises at least one conductor (13) and is adapted to propagate an electromagnetic signal (S, R), wherein a local impedance of the signal line (12, 17, 18, 24) is influenceable by an object (50) in at least one detection region (D1-D4) associated with the signal line (12, 17, 18, 24), and wherein the sensor arrangement (10) comprises, for at least one signal line (12, 17, 18, 24), at least one impedance discontinuity corresponding to a local impedance change; and

- a control device (30) that is operatively coupled to the at least one signal line (12, 17, 18, 24), wherein the control device (30) is adapted to:

- apply (100) a time-dependent detection signal (S) to each signal line (12, 17, 18, 24) and receive a reflection signal (R) from the signal line (12, 17, 18, 24);

- identify (110) at least one characteristic feature (C1 -C4) in the reflection signal (R) and determine a measured timing of the characteristic feature (C1 - C4), wherein the characteristic feature (C1 -C4) is associated with a reflection by an impedance discontinuity of the signal line (12, 17, 18, 24),

- determine (120), for each characteristic feature (C1 -C4), a time shift between the measured timing and a reference timing of the characteristic feature (C1 - C4); and

- detect (130) an object (50) in at least one detection region (D1 -D4) based on the at least one time shift.

2. A system according to claim 1 , wherein the reference timing corresponds to a calibration measurement without an object (50) in any detection region (D1 -D4).

3. A system according to any of the preceding claims, wherein the control device (30) is adapted to identify (110) at least one characteristic feature (C1 -C4) by identifying a flank of the reflection signal (R), wherein the measured timing preferably corresponds to a timing of the flank.

4. A system according to any of the preceding claims, wherein at least one conductor (13) of a signal line (12, 17, 18, 24) is disposed on a dielectric carrier (11 ), and is preferably covered by a dielectric cover (15).

5. A system according to any of the preceding claims, wherein a plurality of signal lines (12, 17, 18, 24) are connected to the control device (30) and/or at least one signal line (12, 17, 18, 24) comprises a plurality of conductors (13).

6. A system according to any of the preceding claims, wherein the control device (30) is coupled to at least one conductor (13) of a signal line (12, 17, 18, 24) via a capacitor (23).

7. A system according to any of the preceding claims, wherein at least one characteristic feature (C1 -C4) is associated with a reflection by an impedance discontinuity at a distal end (12.2) of the signal line (12, 17, 18, 24).

8. A system according to any of the preceding claims, wherein at least one signal line (12, 17, 18, 24) is open terminated, short terminated, or terminated with an impedance element (19).

9. A system according to any of the preceding claims, wherein the sensor arrangement (10) comprises at least one impedance-changing feature (F1 -F3) that represents a local impedance change in the signal line (12, 17, 18, 24) and that is associated with a characteristic feature (C1 -C4) of the reflection signal (R), wherein each impedance-changing feature (F1-F3) separates two detection regions (D1 -D4) of the signal line (12, 17, 18, 24).

10. A system according to any of the preceding claims, wherein the control device is adapted to detect a plurality of characteristic features (C1-C4), and to determine (180) a detection region (D1 -D4) in which the object (50) is disposed based on the time shifts of the characteristic features (C1 -C4).

11 . A system according to any of the preceding claims, wherein the control device is configured to detect the presence of multiple objects in one or several detection regions (D1 -D4).

12. A system according to any of claims 9 to 1 1 , wherein at least one impedancechanging feature (F1 -F3) is a change of a cross-section of a conductor (13) of a signal line (12, 17, 18, 24) and/or a change of a distance between two conductors (13) of a signal line (12, 17, 18, 24) which comprises a plurality of conductors (13).

13. A system according to any of claims 9 to 12, wherein at least one impedancechanging feature (F1 -F3) is a local variation of a distance between two signal lines (12, 17, 18, 24) and/or a local variation of a distance between two portions of a signal line (12, 17, 18, 24).

14. A system according to any of claims 9 to 13, wherein at least one impedancechanging feature (F1 -F3) is a conductive object (21 ) disposed in proximity to a signal line (12, 17, 18, 24) and/or a dielectric object (20) disposed at least in proximity to a signal line (12, 17, 18, 24).

15. A system according to any of the preceding claims, wherein a plurality of signal lines (12, 17, 18, 24) is connected in parallel to the control device (30) and/or a plurality of signal lines (12, 17, 18, 24) is connected in series to the control device (30).

16. A system according to any of the preceding claims, wherein the sensor arrangement (10) is disposed in a vehicle interior component (60) and the detection area (A) corresponds to a surface (60.1 ) of the vehicle interior component (60).

17. A system according to any of the preceding claims, wherein a shell arrangement (70) of a vehicle comprises the sensor arrangement (10), which shell arrangement (70) has an external side (E) and an opposite internal side (I) on which a protection space (75) is located that is protected by the shell arrangement (70).

18. A system according to claim 17, being adapted to detect (130) an object (50) that is a deformed portion (72.1 ) of the shell arrangement (70).

19. A system according to any of the preceding claims 17 to 18, wherein the shell arrangement comprises an inner wall element (71 ) disposed on the internal side (I) relative to the sensor arrangement (10) and an outer wall element (72) disposed on the external side (E) relative to the sensor arrangement (10), wherein the system (1 ) is adapted to detect a deformed portion (72.1 ) of the outer wall element (72).

20. A system according to claim 17, wherein the outer wall element (72), in an undeformed state, is spaced from the sensor arrangement at least in a part of the shell arrangement (70).

21. A system according to any of the preceding claims 17-20, wherein the shell arrangement (70) is disposed on a bottom of the vehicle to protect the protection space (75) from below, wherein the protection space (75) is preferably adapted to receive a battery element (74).

22. A method for object detection by time-domain reflectometry, using:

- a sensor arrangement (10) with at least one signal line (12, 17, 18, 24), which is disposed within a detection area (A), comprises at least one conductor (13) and is adapted to propagate an electromagnetic signal (S, R), wherein a local impedance of the signal line (12, 17, 18, 24) is influenceable by an object (50) in at least one detection region (D1-D4) associated with the signal line (12, 17, 18, 24) and wherein the sensor arrangement (10) comprises, for at least one signal line (12, 17, 18, 24), at least one impedance discontinuity corresponding to a local impedance change; and

- a control device (30) that is operatively coupled to the at least one signal line (12, 17, 18, 24), wherein the control device (30):

- applies (100) a time-dependent detection signal (S) to each signal line (12) and receives a reflection signal (R) from the signal line (12);

- identifies (110) at least one characteristic feature (C1 -C4) in the reflection signal (R) and determines a measured timing of the characteristic feature (C1 -C4), wherein the characteristic feature (C1 -C4) is associated with a reflection by an impedance discontinuity of the signal line (12, 17, 18, 24),

- determines (120), for each characteristic feature (C1 -C4), a time shift between the measured timing and a reference timing of the characteristic feature (C1 -C4); and

- detects (130) an object (50) in at least one detection region (D1-D4) based on the at least one time shift.