Object detection system

Abstract

The present invention relates to an object detection system (1) comprising: an antenna device (3) including at least one antenna; a control device (2) adapted to control the antenna device (3) to transmit radio frequency detection signals (D1, D2) and to detect an object based on a radio frequency response signal received by the antenna device (3); and at least one passive reflector (10) adapted to at least partially reflect the detection signals (D1, D2), the reflector (10) comprising a metamaterial having a plurality of unit cells, the metamaterial comprising at least one dielectric substrate layer and a conductive structure layer disposed thereon, wherein the reflector (10) has a frequency-dependent reflectivity, wherein the control device (2) is adapted to detect the object based at least partially on the spectrum of the response signal. In order to provide an effective means for reliable radar-based object detection, the present invention provides at least one of the at least one reflector (10) having an absorption region (A1, A2) smaller than the frequency bandwidth of the detection signal (D1, D2), and the reflectivity of the reflector (10) decreases relative to the adjacent region in the absorption region, wherein the absorption region is within the frequency bandwidth, and the control device (2) is adapted to detect the object at least in part based on the effect of identifying the absorption region on the spectrum of the response signal.

Description

Technical Field

[0001] This invention relates to an object detection system that uses radio frequency detection signals. Background Technology

[0002] Radar is known to be used to monitor certain areas, such as the interior of a vehicle or a room in a building. This includes detecting the presence and possible location of people. In some cases, a single transmitter and a single receiver can be used. When the scene to be observed is complex, higher resolution sensors are used, such as MIMO radar systems with multiple transmit and receive antennas. One problem with radar sensing applications is that it is often difficult to achieve sufficient coverage of the area or space to be monitored (e.g., the interior of a room or car). Depending on the setup, a person may be at least temporarily outside the sensor's field of view. One reason could be that the radiation emitted by the sensor is weaker in certain areas than in others. Additionally, a person may be at least partially obstructed by a static or moving object, and the corresponding response (reflection and / or Doppler characteristics) is too weak. Therefore, the sensor will not be able to detect a person in some areas of the scene. One way to avoid this problem is to work with multiple sensors distributed throughout the room and operating simultaneously, which hopefully eliminates any "blind spots." However, this is expensive and requires sensor fusion in a central processing unit.

[0003] Aubry et al., in the October 2021 issue of IEEE Transactions on Vehicular Technology, Volume 70, No. 10, entitled "Reconfigurable Smart Surfaces for N-LOS Radar Surveillance,"... Reconfigurable Intelligent Surfaces for N-LOS Radar Surveillance The concept of sensing using reconfigurable (i.e., switchable or programmable) reflective surfaces is disclosed. These reflective surfaces are electronically controlled and require various active components.

[0004] A review of frequency-selective surfaces by Rana Sadaf Anwar et al. in MDPI Applied Sciences, 2018, Volume 8, Issue 9. Frequency Selective Surfaces: A Review The reflective surface, known as the frequency selective surface (FSS), was disclosed.

[0005] Fathnan et al., in the 2020 issue of "Acta Physica Sinica, Vol. 53, Applied Physica Sinica" (J. Phys. D, Appl. Phys.), published a paper titled "Bandwidth confinement and synthesis method for single-resonance ultrathin metasurfaces" (No. 495304). Bandwidth limit and synthesis approach for single resonance ultrathin metasurfaces The design of a reflective surface (called a reflective metasurface) with multiple unit cells, as well as a specific synthesis technique for designing the dispersion of each unit cell, are disclosed in the paper.

[0006] US 2016 / 0359235 A1 discloses a holographic radar reflector comprising a surface including a plurality of substantially first wavelength-scale patterns along one or more portions of the surface, wherein the holographic radar reflector is non-mirror, wherein the first wavelength-scale patterns have amplitude- or phase-dependent variations, and wherein the holographic radar reflector and the first wavelength-scale patterns are configured to reflect electromagnetic radiation emitted from a fixed feed point in varying directions according to portions of the surface that reflect electromagnetic radiation.

[0007] US 2022 / 0393362 A1 discloses a detection device for a system comprising an enclosed space having a metallic environment, the enclosed space containing at least one object disposed of a wave transmitting / receiving identification element, wherein the detection device includes an identification reader adapted to exchange messages with the identification element via at least one wave transmitting / receiving antenna adapted to be mounted in the enclosed space to detect the presence of the identification element. At least one metasurface is adapted to be mounted in the enclosed space and configured to reflect waves originating from the antenna and intended to be received by the identification element according to at least one first-chosen law, and to reflect waves originating from the identification element and intended to be received by the antenna according to at least one second-chosen law. Summary of the Invention

[0008] Therefore, one object of the present invention is to provide an effective means for reliable radar-based object detection.

[0009] The problem is solved by the object detection system according to claim 1.

[0010] This invention provides an object detection system. More specifically, this is a radar-based object detection system. "Detection" can refer to determining the presence of an object. It can also refer to determining the position and / or velocity of an object. Here and below, the term "object" also includes living organisms, such as animals or humans. In the case of living organisms, detection can also refer to vital sign monitoring, i.e., determining whether vital signs can be detected, and / or determining the current value of a vital sign (e.g., heart rate or respiratory rate).

[0011] The system includes an antenna arrangement comprising at least one antenna. According to one embodiment, the antenna arrangement may include multiple antennas, but using a single antenna is within the scope of the invention. Each antenna may also be referred to as a radar antenna and is configured to transmit and / or receive electromagnetic signals having a radar frequency or radio frequency. In the context of the invention, "radio frequency" can specifically be between 9 GHz and 170 GHz. In particular, each antenna may be a simple non-directional antenna configured to transmit signals in all directions and / or receive signals from all directions. For example, each antenna may be a patch antenna on a printed circuit board.

[0012] Furthermore, the system includes a control device adapted to control the antenna device to transmit a radio frequency (RF) detection signal and to detect an object based on an RF response signal received by the antenna device. The detection signal has an RF frequency, which includes the possibility that it includes multiple RF frequencies. Specifically, this can be at least one frequency selected from the 57-64 GHz band, the 79-85 GHz band, or the UWB band. It should be understood that the control device is suitably connected to the antenna device to generate the detection signal, and it includes suitable components required to generate the detection signal, such as an HF generator. Furthermore, the control device is adapted to detect an object based on a response signal received by the antenna device, meaning that it is electrically connected in a suitable manner. Preferably, the response signal is generated by at least one reflection of the detection signal. Optionally, the control device may be adapted to process, analyze, and / or evaluate the response signal. Although “one” detection signal and “one” response signal are mentioned herein, this should be understood to refer to at least one signal, i.e., if the antenna device includes multiple antennas, different detection signals can be transmitted from different antennas, and generally different response signals can be received by different antennas. The control device includes hardware components but may be partially implemented in software. As mentioned above, "detecting an object" can refer not only to the presence of an object, but also to its position, velocity, and / or other attributes. Specifically, the control device is suitable for detecting objects within a detection space. The detection space can be the interior space of a building or vehicle, but it can also be an external space.

[0013] The system also includes at least one passive reflector adapted to at least partially reflect the detection signal. This reflector comprises a metamaterial having multiple unit cells, including at least one dielectric substrate and a conductive structural layer disposed on top of it, thereby giving the reflector a frequency-dependent reflectivity. The reflector is adapted to at least partially reflect the detection signal, meaning it has significant reflectivity over the frequency range of the detection signal. On one hand, "partially" means that a portion of the detection signal may not be directed towards the reflector and therefore cannot be reflected. Furthermore, a portion of the radio frequency radiation may not be reflected but rather absorbed and / or transparent. According to this embodiment, the reflector can also reflect radiation that is not directly derived from the antenna device, but has already been reflected, for example, by the reflector itself, by another reflector, or by any other object (such as the object to be detected). The reflector is passive, meaning it requires no power supply and cannot be switched on or off or controlled. Therefore, the optical properties of the reflector, particularly its reflectivity, are fixed. The reflector comprises a metamaterial having multiple unit cells. The term "metamaterial" means that the unit cells representing the material structure are smaller than a specific wavelength. In this case, the relevant wavelength is given by the detection signal. Therefore, strictly speaking, a metamaterial is a metamaterial used for detecting at least a portion of a signal, preferably for detecting the entire signal. It should be understood that unit cells may not be clearly separated from each other by any physical features. Instead, a metamaterial can be conceptually divided into unit cells. Although other configurations are conceivable, it is preferred that the reflector has unit cells arranged along its surface in a Cartesian or rectangular pattern. As will be explained in more detail below, although all unit cells preferably have the same dimensions, their internal structures can be identical or different. Furthermore, although the rectangular pattern allows for defining two orthogonal directions along which the unit cells are arranged, the surface of the reflector need not be planar, but can be curved and / or angled. In this case, two locally orthogonal directions can be defined, but each direction can be oriented differently at different locations on the reflector.

[0014] The metamaterial comprises at least one dielectric substrate and a conductive structural layer disposed on its upper side. It can be said that the substrate and structural layers are disposed above each other and extend laterally, where the terms "above" and "lateral" should not be interpreted in any restrictive way as the orientation of the metamaterial relative to the direction of gravity. Rather, these terms simply refer to the arrangement of the layers within the metamaterial. Generally, "lateral" refers to the direction in which the layer extends. As mentioned above, the metamaterial need not be planar, but can be curved and / or angled, so "lateral" can refer to different absolute directions depending on its location within the metamaterial. The conductive layer is structured, meaning it is not a single, uninterrupted object, but rather perforated and / or comprising multiple individual elements arranged in a single layer. More specifically, the conductive layer can be said to be laterally structured. The structure is preferably smaller than the minimum wavelength of the detected signal.

[0015] Highly preferred is that the structural layer is at least partially or primarily metallic. That is, preferably, the structural layer comprises at least one metal, such as copper or silver. In this case, it is also referred to as a metallic structural layer. Optionally, the conductive layer may also contain semi-metallic or non-metallic components, for example, as part of an alloy or as part of a metallic ink comprising metal particles and a binder. It can be manufactured using methods such as screen printing, inkjet printing, reverse offset printing, etching of aluminum laminates, or similar methods. Generally, the structural layer consists of at least one component with a conductivity of at least 10. 2 Made of a material with a conductivity of at least 10 S / m, and preferably containing a conductivity of at least 10 6 The metal has a conductivity of S / m. Preferably, the thickness of the structural layer is between 5 μm and 50 μm, more preferably between 10 μm and 25 μm. On the other hand, the dielectric substrate layer is made of at least one material that can be considered a poor conductor or insulator. Such material has a conductivity of less than 10 S / m, less than 0.1 S / m, or less than 10 S / m. -3 S / m. The substrate layer can be made of dielectric materials commonly used in flexible printed electronics, such as polyethylene terephthalate (PET), polyimide (PI), polyetherimide (PEI), polyamide (PA), and the like. These materials are suitable because they have very low loss to electromagnetic radiation. Optionally, the substrate layer can be composed of different materials forming sublayers. Compared to the structural layers, the substrate layer is typically a solid, non-perforated body without lateral structures. The thickness of any substrate layer is typically significantly greater than the thickness of the structural layers. For example, the thickness of the substrate layer can be between 0.05 mm and 2 mm, or between 0.1 mm and 1 mm. The (total) thickness of the metamaterial can preferably be between 50 μm and 2 mm. It should be understood that this thickness is negligible compared to the size of any location or object where a reflector can be mounted.

[0016] Due to the properties of metamaterials, reflectors exhibit frequency-dependent reflectivity. Generally, "reflectivity" represents the amount of reflected radiation for a given incident radiation. More specifically, this can be the square of the Fresnel reflection coefficient, which is the ratio of the amplitude of the reflected field to the incident field. For normal reflectors, such as unstructured metallic surfaces, this reflectivity is either frequency-independent or has negligible frequency dependence. That is, reflectivity may depend on the angle of incidence but not on the frequency or wavelength of the incident wave. This differs for the reflector in the system of this invention. Here, reflectivity is significantly frequency-dependent. Preferably, the metamaterial is designed such that the minimum reflectivity within the frequency range of the detected signal is less than 60%, less than 40%, or less than 20% of the maximum reflectivity within that frequency range. It is understood that the reflectivity coefficient of the reflector is also frequency-dependent. Due to the frequency-dependent reflectivity, the spectrum of the reflected signal differs from the spectrum of the incident signal (e.g., the detected signal). Reflector-specific variations in the spectrum can also be described as the "spectral response" of the reflector. Due to the frequency-dependent reflectivity, the reflector or metamaterial can also be referred to as a dispersion-controlled metasurface. Metamaterials can be designed (or “customized”) to have a desired specific frequency-dependent reflectivity.

[0017] The design of such or similar metamaterials has been described previously, and the influence of various cell design parameters on the reflective behavior of the reflectors has been extensively studied. For example, information on this topic can be found in the aforementioned publications by Fathnan et al. and Anwar et al.

[0018] The control device is adapted to detect objects based at least in part on the spectrum of the response signal. Specifically, the spectrum can be the frequency-dependent strength or frequency-dependent amplitude of the response signal. Any reflected signal not reflected by a reflector (but, for example, by the object to be detected) should have a spectrum approximately the same as the spectrum of the detected signal. However, if the reflected signal originates from a reflector, the spectrum changes significantly. Therefore, if such a reflected signal arrives at the antenna device as part of the response signal, its contribution to the response signal can be distinguished from other signals. This is due to the characteristic spectral response of the reflector. Since reflectivity is frequency-dependent, some parts of the reflected signal are reduced compared to other parts. The reflected signal can contribute to the response signal directly or indirectly. In other words, the reflected signal can be received directly by the antenna device, or indirectly, for example, after it has undergone at least one additional reflection. If the reflected signal originates from a reflector, the contribution of the reflected signal can be distinguished from other signals. In other words, it can be distinguished from any part of the response signal that does not originate from that reflector. This distinction is based on differences in the spectrum. It can also be said that if the reflected signal originates from a reflector, the contribution of the reflected signal to the response signal is identifiable within the response signal. This includes the possibility of a zero contribution, i.e., if the response signal does not contain any part produced by the reflection of the corresponding reflector.

[0019] It is also possible to distinguish specific propagation paths within a room or vehicle from other paths. Using appropriate signal processing techniques, it is possible to determine whether a reflector with its spectral response is part of the propagation path. Typically, the presence or absence of characteristic signals can be used to infer information about the presence of objects such as people, and preferably about the location of the objects. Any information about location can be approximately precise. In some cases, this may only include information about the object being in a certain part or area of ​​a room or vehicle. In other cases, this may refer to the two-dimensional or even three-dimensional coordinates of the object.

[0020] According to the invention, at least one reflector has an absorption region smaller than the frequency bandwidth of the detection signal, and in this absorption region, the reflectivity of the reflector decreases relative to adjacent regions. The absorption region is within the frequency bandwidth, and the control device is adapted to detect an object based at least in part on the effect of identifying the absorption region on the spectrum of the response signal. The absorption region is a frequency region or frequency range with low reflectivity compared to lower and higher frequencies. Although the term "absorption region" is used to indicate that the reduction in reflectivity may be due to absorption, it could also be due to transparency, i.e., radiation passing through the metamaterial. Not limited to this interpretation, the center of the absorption region may represent the resonant frequency of the structural layer. The metamaterial can be specifically designed for the absorption region within a specific frequency range. This absorption region then represents a "signature" or "fingerprint" of the reflector that is easily identifiable within the response signal. In the case of several reflectors, each reflector may have a different absorption region. The absorption region is within the operating bandwidth. In other words, the detection signal has a frequency band or frequency range of the operating bandwidth, and the absorption region is within that frequency band or frequency range. Preferably, the minimum reflectivity within the absorption region is less than 60%, less than 40%, or less than 20% of the maximum reflectivity in adjacent regions.

[0021] The control device is adapted to detect an object based at least in part on identifying the effect of an absorption region on the spectrum of the response signal. As described above, the reflected signal originating from the reflector has a characteristic contribution to the response signal. The absorption region affects the reflected signal, and therefore it affects the response signal. Thus, the effect of the absorption region within the spectrum of the response signal can be identified. By identifying the effect of the absorption region, the control device can determine whether at least a portion of the response signal originates from the reflector. As described above, if the response signal does not contain a contribution from the corresponding reflected signal, the effect can be zero. According to this embodiment, the absence, presence, and / or intensity of such an effect can indicate the presence and / or location of the object.

[0022] It should be understood that determining the position of an object requires information about the position of the reflector relative to the antenna device, and preferably also information about the geometric configuration of the detection space (e.g., a room in a building or the interior of a vehicle) where the object to be detected is located. Such information can be provided explicitly or implicitly to the control device. The reflector can also be considered as a reference marker in the scene. Preferably, the antenna device and at least one reflector are fixed relative to each other. In some embodiments, the reflector can be moved within a limited range without affecting the object detection result. In other embodiments, the reflector can be moved relative to the antenna device, and the control device can receive information about the current position of the reflector. Information about the position of each reflector and / or the geometric configuration of the detection space can be stored in the control device or in memory accessible to the control device. The control device can be adapted to detect objects at least partially based on the position of at least one reflector relative to the antenna device and / or at least partially based on the geometric configuration of the detection space.

[0023] The object detection system of this invention is suitable for a variety of applications. While the system can be used in enclosed environments such as rooms or vehicle interiors, it can also be used in open environments. Possible applications include, but are not limited to, in-vehicle sensing, vital sign monitoring, D-call, smart homes, indoor monitoring in elderly care facilities, activity monitoring in hospital rooms, people counting, occupancy detection and unattended child detection in cars and school buses, monitoring of office environments, and classification of moving objects in indoor or vehicle environments. This invention can also be used for surveillance in urban areas (e.g., near bus stops, train stations, or other public transportation infrastructure), and for burglar alarms, such as burglar alarms for external (outdoor) applications, such as in private gardens, public buildings, industrial areas, etc. Due to its small thickness, the reflector can be easily integrated into wall structures, such as wallpaper or linings inside vehicles. The passive nature of the reflector also facilitates integration, eliminating the need for power or data connections. Therefore, even if the reflector covers a large area, it can be implemented at low cost and is significantly easier to integrate than additional radar sensors.

[0024] Optionally, the metamaterial may include at least one additional layer. For example, a metallic substrate may be disposed below the base layer, i.e., opposite to the structural layer. Like the base layer, the substrate is preferably solid and uninterrupted. Not limited to this function, the substrate may also function to eliminate transport through the metamaterial. The substrate may be made of the same material as the structural layer or a different material. Its thickness may be between 5 μm and 100 μm. Another option is that a dielectric protective layer may be disposed above the structural layer. The protective layer is typically solid and uninterrupted, and covers the entire structural layer. In locations where no structural layer is present, the protective layer may be in direct contact with the aforementioned base layer. It may be made of the same material as the base layer or a different material. Its thickness may be, for example, between 20 μm and 100 μm.

[0025] The detection signal can be a continuous wave signal. In this case, the detection signal can be characterized by a single frequency and correspond to a sinusoidal oscillation. To identify whether the response signal is the result of metamaterial reflection, a sequence of continuous wave signals with different frequencies must be used. In this embodiment, although it may be possible to derive any range information from the analysis of the response signal depending on the number and arrangement of antennas, this may not be feasible. Even without range information, motion can be detected by analyzing the Doppler frequency shift of the response signal. According to another embodiment, the detection signal is a frequency-modulated signal, particularly a frequency-modulated continuous wave (FMCW) signal. Typically, the frequency of the signal is changed periodically, for example, by applying a linear chirp (linear frequency change). However, nonlinear frequency changes and non-periodic frequency changes can be applied. In this embodiment, range information can be derived from a comparison of the detection signal and the response signal. Simultaneously, motion can be detected by analyzing the range as a function of time. According to another embodiment, the detection signal can be a pulse signal. As with frequency-modulated signals, range information can be derived from the analysis of the response signal, essentially by analyzing the delay between the emission of the pulse and the detection of the reflected pulse. Various types of pulses can be used, such as rectangular, sinusoidal, Gaussian, or similar pulses. As described above, if the antenna device includes multiple antennas, detection signals can be applied to several antennas, in which case different detection signals can be applied to each antenna. For example, detection signals applied to different antennas may differ in time. It should be understood that motion detection also allows for the monitoring of vital signs. In some embodiments, the control device may be adapted to determine the position of an object by combining range information retrieved from the response signal with an identification of the effect of the absorption region on the spectrum of the response signal.

[0026] For example, if a pulse signal is used, the antenna device may include a single antenna that transmits a detection signal and receives a response signal. However, most preferably, the antenna device includes at least one transmitting antenna and at least one receiving antenna, and the control device is adapted to control each transmitting antenna to transmit a detection signal and to detect an object based on the response signal received by each receiving antenna. Typically, all antennas are offset from or spaced apart from each other to reduce the risk of electromagnetic interference. As mentioned above, the control device can generate different detection signals using different transmitting antennas (if present). It should be understood that different response signals are typically received by different receiving antennas (if present).

[0027] According to one embodiment, the detection system includes a building in which an antenna device and at least one reflector are installed. Specifically, they may be installed in the same room. The antenna device may be mounted on a wall, pillar, or ceiling, possibly in a recess, and shielded from view by a radiation-transparent cover. The reflector may also be mounted on a wall, pillar, ceiling, floor, or window. Due to its flat shape, the reflector may be integrated into a surface, such as integrated into or hidden behind wallpaper. Control equipment may also be installed in the same building, possibly in the same room, such that the entire object detection system is installed in the building. In this case, it can also be said that the building includes the object detection system. Alternatively, the control equipment may be located in different locations and connected to the antenna device via a wireless or wired connection. The system may be specifically designed to detect people in a building or room, which may include locating people and / or monitoring vital signs. According to another embodiment, the detection system includes a vehicle in which an antenna device and at least one reflector are installed. The antenna device may be mounted on or in the dashboard, side wall, vehicle seat, or ceiling. Again, the antenna device may be shielded from view by a radiation-transparent cover. The reflector may be mounted, for example, on a side wall, vehicle seat, ceiling, floor, or window. Each reflector can be easily integrated into the surface, such as into or behind a trim panel. It can also be integrated into the seat cushion. The control equipment will also be installed in the same vehicle; that is, the entire object detection system is installed within the vehicle. In this case, it can also be said that the vehicle includes the object detection system. This system can be specifically used for occupancy detection, but it can also be used for vital sign monitoring, for example, to detect potential health problems of the driver.

[0028] According to one embodiment, at least one of the at least one reflector is configured to provide a reflection path between the antenna device and an obstruction area where the inserted object is shielded from the antenna device, such that the object in the obstruction area can be detected by a control device. Here and below, the phrase "at least one of the at least one reflector" refers to "the reflector" in an embodiment with only one reflector, and to "at least one of the reflectors" in the case of multiple reflectors. The obstruction area cannot be directly accessed by the antenna device. In other words, it is not within the line of sight of the antenna device. Strictly speaking, if the area is not within the line of sight of any transmitting antenna and / or any receiving antenna, then the area is obstructed. In this case, signals cannot be directly transmitted to the obstruction area and / or reflected signals from the obstruction area cannot be directly received. Therefore, without a reflector, the object in the obstruction area cannot be detected. The obstruction area may be caused by a stationary object such as a wall, pillar, a piece of furniture, a vehicle seat, or the like. The position, orientation, and configuration of the reflector are adapted to provide a reflection path between the antenna device and the obstruction area. In other words, radiation from the antenna device can be reflected into the obstruction area and / or radiation from the obstruction area can be reflected back to the antenna device. Therefore, the control device can detect objects in an obstructed region. On one hand, the object's position can be partially deduced using "conventional" techniques, such as evaluating the signal's time of flight or phase difference. Furthermore, due to the frequency-dependent reflectivity of the reflector, objects in an obstructed region can be identified by the spectrum of the response signal. This can, for example, resolve the ambiguity between an obstructed region and an unobstructed region corresponding to a similar time of flight of the signal. The control device can preferably be adapted to determine whether an object is in an obstructed or unobstructed region based on the effect of the absorption region on the spectrum of the response signal.

[0029] In another embodiment, the control device is adapted to detect an object inserted between an antenna device and at least one of the at least one reflector based on the effect of the inserted object on the spectrum of the response signal, the effect arising from the influence of the inserted object on the absorption region in the spectrum. An object inserted between the antenna device and the reflector can also be referred to as (partially or completely) hidden from the reflector. In the absence of an object, the reflector is in the line of sight of the antenna device. Therefore, the corresponding metamaterial reflection results in a relatively strong contribution to the response signal, and thus the effect of the absorption region is also strong. On the other hand, if an object is inserted between the reflector and the antenna device, less radiation reaches the reflector and less radiation travels from the reflector to the antenna device, so the effect of the absorption region is weak or nonexistent. Therefore, the spectrum of the response signal will be different overall. This embodiment can be further developed to employ multiple reflectors with different reflection characteristics and different absorption regions. Not only can the hiding of different reflectors be identified, but the simultaneous hiding of two (or more) reflectors can also be identified. Based on this information, the position of the object can be inferred with greater accuracy.

[0030] Reflectors can include "homogeneous" metamaterials, since all the unit cells of the metamaterial are identical. However, a single reflector can also include regions with different properties. According to such an embodiment, at least one of the at least one reflector includes multiple blocks, at least two blocks being constructed differently such that they have different frequency-dependent reflectivities. Each block includes multiple unit cells and can extend laterally in two directions. Although each block can include the same unit cells, at least two blocks are constructed differently, i.e., they include different unit cells. Different structures result in different frequency dependencies of reflectivity. For example, two blocks may have different absorption regions. Specifically, a reflector can include several types of blocks (e.g., two or three), with multiple blocks belonging to each type. Different types of blocks can be alternated; for example, a checkerboard pattern can be used in the case of two types. If radiation, such as that of a detection signal, simultaneously radiates several types of blocks, the reflected radiation will have a spectrum affected by the characteristics of all involved types. For example, the spectrum may show multiple absorption regions.

[0031] Preferably, at least one of the at least one structural layer extends laterally along a first direction and a second direction perpendicular to the first direction, and includes a plurality of conductive resonators, each unit cell including one resonator, and every two adjacent resonators of the structural layer are spaced apart along at least one of the first and second directions. The term "laterally" has been explained above. In the case of a planar reflector, the first and second directions represent linear axes. In the case of a non-planar shape (e.g., a curved shape), the two directions may be locally defined, where they are orthogonal. However, depending on the location within the reflector, at least one of these directions may have a different orientation relative to an absolute Cartesian coordinate system. The conductive resonators are structures within the structural layer. Therefore, they are also preferably metallic, i.e., they comprise at least one metal and may be composed primarily of metal. Since the resonators are spaced apart from each other, they represent a spatially and electrically isolated structure. Each unit cell includes one resonator, preferably exactly one resonator. However, the resonators may not be coherent, but comprise multiple separate sections, which can alternatively be considered as individual resonators. The term "resonator" should not be interpreted in any limiting way. However, each resonator may have at least one resonant frequency. If all resonators have the same shape and size, the resonant frequency can be the center of the absorption region. By adjusting the size of the resonators, the reflection, absorption, and / or transmission characteristics of the metamaterial can be adapted to various requirements. Furthermore, the layout of individual resonators affects the phase of radiation during reflection. That is, the geometry and size of the reflector affect the phase difference between the incident and reflected waves. This can also be used to influence the reflection behavior of the reflector. In some embodiments, the lateral dimension of each cell along each of the first and second directions is between 250 μm and 10 mm or between 500 μm and 5 mm. The dimensions along the two directions can be the same or different. The maximum lateral dimension of each resonator is preferably less than 2 mm, and the minimum lateral dimension of each resonator is preferably at least 50 μm. However, it should be understood that, given that for metamaterials, each size of the cell must be smaller than the wavelength, the size limitations also depend on one or more frequencies of the detected signal. The shape of the resonators is not limited to the scope of this invention. Possible examples include linear, hexagonal, rectangular, triangular, T-shaped, H-shaped, cross-shaped, C-shaped, crescent-shaped, circular, star-shaped, or other shapes. Although the lateral dimensions of the unit cell are small, the lateral dimensions of the reflector can be quite large. For example, the lateral dimensions of the reflector can be at least 1 cm, at least 10 cm, or at least 50 cm, while the area or cross-section of the reflector can be at least 1 cm². 2 At least 100cm 2 Or at least 2500cm 2 In some embodiments, the lateral dimension can be even greater than 1m and / or the area of ​​the reflector can be greater than 1m². 2 .

[0032] In some embodiments, each resonator is made of a single material or a mixture of materials, such as conductive ink. In this case, the conductivity (i.e., specific conductivity) of all portions of the resonator is the same. According to another embodiment, at least one of the at least one resonator includes multiple portions with different conductivity. For example, one portion may be metallic and therefore have high conductivity, while another portion may include graphite and therefore have relatively low conductivity. Including such a low conductivity region can significantly increase absorption around the resonant frequency, but it may also affect the resonant frequency itself. By increasing absorption, the aforementioned absorption region can be better distinguished from adjacent frequency regions.

[0033] As already mentioned, reflectors can be easily integrated into various objects. In some embodiments, it can be virtually invisible to the naked eye. According to such an embodiment, the substrate layer is transparent to visible light, and the structural layer includes a transparent structure comprising a plurality of line elements with a maximum width of 1.5 μm. The substrate layer is transparent to visible light, which can specifically refer to light with wavelengths between 380 nm and 780 nm. It should be understood that suitable transparent dielectric materials exist, such as polymer materials. However, since the structural layer must be conductive and preferably metallic, it is made of a material that is opaque in itself. However, in this embodiment, the structural layer is divided into fine line elements, so narrow that they are invisible or virtually invisible to the naked eye. Preferably, each resonator is a transparent structure. While the overall size of such a transparent resonator can be the same as that of a non-transparent resonator, it is composed of the aforementioned line elements. Adjacent line elements can be separated by a spacing of similar width, for example, a maximum of 1.5 μm. For example, if the overall shape of the resonator is a square with a side length of 100 μm, this can be achieved by 33 line elements arranged adjacent to each other or by a single zigzag line element. Preferably, the individual transparent structure of the transparent resonator can have a minimum size of at least 50 μm or at least 100 μm. The transparent reflectors described herein can be integrated into windows, such as room windows or car windows.

[0034] According to a preferred embodiment, at least one of the at least one reflector is a flexible sheet. In other words, the corresponding reflector can be bent without breaking or tearing. On the one hand, flexibility reduces the risk of damaging the reflector during installation. On the other hand, this allows the reflector to be integrated into a variety of surfaces with various shapes. For example, it can be integrated into a planar surface such as a wall in a building, and into a curved surface such as a pillar. It should be understood that the thin structure of the metamaterial facilitates flexible deformation. Furthermore, the base layer can be made of, for example, a polymeric material that allows deformation without damage. In addition, the reflector may include at least one slit to facilitate bending and / or folding it into a desired shape.

[0035] Metamaterials allow for reflective behavior that is impossible with other materials. As mentioned above, the layout of a single resonator affects the phase of the radiation during reflection. By adjusting the phase response of multiple resonators, the direction of the reflected radiation can be influenced and, at least to some extent, customized. One embodiment provides that, for at least one of the at least one reflector, at least one dimension of a resonator varies along one of a first direction and a second direction for different unit cells, thereby adapting the reflector to anomalous reflection, where the absolute values ​​of the incident angle and the reflection angle are different. By changing the size of the resonator from unit cell to unit cell, the phase of the reflected radiation is affected. Such structures are sometimes referred to as gradient metasurfaces. This is described, for example, in the aforementioned article by Fathnan et al. Thus, so-called anomalous reflection can be achieved, where the absolute values ​​of the incident angle and the reflection angle differ from those in the normal reflection process. Instead, the absolute values ​​are different, although the reflection angle still depends on the incident angle. In some embodiments, the reflection angle may be frequency-dependent, while in other embodiments, it is frequency-independent. According to one embodiment, at least one dimension of the resonator varies linearly along at least one of the first and second directions. For example, the corresponding dimension decreases by about 5 μm from one unit cell to the next. Optionally, this linear change can be performed periodically. This linear change results in a single reflection angle corresponding to a single incident angle. One possible application of anomalous reflection is when the orientation of a conventional reflector makes it impossible to integrate into surfaces such as walls, vehicle ceilings, etc., when reflection is required. Anomalous reflection can generate a reflection angle that is at least somewhat independent of the reflector's orientation.

[0036] From one unit cell to the next, the resonator has a variety of possible variations, all of which can lead to beneficial reflection behavior. According to one embodiment, for different cells, at least one dimension varies non-linearly along one of the first and second directions, thereby adapting the reflector to reflect a single incident angle corresponding to multiple reflection angles. In other words, a parallel beam of incident radiation will not result in a parallel reflected beam. This can be used to focus or diffuse reflected radiation, i.e., to produce converging or diverging radiation. Specifically, a set of parallel beams can be reflected and thus spread within a certain angular range. This can be used to efficiently radiate large areas, even if the detected signal strikes the reflector as a narrow beam and / or the reflector has a small surface area. The corresponding reflector can be referred to as a planar multi-directional reflector or even a planar omnidirectional reflector.

[0037] To achieve this invention, it is sufficient for the reflector to consist of just one base layer and one structural layer. However, the structure can be extended to include more layers. According to such an embodiment, at least one of the at least one reflector includes multiple base layers, with one structural layer disposed on the upper side of each base layer. Thus, except for the uppermost layer, each structural layer is inserted between two base layers, one below and one above. In those regions where the structural layers are interrupted, such as between resonators, the base layers can be in direct contact with each other. The structural layers can have the same structure or different structures. For example, resonators of several structural layers can be disposed on top of each other and considered as part of a single unit cell. In this case, the unit cell extends over several structural layers and several base layers. The reflection behavior may be affected by each additional structural layer or each additional resonator.

[0038] It should be understood that although reflectors can be hidden behind transmissive shields such as headliners, trim panels, seat covers, and wallpaper, the presence of the shield can affect the reflector's frequency response. For example, compared to a "bare" reflector (i.e., without a shield), a shield can, for example, shift the resonant frequency and / or the aforementioned absorption region, reducing variations in amplitude or similar parameters. Therefore, when designing metamaterials (i.e., individual cells and entire arrays), the presence of the shield material must be considered in the model. However, if the properties of the shield material are known, its potential effects can be compensated for through the design of the metamaterial. Similarly, the presence of a protective layer can be considered when designing metamaterials.

[0039] The present invention also relates to a passive reflector that can be used in the object detection system of the present invention. The reflector is adapted to at least partially reflect radio frequency signals and comprises a metamaterial having multiple unit cells, the metamaterial comprising at least one dielectric substrate layer and a conductive structural layer disposed on its upper side, thereby giving the reflector a frequency-dependent reflectivity. The reflector has an absorption region, wherein the reflectivity of the reflector decreases relative to adjacent regions. Preferred embodiments of the reflector correspond to those embodiments of the object detection system of the present invention.

[0040] The present invention also relates to an object detection method using an object detection system, comprising: -An antenna device, comprising at least one antenna; - Control equipment; and - At least one passive reflector comprising a metamaterial having multiple unit cells, the metamaterial comprising at least one substrate layer and a conductive structural layer disposed on its upper side, thereby the reflector having a frequency-dependent reflectivity.

[0041] According to this method, a control device controls an antenna device to transmit a radio frequency detection signal, a reflector at least partially reflects the detection signal, and the control device detects an object based on a radio frequency response signal received by the antenna device, wherein the control device detects the object based on the spectrum of the response signal. According to the invention, at least one of the at least one reflector has an absorption region smaller than the frequency bandwidth of the detection signal, and wherein the reflectivity of the reflector decreases relative to adjacent regions, wherein the absorption region is within the frequency bandwidth, and the control device detects the object at least partially based on identifying the effect of the absorption region on the spectrum of the response signal. All these terms have been explained with reference to the object detection system of the invention and will not be explained further. Preferred embodiments of the method of the invention correspond to those embodiments of the system of the invention.

[0042] According to a preferred embodiment of the method, a learning process is performed on a control device to establish a correlation between the spectrum and the detection of an object. The learning process can be performed by the control device, but it can also be based at least in part on an external device used solely for the learning process. In some cases, the learning process can also be a calibration process. In any case, it is used to establish a correlation between the spectrum of the response signal and the detection of the object. The term "correlation" does not necessarily mean determining a correlation function in a mathematical sense, but rather describes more generally the effect of the presence or absence of an object on the spectrum. According to this embodiment, it can also involve the effect of the object's position or other parameters. During the learning process, the antenna device receives multiple response signals, each for different situations, such as the presence or absence of an object, the presence of one or more objects, various object positions, etc. For such a learning process, a calibration object, such as a corner reflector, can be placed at different well-defined locations in various positions while the response signals are being recorded. To distinguish this calibration target from static reflection, the calibration object can, for example, be moved oscillatingly at a well-defined speed during the process and detected using range-Doppler data. Attached Figure Description

[0043] Further details and advantages of the invention will become apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings, in which: Figure 1A This is a top view of the first cell of the reflector used in the object detection system of the present invention; Figure 1B It comes from Figure 1A A perspective view of the unit cell; Figure 2 This is a top view of the second cell of the reflector used in the object detection system of the present invention; Figure 3 This is a top view of the third cell of the reflector used in the object detection system of the present invention; Figure 4A This is a perspective view of the fourth cell of the reflector used in the object detection system of the present invention; Figure 4B It comes from Figure 4A The decomposition diagram of the unit cell; Figure 5 This is a top view of the fifth cell of the reflector used in the object detection system of the present invention; Figure 6 This is the first plot showing frequency-dependent reflectivity; Figure 7 This is a side view of a vehicle having a first embodiment of the object detection system of the present invention; Figure 8 This is the second graph showing frequency-dependent reflectivity; Figure 9 This is a side view of a vehicle having a second embodiment of the object detection system of the present invention; Figure 10A This is a top view of a room having the object detection system of the present invention according to a third embodiment; Figure 10B yes Figure 10A Another top view of the room; Figure 11 It is from Figure 10A The invention of a decision tree for object detection in an object system; Figure 12A This is a side view of a vehicle having a fourth embodiment of the object detection system of the present invention; Figure 12B It comes from Figure 12A Another view of the vehicle; Figure 13 This is a side view of a room having the object detection system of the present invention according to the fifth embodiment; Figure 14 This is a top view of a first embodiment of a reflector used in the object detection system of the present invention; Figure 15 This is the third graph showing frequency-dependent reflectivity; Figure 16 This is a top view of a second embodiment of the reflector used in the object detection system of the present invention; Figure 17 This is the fourth graph showing frequency-dependent reflectivity; Figure 18 This is a top view of a third embodiment of the reflector used in the object detection system of the present invention; Figure 19 This is the first plot showing the position-dependent phase response; Figure 20 This is a top view of a fourth embodiment of the reflector used in the object detection system of the present invention; Figure 21 This is the second diagram showing the position-dependent phase response; Figure 22 It comes from Figure 19 A side view of the reflector; Figure 23 This is a top view of a fifth embodiment of the reflector used in the object detection system of the present invention; Figure 24 It has Figure 14 A perspective view of the column of the reflector; and Figure 25 This is a top view of the sixth cell of the reflector used in the object detection system of the present invention. Detailed Implementation

[0044] exist Figure 1A and Figure 1B The image shows the first cell 11 of the reflector 10 used in the object detection system 1 of the present invention. The entire reflector is in... Figure 14 The diagram shows and includes a metamaterial 20 having a periodic array of unit cells 11 arranged in a Cartesian pattern along a first direction x and a second direction y. The reflector 10 and unit cells 11 include a substrate layer 12 made of a dielectric material. A structural layer 15 is disposed on top of the substrate layer 12 relative to the vertical third direction z. The structural layer 15 includes a plurality of metal resonators 16, one metal resonator in each unit cell 11. The first unit cell 11 includes an H-shaped metal resonator 16 and is square. For example, in... Figure 7 As can be seen, the object detection system 1 includes an antenna device 3 suitable for transmitting radio frequency detection signals D1-D4. The size of the resonator 16 is similar to or smaller than the minimum wavelength of the detection signals D1-D4. Figure 14 In the reflector 10, all cells 11 include the same resonator. A continuous metal substrate is disposed beneath the substrate layer 12. For example, the thickness of the substrate layer 12 can be between 0.05 mm and 1 mm, such as 0.15 mm. The thickness of the structural layer 15 can be between 5 μm and 50 μm, such as 20 μm. The thickness of the substrate 19 can be between 5 μm and 100 μm, such as 50 μm. Due to its small thickness, the reflector 10 is a flexible sheet that can be bent to fit various surface shapes. The shape and size of the resonator 16 affect the reflectivity (or reflection coefficient) and the phase shift or phase response that occurs simultaneously with the reflection process. Specifically, the frequency-dependent reflectivity or spectral response of the reflector 10 may be affected.

[0045] In this case, the reflection coefficients of individual unit cells 11 and metamaterial 20 can be controlled by modifying the geometry of the "H" shape. Using simulation tools for electromagnetic wave propagation (full-wave solvers), the dependence of the geometry on the reflection coefficient can be accurately analyzed. This allows for the control of the amplitude and phase of the reflected signals F1-F4 through design. To some extent, the spectral shape of the reflection coefficient can also be controlled.

[0046] An important parameter for understanding the nonlinear spectral response is the surface impedance, which can be expressed as the inductance and capacitance of the structure. Typically, the inductance can be increased by making the metal wires constituting the resonator 16 thinner. The capacitance can be increased by adding more parallel lines and reducing the gaps between them.

[0047] use Figure 1A and 1B The resonator shape shown is such that resonator 16 primarily responds to microwave radiation with the electric field polarized parallel to the y-direction. Figure 2 A second cell 11 with a different resonator 16 is shown, which allows for reflection almost independently of polarization. This shape is sometimes referred to in the literature as the Jesusalem cross.

[0048] Figure 3 An embodiment with a so-called "double-cracked ring" resonator 16 is shown, i.e., two concentric metal rings with openings on opposite sides. This can also be considered as two coupled resonators 16 in a single unit cell 11. This embodiment represents a compact way of including two coupled resonators and provides more geometric parameters for tuning the spectral response.

[0049] Figure 4A and Figure 4B Another approach including more than one resonator 16, 18 is shown. In this embodiment, the metamaterial 20 and the unit cell 11 include two substrate layers 12, 13 and two metallic structural layers 15, 17. Thus, the two H-shaped resonators 16, 18 are positioned above each other relative to a third direction z, with a substrate layer 12 disposed between them. This architecture is a possible approach that allows for a reasonable level of roughness in the geometry of each metallic resonator 16, 18 and is sufficiently easy and cost-effective to manufacture, while also providing enough degrees of freedom to shape the spectral response.

[0050] In another embodiment, not shown here, an additional very thin dielectric protective layer is disposed on the uppermost substrate layer 12 and the uppermost structural layer 15. The thickness of this protective layer can be, for example, on the order of 50 μm.

[0051] exist Figure 5In another embodiment shown, the resonator 16 includes multiple portions 16.1, 16.2 made of different conductive materials. This can also be used to further influence the spectral response. Here, the resonator includes two metallic primary portions 16.1 that constitute the main part of the resonator 16. These can be made of highly conductive materials such as copper or silver granular ink. The small secondary portion 16.2 of the resonator 16 has lower conductivity and is made of a non-metallic material (e.g., carbon black). The resistance of the entire vertical portion of the “H” structure is controlled by the dimensions of the secondary portion 16.2 and the gap between the primary portion 16.1, which essentially controls the quality factor. Figure 6 It shows the use of from Figure 1A and Figure 1B The unit cell 11 is used as the dashed curve and uses the data from... Figure 5 The unit cell 11 is represented by the frequency-dependent reflectivity of the solid line curve. Both spectra show an absorption region A1, which can be smaller than the frequency bandwidth of the detection signal D1-D4. In this absorption region A1, the reflectivity of reflector 10 decreases relative to the adjacent region. This effect is more pronounced for the solid line curve.

[0052] Figure 7 A first embodiment of the object detection system 1 of the present invention is shown. In this case, the system 1 is installed in a vehicle 30 and is adapted for occupancy detection and vital sign detection. An antenna device 3 is mounted on top of the dashboard, while a control device 2 is mounted next to it. The antenna device 3 radiates primarily on the front seats 31 of the vehicle 30 in the direction of the driver and passengers. Therefore, a portion D2 of the detection signal can be directly radiated from the front seats 31. This configuration provides a very reliable signal from the person in the front seats 31. However, the person in the rear seats 32 is mostly in the obstruction area 30.1, which is at least partially obscured behind the front seats 31. Therefore, a reflector 10 is mounted in the ceiling of the vehicle 30. Thus, another portion D1 of the detection signal is reflected by the reflector, and the reflected signal F1 radiates from the obstruction area 30.1.

[0053] In this example, system 1 with a significant bandwidth is used, for example, operating between a first frequency f1 = 60 GHz and a third frequency f3 = 64 GHz. The frequency-dependent reflectivity of reflector 10 is... Figure 8 The frequency range in which antenna device 3 operates is marked in gray. In this case, two sub-bands are used, one ranging from f1 to the second frequency f2 = 62 GHz, and the other ranging from f2 to f3. Due to the significant absorption region A1, the reflectivity of reflector 10 is very low in the first sub-band, while it is close to 1 (unity) in the second sub-band. Therefore, when evaluating the signal in both sub-bands, the object appearing is more likely to correspond to a location near the front seat 31. These propagation paths are... Figure 7The solid arrows indicate this. When the propagation path includes reflector 10 as shown by the dashed arrows, the response signals R1-R4 received by antenna device 3 (in...) Figure 7 (Not shown in the image) will be significantly stronger in the second subband ranging from f1 to f3. Thus, the use of reflector 10 provides additional information that can be used in signal processing routines to locate and classify objects (i.e., people). Generally, control device 2 can detect and / or locate objects based on the spectrum of response signals R1-R4.

[0054] The reflector 10 is mounted directly behind the headliner material covering the ceiling of the vehicle 30. This keeps the reflector 10 invisible to passengers. The headliner is typically made of relatively low-density foam and textile materials and is practically transparent to microwave radiation. Here, the headliner material must be considered during the design of the reflector 10, as it cannot generally be considered completely transparent to radar signals. If the properties of the headliner material are known, the metamaterial of the reflector 10 can be designed (e.g., through computer simulation) to compensate for any effects of the headliner.

[0055] Figure 9 An alternative embodiment is shown in which the antenna device 3 is attached to the ceiling of the vehicle 30 above the rear seat 32. In this case, an obstruction area 30.1 exists near the front seat 31. The reflector 10 is attached to the curved surface of the dashboard. Therefore, a portion of the detection signal D1 is reflected into the obstruction area 30.1, thereby enhancing the response of the passenger in the front seat 31.

[0056] Figure 10A and Figure 10B Another embodiment is shown, in which system 1 is installed in an L-shaped room 40. This could be a room in a hospital, retirement home, or similar area. Antenna device 3 is mounted to a wall, while control device 2 is shown concealed within the wall, but this is merely exemplary. Reflector 10 is mounted to another wall. Room 40 includes four distinct zones 40.1, 40.2, 40.3, and 40.4, one of which is a shielded zone 40.4 that cannot be directly radiated by antenna device 3. However, reflector 10 is configured to establish a propagation path between antenna device 3 and shielded zone 40.4. Similarly, due to the different spectral responses of reflector 10, signals reflected by reflector 10 (dashed arrows) can be distinguished from signals that do not interact with it (solid arrows). Using range information combined with information from the spectrum of response signals R1-R4, the detected object can be located within one of zones 40.1-40.4. Figure 11A decision tree that can be implemented in control device 2 is shown. If the distance r of the object is less than the first radius r1, the object is in the first region 40.1. If the distance r is between the first radius r1 and the second radius r2, the object is in the second region 40.2. If the distance r is greater than the second radius r2, the spectrum is used to determine whether reflector 10 is included in the propagation path. If not, the object is in the third region 10.3. If yes, the object is in the obstruction region. This concept can be extended to more complex configurations with multiple reflectors 10 and / or multiple antenna devices 3. Other features can be added to this decision process, such as angular binning when using MIMO radar or radar systems where each channel has different radiation polarization (left-hand or right-hand circular polarization, and / or vertical and horizontal linear polarization).

[0057] As configurations become more complex, decision trees can be replaced by other, more advanced artificial intelligence (AI) methods. In such cases, logical independent variables may not have readily available parameters. Instead, a learning or calibration process may be necessary. For such a process, specific highly reflective objects (such as corner reflectors) can be placed at distinct, well-defined locations in each area of ​​the room while recording response signals R1–R4. To distinguish this calibration target from static reflections, it can help make the calibration target oscillate at a well-defined speed during the process and detect it in the distance-Doppler data.

[0058] When one or more people move from one area 40.1–40.4 to the next over a longer period (e.g., a day), their location can be tracked and activity profiles can be generated. Combined with recorded Doppler signatures for detecting respiratory rate and heart rate, this provides meaningful input for vital sign monitoring. When mounted on a wall, the antenna device 3 can be installed at a height of approximately 100–170 cm to provide uniform radiation throughout the room 40 and above small pieces of furniture such as tables and chairs.

[0059] Other situations where using reflector 10 to enhance signal strength may be useful include detecting objects in the trunk of a vehicle (especially in the case of SUVs with relatively high seats), covering the cabins of long vehicles (such as 7-seater vans), buses, recreational vehicles, public transportation vehicles, airplanes, ferries, or the like.

[0060] Figure 12A and 12B Another embodiment of the system 1 of the present invention, also installed in vehicle 30, is shown. Similar to... Figure 9In one embodiment, the antenna device 3 is mounted in the ceiling above the rear seat 32. However, in this case, the reflector 10 is placed inside the rear seat 32, just below the outer fabric material. Thus, the reflectivity and reflectivity of the rear seat are controlled by the design of the reflector 10. The spectral response of the reflector is designed to be distinguishable from other reflections in the vehicle 30. Therefore, the reflected signal F1, reflected by the reflector 10 and constituting part of the response signal R1, can be distinguished from other reflections inside the vehicle 30. If an object (in this case, a person 80) occupies the seat 32, such as... Figure 13 As shown in B, the control device 2 will only record reflections caused by the person 80, not the reflector 10. In this way, the occupancy of that particular seat 32 can be detected.

[0061] This concept can be extended to configurations with more than one reflector 10 and more than one seat 31, 32, for example, one in each of the rear seats 32. In this case, it may also be beneficial to operate radars with more than two sub-bands. For better differentiation, the different reflectors 10 can differ in their spectral responses.

[0062] Figure 13 An embodiment suitable for indoor applications, such as in an office environment, is shown. The detection system 1 is installed in a room 40 with a rectangular outline. An antenna assembly 3 is mounted to one of the long walls. A total of four reflectors 10, 50, 60, and 70 are installed on opposite sides of the room 40. These reflectors are adapted to reflect a large amount of energy back to the antenna assembly 3. Furthermore, each reflector 10, 50, 60, and 70 has a separate spectral response different from the other reflectors.

[0063] In the center of the room, there is a table with six chairs 41-46. Since the propagation paths of the detection signals D1-D4 from antenna device 3 to reflectors 10, 50, 60, and 70, and the propagation paths of the reflected signals F1-F4 (or respectively the response signals R1-R4) cross the table area, the signal strength varies when person 80 is in this area. For example, when person 80 sits on the second chair 42, the response signal R2 from the second reflector 50 and the response signal R3 from the third reflector 60 are affected. A similar effect occurs for the other chairs 41, 43-46. Adding range information, even with very coarse resolution, is sufficient to determine which chairs 41-46 are occupied and which are not.

[0064] Similarly, this concept can be extended to more than one antenna device 3 and even more reflectors 10, 50, 60, 70. For example... Figure 11Similar decision trees or trained AI-based algorithms can be used to locate and / or classify people. Therefore, even using a minimal and cost-effective antenna device 3, location and classification can be provided.

[0065] Figure 14 This is a top view of a first embodiment of the reflector 10. As already mentioned, it comprises a plurality of unit cells 11 arranged in a Cartesian pattern. The substrate layer 12 is thin and flexible and can be made of dielectric materials commonly used in flexible printed electronics, such as polyethylene terephthalate (PET), polyimide (PI), polyetherimide (PEI), polyamide (PA), or similar materials. The resonators 16 of the individual unit cells 11 can be fabricated using methods common in flexible printed circuit technology, such as screen printing, inkjet printing, reverse offset printing, etching of aluminum laminates, or similar methods. Due to the simple architecture, a roll-to-roll process is possible (generally preferred due to high throughput and low cost). In some cases, the required aperture size may be quite large, for example, greater than 1 μm. 2 Therefore, the aforementioned manufacturing method is advantageous compared to PCB or thin-film technologies. In this embodiment, the absorption rate is very high at a specific frequency, which corresponds to... Figure 15 The single absorption region A1 shown is grayed out, with the frequency band of the antenna device 3 between the first frequency f1 and the second frequency f2. Outside the absorption region A1, the reflectivity is close to 1. The size of the cell 11 depends on the frequency band in use. It can be, for example, between 0.5 mm and 5 mm.

[0066] In another embodiment, such as Figure 16 As shown, reflector 10 includes two types of rectangular blocks 10.1 and 10.2 with different resonators 15. Blocks 10.1 and 10.2 are marked in white and gray, respectively. This is an alternative to using multiple resonant elements in each cell, and it simplifies the design. Figure 17 The frequency-dependent reflectivity of the reflector 10 is shown. Due to the different blocks 10.1 and 10.2 of the different resonators 16, the spectrum has two absorption regions A1 and A2.

[0067] Figure 18 Another embodiment is shown, in which the dimensions of the resonator 16 vary linearly in a periodic manner along a first direction x. This results in a locally varying phase response, such as Figure 19 As shown in the figure. Therefore, reflector 10 causes anomalous reflection, where the absolute values ​​of the incident angle and the reflection angle are different. For example, radiation incident perpendicular to the surface of reflector 10 will not be reflected perpendicularly, but will be reflected at a different angle. However, for Figure 18In this embodiment, plane waves are also reflected as plane waves, meaning parallel rays remain parallel. Thus, knowing, for example, the room configuration, the reflection direction can be optimized for the maximum signal amplitude in the obstructed areas 30.1, 40.4 and / or at antenna device 3.

[0068] Figure 20 Another embodiment is shown. Here, the dimensions of the resonator 15 vary non-linearly along the first direction x. This results in a non-linear change in the phase response, such as... Figure 21 As shown. This means that when radiated with a detection signal D1 having a normal incident angle, as... Figure 22 As shown, the reflected signal F1 is distributed over a fairly large angular range. A reflective surface with this phase distribution (profile) can be called a planar multidirectional reflector or even a planar omnidirectional reflector.

[0069] Figure 23 Another embodiment is shown. Here, the reflector 10 is not simply rectangular in shape, but includes multiple cutouts 10.3 to allow integration into curved elements (such as panels inside a vehicle), seats, or the like. This also facilitates bending and folding the reflector 10 during operation without any risk of damage.

[0070] Figure 24 It shows Figure 14 The reflector 10 is wound around a uniformly curved surface, in this case, the surface of a pillar 47 (e.g., in a large office). In this case, even with the same cell 11, the reflected signal can be distributed over a wide angular range.

[0071] It should be noted that, Figure 14 , 16 In models 1, 18, 20, 23, and 24, the size of unit cell 11 relative to reflector 10 is enlarged. Using a more realistic size, it would be much smaller, for example, 50 times smaller (1 / 50th of the original). Similarly, the number of unit cells is typically significantly larger, for example, 1000 cells along one direction.

[0072] Figure 25 Another embodiment of the cell 11 that can be used for a nearly transparent reflector 10 is shown. Therefore, the reflector 10 can be mounted on or integrated into a window of a vehicle 30 or room 40. In addition to including a substrate layer 12 that is transparent to visible light, the resonator 16 of the structural layer 15 is adapted to be a transparent portion. Despite maintaining... Figure 1AThe overall shape is H-shaped, but the metal resonator 16 is divided into multiple fine line elements 16.3, which are separated by fine gaps 16.4. The width of the line elements 16.3 is less than 1.5 μm. The gaps 16.4 may have a similar width. Since the width of the line elements 16.3 is slightly larger than or even smaller than the wavelength of visible light, the resonator 16 may not be visible to the naked eye.

[0073] List of reference numerals 1. Object Detection System 2. Control equipment 3 Antenna Device 10, 50, 60, 70 reflectors Blocks 10.1 and 10.2 10.3 Incision 11 unit cells 12, 13 Basal layer Structural layers 15 and 17 16, 18 resonators 19. Grassroots 20 Metamaterials 30 vehicles 30.1, 40.4 Obstruction Area Seats 31, 32, 41-46 Room 40 Areas 40.1-40.3 80 people A1 and A2 absorption regions D1-D4 detection signals F1-F4 reflected signal R1-R4 response signals x First direction y Second direction z Third direction.

Claims

1. An object detection system (1), comprising: - Antenna device (3), which includes at least one antenna; - A control device (2) adapted to control the antenna device (3) to transmit radio frequency detection signals (D1-D4) and to detect an object (80) based on the radio frequency response signals (R1-R4) received by the antenna device (3), and - At least one passive reflector (10, 50, 60, 70) adapted to at least partially reflect the detection signal (D1-D4), the reflector (10, 50, 60, 70) comprising a metamaterial (20) having a plurality of unit cells (11), the metamaterial (20) comprising at least one dielectric substrate layer (12, 13) and a conductive structural layer (15, 17) disposed on its upper side, thereby the reflector (10, 50, 60, 70) having a frequency-dependent reflectivity. The control device (2) is adapted to detect the object (80) at least in part based on the spectrum of the response signal (R1-R4). Its features At least one of the at least one reflector (10, 50, 60, 70) has an absorption region (A1, A2) smaller than the frequency bandwidth of the detection signal (D1-D4), and the reflectivity of the reflector (10, 50, 60, 70) decreases relative to the adjacent region in the absorption region, wherein the absorption region (A1, A2) is within the frequency bandwidth, and the control device (2) is adapted to detect the object (80) at least in part based on identifying the effect of the absorption region (A1, A2) on the spectrum of the response signal (R1-R4).

2. The object detection system according to claim 1, characterized in that, At least one of the at least one reflector (10, 50, 60, 70) is configured to provide a reflection path between the antenna device (3) and the obstruction area (30.1, 40.4) where the inserted object is obstructed outside the antenna device (3), such that the object (80) in the obstruction area (30.1, 40.4) can be detected by the control device (2).

3. The object detection system according to claim 2, characterized in that, The control device (2) is adapted to determine whether the object (80) is in the occluded region (30.1, 40.4) or in the unoccluded region (40.1-40.3) based on the influence of the absorption region on the spectrum of the response signal (R1-R4).

4. The object detection system according to any one of the preceding claims, characterized in that, The control device (2) is adapted to detect the inserted object (80) based on the effect of an object (80) inserted between the antenna device (3) and at least one of the at least one reflector (10, 50, 60, 70) on the spectrum of the response signal (R1-R4), the effect being generated by the action of the inserted object (80) on the absorption region (A1, A2) in the spectrum.

5. The object detection system according to any one of the preceding claims, characterized in that, At least one of the at least one reflector (10, 50, 60, 70) includes a plurality of blocks (10.1, 10.2), and at least two blocks (10.1, 10.2) are structured differently such that they have different frequency-dependent reflectivities.

6. The object detection system according to any one of the preceding claims, characterized in that, At least one of the at least one structural layer (15, 17) extends laterally along a first direction (x) and a second direction (y) perpendicular to the first direction (x), and includes a plurality of conductive resonators (16, 18), each cell (11) including one resonator (16, 18), and every two adjacent resonators (16, 18) of the structural layer (15, 17) are spaced apart along at least one of the first direction (x) and the second direction (y).

7. The object detection system according to any one of the preceding claims, characterized in that, At least one resonator (16, 18) comprises multiple sections (16.1, 16.2) with different conductivity.

8. The object detection system according to any one of the preceding claims, characterized in that, The substrate layers (12, 13) are transparent to visible light, and the structural layers (16, 18) include a transparent structure (16) comprising a plurality of line elements (16.3) having a maximum width of 1.5 μm.

9. The object detection system according to any one of the preceding claims, characterized in that, At least one of the at least one reflector (10, 50, 60, 70) is a flexible sheet.

10. The object detection system according to any one of the preceding claims, characterized in that, For at least one of the at least one reflector (10, 50, 60, 70), at least one dimension of a resonator (16, 18) varies along one of a first direction (x) and a second direction (y) for different cells (11), thereby the reflector (10, 50, 60, 70) is adapted to anomalous reflection in which the absolute values ​​of the incident angle and the reflection angle are different.

11. The object detection system according to any one of the preceding claims, characterized in that, At least one dimension varies non-linearly for different cells (11) along one of the first direction (x) and the second direction (y), thereby the reflectors (10, 50, 60, 70) are adapted to reflect a single incident angle corresponding to multiple reflection angles.

12. The object detection system according to any one of the preceding claims, characterized in that, At least one of the at least one reflector (10, 50, 60, 70) includes a plurality of base layers (12, 13), wherein a structural layer (16, 18) is disposed on the upper side of each base layer (12, 13).

13. The object detection system according to any one of the preceding claims, characterized in that, The object detection system includes a building or vehicle (30), and at least one of the antenna device (3) and the at least one reflector (10, 50, 60, 70) is installed in the building or vehicle (30).

14. An object detection method using an object detection system (1), comprising: - Antenna device (3), which includes at least one antenna; - Control equipment (2); as well as - At least one passive reflector (10, 50, 60, 70) comprising a metamaterial (20) having a plurality of unit cells (11), the metamaterial (20) comprising at least one dielectric substrate layer (12, 13) and a conductive structural layer (16, 18) disposed on its upper side, thereby the reflector (10, 50, 60, 70) having a frequency-dependent reflectivity. The control device (2) controls the antenna device (3) to transmit radio frequency detection signals (D1-D4), the reflectors (10, 50, 60, 70) at least partially reflect the detection signals (D1-D4), and the control device (2) detects an object (80) based on radio frequency response signals (R1-R4) received by the antenna device (3), wherein the control device (2) detects the object (80) based on the spectrum of the response signals (R1-R4). Its features are: At least one of the at least one reflector (10, 50, 60, 70) has an absorption region (A1, A2) smaller than the frequency bandwidth of the detection signal (D1-D4), and in the absorption region, the reflectivity of the reflector (10, 50, 60, 70) decreases relative to the adjacent region, wherein the absorption region (A1, A2) is within the frequency bandwidth, and the control device (2) detects the object (80) at least in part based on identifying the influence of the absorption region (A1, A2) on the spectrum of the response signal (R1-R4).

15. The detection method according to claim 14, characterized in that, A learning process is performed on the control device (2) to establish the correlation between the spectrum and the detection of the object (80).

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