Patent Application
20240003676
The invention relates to a THz sensor and a THz measuring method for measuring an object to be measured. Further, a measuring device is provided. The measurement may service, in particular, to determine distances and/or layer thicknesses of the object to be measured. The object to be measured may be, in particular, a pipe made of plastics, rubber or another material permeable for THz radiation.
THz sensors für layer thickness measurements and distance measurements generate a THz transmission beam which is emitted along an optical axis towards the object to be measured. Hereby, the THz sensor generally comprises a support device, a THz transceiver and a lens for bundling the THz radiation. Hereby, the THz transceiver comprises an emitter and a receiver which may, in particular, be combined; however, emitter and receiver may be provided as separate units so that the transceiver is then formed by spatially separate embodiments of emitter and receiver.
Advantageously, THz sensors further comprise a waveguide, guiding the THz radiation emitted by the THz transceiver towards the lens. The lens is formed, e.g., from a plastic or even silicon and shaped e.g., as an oval at its front surface, i.e., in the direction facing the object to be measured, generally having a planar rear surface. The emitted THz radiation is bundles by the lens and emitted along the optical axis as THz transmission beam. The THz transmission beam passes through boundary surfaces of the object to be measured, on each of which a part of the THz transmission beam is reflected back due to the transition of the media with different refractive index. Thus, a THz reflection beam travels along the optical axis back to the lens, through the lens to the waveguide and to the THz transceiver, and generates a usable reflection peak for each boundary surface which, therefore, represents the point in time of the reflection.
It is apparent that in such THz measurements multiple reflections may occur, where, in particular, the reflected beam is reflected by the THz sensor back to the object to be measured so that at the boundary surfaces of the object reflections will be created anew and travel back to the THz sensor. In the measuring signal such multiple reflections occur, due to the longer time of flight, as further measuring peaks compromising the measuring signal. Furthermore, disturbing reflections may occur at the lens or the lens surfaces respectively, e.g., reflected from the lens surface back to the waveguide.
The document JP 2013-149846A describes a THz wave generating element which may be adapted to maintain the strength of a radiation when using a conventional antenna and a substrate. Hereby, an excitation by multi-photon absorption is created, whereby the absorption of the THz wave can be reduced by the substrate.
The citation DE 10 2016 120 665 B3 describes a radar sensor unit to be utilized in enclosed environments, in particular, in oil-filled hydraulic cylinders, including a radar electronic device comprising at least one high-frequency antenna for emitting and receiving von high-frequency radiation. Further, a lens for bundling the high-frequency radiation and a metal support with a gap for mounting the radar electronic device are provided. The radar sensor unit preferably operates in the GHz or THz band. The radar electronic device is enclosed by a robust housing which is essentially formed solely by the lens and the support.
The document JP 2002-223017A describes a THz device and a device for generating THz light as well as a device for detecting the THz radiation, wherein the loss of THz radiation is to be reduced.
The citation JP 2015-188174A describes an MMIC—integrated module, in which, to improve the radiation efficiency of a radio wave, a metal reflection plate is formed on an underground of a small cavity opposite an antenna of an MMIC chip.
The document DE 10 2015 122 205 A1 describes a THz measuring device for measuring a layer thickness and/or a distance, wherein a plurality of measurements are carried out in different optical axes and the optical axis of the emitted THz radiation is adjusted during the measurement or in-between measurements, where one or more measurements are used to determine a layer thickness.
The citation WO2021123111A1 describes a waveguide arrangement for guiding electromagnetic waves in a hollow space surrounded by a conducting material, the waveguide arrangement comprising a circuit board material comprising a electrically conductive, plate-shaped back side, a substrate, and a conductive layer arranged on the side of the substrate facing away from the back side. The invention provides for the back side to comprise a surface structure, preferably formed by at least one gap, directly limiting, at least in part, the wave guiding hollow space; and/or that the hollow space is formed in split block technology by connecting the circuit board material as split block base with a corresponding cover as split block top.
It is the object of the invention to create a THz sensor as well as a THz measuring method allowing for accurate THz measurements.
This task is solved by a THz sensor and a THz measuring method according to the independent claims. The sub-claims describe preferred further developments. Hereby, further, a THz measuring device including the THz sensor is provided. The THz measuring method according to the invention may be carried out, in particular, using the THz sensor according to the invention and/or the THz measuring device according to the invention.
Moreover, advantageously, an arrangement consisting of the THz measuring device and the object to be measured is provided, in particular, an arrangement in which the object to be measured is received in a measuring space of the THz measuring device.
Accordingly, the THz radiation is influenced by means of a compensation formation in a compensation area between the lens and the support device. Owing to this influence a reflection of the reflected beam on the THz sensor can be modified such that the multiple reflection peaks are at least reduced if not prevented.
According to the invention, it is recognized that an influence in this area may be sufficient to reduce multiple reflections in the wanted signal.
Advantageously, the THz sensor includes a waveguide which guides the THz radiation between the THz transceiver and the lens. Hereby, advantageously, a central detection area in front of and next to the waveguide formed around the optical axis is not influenced by the compensation formation. This is based on the finding that the reflections at the sensor, which lead to the disturbing multiple reflections, in particular, occur outside the central detection area and, thereby, it is possible to limit the compensation accordingly without disturbing the measuring signal in the central detection area.
The compensation formation may be formed, in particular, in an, e.g., ring-shaped connecting area existing directly around the detection area or, respectively, bordering the detection area, because this provides the largest contribution to the multiple reflections.
Preferably, the compensation area may be provided at the lens, in particular, the rear part of the lens, and/or at the support device, in particular, a front face of the support plate serving as support device, and/or in the gap between the lens and the support device. Thus, suitable spots may be chosen depending on the type of compensation.
According to the invention, several options of influencing are provided, each alone or in combination with others:
Advantageously, the waveguide emits polarized THz radiation, and the waveguide may, e.g., be suitably adapted for this, or an additional polarization filter will be used.
Hereby, according to one embodiment, the rotation may be created by a transpolarization (transverse polarization) structure which extends in the lateral plane, i.e., perpendicular to the optical axis, under a transpolarization angle, in particular, 45°, in relation to the polarization direction (Y).
The transpolarization structure may be made using little expenditure, at small cost and with high accuracy. Moreover, it lies in a mechanically protected are and, therefore, is not subject to direct wear and tear.
When rotating about, e.g., 90°, i.e. where no component remains in the proper plane, only the doubly re-reflected radiation, i.e., a triple reflection peak, can be picked up again; however, this only makes a small contribution.
The transpolarization structure may exhibit, in particular, one or more of the following characteristics:
Hereby the relevant wavelength may be, in particular, the shortest wavelength or an average wavelength of the emitted THz radiation.
According to the invention, advantageously, the relevant wavelength may be selected individually adapted to the various structures. Thus, it is possible, in particular,
The attenuating medium attenuates the THz radiation, in particular, in a relevant wavelength band, e.g., a wavelength band around an average wavelength. Advantageously, the attenuating medium has a refractive index corresponding to the refractive index of the lens, in particular, at the transition to the lens, so that no further reflection occurs between the rear side of the lens and the attenuating medium but, in particular, a reflection only between the attenuating medium and the metal of the reflection plane or, respectively the front side of the support plate. Hereby, the attenuating medium may have a refractive index which is uniform and corresponds to the refractive index of the lens, or corresponds to the refractive index of the lens only at the transition and, e.g., subsequently changes progressively.
The structuring can be formed with little effort, at low cost, without any additional requirements in material, in a protected area, and, in particular, with high accuracy, because the THz radiation allows for precise structuring in the millimeter or centimeter range.
The destructive interference of the re-reflected reflection beam may happen, in particular, by means of an interference structure with a structuring depending on a relevant wavelength, e.g., one quarter of the average wavelength.
According to the invention, it is also apparent, in particular, that these various embodiments can be suitably combined with one another, i.e., so as to complement each other without adversely affecting each other. Thus, the taper allows to leave a gap open into which the attenuating medium can then be introduced as an addendum. The transpolarization structure, too, may be suitably combined e.g., with the attenuating medium without requiring any change of the distance of the support device or support plate respectively, to the lens. Thus, the support plate can still accommodate the lens securely and firmly.
According to an advantageous further development, the waveguide may be formed by two waveguide channels which, owing to their elongates shape, e.g., rectangular shape, each support only a linear polarization. Hereby, the waveguide channels are preferably followed by coupling-in points together forming the compensation area or respectively part of the compensation area. Thereby, a coupling-in into directions orthogonal in relation to one another is achieved.
According to an advantageous further development, an OMT, i.e., Orthomode transducer, or Orthomode coupler respectively may be provided which splits up circular polarized waves or, respectively, joins orthogonal polarized waves. Thereby, a compact and technically secure splitting is achieved.
The THz frequency may be, in particular, in a range between 10 GHz and 10 THz, e.g., 50 GHz and 4 THz, e.g., 50 GHz and 1 THz, and occur using direct time-of-flight measurement, or pulsed radiation. Thus, advantageously, the THz radiation can include even radar radiation and/or microwave radiation.
For the embodiment with polarized light, in particular, a frequency modulation is advantageous, in particular, as a FMCW radar, i.e., frequency modulated continuous radar radiation.
The invention is illustrated in the following using accompanying drawings by means of a few embodiments. It is shown in:
A THz measuring device 1 comprises, inter alia, a THz sensor 2 with an adjustment device 3 and a controller device 4 as well as a measuring space 5 and serves to measure an object to be measured 6, e.g., a pipe made of plastics, rubber, but, e.g., even paper, where the pipe 6 is transported along its pipe axis, i.e., in particular, the axis of symmetry B of the measuring space 5. Besides a pipe or round pipe respectively, e.g., even a rectangular pipe or a profile, e.g., a window profile, a gutter, e.g., a rain gutter, and other geometries may be covered. The THz measuring allows layer thicknesses and distances, as well as even the refractive index 66 of the material to be measured, in particular, after extrusion of the pipe 6, so as to determine, e.g., faults and deformation. The THz sensor 2 may be guided circumferentially around the measuring space 5 or the axis of symmetry B respectively, so as to measure the entire circumference of the pipe 6. Furthermore, a plurality of THz sensors 2 may be arranged circumferentially around the measuring space 5, e.g., even with joint rotational adjustment.
The THz sensor 2 emits a THz transmission beam 8 along it optical axis A into the measuring space 5 and onto the object to be measured 6. Hereby, the THz sensor 2 comprises a THz transceiver 10, e.g., as sensor chip, which is mounted on a support plate 11, a waveguide 12 arranged in front of or, respectively on the THz transceiver 10, and a lens 14, e.g., made of plastics or silicon. The THz radiation emitted by the THz transceiver 10 is first guided via the waveguide 12 and then passes through the lens 14, which bundles the THz radiation thereby forming the THz transmission beam 8, whereby it may be provided, in particular, to focus the THz transmission beam 8 e.g., onto the axis of symmetry B and/or the object to be measured 6. The focusing may be made, e.g., via the adjustment device 3.
The THz transmission beam 8 travels from the THz sensor 2 along the optical axis A through the object to be measured 6, whereby partial reflection occurs on boundary surfaces g1, g2, g3, g4 of materials with different refractive indexes 6 so that a THz reflection beam 15 is reflected along the optical axis A back to the THz sensor 2. Thus, in the case of the single-layer pipe 6 shown here, reflections occur on the front outer surface g1 between air and the pipe 6, subsequently on the boundary surface g2 upon exiting the pipe 6 in its interior space, and, accordingly, subsequent reflections on boundary surfaces g3, g4 upon entry into the pipe 6 and upon subsequent exit. In addition, a mirror for sensing a total reflection may be provided behind the pipe 6. Thus, the boundary surfaces g1, g2, g3, g4 generate partial reflections in the reflected beam 15. Thus, the THz sensor 2 emits a proper measuring signal S1 with one wanted peak P0 each corresponding to the respective partial reflection on each boundary surface g1, g2, g, g4, from which, therefore, layer thicknesses and distances as well as material characteristic such as the refractive index 66 can be determined by the controller device 4 as time-of-flight measurement. Hereby, the refractive index ε6 can be determined as the ratio of the speed of light c0 in a vacuum (or air respectively) to the speed of light c6 in the material of the pipe 6, i.e., ε6=c0/c6).
The THz radiation for forming the THz transmission beam 2 may lie, in particular, in a frequency range between 10 GHz and 10 THz, e.g., between 50 GHz and 5 THz. Thus, is may lie in the Gigahertz and Terahertz band, i.e., in particular, including the radar band and microwave band in total or in part. Hereby, the THz transmission beam 2 may be made as direct time-of-flight measurement, but also as frequency modulation, as well as with pulsed radiation.
In a XYZ coordinate system the X direction extends along the optical axis A, accordingly, the YZ plane perpendicular or, respectively, lateral thereto.
The lens 14 is designed essentially drop-shaped or oval respectively towards the front, i.e., in the x direction facing the object to be measured 6, and with its, e.g., planar rear side 14a supported on and attached to the front face 11a of the support plate 11.
A central detection area 7 extends in the lateral YZ plane around the optical axis A and around the waveguide 12 or, respectively, in the X direction forwards around the optical axis A. Thus, the reflected beam 15 which impinges in this central detection area 7 is received by the waveguide 12 and detected by the THz transceiver 10.
A part of the reflected beam 15 travels in the lateral YZ plane outside the detection area 7 against, e.g., the front face 11a of the support plate 11, is reflected again here, thereby travelling again in the X direction forwards through the lens 14, essentially along the optical axis A towards the object to be measured 6 so that it is partially reflected anew on the boundary surfaces g1, g2, g3 and g4 and travels back to the sensor 2 as double reflected beam 15-2 and is received by the THz transceiver 10. Thus, an additional measuring peak P1 will appear later in time owing to the double reflection on the first boundary surface g1 which, when properly evaluated, corresponds to the measuring peak wanted reflection peak respectively at a distance which, owing to the longer path or time of flight respectively in addition to the distance d1, corresponds to the distance d2 from the front face 11a to the boundary surface g1. Thus, a perceived boundary surface at a distance d1+d2 can be detected.
Thus, in
According to the invention, a compensation formation 17 is provided which is shown in various embodiments. It serves to compensate, in particular, to avoid or reduce the multiple reflection peaks, in particular, the double reflection peaks P1. The compensation formation 17 is provided, in particular, in a compensation area 9 formed between the lens 14 and the support plate 11.
The compensation area 9
Thus, the structure width b16 e.g., may lie in a range between 1/10 λ and ⅕ λ. The profile height h16 may lie e.g., in a range of a quarter of λ or ¼ λ respectively.
The transpolarization structure 16 runs at a structure angle α16 of 45° in relation to the Y direction and the Z direction in reflection plane as YZ plane, i.e., in particular, the front face 11a.
εr=ε′r+iε″r,
Where the correlation between
n
2=½√{square root over ((ε′r2+ε″r2+ε′r))}
For small values of ε″r it can be assumed that n2=ε′r,
where, in particular, the imaginary part ε″r indicates the attenuating by the attenuating medium 18.
Hereby, the complex relative permittivity is not limited to a constant value, but may, e.g., change gradually within the medium so that no sharp discontinuity in permittivity exists on the boundary surface to the lens, while the attenuation, e.g., consistently increases along beam path.
By introducing the attenuating medium 18 with a high attenuation value ε″ the reflection between the lens rear side 14a and the metal of the support device or, respectively, the front face 11a can be suppressed or strongly reduced respectively, without compromising the wanted signal.
The difference in the value of Cr between two dielectric media indicates the strength or height respectively of the reflection caused on the respective boundary layer. Thus, it is possible to suppress the reflection by a medium or attenuating medium 18 respectively, which meets the following conditions:
The embodiments of
Hereby, the depths d, d22a, d22b, d22c, of which only the depth d22c of the recess 22c is shown in this drawing, are dimensioned such that a beam reflected in these recesses will each have a change in path length compared to the beam reflected on the surface 11a or, respectively, the remaining areas 22d between the recesses 22a, 22b, 22c that will lead overall to a destructive interference. Thus, e.g., the structure recess 22a has a depth of λ/4 so that the reflected beam 15, which travels into the recess 22a and later exits the recess 22a after being reflected, has a change in path length of 2×λ/4=λ/2 compared to the beam reflected on the surface 11a, respectively, the areas 22d, i.e., interferes destructively with the beam components reflected on the area 22d. The further recesses 22b, 22c may have depths of multiples of λ/4, where they, in particular, each also alternate in a lateral direction with area 22d so as to form an effective destructive interference.
Hereby, various type of interference structuring 22 are possible which meet these requirements that the beam components which are reflected in the various recesses 22a, 22b, 22c and 22d have the appropriate changes in path length, at a corresponding or equal level of energy or beam intensity respectively, so that a complete or mostly destructive interference occurs.
The reflected beam 15 coming through the lens 14 travels to the leans rear side 14a, i.e., the transition to the coating 24, where the first partial reflected beam R1 is generated,
Depending on the ratio of the refractive indexes (permittivities) n14, n24 and n25
Hereby, this embodiment is referred to, in particular, at least one relevant wavelength λ, preferably to a plurality of relevant wavelengths A.
The partial reflected beams R1 and R2 form a destructive interference when, in particular, the following is true for the wavelength λ:
Hereby, preferably, the central detection area 7 around the optical axis A is kept open again.
The medium 25 as air may be present, in particular, in an arrangement of the lens 24 in front of the plate 11,
Hereby, the embodiment of
In this embodiment, the THz transceiver 10 is formed by a transmitter 10a and a receiver 10b; however, in principle, the THz transceiver 10 may be formed on a FMCW radar chip.
According to the embodiment of
| Number | Date | Country | Kind |
|---|---|---|---|
| 102020132330.1 | Dec 2020 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2021/100962 | 12/2/2021 | WO |
