THZ SENSOR AND THZ METHOD FOR MEASURING AN OBJECT TO BE MEASURED

Abstract

The invention relates to a THz sensor (2) for measuring an object to be measured (6), in particular, a pipe, the THz sensor (2) comprising: a THz transceiver (10) for emitting and receiving THz radiation, a lens (14) for bundling the THz radiation emitted by the THz transceiver (10) and emitting a THz transmission beam (8) along the optical axis (A) and for receiving a THz reflection beam (15), a support device (11), on which the lens (14) and/or the THz transceiver (10) is accommodated or fastened.

Hereby, it is provided that a THz radiation-influencing compensation formation for modifying and/or reducing incident THz radiation is provided in a compensation area between the lens and the support device (11).

Claims

1-21. (canceled)

22. A THz sensor for measuring an object to be measured, in particular, a pipe, the THz sensor comprising: a THz transceiver for emitting and receiving THz radiation, a lens for bundling the THz radiation emitted by the THz transceiver and emitting a THz transmission beam along the optical axis and for receiving a THz reflection beam, a support device, on which the lens and/or the THz transceiver is accommodated or fastened, wherein a THz radiation-influencing compensation formation for modifying and/or reducing incident THz radiation is provided in a compensation area between the lens and the support device.

23. The THz sensor of claim 22, further comprising a waveguide provided between the lens and the THz transceiver and configured to conduct emitted or incident THz radiation, the compensation area being formed outside a central detection area formed in front of the waveguide and/or around the detection area.

24. The THz sensor of claim 23, wherein the compensation area is formed in a, in particular, ring-shaped, connecting area directly joining the detection area in a plane perpendicular or lateral to the optical axis.

25. The THz sensor of claim 22, wherein the compensation area includes one or more of the following elements or parts: a rear part of the lens, in particular, a rear side of the lens, the support device, in particular, a front face of the support device, and a gap between the rear side of the lens and the support device.

26. The THz sensor of claim 22, wherein the compensation area is designed such that it influences THz radiation, in particular, a reflected beam travelling from the lens to the support device, in one or more of the following manners: a) rotating a polarization plane, b) attenuating the THz radiation, c) deflecting or reflecting the incident reflected beam at least in part in a lateral or perpendicular direction in relation to the optical axis, d) forming a destructive interference, in particular, by reflection of the incident reflected beam in reflection surfaces of an interference structure offset against one another, e) forming a destructive interference by means of a coating on the lens surface, in particular, rear side of the lens, with optical transitions from the lens to the coating and from the coating to a further medium, the lens, the coating and the further medium having different refractive indexes and/or different permittivity, in particular, by reflection of the incident reflected beam on the boundary surfaces of the lens surface to the coating and from the coating to the medium, e.g., the medium being air or metal, e.g., metal layer on the coating.

27. The THz sensor of claim 22, wherein the THz transceiver is adapted for output and measurement using time-of-flight measurement and/or using frequency modulated radiation and/or for output and detection of pulsed radiation, in particular, in a frequency range between 10 GHz and 10 THz, preferably 50 GHz and 4 THz, e.g., 50 GHz and 3 THz.

28. The THz sensor of claim 22, wherein the THz sensor is configured to emit the THz transmission beam in polarized form and to detect merely a polarized reflected beam, in particular, by means of a polarized design of the waveguide and/or by means of a polarization filter.

29. The THz sensor of claim 28, wherein the compensation formation is adapted to reflect the incident reflected beam with a rotation of its polarization plane about an angle of rotation, in particular, about 90.

30. The THz sensor of claim 28, wherein compensation formation comprises a transpolarization (transverse polarization) structure extending in the plane perpendicular to the optical axis in a structure direction extending at a transpolarization angle, in particular, 45, in relation to the polarization direction, for rotating the polarization direction upon reflection in a direction perpendicular to the polarization direction.

31. The THz sensor of claim 30, wherein the transpolarization structure exhibits one or more of the following characteristics: profilings extending in the structure direction, e.g., structure elevations and structure recesses formed between the structure elevations, e.g., as rectangular profiling, a structure width that is smaller than a relevant wavelength of the THz radiation, e.g., in a range between one tenth and one half of the relevant wavelength, e.g., with the shortest wavelength of the used THz wavelength band as relevant wavelength, a structure height, e.g., profile height, which is, e.g., equal to one quarter of the relevant wavelength, e.g., at an average wavelength of the used THz wavelength band as relevant wavelength, e.g., where h16=/4+n*/2, with as relevant wavelength, h16 as structure height, e.g., profile height, n as integer multiple, including zero, in particular, with the shortest wavelength of the emitted THz radiation as relevant wavelength.

32. The THz sensor of claim 28, wherein, in the compensation area, behind and/or inside the lens, two separate waveguide channels are formed which pass, owing to their shapes, in particular, as elongated rectangles, each only exactly one linear polarization direction, where the two polarization directions of the two waveguide channels are orthogonal in relation to one another.

33. The THz sensor of claim 22, wherein an Orthomode coupler is provided in the compensation area which splits the THz transmission beam in two opposingly circularly polarized waves and/or joins orthogonally polarized waves.

34. The THz sensor of claim 22, wherein an attenuating medium is provided in a gap between the rear side of the lens and a metal front side of the support plate, the attenuating medium THz radiation attenuating in a wavelength range about an average wavelength.

35. The THz sensor of claim 34, wherein the attenuating medium exhibits a complex relative permittivity .sub.r which is described by a real part .sub.r and an imaginary part .sub.r as .sub.r, .sub.r+i.sub.r (equation 1), where the imaginary part .sub.r describes an attenuation value of the attenuating medium, and a refractive index of the attenuating medium corresponds to a refractive index of the lens, so as to avoid reflections between the lens rear side and the attenuating medium.

36. The THz sensor of claim 22, wherein a front face of the support device exhibits a taper in the compensation area, in particular, in the connecting area around an average detection area, the taper, in particular, sloping towards the rear, to deflect the reflection beam incoming along the optical axis into the gap at least in part in a direction perpendicular to the optical axis, e.g., laterally outwards.

37. The THz sensor of claim 22, wherein an interference structure is formed in the reflection plane, to reflect the reflection beam incoming into the gap while creating a destructive interference, including a plurality of structure recesses for creating reflections of different path lengths which equal suitable values of a relevant or several relevant wavelengths of a wavelength range of the emitted THz radiation, e.g., including structure recesses or structure elevations respectively, e.g., profile heights corresponding to one quarter of the relevant wavelength plus a multiple integer of on half of the relevant wavelength.

38. The THz sensor of claim 22, wherein the lens has an arched, e.g., oval front face and a planar and/or structured lens rear side by means of which the lens is directly or indirectly attached to the support device.

39. A THz measuring device for measuring an object to be measured, in particular, a pipe made of plastics, rubber or an organic material, the THz measuring device comprising at least one THz sensor (2) according to claim 22 for emitting a THz transmission beam and receiving a THz reflection beam, a controller device adapted to receive a measuring signal of the THz transceiver and to determine distances and/or layer thicknesses of an object to be measured, and a measuring space for accommodating the object to be measured.

40. The THz measuring device of claim 39, further comprising a housing surrounding a measuring space for accommodating the object to be measured, the THz sensor being provided on the housing, in particular, including a plurality pf THz sensors and/or rotational arrangement of the THz sensor on the housing for rotating or revolving around the measuring space so as to measure the entire circumference of the object to be measured.

41. A THz measuring method for measuring distances and/or layer thicknesses of an object to be measured, e.g., a pipe made of plastics, rubber or an organic material, using a THz sensor, wherein a THz transmission beam is emitted from a THz transceiver of the THz sensors along an optical axis through a measuring space onto the object to be measured, a THz reflection beam is reflected back from boundary surfaces of the object to be measured along the optical axis, where the THz reflection beam is detected by the THz transceiver in a detection area formed centrally around the optical axis, and a measuring signal including at least one wanted reflection peak is generated, and at least one distance and/or one layer thickness and/or one refractive index of the object to be measured is determined from the measuring signal by evaluation, where the reflected beam is influenced in a compensation area around the detection area in such a manner that multiple reflection components, guided back to the object to be measured by new reflection of the reflected beam at the THz sensor and created after reflection at the object to be measured are at least reduced in the measuring signal by means of detection in the THz transceiver.

42. The THz measuring method of claim 41, wherein the THz reflection beam, in the compensation area, in particular, in a connecting area joining the detection area in lateral directions, is influenced in one or more of the following manners: a) rotating the polarization plane, in particular, about 90, using a transpolarization structure, b) attenuating the reflected beam in the gap, e.g., by means of an attenuating medium, c) deflecting the reflected beam away in a lateral direction, in particular, away from the optical axis, d) forming a destructive interference of the re-reflected reflected beam, in particular, by means of an interference structure having a structuring depending on a relevant wavelength, e.g., one quarter of the average wavelength.

Description

[0046] The invention is illustrated in the following using accompanying drawings by means of a few embodiments. It is shown in:

[0047] FIG. 1 a THz measuring device for measuring a pipe as object to be measured;

[0048] FIG. 2 the construction of a THz sensor in a lateral view;

[0049] FIG. 3 a top view on the sensor support without lens;

[0050] FIG. 4 a diagram of a measuring signal with multiple reflections;

[0051] FIG. 5 an embodiment with transpolarization;

[0052] FIG. 6 the embodiment of the sensor with transpolarizing structure;

[0053] FIG. 7 an embodiment with attenuation of the reflections;

[0054] FIG. 8 an unchanged sensor and beneath it an embodiment with a taper in the reflection plane;

[0055] FIG. 9 an embodiment with structuring of the reflection plane for a destructive interference;

[0056] FIG. 10 the construction of a THz sensor in a sectional side view, corresponding to FIG. 2;

[0057] FIG. 11 embodiments with coating of the lens for a destructive interference;

[0058] FIG. 12 a further embodiment with two channels,

[0059] FIG. 13 a section through the lens from FIG. 12,

[0060] FIG. 14 a further embodiment with an OMT.

[0061] 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.

[0062] 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.

[0063] 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 6 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., 6=c0/c6).

[0064] 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.

[0065] In a XYZ coordinate system the X direction extends along the optical axis A, accordingly, the YZ plane perpendicular or, respectively, lateral thereto.

[0066] 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.

[0067] 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.

[0068] FIG. 4 shows a time diagram of a measuring signal S1 with a wanted signal peak P0 which is generated by proper reflection of the THz transmission beam 8 on a boundary surface, e.g., g1. As a matter of principle, in addition to the wanted signal peak P0, unwanted multiple reflections will occur which may lead to multiple reflection peaks P1, P2, P3, . . . , as shown in FIG. 4. The reflected beam 15 emitted from the THz sensor 2 along the optical axis A onto the object to be measured 6 and reflected on the boundary surfaces g1, g2, g3 and g4 again passes through the lens 14, whereby the part of the reflected beam 15 coming in centrally in the travels into the waveguide 12 and to the THz transceiver 10 and generates the wanted reflection peak P0. Thus, according to FIG. 4, the wanted reflection peak P0 will appear in the measuring signal S1 with a time of flight that corresponds to the distance d1 of the boundary surface g1 in relation to the THz transceiver 10. Hereby, distances are determined as double the path length of the THz radiation from the sensor 2 to the boundary surface g1 and back to the sensor 2.

[0069] 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.

[0070] Thus, in FIG. 4, owing to the multiple reflection peaks P1, P2, P3 . . . may occur which lie in areas in which proper measuring peaks are to be expected also because, e.g., the front wall area with the boundary surfaces g1, g2 lies temporally before the rear wall area with the boundary surfaces g3, g4 so that the double reflection peak of g1 may get into the time range of g3 or g4. Thus, the superimposition may compromise the evaluation.

[0071] 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.

[0072] The compensation area 9 [0073] extends in the YZ plane, in particular, outside the central detection area 7, to avoid any influence of the directly received measuring signal of the proper single reflection, i.e., with the wanted reflection peak P0, [0074] whereby it may encompass in the X direction the rear side 14a of the lens 14, the front face 11a of the support plate 11, and a gap potentially created in-between these.

[0075] FIGS. 5, 6 show an embodiment with transpolarization (transverse polarization). Hereby, the THz sensor 2 emits a polarized THz transmission beam 8 which oscillates, e.g., in the xy plane. In the compensation area 9 a transpolarization structure 16 is formed, as shown in FIG. 6, which rotates the polarization plane of incident THz radiation about 90. Thus, in the second reflection of the reflected beam 15 the polarization is rotated about 90 so that the reflected beam exhibits a polarization rotated by 90 compared to the transmitted beam 8 and oscillates, e.g., in the xz plane. The doubly reflected beam will be reflected again accordingly on the boundary surfaces g1, g2, g3, g4 and travels as doubly reflected beam 15-2 through the lens 14 back to the waveguide 12. However, because only the emitted polarization direction of the THz transmission beam 8 is able to couple-in again into the waveguide 12 and to the THz transceiver 10, the doubly reflected beam 15-2 will no longer be measured. In principle, the THz beam reflected again on the reflection plane, i.e., e.g., the font face 11a, which, therefore, again oscillates in the XY plane following double rotation of the polarization, may subsequently, after reflection on the boundary surfaces g1 through g4, again lead to a measuring peak; however, for one thing, this will be significantly smaller and, for another, can be subsequently recognized and subtracted. In particular, according to the above embodiments, the double reflections are problematic because, in particular, the double reflections on the front boundary surfaces g1, g2 may lie in the area of the proper measuring signals of the rear boundary surfaces g3, g4 making them more difficult to recognize and subtract.

[0076] FIG. 6 shows an advantageous embodiment of the transpolarization structure 16, where on the reflection plane, i.e., in particular, the front face 11a, a profiling is formed, in particular, as a formation of structure elevations, i.e., in particular, profiles 16a, and structure recesses 16b. i.e., slots or grooves. the transpolarization structure 16 may be designed, in particular, as a rectangular structure, i.e., with vertical walls between the profiles 16a and the slots 16b, where the transpolarization structure 16 preferably exhibits a structure width b16, i.e., the width of one unit made of profile 16a and slot 16b, smaller than the wavelength A or the average wavelength A.

[0077] Thus, the structure width b16 e.g., may lie in a range between 1/10 and . The profile height h16 may lie e.g., in a range of a quarter of or respectively.

[0078] The transpolarization structure 16 runs at a structure angle 16 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.

[0079] FIG. 7 shows an embodiment with attenuation of the reflected beam 15 by means of an attenuating medium 18 which is introduced in a gap 19 between the lens rear side 14a and the front face 11a of the support plate 11, leaves the central detection area 7 open and attenuates the THz radiation in the relevant frequency range. Such an attenuating medium 18 can be described as complex relative permittivity r, i.e.,

.sub.r=.sub.r+i.sub.r,

[0080] Where the correlation between [0081] the complex relative permittivity r, [0082] the refractive index n and [0083] the absorption coefficient k [0084] is defined, in particular, by

n.sup.2={square root over ((r.sup.2+r.sup.2+r))}

[0085] For small values of .sub.r it can be assumed that n.sup.2=.sub.r,

where, in particular, the imaginary part .sub.r indicates the attenuating by the attenuating medium 18.

[0086] 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.

[0087] By introducing the attenuating medium 18 with a high attenuation value 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.

[0088] 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: [0089] a maximum attenuating value .sub.r18 of the attenuating medium 18, [0090] the amount of the complex relative permittivities Cr of the media 18, 14 is equal at the transition of the materials, i.e., [0091] .sub.r, 18=.sub.r, 14.
Since the central detection area 7 is kept open neither the THz transmission beam 2 nor the central part of the reflected beam 15 are attenuated.

[0092] FIG. 8 shows in the upper part an unchanged design of the sensor 2 in the detection area 7 and the connecting area 21, and at the bottom an embodiment with a taper for lateral deflection of disturbing components of the reflected beam 15. Hereby, the support plate 11 on the support plate front face 11a is structured, in particular, sloped, such that the reflected beam 15 outside the central detection area 7 upon impingement on the front face 11a of the support plate 11 is laterally deflected somewhat, i.e., is reflected back not exactly perpendicularly along the optical axis A. Hereby, the reflection plane, i.e., the front face 11a, in particular, in a connecting area 21 in the immediate vicinity of the waveguide 12 or, respectively, of the detection area 7 formed in front of the waveguide is sloped so that a taper 20, in particular, laterally sloping to the outside, is formed around the waveguide 12. Hereby, it was measured that this central connecting area 21 around the waveguide 12 is responsible for a large portion of the double reflected radiation, and therewith, according to the invention, is significantly reduced by the taper.

[0093] The embodiments of FIGS. 5, 6, 7, 8, 9 can be advantageously combined. Thus, in particular, the attenuating medium 18 may be provided in addition to the taper 20. The attenuating medium 18 may, in particular, be introduced in the intermediate area 19 exposed by the taper 20, shown in FIG. 8 as a dotted region. This also guarantees that no attenuating medium 18 reaches the area in front of the waveguide 12.

[0094] FIG. 9 shows a further embodiment for suppressing the multiple reflections, where in the reflection plane, i.e., in particular, the front face 11a of the support plate 11, outside the detection area 7, in particular, in the connecting area 21, an interference structuring 22 is formed, allowing for a widest possible destructive interference of the impinging and re-reflected reflected beam 15. To that end, starting from the front face 11a, structure recesses 22a, 22b, 22c with varying depths are formed so that the reflected beam 15 is reflected, for one thing, on the remaining areas 22d of the original surface 11a of the support plate 11, and, for another, in the various recesses 22a, 22b, 22c.

[0095] 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 /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 2/4=/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 /4, where they, in particular, each also alternate in a lateral direction with area 22d so as to form an effective destructive interference.

[0096] 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.

[0097] FIG. 11 shows an embodiment wherein on the lens surface, in particular, the lens rear side 14a, a coating 24 is applied as a consistent layer. Thus, the representation of FIG. 11 essentially corresponds to that of FIG. 7. The coating 24 is followed by a medium 25 which, according to different embodiments, may be, e.g., air or even, e.g., a metal layer. Hereby, the materials of the layers 24 and 25, i.e., in particular, the refractive indexes (permittivities) n14, n24 and n25 of the materials of the media of 14, 24 and 25 as well as the thickness d24 of the layer 24 are chosen such that a destructive interference of the partial reflected beams R1 and R2 occurs on the boundary surfaces 14a of the lens 14 and 24a of the coating 24:

[0098] 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, [0099] further, the reflected beam 15 travels through the coating 24 and to the boundary surface 24a, i.e., the transition from the coating 24 to the medium 25, where the second partial reflected beam R2 is generated.

[0100] Depending on the ratio of the refractive indexes (permittivities) n14, n24 and n25 [0101] a phase jump of one-half lambda will occur on the boundary surfaces 14a and 24a when the reflected beam 15 travels from an optically thinner medium (smaller refractive index or smaller n respectively) to an optically thicker medium (larger refractive index n), [0102] or there will be no phase jump when the reflected beam 15 travels from an optically thicker medium (larger refractive index or larger n respectively) to an optically thinner medium (smaller refractive index or smaller n respectively)

[0103] Hereby, this embodiment is referred to, in particular, at least one relevant wavelength , preferably to a plurality of relevant wavelengths A.

[0104] The partial reflected beams R1 and R2 form a destructive interference when, in particular, the following is true for the wavelength : [0105] A) if n 24 is larger than n 14: [0106] R1 exhibits a phase jump of /2, [0107] A1) if n 25 is smaller than n 24, e.g., with air as the medium 25, i.e., n 25=1, [0108] then R2 will appear without phase jump, where, in that case, preferably d24_=/2 is chosen, possibly even d24_=/2+Z*/2
where Z is an integer, i.e., Z=0, 1, 2, 3 [0109] A2) if n 25 is larger than n 24, e.g., with metal as the medium 25, e.g., a metal layer, e.g., metal vaporization, or even a thicker attenuating medium 18 of the embodiment shown above in FIG. 7, then R2 will appear with a phase jump, where, in that case, preferably d24_=/4 is chosen, possibly even d24_=/4+Z*/2
where Z is an integer, i.e., Z=0, 1, 2, 3 [0110] B) if n 24 is smaller than n 14: [0111] R1 has no phase jump, [0112] B1) if n 25 is smaller than n 2, e.g., with air as the medium 25, i.e., n 25=1, [0113] then R2 will appear without phase jump, where, in that case, preferably d24_=/4 is chosen, possibly even d24_=/4+Z*/2
where Z is an integer, i.e., Z=0, 1, 2, 3 [0114] B2) if n 25 is larger than n 24, e.g., with metal as the medium 25 25, e.g., a metal layer, e.g., metal vaporization, or even a thicker attenuating medium 18 of the embodiment shown above in FIG. 7, so then R2 will appear with a phase jump, where, in that case, preferably d24_=/2 is chosen, possibly even d24_=/2+Z*/2
where Z is an integer, i.e., Z=0, 1, 2, 3

[0115] Hereby, preferably, the central detection area 7 around the optical axis A is kept open again.

[0116] The medium 25 as air may be present, in particular, in an arrangement of the lens 24 in front of the plate 11, [0117] the medium 25 as a thicker medium in the case of, e.g., the aforementioned metal coating but also another coating.

[0118] Hereby, the embodiment of FIG. 11 may be combined well, in particular, with the embodiment of FIG. 7, in that the medium 25 of FIG. 11 is chosen as an attenuating material 18.

[0119] FIG. 12, 13 shows a further embodiment, wherein, in contrast to the embodiment of FIG. 2, 3, instead of a waveguide 12, two waveguide channels 112a, 112b are formed each supporting only one linear polarization due to their elongated rectangular shape. The two rectangular waveguide channels 112a, 112b are designed orthogonal in relation to one another in that they are formed in elongated shapes in directions orthogonal in relation to one another, e.g., z and y of the yz plane. Thus, the waveguide channels 112a, 112b are followed on the right side by the coupling-in points which together form the compensation formation 17 and a compensation area 9 or, respectively, are part of the compensation area 9. Hereby, a coupling-in is achieved in directions orthogonal in relation to one another.

[0120] 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.

[0121] According to the embodiment of FIG. 14, an OMT 212, i.e., Orthomode transducer or, respectively, Orthomode coupler is provided as compensation formation 17 or part of the compensation formation 17, splitting up circular polarized waves, or, respectively, joins orthogonal polarized waves. Thus, in this case, preferably, the OMT 212 forms a square waveguide 12 in its right-hand area.

LIST OF REFERENCE NUMERALS

[0122] 1 THz measuring device [0123] 2 THz sensor [0124] 3 adjustment device [0125] 4 controller device [0126] 5 measuring space [0127] 6 object to be measured, e.g., plastic pipe [0128] 7 central detection area [0129] 8 THz transmission beam [0130] 9 compensation area between lens 14 and support device 11 [0131] 10 THz transceiver, e.g., sensor chip [0132] 10a THz-Transmitter or THz transceiver [0133] 10b THz-Receiver [0134] 11 support device, e.g., support plate, sensor holder [0135] 11a front side of plate, in particular, reflection plane [0136] 12 waveguide [0137] 14 lens [0138] 14a rear side of lend [0139] 15 reflected beam [0140] 15-2 doubly reflected beam [0141] 16 transpolarization structure [0142] 16a structure elevation [0143] 16b structure recess [0144] b16 structure width [0145] h16 profile height [0146] a16 structure angle [0147] 17 compensation formation [0148] 18 attenuating medium [0149] 19 gap [0150] 20 taper [0151] 21 connecting area [0152] 22 interference structure [0153] 22a, 22b, 22c structure recess of the interference structure 22 [0154] 22d remaining area, structure recess=0 of the interference structure [0155] 24 coating [0156] 24a boundary surface of the coating 24 as transition from the coating 24 to the medium 25 [0157] 25 medium, e.g., air, metal [0158] 112a, 112b elongate waveguide channels, in orthogonal orientation, for conducting exactly one polarization direction [0159] 212 Orthomode Transducer (OMT) structure [0160] A optical axis of the THz sensor 2 [0161] B axis of symmetry of the THz measuring device 1, in particular, also pipe axis [0162] c6 speed of light in the material of the object to be measured 6 [0163] c0 speed of light in vacuum, air [0164] d1 distance of the boundary surface g1 to the THz sensor 2 [0165] d2 distance of the front face 11a to the boundary surface g1 [0166] .sub.r permittivity [0167] .sub.r real part, refractive index [0168] .sub.r attenuation, attenuation value [0169] .sub.r, Medium dielectricity of the media, where medium=6, 14, 18 [0170] g1, g2, g3, g4 boundary surfaces of the object to be measured 6 [0171] P0 wanted reflection peak [0172] P1 double reflection peak [0173] P2, P3, P4 higher multiple reflection peaks