Method and device for processing data associated with a model characterizing the propagation of terahertz electromagnetic waves

Abstract

The present invention relates to a method for processing data associated with a model characterizing the propagation of terahertz (THz) radiation in a spatial domain, the spatial domain comprising at least one terahertz device for emitting and / or receiving terahertz electromagnetic waves and / or at least one object that can be subjected to terahertz electromagnetic waves. The method includes providing a model and characterizing the propagation of terahertz electromagnetic waves in the region of at least one interface between two adjacent media in the spatial domain using the model. The model has conditions that depend on at least one of the following factors: a) the frequency of the terahertz electromagnetic waves; and b) the spatial extension of at least one of the two adjacent media, e.g., along a first spatial direction.

Description

[Technical Field]

[0001] The present disclosure relates to a method for processing data associated with a model that characterizes the propagation of terahertz (THz) electromagnetic waves in the spatial domain.

[0002] The present disclosure further relates to a device for processing data associated with a model that characterizes the propagation of terahertz (THz) electromagnetic waves in a spatial domain. Summary of the Invention

[0003] An exemplary embodiment relates to a method for processing data associated with a model characterizing the propagation of terahertz (THz) electromagnetic waves in a spatial domain that includes at least one terahertz device for emitting and / or receiving terahertz electromagnetic waves and / or at least one object that can be exposed to terahertz electromagnetic waves. The method includes providing a model and characterizing the propagation of the terahertz electromagnetic waves in a region at at least one interface between two adjacent media in the spatial domain using the model. The model characterizes the THz electromagnetic waves and includes conditions that depend on at least one of the following factors: a) the frequency of the terahertz electromagnetic waves; and b) the spatial extension and / or position of at least one of the two adjacent media, e.g., along a first spatial direction.

[0004] In another exemplary embodiment, a model is provided for characterizing at least one reflection and / or transmission of terahertz electromagnetic waves at at least one interface between at least two media, e.g., the model characterizes some reflections and / or transmissions of terahertz electromagnetic waves at at least two interfaces between different media, e.g., a condition characterizing the terahertz electromagnetic waves has a different value at each of the at least two interfaces.

[0005] In another exemplary embodiment, a model is provided for characterizing one or more reflections and / or transmissions of terahertz electromagnetic waves at a plurality of interfaces between every two adjacent media in the spatial domain by a coherent superposition function, where conditions are provided as weighting factors, e.g., weighting factors other than at least some components of the coherent superposition function.

[0006] In another exemplary embodiment, a model having a first component is provided that characterizes a sample measurement of an object in a reflection or transmission geometry with terahertz electromagnetic radiation. For example, the first component can be characterized in the frequency domain in a reflection geometry based on the following mathematical formula:

[0007]

number

[0008] In another exemplary embodiment, a model having a second component is provided that characterizes a reference measurement of a reference object in a reflection or transmission geometry by terahertz electromagnetic waves. For example, the second component can be characterized in the frequency domain in a reflection geometry, for example, based on the following formula:

[0009]

number

[0010] In another exemplary embodiment, a model is provided that can be characterized for example for a reflection arrangement in the frequency domain, for example based on the following equation:

[0011]

number

[0012] In another exemplary embodiment, as an alternative or in addition to a) the frequency of the terahertz electromagnetic waves and / or b) the spatial extension and / or position of at least one of the two adjacent media, e.g., along a first spatial direction, conditions are provided that depend on at least one of the following factors: c) the reflection index characterizing the number and succession of reflections and / or transmissions, d) the angular orientation of the terahertz device relative to the object and / or reference object, e) the distance between the at least one terahertz device and / or at least one object, f) surface characteristics of the at least one object, such as the surface shape and / or surface roughness.

[0013] In another exemplary embodiment, a model is provided to model distance-dependent spectral changes in the transmission function of terahertz electromagnetic waves as distance-dependent and / or depth-dependent attenuation and / or amplification, e.g., using conditions and / or weighting factors.

[0014] In another exemplary embodiment, a model is provided to model angle-dependent spectral changes in the transmission function of terahertz electromagnetic waves as angle-dependent attenuation and / or amplification, for example, using conditions and / or weighting factors.

[0015] In another exemplary embodiment, a model is provided that models spectral changes in the transmission function of terahertz electromagnetic waves based on at least one surface characteristic of at least one object, such as based on surface shape and / or surface roughness, for example, using conditions and / or weighting factors.

[0016] In another exemplary embodiment, a model is provided to include an object having several layers of different media, for example, the model characterizing at least one of the following elements: a) reflections and / or transmissions of terahertz electromagnetic radiation in the object, such as between adjacent layers, b) multiple reflections and / or multiple transmissions of terahertz electromagnetic radiation in the object, c) virtual reflection and / or transmission points in the object, which may be characterized, for example, by a reflection index, and d) coherent superposition of various reflections and / or transmissions of terahertz electromagnetic radiation in the object.

[0017] In another embodiment, a method is provided to further include determining the conditions and / or respective values ​​of the conditions based on an optical model of the system characterizing the terahertz device and the target and / or reference object, as well as optionally the ambient medium around the terahertz device and the target or reference object, e.g., the optical model characterizing the spectral transmission function of terahertz electromagnetic radiation within the system.

[0018] In another exemplary embodiment, a method is provided to further include determining the conditions and / or individual values ​​of the conditions based on an optical model of the system that characterizes the terahertz device and the target and / or reference object, as well as optionally the ambient medium around the terahertz device and the target or reference object, the optical model characterizing, for example, the amplitude and phase over the spatial extension of the terahertz electromagnetic wave within the system.

[0019] In another exemplary embodiment, an optical model is provided that takes into account the diffraction effects of terahertz electromagnetic waves.

[0020] In another exemplary embodiment, a method is provided to further include determining an optical model based on modeling by a) ray tracing, and / or b) a description based on diffraction theory by diffraction integrals, e.g., Collins integrals, and / or c) parametric calculations with model functions, and optionally calibrating this optical model, wherein, for example, determining and / or calibrating the optical model is performed by frequency decomposition techniques.

[0021] In another exemplary embodiment, a method is provided for further comprising calibrating the optical model, e.g., for the spectral transmission function and / or spatial amplitude and / or phase, based on at least one of the following factors: a) the angle between the optical axis of the terahertz device and a surface normal to the object or reference object; b) the distance between the terahertz device and the surface of the object or reference object; c) surface characteristics of at least one object and / or reference object, e.g., based on the shape, such as the curvature of the surface, and / or the roughness of the surface; d) the frequency of the terahertz electromagnetic waves.

[0022] In another exemplary embodiment, a method is provided for further comprising varying the spatial positions of the reflection and / or transmission points characterized by the model and deriving a property, such as the thickness of at least one layer in the medium of interest, based on the varying, wherein at least one of the following elements is used to derive the property: a) performing a correlation method, b) performing a pattern recognition method, c) determining maxima and / or minima, d) utilizing a machine learning method, e) performing a fitting method, for example by adapting a model based on a least squares method.

[0023] In another exemplary embodiment, condition values ​​or weighting factors are provided that do not change when changing the spatial location of the reflection and / or transmission points, for example in the process of determining the layer thickness of the object.

[0024] In another exemplary embodiment, a varying condition value, or weighting factor, is provided when varying the spatial location of the reflection and / or transmission points, for example, in the process of determining the layer thickness of the object.

[0025] In another exemplary embodiment, interpolated condition values ​​or weighting factors are provided when varying the spatial positions of the reflection and / or transmission points, e.g., by utilizing available values. In another exemplary embodiment, a method is provided for determining, e.g., to pre-calculate at least one component of the model and / or optical model, and optionally, further including at least temporarily storing, e.g., in a database, a result of this pre-calculation determination.

[0026] In another exemplary embodiment, a method is provided for further comprising determining reference data for several different spatial arrangements of the terahertz device and the object or reference object relative to one another, which further comprises: arranging, e.g., the terahertz device and the object and / or reference object relative to one another in a given arrangement; determining reference data for the given arrangement; and, again optionally, repeating the arranging and determining steps until a predetermined termination criterion is reached. The arranging includes, e.g., positioning the terahertz device and / or the object or reference object by a positioning device, such as a robot.

[0027] In another exemplary embodiment, the reference data may be stored at least intermittently by at least one database.

[0028] In another exemplary embodiment, a method is provided for further including determining, using a sensor, such as an additional sensor, at least one of the following: a) the distance between the terahertz device and the target or reference object, b) the angular orientation between the terahertz device and the target or reference object in a one-dimensional or two-dimensional arrangement, and c) the shape, such as the curvature, of the surface of the target or reference object. In another exemplary embodiment, optical sensors (e.g., laser ranging and / or laser angle measurement), and / or acoustic sensors (e.g., ultrasonic sensors), and / or sensors based on the use of electromagnetic waves, such as radar sensors, may be used for this purpose.

[0029] In another exemplary embodiment, a method is provided to further include utilizing distance and / or angular orientation and / or shape of the model, for example, to determine the conditions and / or individual values ​​of the conditions.

[0030] In another exemplary embodiment, a method is provided for determining whether at least one region of interest, e.g., a reflection point, for which condition values ​​and / or reference data are available, e.g., which may be characterized via a calculated and / or calibrated transmission function, is located within a parameter range (e.g., which may be characterized by a distance range and / or an angle range), and based on this determination, varying its spatial location, e.g., distance and / or angle, e.g., by at least one positioning device (e.g., a robot), for example, repeating this varying spatial location until the region of interest is located within said parameter range, and optionally performing evaluation.

[0031] Another exemplary embodiment refers to a device for carrying out the methods according to these embodiments.

[0032] Another exemplary embodiment refers to a machine-readable storage medium comprising instructions that, when executed by a computer, cause the computer to perform a method according to an embodiment.

[0033] Another exemplary embodiment refers to a computer program comprising instructions that, when executed by a computer, cause the computer to perform a method according to an embodiment.

[0034] Another exemplary embodiment refers to a data transmission signal transmitting and / or characterizing the above computer program according to the embodiment.

[0035] Another exemplary embodiment refers to the use of a method according to an embodiment, and / or a device according to an embodiment, and / or a machine-readable storage medium according to an embodiment, and / or a computer program according to an embodiment, and / or a data transmission signal according to an embodiment for at least one of the following elements: a) determining at least one characteristic of an object, such as, for example, the thickness of at least one layer of the object; b) improving the accuracy of the model by taking into account propagation of terahertz electromagnetic waves in non-planar forms, such as, but not limited to, planar waves; c) taking into account the dependence of the spectral transmission function on the distance to the terahertz device; d) taking into account the dependence of the spectral transmission function on the angle relative to the terahertz device; e) taking into account surface characteristics of at least one object or reference object based on, for example, the shape, such as the curvature of the surface, and / or the roughness of the surface.

[0036] Further features, use options, and advantages can be seen in the following description of exemplary embodiments represented in the drawings. All of the features described or represented herein, by themselves or in any combination, form the object of exemplary embodiments, regardless of how they are summarized in the claims or in the back references, and regardless of how they are configured and / or represented in the description and / or drawings. [Brief explanation of the drawings]

[0037] [Figure 1] FIG. 1 shows a simplified block diagram of a THz device for use with exemplary embodiments. [Figure 2] FIG. 10 is a diagram that schematically illustrates a simplified flow diagram according to another exemplary embodiment. [Figure 3] FIG. 10 is a diagram that schematically illustrates a simplified block diagram according to another exemplary embodiment. [Figure 4A] FIG. 10 is a diagram that schematically illustrates a simplified block diagram according to another exemplary embodiment. [Figure 4B] FIG. 10 is a diagram that schematically illustrates a simplified block diagram according to another exemplary embodiment. [Figure 5] FIG. 10 is a diagram that schematically illustrates a simplified block diagram according to another exemplary embodiment. [Figure 6] FIG. 10 is a diagram that schematically illustrates a simplified block diagram according to another exemplary embodiment. [Figure 7] FIG. 10 is a diagram that schematically illustrates a simplified flow diagram according to another exemplary embodiment. [Figure 8] FIG. 10 is a diagram that schematically illustrates a simplified flow diagram according to another exemplary embodiment. [Figure 9] FIG. 10 is a diagram that schematically illustrates a simplified block diagram according to another exemplary embodiment. [Figure 10] FIG. 10 is a diagram that schematically illustrates a simplified flow diagram according to another exemplary embodiment. [Figure 11] FIG. 10 is a diagram that schematically illustrates a simplified flow diagram according to another exemplary embodiment. [Figure 12] FIG. 10 is a diagram that schematically illustrates a simplified flow diagram according to another exemplary embodiment. [Figure 13] FIG. 10 is a diagram that schematically illustrates a simplified flow diagram according to another exemplary embodiment. [Figure 14] FIG. 10 is a diagram that schematically illustrates a simplified flow diagram according to another exemplary embodiment. [Figure 15] FIG. 10 is a diagram that schematically illustrates a simplified flow diagram according to another exemplary embodiment. [Figure 16] FIG. 10 is a diagram that schematically illustrates a simplified block diagram according to another exemplary embodiment. [Figure 17]10A-10C are diagrams that schematically illustrate aspects of usage options according to another exemplary embodiment. [Figure 18] FIG. 10 is a diagram that schematically illustrates a simplified block diagram according to another exemplary embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0038] 1 shows a schematic block diagram of a THz device 10 suitable for use with a method according to an example embodiment. The THz device 10 is configured to emit and / or receive THz electromagnetic waves TS, such as THz electromagnetic waves TS reflected by or transmitted through an object 20.

[0039] Another exemplary embodiment in Fig. 2 relates to a method for processing data DAT (Fig. 1) associated with a model MOD characterizing the propagation of terahertz (THz) electromagnetic waves TS in a spatial domain RB that includes at least one terahertz device 10 for emitting and / or receiving terahertz electromagnetic waves TS and / or at least one object 20 that can be exposed to the terahertz electromagnetic waves TS. The method includes providing 100 (Fig. 2) a model MOD and characterizing (e.g., describing) 102 the propagation of the terahertz electromagnetic waves TS in a region at at least one interface GF (see Fig. 3) between two adjacent media M1, M2 in the spatial domain RB. This model MOD characterizes the THz electromagnetic wave TS and includes a condition T that depends on at least one of the following factors: a) the frequency of the terahertz electromagnetic wave TS, b) the spatial extension D and / or the position of at least one of the two adjacent media M1, M2, for example along a first spatial direction Rx.

[0040] In another exemplary embodiment, two adjacent media M1, M2 in the spatial region RB may be important in the THz device 10 (e.g., a THz emitter (not shown in FIG. 1) and / or an optional beam-shaping THz optical system, etc.) and / or a medium present in the environment UM of the spatial region RB, such as ambient air and / or dry air and / or protective gas, may be important in the object 20. See the exemplary layer structure M1, M2 according to FIG. 3.

[0041] In another exemplary embodiment, the spatial extent D may be a thickness, such as the layer thickness of the layer M1 in the object 20.

[0042] FIG. 3 shows an exemplary structure of the object 20, e.g., according to FIG. 1. This given structure has, e.g., four layers 20-1, 20-2, 20-3, and 20-4, each composed of a corresponding material M1, M2, M3, and M4. Reference symbol GF-0 denotes the interface between medium M1 of layer 20-1 and the surrounding medium present in the environment UM (FIG. 1). Reference symbol GF-1 denotes the interface between medium M1 of layer 20-1 and medium M2 of layer 20-2. Reference symbol GF-2 denotes the interface between medium M2 of layer 20-2 and medium M3 of layer 20-3. Reference symbol GF-3 denotes the interface between medium M3 of layer 20-3 and medium M4 of layer 20-4. THz electromagnetic waves propagated within the structure according to FIG. 4A are represented in FIG. 4A by dashed block arrows TS.

[0043] 4B shows an example of a structure similar to that according to FIG. 4A with details of the reflection and / or transmission of some of the components of the THz electromagnetic wave TS. The THz electromagnetic wave TS is emitted, for example, in the form of a THz pulse, which is explained by way of example below.

[0044] In another exemplary embodiment, the medium M1 may represent the surrounding medium present in the environment UM, for example between the THz device 10 and the object 20.

[0045] In another exemplary embodiment, the medium M4 may represent, for example, a metallic substrate on which two layers 20-2, 20-3, in this example two, made of other media M2, M3 may be arranged, these layers being made of a coating material containing a polymer, for example a paint for coating the substrate M4.

[0046] In another exemplary embodiment, a model MOD (FIG. 1) is provided to characterize at least one reflection r0, r1, r2, r0', r1' (FIG. 4B) and / or transmission t0, t1, t0', t1' of a terahertz electromagnetic wave TS at at least one interface GF-1, GF-2, GF-3 between at least two media M1, M2, M3, M4. For example, the model MOD characterizes multiple reflections and / or transmissions of the terahertz electromagnetic wave TS at at least two interfaces between various different media. For example, the condition T (FIG. 1) characterizing the terahertz electromagnetic wave has different values ​​T-1, T-2 (FIG. 4A), T-1, T-2, T-3 (FIG. 4B) at each of the at least two interfaces.

[0047] In another exemplary embodiment, a model MOD is provided to characterize one or more reflections and / or transmissions of a terahertz electromagnetic wave TS at a plurality of interfaces GF-0, GF-1, GF-2, GF-3 between every two adjacent media M1, M2, M3, M4 (FIGS. 4A, 4B) in the spatial domain RB (FIG. 1) by a coherent superposition function. Conditions T are provided as weighting factors G, for example as weighting factors other than at least some components of the coherent superposition function.

[0048] 5, a model MOD having a first component MOD-1 is provided that characterizes a sample measurement of the object 20 in a reflection or transmission geometry by a terahertz electromagnetic wave TS. For example, the first component MOD-1 can be characterized in the frequency domain, for example in a reflection geometry based on the following formula:

[0049]

number

[0050]

number

[0051] 5, a model MOD is provided having a second component MOD-2 that characterizes a reference measurement of a reference object 20′ in a reflection or transmission geometry by a terahertz electromagnetic wave TS. The second component MOD-2 can be characterized in the frequency domain, for example in a reflection geometry based on the following formula:

[0052]

number

[0053] In another exemplary embodiment, a model MOD (FIG. 1, FIG. 5) is provided that can be characterized for a reflection arrangement (FIG. 6) in the frequency domain, for example based on the following equation:

[0054]

number

[0055] In another exemplary embodiment, alternatively or in addition to a) the frequency and / or angular frequency of the terahertz electromagnetic wave TS and / or b) the spatial extension and / or position (e.g. characterized by coordinates x, y, z) of at least one of the two adjacent media, for example along a first spatial direction Rx, the following factors may be used: c) a reflection index R, characterizing the number and succession of reflections and / or transmissions; d) an angular orientation of the terahertz device 10 with respect to the object 20 (e.g. the optical axis of the THz device 10); A condition T and / or a weighting factor G (e.g., the formula symbols G(D,R,ω,x,y,z,α,β,Ω)) is provided that depends on at least one of: e) at least one angle α, β (see FIG. 9 ) between the optical axis OA and the normal vector 20a-n of the surface 20a; f) a distance L, for example, between the at least one terahertz device 10 and / or the at least one object 20; f) characteristics of the surface 20a of the at least one object 20, such as the shape of the surface 20a and / or the roughness of the surface 20a.

[0056] In another exemplary embodiment, the sum in the following part of the formula is not evaluated to an upper boundary "infinity", but to a predetermined finite value R of the reflectivity index, mentioned here as an example. max Therefore, in another exemplary embodiment, the following applies:

[0057]

number

[0058]

number

[0059]

number

[0060]

number

[0061] In another exemplary embodiment, R max The value of may be selected, for example, based on at least one of the following factors: a) desired accuracy; b) available computing power.

[0062] In another exemplary embodiment, a model MOD is provided to model distance-dependent spectral changes in the transmission function of the terahertz electromagnetic wave TS as distance-dependent and / or depth-dependent attenuation and / or amplification, e.g., using the condition T and / or weighting factors G( ).

[0063] In another exemplary embodiment, a model MOD is provided to model angle-dependent spectral changes in the transmission function of the terahertz electromagnetic wave TS as angle-dependent attenuation and / or amplification, e.g., using the condition T and / or weighting factors G( ).

[0064] In another exemplary embodiment, a model MOD is provided to model the spectral changes of the transmission function of the terahertz electromagnetic wave TS based on properties of the at least one surface 20a of the at least one object 20, such as based on the shape of the surface 20a and / or the roughness of the surface 20a, for example by using conditions T and / or weighting factors G( ).

[0065] In another exemplary embodiment, the model MOD allows for modeling of the propagation of the THz electromagnetic wave TS, which may be referred to as "differential modeling." Thus, for example, it is possible to take into account the path of individual reflections specifically for modeling purposes (and / or, for example, due to the importance of any individual reflection).

[0066] In another exemplary embodiment, the model MOD is a model of reflection and transmission of (partial) pulses of the THz electromagnetic wave TS, e.g., R maxThis allows for an individual description of possible combinations up to a predetermined maximum order, which may be characterized by a value. In another exemplary embodiment, the thickness-dependent distance at individual reflection points (e.g., interface regions) is defined using a corresponding trajectory for each such point. Thus, in another exemplary embodiment, it is possible to efficiently integrate geometric effects of the object 20 derived from the sample (whereby, in another exemplary embodiment, distance-dependent spectral changes in the transmission function may be modeled as depth-dependent attenuation).

[0067] In another exemplary embodiment, a model MOD is provided to include an object 20 having several layers 20-1, 20-2, 20-3, 20-4 ( FIG. 4B ) of at least partially different media M1, M2, M3, M4, for example, the model MOD characterizing at least one of the following elements: a) reflections and / or transmissions of the terahertz electromagnetic wave TS in the object 20, such as between adjacent layers, b) multiple reflections and / or multiple transmissions of the terahertz electromagnetic wave TS in the object 20, c) virtual reflection and / or virtual transmission points in the object 20, which may be characterized, for example, by a reflection index R, d) coherent superposition of various reflections and / or transmissions of the terahertz electromagnetic wave TS in the object 20.

[0068] 7, a method is provided to further include determining 110 the condition T and / or individual values ​​of the conditions T, T, T, ..., based on an optical model MOD-OPT of the system SYS (FIG. 1) that characterizes the terahertz device 10 and the object 20 and / or the reference object 20' (FIG. 6), and optionally, the ambient medium UM around the terahertz device 10 and the object 20 or the reference object 20'. For example, the optical model MOD-OPT characterizes a spectral transmission function of the terahertz electromagnetic wave TS within the system SYS.

[0069] In other exemplary embodiments, measurements can be performed using the reflection principle mentioned above by way of example. For example, the dashed block 12 in Fig. 6 represents an optical detector for detecting THz electromagnetic waves TS, e.g. THz electromagnetic waves reflected by (reference) objects 20, 20'.

[0070] In another exemplary embodiment, as an alternative or in addition to the reflection principle mentioned above by way of example, measurements can be performed using the transmission principle, see the optional THz detector 12' on the right side of Fig. 6. This makes it possible to detect a component TS' of a THz electromagnetic wave TS transmitted by, for example, a (reference) object 20, 20'. For embodiments based on measurements according to the transmission principle, the aspects of the model MOD described herein and the use of the condition T will apply in a corresponding manner.

[0071] 7, a method is provided to further include determining 110 the condition T and / or individual values ​​T-1, T-2, T-3, ... at the condition T based on an optical model MOD-OPT of the system SYS characterizing the terahertz device 10 and the object 20 and / or the reference object 20', and optionally the surrounding medium UM around the terahertz device 10 and the object 20 or the reference object 20'. The optical model MOD-OPT characterizes, for example, the amplitude and phase over the spatial extension of the terahertz electromagnetic wave TS within the system SYS.

[0072] In another exemplary embodiment, an optical model MOD-OPT is provided that takes into account the diffraction effects of the terahertz electromagnetic wave TS.

[0073] Optional step 112 of FIG. 7 represents determining and / or utilizing a condition T or its value, for example, a model MOD.

[0074] 8, a method is provided to further include determining 120 an optical model MOD-OPT based on modeling by a) ray tracing 120a, and / or b) a description based on diffraction theory by a diffraction integral, e.g., the Collins integral 120b, and / or c) a parametric calculation with a model function 120c, and optionally calibrating 122 the optical model MOD-OPT, wherein, for example, determining 120 and / or calibrating 122 the optical model MOD-OPT is performed by frequency decomposition techniques.

[0075] In another exemplary embodiment, a method is provided for further comprising calibrating 122 the optical model MOD-OPT, e.g., for the spectral transmission function and / or spatial amplitude and / or phase, based on at least one of the following elements: a) the angle α(β) between the optical axis OA (FIG. 9) of the terahertz device 10 and the surface 20a-n normal to the object 20 or the reference object 20′; b) the distance L between the terahertz device 10 and the surface 20a, 20a' of the object 20 or the reference object 20′; c) characteristics of the surface 20a of at least one object 20 and / or reference object 20′, e.g., based on the shape FO, e.g., the curvature of the surface 20a, 20a′, and / or the roughness of the surface 20a, 20a′; d) the frequency of the terahertz electromagnetic wave TS.

[0076] Dashed block 11 in Figure 9 represents an optional emitter for generating THz electromagnetic waves TS. Dashed block 12 in Figure 9 symbolizes an optional detector for detecting the THz electromagnetic waves TS, e.g., portions of the THz electromagnetic waves TS reflected or transmitted by the object 20 and / or the reference object 20'.

[0077] In an exemplary embodiment, the calculations for the purpose of determining the optical model MOD-OPT are performed by starting, for example, at a "start plane" (which may be characterized, for example, by the THz emitter 11) and extending (including variations in the position of the object 20 in local and / or angular ranges) to the object 20 via an optional optical (THz) system (not shown). This may be provided, in appropriate return, via the optional optical system described above from the object 20 to the THz detector 12 ("target plane").

[0078] In another exemplary embodiment, by varying the geometry (taking into account disturbances in the shape of the object 20 and / or distances and angles in one or two spatial directions), a transfer function for the THz signal can be calculated by frequency decomposition techniques, based on which, in another exemplary embodiment, for example, the condition T can be determined.

[0079] In another exemplary embodiment, the receive path and the transmit path can be calculated independently in advance and stored, for example, in a database DB. The receive path can be characterized, for example, by the distance from the object 20 to the THz detector 12. The receive path can be characterized, for example, by the distance from the THz emitter 11 to the object 20.

[0080] In another exemplary embodiment, the model used as the optical model MOD-OPT may be a parametric optical model based on, for example, an ABCD matrix, which characterizes, for example, the moments of the power density distribution and / or the propagation of these moments.

[0081] In another exemplary embodiment, the model used as the optical model MOD-OPT may be, for example, a numerical optical model.

[0082] 10, a method is provided to further include varying 130 the spatial locations (e.g., regions of interfaces GF-0, GF-1, ...) of the reflection and / or transmission points characterized by the model MOD, and deriving 132 a characteristic D-M2 (FIG. 4B), such as a thickness D-M2 of at least one layer 20-2 in a medium M2 of the object 20, based on the varying 130. For example, at least one of the following elements is used to derive 132 the characteristic: a) performing a correlation method 132a, b) performing a pattern recognition method 132b, c) determining maxima and / or minima 132c, d) utilizing a machine learning method 132d, e) performing a fitting method 132e (FIG. 11).

[0083] Put another way, in another exemplary embodiment, at least one parameter of the model MOD is a transmission function for the THz electromagnetic wave TS characterized by the model

[0084]

number

[0085] In another exemplary embodiment in Figure 12, a method is provided to determine 140 to pre-calculate at least one component of the model and / or optical model, and optionally further include at least temporarily storing 142, for example, a result VE of the determination of pre-calculation 140. For example, the result VE is stored in a database DB (see also Figure 1).

[0086] In another exemplary embodiment, pre-calculating 140 the model MOD and / or at least components MOD-1, MOD-2 of the model MOD, for example for a plurality of possible parameter values ​​(e.g., layer thicknesses D-M2 of various layers in the object 20), allows for efficient determination of a property of the object 20 (e.g., layer thickness D-M2 of layer 20-2), for example by comparing the transmission function H( ) of the THz electromagnetic wave TS with at least one possible transmission function predetermined by pre-calculating 140.

[0087] 13 , a method is provided to further include determining 150 reference data RD for several different spatial configurations (e.g., distance L and / or at least one angle α, β) of the terahertz device 10 and the object 20 or reference object 20′ relative to one another, e.g., arranging 150a the terahertz device 10 and the object 20 and / or reference object 20′ relative to one another in a given configuration, determining 150b the reference data RD for the given configuration, and also optionally repeating 152 the steps of arranging 150a and determining 150b until a predetermined termination criterion is reached. This arranging 150a includes, for example, positioning the terahertz device 10 and / or the object 20 or reference object 20′ by a positioning device PE, PE′ ( FIG. 9 ), such as a robot.

[0088] 14 , a method is provided to further include using (e.g., additional) sensors to determine 160 at least one of the following: a) distance L, AB between the terahertz device 10 and the object 20 or reference object 20′, b) angular orientation WA between the terahertz device 10 and the object 20 or reference object 20′, for example, in a one-dimensional configuration (i.e., characterized by angle α) or a two-dimensional configuration (i.e., characterized by angles α and β), and c) shape FO, such as curvature, of surface 20 a of the object 20 or reference object 20′. In another exemplary embodiment, optical sensors (e.g., laser ranging and / or laser angle measurement), and / or acoustic sensors (e.g., ultrasonic sensors), and / or sensors based on the use of electromagnetic waves, such as radar sensors, may be used for determining 160.

[0089] In another exemplary embodiment in FIG. 14, a method is provided to further include utilizing 162 the distance L, AB and / or angular orientation WA, and / or shape FO of the model MOD to determine, for example, the condition T and / or individual values ​​of the condition T.

[0090] In another exemplary embodiment in FIG. 15 , a method is provided for further comprising determining 170 whether at least one region of the object, e.g., reflection point GF (and / or all significant reflection points, i.e., all reflection points that provide a predetermined minimum contribution to the measurement and / or measurement result), is located within a parameter range (e.g., characterized by a distance range and / or an angle range). To that end, values ​​T-1, T-2, T-3, ..., of condition T, which can be characterized, e.g., via a calculated and / or calibrated transmission function, and / or reference data RD are available, and based on determining 170, modifying 172 an appropriate spatial arrangement, e.g., distance and / or angle, is determined. For example, modifying 172 is repeated 173, e.g., until the region of the object is located within the above-mentioned parameter range, and optionally performing evaluation 174. In another exemplary embodiment, evaluating 174 can also be performed for the purposes of pre-calculation 140 ( FIG. 12 ).

[0091] Another exemplary embodiment in FIG. 16 refers to a device 200 for carrying out the method according to these embodiments.

[0092] In another exemplary embodiment, a device 200 is provided that includes a computing device ("computer") 202 and a storage device 204 associated with the computing device 202 for temporarily storing at least one of the following elements: a) data DAT (e.g., a model MOD and / or at least a part of a database DB (FIG. 1)); b) a computer program PRG, in particular for performing a method according to an embodiment.

[0093] In another preferred embodiment, the storage device 204 comprises a volatile memory 204a (eg, a working memory (RAM)) and / or a non-volatile memory 204b (eg, a flash EEPROM).

[0094] In another exemplary embodiment, computing device 202 comprises and / or is configured with at least one of the following elements: a microprocessor (μP), a microcontroller (μC), an application specific integrated circuit (ASIC), a system on a chip (SoC), a programmable logic device (e.g., a field programmable gate array, FPGA), a hardware circuit, or any combination thereof.

[0095] Another exemplary embodiment refers to a machine-readable storage medium SM comprising instructions PRG' which, when executed by a computer 202, cause the computer 202 to perform a method according to the embodiment.

[0096] Another exemplary embodiment refers to a computer program PRG comprising instructions which, when executed by a computer 202, cause the computer 202 to carry out a method according to an embodiment.

[0097] Another exemplary embodiment refers to a data transmission signal DCS that characterizes and / or transmits a computer program PRG according to an embodiment. The data transmission signal DCS can be received, for example, via an optional data interface 206 in the device 200.

[0098] In another exemplary embodiment, the at least one positioning device PE, PE′ may also be controlled, for example via the data interface 206 .

[0099] Another exemplary embodiment in FIG. 17 is a method according to an embodiment, and / or a device according to an embodiment, and / or a machine-readable storage medium according to an embodiment, and / or a computer program according to an embodiment, and / or the following elements: a) determining 302 at least one characteristic of the object 20, such as, for example, a layer thickness D-M2 of at least one layer 20-2 of the object 20; b) improving 304 the accuracy of the model MOD by taking into account propagation of the terahertz electromagnetic wave TS in a non-planar form, such as, for example, but not limited to, a planar wave; c) determining a distance L to the terahertz device 10; or taking into account 306 the dependence of the spectral transmission function on the angular orientation between the terahertz device 10 and the object 20 and / or the shape and / or surface properties of the object 20; d) taking into account 306 the dependence of the spectral transmission function on the angles α, β relative to the terahertz device 10; e) taking into account 308 the properties of the surface 20a of at least one object 20 or reference object 20' based on the shape FO, e.g. the curvature of the surface 20a, 20a' and / or the roughness of the surface 20a, 20a'.

[0100] 18 shows a simplified block diagram according to another exemplary embodiment. Shown is an arrangement, e.g., a measurement object, having two paint layers 20-1, 20-2 applied on a substrate 20-3 (e.g., metal), with an ambient medium UM, e.g., air, around the arrangement. Exemplary embodiments and aspects will be described hereinafter with reference to the arrangement according to FIG. 18. By way of example, incoming and outgoing plane waves of THz electromagnetic waves are distinguished by the symbols "+" / "-".

[0101] In another exemplary embodiment, one or several of the following additional parameters (related to the formulas described above) may be provided for the model MOD (FIG. 1): F - A,n(ω): Frequency-dependent field strength of a backward-propagating THz pulse in air at the nth repetition step F - 1,n (ω): Frequency-dependent field strength of the backward-propagating THz pulse in the first paint layer (“Layer 1” 20-1) at the n-th repetition step F - 2,n (ω): Frequency-dependent field strength of the backward-propagating THz pulse in the second paint layer (“Layer 2”) 20-2 at the n-th repetition step F + A,n (ω): Frequency-dependent field strength of the forward-propagating THz pulse in air UM at the n-th repetition step F + 1,n (ω): Frequency-dependent field strength of the forward-propagating THz pulse in the first paint layer 20-1 at the n-th repetition step F + 2,n (ω): Frequency-dependent field strength of the forward-propagating THz pulse in the second paint layer 20-2 at the n-th repeat step ·r 12 : Reflection coefficient at the layer 1 / layer 2 boundary layer ·r 21 : Reflection coefficient at the layer 2 / layer 1 boundary layer ·t 12 : Permeability coefficient at the layer 1 / layer 2 boundary layer ·t 21 : Permeability coefficient at the layer 2 / layer 1 boundary layer ·r 2S : Reflection coefficient at the layer 2 / substrate 20-3 boundary layer D1: Layer thickness of layer 1 (layer 20-1) D2: Layer thickness of layer 2 (layer 20-2) R1: Reflectance index of layer 1 R2: Reflectance index of layer 2 n1 and n2 are the refractive indices of layer 1 and layer 2 ∈1, ∈2 are the extinction coefficients of layers 1 and 2

[0102] In another exemplary embodiment, one or several of the following phase conditions (eg, as dependent parameters) may be provided for the model MOD (FIG. 1):

[0103]

number

[0104]

number

[0105]

number

[0106] In another exemplary embodiment, multiple reflections can be taken into account, so that an unlimited number of conditions can be generated. The electric field F reaching the THz detector 12, 12′ (FIG. 6) can be generated by an arrangement according to FIG. - A In another exemplary embodiment, is defined by a continuous sequence characterized, for example, by the following formula:

[0107]

number

[0108] In another exemplary embodiment, the electric field in the layers 20-1, 20-2 (and optionally the surrounding medium UM) associated with the propagating THz electromagnetic wave is defined according to or characterized by at least one of the following mathematical expressions, e.g., by a corresponding sequence:

[0109]

number

[0110]

number

[0111]

number

[0112]

number

[0113]

number

[0114] In another exemplary embodiment, the starting condition is selected as follows: F + A,1 (ω)=I0(ω,x,y,z)e -iΦ0(ω,x,y,z) :Incoming electric field F - A,1 (ω)=F + 1,1 (ω)=F - 1,1 (ω)=F + 2,1 (ω)=F - 2,1 (ω)=0

[0115] In another exemplary embodiment, another condition is selected as follows: F + A,n (ω)=0 (only one input THz pulse) F - A,n (ω)=r 1A F - 1,n-1 (ω)+r A1 F + A,n-1 (ω) F - 1,n (ω)=r 12 A(1)F +1,n-1 (ω)+B(1)t 21 F - 2,n-1 (ω) F + 1,n (ω)=F - 1,n-1 (ω)r 1A +t A1 F + A,n-1 (ω) F - 2,n (ω)=F + 2,n-1 (ω)r 2S A(2) F + 2,n (ω)=F + 1,n-1 (ω)t 12 B(1)+F - 2,n-1 r 21

[0116] In another exemplary embodiment, the transfer function is determined as follows:

[0117] Reflected THz pulse F - v takes into account the distance traveled in air and is additionally corrected by the deviation ΔD between the measurement in the layer packets 20-1, 20-2 and the reference measurement (see also FIG. 6).

[0118]

number

[0119] In another exemplary embodiment, the reference measurement is as follows:

[0120]

number

[0121] In order to take into account various distance ("z") dependencies, in another exemplary embodiment the above-described condition T and / or the condition G(D1, R1(n), D2, R2(n), ω, x, y, z, α, β), also called weighting factors (or contour factors), are inserted. For this purpose, in another exemplary embodiment, the outgoing rays are provided with correction factors. F + A,n (ω)=0 (e.g., only one incident THz pulse) F - A,n (ω)=(t 1A F - 1,n-1 (ω)+r v1 F + A,n-1 (ω))·G(D1,R1(n),D2,R2(n),ω,x,y,z,α,β) F - 1,n (ω)=r 12 A(1)F + 1,n-1 (ω)+B(1)t 21 F - 2,n-1 (ω) F + A,n (ω)=F - 1,n-1 (ω)r 1A +t A1 F + A,n-1 (ω) F + A,n (ω)=F + 2,n-1 (ω)r 25 A(2) F + 2,n (ω)=F + 1,n-1 (ω)t 12 B(1)+F - 2,n-1 (ω)r 21 Here, for example, R1(n) and R2(n) characterize the number of reflections of the THz electromagnetic wave in layer 1 or layer 2. These conditions can be determined in another exemplary embodiment, for example, when calculating the sequence by the validity of A(1) and A(2) in each condition.

[0122] In another exemplary embodiment, it is possible to establish a generalization of the model MOD to apply to "L-layer objects" (arrangements and / or measurement objects having several L layers), where F m,n represents the electric field of the THz electromagnetic wave in the mth layer for the nth iteration step, and can be characterized, for example, by: F - m,n (ω)=r m,m+1 A(m)F + m,n-1 (ω)+B(m)t m+1,m Fm +1,n-1 (ω) F + m,n =F - m,n-1 (ω)r m,m-1 +t m-1,m F + m-1,n-1 (ω)

[0123] In another exemplary embodiment, the following special cases may be considered: F - 1,n (ω)=r 12 A(1)F + 1,n-1 (ω)+B(1)t 21 F - 2,n-1 (ω) F + 1,n (ω)=F - 1,n-1 (ω)r 1A +t 1A F + A,n-1 (ω) ·m=L(letzte Schicht) ·r m,m+1 =r L,S ,F- m+1,n-1 (ω)=0

[0124] Disclosure Terms: F + A,1 (ω)=I0(ω,x,y,z)e -iΦ0(ω、x,y,z) : Incoming electric field, all other conditions are e.g. zero.

[0125] In another exemplary embodiment, the principles according to the present invention can thus also be applied to objects of the L layer and / or to models MOD, MOD-1, MOD-2 for objects of the L layer, for example.

Claims

1. A method for processing data (DAT) associated with a model (MOD) characterizing the propagation of terahertz (THz) electromagnetic waves (TS) in a spatial domain (RB) to detect (302) at least one property of an object (20), said spatial domain (RB) comprising at least one terahertz device (10) for transmitting and / or receiving terahertz electromagnetic waves (TS) and / or at least one object (20) that can be exposed to said terahertz electromagnetic waves (TS), said method comprising the steps of: providing (100) said model (MOD); and characterizing (102) the propagation of a terahertz electromagnetic wave (TS) in the region of at least one interface (GF) between two adjacent media (M1, M2) in said spatial domain (RB) using a model (MOD), said model (MOD) having conditions (T) that characterize the THz electromagnetic wave and that depend on at least one of the following factors: a) the frequency of the terahertz electromagnetic wave (TS), b) the spatial extension (D) and / or the position of at least one of said two adjacent media (M1, M2), said model (MOD) characterizing (102) the propagation of a terahertz electromagnetic wave (TS) in the region of at least one interface (GF) between two adjacent media (M1, M2) in said spatial domain (RB) using a coherent superposition function. ０ , r １ , r ２ , r ０ ',r １ ') and / or transmission (t ０ , t １ , t ０ ',t １ '), wherein the condition (T) is provided as a weighting factor (G) for at least some components of the coherence convolution function.

2. The model (MOD) includes at least one reflection (r ) of the terahertz electromagnetic wave (TS) at at least one of the interfaces (GF: GF-1, GF-2, GF-3) between at least two of the media (M1, M2, M3, M4). ０ , r １ , r ２ , r ０ ',r １ ') and / or transmission (t ０ , t １ , t ０ ',t １ The model (MOD) characterizes the multiple reflections (r ′) of the terahertz electromagnetic wave (TS) at at least two interfaces (GF-1, GF-2, GF-3) between various different media (M1, M2, M3). ０ , r １ , r ２ , r ０ ',r １ ') and / or transmission (t ０ , t １ , t ０ ',t １ 2. The method of claim 1, wherein the condition (T) characterizing the terahertz electromagnetic wave (TS) has different values ​​(T-1, T-2, T-3) for each of at least two of the boundaries (GF-1, GF-2), and the condition (T) is provided as a weighting coefficient (G) other than one of at least some components of the coherence convolution function.

3. 2. The method of claim 1, wherein the model (MOD) has a first component (MOD-1) that characterizes a sample measurement of the object (20) in a reflection or transmission configuration by terahertz electromagnetic waves (TS), and the first component (MOD-1) can be characterized in the frequency domain.

4. For the reflective configuration, the first component (MOD-1) is characterized based on the following equation: [Equation 1] Here, F Ｓ (ω, x, y, z) characterizes the field strength of the sample signal, which may be frequency dependent, where ω characterizes the angular frequency associated with the frequency of the terahertz electromagnetic wave (TS), where x characterizes a first spatial coordinate, where y characterizes a second spatial coordinate, where z characterizes a third spatial coordinate, and where I ０ (ω, x, y, z) characterizes the field intensity of the terahertz electromagnetic wave (TS), which may be frequency dependent, at the emitter (11) that generates the terahertz electromagnetic wave (TS), where exp[ ] characterizes an exponential function, where i characterizes the imaginary unit, where c ０ characterizes the speed of light in a vacuum, where L characterizes the distance between the terahertz device (10) and the reference object (20′), where ΔD characterizes the deviation between the reference object (20′) and the object (20), where n Ａ characterizes the refractive index of the medium present in said spatial region (RB), where ∈ Ａ characterizes the extinction coefficient of the medium present in said spatial region (RB), where Φ ０ (ω, x, y, z) characterizes the phase of the terahertz electromagnetic wave (TS), which may be frequency dependent, at the emitter (11) that generates the terahertz electromagnetic wave (TS), where t Ａ１ characterizes the transmission coefficient at the interface (GF-0) between the medium present in the spatial region (RB) and the layer (20-1) characterizing the surface (20a) of the object (20), where t １Ａ characterizes the transmission coefficient at the interface (GF-0) between the layer (20-1) characterizing the surface (20a) of the object (20) and a medium present in the spatial region (RB), where r １Ｓ characterizes the reflection coefficient at the interface (GF-3) between the layer (20-3) and the substrate (20-4) of the object (20), where R characterizes the reflection index characterizing the number and / or sequence order of the reflection and / or transmission of the terahertz electromagnetic wave (TS), where r １Ａ characterizes the reflection coefficient at the interface (GF-0) between the layer (20-1) characterizing the surface (20a) of the object (20) and a medium present in the spatial region (RB), where G(D, R, ω, x, y, z, α, β, Ω) characterizes the condition (T) characterizing the THz electromagnetic wave or weighting factor (G), where D characterizes the layer thickness of the layer, where n characterizes the refractive index of the layer, where ∈ characterizes the extinction coefficient of the layer, where r Ａ１ characterizes the reflection coefficient at the interface (GF-0) between a medium present in the spatial domain (RB) and a layer (20-1) characterizing the surface (20a) of the object (20), where α and / or β characterize the angular orientation of the terahertz device (10) with respect to the object (20), and where Ω characterizes the properties of the surface (20a) of the object (20), the properties of the surface (20a) of the object (20) comprising at least one of the following elements: a) the shape of the surface (20a), b) the roughness of the surface (20a), and the first component (MOD-1) is characterized based on the following mathematical formula: [Equation 2] Here, R ｍａｘ <∞.

5. The method of claim 1, wherein the model (MOD) has a second component (MOD-2) that characterizes a reference measurement of a reference object (20') in a reflection or transmission configuration by terahertz electromagnetic waves (TS), and the second component (MOD-2) is characterized in the frequency domain.

6. For the reflective configuration, the second component (MOD-2) is characterized based on the following equation: [Equation 3] where F(ω, x, y, z) characterizes the frequency-dependent field strength of the reference signal, where r ＡＭ characterizes the reflection coefficient at the interface (GF-0') between a medium present in the spatial domain (RB) and the surface (20a') of the reference object (20').

7. The model (MOD) for a reflection geometry is characterized in the frequency domain based on the following equation: [Equation 4] where H(ω) characterizes the transmission function of the terahertz radiation (TS) relative to a reference measurement, and the model can be characterized in the frequency domain based on the following equation: [Equation 5] The method of claim 1.

8. The condition (T) may be, alternatively or in addition to: a) the frequency of the terahertz electromagnetic wave (TS), and / or b) the spatial extension (D) and / or the position of at least one of the two adjacent media (M1, M2), the following factors: c) reflection (r ０ , n, r ２ , r ０ ',r １ ') and / or transmission (t ０ , t １ , t ０ ',t １ d) an angular orientation of the terahertz device with respect to the object and / or a reference object; e) a distance between at least one of the terahertz devices and / or at least one of the objects; f) a surface characteristic of at least one of the objects, such as a shape of the surface and / or a roughness of the surface.

9. Using the conditions (T) and / or weighting factors (G), the model (MOD) models the distance-dependent spectral change of the transmission function of the terahertz electromagnetic radiation (TS) as a distance-dependent and / or depth-dependent attenuation and / or amplification, and / or Using the conditions (T) and / or weighting factors (G), the model (MOD) models the angular dependent spectral changes of the transmission function of the terahertz electromagnetic radiation (TS) as angular dependent attenuation and / or amplification, and / or 2. The method of claim 1, wherein using the conditions (T) and / or weighting coefficients (G), the model (MOD) models a spectral change in the transmission function of the terahertz electromagnetic radiation (TS) based on at least one characteristic of a surface (20a) of at least one of the objects (20), such that the spectral change is based on the shape of the surface (20a) and / or the roughness of the surface (20a).

10. 2. The method of claim 1, wherein the model (MOD) comprises an object having several layers (20-1, 20-2, 20-3, 20-4) of different media (M1, M2, M3, M4), and the model (MOD) characterizes at least one of the following elements: a) reflections and / or transmissions of terahertz electromagnetic waves (TS) in the object (20) between adjacent layers, b) multiple reflections and / or multiple transmissions of terahertz electromagnetic waves (TS) in the object (20), c) virtual reflection and / or transmission points of the object (20), which may be characterized by a reflection index, d) a coherence superposition function of the various reflections and / or transmissions of terahertz electromagnetic waves (TS) in the object (20).

11. 2. The method of claim 1, further comprising determining (110) the condition (T) and / or individual values ​​(T-1, T-2, T-3, ...) of the condition (T) based on an optical model (MOD-OPT) of a system (SYS) characterizing the terahertz device (10) and the object (20) and / or reference object (20'), as well as the ambient medium (UM) around the terahertz device (10) and the object (20) or reference object (20').

12. 12. The method of claim 11, wherein the optical model (MOD-OPT) characterizes the spectral transmission function of terahertz electromagnetic waves (TS) within the system (SYS), wherein the optical model (MOD-OPT) characterizes the amplitude and phase over the spatial extension of terahertz electromagnetic waves (TS) within the system (SYS).

13. The method according to claim 11, wherein the optical model (MOD-OPT) takes into account diffraction effects of terahertz electromagnetic waves (TS).

14. 12. The method of claim 11, further comprising: determining (120) an optical model (MOD-OPT) based on modeling by a) ray tracing (120a), and / or b) description based on diffraction theory (120b) by diffraction integrals, and / or c) parametric calculations (120c) with model functions, and calibrating (122) said optical model (MOD-OPT), wherein determining (120) and / or calibrating (122) said optical model (MOD-OPT) is performed by frequency decomposition techniques.

15. 15. The method of claim 14, further comprising: calibrating (122) the optical model (MOD-OPT) for a spectral transmission function and / or spatial amplitude and / or phase based on at least one of the following factors: a) an angle (α, β) between an optical axis (OA) of the terahertz device (10) and a surface (20a-n) normal to the object (20) or a reference object (20'); b) a distance (L) between the terahertz device (10) and a surface (20a) of the object (20) or a reference object (20'); c) characteristics of the surface (20a), the surface (20a, 20a') and / or the roughness characteristics of the surface (20a, 20a') of at least one of the object (20) and / or reference object (20'); and d) a frequency of the terahertz electromagnetic wave (TS).

16. 15. The method of claim 14, further comprising: varying (130) the spatial positions of the reflection points (GF-0, GF-1, GF-2, ...) and / or transmission points (GF-0, GF-1, GF-2, ...) characterized by the model (MOD); and deriving (132) a thickness (D-M2) characteristic of at least one layer (20-2) in a medium (M2) of the object (20) based on the varying (130), wherein at least one of the following elements is used for the deriving (132): a) performing a correlation method (132a); b) performing a method for pattern recognition (132b); c) determining maxima and / or minima (132c); d) utilizing a machine learning method (132d); e) performing a fitting method (132e).

17. 12. The method according to claim 11, further comprising determining (140) by pre-calculating at least one component (MOD-1, MOD-2) of the model (MOD) and / or the optical model (MOD-OPT), as well as at least temporarily storing (142) a result (VE) of the determining (140) by pre-calculation, wherein the result (VE) is stored in a database (DB).

18. 15. The method of claim 14, further comprising determining (150) reference data (RD) for several different spatial arrangements of the terahertz device (10) and the object (20) or reference object (20') relative to each other, wherein the determining (150) comprises: arranging (150a) the terahertz device (10) and the object (20) and / or reference object (20') in a given arrangement relative to each other; determining (150b) the reference data (RD) for the given arrangement; and repeating (152) the arranging steps (150a) and the determining steps (150b) until a predetermined final reference is reached, wherein the arranging (150a) comprises positioning the terahertz device (10) and / or the object (20) or reference object (20') by a positioning device (PE, PE').

19. 15. The method of claim 14, further comprising using a sensor to determine (160) at least one of the following factors: a) a distance (L, AB) between the terahertz device (10) and the object (20) or reference object (20'); b) an angular orientation (WA) between the terahertz device (10) and the object (20) or reference object (20') in a one-dimensional or two-dimensional arrangement; and c) a shape (FO) of the object (20) or reference object (20') at a surface (20a, 20a').

20. For the said condition (T), and / or for the said model (MOD) which determines the individual values (T-1, T-2, T-3, ···) of the said condition (T), based on the distance (AB) and / or angular orientation (WA), and / or the shape (FO) of the said surface (20a, 20a') and / or the roughness of the said surface (20a, 20a'), further including using the characteristics of the surface (20a) of at least one of the said object (20) or reference object (20') (162), the method according to claim 19.

21. Determining whether at least one region of the object is located within a parameter range where the values (T-1, T-2, T-3, ···) of the said condition (T), and / or the said reference data (RD) which can be characterized via a calculated and / or calibrated transmission function, are available (170); and based on the said determination (170), changing the spatial arrangement, distance, and / or angle (172), further including, where the said changing (172) is repeated (173) until the region of the object is located within the said parameter range, and performing an evaluation (174), the method according to claim 18.

22. A device (200) for executing the method according to claim 1.

23. For at least one of the following elements: a) determining at least one characteristic of the object (20) (302); b) enhancing the accuracy of the model (MOD) by taking into account the propagation of terahertz electromagnetic waves (TS) in a non-flat form (304); c) taking into account the dependence of the spectral transmission function on the distance (L, AB) to the terahertz device (10) (306); d) taking into account the dependence of the spectral transmission function on the angle (α, β) with respect to the said terahertz device (10) (310); e) taking into account the characteristics of the surface (20a) of at least one of the said object (20) or reference object (20') based on the shape (FO) of the surface (20a, 20a') and / or the roughness of the surface (20a, 20a') (308), the method according to claim 1, and / or the usage method (300) of the device (200) according to claim 22.

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