Imaging system and method for material characterization of a sample

An imaging system for material characterization of a sample is provided. Said imaging system comprises at least two imaging arrays configured to form at least one imaging array pair. In this context, the imaging system is configured to perform at least one reflection measurement with the aid of at least one imaging array. Furthermore, the imaging system is configured to perform at least one transmission measurement with the aid of the at least one imaging array pair. In addition to this, the imaging system is configured to determine material characteristics of the sample on the basis of the at least one reflection measurement and/or the at least one transmission measurement.

PRIORITY

This application claims priority of the European patent application EP 20 195 911.1 filed on Sep. 14, 2020, which is incorporated by reference herewith.

FIELD OF THE INVENTION

The invention relates to an imaging system for material characterization of a sample and an imaging method for material characterization of a sample.

BACKGROUND OF THE INVENTION

Generally, in times of an increasing number of applications employing radar systems comprising radar covers such as autonomous vehicles comprising radomes, there is a growing need of an imaging system for material characterization of a sample and an imaging method for material characterization of a sample in order to ensure a correct functioning of such applications especially on the basis of a highly accurate and efficient material characterization with respect to a sample such as said radomes.

WO 2020/074667 A1 relates to a radome measuring system configured to perform a radome measurement. Said system comprises a transmission antenna on one side of a radome, wherein said transmission antenna is configured for emitting electromagnetic waves, and a receiving antenna on another side of the radome, wherein said receiving antenna is configured for receiving electromagnetic waves, and a measuring device being configured to measure a difference between the transmitted and received electromagnetic waves for inferring a feature of a radome being positioned between the transmission antenna and the receiving antenna. Ns it can be seen, due to the foregoing arrangement and configuration, said radome measuring system exclusively allows for a transmission measurement, which disadvantageously leads to an inaccurate and inefficient characterization of the radome.

Accordingly, there is a need among others to provide an imaging system for material characterization of a sample and an imaging method for material characterization of a sample, whereby both a high accuracy and efficiency are ensured with respect to the material characterization of the sample such as a radome.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, an imaging system for material characterization of a sample is provided. Said imaging system comprises at least two imaging arrays configured to form at least one imaging array pair. In this context, the imaging system is configured to perform at least one reflection measurement with the aid of at least one imaging array. Furthermore, the imaging system is configured to perform at least one transmission measurement with the aid of the at least one imaging array pair. In addition to this, the imaging system is configured to determine material characteristics of the sample on the basis of the at least one reflection measurement and/or the at least one transmission measurement. Advantageously, both a high accuracy and efficiency are ensured with respect to the material characterization of the sample.

According to a first preferred implementation form of the first aspect of the invention, at least one, preferably each, of the at least two imaging arrays comprises or is a monostatic or multistatic array. Advantageously, for instance, accuracy can further be increased.

According to a second preferred implementation form of the first aspect of the invention, the sample comprises or is a device under test or a radome. Advantageously, for example, a high flexibility can be ensured.

According to a further preferred implementation form of the first aspect of the invention, the respective imaging arrays of the corresponding imaging array pair are arranged in a manner that said respective imaging arrays face each other. Advantageously, for instance, efficiency can further be increased.

According to a further preferred implementation form of the first aspect of the invention, the at least two imaging arrays, preferably the respective imaging arrays of the corresponding imaging array pair, are synchronized and/or phase coherent. Advantageously, for example, inaccuracies can be reduced in an efficient manner.

According to a further preferred implementation form of the first aspect of the invention, at least one, preferably each, of the at least two imaging arrays is placed at a desired angle of incidence. Advantageously, for instance, efficiency can further be increased.

According to a further preferred implementation form of the first aspect of the invention, the imaging system is configured to determine the electrical thickness across the sample and/or homogeneity information with respect to the sample on the basis of the at least one transmission measurement, preferably on corresponding phase information thereof. Advantageously, for example, flexibility can further be increased, which leads to reduced inefficiencies.

According to a further preferred implementation form of the first aspect of the invention, the imaging system is configured to present the at least one transmission measurement and/or the at least one reflection measurement as at least one image especially in order to provide information regarding variations across the corresponding material plane of the sample. Advantageously, for instance, such a presentation or visualization, respectively, further increases efficiency due to a simple interpretation of the measurements.

According to a further preferred implementation form of the first aspect of the invention, the imaging system is configured to realize small incident angles especially by using a proper ratio between a respective aperture dimension and a corresponding sample distance. Advantageously, for example, vector network analyzer comparable reflectivity and transmissivity measurements can be ensured, which leads to an increased efficiency.

According to a further preferred implementation form of the first aspect of the invention, the aperture dimension is significantly smaller than the sample distance. Advantageously, for instance, the proper ratio between the aperture dimension and the sample distance can be chosen in an efficient manner.

According to a further preferred implementation form of the first aspect of the invention, the imaging system is configured to determine measurement results being comparable to reference measurement results provided by a common measurement device, preferably a vector network analyzer. Advantageously, for example, not only efficiency but also accuracy can be increased.

According to a further preferred implementation form of the first aspect of the invention, with respect to the at least one reflection measurement and/or the at least one transmission measurement, the imaging system is configured to perform at least one broadband measurement across several frequencies especially in order to determine a frequency response for various locations of the sample. Advantageously, for instance, a frequency sweep may be applied in order to ensure a high efficiency.

According to a further preferred implementation form of the first aspect of the invention, the imaging system is configured to determine the permittivity, preferably the relative permittivity, of the sample on the basis of the frequency response. Advantageously, for example, flexibility of measurements can further be increased, which reduces inefficiencies.

According to a second aspect of the invention, an imaging method for material characterization of a sample is provided. Said imaging method comprises the steps of forming at least one imaging array pair with the aid of at least two imaging arrays, performing at least one reflection measurement with the aid of at least one of the at least two imaging arrays, performing at least one transmission measurement with the aid of at least one of the at least one imaging array pair, and determining material characteristics of the sample on the basis of the at least one reflection measurement and/or the at least one transmission measurement. Advantageously, both a high accuracy and efficiency are ensured with respect to the material characterization of the sample.

According to a first preferred implementation form of the second aspect of the invention, the imaging method further comprises the step of determining the electrical thickness across the sample and/or homogeneity information with respect to the sample on the basis of the at least one transmission measurement, preferably on corresponding phase information thereof. Advantageously, for example, flexibility can further be increased, which leads to reduced inefficiencies.

According to a second preferred implementation form of the second aspect of the invention, at least one, preferably each, of the at least two imaging arrays comprises or is a monostatic or multistatic array. Advantageously, for instance, accuracy can further be increased.

According to a further preferred implementation form of the second aspect of the invention, the sample comprises or is a device under test or a radome. Advantageously, for example, a high flexibility can be ensured.

According to a further preferred implementation form of the second aspect of the invention, the imaging method further comprises the step of arranging the respective imaging arrays of the corresponding imaging array pair in a manner that said respective imaging arrays face each other. Advantageously, for instance, efficiency can further be increased.

According to a further preferred implementation form of the second aspect of the invention, the at least two imaging arrays, preferably the respective imaging arrays of the corresponding imaging array pair, are synchronized and/or phase coherent. Advantageously, for example, inaccuracies can be reduced in an efficient manner.

According to a further preferred implementation form of the second aspect of the invention, the imaging method further comprises the step of placing at least one, preferably each, of the at least two imaging arrays at a desired angle of incidence. Advantageously, for instance, efficiency can further be increased.

According to a further preferred implementation form of the second aspect of the invention, the imaging method further comprises the step of presenting the at least one transmission measurement and/or the at least one reflection measurement as at least one image especially in order to provide information regarding variations across the corresponding material plane of the sample. Advantageously, for instance, such a presentation or visualization, respectively, further increases efficiency due to a simple interpretation of the measurements.

According to a further preferred implementation form of the second aspect of the invention, the imaging method further comprises the step of realizing small incident angles especially by using a proper ratio between a respective aperture dimension and a corresponding sample distance. Advantageously, for example, vector network analyzer comparable reflectivity and transmissivity measurements can be ensured, which leads to an increased efficiency.

According to a further preferred implementation form of the second aspect of the invention, the aperture dimension is significantly smaller than the sample distance. Advantageously, for instance, the proper ratio between the aperture dimension and the sample distance can be chosen in an efficient manner.

According to a further preferred implementation form of the second aspect of the invention, the imaging method further comprises the step of determining measurement results being comparable to reference measurement results provided by a common measurement device, preferably a vector network analyzer. Advantageously, for example, not only efficiency but also accuracy can be increased.

According to a further preferred implementation form of the second aspect of the invention, with respect to the at least one reflection measurement and/or the at least one transmission measurement, the imaging method further comprises the step of performing at least one broadband measurement across several frequencies especially in order to determine a frequency response for various locations of the sample. Advantageously, for instance, a frequency sweep may be applied in order to ensure a high efficiency.

According to a further preferred implementation form of the second aspect of the invention, the imaging method further comprises the step of determining the permittivity, preferably the relative permittivity, of the sample on the basis of the frequency response. Advantageously, for example, flexibility of measurements can further be increased, which reduces inefficiencies.

With respect toFIG.1, a block diagram of an exemplary embodiment of an inventive imaging system10for material characterization of a sample11is shown. According toFIG.1, the imaging system10comprises at least two imaging arrays, exemplarily the two imaging arrays12a,12b, configured to form at least one imaging array pair. In this context, the imaging system10is configured to perform at least one reflection measurement, exemplarily the two reflection measurements13a,13b, with the aid of the corresponding imaging array12aor12b, respectively.

Furthermore, the imaging system10is configured to perform at least one transmission measurement, exemplarily the two transmission measurements14a,14b, with the aid of the corresponding imaging array pair, which exemplarily comprises the two imaging arrays12aand12. Moreover, the imaging system10is basically configured to determine material characteristics of the sample11on the basis of at least one of the two exemplary reflection measurements13a,13band/or at least one of the two exemplary transmission measurements14a,14b.

Exemplarily, the imaging system10is preferably configured to determine the material characteristics of the sample11on the basis of the two exemplary reflection measurements13a,13band the two exemplary transmission measurements14a,14b. It is noted that it might be particularly advantageous if the corresponding result of the at least one reflection measurement and/or the at least one transmission measurement is formulated and/or interpreted as at least one scattering parameter.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the context of the first exemplary embodiment according toFIG.1, the reflection measurement13amay result in a first reflection coefficient S11, whereas the reflection measurement13bmay result in a second reflection coefficient S22. By analogy therewith, the transmission measurement14amay result in a first transmission coefficient S21, whereas the transmission measurement14bmay result in a second transmission coefficient S12.

With respect to the imaging arrays12aand12b, it is noted that at least one, preferably each, of the two imaging arrays12,12bmay comprise or be a monostatic or multistatic array. Exemplarily, both imaging arrays12a,12bare multistatic arrays.

In this context, it is further noted that at least one, especially each, of said imaging arrays12a,12bmay comprise between 50 and 150 transmitting elements and/or between 50 and 150 receiving elements, preferably between 80 and 120 transmitting elements and/or between 80 and 120 receiving elements, more preferably between 90 and 100 transmitting elements and/or between 90 and 100 receiving elements, most preferably 94 transmitting elements and/or 94 receiving elements.

Alternatively, at least one, especially each, of said imaging arrays12a,12bmay comprise between 50 and 150 transceiving elements, preferably between 80 and 120 transceiving elements, more preferably between 90 and 100 transceiving elements, most preferably 94 transceiving elements. With respect to the sample11, it is noted that the sample11may especially comprise or be a device under test or a radome.

As it can further be seen fromFIG.1, the respective imaging arrays12a,12bof the corresponding imaging array pair are arranged in a manner that said respective imaging arrays12a,12bface each other. In this context, it is noted that a distance between the imaging arrays12a,12b may be between0.2 and 2 meters, preferably between 0.3 and 1.5 meters, more preferably between 0.4 and 0.8 meters, most preferably 0.6 meters.

It is further noted that it might be particularly advantageous if the two imaging arrays12a,12bforming the corresponding imaging array pair are synchronized and/or phase coherent. In this context, it is noted that said synchronization and/or phase coherence can be achieved with the aid of the same signal source. Alternatively, said synchronization and/or phase coherence can be achieved with the aid of separate signal sources being synched such as at least two signal sources being synched.

It is further noted that said same signal source may preferably comprise or be a direct digital synthesizer (DDS). Alternatively, at least one, especially each, of said separate signal sources may comprise or be a direct digital synthesizer.

Again, with respect to the imaging arrays12a,12b, it is noted that the imaging arrays12a,12bare placed at a desired angle of incidence. With respect to the imaging system10, it is noted that the imaging system10may preferably be configured to determine the electrical thickness across the sample11and/or homogeneity information with respect to the sample11on the basis of the at least one transmission measurement14a,14b, preferably on corresponding phase information thereof.

In addition to this or as an alternative, the imaging system may be configured to present the at least one transmission measurement14a,14band/or the at least one reflection measurement13a,13bas at least one image especially in order to provide information regarding variations across the corresponding material plane of the sample11.

Further additionally or further alternatively, the imaging system10may preferably be configured to realize small incident angles especially by using a proper ratio between a respective aperture dimension and a corresponding sample distance. In this context, it might be particularly advantageous if the aperture dimension is significantly smaller than the sample distance.

Furthermore, the imaging system10may especially be configured to determine measurement results being comparable to reference measurement results provided by a common measurement device, preferably a vector network analyzer.

It is noted that especially in the case of a multistatic array and a proper measurement setup, the respective transmission and reflection measurement may preferably be equivalent to a single incidence measurement, which may advantageously lead to comparable results to reference setups especially with a vector network analyzer.

In the context of said proper measurement setup, it might be particularly advantageous if the aperture dimension is significantly smaller than the sample distance as already mentioned above. With the aid of such a configuration, small angles of incidence and reflection may preferably be realized.

Moreover, with respect to the at least one reflection measurement13a,13band/or the at least one transmission measurement14a,14b, the imaging system10may be configured to perform at least one broadband measurement across several frequencies especially in order to determine a frequency response for various locations of the sample11.

In this context, it is noted that said broadband measurement can be achieved with the aid of a frequency sweep and/or a pulse measurement preferably by means of a coherent pulse detector. It is further noted that it might be particularly advantageous if the respective frequency range of said broadband measurement is between 50 and 100 gigahertz, preferably between 60 and 90 gigahertz, more preferably between 70 and 80 gigahertz, most preferably between 74 and gigahertz. Furthermore, the imaging system10may especially be configured to determine the permittivity, preferably the relative permittivity, of the sample11on the basis of the frequency response.

The first exemplary embodiment of the inventive imaging system according toFIG.1, which comprises two arrays, can especially be used in the context of a material characterization of a sample for a single incident angle. The second exemplary embodiment according toFIG.2, which comprises multiple arrays, can especially be used in the context of a material characterization of a sample for multiple incident angles. Before said second exemplary embodiment will be explained in greater detail in the following, it is generally noted that with respect to a material characterization of a sample for at least two incident angles, it might be particularly advantageous if the imaging system comprises at least three, preferably at least four, imaging arrays.

Now, with respect to the second exemplary embodiment, as it can be seen fromFIG.2, the respective imaging system20for material characterization of the sample11comprises multiple imaging arrays exemplarily six imaging arrays12a,12b,12c,12d,12e,12f, configured to form multiple imaging array pairs, exemplarily three imaging array pairs. In this exemplary case, the imaging arrays12aand12bform a first imaging array pair, the imaging arrays12cand12dform a second imaging array pair, and the imaging arrays12eand12fform a third imaging array pair. With respect to the second exemplary embodiment ofFIG.2, it is noted that the above explanations regarding the first exemplary embodiment according toFIG.1analogously apply.

Now, with respect to both the first exemplary embodiment of the inventive imaging system according toFIG.1and the second exemplary embodiment according toFIG.2, it is generally noted that it might be particularly advantageous if the inventive imaging system comprises at least two imaging arrays, preferably full-electronic imaging arrays, especially with two-dimensional monostatic or multistatic sampling. Furthermore, measurements of two-dimensional reflection and transmission images especially with magnitude and phase information may be performed by the imaging system. Moreover, the imaging system may especially extract reflectivity and transmissivity from corresponding magnitude images.

It might be particularly advantageous if the imaging system is configured to extract homogeneity from the respective phase information of the corresponding transmission image. In this context, variation of phase values may especially correspond to variations of the electrical thickness of the sample. In addition to this or as an alternative, the imaging system may be configured to extract the respective frequency response of reflectivity and transmissivity especially for specific pixel positions and/or locations of the sample preferably in the case of a broadband setup.

Furthermore, it might be particularly advantageous if small incident angles are realized by a proper ratio between aperture dimension and sample distance especially in the case of multistatic arrays, which preferably results in vector network analyzer comparable reflectivity and transmissivity measurements. It is noted that the above general explanations regarding the first and the second exemplary embodiment of the inventive imaging system analogously apply for the exemplary embodiment of the inventive imaging method as described in the following.

Finally,FIG.3shows a flow chart of an exemplary embodiment of the inventive imaging method for material characterization of a sample. In a first step100, at least one imaging array pair is formed with the aid of at least two imaging arrays. Then, in a second step101, at least one reflection measurement is performed with respect to the sample with the aid of at least one of the at least two imaging arrays. Furthermore, in a third step102, at least one transmission measurement is performed with respect to the sample with the aid of at least one of the at least one imaging array pair. In addition to this, in a fourth step103, material characteristics of the sample are determined on the basis of the at least one reflection measurement and/or the at least one transmission measurement.

It might be particularly advantageous if the imaging method further comprises the step of determining the electrical thickness across the sample and/or homogeneity information with respect to the sample on the basis of the at least one transmission measurement, preferably on corresponding phase information thereof. With respect to the at least two imaging arrays, it is noted that at least one, preferably each, of the at least two imaging arrays may comprise or be a monostatic or multistatic array. With respect to the sample, it is noted that the sample may especially comprise or be a device under test or a radome.

Additionally or alternatively, the imaging method may further comprise the step of arranging the respective imaging arrays of the corresponding imaging array pair in a manner that said respective imaging arrays face each other. It is further noted that it might be particularly advantageous if the at least two imaging arrays, preferably the respective imaging arrays of the corresponding imaging array pair, are synchronized and/or phase coherent.

In this context, the imaging method may additionally or alternatively comprise the step of configuring the at least two imaging arrays, preferably the respective imaging arrays of the corresponding imaging array pair, in a manner that the at least two imaging arrays, preferably the respective imaging arrays of the corresponding imaging array pair, are synchronized and/or phase coherent. Furthermore, the imaging method may further comprise the step of placing at least one, preferably each, of the at least two imaging arrays at a desired angle of incidence.

Moreover, the imaging method may further comprise the step of presenting the at least one transmission measurement and/or the at least one reflection measurement as at least one image especially in order to provide information regarding variations across the corresponding material plane of the sample. In addition to this or as an alternative, the imaging method may further comprise the step of realizing small incident angles especially by using a proper ratio between a respective aperture dimension and a corresponding sample distance. In this context, the aperture dimension may preferably be significantly smaller than the sample distance.

Furthermore, it might be particularly advantageous if the imaging method further comprises the step of determining measurement results being comparable to reference measurement results provided by a common measurement device, preferably a vector network analyzer.

Additionally or alternatively, with respect to the at least one reflection measurement and/or the at least one transmission measurement, the imaging method may further comprise the step of performing at least one broadband measurement across several frequencies especially in order to determine a frequency response for various locations of the sample. In addition to this or as an alternative, the imaging method may comprise the step of determining the permittivity, preferably the relative permittivity, of the sample on the basis of the frequency response.