HK1131663B - Hf measurement system, method for the calibration thereof, and method for determining scattering parameters with this hf measurement system - Google Patents

Description

High-frequency measuring device, method for calibrating such a device and method for determining a scattering parameter using such a high-frequency measuring device

The invention relates to a method for calibrating a high-frequency measuring device (HF measuring device) having N test ports, where N is an integer greater than or equal to 1, in particular a method for calibrating a vector network analyzer for determining a scattering parameter of a measurement object by means of N port measurements, where N is an integer greater than or equal to 1, wherein a high-frequency test signal (HF test signal) is fed into a first electrical line connected to the measurement object or to a circuit containing the measurement object, wherein for each port a high-frequency signal (HF signal) transmitted via a second electrical line is coupled out by a second electrical line, in particular a planar line, connected to the measurement object at a first coupling point and at a second coupling point at a distance from the first coupling point, wherein the HF signal coupled out from the two coupling points by two of the two ports is respectively directed toward the measurement point or the coupling point with respect to the second electrical line at each measurement point or coupling point The HF test signal of the HF signal transmitted by the object and of the HF signal leaving the measurement object on the second electrical conductor determines the amplitude and/or the phase and calculates therefrom the scattering parameter of the measurement object, as described in the preamble of claim 1.

The invention further relates to a method for determining a scattering parameter of a measurement object by means of a high-frequency measuring device (HF measuring device) having N test ports, where N is an integer greater than or equal to 1, by means of N ports, where N is an integer greater than or equal to 1, wherein a high-frequency test signal (HF test signal) is fed into a first electrical line connected to the measurement object or to an electrical circuit containing the measurement object, wherein for each port a high-frequency signal (HF signal) transmitted via a second electrical line is coupled out by a second electrical line, in particular a planar line, connected to the measurement object at a first coupling location and at a second coupling location at a distance from the first coupling location, wherein the HF signals coupled out by two of the ports at the two coupling locations are respectively of the HF signal transmitted toward the measurement object per measurement location or coupling location relative to the second electrical line and leave the measurement object at the second electrical line The HF test signal of the HF signal proceeding from the object is evaluated for amplitude and/or phase and the scattering parameters of the object are calculated therefrom, as described in the preamble of claim 12.

The invention finally relates to an HF measuring device for determining scattering parameters of a measurement object, in particular a vector network analyzer, having N test ports, where N is an integer greater than or equal to 1, and having an HF test signal source which can be connected to a first electrical line connected to the measurement object, as described in the preamble of claim 17.

DE10308280a1 discloses a method for calibrating an HF measuring device, a method for determining scattering parameters and such an HF measuring device. It is advantageous when developing complex planar microwave circuits consisting of a plurality of sub-circuits to determine the scattering parameters of each sub-circuit separately. This allows the efficiency of the different sub-circuits to be analyzed and checked independently. This can advantageously be achieved with a contactless measuring method. By means of a contactless measuring probe, part of the complex signal energy before and after the object to be measured (DUT) on the planar electrical transmission line is coupled out and transmitted to the receiver. From this coupled-out signal, the scattering parameter is then calculated. However, the system dynamics of such a measuring system depend to a large extent on the distance between the two contactless measuring probes. Such a measuring system can therefore only be used in a narrow frequency band.

The object of the invention is to provide a method and an HF measuring device of the type mentioned above, which enable an improved measurement accuracy over a large bandwidth.

According to the invention, the above object is achieved by a calibration method of the above-mentioned type with the features of claim 1, a method for determining a scattering parameter of the above-mentioned type with the features of claim 12, and an HF measuring device of the above-mentioned type with the features of claim 17. The other claims describe advantageous embodiments of the invention.

According to the invention, in a calibration method of the above-mentioned type, the rf signal transmitted on the second electrical conductor is coupled out at least three mutually spaced-apart coupling positions for at least one port of the rf measuring device, wherein for each pair of the at least three coupling positions at least one scattering parameter is determined for at least one frequency of the rf test signal using a predetermined calibration method with at least one calibration standard whose scattering parameter is known as a measurement object, wherein for all pairs of combinations at least one scattering parameter value determined at one frequency of the rf test signal is compared with at least one known scattering parameter value of the calibration standard, wherein such pairs of coupling positions are stored as first and second measurement positions which are preferably used when measuring an unknown measurement object for this frequency, the difference between the scattering parameter value determined at such a combination of coupling positions and the known scattering parameter of the calibration standard being minimal .

The advantage of the method described above is that a better broadband measurement dynamics is obtained, since the first and second coupling positions for measuring the scattering parameter are always selected from three or more existing coupling positions in such a way that the measured values deviate from the actual values to a minimum, i.e. the measurement errors are minimized.

An SOL method using, for example, calibration standards "short", "open", and "load", or an 8-item method or a 12-item method or a multi-port calibration method is used as the calibration method. Alternatively, the SOLT, LLR, TRM, TAN, TLN or LNN method may be used as the calibration method.

In order to achieve a measurement with as little influence as possible on the electrical properties of the measurement object, the coupling of the HF signal at the coupling point is preferably contactless, for example a capacitive coupling or an inductive coupling, or both capacitive and inductive couplings are used, or is achieved by means of electron-optical measuring methods, by means of force microscopes or by means of electromagnetic measuring methods. Various contactless and/or contact methods for determining the amplitude and phase of electromagnetic waves are suitable according to the invention.

Another additional coupling position can be obtained by a simple method: for example, the HF signals coupled out of the second electrical line from at least two coupling points are combined together by means of at least one mathematical operation and/or at least one algorithm, resulting in an HF signal, in particular combined by addition or subtraction, and then transmitted to further subsequent signal processing at this test port.

In an exemplary embodiment, a measuring probe is used, which is placed sequentially at the coupling position.

In a further alternative embodiment, two or more, in particular a number corresponding to the number of coupling positions, measurement probes are applied per test port.

For the subsequent error analysis during the measurement of the unknown measurement object, a mathematical relationship between the measurement probes during the calibration is determined and stored.

According to the invention, in a measuring method of the above-mentioned type, for each frequency of the HF test signal, the pair-wise combination of coupling positions stored for that frequency in the calibration method described above is selected as the first and second coupling positions.

The advantage of this measurement method is that the measurement accuracy is improved for large bandwidths.

A further improvement of the accuracy of the measurement results can be achieved in that: for each frequency of the HF test signal, in addition to the determination of the scattering parameter using the stored coupling position pair-wise combination, the determination of the scattering parameter is also carried out using one or more coupling position pair-wise combinations which, in the calibration method according to at least one of claims 1 to 11, have a determined scattering parameter value which differs from the scattering parameter of the known calibration standard only by a greater amount than the stored coupling position pair-wise combination, wherein the mean value for the respective scattering parameter is calculated from all values of the respective scattering parameter determined for a frequency of the HF test signal. This reduces the effect of measurement errors, for example due to incorrectly positioned coupling positions in relation to the time of calibration.

In order to detect defective measurement probes, the mathematical relationships between the plurality of measurement probes determined during calibration are re-determined and compared with the values obtained during calibration when measuring unknown measurement objects, and defective measurement probes are identified on the basis of their differences.

According to the invention, in an HF measuring device of the above-mentioned type, at least three mutually spaced coupling points are provided for at least one test port for coupling out an HF signal transmitted on a second electrical conductor, in particular a planar line, which is connected to the measurement object.

The HF measuring device described above has the advantage that for each measurement a corresponding coupling position pair can be selected, which has a small measurement error.

In a preferred embodiment, for each coupling position a separate measuring probe is provided, which is placed at the respective coupling position.

In a further alternative embodiment, a single measurement probe and means for moving the measurement probe to the coupling position are provided for each test port.

In a further alternative embodiment, a number of measurement probes is provided for each test port, the number of measurement probes being greater than or equal to 2 and less than or equal to the number of coupling positions minus 1, wherein the HF measurement device has at least one device for moving at least one measurement probe to a different coupling position.

For example, at least one measuring probe is designed as a contactless or contact measuring probe.

In a preferred embodiment, the at least one measuring probe is designed to be capacitively or inductively coupled, or to be coupled both capacitively and inductively, or to be coupled out by means of an electro-optical method, or by means of a force microscope, or by means of an electromagnetic measuring method.

The invention is explained in detail below with the aid of the figures. In the drawings:

figure 1 shows a simulation model of a single port measurement according to the invention,

figure 2 shows the system dynamics for different pairs of coupling positions,

figure 3 shows the system dynamics after calibration of the system according to the invention,

FIG. 4 shows a schematic circuit diagram of a first preferred embodiment of an HF measuring device with a two-port vector network analyzer according to the invention, an

Fig. 5 shows a schematic circuit diagram of a second preferred embodiment of an HF measuring device according to the invention with a four-port vector network analyzer.

The simulation model of the single-port measurement according to the invention shown in fig. 1 comprises a signal source 10 which feeds an HF test signal with a power level of 1dBm into an electrical conductor 12 in the form of a lossless 50 Ω transmission line. The contactless, in this case capacitive coupling at the three coupling locations 14, 16, 18 is represented by three ideal capacitors 20, 22, 24. The capacitive coupling at the coupling locations 14, 16, 18 is by way of example only. Inductive coupling may also be used, or a mixture of capacitive and inductive coupling or other coupling may be used. The voltage coupled out is measured at the position m₁26，m₂28 and m₃The receiver, represented in the form 30, is determined by means of a 50 omega system. White Gaussian Noise (WGN) generator 32 at measurement position m₁26，m₂28 and m₃The rear 30 is coupled in a known manner at typically-118 dBm and 50 omega. The measurement object 34, also called dut (device Under test), is connected to the electrical leads 12. The first section 36 of the electrical conductor 12 between the first coupling location 14 and the second coupling location 16 has a length l₁The second section 38 of the electrical conductor 12 between the second coupling location 16 and the third coupling location 18 has a length l₂And the third section 40 of the electrical line 12 between the third coupling location 18 and the measurement object 34 has a length l₃. Such as the above-mentioned segments 36, 38 of the electrical conductor 12, have a lengthl₁22mm and l₂78mm, i.e. a distance of 22mm between the first and second coupling points 14, 16 and a distance of 78mm between the second and third coupling points 16, 18, results in a length l of the electrical line 12 for the distance between the first and third coupling points 14, 18₁+l₂100 mm. A conventional calibration, such as an SOL calibration, is performed at reference numeral 52. Further calibration of the HF measuring device takes place at reference numeral 54, as described below:

a conventional SOL calibration is first performed for each of the three possible pairwise combinations of coupling locations 14, 16, 18 with a 50 Ω standard load ("load"), a short standard ("short"), and an open standard ("open"). This is merely an example and other calibration methods may be applied. The scattering parameter S is then determined for each pair-wise combination of coupling positions 14, 16, 18 for a standard calibration load of 50 Ω₁₁The value of (c). This is also merely an example and other scattering parameters and other calibration standards may be used. It is important that the expected value of the measured scattering parameter is known for the calibration standard applied as a DUT. In the above case, "standard load" is taken as DUT, | S₁₁The value of | in dB should be as low as possible, since ideally no reflection occurs at the "standard load".

FIG. 2 is a plot of a 50 Ω standard calibration load ("load") as the DUT at measurement locations 14, 16, 18 for the same capacitive measurement probe, with the vertical axis 42 representing a simulated scattering parameter | S₁₁In dB (equivalent to the measured scattering parameter), the horizontal axis 44 represents frequency in GHz. This figure represents the system dynamics resulting from the simulation. The first curve 46 is shown for the first and second coupling positions 14, 16, i.e. for the measurement position m₁26 and m₂28，|S₁₁I.e. decibel value versus frequency, the second curve 48 is the curve for the second and third coupling positions 16, 18, i.e. for the measurement position m₂28 and m₃30，|S₁₁The | decibel value versus frequency curve, and a third curve 50 ofWhen the first and third coupling positions 14, 18 are applied, i.e. for the measuring position m₁26 and m₃30，|S₁₁I decibel value versus frequency. The spacing l between the coupling locations 14, 16 and 18₁And l₂Chosen so that the maximum positions of the curves 46, 48 and 50 do not overlap. To calibrate the system, a pair-wise combination of the respective coupling positions 14, 16, 18 is now determined for each frequency point, for which pair-wise combination the scattering parameter | S₁₁Value of | decibel and | S₁₁There is a minimum separation, i.e., a minimum difference, between the desired decibel values of i. These coupling position pairs are stored as preferred coupling position pairs for the respective frequency points and are applied to the respective frequency points when measuring unknown measurement objects or DUTs at a later time. This method is hereinafter referred to as "disparity calibration". The SOL calibration is performed accordingly at 52 and the differential calibration is performed at 54. The DSOL calibration, i.e. the differential SOL calibration, is generally indicated by 55.

Figure 3 shows the system dynamics resulting from the above differential calibration (simulation). The vertical axis 42 represents the scattering parameter | S₁₁In dB, the horizontal axis 44 represents frequency in GHz. It can be clearly seen that the system dynamics is greatly improved at the original poorer frequency through differential calibration. A gain of 70dB can be achieved at 6.8GHz by effectively selecting the spacing of the coupling locations 14, 16 and 18. Furthermore differential calibration leads to an extension of the usable frequency range of the measuring device.

Fig. 4 shows by way of example a first preferred embodiment of an HF measuring device according to the invention based on a two-port vector network analyzer 56. The two-port vector network analyzer 56 comprises a signal source for generating an HF test signal, a first switch 58 and four measuring positions m₁60，m₂62，m₃64 and m₄66, two measurement locations for each test port. First switch 58 selectively connects signal source 10 to electrical conductors in the form of planar conductors 68, 70 located at the front and rear, planar conductors 68, 70 leading to DUT34 on different sides so that test signals can be coupled in both the front and rear of DUT 34. To vector at two portsThe network analyzer 56 couples out the forward and backward waves on the electrical conductor 12 internally, measuring the position m₁60，m₂62，m₃64 and m₄66 are separate from the internal structure of the two-port vector network analyzer 56. And a first and a second measuring position m₁60，m₂62 are optionally connected via a second switch 72 to 5 measuring probes 74 assigned to a first port of the two-port vector network analyzer 56, such that one of the measuring probes 74 is connected to a first measuring position m₁60, and the other of the measuring probes 74 is connected to a second measuring position m₂62 are connected. Similarly, a third switch 76 is provided which selectively connects another 5 measurement probes 78 assigned to a second port of the two-port vector network analyzer 56 with the third and fourth measurement locations m₃64，m₄66 are connected such that one of the measuring probes 78 is in a third measuring position m₃64 and the other of the measuring probes 78 is connected to a fourth measuring position m₄66 are connected. The switches 72, 76 and the measurement probes 74, 78 are each disposed on a substrate 80. A measurement probe 74 assigned to a first port of the two-port vector network analyzer 56 is placed near the front planar wire 68 to couple out HF signals from the front planar wire 68 at different coupling locations, and a measurement probe 78 assigned to a second port of the two-port vector network analyzer 56 is placed near the rear planar wire 70 to couple out HF signals from the rear planar wire 70 at different coupling locations. The switches 72, 76 enable selection of a pair-wise configuration of coupling positions at which the measurement probes 74 and 78 are located. A control device 82, in particular a computer, controls the two-port vector network analyzer 56 and controls the switches 72 and 76 via a voltage source 84.

Fig. 5 shows by way of example a second preferred embodiment of an HF measuring device according to the invention based on a four-port vector network analyzer 90. The four-port vector network analyzer 90 comprises a signal source 10 for generating an HF test signal, a first switch 58 and 8 measurement positions m₁92，m₂94，m₃96，m₄98，m₅100，m₆102，m₇104 and m₈106, each test port corresponds to two test locations. The first 4 measurement positions m₁92，m₂94，m₃96 and m₄98 are each connected to one of the measuring probes 74, which are arranged at coupling points on the front planar line 68. Four further measuring positions m₅100，m₆102，m₇104 and m₈106 are each connected to one of the measuring probes 78, which are arranged at the coupling point on the rear planar line 70. By applying these eight measurement positions m₁92，m₂94，m₃96，m₄98，m₅100，m₆102，m₇104 and m₈106, the second and third switches of the embodiment shown in fig. 4 may be omitted. Here, the selection of the coupling position pair or of each two measuring probes 74 or 78 is carried out within the four-port vector network analyzer 90, i.e. the differential calibration is carried out in the network analyzer.

The use of more than two measurement probes per measurement port shows an improvement of the contactless network analysis method. The redundancy obtained by adding a measurement probe is used to improve the dynamic characteristics, so that a broadband measurement system can be formed. For this purpose, a conventional calibration is carried out for each possible combination of measuring probes during the differential calibration. After this calibration, measurements are made for each probe pair combination in turn on a calibrated reference impedance, e.g., a standard load or calibration line. From the test results of the calibration, the dynamic behavior can be deduced. The dynamic range of each measurement probe combination is now compared for each frequency point within the program. The probe pair with the largest measurement dynamics is selected. The selected probe pair for each frequency point is stored in a memory and used for the measurement of an unknown measurement object.

In addition, other optimization criteria can be used in the contactless differential measurement system, for example, redundancy of additional probe pairs for improving measurement accuracy. For example, in a frequency range in which a plurality of measuring probe pairs have similar dynamics, the measuring probe measurements for one measurement are averaged. This reduces the effect of measurement errors, for example, caused by incorrect positioning of the measurement probe.

Furthermore, the redundancy can be used to identify defective or incorrectly positioned measurement probes. If a defective probe is identified, it may be electronically excluded from use for measurement, or a fault condition may be presented to the user. In order to detect defective measurement probes, the mathematical relationship between the measurement probes is determined, for example, during calibration. It is then checked whether this mathematical relationship is fulfilled each time an unknown measurement object is measured.

The embodiment of the measuring probe is arbitrary. The probes may be implemented planar or three-dimensional, wherein the probes do not have to be identical. Measurement probes having different coupling forms may be used in combination. For compactness, a planar design on the substrate is preferred.

A coupling position can also be understood as a combination of a plurality of probes (for example a combination of two probe measurement positions). For each frequency point, a probe pair is selected that is most suitable for measurement use, for example, in terms of dynamics, measurement accuracy, and the like. This selection is made when known standard components, such as standard loads, are measured in reverse.

Claims (24)

1. A method for calibrating a high-frequency measuring device having N test ports, where N is an integer greater than or equal to 1, for determining a scattering parameter of a measurement object by means of N port measurements, where N is an integer greater than or equal to 1, where a high-frequency test signal is fed into a first electrical line connected to the measurement object or to an electrical circuit containing the measurement object, where for each port a high-frequency signal carried on a second electrical line connected to the measurement object is coupled out at a first coupling location and at a second coupling location at a distance from the first coupling location, where the high-frequency signals coupled out by two of the ports at the two coupling locations are determined in each case by the high-frequency test signal of the high-frequency signal proceeding toward the measurement object on the second electrical line and the high-frequency test signal of the high-frequency signal proceeding away from the measurement object on the second electrical line at each measurement location or coupling location, and calculating therefrom a scattering parameter of the measurement object, characterized in that, for at least one port of the high-frequency measuring device, the high-frequency signals transmitted on the second electrical conductor are coupled out at least three coupling locations at a distance from one another, wherein for each pair-wise combination of the at least three coupling positions at least one scattering parameter is determined for at least one frequency of the high-frequency test signal with a predetermined calibration method with at least one calibration standard as measurement object for which the scattering parameter is known, for all pairs of combinations, the value of the at least one scattering parameter determined at one frequency of the high-frequency test signal is compared with the known value of the at least one scattering parameter of the calibration standard, wherein the following coupled position pair-wise combinations are stored as first and second measuring positions preferably used when measuring the unknown measuring object for this frequency: i.e. the difference between the determined value of the scattering parameter and the known scattering parameter of the calibration standard is minimal for such a combination of coupling positions.

2. The method of claim 1, wherein the high frequency measurement device is a vector network analyzer.

3. The method of claim 2, wherein the second electrical lead is a planar lead.

4. Method as claimed in any of the foregoing claims, characterized in that the coupling-out of the high-frequency signal at the coupling location is effected contactlessly.

5. Method according to one of claims 1 to 3, characterized in that the coupling-out of the high-frequency signal at the coupling location is a capacitive coupling or an inductive coupling, or both capacitive and inductive couplings are used, or is effected by means of an electro-optical measuring method, by means of a force microscope, or by means of an electromagnetic measuring method.

6. A method as claimed in any one of claims 1 to 3, characterized in that the high-frequency signals coupled out of the second electrical conductor from the at least two coupling locations are combined together by means of at least one mathematical operation and/or at least one algorithm to obtain a high-frequency signal, which is then transmitted to further signal processing at the test port.

7. A method as claimed in claim 6, characterized in that the high-frequency signals coupled out of the second electrical conductor from at least two coupling locations are combined together by adding or subtracting to obtain a high-frequency signal.

8. A method as claimed in any one of claims 1 to 3, characterized by using one measuring probe which is placed at a plurality of coupling positions sequentially.

9. A method as claimed in any one of claims 1 to 3, wherein two or more measurement probes are used per measurement port.

10. The method of claim 9, wherein each measurement port uses a number of measurement probes corresponding to the number of coupling locations.

11. A method according to claim 10, wherein the mathematical relationship between the measurement probes is determined and stored at calibration.

12. Method for determining a scattering parameter of a measurement object by means of a high-frequency measuring device having N test ports, where N is an integer greater than or equal to 1, which high-frequency measuring device is calibrated in accordance with at least one of claims 1 to 8, wherein N ports are used for measuring, N being an integer greater than or equal to 1, wherein a high-frequency test signal is fed into a first electrical line connected to the measurement object or to an electrical circuit containing the measurement object, wherein for each port a high-frequency signal transmitted on a second electrical line is coupled out of the second electrical line at a first coupling position of the second electrical line connected to the test object and at a second coupling position at a distance from the first coupling position, and the high-frequency signals coupled out by two of the ports at the two coupling positions, respectively, proceed toward the measurement object per coupling position with respect to the second electrical line and leave the measurement pair on the second electrical line High-frequency test signals like the advancing high-frequency signal are used to determine the amplitude and/or phase and to calculate the scattering parameters of the measurement object therefrom, characterized in that for each frequency of the high-frequency test signal, the pair-wise combination of the coupling positions stored for this frequency in the calibration method according to at least one of claims 1 to 11 is selected as the first and second coupling positions.

13. The method of claim 12, wherein the high frequency measurement device is a vector network analyzer.

14. A method according to claim 12 or 13, wherein the second electrical conductor is a planar conductor.

15. Method according to one of claims 12 to 13, characterized in that for each frequency of the high-frequency test signal, in addition to the determination of the scattering parameter using the stored coupling position pair-wise combination, the determination of the scattering parameter is effected with one or more coupling position pair-wise combinations which have in the calibration according to at least one of claims 1 to 11 a value of the determined scattering parameter which differs only by more than the stored coupling position pair-wise combination from the known scattering parameter of the calibration standard, wherein the mean value of the respective scattering parameter is calculated on the basis of all values determined for the respective scattering parameter for one frequency of the high-frequency test signal.

16. A method as claimed in any one of claims 12 to 13, characterized in that, during measurement on an unknown measurement object, the mathematical relationships between the plurality of measurement probes determined during calibration are re-determined and compared with the values obtained during calibration, and defective measurement probes are identified on the basis of their differences.

17. A high-frequency measuring device for determining a scattering parameter of a measuring object, which measuring device has N test ports, where N is an integer greater than or equal to 1, and has a source (10) for generating a high-frequency test signal, which source for generating the high-frequency test signal can be connected to a first electrical line (12, 68, 70) connected to the measuring object (34), characterized in that at least three mutually spaced coupling locations (14, 16, 18) are provided for at least one test port for coupling out a high-frequency signal transmitted on a second electrical line (12, 68, 70) connected to the measuring object (34).

18. High frequency measuring device according to claim 17, characterized in that for each coupling position (14, 16, 18) a separate measuring probe (74, 78) is provided, which is arranged at the respective coupling position.

19. A high frequency measuring device according to claim 17, characterized in that for each test port there is provided a single measuring probe and means for moving the measuring probe to the coupling positions.

20. The high frequency measurement device according to claim 17, wherein for each test port a number of measurement probes is provided which is greater than or equal to 2 and less than or equal to the number of coupling positions minus 1, wherein the high frequency measurement device has at least one means for moving at least one measurement probe to a different coupling position.

21. High frequency measuring device according to one of the claims 18 to 20, characterized in that at least one measuring probe (74, 78) is constructed contactless or contactable.

22. The high frequency measurement device according to any one of claims 17 to 20, characterized in that the high frequency measurement device is a vector network analyzer.

23. High frequency measuring device according to one of the claims 17 to 20, characterized in that the second electrical conductor (12, 68, 70) is a planar conductor.

24. The high-frequency measuring device according to one of claims 17 to 20, characterized in that the at least one measuring probe (74, 78) is configured to be capacitively or inductively coupled, or to be coupled using simultaneous capacitive and inductive coupling, or to be coupled by means of an electro-optical measuring method, by means of a force microscope, or by means of an electromagnetic measuring method.