RU2688902C1 - Non-contact microrelief sensor - Google Patents

Abstract

FIELD: measuring equipment.

SUBSTANCE: invention can be used to detect and measure microrelief of surface from metals and dielectrics, as well as to surface defectoscopy and detection of inhomogeneity of near-surface layers. Non-contact microrelief sensor consists of one or more microwave resonators located near the analyzed surface and operating using the standing wave amplitude variation effect in the resonator depending on the gap shape between the resonator and the surface, as well as on the surface material properties in the area of its interaction with the resonator. According to the invention, the resonator used is a planar structure on a dielectric substrate, having two resonant slots, in-phase excited by a high-frequency signal, and equipped with a separate port for reading an antiphased signal of such resonance slots.

EFFECT: invention enables to divide the signal into two channels, in which signals which depend on the distance between the sensor and the surface are separately recorded and signals depending on the relief gradient in the active region of the sensor, in addition, such a sensor enables to substantially increase the sensitivity and information content of measurements in the near electromagnetic field microscopy mode.

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Description

The invention can be used as a sensor as part of an electronic-mechanical device designed to certify the surface of metals and dielectrics, as well as their combination, using the method of mechanical scanning, including the detection and measurement of microrelief, as well as for the purposes of surface detection and detection of heterogeneity of the surface layers in a wide range of sizes, from millimeters to fractions of a micrometer, including in hard-to-reach places, for example, during preventive research m -metallic and polymeric wall pipes used for pumping corrosive liquids, including oil.

Analogues of the contactless microrelief sensor (BDM) are a whole family of sensors used in so-called near field microscopy, for example, described in the review [Bjorn T. Rosner, Daniel W. van der Weide. "High-frequency near-field microscopy". Review of Scientific Instruments 73, 2505 (2002); https://doi.Org/10.1063/l.1482150]. These are active sensors, which, unlike far-field sensors (radars), affect an electromagnetic field on a test surface located at small distances compared to the field concentration zone emitted by the sensor (from millimeters to fractions of a micrometer). Such a sensor, or a range of sensors (multi sensor), is associated with specialized electronic circuits, which may include, among other things, a standard impedance meter (S-parameter meter), which records the level of reflection and passage of currents in the sensor circuits depending on its clearance with the surface. The measurement results can be processed using a personal computer (PC) using special software (software). Methods for creating such software are described, for example, in [CB. Chinas. Fundamentals of technical diagnostics of objects of transport and storage of oil and gas. Electronic educational and methodical complex.

http://doidpo.rusoil.net/pluginfile.php/15820/mod resource / content / 1 / Fundamental s% 20of% 20technical% 20diagnostics / index.html]. Such software visualizes variations of the sensor impedance in the coordinates of the surface under study, and after appropriate calibration, allows you to get a mathematically accurate description of the relief or a map of inhomogeneities in the volume adjacent to the surface due to porosity or alien inclusions.

Structurally, the sensitive area of the known near-field sensors (DBP) is located near the end of the waveguide, for example, a coaxial cable, which can be a magnetic radiator if equipped with a wire loop, as described in [M. Kanda, "An Electromagnetic Near-Field Sensor for Simultaneous Electric and Magnetic-Field Measurements," IEEE Transactions on Electromagnetic Compatibility (Volume: EMC-26, Issue: 3) pp.102-110 (Aug. 1984) https: // doi .org / 10.1109 / TEMC. 1984.304200].

Another family-analogue in the field of flaw detection can be called pure magnetic sensors for pipes made of ferromagnetic alloys, in which defects (shells) are detected by a change in the magnetic gap between the pipe wall and the magnetic head. These heads are mounted on a self-propelled carrier, which has the ability to move inside the steel pipe. Such a carrier can be programmed and accumulate information about the magnetic low-frequency interaction of the heads with the pipe wall, taking into account the coordinate of carrier movement along the pipe, see, for example, [Pipeline indicator of defects in field pipelines. http://intron-vtd.ru/4.html]. However, magnetic sensors can only work with products from ferromagnetic alloys.

A disadvantage of existing sensors, both near-field and magnetic, described above, is their sensitivity to distance from an ideal surface. On the one hand, distance sensitivity is a measure of identifying a microrelief, but on the other hand, the same effect is possible due to the imperfection of scanning mechanics, which can lead to uneven clearance between the probe and the surface during movement of the sensor along a wavy (generally defect-free) surface. At the same time, it reduces the sensitivity and accuracy of measurements, systematic errors appear, and random or periodic vibration effects can lead to a false conclusion about the quality of the surface under study.

The closest prototype of the resonant near-field sensor is described in [D.E. Steinhauer, C.P. Vlahacos, S.K. Dutta, V.J. Feenstra, F.S.Wellstood, and S.M. Anlage, "Quantitative imaging of the microscope. Appl. Phys. Lett. 72, 861 (1998) https://doi.Org/10.1063/l.120918]. The prototype sensor is a segment of a cylindrical coaxial cable (below - coax), which has a length of about half the wavelength at the frequency of the measuring current. At one end, the central core of the coax is connected to the reflection coefficient meter through a small capacitor, and at the other, probing end, the central core is located as close as possible to the surface under study so that it has a noticeable electrical capacitance. When the surface relief changes, there is a change in the electrical capacitance of the probe end of the sensor with the surface, and a change occurs in the level of the signal reflected from the resonator, which is considered to be a detection of the inhomogeneity of the certified surface. The probe end of the resonator and the test surface are moved relative to each other with the help of the X-Y-Z translator. The measured complex reflection coefficient as a function of coordinates is used to construct a surface map. The resolution in the scanning plane is tenths of the cross section of the probe end of the resonator, that is, it depends on the possibilities of its miniaturization, and is about 10 microns.

The disadvantage of the prototype sensor, as mentioned above, is the inability to separate two different effects causing a sensor response: changing the distance to an ideal surface and the presence of a surface defect, since the complex reflection coefficient of such a resonator from the measuring system depends, in the first approximation, on the capacitance probe end, that is, from the distance between the probe end of the resonator and the surface under study.

The technical result is expressed in the fact that the new non-contact sensor of the microrelief allows the signal to be divided into two channels, in which the signals depending on the distance between the sensor and the surface and the signals depending on the gradient of the relief in the active region of the sensor are recorded separately. Such a sensor makes it possible in principle to increase the sensitivity and informativeness of measurements in the microscopy mode of a near electromagnetic field.

The technical result is achieved by the non-contact micro-relief sensor consisting of one or several microwave resonators, each of which is located near the surface under study, and working with the effect of changing the amplitude of the standing wave in the resonator depending on the shape of the gap between the resonator and the surface, as well as material properties of the surface in the region of its interaction with the resonator, and characterized in that a planar structure on the dielectric is used as the resonator zhke comprising two resonant slots are excited in phase high frequency signal, and provided with a separate port for reading such resonant antiphase signal slits.

Figure 1 qualitatively illustrates the topology and operation of the new sensor. Common-mode excitation of two slots is produced by the source i ₁ and, by measuring the voltage V ₁ , it is possible to measure the impedance of this symmetric (even) mode. If the amplitudes in the two slits are not equal to each other or these oscillations are not in-phase, then their difference is recorded with a V ₂ meter. The arrows in FIG. 1 shows the electric field vectors of the slots E ₁ and E ₂ . The difference (odd) mode is characterized by the vector sum E ₃ = E ₁ + E ₂ , that is, it is a combination of the fields of two slots and is recorded as a signal of the V ₂ jumper. For an even mode of a coplanar waveguide, the condition V ₂ = 0 is always satisfied, that is, an odd mode cannot occur while maintaining full symmetry or simply changing the distance between the open ends of two resonator slots and the surface if the sensor and the surface are mutually orthogonal. In the presence of a micro-gradient surface, the V ₂ signal becomes non-zero. The recorded current in the jumper can be called the differential signal of the two slots, and the sensor itself is a differential sensor, since, due to the different electrical capacitance of each of the slots with the surface, the amplitudes of the opposing fields E ₁ and E _{2 are} not equal and cannot compensate each other. In the FIG. 1 configuration meter V ₁ and V ₂ separately recorded integral and differential sensor signals, which more accurately (with high resolution) characterizes the surface profile.

Figure 2 is a sketch of the technical implementation of the device using the technology of printed circuit boards or the technology of thin films. This structure is an accurate three-dimensional image of the electromagnetic model, made in the licensed electromagnetic modeling program "Microwavw Office" (MWO) of the NI AWR company (USA). Calculations using this software were used to confirm the stated electrodynamic properties of the new sensor. External to the device electrodynamic circuits - waveguides (coaxial cables) are not shown, as they may have standard solutions and do not pretend to originality. The numbers in FIG. 2 marked: 1 - electromagnetic equivalent of a metal surface with a defect, which is indicated by the arrow and is in the active area of the device; 2 - electromagnetic excitation port of the resonator to which the circuit number of port No. 1 is assigned, and to which the recorder V ₁ is connected (see Fig. 1) for recording the reflection (parameter S ₁₁ ); 3 - series connection of electromagnetic ports No. 2 and No. 3, to which the recorder V _{2 is} connected (see Fig. 1 on the right) for measuring the parameter S ₂₁ . Electrodynamic circuits external to the device — waveguides (coaxial cables) are connected to ports 2 and 3 and are shown conventionally as two-wire lines. The physical elements of these circuits are not shown, since they can have standard solutions and do not claim to originality. The length of the slits is about 3/4 the length of the electromagnetic wave in the slit, taking into account the dielectric constant of the substrate. In the central conductor of the coplanar line at a distance of half the wavelength from the sensitive zone there is a narrow gap, which plays the role of the excitation capacitance, similar to a small capacitor in the coaxial prototype https://doi.org/10.1063/1.1482150.

Figure 3 illustrates the reciprocal electrodynamic configurations of the sensor and the surfaces used to demonstrate the interaction of the new sensor with heterogeneity. Heterogeneity in the form of a notch in a metal with a depth of 250 μm and a length of 500 μm (on the right) and the planar sensor itself gradually move relative to each other. Three characteristic cases of mutual arrangement are shown: two asymmetrical, but mirror-like with respect to the sensor axis and the third, symmetric with respect to its axis. The digital indications in FIG. 3 coincide with the notation in FIG. 2

Figure 4 shows the results of modeling the reflection of the structure shown in FIG. 2, when it is successively modified by a shift, as shown in FIG. 3 (modification sequence - from top to bottom). The corresponding dependences of the amplitude and phase of the reflected signal are presented as standard parameter S ₁₁ (complex reflection loss coefficient). Curve 4 (amplitude) and curve 5 (phase) correspond to the case when the electromagnetic equivalent of a metal surface with a defect is located, as shown in the upper part of FIG. 3. Curves 6 (amplitude) and 7 (phase) correspond to the case when the heterogeneity is in the middle position, as shown in the middle part of FIG. 3. Curves 8 (amplitude) and 9 (phase) correspond to the case when the heterogeneity is in the lower position, as shown in the lower part of FIG. 3. From FIG. 4 that in the upper and lower positions shown in FIG. 3. The characteristics of S ₁₁ are indistinguishable from each other. The data in FIG. 4 are obtained using an electromagnetic model in which electromagnetic ports No. 2 and No. 3 are connected by an air bridge loaded with an impedance of 50 Ohms (the second port of a circuit meter), as shown in FIG. 1. From FIG. 4, it can be seen that the changes in the amplitude of the reflected signal do not exceed 1 dB in amplitude and 10 degrees in phase, while there are some (symmetric) defect positions at which the signal has the same parameters. This can lead to repeated detection of the same inhomogeneity, but with different mutual coordinates of the sensor and the object under study (repeated, false detection). Presented in FIG. 4 data reflects a fundamental limitation in resolution for both the prototype in its classical coaxial version and the coplanar sensor in its single-mode version.

Figure 5 shows the simulation results of the new sensor with the added channel reading the differential mode V ₂ (see. Fig. 1). FIG. 5 shows the transmission coefficient to the second port of the network meter S ₂₁ calculated for different positions of heterogeneity, completely similar to the way it was done to build FIG. 4. Curve 10 (amplitude) and curve 11 (phase) correspond to the case when the electromagnetic equivalent of a metal surface with a defect is located, as shown in the upper part of FIG. 3. Curves 12 (amplitude) and 13 (phase) correspond to the case when the heterogeneity is in the middle position, as shown in the middle part of FIG. 3. The curves 14 (amplitude) and 15 (phase) correspond to the case when the non-uniformity is in the lower position, as shown in the lower part of FIG. 3. Curves 10 and 14 in FIG. 5 show that the same inhomogeneity of the relief, located symmetrically, give the same, but incomparably greater response relative to the symmetric position (curve 12). This response is more than 30 dB (1000 times) instead of 1 dB (1.2 times) for the prototype, that is, approximately 5000 times more. In this case, the phase shift shown by curves 11 and 15 reaches 180 degrees instead of 10 degrees in the prototype and smoothly changes from negative to positive values. This allows you to distinguish not only the absolute value, but also the direction of the gradient profile of the heterogeneity, eliminating the effect of repeated (false) detection. The graph in FIG. 5 characterizes the technical result of applying a new sensor, demonstrating the possibility of a multiple increase in the dynamic range of measurement, and hence sensitivity, with the help of a new sensor.

The invention is as follows. The scale of the microrelief to be registered and the frequency at which such registration will take place is determined. In the first approximation, the size of the gaps in the metal should be of the same order as the size of the detected inhomogeneity (in width and depth). Detailed line geometry is selected taking into account other general rules for designing microwave devices. Photolithographic methods are used to fabricate the planar structure of the resonator, shown above in FIG. 2 and FIG. 3, but not including the electromagnetic equivalent of a metal surface with a defect, indicated in FIG. 2 and FIG. 3 digits 1. As a blank, either a standard metal-foiled dielectric (fiberglass laminate, high-frequency laminate, etc.) can be used, or thin-film technology can be applied to apply thin films of metal or dielectric to a dielectric substrate and achieve the highest accuracy and extreme miniaturization of the device. Depending on the sensor dimensions selected, a standard coaxial connector is connected to point 2 (electromagnetic excitation port of the resonator) or - transfer to a microstrip, coaxial or slotted line, equipped with a standard coaxial connector and forming port No. 1 of the Vi recorder (see. Fig. 1) to measure the reflection on the main mode of the coplanar resonator (parameter S ₁₁ ); using standard symmetric feeders (for example, television antennas), node 3 is connected to a two-wire or slit line with metallization lying in the plane perpendicular to the sensor substrate and having at the other end a transition adapter to the desired type of line (coaxial or microstrip) to which it is connected port number 2 of the network meter for registering the parameter S _{21 of the} differential signal V ₂ (the parasitic mode of the coplanar waveguide). The finished sensor is mounted on a movable platform that provides mechanical scanning of the certified surface at a distance of the order of the width of the slits. In the process of mechanical scanning, a recording is made, and further, a comparison is made of the amplitudes and phases of the signal S ₂ i and the corresponding surface coordinates using the appropriate software.

FIG. Figure 6 shows schematically possible configurations from several sensors (multi sensor): for testing a flat surface according to the principle of a flatbed scanner (left) and for a curved surface, for example, for longitudinal in-line diagnostics (right).

The principle of the device is that the AC signal is applied to the conductor at point 2 (see Fig. 2) and excites the resonator, which sets the standing wave mode, determined by the length of the resonator and its boundary conditions. One of the boundary conditions is fixed (from the side of the exciting electrode 2), and the second depends on the configuration of the gap with the surface 1 under study and the properties of the surface itself, more specifically, on the surface impedance at the resonator frequency. The impedance of the resonator at the point of excitation 2 is measured by a standard two-port analyzer of alternating current circuits in the mode of the reflected signal (S ₁₁ ). The level of the differential signal is measured as the transmitted signal from the side output 3 with the same analyzer (S ₂₁ ). The described sensor or sample is mounted on a movable platform XYZ, as shown in FIG. 6, which moves along the surface in a predetermined manner under the control of a PC. When the XYZ platform moves along an ideal geometric plane with uniform properties, the impedance of the resonator at point 2 and the signal level at point 3 do not change, and the signal at point 3 is close to zero. If a parasitic vibration occurs in the direction normal to the surface in the XYZ platform movement, then the impedance at point 2 may change in accordance with the change in the gap. The same can happen if the sensor alignment in the pipeline shown in FIG. 6 on the right. The level of the differential signal at point 3 (S ₂₁ ) will remain negligibly small, since the local symmetry of the sensor field is preserved. If there is a heterogeneity of the material, or there is pollution on the surface in the form of a protrusion or sink of corrosion, then at a certain position of the platform the impedance of the two sensor slots becomes unequal, and at point 3 a non-zero odd mode signal appears, as shown in FIG. 5. The resolution (detection accuracy) of the described irregularities depends on the width of the sensor slits and on the distance to the surface. The best condition can be considered when the gaps and the distance to the surface have the same order of magnitude with the expected surface roughness. With the use of micron-resolution lithography, this accuracy can be fractions of a micrometer. By installing various sensors in the system, it is possible to independently optimize the range of measured inhomogeneities, both in scale in the plane and in the relief amplitude.

Claims (1)

Non-contact microrelief sensor consisting of one or several microwave resonators located near the surface under study and operating using the effect of changing the amplitude of the standing wave in the resonator depending on the shape of the gap between the resonator and the surface, as well as on the material properties of the surface in its interaction with the resonator, and characterized in that a planar structure on a dielectric substrate containing two resonant slots is used as a resonator, we in phase excite e high frequency signal, and provided with a separate port for reading such resonant antiphase signal slits.

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