Microwave and millimeter wave near-field subsurface microscopic imaging device and method based on signal interference

Abstract

The invention belongs to the technical field of near-field imaging, and particularly relates to a microwave and millimeter wave near-field subsurface microscopic imaging device and method based on signal interference, and the device comprises a vector network analyzer, a signal separation device, a phase adjustment device, a semi-steel coaxial line, a displacement platform, and an industrial control computer. The vector network analyzer comprises a signal separation unit, a frequency synthesis source, a first receiver and a second receiver, wherein the frequency synthesis source, the first receiver and the second receiver are respectively connected with the signal separation unit and used for generating microwave and millimeter wave test signals. The signal separation device is respectively connected with the vector network analyzer, the phase adjusting device and the semi-steel coaxial line, and the displacement table is connected with the vector network analyzer through the industrial personal computer; the tail end of the semi-steel coaxial line, which is far away from the signal separation device, is provided with a conical needle tip-shaped near-field probe; and the needle tip of the near-field probe is vertical to the surface of a to-be-detected sample arranged on the displacement table.

Description

Technical Field

[0001] This invention belongs to the field of near-field imaging technology, specifically relating to a microwave and millimeter-wave near-field subsurface microscopic imaging device and method based on signal interference. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Microwaves and millimeter waves have important applications in imaging and detection. However, limited by the Rayleigh diffraction limit, the highest resolution of existing microwave and millimeter wave far-field imaging techniques is only on the order of wavelength, which cannot achieve precise detection of the materials under test. Microwave and millimeter wave near-field imaging techniques use subwavelength-scale tips to achieve tight focusing of near-field signals, which can overcome the Rayleigh diffraction limit and has important applications in high-resolution testing of materials.

[0004] Currently, some researchers have studied near-field imaging devices based on coaxial resonant cavities. These devices achieve impedance matching between the test probe and the vector network detector (VNDD) using a coaxial resonant cavity, and employ subwavelength-scale tips for super-resolution sample detection, effectively enabling near-field super-resolution imaging in the microwave and millimeter-wave bands. However, existing coaxial resonant cavity near-field imaging technologies often require the design and manufacture of high-precision coaxial resonant cavity probes. Furthermore, due to limitations in the resonance principle, they can only be tested within a narrow band, and the test frequency is generally fixed. When the test frequency needs to be changed, coaxial resonant cavity probes with different resonant frequencies must be redesigned and manufactured, resulting in high costs. Therefore, there is an urgent need to develop a microwave and millimeter-wave near-field imaging detection technology with adjustable test frequencies. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a microwave and millimeter-wave near-field subsurface microscopic imaging device and method based on signal interference. It employs a near-field probe to achieve near-field super-resolution imaging, utilizes the principle of signal interference to eliminate strong reflective background signals, adjusts the test frequency through a phase adjustment device, and combines a vector network analyzer to generate the excitation signal and receive the test signal. This enables microwave and millimeter-wave near-field subsurface microscopic imaging while simultaneously allowing for test frequency adjustment.

[0006] According to some embodiments, the first aspect of the present invention provides a microwave and millimeter-wave near-field subsurface microscopic imaging device based on signal interference, employing the following technical solution: A microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interferometry includes a vector network analyzer, a signal separation device, a phase adjustment device, a semi-steel coaxial line, a displacement stage, and an industrial control computer. The vector network analyzer includes a signal separation unit and a frequency synthesis source, a first receiver, and a second receiver, all connected to the signal separation unit for generating microwave / millimeter-wave test signals. The signal separation device is connected to the vector network analyzer, the phase adjustment device, and the semi-steel coaxial line. The displacement stage is connected to the vector network analyzer via the industrial control computer. A tapered, needle-like near-field probe is disposed at the end of the semi-steel coaxial line away from the signal separation device, and the tip of the near-field probe is perpendicular to the surface of the sample to be tested disposed on the displacement stage.

[0007] As a further technical limitation, the microwave millimeter-wave test signal undergoes down-conversion modulation processing under the action of the first receiver to generate a first reference signal; the generated first reference signal is then processed by the signal separation device to obtain a second reference signal and a second test signal.

[0008] Furthermore, the obtained second reference signal is phase-adjusted and reflected under the action of the phase adjustment device to obtain a reflected second reference signal, which is then reflected back to the signal separation device.

[0009] Furthermore, the obtained second test signal interacts with the sample under test under the action of the semi-steel coaxial line to obtain a reflected second test signal containing the information of the sample under test, and the obtained reflected second test signal is then reflected back to the signal separation device.

[0010] Furthermore, the reflected second reference signal and the reflected second test signal are combined and interfered with by the signal separation device to obtain an interference signal.

[0011] Furthermore, the frequency interval of the valleys of the interference signal for ;in, For free space wave speed, The relative permittivity of the dielectric filling medium for the coaxial line, The equivalent electrical length of the phase adjustment device, It is the equivalent electrical length of the coaxial line of the semi-steel.

[0012] Furthermore, the obtained interference signal is coupled to the second receiver after passing through the signal separation unit. The interference signal undergoes down-conversion modulation processing under the action of the second receiver to generate the first test signal.

[0013] Furthermore, based on the vector network analyzer, the first test signal and the first reference signal are compared to obtain the amplitude and phase of the test curve.

[0014] Furthermore, the phase adjustment device and the coaxial line have different equivalent electrical lengths, resulting in different periodicities of the interference signal frequencies. Different interference frequencies can be selected according to the test requirements, and the test frequency of each interference signal can be adjusted by finely adjusting the phase difference between the equivalent electrical length of the semi-steel coaxial line and the equivalent electrical length of the phase adjustment device.

[0015] According to some embodiments, the second aspect of the present invention provides a microwave and millimeter-wave near-field subsurface microscopic imaging method based on signal interferometry, which adopts the microwave and millimeter-wave near-field subsurface microscopic imaging device based on signal interferometry provided in the first aspect, and employs the following technical solution: A microwave / millimeter-wave near-field subsurface microscopic imaging method based on signal interferometry includes: Microwave and millimeter-wave test signals are generated based on frequency synthesis sources, and interference signals and test curves are generated in a microwave and millimeter-wave near-field subsurface microscopic imaging device based on signal interference. A near-field probe is used to focus on the surface of the sample under test, and microwave and millimeter-wave near-field subsurface microscopic imaging based on signal interference is obtained by adjusting the displacement stage.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a near-field probe to achieve near-field super-resolution imaging, utilizes the principle of interference to eliminate strong reflection background signals, and employs a vector network analyzer to generate excitation signals and receive test signals, enabling near-field super-resolution subsurface microscopic imaging in microwave and millimeter-wave applications. It also employs a signal separation device to achieve interference based on test and reference signals, a phase adjustment device to adjust the interference frequency, a subwavelength-scale probe to achieve tight focusing of near-field signals, and a vector network analyzer to generate excitation signals and receive test signals. This allows for near-field subsurface super-resolution microscopic imaging of the sample under test, and the test frequency can be adjusted according to testing needs, achieving near-field subsurface super-resolution microscopic imaging with adjustable test frequency. Attached Figure Description

[0017] The accompanying drawings, which form part of this embodiment, are used to provide a further understanding of this embodiment. The illustrative embodiments and their descriptions are used to explain this embodiment and do not constitute an improper limitation of this embodiment.

[0018] Figure 1 This is a schematic diagram of the structure of the microwave and millimeter-wave near-field subsurface microscopic imaging device based on signal interference in Embodiment 1 of the present invention. Figure 2This is a schematic diagram of the test curve when the difference between L1 and L2 is 300 mm in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the test curve of the PP material thin dielectric plate and air in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram showing the difference in the amplitude of the test curves between air and the sample of the medium to be tested in Embodiment 1 of the present invention. Figure 5 This is a schematic diagram of the test curves for air and thin medium near the interference frequency in Embodiment 1 of the present invention; Figure 6 This is a schematic diagram showing the difference in the amplitude of the test curves between the PP material thin dielectric plate and air in Embodiment 1 of the present invention; Figure 7 This is a schematic diagram of the microwave and millimeter-wave near-field amplitude microscopic imaging results of a PP material thin dielectric plate in Embodiment 1 of the present invention; Figure 8 This is a schematic diagram of the microwave and millimeter-wave near-field phase microscopy imaging results of a PP material thin dielectric plate in Embodiment 1 of the present invention; Figure 9 This is a schematic diagram of the near-field phase test curve of microwave and millimeter waves based on the interference principle in Embodiment 1 of the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0021] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0022] In this invention, terms such as "upper," "lower," "left," "right," "front," "back," "vertical," "horizontal," "side," and "bottom" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are used only to facilitate the description of the structural relationships of the various components or elements of this invention and do not specifically refer to any component or element in this invention. They should not be construed as limiting the invention.

[0023] In this invention, terms such as "fixed connection," "connected," and "linked" should be interpreted broadly, indicating a fixed connection, an integral connection, or a detachable connection; a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can determine the specific meaning of these terms in this invention based on the specific circumstances, and they should not be construed as limitations on the invention.

[0024] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0025] Example 1 Embodiment 1 of the present invention introduces a microwave and millimeter-wave near-field subsurface microscopic imaging device based on signal interference.

[0026] like Figure 1 The device, a microwave / millimeter-wave near-field subsurface microscopic imaging apparatus based on signal interferometry, includes a vector network analyzer, a signal separation device, a phase adjustment device, a semi-steel coaxial line, an X-axis displacement stage, a Y-axis displacement stage, and an industrial control computer. The vector network analyzer includes a signal separation unit and a frequency synthesis source, a first receiver, and a second receiver, all connected to the signal separation unit for generating microwave / millimeter-wave test signals. The signal separation device is connected to the vector network analyzer, the phase adjustment device, and the semi-steel coaxial line. The X-axis and Y-axis displacement stages are connected to the vector network analyzer via the industrial control computer. A conical, needle-like near-field probe is positioned at the end of the semi-steel coaxial line away from the signal separation device, with the probe tip perpendicular to the surface of the sample to be tested on the displacement stage.

[0027] In this embodiment, the frequency synthesis source in the vector network analyzer host generates a frequency of... The microwave and millimeter-wave test signal is split into two paths after passing through the signal separation unit. One path enters the first receiver, and the other path enters the signal separation device. The test signal entering the first receiver undergoes down-conversion demodulation processing to obtain the first reference signal R1. The signal entering the signal separation device is split into two paths, namely the second reference signal S1 and the second test signal S2. S1 enters the phase adjustment device with an equivalent length of L1 that is either short-circuited or open-circuited at the end. S1 is reflected at the end of the phase adjustment device to obtain the reflected second reference signal. The obtained reflected second reference signal is then transmitted back to the signal separation device along the phase adjustment device.

[0028] S2 is the second test signal, which enters a semi-steel coaxial cable of length L2. The end of the semi-steel coaxial cable has a tapered needle tip, which is located vertically within a short distance of the surface of the sample to be tested. After S2 is transmitted to the end of the semi-steel cable, the needle tip interacts with the sample to obtain a reflected second test signal containing the information of the sample to be tested. The obtained reflected second test signal is reflected back to the signal separation device along the semi-steel coaxial cable.

[0029] In this embodiment, the reflected second reference signal and the reflected second test signal interfere after being combined in the signal separation device to obtain an interference signal. After entering the signal separation unit in the vector network, the interference signal is coupled to the second receiver. The second receiver performs down-conversion demodulation processing on the interference signal to obtain the first test signal A.

[0030] The vector network analyzer calculates the amplitude and phase of the test curve S11 by comparing the first test signal A with the first reference signal R1. According to the principle of interference, the frequency interval of the troughs of the interference signal... for ;in, For free space wave speed, The relative permittivity of the filling medium for the coaxial line.

[0031] In this embodiment, when the test frequency is close to the frequency where the trough of the interference signal is located, the change in the interference signal caused by a small change in the sample under test is the largest. The frequency with the largest change in the interference signal is selected as the test frequency point. The X-axis and Y-axis displacement stages are controlled by an industrial control computer to move, and the displacement stages can drive the sample located on them to perform two-dimensional motion. The vector network analyzer records the amplitude and phase of each test frequency point in the two-dimensional scanning plane, and finally, the near-field amplitude and phase images of the sample under test can be obtained.

[0032] The phase adjustment device has a different equivalent electrical length than the coaxial line, thus creating multiple periodic interference frequencies. Different interference frequencies can be selected for testing according to requirements. Furthermore, the phase difference between L1 and L2 can be finely adjusted to achieve control over each interference test frequency.

[0033] This embodiment uses a needle tip to focus the electromagnetic wave test signal onto the sample surface, thus enabling near-field super-resolution microscopy that breaks the diffraction limit. The electromagnetic waves focused at the tip of the needle have a certain penetrating effect on the sample, thus enabling near-field subsurface microscopy imaging of the sample under test.

[0034] To achieve signal interference, the signal separation device in this embodiment can be a power divider or a coupler.

[0035] To achieve the phase adjustment function of the signal, the phase adjustment device in this embodiment can be a phase shifter or a phase shifting cable of different lengths.

[0036] like Figure 2 The S11 test curve shown is obtained when the difference between L1 and L2 is 300 mm. It can be seen that periodic interference appears in the test curve at this point. Based on the frequency interval of the interference signal troughs... According to the formula, when the difference between L1 and L2 is 300 mm, the frequency interval of the interference curve trough is 0.34 GHz, and the measured value is 0.35 GHz, which is basically consistent with the theoretical value.

[0037] As one or more embodiments, a thin dielectric plate of PP material with a thickness of approximately 2 mm was tested. Figure 3 The enlarged view of the S11 amplitude test curves for air and thin dielectric near the interference frequency shows that the S11 amplitude test curve for the PP material thin dielectric plate is significantly different from that for air. Figure 3 By measuring the 3dB value of the air quality curve, the quality factor Q can be calculated to reach 19703. This high quality factor helps to achieve high-sensitivity testing of the sample.

[0038] like Figure 4 The difference between the S11 amplitude test curve of the PP material thin dielectric plate and the S11 amplitude test curve of air can be seen. It can be seen that the test curves of the two media are very different near the interference frequency. Therefore, the material can be imaged based on the difference in amplitude between the two.

[0039] like Figure 5 The enlarged view of the S11 phase test curves for air and thin dielectric near the interference frequency shows that the S11 phase test curve for the PP material thin dielectric plate is significantly different from that for air. Figure 6 The difference between the S11 phase test curve of the PP material thin dielectric plate and the S11 phase test curve of air can be seen. It can be seen that the test curves of the two media are very different near the interference frequency. Therefore, the material can be imaged based on the difference in phase between the two.

[0040] As one or more implementation methods, near-field imaging tests were performed on a perforated PP material thin dielectric plate covered with an opaque thin dielectric at a test frequency of 10.8378 GHz, with a test range of 70 mm × 75 mm. Figure 7 and Figure 8 The normalized near-field amplitude imaging results and near-field phase test results are shown. It can be seen that both clearly reveal the boundaries and internal pore shapes of the PP thin dielectric substrate.

[0041] like Figure 9 The microwave / millimeter-wave near-field phase test curves based on the interferometry principle shown demonstrate a lateral resolution of 5 mm. The test frequency used in this example is 10.8378 GHz, corresponding to a wavelength of 27.68 mm. The imaging resolution in this example reaches 1 / 5.5 of the test wavelength. This experimental example illustrates the near-field subsurface super-resolution microscopy imaging capability of this embodiment.

[0042] This embodiment achieves higher resolution by using a finer needle tip and controlling the distance between the needle tip and the sample to a closer range.

[0043] This embodiment employs a near-field probe to achieve near-field super-resolution imaging, utilizes the principle of interference to eliminate strong reflection background signals, and employs a vector network analyzer to generate excitation signals and receive test signals, enabling near-field super-resolution subsurface microscopic imaging in microwave and millimeter-wave ranges. It uses a signal separation device to achieve interference based on test and reference signals, a phase adjustment device to adjust the interference frequency, a subwavelength-scale probe to achieve tight focusing of near-field signals, and a vector network analyzer to generate excitation signals and receive test signals. This allows for near-field subsurface super-resolution microscopic imaging of the sample under test, and the test frequency can be adjusted according to testing needs, achieving near-field subsurface super-resolution microscopic imaging with adjustable test frequency.

[0044] Example 2 Embodiment 2 of the present invention introduces a microwave and millimeter-wave near-field subsurface microscopic imaging method based on signal interference, which adopts the microwave and millimeter-wave near-field subsurface microscopic imaging device based on signal interference described in Embodiment 1.

[0045] A microwave / millimeter-wave near-field subsurface microscopic imaging method based on signal interferometry includes: Microwave and millimeter-wave test signals are generated based on frequency synthesis sources, and interference signals and test curves are generated in a microwave and millimeter-wave near-field subsurface microscopic imaging device based on signal interference. A near-field probe is used to focus on the surface of the sample under test, and microwave and millimeter-wave near-field subsurface microscopic imaging based on signal interference is obtained by adjusting the displacement stage.

[0046] The detailed steps are the same as the working principle of the microwave and millimeter-wave near-field subsurface microscopic imaging device based on signal interference provided in Example 1, and will not be repeated here.

[0047] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

[0048] The above description is merely a preferred embodiment of this practice and is not intended to limit the scope of this practice. Various modifications and variations can be made to this practice by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this practice should be included within the protection scope of this practice.

Claims

1. A microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interferometry, characterized in that, The system includes a vector network analyzer, a signal separation device, a phase adjustment device, a semi-steel coaxial line, a displacement stage, and an industrial control computer. The vector network analyzer includes a signal separation unit and a frequency synthesis source, a first receiver, and a second receiver, all connected to the signal separation unit for generating microwave and millimeter-wave test signals. The signal separation device is connected to the vector network analyzer, the phase adjustment device, and the semi-steel coaxial line. The displacement stage is connected to the vector network analyzer via the industrial control computer. A tapered, needle-like near-field probe is provided at the end of the semi-steel coaxial line furthest from the signal separation device, and the tip of the near-field probe is perpendicular to the surface of the sample to be tested on the displacement stage.

2. The microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interference as described in claim 1, characterized in that, The microwave and millimeter-wave test signal undergoes down-conversion modulation processing under the action of the first receiver to generate a first reference signal; the generated first reference signal is then processed by the signal separation device to obtain a second reference signal and a second test signal.

3. The microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interference as described in claim 2, characterized in that, The obtained second reference signal is phase-adjusted and reflected under the action of the phase adjustment device to obtain a reflected second reference signal, which is then reflected back to the signal separation device.

4. The microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interference as described in claim 3, characterized in that, The obtained second test signal interacts with the sample under test under the action of the semi-steel coaxial line to obtain a reflected second test signal containing the information of the sample under test, and the obtained reflected second test signal is then reflected back to the signal separation device.

5. The microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interference as described in claim 4, characterized in that, The reflected second reference signal and the reflected second test signal are combined and interfered with by the signal separation device to obtain an interference signal.

6. The microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interference as described in claim 5, characterized in that, The frequency interval of the valleys of the interference signal for ;in, For free space wave speed, The relative permittivity of the dielectric filling medium for the coaxial line, The equivalent electrical length of the phase adjustment device, It is the equivalent electrical length of the coaxial line of the semi-steel.

7. The microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interference as described in claim 5, characterized in that, The obtained interference signal is coupled to the second receiver after passing through the signal separation unit. The interference signal is then down-converted and regulated by the second receiver to generate the first test signal.

8. The microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interference as described in claim 7, characterized in that, The vector network analyzer performs a ratio calculation between the first test signal and the first reference signal to obtain the amplitude and phase of the test curve.

9. The microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interference as described in claim 7, characterized in that, The phase adjustment device and the coaxial line have different equivalent electrical lengths, resulting in different periodicities of the interference signal frequencies. Different interference frequencies are selected according to the test requirements. The test frequency of each interference signal is adjusted by finely adjusting the phase difference between the equivalent electrical length of the semi-steel coaxial line and the equivalent electrical length of the phase adjustment device.

10. A microwave / millimeter-wave near-field subsurface microscopic imaging method based on signal interferometry, employing the microwave / millimeter-wave near-field subsurface microscopic imaging device based on signal interferometry as described in any one of claims 1-9, characterized in that, include: Microwave and millimeter-wave test signals are generated based on frequency synthesis sources, and interference signals and test curves are generated in a microwave and millimeter-wave near-field subsurface microscopic imaging device based on signal interference. A near-field probe is used to focus on the surface of the sample under test, and microwave and millimeter-wave near-field subsurface microscopic imaging based on signal interference is obtained by adjusting the displacement stage.

Images