Non-focusing near-field scanning imaging equipment and scanning imaging system

Abstract

The invention discloses a non-focusing type near-field scanning imaging device and a scanning imaging system, and relates to the technical field of object imaging, and the non-focusing type near-field scanning imaging device comprises a signal source, a signal receiving and transmitting module, a detection module and an imaging module. The signal source is used for generating an original radio frequency signal and sending the original radio frequency signal to the signal transceiving module; the signal transceiving module is used for generating a first radio frequency signal based on the original radio frequency signal and sending the first radio frequency signal to the detection module based on a non-focusing mode; the detection module is used for scanning an object to be imaged under a set frequency based on the first radio frequency signal to obtain a second radio frequency signal and sending the second radio frequency signal to the signal transceiving module; and the signal transceiving module is also used for extracting the near-field signal carried by the second radio frequency signal and sending the near-field signal to the signal extraction module, so that the complexity of the overall structure of the near-field scanning imaging equipment is further simplified, and the control difficulty is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of object imaging, and specifically, relates to a non-focusing near-field scanning imaging device and a scanning imaging system. Background Art

[0002] Because terahertz waves are between microwaves and infrared radiation in the entire electromagnetic spectrum and have the special properties of both, due to their low photon energy and strong penetrability, terahertz wave imaging technology has broad application prospects in quality control, non-destructive monitoring, biomedicine, etc. However, due to the limitation of the diffraction resolution limit, the resolution of traditional far-field terahertz wave imaging systems usually does not exceed the micron level. Therefore, traditional far-field terahertz wave imaging systems cannot meet the requirements of imaging sub-micron features such as the surface characteristics of nanomaterials and biological cells. Currently, the near-field scanning imaging method based on tip scattering has been proven to be able to break through the limit of diffraction resolution, and its resolution is only limited by the curvature radius of the scattering tip. For example, the patent application with the publication number CN117269100A discloses a zero-intermediate-frequency compact reflective terahertz near-field scanning microscope, and its structure is as Figure 1 shown. This patent application is based on the focusing mode. Although it can achieve imaging of the surface characteristics of nanomaterials, due to the use of a double-lens focusing unit to focus terahertz waves in the scanning imaging module, this solution has the following defects:

[0003] (1) It increases the complexity of the overall structure;

[0004] (2) The terahertz waves after beam expansion and collimation are focused on the tip of the atomic force microscope through two lenses, and the signal-to-noise ratio of the obtained near-field signal is relatively low, resulting in low imaging quality;

[0005] (3) The double-lens focusing unit is prone to interference with the mechanical structure of the atomic force microscope tip control part, and it is necessary to adjust the atomic force microscope and the double-lens focusing unit multiple times, with a large operation difficulty. Summary of the Invention

[0006] Embodiments of the present invention provide a non-focusing near-field scanning imaging device and a scanning imaging system to solve the defects existing in the prior art.

[0007] To achieve the above object, the non-focusing near-field scanning imaging device and the scanning imaging system provided by the embodiments of the present invention include the following technical solutions:

[0008] In a first aspect, the non-focusing near-field scanning imaging device provided by the embodiments of the present invention includes:

[0009] A signal source for generating an original radio frequency signal and transmitting the original radio frequency signal.

[0010] A signal transceiver module, configured to receive the original radio frequency signal, generate a first radio frequency signal based on the original radio frequency signal, and transmit the first radio frequency signal based on a non-focusing mode.

[0011] A detection module, configured to receive the first radio frequency signal and scan an item to be imaged at a set frequency based on the first radio frequency signal, obtain a second radio frequency signal, and transmit the second radio frequency signal to the signal transceiver module.

[0012] The signal transceiver module is configured to receive the second radio frequency signal and extract the near-field signal carried by the second radio frequency signal.

[0013] A signal extraction module, configured to receive the near-field signal, extract the amplitude information corresponding to the near-field signal, and transmit the amplitude information corresponding to the near-field signal.

[0014] An imaging module, configured to receive the amplitude information corresponding to the near-field signal and image the item to be imaged according to the amplitude information corresponding to the near-field signal and the position information of each point sent by the detection module.

[0015] In some examples, the signal transceiver module includes:

[0016] A frequency multiplier, configured to convert the original radio frequency signal into a terahertz wave and transmit the terahertz wave.

[0017] A power splitter, configured to receive the terahertz wave, divide the terahertz wave into a first radio frequency signal and a third radio frequency signal according to power, and transmit the first radio frequency signal and the third radio frequency signal respectively.

[0018] A directional coupler, configured to receive the first radio frequency signal and transmit the first radio frequency signal.

[0019] An antenna unit, configured to receive the first radio frequency signal sent by the directional coupler and transmit the first radio frequency signal.

[0020] The antenna unit is further configured to receive the second radio frequency signal sent by the detection module and transmit the second radio frequency signal to the directional coupler.

[0021] The directional coupler is further configured to receive the second radio frequency signal and transmit the second radio frequency signal.

[0022] In some examples, the signal transceiver module further includes:

[0023] A low-noise amplifier, configured to receive the second radio frequency signal sent by the directional coupler, amplify the second radio frequency signal, and transmit the amplified second radio frequency signal.

[0024] A mixer is configured to receive the amplified second radio frequency signal and perform a homodyne operation on the amplified second radio frequency signal to obtain a modulation signal corresponding to the amplified second radio frequency signal and transmit the modulation signal.

[0025] The DC blocker is configured to receive the modulation signal, filter out the DC signal in the modulation signal and transmit the modulation signal after filtering out the DC signal to the signal extraction module.

[0026] In some examples, the signal extraction module includes:

[0027] A lock-in amplifier is configured to extract the amplitude information corresponding to the near-field signal in the modulation signal transmitted by the DC blocker and transmit the amplitude information corresponding to the near-field signal.

[0028] A low-pass filter is configured to receive the amplitude information corresponding to the near-field signal, denoise the amplitude information corresponding to the near-field signal and transmit the amplitude information corresponding to the near-field signal after denoising.

[0029] A data processing unit is configured to receive the amplitude information corresponding to the near-field signal after denoising and demodulate the amplitude information corresponding to the near-field signal.

[0030] The display unit is configured to display the amplitude information corresponding to the near-field signal after demodulation.

[0031] In some examples, the signal transceiver module further includes:

[0032] A mechanical fine-tuning unit is configured to adjust the antenna unit so that the first radio frequency signal emitted by the antenna unit is directly radiated to the detection module.

[0033] In some examples, the detection module is an atomic force microscope.

[0034] In some examples, the mechanical fine-tuning unit is a three-dimensional moving platform.

[0035] In a second aspect, the scanning imaging system provided by an embodiment of the present invention includes the non-focusing near-field scanning imaging device disclosed in the first aspect.

[0036] The beneficial effects of the present invention compared with the prior art are as follows:

[0037] (1) By adopting a non-focusing mode and not using a dual-lens focusing unit, the first radio frequency signal is directly radiated to the detection module, further simplifying the complexity of the overall structure of the near-field scanning imaging device;

[0038] (2) Since the signal transceiver module directly radiates the first radio frequency signal to the detection module, omitting the focusing process, the signal-to-noise ratio of the near-field signal output by the detection module is improved in the case of short-distance signal transmission and reception, and the imaging quality is high.

[0039] (3) It avoids the interference between the double-lens focusing unit and the detection module during the focusing adjustment process, reducing the operation difficulty. Description of the Drawings

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0041] Figure 1 It is a schematic diagram of the overall structure of an existing near-field scanning imaging device;

[0042] Figure 2 It is a schematic diagram of the overall structure of a non-focusing near-field scanning imaging device provided by an embodiment of the present invention;

[0043] Figure 3 It is a schematic diagram of the internal circuit of a non-focusing near-field scanning imaging device provided by an embodiment of the present invention;

[0044] Figure 4 It shows a schematic diagram of the signal transceiver module transmitting the first radio frequency signal to the detection module based on the non-focusing mode provided by an embodiment of the present invention;

[0045] Figure 5 It is a schematic diagram of a partial image of a silicon-gold sample obtained by using the non-focusing near-field scanning imaging device provided by an embodiment of the present invention;

[0046] Figure 6 It is a schematic diagram of another partial image of a silicon-gold sample obtained by using the non-focusing near-field scanning imaging device provided by an embodiment of the present invention. Detailed Embodiments

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. The specific implementation manners of the present invention will be further described in detail below with reference to the drawings and embodiments. The following embodiments are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0048] Embodiment 1

[0049] As Figure 2 and Figure 3 shown, the non-focusing near-field scanning imaging device provided by the embodiment of the present invention includes a signal source, a signal transceiver module, a detection module, a signal extraction module, and an imaging module, where:

[0050] The signal source is configured to generate an original radio frequency signal and send the original radio frequency signal to the signal transceiver module.

[0051] Specifically, the signal source is a radio frequency signal source capable of generating and outputting a radio frequency signal. A high-frequency electromagnetic wave with long-distance transmission ability is called a radio frequency signal. Due to this characteristic of the radio frequency signal, radio frequency technology is widely used in the field of wireless communication.

[0052] The signal transceiver module is configured to receive the original radio frequency signal and generate a first radio frequency signal based on the original radio frequency signal, and send the first radio frequency signal to the detection module based on the non-focusing mode.

[0053] In some examples, the signal transceiver module includes:

[0054] A frequency multiplier configured to convert the original radio frequency signal into a terahertz wave and send the terahertz wave to a power divider.

[0055] Specifically, the terahertz wave is an electromagnetic wave with a frequency between 0.1 THz and 10 THz, and the wavelength is approximately between 0.03 and 3 mm, which is between microwaves and infrared rays. The terahertz wave band can cover the characteristic spectra of substances such as semiconductors, plasmas, organisms, and biological macromolecules, which can deepen and expand human understanding of some basic scientific issues in physics, chemistry, astronomy, informatics, and life sciences. Terahertz technology can be widely applied in fields such as radar, remote sensing, homeland security, high-security data communication and transmission, atmosphere and environmental monitoring, real-time biological information extraction, and medical diagnosis.

[0056] A power splitter is used to divide a terahertz wave into a first radio frequency signal and a third radio frequency signal according to power, send the third radio frequency signal to a mixer, and send the first radio frequency signal to a directional coupler. Among them, the third radio frequency signal is used as a local oscillator signal to drive the mixer.

[0057] The directional coupler is used to send the first radio frequency signal to the antenna unit.

[0058] The antenna unit is used to send the first radio frequency signal to the detection module.

[0059] Specifically, the antenna unit is a horn antenna 1.

[0060] Among them, as Figure 4 shown, based on the non-focusing mode, the signal transceiver module sends the first radio frequency signal to the atomic force microscope 2 through the horn antenna 1. Through the non-focusing mode, without using a double-lens focusing unit, the first radio frequency signal is directly radiated to the detection module, which can further simplify the complexity of the overall structure of the near-field scanning imaging device.

[0061] The detection module is used to scan the item to be imaged at a set frequency based on the first radio frequency signal, obtain a second radio frequency signal, and send the second radio frequency signal to the signal transceiver module.

[0062] In some examples, the detection module is an atomic force microscope 2. Among them, the detection module is driven by the first radio frequency signal, and the atomic force microscope 2 scans the sample through the tip so that the output second radio frequency signal carries sample surface information at each order frequency point of the tip vibration. The item to be imaged is scanned when the relative position between the tip of the atomic force microscope and the horn antenna 1 remains unchanged. When the detection module is an atomic force microscope 2, the set frequency is the vibration frequency of the probe in the atomic force microscope.

[0063] The signal transceiver module is further used to extract the near-field signal carried by the second radio frequency signal and send the near-field signal to the signal extraction module.

[0064] In some examples, the signal transceiver module further includes:

[0065] A low-noise amplifier is used to amplify the second radio frequency signal and send the amplified second radio frequency signal to the mixer. Among them, the intensity of the amplified second radio frequency signal is relatively large, which is convenient for subsequent detection.

[0066] The mixer is used to perform a frequency mixing operation on the amplified second radio frequency signal to obtain a modulation signal corresponding to the amplified second radio frequency signal and send the modulation signal to the DC blocker.

[0067] A DC blocker, which is used to filter out the DC signal in the modulation signal and send the modulation signal after filtering out the DC signal to the signal extraction module.

[0068] Among them, since the focusing operation of the first RF signal by the double-lens focusing unit is omitted, by changing the position of the horn antenna 1, the distance between the horn antenna 1 and the atomic force microscope 2 can be shortened, so that the antenna unit can directly radiate the first RF signal to the tip of the atomic force microscope 2, making the signal-to-noise ratio of the near-field signal output by the detection module relatively high and the imaging quality high. At the same time, the situation where the double-lens focusing unit and the detection module are prone to interference during the focusing adjustment process is avoided, reducing the operation difficulty.

[0069] A mechanical fine-tuning unit, which is used to adjust the antenna unit so that the first RF signal emitted by the antenna unit is directly radiated to the detection module.

[0070] In some examples, the mechanical fine-tuning unit is a three-dimensional moving platform.

[0071] Specifically, the mechanical fine-tuning unit is integrated with other devices such as the antenna unit to form a signal transceiver module. The mechanical fine-tuning unit controls the emission direction of the antenna unit by adjusting the rotation of the antenna unit in the X, Y, and Z directions, so that the first RF signal can be radiated to the detection module before divergence.

[0072] A signal extraction module, which is used to extract the amplitude information corresponding to the near-field signal and send the amplitude information corresponding to the near-field signal to the imaging module.

[0073] Specifically, the second RF signal includes a background signal, a noise signal generated when the first RF signal drives the detection module at a set distance, and a near-field signal generated when the detection module scans the item to be imaged. Among them,

[0074]

[0075] In formula (1), η is the reception coefficient, σ is the scattering coefficient, F m is the coefficient corresponding to each order of the near-field signal, ω i is the frequency of the first RF signal, Ω is the vibration frequency of the probe, m is the order of the extracted signal, θ 0 is a fixed phase difference, and α is the superposition coefficient of the signal as the near-field signal.

[0076] In some examples, the signal extraction module includes:

[0077] A lock-in amplifier, which is used to extract the amplitude information corresponding to the near-field signal in the modulation signal sent by the DC blocker and send the near-field signal to the low-pass filter.

[0078] Specifically, the detection module generates a control signal by itself and uses this control signal as an external reference signal of the lock-in amplifier to extract the near-field signal from the second radio frequency signal.

[0079] A low-pass filter is used to denoise the amplitude information corresponding to the near-field signal and send the denoised amplitude information corresponding to the near-field signal to the data processing unit.

[0080] The data processing unit is used to demodulate the amplitude information corresponding to the near-field signal.

[0081] The display unit is used to display the amplitude information corresponding to the demodulated near-field signal.

[0082] Specifically, it is possible to judge whether it is necessary to adjust the antenna unit according to the amplitude information corresponding to the near-field signal displayed by the display unit, so that the intensity of the first radio frequency signal received by the detection module is maximized at a set distance.

[0083] The imaging module is used to image the item to be imaged according to the near-field signal carried by the second radio frequency signal and the position information of each point sent by the detection module.

[0084] Specifically, a surface information image of a sample within a scanning range is obtained by controlling the movement of the tip of the atomic force microscope module, that is, by means of point-by-point scanning. The imaging module images the surface information of each point according to the amplitude information of the near-field signal generated at a set frequency and according to the coordinate information of each point. Combining the imaging results of the surface information of each point, the imaging result P(x, y) of the item to be detected at the point (x, y) is obtained. Among them,

[0085] P m (x, y) = α|F m | (2)

[0086] In formula (2), α is the superposition coefficient when the signal is a near-field signal, and ∣F m ∣ is the amplitude information of the near-field signal.

[0087] Embodiment 2

[0088] The process of imaging using the non-focusing near-field scanning imaging device provided by the embodiment of the present invention is as follows:

[0089] Step 1: Place the test sample

[0090] Place the item to be imaged on the sample stage of the atomic force microscope, adjust the laser and antenna unit of the atomic force microscope. After the adjustment is completed, place the probe on the sample and operate in the Tapping mode. Turn on the power supplies of some devices in the signal transceiver module and the signal extraction module, use the lock-in amplifier in the signal extraction module to detect the signal amplitude, and according to the detection result, finely adjust the corresponding optical path of the signal transceiver module.

[0091] Step 2: Near-field signal acquisition and image imaging

[0092] The terahertz wave generated by the signal source is divided into two paths by a power splitter. One path is used as the local oscillator signal to drive the mixer, and the other end is transmitted to the horn antenna through a directional coupler and directly radiated to the tip of the atomic force microscope. The atomic force microscope controls the movement of the tip to perform a point-by-point scan of the sample to be imaged. Among them, the directional coupler is used to achieve the transceiver isolation of electromagnetic waves at terahertz frequencies. The near-field signal generated by the tip acting on the sample to be imaged in the Tapping mode returns through the original optical path. The near-field signal is amplified by the directional coupler and the low-noise amplifier module in sequence and then mixed with the local oscillator signal. The mixed near-field signal removes the DC signal through a DC blocker and then is sent to the lock-in amplifier. The lock-in amplifier extracts the amplitude information of the near-field signal to image the surface features of each point of the item to be imaged.

[0093] Taking a silicon-gold sample as an example, the local images obtained by imaging it with the non-focusing near-field scanning imaging device provided by the embodiment of the present invention are respectively as shown in Figures 5 and Figure 6 as shown. Among them, Figure 5 is the local image obtained by scanning a local area of the silicon-gold sample at a frequency of f, Figure 6 is the local image obtained by scanning the same local area of the silicon-gold sample at a frequency of 2f.

[0094] It should be clear that the present invention is not limited to the specific configurations and processes described above and shown in the figures. For the sake of brevity, the detailed descriptions of known methods are omitted here. In the above embodiments, several specific steps are described and shown as examples. However, the method process of the present invention is not limited to the specific steps described and shown. Those skilled in the art can make various changes, modifications and additions, or change the order between steps after understanding the spirit of the present invention.

[0095] In addition, the "first", "second" and similar terms used in this disclosure do not represent any order, quantity or importance, but are only used to distinguish different parts.

[0096] The above are only specific embodiments of the present invention. Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the systems, modules, and units described above can refer to the processes in the foregoing method embodiments, and will not be elaborated herein. It should be understood that the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should all be covered within the protection scope of the present invention.

Claims

1. A non-focusing near-field scanning imaging device, comprising: A signal source, used to generate an original radio frequency signal and send the original radio frequency signal; A signal transceiver module, configured to receive the original radio frequency signal, generate a first radio frequency signal based on the original radio frequency signal, and send the first radio frequency signal based on a non-focusing mode; A detection module is used to receive the first radio frequency signal and scan the object to be imaged at a set frequency based on the first radio frequency signal, obtain a second radio frequency signal and send the second radio frequency signal to the signal transceiver module; wherein, The signal transceiver module is also used to extract the near-field signal carried by the second radio frequency signal and send the near-field signal; A signal extraction module, configured to receive the near-field signal, extract amplitude information corresponding to the near-field signal, and send the amplitude information corresponding to the near-field signal; The imaging module is used to receive the amplitude information corresponding to the near-field signal and to image the object to be imaged according to the amplitude information corresponding to the near-field signal and the position information of each point sent by the detection module.

2. The non-focusing near-field scanning imaging device according to claim 1, characterized in that: The signal transceiver module comprises: A frequency multiplier, used for converting the original radio frequency signal into a terahertz wave and transmitting the terahertz wave; a power divider, configured to receive the terahertz wave, divide the terahertz wave into a first radio frequency signal and a third radio frequency signal according to power, and send the first radio frequency signal and the third radio frequency signal respectively; a directional coupler, configured to receive the first radio frequency signal and send the first radio frequency signal; an antenna unit, configured to receive a first radio frequency signal sent by the directional coupler and send the first radio frequency signal; The antenna unit is further used to receive a second radio frequency signal sent by the detection module and send the second radio frequency signal to the directional coupler; The directional coupler is further configured to receive the second radio frequency signal and send the second radio frequency signal.

3. The non-focusing near-field scanning imaging device according to claim 1 or 2, characterized in that: The signal transceiver module also includes: a low noise amplifier, configured to receive a second radio frequency signal sent by the directional coupler, amplify the second radio frequency signal and send the amplified second radio frequency signal; A mixer, configured to receive the amplified second radio frequency signal and perform a same-frequency operation on the amplified second radio frequency signal to obtain a modulation signal corresponding to the amplified second radio frequency signal and send the modulation signal; The DC block is used to receive the modulated signal, filter out the DC signal in the modulated signal, and send the modulated signal after the DC signal is filtered out to the signal extraction module.

4. The non-focusing near-field scanning imaging device according to claim 2 or 3, characterized in that: The signal extraction module comprises: A lock-in amplifier, used for extracting amplitude information corresponding to a near-field signal in the modulated signal sent by the DC block and sending the amplitude information corresponding to the near-field signal; a low-pass filter, configured to receive the amplitude information corresponding to the near-field signal, denoise the amplitude information corresponding to the near-field signal, and send the amplitude information corresponding to the denoised near-field signal; A data processing unit, configured to receive the amplitude information corresponding to the denoised near-field signal and demodulate the amplitude information corresponding to the near-field signal; The display unit is used to display the amplitude information corresponding to the demodulated near-field signal.

5. The non-focusing near-field scanning imaging device according to claim 2, characterized in that: The signal transceiver module also includes: The mechanical fine-tuning unit is used to adjust the antenna unit so that the first radio frequency signal emitted by the antenna unit is directly radiated to the detection module.

6. The non-focusing near-field scanning imaging device according to claim 1, characterized in that: The detection module is an atomic force microscope.

7. The non-focusing near-field scanning imaging device according to claim 5, characterized in that: The mechanical fine-tuning unit is a three-dimensional mobile platform.

8. A scanning imaging system, characterized in that: A non-focused near-field scanning imaging device comprising any one of claims 1-7.

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