Near-field imaging device and method based on vector network analyzer

Abstract

The invention belongs to the technical field of near-field imaging, and particularly relates to a near-field imaging device and method based on a vector network analyzer. The vector network analyzer host is used for outputting a radio frequency local oscillator signal and a radio frequency test signal and receiving an intermediate frequency test signal; the millimeter wave terahertz spread spectrum module is used for frequency multiplication and signal separation of radio frequency test signals; frequency multiplication is carried out on the radio frequency local oscillation signal, and the frequency multiplication radio frequency local oscillation signal and a near-field signal are mixed and then output; an antenna, a quasi-light path and a near-field scanning control module; and the control machine is respectively connected with the vector network analyzer host and the near-field scanning control module. According to the millimeter wave terahertz near-field imaging device based on the vector network analyzer, generation and demodulation processing of millimeter wave terahertz test signals can be realized at the same time through the vector network analyzer host, and the size and the weight of a millimeter wave terahertz near-field imaging test system are reduced; and the integration level of the millimeter wave terahertz near-field imaging test system is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of near-field imaging, and particularly relates to a near-field imaging device and method based on a vector network analyzer. BACKGROUND

[0002] Millimeter wave terahertz waves have important applications in the field of imaging detection, etc. However, due to the constraint of Rayleigh diffraction limit, the imaging resolution of the existing millimeter wave terahertz far-field imaging technology is about the wavelength level at most, and high-precision detection of new materials cannot be achieved. Therefore, researchers have developed electronic millimeter wave terahertz near-field imaging technology.

[0003] The electronic millimeter wave terahertz near-field imaging technology uses a nanometer needle tip to realize tight focusing of a near-field signal, and can break through the constraint of Rayleigh diffraction limit, and has important applications in high-resolution testing of new materials. At present, the electronic millimeter wave terahertz near-field imaging device uses two microwave signal sources and a millimeter wave terahertz spread spectrum module to generate a terahertz test signal, uses a nanometer probe to realize super-resolution detection of a sample, and uses a lock-in amplifier to realize reception of the terahertz near-field signal. This scheme can effectively realize millimeter wave terahertz near-field super-resolution imaging, but the test signal needs two separate microwave signal sources and a single millimeter wave terahertz spread spectrum module, and the signal reception needs a dedicated lock-in amplifier receiving device, resulting in a large overall system volume and weight, low integration degree, and difficulty in meeting the use requirements of volume and integration degree in specific occasions, so it is urgent to develop a miniaturized and high-integration millimeter wave terahertz near-field imaging detection technology. SUMMARY

[0004] To solve the problems in the prior art, one of the purposes of the present application is to provide a near-field imaging device based on a vector network analyzer, and the second purpose is to provide a near-field imaging method based on a vector network analyzer.

[0005] The technical solution adopted by the present application to solve its technical problems is as follows: a near-field imaging device based on a vector network analyzer, comprising: a vector network analyzer host, configured to output a radio frequency local oscillator signal and a radio frequency test signal, and receive an intermediate frequency test signal; a millimeter wave terahertz spread spectrum module, configured to frequency multiply and separate the radio frequency test signal, frequency multiply the radio frequency local oscillator signal, and output the frequency multiplied radio frequency local oscillator signal after being mixed with a near-field signal; an antenna, configured to radiate a terahertz signal to a quasi-optical light path and receive a near-field signal; the quasi-optical light path, configured to collimate and transmit the terahertz signal, focus the collimated and transmitted terahertz signal to a probe needle tip position in a near-field scanning control module, and reversely collect and converge a modulated signal to a terahertz horn antenna position; the near-field scanning control module, configured to drive a near-field probe to make a vertical direction frequency of The simple harmonic vibration of the probe is detected and the vibration signal of the probe is used as the control signal; The control machine is connected to the vector network analyzer host and the near-field scanning control module respectively. It controls the near-field scanning control module to perform line-by-line scanning, and at the same time controls the vector network analyzer host through the program control mode to return the millimeter-wave terahertz near-field test data of the vector network analyzer; the control machine plots the obtained vector network analyzer millimeter-wave terahertz test signal line by line to obtain the near-field imaging image result of the sample to be tested.

[0006] Preferably, the vector network analyzer host has a built-in frequency synthesis local oscillator source for generating a radio frequency local oscillator signal, a frequency synthesis RF source for generating a radio frequency test signal, and an intermediate frequency receiver for receiving an intermediate frequency test signal; the output end of the frequency synthesis local oscillator source is connected to the input interface of the signal separation unit A, and the output end of the frequency synthesis RF source is connected to the input interface of the signal separation unit B.

[0007] Preferably, the millimeter wave terahertz spectrum expansion module has a built-in frequency multiplication unit B for receiving RF local oscillator signals, a frequency multiplication unit A for receiving RF test signals, a signal separation unit C and a mixer. The output end of the frequency multiplication unit B whose input interface is connected to the output end of the signal separation unit A is connected to the local oscillator input interface of the mixer, the output end of the frequency multiplication unit A whose input interface is connected to the output end of the signal separation unit B is connected to the input interface of the signal separation unit C, and the signal separation unit C is provided with a first output end and a second output end, the first output end inputs a signal to the antenna, and the second output end inputs a signal to the RF input interface of the mixer.

[0008] Preferably, the antenna is a terahertz horn antenna.

[0009] A near-field imaging method based on a vector network analyzer, the steps are as follows: S1. After frequency doubling and signal separation, the RF test signal is radiated to the quasi-optical path through the terahertz horn antenna. The quasi-optical path collimates and transmits the terahertz signal and focuses it to the probe tip position in the near-field scanning control module. S2, the near-field probe makes a vertical frequency of The near-field probe modulates the incident millimeter-wave terahertz wave and scatters the modulated signal into free space. S3, the modulated signal is collected through the original quasi-light path and converged to the position of the terahertz horn antenna, and the terahertz horn antenna receives the near-field signal; S4, after signal separation and frequency multiplication, the RF local oscillator signal is mixed with the near-field signal to obtain a frequency of The intermediate frequency test signal, is the frequency of the intermediate frequency carrier signal; S5, intermediate frequency test signal is used for near-field imaging.

[0010] Preferably, in step S2, the signal source in the near-field scanning control module provides a driving signal for the scanner A, and the scanner A drives the near-field probe to make a simple harmonic vibration in the vertical direction with a frequency of .

[0011] Preferably, the method further comprises: real-time precision control of the distance between the probe and the sample, a laser source in the near-field scanning control module irradiates the end of the probe cantilever, the reflected light is detected by a detector, the detector converts the light signal into an electric signal, and then outputs the electric signal to a phase-locked loop unit PLL for frequency locking, and then outputs to a PID control unit, the PID control unit detects the signal, compares it with a set value, and outputs an error signal to the scanner B.

[0012] Preferably, in step S1, the radio frequency test signal is multiplied to the terahertz wave band; and in step S4, the radio frequency local oscillator signal is multiplied to the terahertz wave band.

[0013] Preferably, in step S5, the intermediate frequency test signal is input to the test intermediate frequency input interface of the vector network analyzer host, the vector network analyzer test mode is set to the receiver measurement mode, the frequency offset measurement function of the vector network analyzer is adopted, and the frequency offset is set to , so that the intermediate frequency receiver of the vector network analyzer host can demodulate and process the near-field signal at the frequency of ; the control machine controls the near-field scanning control module to make line-by-line scanning, and controls the vector network analyzer host to return the millimeter wave terahertz near-field test data of the vector network analyzer through the program control mode; and the control machine draws the obtained millimeter wave terahertz test signal of the vector network analyzer line by line, and obtains the near-field imaging image result of the sample to be tested.

[0014] Compared with the prior art, the present application has the following beneficial effects: 1. The millimeter wave terahertz near-field imaging device based on the vector network analyzer can generate and demodulate the millimeter wave terahertz test signal through the vector network analyzer host, so as to reduce the volume and weight of the millimeter wave terahertz near-field imaging test system and improve the integration of the millimeter wave terahertz near-field imaging test system.

[0015] 2. The receiver mode and the frequency offset measurement function of the vector network analyzer are adopted to directly realize the demodulation and reception of the millimeter wave terahertz near-field signal, so as to realize the near-field super-resolution imaging. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is a schematic diagram of the near-field imaging device based on the vector network analyzer.

[0017] Figure 2 It is a result diagram of the silicon gold sample terahertz near-field imaging in the application of the near-field imaging device. DETAILED DESCRIPTION

[0018] In order to facilitate the understanding of the present application, the present application will be described in more detail below in conjunction with the accompanying drawings and specific embodiments. However, the present application can be implemented in many different forms and is not limited to the embodiments described in the present specification. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosed content of the present application more thorough and comprehensive.

[0019] A near-field imaging device based on a vector network analyzer, in particular a scattering type millimeter wave terahertz near-field imaging device based on a vector network analyzer, combines Figure 1 understanding, the basic components include: a vector network analyzer host, a millimeter wave terahertz spread spectrum module, an antenna, a quasi-optical light path, a near-field scanning control module, a control machine, etc. Among them: The vector network analyzer host has a frequency synthesis local oscillator source for generating a radio frequency local oscillator signal, a frequency synthesis radio frequency source for generating a radio frequency test signal, and an intermediate frequency receiver for receiving an intermediate frequency test signal; the output end of the frequency synthesis local oscillator source is connected to the input interface of the signal separation unit A, and the output end of the frequency synthesis radio frequency source is connected to the input interface of the signal separation unit B.

[0020] The millimeter wave terahertz spread spectrum module has a frequency multiplication unit B for receiving a radio frequency local oscillator signal, a frequency multiplication unit A for receiving a radio frequency test signal, a signal separation unit C, and a frequency mixer. The output end of the frequency multiplication unit B connected to the input interface of the signal separation unit A is connected to the local oscillator input interface of the frequency mixer, the output end of the frequency multiplication unit A connected to the output end of the signal separation unit B is connected to the input interface of the signal separation unit C, and the signal separation unit C is provided with a first output end and a second output end. The first output end inputs a signal to the antenna, and the second output end inputs a signal to the radio frequency input interface of the frequency mixer.

[0021] The antenna adopts a terahertz horn antenna, and radiates the terahertz signal output by the signal separation unit C to the quasi-optical light path.

[0022] The quasi-optical light path collimates and transmits the terahertz signal and then focuses it to the position of the probe needle tip in the near-field scanning control module.

[0023] The near-field scanning control module has a sample placed above the scanner B, a near-field probe located above the sample, a scanner A, a signal source, a laser source, and a detector placed above the near-field probe, and the detector is connected to the PLL and the PID. The signal source provides a driving signal to the scanner A, the scanner A drives the near-field probe to make a vertical frequency of The near-field scanning control module detects the vibration signal of the probe as a control signal; the laser source irradiates to the end of the probe cantilever, and the reflected light signal is detected by the detector, which converts the light signal into an electrical signal and then outputs to the phase-locked loop unit PLL for frequency locking, and then outputs to the PID control unit. The PID control unit detects the signal and compares it with the set value, and outputs the error signal to the scanner B, so as to realize real-time and precise control of the distance between the probe and the sample.

[0024] The control machine controls the near-field scanning control module to perform line-by-line scanning, and controls the vector network analyzer host computer to return the millimeter wave terahertz near-field test data of the vector network analyzer through a programmed mode; the control machine draws the obtained millimeter wave terahertz test signal of the vector network analyzer line by line, and obtains the near-field imaging image result of the sample to be tested.

[0025] The working principle of the technical scheme is as follows: the frequency synthesis local oscillator signal of the vector network analyzer host computer outputs a radio frequency local oscillator signal, which is output to the input interface of the frequency multiplication unit B of the millimeter wave terahertz spread spectrum module after passing through the signal separation unit A, and the frequency multiplication unit B outputs the local oscillator signal to the local oscillator interface of the mixer as a local oscillator signal after frequency multiplication to the terahertz wave band; the frequency synthesis radio frequency source of the vector network analyzer host computer outputs a radio frequency test signal, which is output to the input interface of the frequency multiplication unit A of the millimeter wave terahertz spread spectrum module after passing through the signal separation unit B, and the frequency multiplication unit A inputs the radio frequency signal to the signal separation unit C after frequency multiplication to the terahertz wave band, and the terahertz horn antenna radiates the terahertz signal to the quasi-optical light path; the quasi-optical light path collimates and transmits the terahertz signal and focuses it to the position of the probe tip in the near-field scanning control module.

[0026] The signal source in the near-field scanning control module provides a driving signal to the scanner A, and the scanner A drives the near-field probe to perform simple harmonic vibration in the vertical direction with a frequency of The near-field scanning control module detects the vibration signal of the probe as a control signal, specifically, the laser source in the near-field scanning control module irradiates to the end of the probe cantilever, and the reflected light signal is detected by the detector, which converts the light signal into an electrical signal and then outputs to the phase-locked loop unit PLL for frequency locking, and then outputs to the PID control unit. The PID control unit detects the signal and compares it with the set value, and outputs the error signal to the scanner B, so as to realize real-time and precise control of the distance between the probe and the sample.

[0027] The near-field probe performs simple harmonic vibration in the vertical direction with a frequency of The simple harmonic vibration of the probe can realize modulation of the incident millimeter wave terahertz wave, and the probe scatters the modulation signal to free space, which is collected through the original quasi-optical path and converged at the position of the terahertz horn antenna. The horn antenna receives the near-field signal, which is transmitted to the radio frequency input interface of the mixer through the signal separation unit C. The mixer mixes the near-field signal with the local oscillator signal to obtain an intermediate frequency test signal with a frequency of , wherein is the frequency of the intermediate frequency carrier signal generated by the millimeter wave terahertz spread spectrum module. The intermediate frequency test signal is input to the test intermediate frequency input interface of the vector network analyzer host. By setting the vector network analyzer test mode to the receiver measurement mode and using the frequency offset measurement function of the vector network analyzer, the frequency offset is set to , so that the intermediate frequency receiver of the vector network analyzer host can demodulate the near-field signal at the frequency of .

[0028] The control machine controls the near-field scanning control module to perform line-by-line scanning, and simultaneously controls the vector network analyzer host to return the millimeter wave terahertz near-field test data of the vector network analyzer through the program control mode. The control machine draws the obtained millimeter wave terahertz test signal of the vector network analyzer line by line, and can obtain the near-field imaging image result of the sample to be tested. Figure 2 The silicon gold sample terahertz near-field imaging test result based on the vector network analyzer is given. Figure 2 Fig. 2 is an imaging effect diagram of a silicon gold sample interface using the device of the present application, and the imaging range is 80um*80um. The left side of the image 2 is the imaging result of the silicon part in the silicon gold interface, and the right side is the imaging result of the gold part in the silicon gold interface. It can be seen that the present application can realize high-resolution imaging of the silicon gold material interface, that is, the scattering type millimeter wave terahertz near-field imaging device based on the vector network analyzer in the present application can realize near-field scattering signal super-resolution microscopic imaging.

[0029] The millimeter wave terahertz near-field imaging method based on the vector network analyzer provided by the present application directly realizes demodulation and reception of the millimeter wave terahertz near-field signal by using the receiver mode (the intermediate frequency frequency is ) and the frequency offset measurement function (the frequency offset is the probe modulation frequency ) of the vector network analyzer, so as to realize near-field super-resolution imaging. The millimeter wave terahertz near-field imaging device based on the vector network analyzer can simultaneously realize generation and demodulation processing of the millimeter wave terahertz test signal through the vector network analyzer host, reduce the volume and weight of the millimeter wave terahertz near-field imaging test system, and improve the integration of the millimeter wave terahertz near-field imaging test system.

[0030] Any technical features in the above-described embodiments can be combined in any manner, and, for the sake of brevity, the foregoing description has not described all possible combinations of the technical features. However, it is contemplated that the scope of the disclosure encompasses all possible combinations of the technical features.

Claims

1. A near-field imaging device based on a vector network analyzer, characterized in that: include: Vector network analyzer host, used for outputting RF local oscillator signals and RF test signals and receiving IF test signals; Millimeter-wave terahertz spectrum expansion module for frequency multiplication and signal separation of RF test signals; frequency-multiplying the RF local oscillator signal and mixing the frequency-multiplied RF local oscillator signal with the near-field signal and outputting the mixed signal; Antenna, which radiates the terahertz signal into the quasi-optical path and receives the near-field signal; The quasi-optical path collimates and transmits the terahertz signal and focuses it to the probe tip position in the near-field scanning control module and reversely collects and converges the modulated signal to the terahertz horn antenna position; The near-field scanning control module drives the near-field probe to do vertical scanning at a frequency of The simple harmonic vibration of the probe is detected and the vibration signal of the probe is used as the control signal; The control machine is connected to the vector network analyzer host and the near-field scanning control module respectively. It controls the near-field scanning control module to perform line-by-line scanning, and at the same time controls the vector network analyzer host through the program control mode to return the millimeter-wave terahertz near-field test data of the vector network analyzer; the control machine plots the obtained vector network analyzer millimeter-wave terahertz test signal line by line to obtain the near-field imaging image result of the sample to be tested.

2. The near-field imaging device based on a vector network analyzer according to claim 1, characterized in that: The vector network analyzer host has a built-in frequency synthesis local oscillator source for generating a radio frequency local oscillator signal, a frequency synthesis RF source for generating a radio frequency test signal, and an intermediate frequency receiver for receiving an intermediate frequency test signal; the output end of the frequency synthesis local oscillator source is connected to the input interface of the signal separation unit A, and the output end of the frequency synthesis RF source is connected to the input interface of the signal separation unit B.

3. The near-field imaging device based on a vector network analyzer according to claim 1, characterized in that: A millimeter-wave terahertz spectrum expansion module has a built-in frequency multiplication unit B for receiving a radio frequency local oscillator signal, a frequency multiplication unit A for receiving a radio frequency test signal, a signal separation unit C, and a mixer. The output end of the frequency multiplication unit B, whose input interface is connected to the output end of the signal separation unit A, is connected to the local oscillator input interface of the mixer. The output end of the frequency multiplication unit A, whose input interface is connected to the output end of the signal separation unit B, is connected to the input interface of the signal separation unit C. The signal separation unit C is provided with a first output end and a second output end. The first output end inputs a signal to the antenna, and the second output end inputs a signal to the radio frequency input interface of the mixer.

4. The near-field imaging device based on a vector network analyzer according to claim 1, characterized in that: The antenna adopts a terahertz horn antenna.

5. A near-field imaging method based on a vector network analyzer, characterized in that: Here are the steps: S1, after the RF test signal is processed by frequency doubling and signal separation, it is radiated to the quasi-optical path through the terahertz horn antenna. The quasi-optical path collimates and transmits the terahertz signal and focuses it to the probe tip position in the near-field scanning control module. S2, the near-field probe makes a vertical frequency of The near-field probe modulates the incident millimeter-wave terahertz wave and scatters the modulated signal into free space. S3, the modulated signal is collected through the original quasi-light path and converged to the position of the terahertz horn antenna, and the terahertz horn antenna receives the near-field signal; S4, after signal separation and frequency multiplication, the RF local oscillator signal is mixed with the near-field signal to obtain a frequency of The intermediate frequency test signal, is the frequency of the intermediate frequency carrier signal; S5, intermediate frequency test signal is used for near-field imaging.

6. The near-field imaging method based on a vector network analyzer according to claim 5, characterized in that: Step S2: The signal source in the near-field scanning control module provides a driving signal to the scanner A, and the scanner A drives the near-field probe to perform vertical scanning at a frequency of Simple harmonic oscillation.

7. The near-field imaging method based on a vector network analyzer according to claim 6, characterized in that: Also includes: Real-time precision control of the distance between the probe and the sample. The laser source in the near-field scanning control module irradiates the end of the probe cantilever, which is detected by the detector after reflection. The detector converts the optical signal into an electrical signal and outputs it to the phase-locked loop unit PLL for frequency locking. The signal is then output to the PID control unit. The PID control unit detects the signal, compares it with the set value, and outputs the error signal to scanner B.

8. The near-field imaging method based on a vector network analyzer according to claim 5, characterized in that: In step S1, the radio frequency test signal is frequency-multiplied to the terahertz band; in step S4, the radio frequency local oscillator signal is frequency-multiplied to the terahertz band.

9. The near-field imaging method based on a vector network analyzer according to claim 5, characterized in that: Step S5: Input the intermediate frequency test signal to the test intermediate frequency input interface of the vector network analyzer host, set the vector network analyzer test mode to the receiver measurement mode, and use the frequency deviation measurement function of the vector network to set the frequency offset to , thus ensuring that the intermediate frequency receiver of the vector network analyzer host can be Demodulate the near-field signal at the frequency; The control machine controls the near-field scanning control module to perform line-by-line scanning, and at the same time controls the vector network analyzer host through the program control mode to return the millimeter-wave terahertz near-field test data of the vector network analyzer; the control machine plots the obtained vector network analyzer millimeter-wave terahertz test signal line by line to obtain the near-field imaging image result of the sample to be tested.

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