CN114894095B - Cantilever beam displacement measuring device and measuring method - Google Patents

Abstract

The invention provides a cantilever beam displacement measuring device and a measuring method. The cantilever beam displacement measuring device of the present invention includes a cantilever beam, a laser, an optical interference system, a photodetector, and a first controller, which generates a temperature for controlling the laser according to the difference between the detected temperature value of the laser and the target temperature control signal to control the temperature of the laser to the target temperature; and a second controller, which generates the displacement signal of the cantilever beam according to the difference between the interference light intensity voltage signal output by the photodetector and the specified reference voltage value, and The displacement signal is output to the first controller as a target temperature-related signal, and the first controller controls the temperature of the laser to change the wavelength of the output laser, thereby performing feedback control on the light intensity voltage signal. By adopting the device and method of the invention, the sensitivity and dynamic range of the static displacement measurement of the cantilever beam can be improved.

Description

Cantilever beam displacement measuring device and measuring method

technical field

The invention belongs to the research field of sensitive force detection, and in particular relates to a cantilever beam displacement measuring device and a measuring method based on a laser interference ranging method.

Background technique

Cantilever beam displacement measurement is one of the important methods for sensitive force detection, such as magnetic torque measurement of nanoscale magnetic samples, Casimir effect, magnetic resonance force test, etc. A cantilever beam with a fixed end and a free end can be used to measure torque acting on a magnetic sample. Torque causes the cantilever to bend, and to measure the cantilever bend is to measure the displacement of the free end of the cantilever. Since the displacement of the cantilever beam corresponds to the torque received by the cantilever beam, the meanings of cantilever beam displacement measurement and cantilever beam torque measurement in this specification are roughly the same, and the two expressions are mixed.

The displacement measurement of the cantilever beam is mainly divided into two types: electrical method and optical method.

There are three main methods to measure the displacement of the cantilever beam electrically: capacitive coupling, piezoresistive effect, and piezoelectric effect. The bending of the cantilever beam causes changes in the capacitance, piezoresistance and piezoelectric voltage on the cantilever beam and the substrate. The reading of the voltage is used to determine the magnitude of the torque on the cantilever beam. When the capacitive coupling effect is used to measure the displacement of the cantilever beam, the cantilever beam and the substrate form a parallel plate capacitance. After the cantilever beam is displaced, the capacitance value of the parallel plate changes, and the change of capacitance corresponds to the displacement of the cantilever beam. In the mechanical linear region of the cantilever beam Inside, judge the torque on the cantilever beam by reading the capacitance. When the piezoresistive effect is used to measure the displacement of the cantilever beam, the piezoresistive material is used near the root of the cantilever beam, that is, the position where the cantilever beam has the largest bending range. When the cantilever beam is bent by torque, the piezoresistive material is subjected to pressure to cause its resistance to change. . Cantilever structures that use the piezoelectric effect to measure cantilever displacement are similar to the piezoresistive effect.

Optical methods usually use the reflection of the laser on the surface of the cantilever beam and the reflected light from the exit end of the fiber to form an interference signal. The measurement system shown in FIG. 1 includes a laser 101 , a fiber coupler 103 , an optical fiber 104 , a lens 105 , a cantilever beam 106 and a photodetector 102 . The laser light from the laser 101 is focused on the reflective surface of the cantilever beam 106 through the fiber coupler 103, the optical fiber 104 and the lens 105, and the light reflected on the reflective surface returns to the optical fiber 104 and optically interferes with the reflected light at the exit end face of the optical fiber Interfering optical signals are formed. The interference light signal is transmitted to the photodetector 102 through the fiber coupler 103 and converted into a voltage signal.

Optical methods of cantilever beam force detection are more sensitive than electrical methods. This is because the cantilevers used in the electrical method need to integrate the functions of capacitive coupling, piezoresistive effect and piezoelectric effect, which makes it impossible for these cantilever beams to have a very low elastic coefficient. The cantilever beam used in laser interferometry does not have this limitation. It can use pure silicon cantilever beam, and the elastic coefficient can reach the order of 1mN/m.

Contents of the invention

The technical problem to be solved in the present invention

In the optical method of cantilever beam force detection, an interference cavity is formed between the cantilever beam and the light emitting end face of the fiber. The displacement of the cantilever beam causes the change of the length of the interference cavity, which will cause the change of the interference light intensity. Fig. 2 is a graph showing changes in the intensity of interference signals when the length of the interference cavity is changed. As shown in Figure 2, when the length of the interference cavity is changed (the distance between the cantilever beam and the exit end face of the fiber) during laser interferometry, the interference signal changes periodically, and the interference signal is sinusoidal. It can be clearly seen from Figure 2 that the relationship between the displacement of the cantilever beam and the strength of the interference signal is not linear. If the displacement of the cantilever beam is measured in this way, the dynamic range of the measurement signal will be extremely small. Therefore, when laser interferometry and cantilever beams are used for weak force detection, the change of the resonant frequency of the cantilever beam is usually measured to characterize the strength of the force. This is the dynamic mode of force detection. Because when measuring the resonant frequency of the cantilever beam, it is only necessary to keep the vibration amplitude of the cantilever beam in a very small range, and will not exceed the dynamic range of the interference signal, as shown in the thickened part on the sinusoidal line in Figure 2.

However, there are limitations in the dynamic measurement method, which will be described below with dynamic magnetic torque measurement. First of all, the dynamic measurement method measures the resonant frequency of the cantilever beam. The change of the resonant frequency reflects the magnitude of the torque on the cantilever beam. However, the change of the resonant frequency cannot directly reflect the magnitude of the torque. The change of resonance frequency is jointly determined by the magnetization M of the sample and the magnetic anisotropy coefficient H, which makes it extremely difficult to deduce useful parameters such as the magnetization of the sample from the change of resonance frequency when applying the dynamic measurement method. In comparison, the method of directly measuring the displacement of the cantilever caused by the torque of the magnetic sample in the magnetic field is also called static measurement of the cantilever, and the relationship between the displacement and the magnetization is much simpler.

In addition, the sensitivity of the dynamic measurement method to measure torque depends on the elastic coefficient k and quality factor Q of the cantilever beam. In the dynamic magnetic torque measurement, the Q value of the cantilever beam will be affected by the difference of the magnetization state of the sample. For example, in the dynamic magnetic torque test of MnSi nanosheets, there is obvious magnetization loss after the magnetic field is greater than 0.4T. In this magnetic field range, the Q value of the cantilever beam decreases, and the signal-to-noise ratio of the measured resonance frequency decreases, which corresponds to increase in noise.

Although the current ubiquitous electrical ranging cantilever can also achieve static torque measurement, its sensitivity cannot be compared with that of optical interferometry.

The present invention is made in response to the above problems, and its purpose is to provide a cantilever beam displacement measurement device and method suitable for laser interferometry, which can realize static measurement of cantilever beam displacement with improved sensitivity and dynamic range.

Technical solutions to technical problems

In order to solve the above technical problems, the present invention provides a cantilever beam displacement measuring device, which is characterized in that it includes: a cantilever beam, which can carry the object to be measured, including a fixed end and a free end, and the free end has a light reflecting surface the laser, which can change the wavelength of the output laser by controlling its temperature; the optical interference system, the laser output by the laser can be irradiated to the light reflecting surface of the cantilever beam through the optical interference system, in the The light reflected by the light-reflecting surface can return to the optical interference system and interfere with light to generate interference light; a photodetector can detect the interference light and convert the light intensity of the interference light into a light intensity voltage signal a first controller, which generates a control signal for controlling the temperature of the laser according to the difference between the detected temperature value of the laser and the target temperature, to control the temperature of the laser to the target temperature; and the second control A device, which generates a displacement signal of the cantilever beam according to the difference between the light intensity voltage signal output by the photodetector and a specified reference voltage value, and outputs the displacement signal to the first controller as a target temperature-related signal , performing feedback control on the light intensity voltage signal by causing the first controller to control the temperature of the laser to change the wavelength of the output laser light.

Preferably, the predetermined reference voltage value is a voltage value of the light intensity voltage signal at which a change rate of the light intensity voltage signal with respect to a change in the wavelength or a displacement of the cantilever beam becomes a maximum value.

Preferably, the specified reference voltage value is obtained by obtaining the maximum value and the minimum value of the light intensity voltage signal, and calculating the average value of the maximum value and the minimum value.

Preferably, the first controller is a first PID controller, the detected temperature value of the laser and the target temperature-related signal are its input signals, and the control signal for controlling the temperature of the laser is its output signal, so The second controller is a second PID controller, the light intensity voltage signal output by the photodetector and the specified reference voltage are its input signals, the displacement signal of the cantilever beam is its output signal, and the output signal is used as A target temperature related signal is output to the first PID controller.

Preferably, the optical interference system includes a fiber coupler and an optical fiber, the laser output by the laser enters the optical fiber through the optical fiber coupler, and the laser light emitted from the light output end of the optical fiber irradiates the cantilever beam. The light reflecting surface, the light reflected on the light reflecting surface returns to the optical fiber through the light exit end of the optical fiber, and optically interferes with the light reflected at the light exit end of the optical fiber, and the photodetector coupled with the optical fiber coupler to receive the interference light.

Preferably, the laser is a wavelength-tunable semiconductor laser.

Preferably said cantilevers are made of pure silicon.

Preferably, the measured object is a magnetic sample, and the external force is applied by an external magnetic field.

In addition, the present invention provides a method for measuring the displacement of a cantilever beam, using the above-mentioned cantilever beam displacement measuring device to measure the displacement of the cantilever beam, which is characterized in that it includes: the step of placing the measured object on the cantilever beam; The temperature of the laser changes the wavelength of the laser, irradiating the laser on the cantilever beam to cause light interference to obtain the light intensity voltage signal of the interference light, and determining the reference voltage value of the light intensity voltage signal based on the light intensity voltage signal the step of locking the light intensity voltage signal at the reference voltage value by using the first controller and the second controller to perform feedback control; applying an external force to the measured object to cause displacement , the step of measuring the displacement based on the displacement signal output by the second controller.

Beneficial effect

1. The present invention locks the working point and compensates in real time on the laser interference light intensity (ranging) signal by changing the wavelength of the laser, so that the original nonlinear measurement relationship becomes linear, thereby improving the sensitivity, and making the improved measurement system become Suitable for static displacement measurements.

2. Because the displacement can be compensated by changing the wavelength of the laser, the interference light intensity signal can be pulled back to the locked working point, so the dynamic range of the measurement is greatly improved.

3. As far as the cantilever beam is concerned, since the static displacement measurement sensitivity of the cantilever beam depends on the elastic coefficient of the cantilever beam and has nothing to do with the quality factor of the cantilever beam, the static displacement measurement is more tolerant to the quality of the cantilever beam. The cantilever beam made of pure silicon can achieve a lower elastic coefficient and further improve the sensitivity.

Description of drawings

Figure 1 is a schematic diagram of a fiber optic interferometry system for measuring the displacement of a cantilever beam.

Fig. 2 is a graph showing changes in the intensity of interference signals when the length of the interference cavity is changed.

Fig. 3 is a schematic diagram showing a feedback control structure for operating point locking and temperature compensation according to an embodiment of the present invention.

FIG. 4 is a circuit diagram showing an example of an internal circuit configuration of a PID controller.

FIG. 5A is an SEM photograph showing a MnSi microsheet, and FIG. 5B is an SEM photograph showing a state in which an MnSi microsheet is mounted on a cantilever beam.

FIG. 6A is the test result of the dynamic measurement method for measuring the change of resonance frequency, and FIG. 6B is the test result of the static displacement of the cantilever beam measured by the static measurement method using temperature compensation.

Detailed ways

The specific implementation manners of the present invention will be described below in conjunction with the accompanying drawings.

In the following embodiments, when referring to numbers and the like (including numbers, values, amounts, ranges, etc.) of elements, except for the cases where it is particularly clearly stated and the case where it is clearly limited to a specific number in principle, it does not mean Limited to the specific number, may be above or below the specific number.

In addition, in the following embodiments, the structural elements (including step elements, etc.) are not necessarily essential except for the case where it is particularly clearly stated and the case where it is clearly understood as essential in principle, and the description may also be included. Elements not expressly mentioned in , need not be stated.

The invention is a cantilever beam displacement measuring device and method based on a laser interference ranging system. Specifically, one embodiment of the present invention adopts the optical fiber interferometry system for measuring the displacement of a cantilever shown in FIG. Detector 102. The laser light from the laser 101 is focused on the reflective surface of the cantilever beam 106 through the fiber coupler 103, the optical fiber 104 and the lens 105, and the light reflected on the reflective surface returns to the optical fiber 104 and optically interferes with the reflected light at the exit end face of the optical fiber Interfering optical signals are formed. The interference light signal is transmitted to the photodetector 102 through the fiber coupler 103 and converted into a voltage signal.

However, the optical interference system for measuring the displacement of a cantilever beam of the present invention is not limited to the use of an optical fiber interference system having a fiber coupler and an optical fiber. According to the following description, it can be seen that the technical means adopted in the present invention is to lock the working point and compensate the interference light intensity signal, so as long as it is an optical interference system (such as a polarizing beam splitter) that can generate optical interference with the reflected light from the cantilever , a half-mirror and a quarter-wave plate), the adoption of the technical solution of the present invention can realize the static measurement of the cantilever beam displacement with improved sensitivity and dynamic range.

The object of the present invention is to provide a cantilever beam displacement measurement device and method suitable for laser interferometry, which can realize static measurement of cantilever beam displacement with improved sensitivity and dynamic range. The measuring device and method disclosed in the present invention mainly solve technical problems by locking the working point and compensating, so that the original nonlinear measurement relationship becomes linear, thereby improving the sensitivity and dynamic range of the measurement signal.

Fig. 2 is a graph showing the change in the intensity of the interference signal when the laser wavelength or the length of the interference cavity is changed. As shown in Figure 2, when the length of the interference cavity is changed (the distance between the cantilever beam and the exit end face of the fiber) during laser interferometry, the interference signal changes periodically, and the interference signal is sinusoidal. On the sinusoidal interference signal, the slope of the maximum point is a and b, that is to say, the cantilever beam has the same displacement, and the voltage change corresponding to a or b is the largest, that is, the displacement measurement at a and b is the most sensitive. In order to always get the best sensitivity, the best state is to always work on point a or b on the interference signal, but when the cantilever beam is displaced, the interference signal must deviate from point a or b.

The inventor noticed that not only the displacement of the cantilever beam can cause the interference signal, but also the change of the laser wavelength can cause the interference signal, then the wavelength change of the laser can be used to compensate the displacement change of the cantilever beam, so that the interference signal can always be maintained in a or b. For example, the initial interference signal is at point a, and the voltage is V. The sample on the cantilever beam is subjected to torque to displace the cantilever beam by 10nm, shortening the interference cavity, and the corresponding interference signal deviates from point a and moves to the right, reaching V+ΔV; In order to keep the interference signal at V, the wavelength of the laser can be changed. The increase of the wavelength corresponds to the rightward movement of the interference curve in Figure 2. Changing the wavelength Δλ of an appropriate size makes the interference signal change -ΔV, and the interference caused by the displacement of the cantilever beam can be reduced The signal change ΔV is compensated, so that the interference signal is always locked at point a. It can be seen that the change of wavelength Δλ is proportional to the displacement of the cantilever beam, so the working point of the interference signal is locked at a by adjusting the laser wavelength, and the change of the laser wavelength is the displacement change of the cantilever beam. Because point a has the largest slope, it is the most sensitive to measure displacement. In addition, because the displacement can be compensated by changing the wavelength of the laser, the interference signal can be pulled back to point a or point b, so the dynamic range of the measurement is much higher than the linear region of the interference signal.

Fig. 3 is a schematic diagram showing a feedback control structure for operating point locking and temperature compensation according to an embodiment of the present invention. The feedback control structure shown in FIG. 3 will be described in detail in the embodiment part, and its working principle is mainly explained here. The wavelength of the laser can be achieved by controlling the temperature of the laser. In order to accurately control the temperature of the laser, it is necessary to control the temperature of the laser. In this embodiment, temperature control is performed using PID control. The above-mentioned operating point with the largest slope on the locking interference signal also requires feedback control. In this embodiment, the feedback control is also performed using the PID method. Therefore, the measurement system in this embodiment includes two PID control units, namely PID1 and PID2 shown in FIG. 3 . PID1 is used to precisely control the temperature of the laser, and PID2 is used to lock the working point on the maximum slope point on the interference curve.

The PID controller is a feedback loop component that compares the collected data with a reference value, and then uses this difference to calculate a new input value. The purpose of this new input value is to make the data of the system reach or maintain at Reference. Different from other simple control operations, the PID controller can adjust the input value according to the historical data and the occurrence rate of the difference, which can make the system more accurate and stable.

In the signal compensation method, the function of locking the operating point at the maximum slope is preferably realized using PID control technology. PID is currently the most widely used regulator, and the control law is proportional (Proportional), integral (Integral), and differential (Derivative) control , referred to as PID control, it is actually an algorithm.

However, the temperature control of the laser and the feedback control for locking the operating point of the interference signal are not limited to PID control, and can also be implemented in other ways. For example, the first controller and the second controller can be configured by a computer program, and they respectively realize the functions of PID1 and PID2 shown in FIG. 3 .

It is preferred to use a laser which itself contains temperature control components, such as a wavelength tunable semiconductor laser. The TEC± of the semiconductor laser is the pin of the temperature control component, which is used to control the temperature of the semiconductor laser, and the Thermistor is the pin of the temperature sensor, which is used to measure the temperature of the semiconductor laser. The difference between the measured temperature and the target temperature is used as the input of PID1, and the output of PID1 is used to stimulate the TEC to control the temperature.

PID2 is used to lock the position of the working point of the interference signal, and select the light intensity voltage signal whose change rate of the light intensity voltage signal relative to the wavelength or the displacement of the cantilever beam becomes the maximum value. Specifically, point a or point b of the sinusoidal interference signal is selected as the working point, as shown in Figure 2, the slope of point a is negative, the PID feedback is negative, the slope of point b is positive, and the PID feedback is positive. If point a is selected as the working point, the temperature of the laser is adjusted to the laser temperature corresponding to point a. At this time, the output voltage of the photoelectric converter corresponding to point a is V, and the PID control unit is used to control the temperature of the laser with feedback, so that the photoelectric converter The voltage of V is locked at V, so that the fixed operating point is at the maximum slope on the interference curve. The difference between operating point a and b is that the slope is different, one uses positive feedback, and the other uses negative feedback.

Preferably, the locked operating point voltage signal is obtained by obtaining the maximum value and the minimum value of the light intensity voltage signal, and calculating the average value of the maximum value and the minimum value. As shown in Figure 2, when the temperature of the laser is changed, the light intensity of the optical interference signal will change periodically. In this embodiment, the change of the light intensity measured by the photodetector is converted into a voltage signal and collected by a data acquisition card, and the sinusoidal graph shown in Figure 2 can be obtained, and the average value of the maximum and minimum values on the graph is It is the point with the largest slope, as shown in point a and b in Figure 2. After the interference signal is collected and entered into the computer, the maximum and minimum values on the graph can be obtained through software programming and then averaged to determine the voltage value of point a and point b.

The working point corresponds to the voltage value when the slope of the interference signal is the largest. When an external force is applied, the cantilever beam is displaced, that is, the length of the interference cavity changes, and the working point moves on the interference curve. If the wavelength (temperature) of the laser is controlled so that the working point moves in the opposite direction on the interference curve, the working point can be kept at the point with the maximum slope on the interference curve. This process is controlled by PID2, that is, the voltage value at the time of the maximum slope in the interference signal is input to PID2 as the reference voltage value, and the working point is locked in real time at the maximum slope position on the interfering curve. The change of the wavelength (temperature) of the laser is proportional to the displacement of the cantilever beam, which reflects the magnitude of the torque acting on the cantilever beam. The output of PID2 is the signal of static displacement measurement.

Use the cantilever beam displacement measuring device of the present invention to measure the displacement of the cantilever beam The cantilever beam displacement measuring method may include the following steps:

The step of placing the object under test on the cantilever beam;

By controlling the temperature of the laser to change the wavelength of the laser, irradiating the cantilever beam with laser light to cause light interference to obtain the light intensity voltage signal of the interference light, and determine the reference of the light intensity voltage signal based on the light intensity voltage signal step of voltage value;

a step of locking the light intensity voltage signal at a reference voltage value by performing feedback control using the first controller and the second controller;

A step of applying an external force to the measured object to cause displacement, and measuring the displacement based on the displacement signal output by the second controller.

(Example)

A specific embodiment of the present invention will be described below with reference to the accompanying drawings.

The invention is a cantilever beam displacement measuring device and method based on a laser interference ranging system. Specifically, this embodiment adopts the optical fiber interferometry system shown in FIG. 1 for measuring the displacement of a cantilever beam. In this system, the laser used is a DFB semiconductor laser produced by Kongtum, which generates single-mode laser with a wavelength of 1100-2000nm. The temperature measurement element and the temperature control element are integrated inside the laser. The Thermistor terminal is the thermistor port for measuring the laser temperature; the TEC± terminal is the port of the temperature control component for controlling the laser temperature.

The laser light emitted from the laser is introduced into the optical fiber through the 90:10 single-mode fiber coupler produced by Thorlabs, and focused on the cantilever beam through the lens. The output of the coupler is converted into a voltage signal by the photodetector.

Fig. 3 is a schematic diagram showing a feedback control structure for operating point locking and temperature compensation according to an embodiment of the present invention. The feedback control structure includes two PID control units. Wherein, the feedback voltage terminal of PID1 is connected to the thermistor port of the laser 201, the target voltage terminal of PID1 is connected to the output voltage terminal of PID2, and the output voltage terminal of PID1, namely the control terminal, is connected to the port of the temperature control part of the laser 201. The feedback voltage terminal of PID2 is connected to the photodetector 202, the reference voltage value of the light intensity voltage signal is input to the target voltage terminal of PID2, and the output voltage terminal of PID2, namely the control terminal, is connected to the target voltage terminal of PID1.

The function of PID1 is to precisely control the temperature of the semiconductor laser, that is, to precisely control the wavelength of the laser. When measuring the laser temperature, a constant current passes through the temperature sensor, and the voltage value at the thermistor port is equivalent to the laser temperature as the feedback signal (Feedback Signal) of PID1. The expected value (Desired State) of PID1 is the compensation value of temperature (wavelength).

The function of PID2 is to compensate the displacement of the cantilever beam. Its expected value (Desired State) is the maximum slope point on the interference curve that needs to be locked, that is, the reference voltage value, the feedback signal (Feedback Signal) is the interference voltage signal output by the photodetector, and the output of the control terminal (Control Signal) is The displacement signal, multiplied by a fixed proportional coefficient is the target temperature that the laser needs to reach, which is the expected value of PID1 (Desired State). Therefore, the displacement signal output by the control terminal of PID2 is the target temperature-related signal of the laser.

FIG. 4 is a circuit diagram showing an example of an internal circuit configuration of a PID controller. The operational amplifiers used in the internal circuit are all opa627, in which the operational amplifiers and resistors and capacitors corresponding to U2, U3, and U4 respectively realize proportional, integral and differential functions, and the variable resistors R16, R17, and R18 respectively control the proportional coefficient, integral coefficient and differential coefficient. U5 is to amplify or reduce the output of the final PID control circuit.

In order to verify the method for measuring the static torque of the cantilever beam by laser interferometric ranging, the specific effect of the present invention is demonstrated by taking the measurement of the magnetic torque of the cantilever beam as an example.

In this experiment, MnSi microsheets are used as the test object, which is a magnetic sample. MnSi microflakes are cut from a MnSi bulk by focused ion beam etching. Figure 5A is an SEM photo of a MnSi microsheet on a Si sheet, and the size of the MnSi microsheet is a sheet of 7 μm x 15 μm x 1 μm, and Figure 5B is a SEM photo of the state where the MnSi microsheet is mounted on a Si cantilever beam. The cantilever beam is made of pure silicon, such as single crystal silicon, and the widened plane at its free end is a reflection surface for laser ranging.

As far as the cantilever beam is concerned, the pure silicon cantilever beam used in optical interferometry can achieve a lower elastic coefficient and further improve sensitivity. Specifically, the static displacement measurement sensitivity of the cantilever depends on the elastic coefficient of the cantilever, while the sensitive dynamic torque measurement not only requires a lower elastic coefficient, but also the higher the quality factor of the cantilever, the more sensitive it is. Therefore, to prepare a cantilever beam for static displacement measurement by optical interferometry, it is only necessary to consider how to reduce the elastic coefficient of the cantilever beam, without considering the high quality factor of the cantilever beam. Therefore, the use of static displacement measurement has a more tolerant requirement on the quality of the cantilever beam.

In the experiment, laser interferometry was used to measure the displacement of the cantilever beam. Under the action of an external magnetic field, the magnetic sample at the free end of the cantilever beam was subjected to torque, which made the cantilever beam bend and changed the resonance frequency of the cantilever beam. In the experiment, dynamic magnetic torque measurement and static magnetic torque measurement were carried out to reflect the magnetization characteristics of magnetic samples. The test temperature is 22K, the sweep field is a cycle from -1T to +1T (-10000Oe to +10000Oe), and the magnetic field is along the in-plane direction of the microsheet.

The dynamic measurement method is to measure the change of the resonance frequency of the cantilever beam with the magnetic field in real time. The measurement of the resonance frequency of the cantilever beam adopts the commonly used phase-locked loop (PLL) technology, and the instrument that realizes this function uses the HF of Zurich Instruments. The static measurement method uses the technique of the present invention. The laser optical path and electrical signal conversion system are shown in Figure 2, the circuit diagram of the PID control unit is shown in Figure 4, and the entire measurement system, that is, the feedback control structure, is shown in Figure 3, where the output of the output voltage port of PID2 is the static measurement displacement signal.

FIG. 6A is the test result of the dynamic measurement method for measuring the change of resonance frequency, and FIG. 6B is the test result of the static displacement of the cantilever beam measured by the static measurement method using temperature compensation. 6A shows the magnetic properties of the MnSi micro-sheets in the out-of-plane direction measured by the dynamic measurement method, and FIG. 6B shows the magnetic properties in the out-of-plane direction of the MnSi micro-sheets measured by the static measurement method. It can be seen from the figure that both the dynamic and static magnetic torque measurements reflect the magnetic properties of MnSi nanosheets, but there is a section of the curve in Figure 6A with relatively high noise, which is due to the fact that the magnetic field is in the section from ±0.4T to ±1T. It is caused by the reduction of the Q value of the cantilever due to the magnetic loss caused by the magnetization state of the sample.

Through the test of the magnetic torque, it shows that the static measurement method of the present invention can measure the torque of the cantilever beam based on the laser interferometry. Compared with the two measurement methods, the data obtained by the static magnetic torque measurement method is cleaner and less affected by other factors.

Claims (9)

1. Cantilever beam displacement measuring device, its characterized in that includes:

the cantilever beam can carry a measured object and comprises a fixed end and a free end, wherein the free end is provided with a light reflecting surface;

a laser capable of changing the wavelength of the output laser light by controlling the temperature thereof;

an optical interference system through which the laser light output from the laser can be irradiated to the light reflection surface of the cantilever, and the light reflected by the light reflection surface can be returned to the optical interference system to generate interference light;

a photodetector capable of detecting the interference light to convert the intensity of the interference light into an intensity voltage signal;

a first controller that generates a control signal for controlling the temperature of the laser according to a difference between a detected temperature value of the laser and a target temperature to control the temperature of the laser to the target temperature; and

and a second controller for generating a displacement signal of the cantilever according to a difference between the light intensity voltage signal output from the photodetector and a predetermined reference voltage value, and outputting the displacement signal to the first controller as a target temperature-related signal, wherein the first controller is configured to control the temperature of the laser to change the wavelength of the output laser light, thereby performing feedback control on the light intensity voltage signal.

2. The cantilever beam displacement measuring apparatus according to claim 1, wherein the prescribed reference voltage value is a voltage value of the light intensity voltage signal at which a change in the light intensity voltage signal with respect to the wavelength or a change rate of displacement of the cantilever beam becomes a maximum value.

3. The cantilever beam displacement measuring apparatus according to claim 2, wherein the prescribed reference voltage value is obtained by taking a maximum value and a minimum value of the light intensity voltage signal and calculating an average value of the maximum value and the minimum value.

4. The cantilever beam displacement measuring apparatus according to any one of claim 1 to 3, wherein,

the first controller is a first PID controller, the detected temperature value and the target temperature related signal of the laser are input signals, the control signal for controlling the temperature of the laser is output signal,

the second controller is a second PID controller, the light intensity voltage signal and the specified reference voltage value output by the photoelectric detector are input signals, the displacement signal of the cantilever beam is output signal, and the output signal is output to the first PID controller as the target temperature related signal.

5. The cantilever displacement measuring apparatus according to any one of claims 1 to 3, wherein the optical interference system includes an optical fiber coupler and an optical fiber, the laser light outputted from the laser enters the optical fiber via the optical fiber coupler, the laser light outputted from the light-outgoing end of the optical fiber is irradiated to the light-reflecting surface of the cantilever, the light reflected at the light-reflecting surface is returned to the optical fiber via the light-outgoing end of the optical fiber, and optically interferes with the light reflected at the light-outgoing end of the optical fiber, and the photodetector is coupled with the optical fiber coupler to receive the interference light.

6. A cantilever displacement measuring device according to any one of claims 1 to 3, wherein the laser is a wavelength tunable semiconductor laser.

7. A cantilever beam displacement measuring apparatus according to any one of claims 1 to 3, wherein the cantilever beam is made of pure silicon.

8. A cantilever beam displacement measuring apparatus according to any one of claims 1 to 3, wherein the object to be measured is a magnetic sample and the external force is applied by an externally applied magnetic field.

9. A cantilever beam displacement measuring method for measuring a displacement of the cantilever beam using the cantilever beam displacement measuring apparatus according to any one of claims 1 to 8, comprising:

a step of loading a test object on the cantilever beam;

a step of obtaining a light intensity voltage signal of the interference light by controlling the temperature of the laser to change the wavelength of the laser and irradiating the cantilever beam with the laser so that the interference of the light occurs, and determining a reference voltage value of the light intensity voltage signal based on the light intensity voltage signal;

a step of locking the light intensity voltage signal at the reference voltage value by performing feedback control using the first controller and the second controller;

and a step of applying an external force to the object to be measured to displace the object to be measured, and measuring the displacement based on the displacement signal output from the second controller.