CN-115200819-B - Cantilever beam resonance frequency and quality factor measurement method and device

CN115200819BCN 115200819 BCN115200819 BCN 115200819BCN-115200819-B

Abstract

Compared with the existing measuring method based on the phase-locked loop (PLL) technology, the measuring method and the measuring device can master the magnetic properties of the sample more comprehensively, and have good measuring stability when dealing with the abrupt change of the cantilever Liang Pinzhi factor. The measuring method comprises a cantilever beam driving step, a free damping signal obtaining step and a data processing step, wherein the cantilever beam is driven to vibrate by a driving signal with a first frequency, then the driving signal is stopped, the free damping vibration signal of the free end of the cantilever beam is obtained in response to the stopping of the driving signal, and the obtained free damping vibration signal is processed to obtain the resonance frequency and the quality factor of the cantilever beam.

Inventors

DU HAIFENG
WANG NING

Assignees

中国科学院合肥物质科学研究院
中国科学院合肥物质科学研究院

Dates

Publication Date: 20260421
Application Date: 20220713
Priority Date: 20220713

Claims (8)

1. In a cantilever force measuring apparatus in a dynamic operation mode, a method for measuring a resonance frequency and a quality factor of a cantilever beam on which a sample is placed in real time and simultaneously, comprising: a cantilever beam driving step, wherein the cantilever beam is driven to vibrate by a driving signal with a first frequency, and then the driving signal is stopped; A free damping signal acquisition step of acquiring a free damping vibration signal of a free end of the cantilever in response to a stop of the drive signal, and A data processing step, wherein the obtained free damping vibration signal is processed to obtain the resonance frequency and quality factor of the cantilever beam, In the data processing step, the resonance frequency is obtained by obtaining a peak position after fourier transforming the free damped vibration signal, and the quality factor is obtained by obtaining an outer envelope of the free damped vibration signal and fitting the outer envelope, The cantilever beam force measuring device sequentially applies a plurality of different magnetic fields to obtain the resonance frequency and the quality factor of the cantilever beam under each magnetic field, In the case where the current magnetic field is the first applied magnetic field, in the cantilever driving step, the frequency spectrum of the cantilever is first swept to obtain a swept resonant frequency, the swept resonant frequency is used as the first frequency, In the case where the current magnetic field is not the first applied magnetic field, the resonance frequency obtained in the data processing step under the last applied magnetic field is used as the first frequency in the cantilever driving step.
2. The method for measuring the resonance frequency and the quality factor of the cantilever according to claim 1, wherein: In the data processing step, fourier transforming the free damped vibration signal, fitting the obtained spectral curve with a lorentz line pattern using the value of x obtained by the fitting as the resonance frequency, Where a, b, c are fitting parameters and y (f) represents the amplitude of the formants of the spectral curve as a function of frequency.
3. The method for measuring the resonance frequency and the quality factor of the cantilever according to claim 2, wherein: In the data processing step, fitting the outer envelope line by using the following formula, using the Q value obtained by fitting as the quality factor, Where U (t) is the amount of attenuation of the cantilever amplitude over time, U 0 is the initial value at the beginning of the attenuation, and ω is the resonant frequency obtained.
4. The method for measuring the resonance frequency and the quality factor of the cantilever according to claim 1, wherein: In the cantilever driving step, after the cantilever stops vibrating after a period of time passes after the driving signal is stopped, the driving signal of the first frequency is used for driving the cantilever again, thereby repeatedly driving and stopping the cantilever for a plurality of times, Acquiring a plurality of the free damping vibration signals in the free damping signal acquisition step, In the data processing step, a plurality of the free damped vibration signals are averaged and then subjected to subsequent processing.
5. The method for measuring the resonance frequency and the quality factor of the cantilever according to claim 1, wherein: And obtaining the outer envelope line by a method of correcting the free damping vibration signal and averaging a smooth curve.
6. A measuring device for measuring resonance frequency and quality factor of a cantilever beam, which is provided in a cantilever beam force measuring device in a dynamic operation mode, and measures resonance frequency and quality factor of a cantilever beam on which a sample is loaded under an applied current magnetic field in real time and simultaneously, comprising: a drive signal output unit that outputs a drive signal of a first frequency to a drive unit of the cantilever-force measuring device, drives the cantilever to vibrate, and then stops outputting the drive signal; A free damping signal acquisition unit for acquiring a free damping vibration signal of the free end of the cantilever in response to a stop of the drive signal, and A control unit that processes the free damping vibration signal acquired by the free damping signal acquisition unit to obtain a resonance frequency and a quality factor of the cantilever beam, Wherein the control unit obtains the resonance frequency by obtaining a peak position after fourier transforming the free damped vibration signal, obtains the quality factor by obtaining an outer envelope of the free damped vibration signal and fitting the outer envelope, The cantilever beam force measuring device sequentially applies a plurality of different magnetic fields to obtain the resonance frequency and the quality factor of the cantilever beam under each magnetic field, In the case that the current magnetic field is the first applied magnetic field, the frequency spectrum of the cantilever beam is measured by frequency sweeping to obtain a frequency-sweeping resonance frequency, the driving signal output part uses the frequency-sweeping resonance frequency as the first frequency, In the case where the current magnetic field is not the first applied magnetic field, the drive signal output section uses the resonance frequency obtained by the control section under the magnetic field applied last as the first frequency.
7. The cantilever resonance frequency and quality factor measurement apparatus of claim 6, wherein: the control unit performs Fourier transform on the free damped vibration signal, fits the obtained spectral curve to a Lorentzian line type using an x value obtained by fitting as a calculated resonance frequency, Where a, b, c are fitting parameters and y (f) represents the amplitude of the formants in the frequency domain as a function of frequency.
8. The cantilever resonance frequency and quality factor measurement apparatus of claim 7, wherein: the control unit fits the outer envelope line by using the following formula, uses the Q value obtained by fitting as the obtained quality factor, Where U (t) is the amount of attenuation of the cantilever amplitude over time, U 0 is the initial value at the beginning of the attenuation, and ω is the resonant frequency obtained.

Description

Cantilever beam resonance frequency and quality factor measurement method and device Technical Field The invention belongs to the field of sensitivity detection research, and particularly relates to a measuring method of a cantilever beam resonance frequency and a quality factor, in particular to a method for simultaneously measuring the cantilever beam resonance frequency and the quality factor in real time. Background The micro-cantilever beam (hereinafter referred to as a cantilever beam) displacement measurement based on laser interferometry is one of the important methods for sensitivity detection, and has important applications in the aspects of magnetic torque measurement, measurement of Cashmere force, magnetic resonance force measurement and the like of nanoscale magnetic samples. The cantilever beam operating modes include a static operating mode and a dynamic operating mode. Taking Dynamic Cantilever Magnetometry (DCM) for measuring a micro-nano magnetic sample as an example, a nano cantilever beam with a low elastic coefficient is used, a magnetic material sample is fixed at the free end of the cantilever beam, an external magnetic field is applied to enable the sample to be subjected to torque action, so that the resonance frequency of the cantilever beam (including the sample) is changed, and then the change of the resonance frequency of the cantilever beam under different magnetic fields is measured to reflect the magnetic property of the sample. In general, the dynamic cantilever magnetometry method only measures the resonant frequency of the cantilever beam, and the resonant frequency of the cantilever beam and its variation can be measured in real time using phase-locked loop PLL techniques. With the development of dynamic cantilever magnetometry, it has been found that the change in the magnetic field due to the magnetism of the cantilever free end (vibrating end) sample not only affects the resonance frequency of the cantilever, but also affects the quality factor of the cantilever, and the change in the quality factor of the cantilever can reflect the characteristics of magnetic properties for some samples. Therefore, in order to more fully grasp the magnetic properties of the sample, it is desirable to be able to measure the resonance frequency and the quality factor of the cantilever beam simultaneously under different magnetic fields. However, when the PLL technology is used to measure the resonant frequency of the cantilever beam, the information of the quality factor of the cantilever beam cannot be obtained at the same time, and the quality factor needs to be measured separately. In addition, when the magnetism of the sample is in different magnetization states along with the change of the magnetic field, and the quality factor (for example, abrupt change of the quality factor) of the cantilever beam can be significantly changed, a measurement method adopting the phase-locked loop PLL technology may lose a locking effect, so that the measurement becomes extremely unstable and even is forced to stop. Therefore, a new measurement method needs to be developed, which can obtain the resonance frequency and the quality factor of the cantilever beam simultaneously and in real time, and make the measurement more stable and reliable. Disclosure of Invention Technical problem to be solved by the invention As described above, the force detection method based on the cantilever beam in the dynamic working mode reflects the stress condition of the sample by measuring the change of the resonance frequency of the cantilever beam, and further reflects the magnetic property of the sample. The measurement of the resonant frequency of the cantilever beam currently adopts the phase-locked loop PLL technology, and in order to facilitate understanding of the present invention, the basic principle and the main problems thereof are specifically described below. Fig. 1 schematically shows the amplitude response curve and the frequency response curve of a cantilever beam under a constant magnetic field. In fig. 1, (a) shows an amplitude response curve, the horizontal axis is the frequency at which the cantilever is driven by a driving part (e.g., piezoelectric ceramic, etc.) at the fixed end of the cantilever, and the vertical axis shows the vibration amplitude at the free end of the cantilever at different driving frequencies. As shown in fig. 1 (a), the frequency response curve of the cantilever has a prominent peak, the position of which represents the position of the cantilever resonance frequency f 0. In fig. 1b, the frequency response curve is shown, the horizontal axis represents the frequency of driving by the driving unit, the vertical axis represents the cantilever beam phase shift amount, and the phase difference (phase lag amount) between the driving signal and the cantilever beam free end vibration signal is shown. As shown in fig. 1 (b), the phase response curve of the cantilever beam is near