Quartz crystal microbalance based on cubic overtone resonance mode and sensibilization method thereof

Abstract

The invention relates to the technical field of sensing detection, and discloses a quartz crystal microbalance based on a triple overtone resonance mode and a sensibilization method thereof, the sensibilization method comprises the following steps: using a triple harmonic drive circuit to drive a quartz crystal resonator sensing unit, enabling the quartz crystal resonator sensing unit to generate bridge oscillation in the triple overtone resonance mode, outputting a first electric signal containing a third harmonic frequency sweeping signal; detecting the third harmonic frequency sweep signal to obtain third resonance information, and performing inversion based on the change of the third resonance information to obtain to-be-detected micro-mass change information; wherein the tertiary resonance information comprises tertiary resonance frequency and tertiary resonance bandwidth. By adopting the third harmonic drive circuit, the quartz crystal microbalance works in a third overtone resonant mode, the third overtone resonant frequency of the quartz crystal microbalance is obviously higher than the fundamental frequency resonant frequency, and the sensitivity of the quartz crystal microbalance in the third overtone resonant mode is obviously improved as the sensitivity is in direct proportion to the resonant frequency.

Description

Technical Field

[0001] The present application relates to the technical field of sensing detection, and specifically, to a quartz crystal microbalance based on the third overtone resonance mode and a method for enhancing its sensitivity. Background Art

[0002] A quartz crystal microbalance is a highly sensitive micro-mass sensing instrument that can provide nanogram-level mass detection accuracy and has been widely used in basic research and applied research fields such as biochemical process analysis, humidity measurement, detection of harmful gases such as volatile organic compounds, medical diagnosis, and analysis of environmental heavy metal content. At present, the sensitivity is mainly improved by increasing the fundamental resonance frequency of the quartz crystal microbalance wafer or developing a specific sensitive film. However, when improving the sensitivity by increasing the fundamental resonance frequency of the wafer, the process requirements for the wafer are very high and the lifespan of the wafers that can meet the conditions is short; when improving the sensitivity by developing a specific sensitive film, there are often situations where the detection error is relatively high. Therefore, developing a new method for improving the sensitivity of a quartz crystal microbalance is one of the important challenges faced.

[0003] Content of the Application

[0004] The present application aims to solve at least one of the technical problems in the related art to some extent. To this end, an object of the present application is to propose a quartz crystal microbalance based on the third overtone resonance mode and a method for enhancing its sensitivity. The sensitivity of the quartz crystal microbalance using the sensitivity enhancement method of the present application is significantly improved.

[0005] In the first aspect of the present application, a method for enhancing the sensitivity of a quartz crystal microbalance based on the third overtone resonance mode is proposed, including: driving a quartz crystal resonator sensing unit using a third harmonic driving circuit to cause the quartz crystal resonator sensing unit to perform a bridge oscillation in the third overtone resonance mode and output a first electrical signal containing a third harmonic sweep signal; detecting the third harmonic sweep signal to obtain third resonance information, and inversely obtaining the micro-mass change information to be detected based on the change of the third resonance information; wherein, the third resonance information includes a third resonance frequency and a third resonance bandwidth.

[0006] Through the driving of the third harmonic driving circuit, the quartz crystal resonator sensing unit operates in the third overtone resonance mode. The oscillation frequency during the bridge oscillation is three times the fundamental resonance frequency. When performing mass detection, the same small mass change appears on the electrode surface, and the change amount of the third overtone resonance frequency caused is significantly greater than the change amount of the fundamental resonance frequency caused. Thus, the sensitivity of the quartz crystal microbalance is improved.

[0007] In addition, the method for enhancing the sensitivity of a quartz crystal microbalance based on the third overtone resonance mode according to the above embodiments of the present application may further have the following additional technical features:

[0008] In some embodiments of the present application, before detecting the third harmonic swept-frequency signal, a signal processing step is further included, and the signal processing step includes: suppressing the non-third harmonic swept-frequency signal in the first electrical signal to obtain a second electrical signal containing the third harmonic swept-frequency signal. Suppressing the non-third harmonic swept-frequency signal is beneficial to improving the purity of the electrical signal, thereby improving the sensitivity of the quartz crystal microbalance.

[0009] In some embodiments of the present application, the signal processing step further includes: amplifying the second electrical signal to obtain a third electrical signal containing the amplified third harmonic swept-frequency signal; detecting the amplified third harmonic swept-frequency signal to obtain the third resonance information. Thus, the weak electrical signal can be enhanced, which helps to improve the anti-interference ability of the signal.

[0010] In some embodiments of the present application, the signal processing step further includes: suppressing the non-third harmonic swept-frequency signal in the third electrical signal to obtain a fourth electrical signal containing the amplified third harmonic swept-frequency signal. Thus, the purity of the electrical signal is further improved, ensuring the quality stability of the final output signal, thereby improving the sensitivity.

[0011] In some embodiments of the present application, after obtaining the third resonance information, it further includes: feeding back the amplified third harmonic swept-frequency signal to the quartz crystal resonator sensing unit to form an oscillation. Thus, it helps to precisely control and adjust the oscillation frequency of the quartz crystal, reduce the error in the signal processing process, thereby continuously generating an oscillation signal with a specific frequency, and finally forming a feedback signal.

[0012] In a second aspect of the present application, the present application provides a quartz crystal microbalance based on the third overtone resonance mode, and the quartz crystal microbalance includes: a quartz crystal resonator sensing unit; a third harmonic driving circuit, which is electrically connected to the quartz crystal resonator sensing unit and is used to drive the quartz crystal resonator sensing unit to generate a bridge oscillation in the third overtone resonance mode and output a first electrical signal containing a third harmonic swept-frequency signal; a signal conversion unit, which is electrically connected to the quartz crystal resonator sensing unit and is used to receive the third harmonic swept-frequency signal; a third resonance information detection unit, which is electrically connected to the signal conversion unit and is used to detect the third harmonic swept-frequency signal to obtain the third resonance information and transmit the third resonance information to the signal conversion unit. Thus, the obtained quartz crystal microbalance has high sensitivity.

[0013] In some embodiments of the present application, the quartz crystal microbalance may further include: a frequency selection network unit, disposed between the quartz crystal resonator sensing unit and the signal conversion unit, and electrically connected to the quartz crystal resonator sensing unit and the signal conversion unit, for suppressing non-third harmonic sweep signals in the first electrical signal and outputting a second electrical signal containing the third harmonic sweep signal. This is beneficial to improving the purity of the electrical signal, ensuring the quality stability of the final output signal, and thus improving the sensitivity.

[0014] In some embodiments of the present application, the quartz crystal microbalance further includes: an amplifier, disposed between the frequency selection network unit and the signal conversion unit, and electrically connected to the frequency selection network unit and the signal conversion unit, for amplifying the second electrical signal and outputting a third electrical signal containing the amplified third harmonic sweep signal. Thereby, weak electrical signals can be enhanced, thus improving the anti-interference ability of the signal.

[0015] In some embodiments of the present application, the quartz crystal microbalance further includes: a harmonic suppression circuit, disposed between the amplifier and the signal conversion unit, and electrically connected to the amplifier and the signal conversion unit, for suppressing non-third harmonic sweep signals in the third electrical signal and outputting a fourth electrical signal containing the amplified third harmonic sweep signal. This is beneficial to further improving the purity of the electrical signal, ensuring the quality stability of the final output signal, and thus improving the sensitivity.

[0016] In some embodiments of the present application, the quartz crystal microbalance further includes: a feedback network unit, disposed between the quartz crystal resonator sensing unit and the signal conversion unit, and electrically connected to the quartz crystal resonator sensing unit and the signal conversion unit, for feeding back the amplified third harmonic sweep signal to the quartz crystal resonator sensing unit to form an oscillation. Thereby, it helps to precisely control and adjust the oscillation frequency of the quartz crystal, reduce errors in the signal processing process, and thus continuously generate an oscillation signal of a specific frequency, ultimately forming a feedback signal. Description of the Drawings

[0017] Figure 1 is a schematic flow chart of a method for enhancing the sensitivity of a quartz crystal microbalance based on the third overtone resonance mode according to an embodiment of the present application.

[0018] Figure 2 is a schematic diagram of a third harmonic drive circuit according to an embodiment of the present application.

[0019] Figure 3 is a schematic flow chart of a method for enhancing the sensitivity of a quartz crystal microbalance based on the third overtone resonance mode according to an embodiment of the present application.

[0020] Figure 4 Schematic diagram of the sensitivity enhancement method of a quartz crystal microbalance based on the third overtone resonance mode according to an embodiment of the present application.

[0021] Figure 5 Schematic diagram of the sensitivity enhancement method of a quartz crystal microbalance based on the third overtone resonance mode according to an embodiment of the present application.

[0022] Figure 6 Schematic diagram of the sensitivity enhancement method of a quartz crystal microbalance based on the third overtone resonance mode according to an embodiment of the present application.

[0023] Figure 7 Schematic diagram of the structure of a quartz crystal microbalance device based on the third overtone resonance mode according to an embodiment of the present application.

[0024] Figure 8 Schematic diagram of the structure of a quartz crystal microbalance device based on the third overtone resonance mode according to an embodiment of the present application.

[0025] Figure 9 Schematic diagram of the structure of a quartz crystal microbalance device based on the third overtone resonance mode according to an embodiment of the present application.

[0026] Figure 10 Schematic diagram of the structure of a quartz crystal microbalance device based on the third overtone resonance mode according to an embodiment of the present application.

[0027] Figure 11 Schematic diagram of the structure of a quartz crystal microbalance device based on the third overtone resonance mode according to an embodiment of the present application.

[0028] Figure 12 Schematic diagram of the comparison of the frequencies and bandwidths between a quartz crystal resonator sensing unit based on the third overtone resonance mode and a quartz crystal resonator sensing unit based on the fundamental frequency mode according to an embodiment of the present application.

[0029] Figure 13 Comparison diagram of the sensitivities between a quartz crystal microbalance based on the third overtone resonance mode and a quartz crystal microbalance based on the fundamental frequency mode according to an embodiment of the present application. Detailed implementation manners

[0030] The embodiments of the present application are described in detail below. The described embodiments are exemplary and are intended to explain the present application and should not be construed as limiting the present application.

[0031] The present application is completed based on the following discoveries and understandings of the inventor:

[0032] As described above, the current methods for improving the sensitivity of quartz crystal microbalance wafers mainly include increasing the fundamental resonance frequency or developing specific sensitive films. Specifically, increasing the fundamental resonance frequency of the wafer requires thinning the thickness of the wafer, which not only requires improving the wafer processing technology, but also excessive thinning of the wafer thickness will lead to a decrease in the strength of the wafer, making it fragile, thus reducing the reliability and lifespan of the wafer; improving the mass sensitivity by developing a specific sensitive film is to coat the film on the electrode surface of the sensor to enrich the substance to be detected on the sensitive film, so as to achieve the purpose of detecting specific substances. However, since the substance to be detected often contains many other components and its amount may be extremely small in the environment, it is inevitably affected by other substances, and there are often many situations where it cannot be detected or the detection error is relatively high, resulting in an unsatisfactory detection effect. Through further exploration, the inventor has developed a new method that can improve the sensitivity of the quartz crystal microbalance. This method has no special requirements for the wafer preparation process and thickness, and at the same time has a relatively low detection error.

[0033] In the first aspect of the present application, a method for enhancing the sensitivity of a quartz crystal microbalance based on the third overtone resonance mode is proposed. Referring to Figure 1 , the method includes the following steps:

[0034] S10: Use a third-harmonic drive circuit to drive the quartz crystal resonator sensing unit, so that the quartz crystal resonator sensing unit generates a bridge oscillation in the third overtone resonance mode, and outputs a first electrical signal containing a third-harmonic swept-frequency signal.

[0035] In this step, a third-harmonic swept-frequency signal is generated by the third-harmonic drive circuit and sent to the quartz crystal resonator sensing unit, enabling it to operate in the third overtone resonance mode. Since the quartz crystal resonator sensing unit oscillates at the third-harmonic frequency, the first electrical signal output mainly contains the third-harmonic swept-frequency signal, and there may also be some noise (such as other harmonic signals). The first electrical signal containing the third-harmonic swept-frequency signal can be used as the input for subsequent signal processing steps.

[0036] In some embodiments of the present application, the third overtone resonance refers to the resonance phenomenon that occurs in the quartz crystal resonator sensing unit when the driving frequency reaches three times the system natural frequency (i.e., the third-harmonic swept-frequency signal).

[0037] In some embodiments of the present application, the structure of the third-harmonic drive circuit, referring to Figure 2 , includes an operational amplifier (A V ), resistors (R1, R2, R f ), and a quartz crystal resonator (Z R) etc. The non-inverting input terminal of the operational amplifier is grounded (GND1) through R1, the output terminal of the operational amplifier is connected to the inverting input terminal through R2, and one end of the quartz crystal resonator (Z R ) is connected to the inverting input terminal of the operational amplifier, and the other end is grounded (GND1). At the same time, R f is connected between the inverting input terminal and the quartz crystal resonator sensing unit.

[0038] In some embodiments of the present application, when the quartz crystal resonator sensing unit operates in the third overtone resonance mode, the equivalent circuit model includes elements such as dynamic inductance, dynamic capacitance, and dynamic resistance, and Z Q is the equivalent impedance under the combined action of these elements. Thus, a loop with feedback is formed, enabling the circuit to achieve a specific oscillation function to meet the oscillation of the quartz crystal resonator sensing unit in the third overtone mode.

[0039] Specifically, in the case of a smaller load, Z Q can be replaced by the dynamic resistance R; for a large load, the influence of the parasitic capacitance and static capacitance of the quartz crystal resonator sensing unit on the frequency will be more serious, and an inductor can be connected in parallel at both ends to offset the influence of the parasitic capacitance and static capacitance.

[0040] In some embodiments of the present application, the quartz crystal resonator sensing unit may include a quartz wafer and two electrodes. The two electrodes are disposed opposite to each other on two surfaces in the thickness direction of the quartz wafer, and the two electrodes are electrically connected to the third harmonic drive circuit to transmit a drive electrical signal to the quartz wafer, and the quartz wafer with piezoelectric effect can oscillate under the action of the drive electrical signal.

[0041] In some embodiments, the quartz crystal resonator sensing unit may further include a bracket and a housing. Specifically, the quartz wafer with electrodes on its surface can be installed on the bracket to ensure the stability of their positional relationship, and then the bracket with the quartz wafer is placed in the housing for encapsulation to form a complete quartz crystal resonator sensing unit. It can be understood that in different packaging forms and application scenarios, the specific structures and arrangement manners of each part in the quartz crystal resonator sensing unit may vary slightly, and the present application does not make any restrictions.

[0042] In some embodiments of the present application, the quartz wafer may be of the AT cut type. This quartz wafer has good temperature stability, a suitable frequency range, and a high quality factor, which means it can maintain oscillation with less energy loss, has good frequency stability and low phase noise.

[0043] In this text, the AT cut type refers to a quartz wafer obtained by cutting a quartz crystal at an angle of approximately 35°15′ with respect to the optical axis. The resulting quartz wafer has excellent properties and can have stable frequency characteristics within a relatively wide temperature range.

[0044] In some embodiments of the present application, the quartz wafer may be circular. A circle has a high degree of symmetry, and the physical properties in all directions are relatively uniform, which is beneficial to improving the stability and reliability of the wafer performance.

[0045] In some embodiments of the present application, the fundamental frequency of the quartz wafer may be 5 MHz to 20 MHz, specifically, it may be 5 MHz, 8 MHz, 10 MHz, 12 MHz, 15 MHz, 17 MHz, 20 MHz, etc. When the fundamental frequency of the quartz wafer is within the above range, it can maintain good physical and chemical stability, and is relatively less affected by external environmental factors (such as temperature, humidity, pressure, etc.), thereby ensuring the stability of its oscillation frequency. It will neither cause difficulties in the quartz wafer process due to too high a fundamental frequency, nor fail to meet the requirements of various electronic circuits when the fundamental frequency is too low.

[0046] In some embodiments of the present application, the diameter of the quartz wafer is 5.1 mm to 8.7 mm. Specifically, it can be 5.1 mm / 8.7 mm. When the diameter of the quartz wafer is within the above range, it can be conveniently used and is suitable for the scenario of miniaturized sensors.

[0047] In some embodiments of the present application, the thickness of the quartz wafer is 83 microns to 167 microns. Specifically, it can be 83 microns, 85 microns, 90 microns, 95 microns, 100 microns, 105 microns, 110 microns, 115 microns, 120 microns, 125 microns, 130 microns, 135 microns, 140 microns, 145 microns, 150 microns, 155 microns, 160 microns, 165 microns, 167 microns, etc. When the thickness of the quartz wafer is within the above range, it can ensure that the wafer is not too thin, thus being suitable for mass production; at the same time, the wafer is not too thick, which would cause its fundamental frequency to be low, thereby reducing the sensitivity of the quartz crystal microbalance sensor.

[0048] In some embodiments of the present application, the materials of the two electrodes can be gold, silver, aluminum, etc. Thus, it has good electrical conductivity and helps to achieve the transmission of electrical signals.

[0049] In some embodiments of the present application, the electrodes can be circular electrodes, square electrodes, annular electrodes, etc. Different electrode shapes can be applied in different scenarios, and the application range is wider.

[0050] In some embodiments of the present application, the electrode may be a circular electrode, and the diameter of the circular electrode may be 2.0 mm to 5.1 mm. Specifically, it may be 2.0 mm, 2.3 mm, 2.5 mm, 2.7 mm, 3.0 mm, 3.2 mm, 3.5 mm, 3.7 mm, 4.0 mm, 4.2 mm, 4.7 mm, 5.0 mm, 5.1 mm, etc. When the diameter of the circular electrode is within the above range, a relatively high sensitivity of the quartz crystal microbalance can be ensured. If the electrode diameter is too small, the measurement error will increase; if the electrode diameter is too large, the sensitivity will decrease.

[0051] In some embodiments of the present application, the thickness of the electrode is 500 Å to 2000 Å. Specifically, it may be 500 Å, 600 Å, 800 Å, 1000 Å, 1100 Å, 1300 Å, 1500 Å, 1700 Å, 1900 Å, 2000 Å, etc. When the electrode thickness is within this range, a relatively high sensitivity of the quartz crystal microbalance can be ensured. If the electrode thickness is too small, the measurement error will increase; if the electrode thickness is too large, the sensitivity will decrease.

[0052] S20: Detect the third-harmonic swept-frequency signal to obtain third-harmonic resonance information, and inversely calculate the micro mass change information to be detected based on the change of the third-harmonic resonance information; wherein, the third-harmonic resonance information includes the third-harmonic resonance frequency and the third-harmonic resonance bandwidth.

[0053] In this step, a first electrical signal containing a third-harmonic swept-frequency signal sent by the quartz crystal resonator sensing unit can be received. By detecting the above electrical signal, the third-harmonic resonance information can be obtained. Based on the change of the third-harmonic resonance information, the micro mass change information to be detected can be inversely calculated, thereby realizing mass detection.

[0054] In some embodiments, the third-harmonic resonance information may include the third-harmonic resonance frequency and the third-harmonic resonance bandwidth. Taking the third-harmonic resonance information as the third-harmonic resonance frequency as an example, the third-harmonic resonance frequency can be detected by a frequency meter. When a substance is adsorbed or deposited on the surface of the quartz wafer, the mass load on the surface of the quartz wafer will increase. According to the Sauerbrey theory, the mass load causes the crystal oscillation frequency to decrease. By measuring the change of the third-harmonic resonance frequency, the change of the mass on the surface of the quartz wafer can be calculated, thereby realizing the detection of mass.

[0055] In some embodiments of the present application, the third-harmonic resonance bandwidth refers to a frequency range near the third-harmonic resonance frequency in the third-overtone resonance mode, within which the quartz wafer can vibrate effectively. The third-harmonic resonance bandwidth is related to the damping of the vibration of the quartz wafer. When the mass on the surface of the quartz wafer changes, it will cause a change in the damping of the vibration, and then cause a change in the third-harmonic resonance bandwidth, thereby realizing the detection of mass.

[0056] Specifically, for the test of the third harmonic resonance bandwidth, the frequency sweep method can be adopted. By using the frequency sweep method, a signal whose frequency changes with time is detected. The measured system or circuit will have different responses to signals of different frequencies. By measuring and analyzing these responses, the third harmonic resonance bandwidth can be obtained.

[0057] By adopting the above method of the present application, the sensitivity of the quartz crystal microbalance can be greatly improved.

[0058] Specifically, according to the Sauerbrey theory, the sensitivity S of the quartz crystal microbalance can be calculated by the following formula:

[0059]

[0060] where n is the harmonic number (n = 1, 3, 5, 7, 9..., n = 1 represents the fundamental frequency mode, n = 3 represents the third harmonic resonance mode. Theoretically, the third harmonic resonance frequency f3 = 3×f0); f0 is the fundamental resonance frequency; A is the area of the electrode; μ q is the shear modulus of the AT-cut quartz wafer; ρ q is the density of the quartz wafer. It can be seen from the above calculation formula that the sensitivity enhancement method of the quartz crystal microbalance based on the third harmonic resonance mode in the present application is the 3rd harmonic mode (i.e., n = 3). The quartz crystal resonator sensing unit operates in the third harmonic resonance mode. The oscillation frequency during bridge oscillation is three times the fundamental resonance frequency. When performing mass detection, the same small mass change appears on the electrode surface, and the change amount of the third harmonic resonance frequency caused is significantly greater than the change amount of the fundamental resonance frequency caused, which is easier to detect. Therefore, the sensitivity of the quartz crystal microbalance sensor can be effectively improved. It can be seen from the above calculation formula that the sensitivity of the quartz crystal microbalance in the third harmonic mode is three times that in the fundamental resonance frequency mode.

[0061] In some embodiments of the present application, in order to further improve the detection accuracy, before detecting the third harmonic frequency sweep signal, a signal processing step is further included to remove the noise other than the third harmonic frequency sweep signal. Specifically, referring to Figure 3 , the signal processing step may include:

[0062] S30: Suppress the non-third harmonic frequency sweep signal in the first electrical signal to obtain a second electrical signal containing the third harmonic frequency sweep signal.

[0063] In this step, the received first electrical signal is processed. For example, through a specific filter or signal processing algorithm, the non-third harmonic frequency sweep signal in the first electrical signal is attenuated or eliminated as much as possible.

[0064] Specifically, the non-third-harmonic swept-frequency signal includes a fundamental-frequency signal and other higher-harmonic signals, and the other higher-harmonic signals may include a fifth-harmonic signal, a seventh-harmonic signal, etc. Thus, it helps to obtain a purer third-harmonic swept-frequency signal.

[0065] In some embodiments of the present application, referring to Figure 4 , the signal processing step further includes:

[0066] S40: Amplify the second electrical signal to obtain a third electrical signal containing an amplified third-harmonic swept-frequency signal; detect the amplified third-harmonic swept-frequency signal to obtain the third resonance information.

[0067] In this step, an amplifier is used to amplify the second electrical signal. The amplifier will increase the amplitude of the input second electrical signal according to its own characteristics and settings to obtain a third electrical signal containing an amplified third-harmonic swept-frequency signal. Thus, the signal loss during transmission can be compensated, enabling it to be transmitted over a longer distance. At the same time, the anti-interference ability of the signal is improved, ensuring the stability and integrity of the amplified third-harmonic swept-frequency signal in the third electrical signal.

[0068] In some embodiments of the present application, referring to Figure 5 , the signal processing step further includes:

[0069] S50: Suppress the non-third-harmonic swept-frequency signal in the third electrical signal to obtain a fourth electrical signal containing the amplified third-harmonic swept-frequency signal.

[0070] In this step, in order to minimize the noise in the third electrical signal as much as possible, the non-third-harmonic swept-frequency signal in the third electrical signal can be further suppressed (for example, a specific filter can be used to suppress the non-third-harmonic swept-frequency signal). Compared with the amplified third-harmonic swept-frequency signal in the third electrical signal, the amplified third-harmonic swept-frequency signal is significantly enhanced and highlighted in the fourth electrical signal. Thus, the purity of the amplified third-harmonic swept-frequency signal is further improved, ensuring the quality stability of the final output signal, and thereby improving the sensitivity.

[0071] In some embodiments of the present application, referring to Figure 6 , after obtaining the amplified third resonance information, it further includes:

[0072] S60: Feed back the amplified third-harmonic swept-frequency signal to the quartz crystal resonator sensing unit to form an oscillation.

[0073] In this step, the feedback signal can compensate for the energy loss of the quartz crystal resonator sensing unit during oscillation, and the phase of the feedback signal matches the bridge oscillation phase of the quartz crystal resonator sensing unit, enabling the formation of a stable oscillation. This helps to precisely control and adjust the oscillation frequency of the quartz crystal resonator sensing unit, reduce errors in the signal processing process, thereby continuously generating an oscillation signal of a specific frequency, and ultimately forming a feedback signal.

[0074] It should be noted that when the amplified third-harmonic swept-frequency signal is fed back to the quartz crystal resonator sensing unit to form an oscillation, the vibration signal corresponding to the oscillation is converted into an electrical signal to constitute a first electrical signal.

[0075] In some embodiments of the present application, referring to Figure 2 , when forming the oscillation, the third-harmonic drive circuit can meet the following conditions:

[0076] Amplitude condition: The loop gain of the third-harmonic drive circuit is equal to 1, that is, ∣A v β∣ = 1;

[0077] Phase condition: The total phase shift of the third-harmonic drive circuit is 0° or 360°, that is, ∠A v +β = 0°.

[0078] Wherein, A V is the gain of the amplifier, and β is the feedback coefficient.

[0079] Specifically, the feedback coefficient β = β p -β n , where β p is the positive feedback coefficient in the oscillation circuit when the quartz crystal resonator sensing unit operates in the third overtone resonance mode, and β n is the negative feedback coefficient in the oscillation circuit when the quartz crystal resonator sensing unit operates in the third overtone resonance mode. The positive feedback coefficient and the negative feedback coefficient satisfy the following formula

[0080] β p = R1 / (R1 + R2)

[0081] β n = Z Q / (R f + Z Q )

[0082] Meeting the above conditions is beneficial to better form an oscillation and improve the stability of the electrical signal.

[0083] In the second aspect of the present application, a quartz crystal microbalance based on the third overtone resonance mode is proposed. Referring to Figure 7, the quartz crystal microbalance includes: a quartz crystal resonator sensing unit; a third-harmonic driving circuit electrically connected to the quartz crystal resonator sensing unit, generating a third-harmonic swept-frequency signal for driving the quartz crystal resonator sensing unit to generate a bridge oscillation in the third overtone resonance mode, and outputting a first electrical signal containing the third-harmonic swept-frequency signal; a signal conversion unit electrically connected to the quartz crystal resonator sensing unit for receiving the third-harmonic swept-frequency signal; a third-resonance information detection unit electrically connected to the signal conversion unit for detecting the third-harmonic swept-frequency signal to obtain third-resonance information and transmitting the third-resonance information to the signal conversion unit.

[0084] The detection principle of this quartz crystal microbalance is to drive through a third-harmonic driving circuit to generate a third-harmonic swept-frequency signal and transmit the third-harmonic swept-frequency signal to the quartz crystal resonator sensing unit. Utilizing the piezoelectric effect of the quartz crystal, this characteristic enables the quartz crystal resonator to generate stable vibrations under a specific alternating electric field, and its vibration frequency is very sensitive to the mass change of the adsorbed substance on the surface of the quartz wafer. Therefore, it is used as a sensing unit to detect the changes of various physical quantities. Since the quartz crystal resonator sensing unit oscillates at the third-harmonic frequency, the main component of the output first electrical signal is the third-harmonic swept-frequency signal. The signal conversion unit receives and converts and processes the first electrical signal and transmits it to the third-resonance information detection unit. The third-resonance information detection unit can detect the third-harmonic swept-frequency signal to obtain third-resonance information such as frequency and bandwidth, and mass detection can be achieved based on the third-resonance information.

[0085] In addition, the third-resonance information detected by the third-resonance information detection unit can also be transmitted to the signal conversion unit so that the signal conversion unit can output the third-resonance information to other external devices for display, storage, and analysis.

[0086] In some embodiments of the present application, referring to Figure 8 , the quartz crystal microbalance based on the third overtone resonance mode further includes: a frequency selection network unit disposed between the quartz crystal resonator sensing unit and the signal conversion unit, electrically connected to the quartz crystal resonator sensing unit and the signal conversion unit, for suppressing the non-third-harmonic swept-frequency signals in the first electrical signal and outputting a second electrical signal containing the third-harmonic swept-frequency signal. When the quartz crystal microbalance is working, it will inevitably generate certain noise. The function of the frequency selection network unit is to filter the third-harmonic swept-frequency signal and suppress other signals at the same time. Setting the frequency selection network unit is beneficial to improving the purity of the electrical signal, ensuring the quality stability of the final output signal, and thus improving the sensitivity.

[0087] Specifically, the frequency selection network unit can be a parallel LC filter. Thus, non-third-harmonic swept signals can be effectively suppressed, and at the same time, the LC filter has a simple structure and low cost.

[0088] In some embodiments of the present application, the parallel LC filter needs to be tuned to the third-harmonic frequency during operation, which helps to attenuate or eliminate as much as possible other frequency components in the first electrical signal except for the third harmonic.

[0089] In some embodiments of the present application, referring to Figure 9 , the quartz crystal microbalance based on the third overtone resonance mode further includes: an amplifier, disposed between the frequency selection network unit and the signal conversion unit, electrically connected to the frequency selection network unit and the signal conversion unit, for amplifying the second electrical signal and outputting a third electrical signal containing the amplified third-harmonic swept signal. The amplifier will increase the amplitude of the input second electrical signal according to its own characteristics and settings, which helps to increase the electrical signal strength, thereby improving the anti-interference ability of the signal and realizing the detection of minute physical changes.

[0090] Specifically, the amplifier can be an operational amplifier, which helps to provide sufficient gain to maintain its oscillation.

[0091] In some embodiments of the present application, referring to Figure 10 , the quartz crystal microbalance based on the third overtone resonance mode further includes: a harmonic suppression circuit, disposed between the amplifier and the signal conversion unit, electrically connected to the amplifier and the signal conversion unit, for suppressing non-third-harmonic swept signals in the third electrical signal and outputting a fourth electrical signal containing the amplified third-harmonic swept signal. This helps to further improve the purity of the electrical signal, ensure the quality stability of the final output signal, and thus improve the sensitivity.

[0092] The harmonic suppression circuit is used to further suppress non-third-harmonic swept signals in the third electrical signal, which can further reduce the possibility of non-third-harmonic swept signals interfering with the subsequent signal conversion unit, so that the signal conversion is more accurate and the sensitivity of the quartz crystal microbalance is further improved.

[0093] In some embodiments of the present application, referring to Figure 11 , the quartz crystal microbalance based on the third overtone resonance mode further includes: a feedback network unit, disposed between the quartz crystal resonator sensing unit and the signal conversion unit, electrically connected to the quartz crystal resonator sensing unit and the signal conversion unit, for feeding back the amplified third-harmonic swept signal to the quartz crystal resonator sensing unit to form an oscillation.

[0094] The feedback network unit feeds back the amplified third - harmonic swept - frequency signal to the quartz crystal resonator sensing unit to form an oscillation. The oscillation means that the output signal is fed back to the input end through negative feedback, that is, the amplified third - harmonic swept - frequency signal is fed back to the quartz crystal resonator sensing unit to enable it to oscillate continuously. Thus, the quartz crystal resonator sensing unit generates a very stable third - harmonic frequency signal, which can further improve the signal stability.

[0095] Through the quartz crystal microbalance based on the third - overtone resonance mode of this application, the sensitivity can be three times that of the fundamental resonance frequency mode.

[0096] As an example, referring to Figure 11 , the quartz microbalance based on the third - overtone resonance mode of this application is described in detail. It includes: a third - harmonic driving circuit, a quartz crystal resonator sensing unit, a frequency - selection network unit, an amplifier, a harmonic suppression circuit, a feedback network unit, a signal conversion unit, and a third - resonance information detection unit. The third - harmonic driving circuit is electrically connected to the quartz crystal resonator sensing unit and is used to drive the quartz crystal resonator sensing unit to generate a bridge - type oscillation in the third - overtone resonance mode and output a first electrical signal containing a third - harmonic swept - frequency signal; the frequency - selection network unit is electrically connected to the quartz crystal resonator sensing unit and is used to suppress the non - third - harmonic swept - frequency signals in the first electrical signal and output a second electrical signal containing a third - harmonic swept - frequency signal; the amplifier is electrically connected to the frequency - selection network unit and is used to amplify the second electrical signal and output a third electrical signal containing an amplified third - harmonic swept - frequency signal; the harmonic suppression circuit is electrically connected to the amplifier and is used to suppress the non - third - harmonic swept - frequency signals in the third electrical signal and output a fourth electrical signal containing an amplified third - harmonic swept - frequency signal; the signal conversion unit is electrically connected to the harmonic suppression circuit and is used to receive the fourth electrical signal; the third - resonance information detection unit is electrically connected to the signal conversion unit and is used to detect the third - harmonic swept - frequency signal in the fourth electrical signal to obtain third - resonance information (frequency, bandwidth, etc.), and inversely obtain the micro - mass change information to be detected based on the change of the third - resonance information, so as to achieve the detection purpose, and at the same time, it can transmit the third - resonance information to the signal conversion unit; the feedback network unit is electrically connected to the quartz crystal resonator sensing unit and the signal conversion unit and is used to feed back the amplified third - harmonic swept - frequency signal in the fourth electrical signal to the quartz crystal resonator sensing unit to form an oscillation.

[0097] As an example, referring to Figure 12, under the conditions that the driving circuits are the third - harmonic driving circuit and the fundamental - frequency mode driving circuit respectively, the schematic diagrams of the frequency and bandwidth of the quartz crystal resonator sensing unit are obtained. The fundamental - frequency resonance frequency (f0) and the corresponding fundamental - frequency resonance bandwidth (2Γ0) of the quartz crystal resonator sensing unit are obtained under the drive of the fundamental - frequency mode driving circuit; the third - overtone resonance frequency (f3) and the corresponding third - overtone resonance bandwidth (2Γ3) of the quartz crystal resonator sensing unit are obtained under the drive of the third - harmonic driving circuit. The tiny mass load on the electrode surface causes the shifts of f0 and f3, and causes the changes of 2Γ0 and 2Γ3. By extracting the information of both, the change information of the tiny mass load is inversely obtained, so as to realize the sensing and detection of the tiny mass.

[0098] Based on the comparison of the sensitivity of the quartz crystal microbalance based on the third - overtone resonance mode and the sensitivity of the quartz crystal microbalance based on the fundamental - frequency mode, refer to Figure 13 , according to the sensitivity calculation formula S = Δf / Δm in the Sauerbrey theory, where Δm is the change amount of the mass of the substance adsorbed on the surface of the quartz wafer, which can be measured by a three - electrode electrochemical plating platform, and Δf is the change amount of the quartz crystal oscillation frequency, which can be obtained by a frequency counter. Compared with the sensitivity of the quartz crystal microbalance based on the fundamental - frequency mode, the actual sensitivity of the quartz crystal microbalance based on the third - overtone resonance mode is increased by 2 - 4 times, which greatly improves the sensitivity of the third - overtone resonance mode in the field of sensing and detection and improves the sensing performance.

[0099] Although the embodiments of the present application have been shown and described above, it can be understood that the above - mentioned embodiments are exemplary and should not be construed as limitations to the present application. Those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above - mentioned embodiments within the scope of the present application.

Claims

1. A sensitivity enhancement method for a quartz crystal microbalance based on the third overtone resonance mode, characterized in that, Comprising: Using a third - harmonic driving circuit to drive a quartz crystal resonator sensing unit, causing the quartz crystal resonator sensing unit to generate a bridge - type oscillation in the third - overtone resonance mode, and outputting a first electrical signal containing a third - harmonic swept - frequency signal; Detecting the third - harmonic swept - frequency signal to obtain third - resonance information, and inversely obtaining the detected micro - mass change information based on the change of the third - resonance information; Wherein, the third - resonance information includes a third - resonance frequency and a third - resonance bandwidth.

2. The sensitization method according to claim 1, wherein Before detecting the third - harmonic swept - frequency signal, it further includes a signal - processing step, and the signal - processing step includes: Suppressing non - third - harmonic swept - frequency signals in the first electrical signal to obtain a second electrical signal containing the third - harmonic swept - frequency signal.

3. The sensitization method according to claim 2, characterized in that The signal - processing step further includes: Amplifying the second electrical signal to obtain a third electrical signal containing an amplified third - harmonic swept - frequency signal; Detecting the amplified third - harmonic swept - frequency signal to obtain the third - resonance information.

4. The sensitization method according to claim 3, wherein The signal - processing step further includes: Suppressing non - third - harmonic swept - frequency signals in the third electrical signal to obtain a fourth electrical signal containing the amplified third - harmonic swept - frequency signal.

5. The sensitization method according to claim 4, wherein After obtaining the amplified third - resonance information, it further includes: Feeding back the amplified third - harmonic swept - frequency signal to the quartz crystal resonator sensing unit to form an oscillation.

6. A quartz crystal microbalance based on the third overtone resonance mode, characterized in that, Comprising: A quartz crystal resonator sensing unit; Driven by a third - harmonic driving circuit, electrically connected to the quartz crystal resonator sensing unit, and used to drive the quartz crystal resonator sensing unit to generate a bridge - type oscillation in the third - overtone resonance mode, and output a first electrical signal containing a third - harmonic swept - frequency signal; A signal - conversion unit, electrically connected to the quartz crystal resonator sensing unit, and used to receive the third - harmonic swept - frequency signal; A third - resonance information detection unit, electrically connected to the signal - conversion unit, and used to detect the third - harmonic swept - frequency signal to obtain third - resonance information, and transmit the third - resonance information to the signal - conversion unit.

7. The quartz crystal microbalance according to claim 6, characterized in that, It further includes: A frequency - selection network unit, arranged between the quartz crystal resonator sensing unit and the signal - conversion unit, and electrically connected to the quartz crystal resonator sensing unit and the signal - conversion unit, and used to suppress non - third - harmonic swept - frequency signals in the first electrical signal and output a second electrical signal containing the harmonic signal.

8. The quartz crystal microbalance according to claim 7, characterized in that, It further includes: An amplifier, arranged between the frequency - selection network unit and the signal - conversion unit, and electrically connected to the frequency - selection network unit and the signal - conversion unit, and used to amplify the second electrical signal and output a third electrical signal containing an amplified third - harmonic swept - frequency signal.

9. The quartz crystal microbalance according to claim 8, characterized in that, It further includes: A harmonic - suppression circuit, arranged between the amplifier and the signal - conversion unit, and electrically connected to the amplifier and the signal - conversion unit, and used to suppress non - third - harmonic swept - frequency signals in the third electrical signal and output a fourth electrical signal containing the amplified third - harmonic swept - frequency signal.

10. The quartz crystal microbalance according to claim 9, characterized in that, It further includes: A feedback network unit is disposed between the quartz crystal resonator sensing unit and the signal conversion unit, and is electrically connected to the quartz crystal resonator sensing unit and the signal conversion unit. It is used to feedback the amplified third-harmonic swept signal to the quartz crystal resonator sensing unit to form an oscillation.

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