Photoinduced thermoelastic spectrum tuning fork with double-helix structure and preparation method thereof

Abstract

The invention relates to a light-induced thermoelastic spectrum tuning fork with a double-helix structure and a preparation method thereof, a pair of vibration arms of the tuning fork are wound to form the double-helix structure, the tuning fork is installed on a base, the radius of a spiral curve of each vibration arm is gradually reduced from the vibration end of the tuning fork to the installation end of the base according to the Fibonacci sequence R = 0.168 n mm, n represents the number of turns of the spiral curve of the vibrating arm relative to the vibrating end of the tuning fork. Compared with the prior art, the tuning fork quality factor is remarkably improved, and the detection sensitivity and the system stability are enhanced.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of acoustic measurement and acoustic sensing technology, and relates to a light-induced thermoelastic spectrum tuning fork with a double-helix structure and a preparation method thereof. BACKGROUND

[0002] Light-induced thermoelastic spectrum (LITES) is a high-precision gas detection technology, which is widely used in trace gas analysis, such as environmental monitoring, industrial safety, power equipment diagnosis, etc. The performance of a quartz tuning fork (QTF) as the core acoustic detection element of LITES directly determines the detection limit and reliability of the system.

[0003] Traditional quartz tuning forks usually have two straight arms, with an oscillation frequency of about 32.768 kHz and a quality factor (Q value) of about several thousand to tens of thousands in air, which limits the signal amplification capability and makes it difficult to achieve ultra-low concentration gas detection. At the same time, the prepared straight arms have stress concentration during vibration, resulting in mechanical energy loss, reducing the Q value and long-term stability. In addition, traditional quartz tuning forks are sensitive to transverse vibration, mechanical noise or disturbance environment (such as temperature, pressure changes), and their performance decreases in complex environments, such as inside a transformer or an industrial site.

[0004] Patent CN114157268A discloses a quartz crystal resonator and a manufacturing method thereof, which includes a vibration part and a base part. The vibration part is in the shape of a tuning fork, and includes a first vibration arm and a second vibration arm. The first vibration arm and the second vibration arm are connected to the base part at the intersection. The end of the first vibration arm and the end of the second vibration arm are provided with a frequency adjustment part. Symmetrical through holes are arranged on the first vibration arm and the second vibration arm, and the through holes are arranged in an axial array on the first vibration arm and the second vibration arm. An excitation electrode is arranged on the first vibration arm and the second vibration arm. Although the patent adjusts the vibration characteristics of the resonator by arranging through holes and frequency adjustment parts on the straight vibration arms, the design has problems such as stress concentration, short vibration path, sensitivity to environmental disturbance, etc., which limits the improvement of the Q value and makes it difficult to meet the needs of high-precision gas detection.

[0005] Patent CN116094486A discloses a new type of tuning fork crystal oscillation sheet and its manufacturing method and piezoelectric device, which has a base and a pair of vibration arms extending from the base, the front and back surfaces of the vibration arm have step-shaped grooves formed by photoetching along the thickness direction, and the step-shaped grooves are photoetched along the length direction of the vibration arm; the step-shaped grooves have n steps, which are formed by n times of photoetching; wherein n is a natural number, and n≥2; the outer surface of the step-shaped groove is plated with an electrode. However, the manufacturing process of the patent is complex and the cost is high, the stress concentration problem affects the durability and Q value, the vibration path optimization is insufficient, which limits the energy storage efficiency, and the environmental adaptability is poor, which limits its application in high-precision gas detection or high-stability application. SUMMARY

[0006] The purpose of the present application is to overcome at least one of the above-mentioned defects in the prior art and provide a dual-helical structure photo-induced thermal elastic spectrum tuning fork and its preparation method, which significantly improves the quality factor of the tuning fork, enhances the detection sensitivity and system stability.

[0007] The purpose of the present application can be achieved by the following technical solutions:

[0008] One of the technical solutions of the present application is to provide a dual-helical structure photo-induced thermal elastic spectrum tuning fork, which is wound to form a dual-helical structure, and is installed on a base. The radius of the spiral curve of each vibration arm decreases strictly according to the Fibonacci sequence R=0.168 n mm from the vibration end of the tuning fork to the mounting end on the base, and n represents the number of turns of the spiral curve of the vibration arm relative to the vibration end of the tuning fork.

[0009] Further, the material of the tuning fork is quartz, the total length and total number of turns of the spiral curve of each vibration arm are defined according to the resonant frequency of the tuning fork, and the length of each turn is equal. The specific relationship is as follows:

[0010] The relationship between the total length and total number of turns of the spiral curve and the length of each turn is,

[0011] L=N·l c

[0012] Wherein, L represents the total length of the spiral curve, N represents the total number of turns, and l c represents the length of each turn;

[0013] The relationship between the resonant frequency of the tuning fork and the total length of the spiral curve is,

[0014]

[0015] wherein f represents the resonant frequency of the tuning fork, k represents the equivalent stiffness, p represents the material density, and A represents the cross-sectional area of the vibrating arm;

[0016] The relationship between the resonant frequency of the tuning fork and the total number of turns of the spiral curve is,

[0017]

[0018] wherein h represents the square cross-sectional width of the spiral curve, determined by the wafer, R0 represents the initial radius of the vibrating end, and E represents the Young's modulus of the material of the tuning fork.

[0019] The relationship between the equivalent mass of the vibrating arm of the tuning fork and the material density, the cross-sectional area of the vibrating arm, and the total length of the spiral curve is,

[0020] m∝pAL

[0021] wherein m represents the equivalent mass of the vibrating arm of the tuning fork.

[0022] The relationship between the mechanical energy storage density of the tuning fork and the total mechanical energy in the resonance process, the cross-sectional area of the vibrating arm, and the total length of the spiral curve is,

[0023]

[0024] wherein E mech represents the total mechanical energy in the resonance process of the tuning fork.

[0025] The double helix structure of the Fibonacci sequence arrangement radius significantly extends the length of the vibrating arm in a limited space through winding design. The increase in the length of the vibration path means that more material participates in vibration, thereby increasing the equivalent mass and mechanical energy storage density of the tuning fork. The longer path means that more mechanical energy can be stored at the same vibration frequency, thereby reducing energy dissipation and improving the quality factor (Q value).

[0026] The decreasing radius pattern of the Fibonacci sequence optimizes the stress distribution of the vibrating arm during vibration. During vibration, the spiral radius near the base is smaller and bears a larger fixed constraint force, while the larger radius near the vibrating end provides more freedom. This gradual design gradually transitions the stress from the base to the vibrating end, avoiding the stress concentration phenomenon commonly seen in traditional straight-arm tuning forks. Stress concentration can cause local mechanical energy loss and material fatigue. The decreasing radius of the Fibonacci sequence reduces stress concentration points through smooth geometric transitions, thereby reducing damping effects and improving the Q value.

[0027] The spiral structure of the Fibonacci sequence has natural geometric stability, which reduces the excitation of unintended vibration modes and reduces the coupling effect of environmental noise, thereby enhancing the anti-interference ability of the tuning fork in the light-induced thermoelastic spectroscopy (LITES) system.

[0028] As a preferred technical solution, one end of the tuning fork is firmly fixed to the base to ensure that the tuning fork can vibrate freely.

[0029] Photothermoelastic spectroscopy is a highly sensitive gas detection technology that exploits the interaction between laser light and a target gas to generate a detectable signal. When a laser is irradiated on a gas, the gas absorbs the light energy and generates localized heating, leading to thermal expansion and pressure waves (i.e., sound waves). This is the photothermoelastic effect. The resulting sound waves act on a tuning fork, causing it to vibrate at its resonant frequency with an amplitude proportional to the gas concentration. By measuring this amplitude, the gas concentration can be inferred. The vibration of the tuning fork is converted into an electrical signal through the piezoelectric effect or other detection methods. This electrical signal is amplified and analyzed to ultimately produce a quantitative gas detection result.

[0030] Furthermore, during gas detection using photothermoelastic spectroscopy, the laser beam passes through the intersection of the gap between the two spiral vibrating arms of the tuning fork, ensuring good integration with the photothermoelastic spectroscopy system. The intersection is the area where the distance between the two arms is smallest, and the sound waves here act most directly and effectively on the tuning fork, stimulating resonance to the greatest extent. The laser path through the intersection ensures the repeatability and consistency of each measurement, avoiding signal fluctuations caused by optical path offset. The laser beam passes through the gap instead of directly irradiating the arm, reducing noise caused by reflection or scattering and improving detection clarity.

[0031] One of the technical solutions of the present invention is to provide a method for preparing the double-helix structure photothermoelastic spectroscopy tuning fork, which comprises the following steps:

[0032] S1, cutting quartz to obtain quartz wafers;

[0033] S2. defining a double helix pattern of a tuning fork, uniformly coating a photoresist on the surface of a quartz wafer, exposing, developing, and photoetching a double helix pattern on the photoresist;

[0034] S3, transferring the double helix pattern defined by photolithography onto a quartz wafer by etching to form a double helix structure;

[0035] S4. Depositing electrodes on the surface of the double helix structure to obtain a photothermoelastic spectroscopy tuning fork of the double helix structure.

[0036] Furthermore, in step S1, the single crystal quartz is cut by AT cutting, and the excellent temperature stability and piezoelectric performance of AT cutting are utilized to ensure that the quartz wafer is cut along the appropriate crystal direction, thereby optimizing the piezoelectric effect and mechanical properties.

[0037] The spiral tuning fork usually has a complex double spiral structure and a long vibration path, which makes it more sensitive to temperature fluctuations. If the resonant frequency shifts due to temperature changes, it will directly affect the accuracy and repeatability of the detection. One of the significant features of AT-cut quartz crystal is that its resonant frequency drifts very little when the temperature changes, close to zero temperature coefficient. AT-cut ensures that the tuning fork maintains a stable resonant frequency under different environmental conditions, ensuring the reliable operation of the system.

[0038] AT-cut is along the crystal direction of the quartz crystal, which can maximize the piezoelectric effect of quartz. When the spiral tuning fork is excited by external excitation and vibrates, the AT-cut quartz crystal can ensure that it generates a strong and stable electrical signal. This efficient piezoelectric conversion is particularly critical for capturing weak acoustic wave signals in the photo-thermal-elastic spectroscopy system.

[0039] The vibration mode of the spiral tuning fork (such as symmetric vibration) has specific requirements for its mechanical properties and crystal direction. The crystal direction provided by AT-cut highly matches the geometry of the double spiral structure, which can optimize the mechanical stiffness and vibration characteristics of the tuning fork. This adaptability ensures that the tuning fork has a high Q value and stable vibration amplitude at resonance. High Q value means lower energy loss and stronger signal response, which is crucial for improving detection sensitivity and stability.

[0040] As a preferred technical solution, the double spiral pattern of the tuning fork is defined using a high-precision photoetching machine in step S2, and 3D photoetching is used for exposure to ensure the geometric accuracy of the double spiral pattern, ensuring that the line width, pitch, radius, and three-dimensional shape of the spiral curve are consistent with the design, which directly determines the stability of the resonant frequency, Q value, and vibration mode of the tuning fork.

[0041] Further, the photoresist in step S2 is selected from positive photoresist or negative photoresist, and the light source for exposure emits ultraviolet light, deep ultraviolet light, or electron beam, and is developed using AZ300MIF developer, SU-8 developer, or tetramethylammonium hydroxide (TMAH) solution.

[0042] As a preferred technical solution, the positive photoresist is selected from AZ1500 or AZ P4620, the negative photoresist is selected from SU-8, NR9-1000PY, or HSQ, the wavelength of the ultraviolet light is 365 nm or 405 nm, the wavelength of the deep ultraviolet light is 193 nm or 248 nm, and the solvent of the tetramethylammonium hydroxide solution is water with a concentration of 0.24-0.28 mol / L.

[0043] Further, in step S3, the double helix pattern defined by photolithography is accurately transferred to the quartz wafer by deep reactive ion etching (DRIE). The etching gas for DRIE is selected from sulfur hexafluoride (SF6) or carbon tetrafluoride (CF4), and the passivation gas is selected from octafluorocyclobutane (C4F8) or trifluoromethane (CHF3). By utilizing the high aspect ratio etching characteristics of DRIE, the etching depth and sidewall smoothness are strictly controlled, and the adverse effects of surface defects on Q value are reduced.

[0044] Further, in step S4, the electrode is deposited on the surface of the double helix structure by evaporation or sputtering. The electrode material is selected from one of gold and silver, ensuring that the electrode uniformly covers the surface of the vibrating arm and is distributed along the spiral path. Before cleaning to remove residual photoresist, the deposited electrode will definitely fall on the exposed quartz wafer double helix pattern after etching due to the blocking of the photoresist. The electrode pattern matches the spiral geometry, and the covering electrode is used to excite and detect the piezoelectric vibration of the tuning fork.

[0045] Further, after depositing the electrode in step S4, the tuning fork is cleaned and polished. Cleaning removes residual photoresist and other impurities, and polishing reduces surface roughness and defects, optimizing the mechanical strength and elastic properties of the vibrating arm. The smooth surface reduces stress concentration points and reduces the possibility of crack propagation or mechanical fatigue during vibration, thereby improving the long-term stability of the tuning fork.

[0046] Cleaning and polishing synergistically optimize the surface quality of the tuning fork, reduce energy loss, improve vibration mode stability, and together achieve the improvement of mechanical properties and Q value, ensuring the high sensitivity and reliability of the double helix tuning fork in the photothermal elastic spectroscopy system.

[0047] Further, one or more of acetone, isopropyl alcohol, water, and ethanol is used to clean the tuning fork, and aluminum oxide (Al2O3), silicon dioxide (SiO2), or cerium oxide (CeO2) is used to polish the tuning fork.

[0048] Compared with the prior art, the present application has the following beneficial effects:

[0049] (1) The present application replaces the straight arm of the traditional tuning fork with a double helix structure. The radius of each spiral curve decreases according to the Fibonacci sequence R = 0.168 n mm, and the spiral-shaped tuning fork can increase the vibration path length in a limited space, thereby improving the mechanical energy storage density. The quality factor (Q value) of the tuning fork is higher than that of the traditional tuning fork. High Q value means strong energy storage capacity and low loss, which can effectively improve the detection sensitivity and play a key role in photothermal elastic spectroscopy detection.

[0050] (2) The spiral-shaped tuning fork of the present invention optimizes stress distribution, thereby reducing local stress concentration, reducing energy loss in mechanical vibration, and improving Q value and long-term stability;

[0051] (3) The double helix structure of the present invention has good geometric stability, which can reduce the influence of external vibration, improve the Q value while enhancing the ability to resist lateral vibration interference, reduce environmental noise coupling, and improve working stability in complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 Schematic diagram of the process for preparing a photothermoelastic spectroscopy tuning fork with a double helix structure according to an embodiment of the present invention;

[0053] Figure 2 Schematic diagram of the structure of a double-helix photothermoelastic spectroscopy tuning fork in an embodiment of the present invention.

[0054] Description of the marks in the figure:

[0055] 1—tuning fork, 2—base. DETAILED DESCRIPTION

[0056] The present invention is described in detail below with reference to specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0057] Unless otherwise specified, the equipment used in the following examples are all conventional equipment in the art; the reagents used are all commercially available products or prepared by conventional methods in the art unless otherwise specified. Anything not described in detail in the following examples can be achieved by conventional experimental means in the art.

[0058] The following steps are generally carried out at room temperature unless otherwise specified.

[0059] Example 1:

[0060] A double helix photothermoelastic spectroscopy tuning fork, such as Figure 2 As shown, a pair of vibrating arms of the tuning fork 1 are wound to form a double helix structure. The tuning fork 1 is mounted on the base 2. The radius of the spiral curve of each vibrating arm from the vibrating end of the tuning fork 1 to the mounting end on the base 2 strictly follows the Fibonacci sequence R = 0.168. n mm decreases, and n represents the number of turns of the spiral curve of the vibrating arm relative to the vibrating end of the tuning fork 1;

[0061] The material of the tuning fork 1 is quartz. The total length and total number of turns of the spiral curve of each vibrating arm are defined according to the resonant frequency of the tuning fork 1. The length of each turn is equal. The specific relationship is as follows:

[0062] The relationship between the total length of the spiral curve and the total number of turns and the length of each turn is,

[0063] L = N·l c

[0064] where L represents the total length of the spiral curve, N represents the total number of turns, and l represents the length of each turn; c

[0065] The relationship between the resonant frequency of the tuning fork 1 and the total length of the spiral curve is,

[0066]

[0067] where f represents the resonant frequency of the tuning fork 1, k represents the equivalent stiffness, p represents the material density, and A represents the cross-sectional area of the vibrating arm;

[0068] The relationship between the resonant frequency of the tuning fork 1 and the total number of turns of the spiral curve is,

[0069]

[0070] where h represents the square cross-sectional width of the spiral curve, which is determined by the wafer, R0 represents the initial radius of the vibrating end, and E represents the Young's modulus of the material of the tuning fork 1;

[0071] In this embodiment, the resonant frequency of the tuning fork 1 is 16 kHz, the total length of the spiral curve of each vibrating arm is 10 mm, and the total number of turns is 5;

[0072] One end of the tuning fork 1 is firmly fixed to the base 2 to ensure that the tuning fork 1 can freely vibrate;

[0073] When detecting gas by light-induced thermal elastic spectroscopy (LITES), the laser beam passes through the intersection of the gap between the two spiral vibrating arms of the tuning fork 1, ensuring good integration with the light-induced thermal elastic spectroscopy system. The intersection is the area with the smallest distance between the two arms, and the sound wave acts most directly and effectively on the tuning fork 1, which can maximize the resonance. The laser path through the intersection ensures the repeatability and consistency of each measurement, avoiding signal fluctuations caused by optical path deviation. The laser beam passes through the gap rather than directly irradiating the arm body, reducing noise caused by reflection or scattering and improving the clarity of detection.

[0074] The relationship between the equivalent mass of the vibrating arm of the tuning fork 1 and the material density, the cross-sectional area of the vibrating arm, and the total length of the spiral curve is,

[0075] m ∝ pAL

[0076] where m represents the equivalent mass of the vibrating arm of the tuning fork 1;

[0077] ​The relationship between the mechanical energy storage density of the tuning fork 1 and the total mechanical energy in the resonance process, the cross-sectional area of the vibration arm, and the total length of the spiral curve is,

[0078]

[0079] where E mech represents the total mechanical energy in the resonance process of the tuning fork 1.

[0080] The double helix structure of the Fibonacci sequence arrangement radius significantly extends the length of the vibration arm in a limited space through winding design. The increase in vibration path length means that more material is involved in vibration, thereby increasing the equivalent mass and mechanical energy storage density of the tuning fork 1. A longer path means that more mechanical energy can be stored at the same vibration frequency, thereby reducing energy dissipation and improving the quality factor (Q value).

[0081] The decreasing radius pattern of the Fibonacci sequence optimizes the stress distribution of the vibration arm during vibration. During vibration, the smaller spiral radius near the base 2 bears a larger fixed constraint force, while the larger radius near the vibration end provides more freedom. This gradual design gradually transitions the stress from the base 2 to the vibration end, avoiding the stress concentration phenomenon commonly seen in traditional straight-arm tuning forks. Stress concentration can cause local mechanical energy loss and material fatigue. The decreasing radius of the Fibonacci sequence reduces stress concentration points through smooth geometric transitions, thereby reducing damping effects and improving the Q value.

[0082] The spiral structure of the Fibonacci sequence has natural geometric stability, which reduces the excitation of unintended vibration modes and reduces the coupling effect of environmental noise, thereby enhancing the anti-interference ability of the tuning fork 1 in the photo-thermal elastic spectroscopy system.

[0083] Photo-thermal elastic spectroscopy is a high-sensitivity gas detection technology, the core of which is to use the interaction between laser and target gas to produce a detectable signal. When laser irradiates the gas, the gas absorbs light energy and produces local heating, leading to thermal expansion and pressure waves (i.e. sound waves), which is the photo-thermal elastic effect. The generated sound waves act on the tuning fork 1, causing it to vibrate at a resonance frequency with an amplitude proportional to the gas concentration. By measuring the amplitude, the concentration of the gas can be calculated. The vibration of the tuning fork 1 is converted into an electrical signal through the piezoelectric effect or other detection methods. The electrical signal is amplified and analyzed to ultimately obtain the quantitative detection result of the gas.

[0084] The preparation method of the photo-thermal elastic spectroscopy tuning fork with the above-mentioned double helix structure is shown in Figure 1 , and the specific steps are as follows:

[0085] S1, cutting quartz to obtain a quartz wafer;

[0086] S2, define the double helix pattern of tuning fork 1, uniformly coat photoresist on the surface of the quartz wafer, expose, develop, and photoetch the double helix pattern on the photoresist;

[0087] S3, transfer the photoetched double helix pattern to the quartz wafer by etching to form a double helix structure;

[0088] S4, deposit electrodes on the surface of the double helix structure to obtain a photo-induced thermal elastic spectrum tuning fork with a double helix structure.

[0089] Embodiment 2:

[0090] A photo-induced thermal elastic spectrum tuning fork with a double helix structure and a preparation method thereof, which are basically the same as those of embodiment 1, wherein the specific steps are as follows:

[0091] S1, cut a single crystal quartz by using AT cutting, use the excellent temperature stability and piezoelectric properties of AT cutting to ensure that the quartz wafer is cut along the appropriate crystal direction, optimize the piezoelectric effect and mechanical properties, and obtain a quartz wafer;

[0092] S2, define the double helix pattern of tuning fork 1 using a high-precision photoetching machine, uniformly coat SU-8 negative photoresist on the surface of the quartz wafer, and perform 365 nm wavelength ultraviolet light exposure by using 3D photoetching to ensure the geometric accuracy of the double helix pattern, ensure that the line width, pitch, radius and three-dimensional shape of the spiral curve are consistent with the design, which directly determines the stability of the resonant frequency, Q value and vibration mode of the tuning fork 1, and develop using SU-8 developer to photoetch the double helix pattern on the photoresist;

[0093] S3, precisely transfer the photoetched double helix pattern to the quartz wafer by using deep reactive ion etching (DRIE), select sulfur hexafluoride (SF6) as the etching gas and octafluorocyclobutane (C4F8) as the passivation gas, use the characteristics of deep reactive ion etching with high aspect ratio, strictly control the etching depth and sidewall smoothness, and reduce the adverse effects of surface defects on the Q value to form a double helix structure;

[0094] S4, deposit electrodes on the surface of the double helix structure by sputtering, select gold as the material of the electrodes, ensure that the electrodes uniformly cover the surface of the vibration arm and are distributed along the spiral path, and before cleaning to remove residual photoresist, due to the blocking of the photoresist, the deposited electrodes will definitely fall on the exposed double helix pattern part of the quartz wafer after etching, the electrode pattern matches the spiral geometric shape, the covering electrode is used to excite and detect the piezoelectric vibration of the tuning fork 1, and a photo-induced thermal elastic spectrum tuning fork with a double helix structure is obtained;

[0095] S5, clean the tuning fork 1 with acetone, isopropyl alcohol and deionized water respectively to remove residual photoresist and other impurities;

[0096] S5, polishing the tuning fork 1 using aluminum oxide (AI2O3), the polishing reduces surface roughness and defects, optimizes the mechanical strength and elastic properties of the vibrating arms, the smooth surface reduces stress concentration points, reduces possible crack propagation or mechanical fatigue during vibration, thereby improving the long-term stability of the tuning fork 1.

[0097] The spiral tuning fork 1 generally has a complex double spiral structure and a long vibration path, which makes it more sensitive to temperature fluctuations. If the resonant frequency shifts due to temperature changes, it will directly affect the accuracy and repeatability of the detection. One of the remarkable features of the AT-cut quartz crystal is that its resonant frequency has minimal drift when the temperature changes, close to zero temperature coefficient. The AT-cut ensures that the tuning fork 1 maintains a stable resonant frequency under different environmental conditions through its excellent temperature stability, thereby ensuring the reliable operation of the system.

[0098] The AT-cut is made along the crystal direction of the quartz crystal, which can maximize the piezoelectric effect of the quartz. When the spiral tuning fork is excited and vibrates, the AT-cut quartz crystal can ensure that it generates a strong and stable electrical signal. This efficient piezoelectric conversion is particularly crucial for capturing weak acoustic wave signals in the photothermal elastic spectroscopy system.

[0099] The vibration mode (such as symmetric vibration) of the spiral tuning fork 1 has specific requirements for its mechanical properties and crystal direction. The AT-cut provides a crystal direction that highly matches the geometry of the double spiral structure, which can optimize the mechanical stiffness and vibration characteristics of the tuning fork. This adaptability ensures that the tuning fork has a high Q value and stable vibration amplitude at resonance. A high Q value means lower energy loss and stronger signal response, which is crucial for improving detection sensitivity and stability.

[0100] Cleaning and polishing synergistically optimize the surface quality of the tuning fork 1, reduce energy loss, improve vibration mode stability, and together achieve the improvement of mechanical properties and Q value, ensuring the high sensitivity and reliability of the double spiral tuning fork 1 in the photothermal elastic spectroscopy system.

[0101] Comparative Example:

[0102] A photothermal elastic spectroscopy tuning fork uses a traditional straight arm structure instead of the double spiral structure of Example 1. The vibrating arms are two parallel straight arms, 5mm in length, 0.1mm in cross-sectional width, and 0.05mm in thickness, which is the same size as the cross-sectional size of the double spiral arms of Example 1.

[0103] The preparation method of the above-mentioned photo-thermal elastic spectrum tuning fork adopts the AT-cut quartz of Example 2, photoetching (SU-8 photoresist, ultraviolet light 365 nm exposure, SU-8 developer), deep reactive ion etching (sulfur hexafluoride etching gas, octafluorocyclobutane passivation gas), gold electrode sputtering and cleaning and polishing (acetone, isopropyl alcohol, deionized water cleaning, aluminum oxide polishing) processes to ensure that other parameters are consistent except the vibration arm structure.

[0104] The above-mentioned tuning fork is detected or tested as follows, and then the detection or test results are analyzed.

[0105] Test conditions:

[0106] Environment, air medium, 25℃, 1atm;

[0107] Sample quantity, 5 samples per group (Example 2 and comparative example) are tested to ensure data reliability;

[0108] Laser parameters, power 10mW, modulation frequency 16kHz;

[0109] Test example 1:

[0110] The above-mentioned tuning fork is tested for resonance frequency and Q value, and the specific steps are as follows:

[0111] The tuning fork is fixed on the base and connected to the impedance analyzer;

[0112] In the air medium (25℃, 1atm), an electrical signal is applied to excite the tuning fork, and the resonance frequency and Q value are recorded;

[0113] The measurement is repeated 5 times, and the average value is taken.

[0114] Test example 2:

[0115] The above-mentioned tuning fork is tested for frequency stability, and the specific steps are as follows:

[0116] In the environmental control box, the temperature is raised from 20℃ to 40℃ (step 5℃), and the resonance frequency change is recorded;

[0117] The frequency drift rate (ppm / ℃) is calculated.

[0118] Test example 3:

[0119] The above-mentioned tuning fork is tested for anti-interference ability, and the specific steps are as follows:

[0120] On the vibration table, transverse vibration (frequency 1-100Hz, amplitude 0.1g) is applied, and the Q value change is measured;

[0121] In the photo-thermal elastic spectrum system, the laser is used to excite sound waves, and the response signal (signal-to-noise ratio, SNR) of the tuning fork to weak sound waves is recorded.

[0122] The test results of the tuning forks in Example 2 and Comparative Examples are shown in Table 1.

[0123] The test results of the tuning forks in Example 2 and Comparative Examples are shown in Table 1.

[0124] Parameters Example 2 (double-helical tuning fork) Comparative Example (straight-arm tuning fork) Resonance frequency (kHz) 16.0±0.1 16.0±0.1 Quality factor (Q value) 20,000±500 10,000±300 Frequency drift rate (ppm / °C) 2.5±0.3 5.0±0.5 Q value variation rate (vibration disturbance) -5% (0.1 g, 1-100 Hz) -15% (0.1 g, 1-100 Hz) Signal-to-noise ratio (SNR, dB) 65±2 50±3

[0125] As shown in Table 1, due to the elongated vibration path, optimized stress distribution, enhanced geometric stability and improved sound wave excitation efficiency of the double helix structure of the tuning fork in the examples, the Q value, frequency stability, anti-interference ability and signal-to-noise ratio of the double helix structure of the tuning fork in the examples are significantly better than those of the straight arm structure in the comparative examples. The tuning fork with double helix structure has high sensitivity, high stability and anti-interference ability in the photo-thermal elastic spectroscopy system.

[0126] The above description of the examples is for the purpose of enabling a person of ordinary skill in the art to understand and use the invention. Those skilled in the art can easily make various modifications to these examples and apply the general principles described herein to other examples without inventive labor. Therefore, the present invention is not limited to the above examples, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A double-helix photothermoelastic spectroscopy tuning fork, characterized in that: A pair of vibrating arms of the tuning fork (1) are wound to form a double helix structure. The tuning fork (1) is mounted on a base (2). The radius of the spiral curve of each vibrating arm is R=0.168 from the vibrating end of the tuning fork (1) to the mounting end on the base (2). n mm decreases, and n represents the number of turns of the spiral curve of the vibrating arm relative to the vibrating end of the tuning fork (1).

2. The double-helix photothermoelastic spectroscopy tuning fork according to claim 1, characterized in that: The tuning fork (1) is made of quartz, and the total length and total number of turns of the spiral curve of each vibration arm are defined according to the resonant frequency of the tuning fork (1), and the length of each turn is equal.

3. The double-helix photothermoelastic spectroscopy tuning fork according to claim 1, characterized in that: During gas detection by photothermoelastic spectroscopy, a laser beam passes through the intersection of the gap between the two spiral vibration arms of a tuning fork (1).

4. A method for preparing a double helix structure photothermoelastic spectroscopy tuning fork according to any one of claims 1 to 3, characterized in that: The method comprises the following steps: S1, cutting quartz to obtain quartz wafers; S2, defining a double helix pattern of the tuning fork (1), coating a photoresist on the surface of a quartz wafer, exposing, developing, and etching a double helix pattern on the photoresist; S3, transferring the double helix pattern defined by photolithography onto a quartz wafer by etching to form a double helix structure; S4. Depositing electrodes on the surface of the double helix structure to obtain a photothermoelastic spectroscopy tuning fork of the double helix structure.

5. The method for preparing a double-helix photothermoelastic spectroscopy tuning fork according to claim 4, characterized in that: In step S1, single crystal quartz is cut using an AT cutting method.

6. The method for preparing a double-helix photothermoelastic spectroscopy tuning fork according to claim 4, characterized in that: In step S2 , the photoresist is selected from positive photoresist or negative photoresist, the corresponding exposure light source emits ultraviolet light, deep ultraviolet light or electron beam, and is developed using AZ300MIF developer, SU-8 developer or tetramethylammonium hydroxide solution.

7. The method for preparing a double-helix photothermoelastic spectroscopy tuning fork according to claim 4, characterized in that: In step S3, the double helix pattern defined by photolithography is transferred to the quartz wafer by deep reactive ion etching. The etching gas for deep reactive ion etching is selected from sulfur hexafluoride or carbon tetrafluoride, and the passivation gas is selected from octafluorocyclobutane or trifluoromethane.

8. The method for preparing a double-helix photothermoelastic spectroscopy tuning fork according to claim 4, characterized in that: In step S4, an electrode is deposited on the surface of the double helix structure by evaporation or sputtering, and the material of the electrode is selected from one of gold and silver.

9. The method for preparing a double-helix photothermoelastic spectroscopy tuning fork according to claim 4, characterized in that: After depositing the electrodes in step S4, the tuning fork (1) is cleaned and polished.

10. The method for preparing a double-helix photothermoelastic spectroscopy tuning fork according to claim 9, characterized in that: The tuning fork (1) is cleaned using one or more of acetone, isopropyl alcohol, water, and ethanol, and is polished using aluminum oxide, silicon dioxide, or cerium oxide.

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