VIBRATION MEASUREMENT OF DOUBLE-ENDED TUNING FORKS RESONATOR

To enhance the coherence and reliability of the double-ended tuning fork （DETF） resonator, a measurement system of resonator vibration is presented to check its dynamic characteristics. Laser Doppler techniques are utilized and the relation between DETF vibration velocity and output current of photodetector is obtained. Resonator vibration equation is also analyzed and its driving power only depends on the direct current bias voltage and the amplitude of alternative voltage. Furthermore, a special resonator driving control circuit based on measurement is designed. The amplitude and frequency of circuit is controlled by a computer so that highly stable and strong driving signal can be output. Experiments on driving and measuring double-ended tuning fork have been done, The frequency of driving signal is 8 kHz and the peak-to-peak value of driving voltage is 140 V. Experimental results indicate resonator can be drived stably by driving control circuit and dynamic characteristics of DETF may be measured in real time.

A highly sensitive LITES sensor based on a multi-pass cell with dense spot pattern and a novel quartz tuning fork with low frequency

A highly sensitive light-induced thermoelectric spectroscopy(LITES)sensor based on a multi-pass cell(MPC)with dense spot pattern and a novel quartz tuning fork(QTF)with low resonance frequency is reported in this manuscript.An erbi-um-doped fiber amplifier(EDFA)was employed to amplify the output optical power so that the signal level was further enhanced.The optical path length(OPL)and the ratio of optical path length to volume(RLV)of the MPC is 37.7 m and 13.8 cm^(-2),respectively.A commercial QTF and a self-designed trapezoidal-tip QTF with low frequency of 9461.83 Hz were used as the detectors of the sensor,respectively.The target gas selected to test the performance of the system was acetylene(C2H2).When the optical power was constant at 1000 mW,the minimum detection limit(MDL)of the C2H2-LITES sensor can be achieved 48.3 ppb when using the commercial QTF and 24.6 ppb when using the trapezoid-al-tip QTF.An improvement of the detection performance by a factor of 1.96 was achieved after replacing the commer-cial QTF with the trapezoidal-tip QTF.

Electrode design for multimode suppression of aluminum nitride tuning fork resonators

This paper is focused on electrode design for piezoelectric tuning fork resonators.The relationship between the performance and electrode pattern of aluminum nitride piezoelectric tuning fork resonators vibrating in the in-plane flexural mode is investigated based on a set of resonators with different electrode lengths,widths,and ratios.Experimental and simulation results show that the electrode design impacts greatly the multimode effect induced from torsional modes but has little influence on other loss mechanisms.Optimizing the electrode design suppresses the torsional mode successfully,thereby increasing the ratio of impedance at parallel and series resonant frequencies(R_(p)/R_(s))by more than 80%and achieving a quality factor(Q)of 7753,an effective electromechanical coupling coefficient(kt_(eff)^(2))of 0.066%,and an impedance at series resonant frequency(R_(m))of 23.6 kΩ.The proposed approach shows great potential for high-performance piezoelectric resonators,which are likely to be fundamental building blocks for sensors with high sensitivity and low noise and power consumption.

Compensation of Parasitic Capacitance of Quartz Tuning Fork in AFM

We have built an atomic force microscope using a quartz tuning fork as sensor. The excitation method we adopted, the electrical excitation, introduces stray capacitance into the signal-processing circuit. In this report, we demonstrated a simple but effective method to compensate for this parasitic capacitance by adding a compensator circuit consisting of an inverting amplifier and a capacitor. The capacitor is connected in series with the inverting amplifier and the compensator is connected in parallel with the quartz tuning fork. The resonance curve of the system measured after adding the homemade compensator resembles that of a pure RLC circuit, meaning that the stray capacitance is successfully eliminated. Furthermore, we tried to use our equipment to measure PDMS sample and got clean data. This system can be further combined with confocal microscope and diamond with NV defect to build scanning NV magnetometry.

Finite Element Simulation of the Vibratory Characteristics for Quartz Tuning Fork Gyroscope

The micro quartz crystal tuning fork gyroscope is a new type of vibratory gyroscope. The gyroscope should be analyzed and simulated early in the design stage in order to offer reliable basis for design and to shorten the period of development. Thus the vibratory characteristics of the gyroscope is simulated with the finite element method of coupled field. The optimum exciting frequency and the factors which influence the gyroscope sensitivity are determined. The method for adjusting the frequency deviation between driving and detecting modes is also proposed.

Silicon carbide resonant tuning fork for microsensing applications in high-temperature and high G-shock environments

We present the fabrication and testing of a silicon carbide （SiC） balanced mass doublended tuning fork that survives harsh environments without compromising the device strain sensitivity and resolution bandwidth. The device features a material stack that survives corrosive environments and enables high-temperature operation. To perform hightemperature testing, a specialized setup was constructed that allows the tuning fork to be characterized using traditional silicon electronics. The tuning fork has been operated at 600°C in the presence of dry steam for short durations. This tuning fork has also been tested to 64 000 G using a hard-launch, soft-catch shock implemented with a light gas gun. However, the device still has a strain sensitivity of 66 Hz/μe and strain resolution of 0. 045 μe in a 10 kHz bandwidth. As such, this balanced-mass double-ended tuning fork can be used to create a variety of different sensors including strain gauges, accelerometers, gyroscopes, and pressure transducers. Given the adaptable fabrication process flow, this device could be useful to micro-electro-mechanical systems （MEMS） designers creating sensors for a variety of different applications.

INVESTIGATION OF SENSITIVITY FOR SILICON MICROMECHANICAL TUNING-FORK GYROSCOPE

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Improved Design and Modeling of Micromachined Tuning Fork Gyroscope Characterized by High Quality Factor

This paper proposes an improved design of micromachined tuning fork gyroscope （M-TFG） to decouple the cross talk between driving and sensing directions better and to increase resolution. By employing dual-folds spring suspension, the drive mode and the sense mode are mechanically decoupled. Through careful layout design of the location of the dual-folds spring suspension and the drive combs, the mechanical coupling effect is further decreased by isolating the unwanted excitation from detection. The quality factor investigation demonstrates that high quality factor can be attained by using this structure, which can bring in accurate resolution. As a result, this design has the potential to accomplish low bias drift and accurate resolution for initial level applications.

Highly sensitive CO_(2)-LITES sensor based on a self-designed low-frequency quartz tuning fork and fiber-coupled MPC

A highly sensitive carbon dioxide(CO_(2))sensor based on light-induced thermoelastic spectroscopy(LITES)utilizing a selfdesigned low-frequency quartz tuning fork(QTF)and a fiber-coupled multipass cell(MPC)is reported in this paper.The QTF with a low resonant frequency of 8675 Hz and a high Q factor of 11,675.64 was used to improve its energy accumulation time and the sensor’s signal level.The MPC with the fiber-coupled structure and optical length of 40 m was adopted to significantly increase the gas absorbance and reduce the optical alignment difficulty as well as improve the robustness of the sensor system.A distributed feedback(DFB),near-infrared diode laser with an emission wavelength of 1.57μm was used as an excitation source.The experimental results showed that this CO_(2)-LITES sensor had an excellent linear response to CO_(2) concentrations.The minimum detection limitation(MDL)of this CO_(2)-LITES sensor was obtained to be 445.91 ppm,and it could be improved to 47.70 ppm(parts per million)when the integration time of the system reached 500 s.Further improvement methods for the detection performance of such sensors were also discussed.

基于Chip-on-TEC的高精度晶体振荡器研究

提高晶体振荡器频率稳定度的首要手段是保持温度的稳定。基于热电制冷器具有的恒温特性,采用Chip-on-TEC方法,给出了一种高精度的晶体振荡器的设计方案。利用多物理仿真软件,针对商用的音叉型石英晶体,首次建立了32.768 kHz石英晶片的完整的有限元多物理场仿真模型。仿真结果表明,晶体的谐振频率与商用产品完全相同;基于TEC的晶体振荡器设计方案可以使得晶片温度变化低至0.008℃,对应的频率稳定度5.4×10^(-9)。考虑到高精度切型晶片材料的非易得性,所给出的方案为采用低精度切型晶片设计高精度的晶体振荡器提供了思路。

双通道离轴石英增强光声光谱气体传感器

为了消除杂散光激励石英音叉产生的光热信号对气体检测性能的影响,采用离轴配置谐振管,将两只中央开有槽口的谐振管平行于音叉正面放置在两侧,从而实现了探测光束与石英音叉的隔离,同时降低了系统组装和光路调整的复杂度。将光纤准直器、谐振管、石英音叉、直角棱镜和不锈钢气室进行集成,研制了一种尺寸仅为5.4 cm×4.0 cm×1.5 cm的光声检测模块,在此基础上,建立了一种光声光谱气体检测系统,采用中心波长为1533 nm的分布反馈激光器,通过检测乙炔气体来评估系统性能。实验结果表明,光声信号与气体浓度之间呈现良好的线性-关系,线性拟合优度为0.991。系统的1σ检测下限和对应归一化噪声等效吸收系数分别为11.6×10^(-6)和6.7×10^(-9)W·cm^(-1)·Hz^(-1/2)。对系统的Allan方差分析结果表明,当平均时间为0.5 s时,系统的检测下限为10.22×10^(-6),当平均时间为50 s时,系统检测下限可以达到1.20×10^(-6)。所研制的微小型双通道离轴石英增强光声光谱传感器系统具有体积小、价格低廉、灵敏度高等优点,有利于实现便携式气体检测。

用于痕量H_(2)S检测的音叉设计及性能分析

针对商用标准石英音叉在石英增强光声光谱(Quartz-Enhanced Photoacoustic Spectroscopy,QEPAS)应用的局限性,对声波探测器石英音叉的前6阶振动模态进行了仿真研究,通过优化石英音叉参数,分析各参数对共振频率的影响,设计了一种低共振频率且高品质因数的新型石英音叉。经过测试,该音叉共振频率为12.21 kHz,品质因数高达12068,叉指间隙为0.40 mm,与商用30.72 kHz的标准石英音叉相比,共振频率降低60.25%,叉指间隙提高2倍,能量积累时间提高1.95倍。通过优化耦合共振管长度及光源的激励位置,提高了系统的探测性能。利用波长调制和二次谐波解调技术,得到系统的二次谐波信号与H_(2)S浓度存在良好的线性关系,基于QEPAS技术探测的检测限低至186×10^(-9),实现了H2S的高灵敏度探测。

音叉式防振锤的模态分析及优化设计

通过提高防振锤谐振频率的设计一致性,可提升防振效果。以音叉式防振锤为例,研究其参数优化问题,构建模态分析参数模型,对防振锤关键技术参数进行仿真优化设计。结果表明,参数优化后音叉式防振锤固有频率与期望值近乎相同,验证了优化后参数优越性。

一次盐水精制工序在线监测仪的应用

介绍了一次盐水精制工序两碱含量在线监测仪、钙镁含量在线监测仪和氯化钠浓度在线监测仪的测量原理,对比分析了在线检测数据与人工检测数据,为稳定生产和降低成本奠定了基础。

石英单晶微机械陀螺仪研究进展

对Z切、ST切、AT切三种切割方式的石英单晶微机械陀螺仪的基本工作原理进行了阐述,梳理了不同类型陀螺仪的发展历程,重点介绍了三种石英单晶微机械陀螺仪的设计结构、性能特点及其应用场景,并从灵敏度、动态范围、稳定性、抗冲击性及工作频率等方面对三种类型石英微机械陀螺仪各自的性能优势与面临的技术挑战进行了评述,总结了当前国内外在石英单晶微机械陀螺仪研究领域的主要进展和创新点。最后,针对不同切割方式的石英单晶微机械陀螺仪的结构及工作特点,分析了其各自的优点与不足,进行了总结和对比,讨论了石英微机械陀螺仪的未来发展方向。

臭氧催化氧化污水处理装置运行中防倒流解决方案

天津某污水厂采用高效臭氧催化氧化工艺,在臭氧接触池中,溶解于水的臭氧在催化剂作用下产出极强的氧化性羟基自由基(-OH),可与污水中有机污染物快速发生氧化反应,生成易降解的有机物,从而降低污水中的化学需氧量(COD)。增加臭氧防倒流装置后,解决了水倒流引起的臭氧发生器损坏,提高了设备运行的安全性,保证了臭氧发生器稳定运行。

防爆仪表的温度组别选型难题解决办法

化工装置中存在多种爆炸性气体。防爆仪表在进行防爆选型设计时,仪表的温度组别必须满足爆炸危险区域的要求。项目中工艺介质温度过高,使防爆证书中认证的温度组别低于所在爆炸危险区域要求的组别,无法选到可以使用的音叉液位开关产品。针对此问题,深入分析温度组别防爆的基本原理,结合项目具体爆炸危险区域划分图和工艺介质特性等实际情况,提出了应对不同情形的三种解决思路:合理调整仪表位置、精细划分爆炸危险区域和对仪表防爆保温。最终使选择出的音叉液位开关符合爆炸危险区域温度组别的要求,解决了特殊工况下防爆仪表温度组别选型难题。

Silas和Densitune系统在航道工程中的应用

以连云港港15万t级航道疏浚工程施工期浮泥观测为例,介绍Densitune音叉振动密度仪、Silas适航水深测量系统和悬移质取样器的特性,并根据实测的浮泥层厚度及其分布情况,剖析Silas和Densitune系统在实际工程应用中遇到的问题,供工程设计和运营管理参考。

基于石英音叉探测器的双光谱气体检测技术

将波长调制光声光谱和光热光谱有效结合,提出了一种基于石英音叉探测器和光声光谱与光热光谱技术有效融合的双光谱气体检测技术。以大气中水汽为分析对象,利用1 392 nm附近的近红外半导体激光器搭建了一套基于石英音叉探测器的双光谱探测系统,结合波长调制技术中相位依赖特性,利用差分原理实现了波长调制光声光谱和光热光谱信号的有效叠加和增强,与传统探测方案中采用的单一光谱检测方法相比,有效利用了激光功率,实验结果显示,所提出的双光谱探测技术的总体信噪比分别是光声光谱与光热光谱信噪比的1.97和1.24倍,有效提升了系统检测灵敏度。

基于光致热弹光谱的痕量气体传感技术研究进展

光致热弹光谱(LITES)技术在痕量气体检测领域的应用性能不断提高。主要介绍了基于不同结构吸收池的LITES痕量气体传感技术、提高系统灵敏度的各种技术手段以及LITES痕量气体传感技术的光强修正方法,并对目前LITES痕量气体传感技术的研究进展进行总结,展望了进一步提高系统检测灵敏度的方法,以期LITES痕量气体传感技术在环境监测、工业安全和生命科学等领域发挥更大的作用。