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.

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.

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.

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.

High-precision low-power quartz tuning fork temperature sensor with optimized resonance excitation

This paper presents the design,fabrication,and characterization of a quartz tuning fork temperature sensor based on a new ZY-cut quartz crystal bulk acoustic wave resonator vibrating in a flexural mode.Design and performance analysis of the quartz tuning fork temperature sensor were conducted and the thermal sensing characteristics were examined by measuring the resonance frequency shift of this sensor caused by an external temperature.Finite element method is used to analyze the vibratory modes and optimize the structure of the sensor.The sensor prototype was successfully fabricated and calibrated in operation from 0 to 100 ℃ with the thermo-sensitivity of 70×10-6/℃.Experimental results show that the sensor has high thermo-sensitivity,good stability,and good reproducibility.This work presents a high-precision low-power temperature sensor using the comprehensive thermal characterization of the ZY-cut quartz tuning fork resonator.

INVESTIGATION OF SENSITIVITY FOR SILICON MICROMECHANICAL TUNING-FORK GYROSCOPE

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An automated AFM for nanoindentation and force related measurements

A fully automated atomic force microscope(AFM)is presented.The mechanical motion of the AFM stage was controlled by three steppers.The fine motion of the AFM was controlled by an MCL one-axis piezo plate.A32.768kHz crystal tuning fork(TF)was used as the transducer with a probe attached.An acoustic sensor was used to measure the interactions between the probe and the sample.An SR850lock-in amplifier was used to monitor the TF signals.An additional lock-in amplifier was used to monitor the acoustic signal.A field programmable gate array(FPGA)board was used to collect the data in automatic mode.The main controller was coded with LabVIEW,which was in charge of Z-axis scan,signal processing and data visualization.A manual mode and an automatic mode were implemented in the controller.Users can switch the two modes at any time during the operation.This AFM system showed several advantages during the test operations.It is simple,flexible and easy to use.

Sensitive carbon monoxide detection based on light-induced thermoelastic spectroscopy with a fiber-coupled multipass cell[Invited]

sensor based on light-induced thermoelastic spectroscopy(LITES)with a fiber-coupled multipass cell was demonstrated for carbon monoxide(CO)detection.The fiber-coupled structure has the merits of reducing optical interference and difficulty in optical alignment and increasing system robustness.A 1.57 nm continuous wave distributed feedback diode laser was used as the excitation source.A minimum detection limit of 9 ppm was obtained,and the calculated normalized noise equivalent absorption coefficient was 1.15×10^(-7)cm^(-1)•W•Hz^(-1/2).The reported CO-LITES sensor showed excellent linear concentration response and system stability.