Quartz Tuning Fork Research Articles

Compact all-fiber light-induced thermoelastic spectroscopy for gas sensing.

To overcome the limitations of size, optical alignment, and integration into photonic circuits in previous light-induced thermoelastic spectroscopy (LITES) using free-space optics, a compact all-fiber LITES was proposed for gas sensing. A hollow-core photonic crystal fiber was employed as a waveguide and a microcapillary gas cell simultaneously. A single-mode fiber (SMF) tip was employed to guide light on the quartz tuning fork (QTF) surface. The distance between the SMF tip and the QTF, and the light excitation position on the QTF's surface were optimized experimentally. The detection performance of the all-fiber LITES was evaluated by detecting methane, and a normalized noise equivalent absorption coefficient of ${9.66} \times {{10}^{ - 9}}\; {{\rm cm}^{ - 1}} \cdot {\rm W}\,{{\rm Hz}^{ - 1/2}}$9.66×10-9cm-1⋅WHz-1/2 was realized at a 1 atm pressure and an environmental temperature of $ {\sim} 297\;{\rm K}$∼297K. The combination of fiber sensing and LITES allows a class of LITES sensors with compact size and potential for long-distance and multi-point sensing.

Quartz-enhanced photoacoustic spectroscopic methane sensor system using a quartz tuning fork-embedded, double-pass and off-beam configuration

Development of a methane (CH4) sensor system was reported based on a novel quartz-tuning-fork (QTF)-embedded, double-pass, off-beam quartz-enhanced photoacoustic spectroscopy (DP-OB-QEPAS). A simplified and accurate numerical model was presented to optimize the DP-OB-QEPAS spectrophone and to enhance the detection sensitivity. A compact and fiber-coupled acoustic detection module (ADM) with a volume of 3 × 2×1 cm3 and a weight of 9.7 g was fabricated. A continuous-wave distributed feedback diode laser was used to target the CH4 absorption line at 6046.95 cm−1. With the combination of wavelength modulation spectroscopy (WMS) and second harmonic (2f) detection technique, the CH4 sensor system reveals a 1σ detection limit of 8.62 parts-per-million in volume (ppmv) for a 0.3 s averaging time with an optimized modulation depth of 0.26 cm−1. The proposed CH4 sensor shows a similar or even lower level in the normalized noise equivalent absorption coefficient (NNEA) (1.8 × 10−8 cm−1∙W/√Hz), compared to previously reported QEPAS-based CH4 sensors.

Towards low-cost QEPAS sensors for nitrogen dioxide detection

Increasing awareness of the adverse health effects of air pollution leads to a demand of low-cost sensors for the measurement of pollutants such as NO2. However, commercially available low-cost sensors lack accuracy and long-term stability, and suffer from cross-sensitivity to other gases. These drawbacks can be overcome by the method of quartz-enhanced photoacoustic spectroscopy (QEPAS). In QEPAS modulated light is absorbed by the NO2 molecules, which results in the production of a sound wave. The sound wave is detected by resonance of a quartz tuning fork, which results in a measurable electric signal. Due to the small size of the tuning forks, the gas sensing element can be smaller than 1 cm3. We present the first bare fork QEPAS setup for the ppb-level detection of NO2, which is ideally suited for environmental trace gas detection without the need of using micro-resonators. Micro-resonators are commonly used to amplify photoacoustic signals. However, micro-resonators have different dependencies on environmental conditions than tuning forks, which makes them difficult to operate in changing conditions. In contrast, our bare fork QEPAS setup is more robust and easily adopted by the use of a low-cost temperature and humidity sensor. By using acoustic filters the integration time could be increased to offer higher sensitivity at a continuous flow rate of 200 std cm3 min−1. The 1σ noise equivalent concentration is determined to 21 ppb NO2 in synthetic air for 120 s measurement time, allowing detection which satisfies international health and safety standards thresholds.

Quartz Tuning Fork as a Parametric Resonator in High Magnetic Fields

We present the measurements of a parametrically excited quartz tuning fork in vacuum at very low temperatures ( $$\sim 20$$ mK) and magnetic field of 1.5 Tesla. We show that if a quartz tuning fork is exposed to a high static magnetic field, the motion of the tuning fork in this field modifies its potential energy forming a time-dependent term oscillating at twice of its fundamental frequency. This phenomenon gives an opportunity to study and use the quartz tuning forks as the parametric resonators. Here, we present the technique of the parametric excitation of the quartz tuning forks, and we discuss the results of the measurements.

Quartz Enhanced Photoacoustic Detection Based on an Elliptical Laser Beam

A quartz enhanced photoacoustic spectroscopy (QEPAS) sensor system based on an elliptical laser beam for trace gas detection was demonstrated. A Powell lens was exploited to shape the circular laser beam into an elliptical laser beam for the full utilization of the quartz tuning fork (QTF) prong spacing. Based on the finite element modeling (FEM) simulation software COMSOL, the distribution of acoustic pressure on QTF prongs with different beam shapes was simulated theoretically. The experimental results showed that the QEPAS signal based on the elliptical laser beam had a 1.4-fold improvement compared with the circular laser beam, resulting in a minimum detection limit of 418.6 ppmv and the normalized noise equivalent absorption (NNEA) of 1.51 × 10−6 cm−1 W/√Hz at atmospheric pressure.

Long-path quartz tuning fork enhanced photothermal spectroscopy gas sensor using a high power Q-switched fiber laser

A long-path quartz tuning fork enhanced photothermal spectroscopy (QEPTS) gas sensor using a Q-switched fiber laser is proposed. A theoretical model is used to describe the process of the long-path QEPTS sensor and the factors that affect its performance. We can conclude that long optical path and high power are beneficial to the QEPTS sensor from the theoretical analysis. And we use our long-path QEPTS sensor for C2H2 detection at the wavelength of 1531.59 nm. With the scanning time of 4 s and the peak pulse power of 127.5 mW, an Allan deviation analysis shows that our sensor has a minimum detection limit (MDL) of 6.1 ppbv at the 48 s integration time and a good linear response (R-square = 0.99796).

In-plane quartz-enhanced photoacoustic spectroscopy

An optical gas sensing technique based on in-plane quartz-enhanced photoacoustic spectroscopy (IP-QEPAS) is reported. In IP-QEPAS, the laser beam is aligned in the plane of the quartz tuning fork (QTF) to increase the interaction area between the acoustic wavefront and the QTF. A custom T-shaped QTF with a prong length of 9.4 mm and a resonance frequency of 9.38 kHz was designed and employed in the IP-QEPAS sensor. For comparison, the traditional QEPAS sensor in which the laser beam is perpendicular to the QTF plane (PP-QEPAS) is investigated with the same operating conditions. Theoretical calculations of strain and displacement of the QTF prong were performed to support the advantage of using the IP-QEPAS technique. By selecting water vapor as the gas target, the IP-QEPAS sensor results in a signal more than 40 times higher than that measured with the PP-QEPAS configuration, confirming the potential of this approach.

A microchip microcontroller-based transducer controller for non-contact scanning probe microscopy with phase-locked loop, amplitude, and Q control.

An inexpensive yet versatile transducer controller for non-contact scanning probe microscopy (SPM) based on a PIC32 microcontroller from Microchip Technology, Inc is described. In addition to feedback control using the amplitude or phase of the signal from the non-contact transducer, the controller includes a phase-locked loop for frequency-shift feedback, as well as fixed-amplitude, quality factor (Q) control, and self-excitation modes. Apart from the input amplifiers, output buffers, and the Q-control circuit, all other functions of the controller are instantiated in software on the microchip, enabling rapid changes in operating parameters if needed. The controller communicates with a host personal computer via a simple serial connection. The controller has been tested with a quartz tuning-fork transducer but can be used with any oscillating non-contact transducer.

A one-way coupled model for the vibration of tuning fork-based trace gas sensors driven by a thermoacoustic wave

We present a single computational model for both quartz-enhanced photoacoustic spectroscopy and resonant optothermoacoustic detection trace gas sensors. These sensors employ a quartz tuning fork to detect the acoustic pressure and thermal waves generated when a laser excites a trace gas. The model is based on a coupled system of equations developed by Morse and Ingard for pressure and temperature in a fluid. The pressure and temperature solutions drive the resonant vibration of the tuning fork, which is modeled using the equations of linear elasticity. At high ambient pressure, excellent agreement is obtained with laboratory experiments. This result provides the first quantitative match between a fully computational simulation and experiments for a QEPAS sensor. Such a model could ultimately facilitate sensor design optimization. At low ambient pressure (less than 60 Torr), quantitative agreement is obtained after reweighting the contributions from the pressure and thermal components of the signal. While this result is a substantial improvement over previous results in which a scaling factor was required to obtain agreement at any ambient pressure, at low pressures, it appears that a more accurate physical model may be required to match experimental data.

Performance Enhancement of a Quartz Tuning Fork Sensor Using a Cellulose Nanocrystal-Reinforced Nanoporous Polymer Fiber

A cellulose nanocrystal (CNC)-reinforced polymethylmethacrylate (PMMA) fiber was obtained via electrospinning, and then attached between the two tines of a quartz tuning fork (QTF). The change in the resonance frequency of the CNC/PMMA composite fiber-coated QTF (CP-QTF) was measured upon being exposed to various concentrations of ethanol vapor. The frequency decreased as the ethanol vapor concentration increased, because the modulus of the composite fiber decreased due to the adsorption of the ethanol vapor. The composite fiber obtained at a high relative humidity (RH; 60% RH, CP60 fiber) produced a highly porous structure as a result of the moisture adsorption-induced phase separation of PMMA. The porosity of the CP60 fiber was higher than that of a CNC/PMMA composite fiber obtained at 30% RH (CP30 fiber) or that of a plain PMMA fiber obtained at 60% RH (P60 fiber), because hygroscopic CNCs promote moisture adsorption. The CP60 fiber-coated QTF (CP60-QTF) exhibited a greater frequency change and faster response time than P60-QTF and CP30-QTF upon exposure to ethanol vapor at the same concentration. The enhanced performance of CP60-QTF was attributed to its higher surface area and larger fiber modulus.

Photoacoustic spectroscopy for gas sensing: A comparison between piezoelectric and interferometric readout in custom quartz tuning forks

We report on a comparison between piezoelectric and interferometric readouts of vibrations in quartz tuning forks (QTFs) when acting as sound wave transducers in a quartz-enhanced photoacoustic setup (QEPAS) for trace gas detection. A theoretical model relating the prong vibration amplitude with the QTF prong sizes and electrical resistance is proposed. To compare interferometric and piezoelectric readouts, two QTFs have been selected; a tuning fork with rectangular-shape of the prongs, having a resonance frequency of 3.4 kHz and a quality-factor of 4,000, and a QTF with prong having a T-shape characterized by a resonance frequency of 12.4 kHz with a quality-factor of 15,000. Comparison between the interferometric and piezoelectric readouts were performed by using both QTFs in a QEPAS sensor setup for water vapor detection. We demonstrated that the QTF geometry can be properly designed to enhance the signal from a specific readout mode.

Ultra-high sensitive trace gas detection based on light-induced thermoelastic spectroscopy and a custom quartz tuning fork

A highly sensitive trace gas sensor based on light-induced thermoelastic spectroscopy (LITES) and a custom quartz tuning fork (QTF) is reported. The QTF has a T-shaped prong geometry and grooves carved on the prongs' surface, allowing a reduction of both the resonance frequency and the electrical resistance but retaining a high resonance quality factor. The base of the QTF prongs is the area maximizing the light-induced thermoelastic effect. The front surface of this area was left uncoated to allow laser transmission through the quartz, while on the back side of the QTF, a gold film was coated to back-reflect the laser beam and further enhance the light absorption inside the crystal. Acetylene (C2H2) was chosen as the target gas to test and validate the LITES sensor. We demonstrated that the sensor response scales linearly with the laser power incident on the prong base, and the optimum signal to noise ratio was obtained at an optical power of 4 mW. A minimum detection limit of ∼325 ppb was achieved at an integration time of 1 s, corresponding to a normalized noise equivalent absorption coefficient of 9.16 × 10−10 cm−1W/√Hz, nearly one order of magnitude better with respect to the value obtained with a standard 32.768 kHz QTF-based LITES sensor under the same experimental conditions.

Friction–Load Relationship in the Adhesive Regime Revealing Potential Incapability of AFM Investigations

Reduced friction with increasing normal load in the adhesive regime is revealed by vdW-corrected DFT calculations of various rigid junction models such as Graphene/Graphene, h-BN/h-BN, and Graphene/h-BN. The origin of the friction–load relationship arises from the decreased sliding potential corrugation with increased normal load in the attractive regime of the interfacial separation above its equilibrium. The “negative” coefficient of friction behavior, which is mainly dominated by van der Waals attraction, is expected to appear in many interfaces without significant deformation. However, the friction behavior presented here may be inaccessible to atomic forces microscope (AFM) due to the intrinsic instability. The instruments such as interfacial forces microscope with force-feedback sensor or quartz tuning forks with large stiffness are proposed to measure friction behaviors in the entire attractive region.

Design Optimization of a Compact Double-Ended-Tuning-Fork-Based Resonant Accelerometer for Smart Spindle Applications.

With the rapid developments of the Industrial Era 4.0, numerous sensors have been employed to facilitate and monitor the quality of machining processes. Among them, accelerometers play an important role in chatter detection and suppression for reducing the tool down-time and increasing manufacturing efficiency. To date, most commonly seen accelerometers have relatively large sizes such that they can be installed only on the housing of spindles or the surfaces of workpieces that may not be able to directly capture actual vibration signals or obstruct the cutting process. To address this challenge, this research proposed a compact, wide-bandwidth resonant accelerometer that could be embedded inside high-speed spindles for real-time chatter monitoring and prediction. Composed of a double-ended tuning fork (DETF), a proof mass, and a support beam, the resonant accelerometer utilizes the resonance frequency shift of the DETF due to the bending motions of the structure during out-of-plane accelerations as the sensing mechanism. The entire structure based on commercially available quartz tuning forks (QTFs) with electrodes for symmetric-mode excitations. The advantages of this structure include low noise and wide operation bandwidth thanks to the frequency modulation scheme. A theoretical model and finite element analysis were conducted for designs and optimizations. Simulated results demonstrated that the proposed accelerometer has a size of 9.76 mm × 4.8 mm × 5.5 mm, a simulated sensitivity of 0.94 Hz/g, and a simulated working bandwidth of 3.5 kHz. The research results are expected to be beneficial for chatter detection and intelligent manufacturing.

A Hydrodynamic Model for Measuring Fluid Density and Viscosity by Using Quartz Tuning Forks

A hydrodynamic model of using quartz tuning forks (QTFs) for density and viscosity sensing, by measuring the resonance frequency and quality factor, has been established based on the cantilever beam theory applied to the atomic force microscope (AFM). Two examples are presented to verify the usability of this model. Then, the Sobol index method is chosen for explaining quantitatively how the resonance frequency and quality factor of the QTFs are affected by the fluid density and viscosity, respectively. The results show that the relative mean square error in viscosity of the eight solutions evaluated by the hydrodynamic model is reduced by an order of magnitude comparing with Butterworth–Van Dyke equivalent circuit method. When the measured resonance frequency and quality factor of the QTFs vary from 25,800–26,100 Hz and 28–41, the sensitivities of the quality factor affected by the fluid density increase. This model provides an idea for improving the accuracy of fluid component recognition in real time, and lays a foundation for the application of miniaturized and cost-effective downhole fluid density and viscosity sensors.

Quartz-enhanced photoacoustic spectroscopy employing pilot line manufactured custom tuning forks

Pilot line manufactured custom quartz tuning forks (QTFs) with a resonance frequency of 28 kHz and a Q value of >30, 000 in a vacuum and ∼ 7500 in the air, were designed and produced for trace gas sensing based on quartz enhanced photoacoustic spectroscopy (QEPAS). The pilot line was able to produce hundreds of low-frequency custom QTFs with small frequency shift < 10 ppm, benefiting the detecting of molecules with slow vibrational-translational (V-T) relaxation rates. An Au film with a thickness of 600 nm were deposited on both sides of QTF to enhance the piezoelectric charge collection efficiency and reduce the environmental electromagnetic noise. The laser focus position and modulation depth were optimized. With an integration time of 84 s, a normalized noise equivalent absorption (NNEA) coefficient of 1.7 × 10−8 cm-1∙W∙Hz-1/2 was achieved which is ∼10 times higher than a commercially available QTF with a resonance frequency of 32 kHz.

Damping of a Micro-electromechanical Resonator in the Presence of Quantum Turbulence Generated by a Quartz Tuning Fork

A micro-electromechanical resonator, consisting of a $$125 \times 125\,\upmu \hbox {m}^2$$ center plate suspended $$2\,\upmu \hbox {m}$$ above a substrate, was immersed in $$^4$$ He along with a quartz tuning fork. The tuning fork was placed 5 mm above the resonator and was used to generate turbulence. The damping of the resonator was investigated in the presence of turbulence generated by the tuning fork. We observe a velocity, $$v_c \simeq 5\,\hbox {mm}\,\hbox {s}^{-1}$$ , above which the damping on the resonator is drastically reduced for all tuning fork velocities studied. We attribute this change in damping to the shedding and capture of vortices.

Quartz Tuning Fork Resonance Tracking and application in Quartz Enhanced Photoacoustics Spectroscopy.

The quartz tuning fork (QTF) is a piezoelectric transducer with a high quality factor that was successfully employed in sensitive applications such as atomic force microscopy or Quartz-Enhanced Photo-Acoustic Spectroscopy (QEPAS). The variability of the environment (temperature, humidity) can lead to a drift of the QTF resonance. In most applications, regular QTF calibration is absolutely essential. Because the requirements vary greatly depending on the field of application, different characterization methods can be found in the literature. We present a review of these methods and compare them in terms of accuracy. Then, we further detail one technique, called Beat Frequency analysis, based on the transient response followed by heterodyning. This method proved to be fast and accurate. Further, we demonstrate the resonance tracking of the QTF while changing the temperature and the humidity. Finally, we integrate this characterization method in our Resonance Tracking (RT) QEPAS sensor and show the significant reduction of the signal drift compared to a conventional QEPAS sensor.

Reentrant pinning of a He3 overlayer in a He3−He4 mixture film

We performed quartz crystal microbalance experiments for a $^{3}\mathrm{He}\text{\ensuremath{-}}^{4}\mathrm{He}$ mixture film on an exfoliated single-crystalline graphite using a 32-kHz quartz tuning fork. The decoupled $^{3}\mathrm{He}$ overlayer on the superfluid $^{4}\mathrm{He}$ layer shows a reentrant pinning at a certain temperature ${T}_{3d}$ under a large oscillation amplitude. The pinning state below ${T}_{3d}$ is metastable. After reducing the oscillation amplitude, the $^{3}\mathrm{He}$ overlayer relaxes to a stable pinning state via a depinning state. It is found that the reentrant pinning is triggered by a structure change of the underlying localized $^{4}\mathrm{He}$ layer on the oscillating substrate.

Properties of the 100 kHz Quartz Tuning Forks in Strong Magnetic Fields and Very Low Temperatures

We present the properties of the standard, commercial 100 kHz quartz tuning forks at very low temperatures and high magnetic fields up to 8 Tesla. We show that the resonance frequency of the tuning forks depends weakly on the strength of magnetic field. This makes the quartz tuning forks a promising low-temperature thermometer having the B/T ratio up to 1000. We discuss the physical origin of the observed experimental results.