Tuning Fork Research Articles

Toward the Real-Time and Rapid Quantification of Bacterial Cells Utilizing a Quartz Tuning Fork Sensor.

The quantitative evaluation of bacterial populations is required in many studies, particularly in the field of microbiology. The current techniques can be time-consuming and require a large volume of samples and trained laboratory personnel. In this regard, on-site, easy-to-use, and direct detection techniques are desirable. In this study, a quartz tuning fork (QTF) was investigated for the real-time detection of E. coli in different media, as well as the ability to determine the bacterial state and correlate the QTF parameters to the bacterial concentration. QTFs that are commercially available can also be used as sensitive sensors of viscosity and density by determining the QTFs' damping and resonance frequency. As a result, the influence of viscous biofilm adhered to its surface should be detectable. First, the response of a QTF to different media without E. coli was investigated, and Luria-Bertani broth (LB) growth medium caused the largest change in frequency. Then, the QTF was tested against different concentrations of E. coli (i.e., 102-105 colony-forming units per milliliter (CFU/mL)). As the E. coli concentration increased, the frequency decreased from 32.836 to 32.242 kHz. Similarly, the quality factor decreased with the increasing E. coli concentration. With a coefficient (R) of 0.955, a linear correlation between the QTF parameters and bacterial concentration was established with a 26 CFU/mL detection limit. Furthermore, a considerable change in frequency was observed against live and dead cells in different media. These observations demonstrate the ability of QTFs to distinguish between different bacterial states. QTFs allow real-time, rapid, low-cost, and non-destructive microbial enumeration testing that requires only a small volume of liquid sample.

GSI CTA evaluation of the vertebrobasilar artery in normal adults at high altitude.

Vascular geometry is influenced by several factors during its growth and development. Here, we compared the differences in vertebrobasilar geometry among residents of a plateau region at different altitudes and investigated the relationship between vascular geometry and altitude. Data of some adults in the plateau region who experienced vertigo and headache as the main symptoms but had no evident abnormalities found during imaging examination were collected. They were divided into three groups based on an altitude gradient: group A (1,800-2,500 masl), group B (2,500-3,500 masl), and group C (over 3,500 masl). They underwent head-neck energy-spectrum computed tomography angiography with a gemstone spectral imaging scanning protocol. The following indices were observed: (1) vertebrobasilar geometric configurations (walking, tuning fork, lambda, and no confluence), (2) vertebral artery (VA) hypoplasia, (3) the bending number of bilateral VA intracranial segment, (4) length and tortuosity of the basilar artery (BA), and (5) anteroposterior (AP)-mid-BA angle, BA-VA angle, lateral-mid-BA angle, and VA-VA angle. Of the 222 subjects, 84 of them were included in group A, 76 in group B, and 62 in group C. The number of participants in walking, tuning fork, lambda, and no confluence geometries was 93, 71, 50, and 8, respectively. As altitude increased, the tortuosity of the BA also increased (1.05 ± 0.06 vs. 1.06 ± 0.08 vs. 1.10 ± 0.13, P = 0.005), as did the lateral-mid-BA angle (23.18° ± 9.53° vs. 26.05° ± 10.10° vs. 31.07° ± 15.12°, P = 0.007) and the BA-VA angle (32.98° ± 17.85° vs. 34.51° ± 17.96° vs. 41.51° ± 19.22°, P = 0.024). There was a relatively weak positive correlation between the altitude and the tortuosity of the BA (rs = 0.190, P = 0.005), the lateral-mid-BA angle (rs = 0.201, P = 0.003), and the BA-VA angle (rs = 0.183, P = 0.006) which showed a significant difference. Compared with groups A and B, there were more multibending groups and fewer oligo-bending groups in group C (P < 0.001). There was no difference found in the vertebral artery hypoplasia, actual length of the BA, VA-VA angle, and AP-mid-BA angle among the three groups. As the altitude increased, the tortuosity of the BA and the sagittal angle of the vertebrobasilar arterial system also increased. The increase in altitude can lead to changes in vertebrobasilar geometry.

Highly sensitive light-induced thermoelastic spectroscopy oxygen sensor with co-coupling photoelectric and thermoelastic effect of quartz tuning fork

A light-induced thermoelastic spectroscopy (LITES) gas detection method based on CH3NH3PbI3 perovskite-coated quartz tuning fork (QTF) was proposed. By coating CH3NH3PbI3 thin film on the surface of ordinary QTF, a Schottky junction with silver electrodes was formed. The co-coupling of photoelectric effect and thermoelastic effect of CH3NH3PbI3-QTF results in a significant improvement in detection performance. The oxygen (O2) was select as the target analyte for measurement, and experimental results show that compared with the commercial standard QTF, the introduction of CH3NH3PbI3 perovskite Schottky junction increases the 2f signal amplitude and signal-to-noise ratio (SNR) by ∼106 times and ∼114 times, respectively. The minimum detection limit (MDL) of this LITES system is 260 ppm, and the corresponding normalized noise equivalent absorption coefficient (NNEA) is 9.21 × 10−13 cm−1·W·Hz−1/2. The Allan analysis of variance results indicate that when the average time is 564 s, the detection sensitivity can reach 83 ppm. This is the first time that QTF resonance detection has been combined with perovskite Schottky junctions for highly sensitive optical gas detection.

A novel MIMO antenna with switchable UWB/5G modes for vehicular terminals

AbstractThis paper demonstrates the design and development of a dual‐operating mode multiple‐input and multiple‐output (MIMO) antenna. The MIMO antenna comprises a novel ultrawideband (UWB) antenna with selectively chosen feedlines to obtain bandwidth reconfiguration. The novel UWB monopole evolved from a rectangular monopole whose radiating portion and the ground plane are shaped to obtain broadband impedance matching from 2.3 to 10.7 GHz (Mode 1). The antenna is excited using a 50‐Ω microstrip line. An additional feed path is created and deployed to achieve bandwidth selectivity with a tuning fork bandpass filter (BPF) operating between 2.8 and 4 GHz. Bandwidth selection is performed using a pair of positive–intrinsic–negative diodes. Thus, in the reconfigured state, the monopole is connected to the excitation source through the BPF, restricting the operational bandwidth to 2.8–4.0 GHz (Mode 2). A vertically polarized four‐element MIMO antenna with pattern diversity characteristics is constructed, and the performance parameters are studied. The proposed multiantenna is fabricated and tested in the laboratory. The proposed MIMO antenna offers a measured gain of over 3.51 dBi and total efficiency above 78%. The proposed multielement antenna is suitable for UWB communications, including ISM, LTE2700, and sub‐6 GHz 5G communications at 3.5 GHz in the vehicular environment.

Design and analysis of MEMS tuning fork gyroscope with dual mode ordering

AbstractThis paper reports a MEMS tuning fork gyroscope which can effectively reduce the acceleration output in both drive and sense directions. The structure adjusts the order of mechanical vibration modes through the design of internal and external lever coupling mechanism, moves the spurious in‐phase mode frequency above the antiphase operating frequency, and provides a large frequency separation between the two modes. It provides true mechanical rejection of external shocks and accelerations. Two comparative tuning fork gyroscopes (TFG) structures are designed, which have traditional coupling in the drive direction and sense direction respectively. Through modal simulation, the internal lever‐coupling brings the antiphase drive mode before the in‐phase drive mode and the external lever‐coupling brings the antiphase sense mode before the in‐phase sense mode. The harmonic response simulation of three stiffness unbalanced TFGs verifies that the mode ordering of two directions can effectively suppress the acceleration output. The results show that the new TFG structure can suppress the acceleration output by more than 80%, and the finite element simulation results are consistent with the theoretical calculation.

Ppb-level mid-IR quartz-enhanced photoacoustic sensor for sarin simulant detection using a T-shaped tuning fork

A ppb-level mid-IR quartz-enhanced photoacoustic sensor for the highly sensitive detection of dimethyl methyl phosphonate (DMMP) —the sarin simulant—is developed using a T-shaped tuning fork. The sensor employs a narrow-linewidth mid-IR quantum cascade laser (QCL) to target a strong, interference-free DMMP absorption band. A custom quartz tuning fork with 800-μm prong spacing is employed to avoid significant photothermal noise, thus removing the requirement for an optical spatial filter. The performance of the photoacoustic sensor was optimized in terms of exciting power, modulation frequency, and gas pressure. A minimum detection limit of 6 ppb was achieved at an integration time of 300 ms, which can be further improved to 0.45 ppb at the optimal integration time of 20 s

Quartz tuning fork-based biosensor for the direct detection of human cytomegalovirus

Human cytomegalovirus (HCMV) possess great threat to immunocompromised patients and pregnant women since It can cause disability if left untreated. Especially for unborn babies, if the virus was not detected at early stages, it can cause disabilities as the baby develops. Furthermore, the virus can be asymptomatic, hence, low-cost and rapid detection techniques are desirable. Currently available detection techniques of the virus are labor intensive and demand experienced technicians. For these reasons, new detection techniques are needed to overcome the current challenges associated with conventional techniques. In this work, quartz tuning fork (QTF)-based biosensor was developed for the detection of UL83-antigen of HCMV for the first time. Firstly, QTF coated with gold was functionalized with cysteamine and glutaraldehyde for UL83-antibody immobilization at the QTF surface. Then, the biosensor was tested against a variety of UL83-antigen concentrations. As the UL83-antigen concentration increased, the measured resonance frequency decreased due to increased mass loading at the QTF surface. The sensitivity of the biosensor is 15.91 Hz/ln(ng/mL). Whereas the limit of detection is 0.36 ng/mL. The biosensor showed comparable biosensing performances to those available in the literature. Furthermore, the biosensor demonstrated its selectivity towards UL83-antigen when tested against samples containing a mixture of biomarkers. The reported work demonstrates a platform for the direct and low-cost mass screening of diseases.

Cavitation generated by vibrating quartz tuning fork in concentrated 3He–4He mixture

The state of the problem of cavitation in superfluid helium and the content of previous works on this topic are analyzed. The transition between turbulent flow and cavitation under oscillations of a quartz tuning fork in a normal and superfluid isotopic mixture containing 15% of 3He in the temperature range of 0.5–3 K is studied experimentally. The temperature dependences of the critical velocity for the cavitation onset and the critical transition excitation force are obtained. We compare the results of our measurements with the data obtained by other groups. The results of measurements with tuning forks in restricted and unrestricted geometries suggest that the presence of acoustic emission facilitates the conditions for the onset of cavitation and indirectly confirms the role of vortex lines. A comparison of the temperature dependences of the critical velocity of cavitation onset in pure 4He and a concentrated 3He–4He mixture did not give an unambiguous answer to the reason for the sharp increase of this velocity, at the transition to the superfluid state, and the contributions of both thermal effects and the 3He impurities to the velocity increase.

Automatic Pico Laser Trimming System for Silicon MEMS Resonant Devices Based on Image Recognition

Laser trimming promises an increasing yield in microfabrication for the high performance Micro Electro-Mechanical Systems (MEMS) resonant devices by overcoming manufacturing tolerances and tuning sensors or actuators for certain operating conditions. How to achieve a high precision and efficiency trimming at low cost is the critical issue that the technical communities are most concerned. In this paper, we proposed an automatic laser trimming system for silicon MEMS devices based on a picosecond laser source and image recognition technique (IRT). Through the design of laser focusing optical path and coaxial imaging optical path, the observation of laser machining process is realized. A set of picosecond laser trimming parameters is determined by experiments, which enables a 4um width trench on the silicon resonator. Compared with the femtosecond laser trimming systems, the cost of the pico-laser system is reduced by more than 60%. The shape matching algorithm based on OpenCV and the chord-to-point distance accumulation (CPDA) algorithm for MEMS resonators image measurement solve the problem of inefficiency of manual trimming for complex resonators. A dual-mass tuning fork resonator is used to demonstrate the feasibility of the trimming approach. It is shown that the system realizes a fine-tuning (< 0.3Hz) of the resonant frequencies. The trimming time of a single device using the automatic trimming method is reduced from more than 1 hour manual trimming to less than 1 minute. Finally, the structural stiffness imbalance of tuning fork resonator caused by the manufacturing error is eliminated, which verifies the feasibility of the system.

Trace Gas Detection System Based on Photoacoustic and Photothermal Spectroscopy Using Ring Fiber Laser and Quartz Tuning Fork

In this paper, a dual-spectroscopy gas sensing system based on ring cavity laser and quartz tuning fork (QTF) is designed. 15 m erbium-doped fiber with 1500 ppm doping concentration is used as gain medium, piezoelectric transducer (PZT) and acousto-optic modulator (AOM) are used as detection method. The first fiber collimator (FC) emits laser beam, laser is received by the second FC after passing through an off-beam acoustic micro-resonator (AmR) for quartz-enhanced photoacoustic spectroscopy (QEPAS) signal excitation and enhancement. The received laser is transmitted through the optical fiber and then incident on the QTF prongs by the third FC, which excites and quartz-enhan-ced photothermal spectroscopy (QEPTS) signal. Combined with the ring intra-cavity fiber laser and wavelength scanning and intensity modulation technology, dual-spectroscopy gas detection is realized. Compared with the single detection of QEPAS or QEPTS signals, the detection limit is enhanced. Under the conditions of 400mW pump power and 2500 ppmv acetylene (C <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) gas concentration, the signal to noise ratio (SNR) of QEPAS, QEPTS and dual-spectroscopy signals are 838.07, 1117.47 and 2096.26, respectively, and the minimum detection limits (MDL) of 2.98 ppmv, 2.24 ppmv, 1.19 ppmv are achieved, respectively.

A compact integrated dual-spectroscopy gas detection structure based on QEPAS and QEPTS using a QTF

If the acetylene (C2H2) content in the oxygen production device exceeds the standard, it is highly susceptible to explosion. It is necessary to detect C2H2 gas and reach the detection limit of ppm. A novel single quartz tuning fork (QTF) compact integrated dual-spectroscopy gas detection structure based on quartz-enhanced photoacoustic spectroscopy (QEPAS) and quartz-enhanced photothermal spectroscopy (QEPTS) was designed for improving detection intensity and reducing sensor size. The detection structure (40 mm × 90 mm × 50 mm) includes gas buffer, gas detection structure, and preamplifier circuit. In the structure, an off-beam acoustic micro-resonator (AMR) was used to enhance the photoacoustic signal. After passing the AMR, the laser beam was turned back by the right-angle prism and incident on the side of the QTF fork again to generate the photothermal signal. The silver layer on the QTF surface was chemically etched to further enhance the photothermal signal. For the traditional off-beam photoacoustic excitation, the photothermal signal is excited by the way of laser retracting. The superposition of the dual-spectroscopy detection technology on a single QTF is realized. And the structure is finely integrated which is convenient to carry and measure. Under the same conditions, photoacoustic signal, photothermal signal and dual-spectroscopy signal were measured respectively. The measured dual-spectroscopy signal was approximately the superposition value of photoacoustic signal and photothermal signal, which showed the effective signal lifting effect. With C2H2 as the target gas, the experimental results showed that the signal value of the dual-spectroscopy structure was 1.94 times that of QEPAS structure, 2.18 times that of QEPTS structure. And the minimum detection limit at atmospheric pressure was 6.64 ppm. The integrated dual-spectroscopy structure was compact, and was suitable for small space measurement, mobile measurement, and other fields.

Micro-Quartz Crystal Tuning Fork-Based Photodetector Array for Trace Gas Detection.

In this paper, a micro-quartz crystal tuning fork (M-QCTF) was first demonstrated for developing a low-cost, highly sensitive quartz tuning fork photodetector array for spectroscopic applications. A gas sensing system based on the M-QCTF photodetector and highly sensitive wavelength modulation spectroscopy was developed. Typically, an atmospheric greenhouse gas methane (CH4) molecule was selected as the target analyte for evaluating the M-QCTF and standard commercial QCTF detectivity. The results indicate that the M-QCTF photodetector exhibits ∼3.3 times sensitivity enhancement compared to the standard commercial QCTF. The long-term stability was evaluated by using the Allan deviation analysis method; a minimum detection limit of 1.2 ppm was achieved with an optimal integration time of 85 s, and the corresponding normalized noise equivalent absorption coefficient was calculated to be 4.45 × 10-10 cm-1 W/√Hz. Finally, a two-M-QCTF array detection scheme was experimentally demonstrated, and a signal-to-noise ratio enhancement factor of more than 1.7 times compared to that achieved using a single M-QCTF photodetector was realized, which proves a great potential for developing ultra-sensitive quartz tuning fork photodetector arrays for various applications.

Pemeriksaan dan Edukasi Gangguan Pendengaran Pada Anak Panti Asuhan

Unhealthy ears may cause hearing loss. This issue may affect children to have difficulty communicating with others and decrease learning achievement at school. This community service activity aimed to give knowledge about hearing loss and conduct hearing examinations in orphanage children. This community service was held at the Aulia Al-Ikhlas Orphanage in Sungai Pagar Village, Kampar Kiri Hilir District, Kampar Regency, Riau. At the beginning of the activity, we provided counseling about hearing loss, followed by ear and hearing examinations using a tuning fork. Before and after the counseling, respondents filled out a questionnaire to assess knowledge about hearing loss. Twenty-four residents of the orphanage attended this activity. The questionnaires found that children's knowledge about hearing loss and ear health increased significantly after the counseling. The examination results found cerumen in 14 children, 4 with conductive hearing loss and 2 with sensory neural hearing loss. As a result, this community service activity can increase the knowledge of orphanage children about hearing loss and make their ears cleaner and healthier.

Acoustic emission in bulk normal and superfluid 3He

We present measurements of the damping experienced by custom-made quartz tuning forks submerged in 3He covering frequencies from 20 to 600 kHz. Measurements were conducted in the bulk of normal liquid 3He at temperatures from 1.5 K down to 12 mK and in superfluid 3He-B well below the critical temperature. The presented results complement earlier work on tuning fork damping in 3He, removing possible ambiguities associated with acoustic emission within partially enclosed volumes and extend the probed range of frequencies, leading to a clearly established frequency dependence of the acoustic losses. Our results validate existing models of damping and point toward the same mechanism of wave emission of first sound in normal 3He and liquid 4He and zero sound in superfluid 3He. We observe a steep frequency dependence of the damping ≈f5.5, which starts to dominate around 100 kHz and restricts the use of tuning forks as efficient sensors in quantum fluids. The acoustic emission model can predict the limiting frequencies for various devices, including micro-electromechanical and nano-electromechanical structures developed for quantum turbulence and single vortex dynamics research.

A Miniaturized 3D-Printed Quartz-Enhanced Photoacoustic Spectroscopy Sensor for Methane Detection with a High-Power Diode Laser.

In this invited paper, a highly sensitive methane (CH4) trace gas sensor based on quartz-enhanced photoacoustic spectroscopy (QEPAS) technique using a high-power diode laser and a miniaturized 3D-printed acoustic detection unit (ADU) is demonstrated for the first time. A high-power diode laser emitting at 6057.10 cm-1 (1650.96 nm), with the optical power up to 38 mW, was selected as the excitation source to provide a strong excitation. A 3D-printed ADU, including the optical and photoacoustic detection elements, had a dimension of 42 mm, 27 mm, and 8 mm in length, width, and height, respectively. The total weight of this 3D-printed ADU, including all elements, was 6 g. A quartz tuning fork (QTF) with a resonant frequency and Q factor of 32.749 kHz and 10,598, respectively, was used as an acoustic transducer. The performance of the high-power diode laser-based CH4-QEPAS sensor, with 3D-printed ADU, was investigated in detail. The optimum laser wavelength modulation depth was found to be 0.302 cm-1. The concentration response of this CH4-QEPAS sensor was researched when the CH4 gas sample, with different concentration samples, was adopted. The obtained results showed that this CH4-QEPAS sensor had an outstanding linear concentration response. The minimum detection limit (MDL) was found to be 14.93 ppm. The normalized noise equivalent absorption (NNEA) coefficient was obtained as 2.20 × 10-7 cm-1W/Hz-1/2. A highly sensitive CH4-QEPAS sensor, with a small volume and light weight of ADU, is advantageous for the real applications. It can be portable and carried on some platforms, such as an unmanned aerial vehicle (UAV) and a balloon.

Equivalent Electromechanical Model for Quartz Tuning Fork Used in Atomic Force Microscopy.

Quartz tuning forks (QTFs) are self-sensing and possess a high quality factor, allowing them to be used as probes for atomic force microscopes (AFMs) for which they offer nano-scale resolution of sample images. Since recent work has revealed that utilizing higher-order modes of QTFs can offer better resolution of AFM images and more information on samples, it is necessary to understand the relationship between the vibration characteristics of the first two symmetric eigenmodes of quartz-based probes. In this paper, a model that combines the mechanical and electrical characteristics of the first two symmetric eigenmodes of a QTF is presented. Firstly, the relationships between the resonant frequency, amplitude, and quality factor between the first two symmetric eigenmodes are theoretically derived. Then, a finite element analysis is conducted to estimate the dynamic behaviors of the analyzed QTF. Finally, experimental tests are executed to verify the validity of the proposed model. The results indicate that the proposed model can accurately describe the dynamic properties of a QTF in the first two symmetric eigenmodes either under electrical or mechanical excitation, which will provide a reference for the description of the relationship between the electrical and mechanical responses of the QTF probe in the first two symmetric eigenmodes as well as the optimization of higher modal responses of the QTF sensor.

Quasinormal mode representation of radiating resonators in open phononic systems

Open phononic systems including resonators radiating inside an unbounded medium support localized phonons characterized by a complex frequency. In this context, the concept of elastic quasinormal mode (QNM) arises naturally, as in the cases of nanophotonic and plasmonic open systems. Based on a complex, unconjugated form of reciprocity theorem for elastodynamics, the eigenfunction expansion theorem expressed on the elastic QNM basis yields an accurate approximation to the response function, for an arbitrary excitation. The description of the elastic Purcell effect then requires defining a complex-valued modal volume for each QNM. For validation, we first consider the case a vibrating nylon rod radiating in water. As a second test example, we consider a slender nickel ridge on the surface of a fused silica substrate, before extending our attention to a nanoscale tuning fork composed of two such ridges. In all cases, the response estimated from only a few elastic QNMs agrees with the solution to the elastodynamic equation.

Continuous real-time monitoring of carbon dioxide emitted from human skin by quartz-enhanced photoacoustic spectroscopy

In this study, a skin gas detection system based on quartz enhanced photoacoustic spectroscopy (QEPAS) with a constant temperature collection chamber and an automatic frequency adjustment function was used to collect and monitor carbon dioxide (CO2) emissions from human skin. The detection element of the system is an on-beam structure assembled by a 30.72 kHz quartz tuning fork (QTF). A laser with a wavelength of 4991.26 cm−1 is emitted (with a wavelength adjustment range of 10 cm−1) to excite the QTF. When the integration time is 365 s, the system can achieve a minimum detection limit (MDL) of 2.6 ppmv. The sensitivity of the system is 636.9 ppmv/V. The gas detection system is used to monitor the concentration of CO2 emissions from different parts of the skin and the same part covered by different cosmetics. The CO2 emission rate is defined as the ratio of the skin gas monitoring time of 25 min to the CO2 concentration variable in the gas chamber (volume of 8 mL). The results were collected from three healthy volunteers. Among the six different parts, the cheeks emitted the fastest rate (the average rate was 365.5 ppmv/min) of CO2, and the thighs emitted the slowest rate (the average rate was 56.4 ppmv/min) of CO2. Comparing the experimental results of the six sites at different times, the order of the CO2 emission rate is identical for all six sites. In the experiments with the three cosmetic products (experimental site: forearm), comparing the CO2 emission rate from clean skin with the CO2 emission rate from cosmetic-covered skin shows that sunscreen is the most breathable, followed by barrier cream, and foundation is the least breathable.

ОЦЕНКА СОСТОЯНИЯ СЛУХОВОГО АНАЛИЗАТОРА И АНАЛИЗ ФАКТОРОВ РИСКА У СТУДЕНТОВ

The modern lifestyle of young people is reflected in the state of hearing. Using gadgets and listening to loud music leads to the early development of hearing loss. The purpose of the study is to assess the condition of the auditory analyzer in students. The results of our own research allowed us to identify the main factors leading to hearing loss and assess the condition of the auditory analyzer in 20 students aged 20-22 years. Data collection was carried out on the basis of comprehensive surveys, questionnaires and reports. To assess hearing, anamnesis was collected, external examination of the ear, palpation, otoscopy, whispering and colloquial speech, tests with tuning forks, tonal threshold audiometry at four typical frequencies. The results of the study of the condition of the auditory analyzer showed that in 10% of cases sulfur plugs were detected in the external auditory canal, in 5% of cases – the presence of scars and pathological color of the membrane. The study of auditory function revealed that in 20% of cases, whispered speech was detected from a distance of 4 meters, and not from 6. The values of air and bone conduction during the Rinne test in all cases did not reach the standard values, in 20% of cases the test on the right ear was negative, and on the left ear – in 10%. In Federici's experiment, it was revealed that in 15% of cases, bone conduction was higher than air. The results of the Weber test showed that in 45% of cases the sound was shifted and uneven. The data obtained using a high-frequency tuning fork 2048 showed that in 85% of cases, the air conductivity values of both the right and left ears were below normal values. The study of hearing acuity demonstrated that in 15% of cases the values reached the upper limit of the norm. The results of the questionnaire to identify the determining factors showed that 30% of students noticed hearing impairment. More than 50% of students answered that they often listen to loud music and use headphones. Thus, the main risk factors and the first signs of hearing loss in students were identified.

Quartz-enhanced photoacoustic spectroscopy (QEPAS) and Beat Frequency-QEPAS techniques for air pollutants detection: A comparison in terms of sensitivity and acquisition time

In this work, a comparison between Quartz Enhanced Photoacoustic Spectroscopy (QEPAS) and Beat Frequency-QEPAS (BF-QEPAS) techniques for environmental monitoring of pollutants is reported. A spectrophone composed of a T-shaped Quartz Tuning Fork (QTF) coupled with resonator tubes was employed as a detection module. An interband cascade laser has been used as an exciting source, allowing the targeting of two NO absorption features, located at 1900.07 cm−1 and 1900.52 cm−1, and a water vapor absorption feature, located at 1901.76 cm−1. Minimum detection limits of 90 ppb and 180 ppb were achieved with QEPAS and BF-QEPAS techniques, respectively, for NO detection. The capability to detect multiple components in the same gas mixture using BF-QEPAS was also demonstrated.