Low Frequency Vibration Signal Research Articles

Research on S-type fiber Bragg grating acceleration sensor for low-frequency vibration monitoring.

The acquisition of low-frequency vibration signals in earthquake exploration is a crucial aspect of seismic exploration technology. Addressing the difficulty current fiber optic sensors face in monitoring low-frequency vibrations, this paper proposes an acceleration sensor based on S-type Fiber Bragg Grating (FBG). First, an FBG acceleration sensor model is established and theoretically analyzed. Then, the impact of structural parameters on the sensor's sensitivity and natural frequency is examined, employing the ANSYS finite element analysis software for static stress and modal simulation analysis. Finally, a prototype is developed, and a low-frequency vibration testing system is assembled to test the sensor's performance. The results show that the sensor has a natural frequency of 34Hz, operates in a frequency band of 0.2-14Hz, has a dynamic range of 63.5 dB, a lateral interference of less than 3%, a sensitivity of ∼274.45 pm/g, good linearity, and is insensitive to temperature. The findings provide a reference for the development of similar sensors and further exploration of the lower frequency limit.

Highly Sensitive Biomimetic Crack Pressure Sensor with Selective Frequency Response.

High-sensitivity sensors in practical applications face the issue of environmental noise interference, requiring additional noise reduction circuits or filtering algorithms to improve the signal-to-noise ratio (SNR). To address this issue, this study proposes a biomimetic crack pressure sensor with selective frequency response based on hydrogel dampers. The core of this research is to construct a biomimetic crack pressure sensor with selective frequency response using the high-pass filtering characteristics of gelatin-chitosan hydrogels. This design, inspired by the slit sensilla and stratum corneum structure of spider legs, delves into the material properties and principles of hydrogel dampers, exploring their application in biomimetic crack pressure sensors, including parameter selection, structural design, and performance optimization. By delving into the nuanced characteristics and working principles of hydrogel dampers, their integration in biomimetic crack pressure sensors is examined, focusing on aspects like parameter selection, structural engineering, and performance enhancement to selectively sieve out low-frequency noise and transmit target vibrational signals. Experimental results demonstrate that this innovative sensor, while suppressing low-frequency vibration signals, can selectively detect high-frequency signals with high sensitivity. At different vibration frequencies, the relative change in resistance exceeds 200%, and the sensor sensitivity is 7 × 104 kPa-1. Furthermore, this sensor was applied to human voice detection, and the corresponding results verified its frequency-selective performance evidently. This study not only proposes a new design for pressure sensors but also offers fresh insights into the application of biomimetic crack pressure sensors in intricate environments.

Dual straight-wing FBG accelerometer for low-frequency vibration measurement

Fiber optic accelerometers have a wide range of applications in low-frequency vibration measurement, such as in earthquake monitoring, disaster early warning, underground resource exploration, and anti-seismic monitoring projects for critical structures like dams and bridges. In response to the current issues of Fiber Bragg Gratings (FBG) accelerometers being insensitive to low-frequency vibration signals and challenging to apply in engineering, a dual straight-wing FBG accelerometer for low-frequency vibration measurement is proposed. Firstly, a sensor model is established and theoretically analyzed. Secondly, the impact of the sensor's main structural parameters on sensitivity and natural frequency is analyzed, and the sensor is simulated using ANSYS. Finally, a prototype of the sensor is developed, and a low-frequency vibration testing system is set up to test the sensor's performance. Experimental results show that the accelerometer has a natural frequency of 39.1 Hz, operates in the 5–22 Hz frequency band, and has a sensitivity of 171.7 p.m./g, a dynamic range of 69.82 dB, and a transverse interference resistance of less than 9.5%. This research provides a new reference for the development of similar sensors.

A fibre Bragg grating accelerometer with temperature insensitivity for cable force monitoring of FAST

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) currently holds the distinction of being the largest single-aperture telescope worldwide. To ensure its secure functioning, it is crucial to monitor the cable force on its active reflecting surface cable network structure. In this paper, a fibre Bragg grating (FBG) accelerometer is developed to acquire low-frequency vibration signals of the cables. The sensor’s cantilever beam structure enables high sensitivity measurement of low-frequency signals, while the symmetrical double fibre grating structure effectively eliminates the impact of temperature. The sensor’s specific limiting structure ensures its survival during transportation and installation. A series of laboratory tests have been performed, and they demonstrate the excellent measurement performance, temperature insensitivity and practical usefulness of the accelerometer. Ninety FBG accelerometers are successfully installed on the site of the FAST project, where they are precisely measuring and documenting the magnitude of force exerted on the edge cables.

Bearing fault diagnosis based on spatial filtering constraint feature extraction and deep network

As the core component of a gas turbine, the health condition of the main bearing has a crucial impact on the safe operation of the gas turbine. However, the distribution inconsistency problem existing in the time series data and the nonlinear coupling effect between the data will affect the extraction of characteristic fault features, leading to a decrease in diagnostic accuracy. To solve the above problems, this paper proposes a bearing fault diagnosis method based on frequency domain distribution filter and deep learning. Specifically, a sinusoidal Mel filter bank is designed to extract the fault features of low-frequency vibration signals based on the distribution principle of the traditional Mel filter bank. Then, considering that the fault information contained in other frequency bands of the vibration signals is also not easy to ignore, an inverse sinusoidal Mel filter bank is constructed to further mine the signature fault features of the vibration signals in the middle and high-frequency bands. Finally, the frequency domain distribution filter is proposed by combining the above two filters to reduce the impact of data distribution inconsistency on the accuracy of fault diagnosis. In addition, a deformable convolutional network is applied to further decouple the fault data and improve the spatial separability of the data features. Experiments with inconsistent data distribution are validated on two public datasets, and the diagnostic accuracy reaches 100%; the engineering reliability of the proposed method is verified on the main bearing of a gas turbine, and the accuracy reaches 99.86%.

A dual oblique wing-based low-frequency FBG accelerometer

The low-frequency vibration measurement technology is significant in energy exploration, aerospace, geophysical activities, health monitoring of large engineering structures, etc. A low-frequency FBG accelerometer based on a dual oblique wing is proposed to address the issue of difficulty in accurately measuring low-frequency vibration signals in current fiber Bragg grating accelerometers. Firstly, the structure of this accelerometer was theoretically analyzed and dimension-optimized. Secondly, the static stress analysis and modal simulation analysis are carried out, and the accelerometer is developed. Finally, it is fixed on the vibration table, and the low-frequency vibration test system is built to test the performance. The experimental results show that the natural frequency of the accelerometer is 46 Hz, the working frequency band is 0.1–28 Hz, the sensitivity is 55.6 pm/g, the dynamic range is 48.94 dB, and the resistance to transverse interference of less than 5.62 %. The accelerometer designed in this paper provides a new idea for low-frequency vibration signal measurement.

Low-frequency FBG vibration sensors for micro-seismic monitoring

Vibration sensors are key components in low-frequency micro-seismic monitoring, and their performance directly determines the accuracy of monitoring results. In response to the current problem that fiber Bragg grating (FBG) vibration sensors are difficult to effectively monitor micro-seismic low-frequency vibration signals, a rigid L-shaped beam FBG vibration sensor based on bearings is proposed. Firstly, a sensor model is established and theoretically analyzed; secondly, key parameters are optimized using differential evolution algorithm and imported into COMSOL simulation software for static stress analysis and dynamic characteristic analysis; finally, the sensor prototype is developed and a low-frequency vibration test system is set up to verify the sensor performance. The results reveal that the inherent frequency of the sensor is 57 Hz, with a flat response band of 0.3–35 Hz, a frequency lower limit of 0.05 Hz, a transverse interference degree of 4.5%, an average sensitivity of over 800 pm g−1, a dynamic range of 67.75 dB, favorable linearity, and the ability to achieve temperature self-compensation. Research findings provide new insights into low-frequency micro-seismic monitoring.

Rotating cantilever-based low-frequency double-fiber grating acceleration sensor.

Acceleration sensors play an important role in bridges, dams, seismic monitoring, geological exploration, and more. Aiming at the problem that it is still difficult to accurately measure low-frequency vibration signals with low-frequency acceleration sensors, a high-sensitivity, wide-low-band fiber Bragg grating (FBG) acceleration sensor incorporating a rotating cantilever and springs was proposed. A sensor mechanics model was built, and its key parameters were analyzed theoretically and optimized in size. ANSYS Workbench was used for simulation analysis, and the physical sensor was developed while a low-frequency test platform was established for performance tests. The experimental results suggested that the natural frequency of the sensor was 78Hz, the operating frequency band was 1-55Hz, the sensitivity was 1127.2 pm/g, the transverse interference immunity was less than 5.45%, and the dynamic range was 86.45 dB. With high sensitivity, wide low frequency band, and excellent temperature compensation characteristics, the designed sensor could provide a reference for the design of like FBG acceleration sensors.

Research on low-frequency FBG accelerometer based on double curved beam reed

The precision measurement of low frequency vibration signal is a research hotspot at present. Aiming at the problem that FBG accelerometer is difficult to measure low-frequency vibration effectively at present, a low-frequency FBG accelerometer based on double curved beam reed is proposed. By experimental test, that the sensor has a natural frequency of 41 Hz, flat band at 2–32 Hz, and can detect the low-frequency vibration signal of 1 Hz, the sensitivity is 867.21 pm/g, the linearity is up to 99.95% , and the transverse crosstalk in the flat frequency range is low, which is −22.75 dB. The sensor weighs 200 g and has a volume of 40 cm3.

Simultaneous measurement of vibration and temperature based on FBG and DBR fiber laser beat frequency digital sensing system

A fiber Bragg grating (FBG) and distributed Bragg reflection (DBR) fiber laser sensor combined digital sensing system for both vibration and temperature sensing is proposed. To the best of the authors’ knowledge, this is the first FBG and DBR fiber laser combined dual parameters digital sensing system ever reported. By utilizing both FBG and DBR fiber laser sensor, not only a low frequency vibration detection as low as 0.25 Hz can be achieved, but also temperature and vibration dual parameters sensing can be achieved. External vibration is applied on the FBG which is part of the DBR fiber sensor. The wavelength change of DBR fiber laser sensor’s polarization laser modes is controlled by the FBG. Frequency change of polarization laser modes’ beat frequency (PMBF) signal is closely related to the reflected wavelength change of the sensing FBG. Variational mode decomposition (VMD) algorithm is utilized to denoise the monitored time–frequency signal of PMBF and the denoised signal is fast Fourier transformed (FFT) to get the corresponding vibration frequency. By utilizing this method, extremely low frequency vibration signal can be accurately demodulated. Beat frequency signals (BFS) of multi-longitudinal mode lasers which are generated in the DBR fiber laser sensor are utilized for temperature sensing. Measurement results demonstrate that the dual parameters digital sensing system has an excellent low frequency vibration-sensing capability, simple structure, high SNR, stability and accurate dual parameters sensing without mutual interference.

Cross spring leaf-based high-sensitivity low-frequency dual-FBG acceleration sensor.

The measurement of low-frequency vibration signals is of great significance in seismic monitoring, health monitoring of large and medium-sized engineering structures, and resource exploration. In view of the low sensitivity of fiber Bragg grating (FBG) acceleration sensors in measuring low-frequency vibration signals, a high-sensitivity, low-frequency dual-FBG acceleration sensor is proposed. Theoretical formula derivation and ANSYS software were used to optimize the design and simulation analysis of the structural parameters of the sensor. The real sensor was made based on the simulation results, and a test system was established to test its performance. According to the findings, the natural frequency of the acceleration sensor is 65 Hz. It gives a flat sensitivity response in the low frequency band of 3-45 Hz. The dynamic range is 92.63 dB at 10 Hz, the acceleration sensitivity is 1498.29 pm/g, and the linearity R2 is 0.9998. The relative standard deviation of the sensor repeatability is 1.75%, and the transverse crosstalk in the working frequency band is -33.99dB. Designed with a high sensitivity and excellent temperature compensation capacity in the low-frequency band, the designed sensor is suitable for low- and medium-frequency vibration detection in engineering.

Bone Conduction Hearing Aid

Abstract: The GSM based Soundbite hearing system allows people with hearing disability to hear the sounds via bone conduction to wear an intraoral device and a small microphone in the deaf ear to regain lost hearing. This device consists of GSM modem, PIC16F877A controller and audio amplifier unit. GSM modem will receive incoming calls and automatically answer the call via AT Commands. Then incoming voice signal is converted into low frequency vibration signal that fed through the teeth to cochlea. Unlike implantable bone conduction hearing aids, Sound Bite requires no surgery. Rather, it is the world’s first removable and non-surgical hearing solution to use the well-established principle of bone conduction to imperceptibly transmit sound via the teeth. Custom made for each person, Sound Bite is simple, removable, and totally non-invasive. This paper introduces a novel hearing aid named artificial ultrasonic bone conduction hearing device, which is different from the traditional hearing aid in two sides: 1) sound conduction manner, 2) human perceptive principles. We focus on discussing the structure of the hearing aid and the research of frequency transposition algorithm. In addition, we design algorithm experimental platform and some sample electromechanical transducers.

A hybrid FBG-based load and vibration transducer with a 3D fused deposition modelling approach

A fibre Bragg grating (FBG)-based load and vibration transducer (FLVT) was developed using a 3D fused deposition modelling (FDM) approach. A newly FLVT was designed by the equal-strength cantilever beam in which the FBG sensors were embedded in the beam during the FDM process. The temperature effect was eliminated by the temperature sensor in the vibration sensing unit. The parameters of the proposed FLVT was examined by the finite element method. The simulated results were matched well with the theoretical analysis results and laboratory calibration results. The proposed transducer has the pressure measurement sensitivity of 0.01274 nm kPa−1 for the earth pressure below 150 kPa. In addition, the proposed transducer could accurately measure low-frequency vibration signals with maximum frequency of 4 Hz and the maximum displacement amplitude of 4 mm with sensitivity of 117.6 pm g−1. The measurement accuracy and stability were carried out. Results shown that the maximum relative errors between the calculation results and the experimental results was 1.3%. The effect of vibration direction was also analysed for the proposed FLVT. The results indicated that the transversal vibration has less influence on the longitudinal vibration. The outcome of this study indicated that the proposed FLVT provide a newly approach for the measurement of earth pressure and soil vibration in one transducer which is quit suit for soil mass.

Design and test of a low frequency Fiber Bragg Grating acceleration sensor with double tilted cantilevers

The collection of low-frequency vibration signals is very important for the monitoring research in various fields such as national defense engineering, bridges and dams, aerospace, and the earthquake resistance of civil building structures. During the structural design of existing cantilever Fiber Bragg Grating (FBG) acceleration sensors, the tilt angle of the cantilever is often ignored, therefore, aiming at this problem, this paper proposed a new FBG acceleration sensor with double titled cantilevers, and used formula derivation and ANSYS software to optimize the structural parameters of the proposed sensor and conduct simulation analysis. Then, according to the simulation results, two sensor prototypes were fabricated, one with tilted cantilevers and the other with horizontal cantilevers, then, the performance of the two was tested, compared, and analyzed to verify the impact of the tilt angle of cantilevers on the performance of the sensor. The experimental results showed that, the natural frequency of the proposed sensor was about 46 Hz, which can be used to monitor vibration signals with the 6–30 Hz frequency range; the sensitivity of the proposed sensor was about 4.16 pm/m s−2; and its degree of lateral an-interference was less than 5.62%. Compared with the sensor with horizontal cantilevers, the flat response area of the sensor with tilted cantilevers increased by about 30%, while its sensitivity reduced by about half. The research findings of this paper provide a useful reference for the research on similar type sensors and further expansion of the measurement range of FBG acceleration sensors.

A multi-cantilever beam low-frequency FBG acceleration sensor

The acquisition of 2–50 Hz low-frequency vibration signals is of great significance for the monitoring researches on engineering seismology, bridges & dams, oil & gas exploration, etc. A multi-cantilever beam low-frequency FBG acceleration sensor is proposed against the low sensitivity that predominates in the low-frequency vibration measurement by FBG acceleration sensors. Structural parameters of the sensor is subjected to simulation analysis and optimization design using the ANSYS software; the real sensor is developed based on the simulation results in the following manner: Three rectangular of the cantilever beams are evenly arranged around the mass block at 120°to improve the sensitivity and alleviate the transverse crosstalk of sensor; in the end, a performance test is performed on the sensor. According to the research findings, the sensor, whose natural frequency is approximately 64 Hz, is applicable for monitoring the low-frequency vibration signals within the range 16–54 Hz. The sensor sensitivity is approximately 87.955,{text{pm/m}};{text{s}}^{ - 2}, the linearity being greater than 99%, the transverse interference immunity being lower than 2.58%, and the dynamic range being up to 86 dB. The findings offer a reference for developing sensor of the same type and further improving the sensitivity of fiber optic acceleration sensor.

Temperature-insensitive FBG acceleration sensor based on strain chirp effect

The measurement of low-frequency vibration signals is a very important job in the fields of earthquake early warning, health monitoring of large-scale engineering structures, and geological exploration. Aiming at the problem of Fiber Bragg Grating (FBG) acceleration sensors’ cross-sensitivity to temperature and strain when measuring low-frequency vibration signals, this paper developed an M-shaped double cantilever beam structure that can produce chirp effect with its own structural characteristics, thereby making the sensor insensitive to temperature. Through theoretical analysis and simulation, the paper obtained the relationship between the reflection spectrum bandwidth of the chirped FBG and its acceleration. It adopted a spectrometer and a vibration test system to detect the reflection spectrum bandwidth of the FBG, and then obtained the acceleration. The experimental results showed that, compared with bare fiber grating, the temperature sensitivity of the proposed sensor was significantly lower, and its reflection spectrum bandwidth was not sensitive to temperature changes, moreover, there are good linear relationships between the reflection spectrum bandwidth, the power of the light, and the acceleration. The sensitivity was about 256 pm/g, the natural frequency was 66 Hz; therefore, the proposed sensor had realized high-performance detection of low-frequency vibration signals.

Frequency drift mitigation of Φ-OTDR using difference-fitting method.

A difference-fitting method is proposed to mitigate the low frequency drift of a phase-sensitive optical time domain reflectometry (Φ-OTDR) system caused by laser phase noise. The effective difference region for phase demodulation is theoretically analyzed and experimentally verified, which should be greater than the convolution of the spatial resolution and the length of disturbed optical fiber. Then, a median-fitting algorithm is used to obtain the phase noise of the differential region. The vibration signal of 0.2 Hz is first demodulated with the SNR of 41.79 dB on the optical fiber of 11 km. The low-frequency vibration signals of 0.05 Hz and 0.02 Hz are then successfully restored by using the difference-fitting method, which can effectively eliminate the influence of low frequency drift.

Intelligent Force-Measurement System Use in Shock Tunnel.

The inertial vibration of the force measurement system (FMS) has a large influence on the force measuring result of aircraft, especially on some tests carried out in high-enthalpy impulse facilities, such as in a shock tunnel. When force tests are conducted in a shock tunnel, the low-frequency vibrations of the FMS and its motion cannot be addressed through digital filtering because of the inertial forces, which are caused by the impact flow during the starting process of the shock tunnel. Therefore, this paper focuses on the dynamic characteristics of the performance of the FMS. A new method—i.e., deep-learning-based single-vector dynamic self-calibration (DL-based SV-DSC) of an impulse FMS, is proposed to increase the accuracy of aerodynamic force measurements in a shock tunnel. A deep-learning technique is used to train the dynamic model of the FMS in this study. Convolutional neural networks with a simple structure are applied to describe the dynamic modeling so that the low-frequency vibration signals are eliminated from the test results of the shock tunnel. By validation of the force test results measured in a shock tunnel, the current trained model can realize intelligent processing of the balance signals of the FMS. Based on this new method of dynamic calibration, the reliability and accuracy of force data processing are well verified.

Real-time acceleration sensing with an arctan algorithm based on a modal interferometer.

This study proposes a fiber-optic accelerometer for low-frequency vibration signal detection. The phase velocities of the polarization eigenmodes are affected differently by signals, leading to a polarization rotation of the transmitted lights. The orthogonal square roots of the photovoltages are utilized for an arctan demodulation scheme. Experimental results show that it provides a flat response of 75.04 mrad/g, an average resolution of 13.44 μg/√Hz, and a dynamic range of 111.62 dB below 180 Hz. The environmental instability and sensor complexity are significantly reduced, so that the sensor can be further used in the warning of coal and gas outburst.

Low-frequency vibration transmission and mechanosensory detection in the legs of cave crickets

Vibrational communication is common in insects and often includes signals with prominent frequency components below 200 Hz, but the sensory adaptations for their detection are scarcely investigated. We performed an integrative study of the subgenual organ complex in Troglophilus cave crickets (Orthoptera: Rhaphidophoridae), a mechanosensory system of three scolopidial organs in the proximal tibia, for mechanical, anatomical and physiological aspects revealing matches to low frequency vibration detection. Microcomputed tomography shows that a part of the subgenual organ sensilla and especially the accessory organ posteriorly in this complex are placed closely underneath the cuticle, a position suited to evoke responses to low-frequency vibration via changes in the cuticular strain. Laser-Doppler vibrometry shows that in a narrow low-frequency range the posterior tibial surface reacts stronger to low frequency sinusoidal vibrations than the anterior tibial surface. This finding suggests that the posterior location of sensilla in tight connection to the cuticle, especially in the accessory organ, is adapted to improve detectability of low-frequency vibration signals. By electrophysiological recordings we identify a scolopidial receptor type tuned to 50–300 Hz vibrations, which projects into the central mechanosensory region specialised for processing low-frequency vibratory inputs, and most likely originates from the accessory organ or the posterior subgenual organ. Our findings contribute to understanding of the mechanical and neuronal basis of low-frequency vibration detection in insect legs and their highly differentiated sensory systems.