Flat Frequency Bands Research Articles

Distributed strain monitoring method for structural vibration based on multi-point acceleration measurement

Fiber Bragg Grating (FBG) has been widely used in vibration monitoring due to its advantages of high sensitivity, resistance to electromagnetic interference and ease of networking. This paper proposes a method of distributed strain monitoring for vibrating structures where the surface is unsuitable for attaching FBG. This method utilizes measured multi-point acceleration to calculate dynamic displacement, and subsequently reconstructs distributed strain based on displacement matching and a displacement–strain function. Finite element simulation results demonstrate that the displacement matching scheme has higher strain reconstruction accuracy and broader adaptability. An FBG accelerometer with an equal-strength beam is designed, fabricated, and tested, exhibiting a resonant frequency of 56 Hz and an average sensitivity of 70 pm·g−1 in the flat frequency band. The proposed method is experimentally validated using a 12 m steel pipeline. It’s demonstrated that the displacement reconstruction error is less than 8 %, and the strain reconstruction error is less than 11 %.

Development of low frequency and high sensitivity fiber optic accelerometer based on multi-stage flexure hinges

In order to reduce the stiffness of the flexure hinges, a low-frequency fiber Bragg grating (FBG) accelerometer based on multi-stage flexure hinges is designed. According to the series–parallel connection theory of springs, the acceleration response and anti-interference characteristics of the accelerometer are experimentally studied. The experimental results shows that the accelerometer with multi-stage hinges has a wide flat frequency band and high sensitivity. The resonant frequency is 84.2 Hz, the response sensitivity of the external vibration signal is 927.21 pm/G in the range of 1–60 Hz and the lateral interference degree is 5.8 %. It shows that the acceleration sensing performance of the accelerometer is good. On this basis, changing the hinge radius, thickness or the size of the mass block can further expand the measurement range of the accelerometer, which is expected to be applied in the field of low-frequency oil and gas seismic exploration.

Observation of Flat Frequency Bands at Open Edges and Antiphase Boundary Seams in Topological Mechanical Metamaterials

Motivated by the recent theoretical studies on a two-dimensional (2D) chiral Hamiltonian based on the Su-Schrieffer-Heeger chains [L. Zhu, E. Prodan, and K. H. Ahn, Phys. Rev. B 99, 041117(R) (2019)PRBMDO2469-995010.1103/PhysRevB.99.041117], we experimentally and computationally demonstrate that topological flat frequency bands can occur at open edges of 2D planar metamaterials and at antiphase boundary seams of ring-shaped or tubular metamaterials. Specifically, using mechanical systems made of magnetically coupled spinners, we reveal that the presence of the edge or seam bands that are flat in the entire projected reciprocal space follows the predictions based on topological winding numbers. The edge-to-edge distance sensitively controls the flatness of the edge bands and the localization of excitations, consistent with the theoretical analysis. The analog of the fractional charge state is observed. Possible realizations of flat bands in a large class of metamaterials, including photonic crystals and electronic metamaterials, are discussed.

Temperature-insensitive Fabry–Perot interferometer for microseism sensing based on hollow core photonic crystal fibres

This study proposes an inline temperature-insensitive Fabry–Perot interferometer (TI-FPI) for coal mine microseism sensing based on a cantilever structure. The sensor is fabricated by splicing a section of hollow core photonic crystal fibre (HC-PCF) between a lead-in polarisation-maintaining fibre (PMF) and a multi-mode fibre (MMF) using a CO2 laser splicer. The HC-PCF and MMF are employed as a cantilever beam. An air cavity of the TI-FPI formed by the HC-PCF is modulated via external vibration, leading to a variation in the length. Sensors with air cavities of 407 μm, 698 μm, and 1069 μm are demonstrated. The experimental results show that the lowest temperature response is −0.04 pm/°C. The flat frequency band of the acceleration response can be adjusted by the cantilever beam's length, and the best average sensitivity and resolution of the sensors are 3.45 mV/g and 0.26 mg/√Hz (g is gravity of 9.8 m/s2), respectively. The minimum resolution is 5.04 μg/√Hz at a resonance frequency of 1500 Hz. The sensor is anticipated to have wide application prospects in microseism monitoring in coal mines.

Design and Modeling of a High Sensitivity Fiber Bragg Grating-Based Accelerometer

Use of a detailed theoretical model has allowed the optimization of the design of a high sensitivity accelerometer, based on a fiber Bragg grating (FBG) and an accelerometer based on this design has been demonstrated experimentally. With a universal model based on double-point encapsulation established, the performance of the device in terms of its optimal sensitivity and frequency distribution has been analyzed, with an optimization ‘figure of merit’ using the product of the sensitivity and the resonant frequency being presented. The experimental results obtained indicate that the FBG-based accelerometer thus developed shows a broad, flat frequency band, a corresponding flat range sensitivity of ~152.0pm/G, a resonant frequency of 441.0Hz, and a cross-axis sensitivity of less than 3.6% of the main-axis sensitivity. An accelerometer of this type and with this performance thus has the potential for the important field of low frequency oil-gas seismic exploration.

End-to-End Propagation Noise and Memory Analysis for Molecular Communication over Microfluidic Channels

Molecular communication (MC) between a transmitter and a receiver placed in the chambers attached to a microfluidic channel is investigated. A linear end-to-end channel model is developed capturing the effects of the diffusion and the junction transition at the chambers, as well as the microfluidic channel shapes and the fluid flow. The spectral density of the propagation noise is studied, and the flat frequency bands are identified for the chambers and the microfluidic channel. This suggests that in certain microfluidic design choices, the spectral density of noise may end up naturally being flat. Motivated by this result, the additive white Gaussian noise (AWGN) model is developed based on the chamber, the microfluidic channel, and the fluid flow parameters for the end-to-end propagation noise. Furthermore, the molecular memory is modeled due to inter-diffusion among transmitted molecular signals. The effect of the molecular memory on the end-to-end propagation noise is also analyzed. To substantiate our analytical results, the ranges of physical parameters that yield a linear end-to-end MC channel are investigated. These results show the validity of the AWGN model for MC over microfluidic channels and characterize the impact of the microfluidic channel and chamber geometry on the propagation noise and memory.

Performance Analysis of Infrasound Sensor InSAS2008

It is known that earthquakes generate infrasound. The frequency spectra of the infrasound signals associated with earthquakes are concentrated within a wide frequency range (0.002-0.02 Hz), and have spectral tail extending up to the frequencies 0.1-1 Hz. Therefore, the dynamic characteristics of infrasound sensors should be chosen so as to capture main features of such signals. In this paper, the characteristics of infrasound sensor InSAS2008 developed by Institute of acoustics, Chinese academy of sciences, are described. Its performance indicators are listed and its frequency response is analyzed. The special construction in the mechanical design is developed to overcome drift problem caused by temperature variations. In addition, the infrasound sensor is not affected by nonlinear effects. The calibration results show that infrasound sensor works within a wide and flat frequency band.

Topological photonic bands in two-dimensional networks of metamaterial elements

We show that topological frequency band structures emerge in two-dimensional electromagnetic lattices of metamaterial components without the application of an external magnetic field. The topological nature of the band structure manifests itself by the occurrence of exceptional points in the band structure or by the emergence of one-way guided modes. Based on an electromagnetic network with nearly flat frequency bands of nontrivial topology, we propose a coupled-cavity lattice made of superconducting transmission lines and cavity QED components, which is described by the Jaynes–Cummings–Hubbard model and can serve as a simulator of the fractional quantum Hall effect.

Development of velocity sensor with high frequency band and its application to a vibration isolate table

Abstract The vibration sensors are widely used in the field of vibration control and measurement. In applying the modern control theory to anti-vibration controlled objects, the state variables both the velocity and displacement become useful signals. Then, the velocity sensor in comparison with the acceleration sensor, which is in generally used, is very useful. However, its frequency band is limited by high frequency resonance due to the electrical stiffness. If the velocity sensor having flat frequency band is developed, this sensor becomes easy to handle not only in the control field but also in the measurement filed. Then, this paper shows that the inverse notch filter, which is inserted in the closed loop, flattens out the frequency response originally having high frequency resonance. Firstly, the block diagram of the velocity sensor as a closed system is shown. Its sensitivity, the low break point frequency, and the high frequency resonance are formulated. Secondly, the gain and phase margins are calculated and we try to improve the frequency response based on these indices. Finally, the application of improved velocity sensor to an anti-vibration apparatus is shown.