Polyvinylidene Fluoride-Added Ceramic Powder Composite Near-Field Electrospinned Piezoelectric Fiber-Based Low-Frequency Dynamic Sensors

In this study, near-field electrospining on hollow cylindrical (NFES) process was used to fabricate permanent piezoelectricity of polyvinylidene fluoride (PVDF) piezoelectric nanofibers. With in situ electric poling, mechanical stretching and heating during NFES process, the pre-strained piezoelectric PVDF nanofibers with high stretchability and energy conversion efficiency can be applied at low-frequency ambient vibration to convert mechanical energies into electrical signals. By adjusting rotating velocity of the hollow cylindrical glass tube on X-Y stage, electric field, baking temperature and carbon nanotube (CNT) concentration in PVDF solution, the crystalline of β phase, polarization intensity and morphology of piezoelectric fiber can be controlled. XRD (X-ray diffraction) observation of PVDF fibers was characterized. With electric field 0.5×107 V/m (needle-to-tube distance 2 mm and DC voltage 5 kV), rotating velocity 400 r.p.m, baking temperature 80 °C and 0.03 wt% CNT in NFES process, it reveals a high diffraction peak at 2θ=20.8° of piezoelectric crystal β-phase structure. Then the array nanofibers were transferred onto a parallel copper electrode by using flexible insulation epoxy/PI film to provide packaging protection. When the sensor was tested under 5 Hz vibration frequency, the maximum induced voltage was 29.4 mVp-p.

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Occluded Grape Cluster Detection and Vine Canopy Visualisation Using an Ultrasonic Phased Array

Sensors ◽

10.3390/s21062182 ◽

2021 ◽

Vol 21 (6) ◽

pp. 2182

Author(s):

Baden Parr ◽

Mathew Legg ◽

Stuart Bradley ◽

Fakhrul Alam

Keyword(s):

Near Field ◽

Low Frequency ◽

Volume Estimation ◽

Yield Estimation ◽

3D Scan ◽

Management Processes ◽

Canopy Volume ◽

Ultrasonic Phased Array ◽

Added Benefit ◽

Grape Yield

Grape yield estimation has traditionally been performed using manual techniques. However, these tend to be labour intensive and can be inaccurate. Computer vision techniques have therefore been developed for automated grape yield estimation. However, errors occur when grapes are occluded by leaves, other bunches, etc. Synthetic aperture radar has been investigated to allow imaging through leaves to detect occluded grapes. However, such equipment can be expensive. This paper investigates the potential for using ultrasound to image through leaves and identify occluded grapes. A highly directional low frequency ultrasonic array composed of ultrasonic air-coupled transducers and microphones is used to image grapes through leaves. A fan is used to help differentiate between ultrasonic reflections from grapes and leaves. Improved resolution and detail are achieved with chirp excitation waveforms and near-field focusing of the array. The overestimation in grape volume estimation using ultrasound reduced from 222% to 112% compared to the 3D scan obtained using photogrammetry or from 56% to 2.5% compared to a convex hull of this 3D scan. This also has the added benefit of producing more accurate canopy volume estimations which are important for common precision viticulture management processes such as variable rate applications.

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Liquid encapsulated electrostatic energy harvester for low-frequency vibrations

Journal of Intelligent Material Systems and Structures ◽

10.1177/1045389x12459590 ◽

2012 ◽

Vol 24 (1) ◽

pp. 61-69 ◽

Cited By ~ 17

Author(s):

Ling Bu ◽

Xiaoming Wu ◽

Xiaohong Wang ◽

Litian Liu

Keyword(s):

Polyvinylidene Fluoride ◽

Output Voltage ◽

Energy Harvester ◽

Low Frequency ◽

Electrostatic Energy ◽

Maximum Output ◽

Flowing Liquid ◽

Horizontal Vibration ◽

Low Viscosity ◽

High Relative Permittivity

This article presents the modeling, fabrication, and testing of liquid encapsulated energy harvester using polyvinylidene fluoride electrets. Unlike harvesters reported in previous literature, this liquid encapsulated energy harvester uses flowing liquid rather than conventional resonating structures to induce variable capacitance and is more suitable for low-frequency applications. Prototypes injected with three types of liquid ( N-methyl-2-pyrrolidone, N, N-dimethylformamide, and glycerin) are tested in horizontal vibration and rotary motion mode, respectively. The results show that N, N-dimethylformamide–injected prototypes display the most desirable performance in horizontal vibration testing at 1–10 Hz due to high relative permittivity and low viscosity, with maximum output voltage of 2.32 V and power of 0.18 µW at 10 Hz. Glycerin-injected prototypes perform best at 0.1–1 Hz rotation due to effective movement and highest permittivity, with maximum output voltage of 11.46 V and power of 2.19 µW at 1 Hz.

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Hydrodynamic Noise and Radiated Mechanism of 3D Cavity

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.217-219.2590 ◽

2012 ◽

Vol 217-219 ◽

pp. 2590-2593 ◽

Cited By ~ 1

Author(s):

Yu Wang ◽

Bai Zhou Li

Keyword(s):

Sound Pressure ◽

Near Field ◽

Low Frequency ◽

Dipole Source ◽

Fluctuating Pressure ◽

Common Structure ◽

Hydrodynamic Noise ◽

Near Field Sound ◽

Equivalent Sources ◽

Field Sound

The flow past 3D rigid cavity is a common structure on the surface of the underwater vehicle. The hydrodynamic noise generated by the structure has attracted considerable attention in recent years. Based on LES-Lighthill equivalent sources method, a 3D cavity is analyzed in this paper, when the Mach number is 0.0048. The hydrodynamic noise and the radiated mechanism of 3D cavity are investigated from the correlation between fluctuating pressure and frequency, the near-field sound pressure intensity, and the propagation directivity. It is found that the hydrodynamic noise is supported by the low frequency range, and fluctuating pressure of the trailing-edge is the largest, which is the main dipole source.

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Ground Attenuation Factor Based on Measurements

INTER-NOISE and NOISE-CON Congress and Conference Proceedings ◽

10.3397/in-2021-2405 ◽

2021 ◽

Vol 263 (3) ◽

pp. 3436-3447

Author(s):

Dan Lin ◽

Andrew Eng

Keyword(s):

Near Field ◽

Attenuation Factor ◽

Measurement Data ◽

Low Frequency ◽

Sound Sources ◽

Frequency Sound ◽

Sound Levels ◽

Different Types ◽

Noise Measurements ◽

Field Sound

Assumptions made on the ground types between sound sources and receivers can significantly impact the accuracy of environmental outdoor noise prediction. A guideline is provided in ISO 9613-2 and the value of ground factor ranges from 0 to 1, depending on the coverage of porous ground. For example, a ground absorption factor of 1 is suggested for grass ground covers. However, it is unclear if the suggested values are validated. The purpose of this study is to determine the sound absorption of different types of ground by measurements. Field noise measurements were made using an omnidirectional loudspeaker and two microphones on three different types of ground in a quiet neighborhood. One microphone was located 3ft from the loudspeaker to record near field sound levels in 1/3 and 1 octave bands every second. The other microphone was located a few hundred feet away to record far field sound in the same fashion as the near field microphone. The types of ground tested were concrete, grass, and grass with trees. Based on the measurement data, it was found that grass and trees absorb high frequency sound well and a ground factor of 1 may be used for 500Hz and up when using ISO 9613-2 methodology. However, at lower frequencies (125 Hz octave band and below), grassy ground reflects sound the same as concrete surfaces. Trees absorb more low frequency sound than grass, but less than ISO 9613-2 suggested.

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A New Methodology to Predict the Magnetic Shielding Effectiveness of Enclosures at Low Frequency in the Near Field

IEEE Transactions on Magnetics ◽

10.1109/tmag.2014.2362953 ◽

2015 ◽

Vol 51 (3) ◽

pp. 1-4 ◽

Cited By ~ 14

Author(s):

Amin Frikha ◽

Mohamed Bensetti ◽

Fabrice Duval ◽

Nabil Benjelloun ◽

Frederic Lafon ◽

...

Keyword(s):

Near Field ◽

Low Frequency ◽

Magnetic Shielding ◽

Shielding Effectiveness

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Enhanced transmission efficiency of magneto-inductive wave propagating in non-homogeneous 2-D magnetic metamaterial array

Physica Scripta ◽

10.1088/1402-4896/ac4a3a ◽

2022 ◽

Author(s):

Thi Hong Hiep Le ◽

Thanh Son Pham ◽

Bui Xuan Khuyen ◽

Bui Son Tung ◽

Quang Minh Ngo ◽

...

Keyword(s):

Near Field ◽

Low Frequency ◽

Transmission Efficiency ◽

Position Sensor ◽

Wireless Power ◽

Current Ratio ◽

Enhanced Transmission ◽

Unit Cells ◽

Simulation And Experiment ◽

Ratio Transmission

Abstract In this work, we investigate the propagation of magneto-inductive waves (MIWs) in ordering magnetic metamaterial (MM) structures. The proposed non-homogeneous MM slab consists of 9 × 9 MM unit cells constructed from a five-turn spiral embedded on an FR-4 substrate. External capacitors with the value of 40 pF or 50 pF were added to control the resonant frequency of each unit cell in accordance with the waveguide configurations. The characteristics of metamaterial structures, such as negative permeability, current ratio, transmission response, and field distribution in the waveguide, have been thoroughly analyzed by simulation and experiment. Because of the strong magnetic field confinement in the waveguide, the transmittance after nine elements of the non-homogeneous MM slab is 5.2 times greater than that of the homogeneous MM slab. This structure can be applied to the planar near-field wireless power transfer, position sensor, and low-frequency communication.

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Development of an Improved LMD Method for the Low-Frequency Elements Extraction from Turbine Noise Background

Energies ◽

10.3390/en13040805 ◽

2020 ◽

Vol 13 (4) ◽

pp. 805

Author(s):

Lida Liao ◽

Bin Huang ◽

Qi Tan ◽

Kan Huang ◽

Mei Ma ◽

...

Keyword(s):

Renewable Energy ◽

Wind Turbine ◽

Condition Monitoring ◽

Renewable Energy Sources ◽

Near Field ◽

Low Frequency ◽

Aerodynamic Noise ◽

Frequency Noise ◽

Human Society ◽

Noise Background

Given the prejudicial environmental effects of fossil-fuel based energy production, renewable energy sources can contribute significantly to the sustainability of human society. As a clean, cost effective and inexhaustible renewable energy source, wind energy harvesting has found a wide application to replace conventional energy productions. However, concerns have been raised over the noise generated by turbine operating, which is helpful in fault diagnose but primarily identified for its adverse effects on the local ecosystems. Therefore, noise monitoring and separation is essential in wind turbine deployment. Recent developments in condition monitoring provide a solution for turbine noise and vibration analysis. However, the major component, aerodynamic noise is often distorted in modulation, which consequently affects the condition monitoring. This study is conducted to explore a novel approach to extract low-frequency elements from the aerodynamic noise background, and to improve the efficiency of online monitoring. A framework built on the spline envelope method and improved local mean decomposition has been developed for low-frequency noise extraction, and a case study with real near-field noises generated by a mountain-located wind turbine was employed to validate the proposed approach. Results indicate successful extractions with high resolution and efficiency. Findings of this research are also expected to further support the fault diagnosis and the improvement in condition monitoring of turbine systems.

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Hybrid Method of Modal Analysis and Laser Shock Scanning to Visualize the Pyroshock Propagation in a Tension Joint

Shock and Vibration ◽

10.1155/2019/4389595 ◽

2019 ◽

Vol 2019 ◽

pp. 1-13

Author(s):

Yong-Woon Kim ◽

Jae-Kyeong Jang ◽

Jung-Ryul Lee ◽

Hak-Seong Gim

Keyword(s):

Modal Analysis ◽

Hybrid Method ◽

Response Spectrum ◽

Near Field ◽

Low Frequency ◽

Simulation Method ◽

Experimental Simulation ◽

Laser Shock ◽

Simulation Results ◽

Tension Joint

The use of pyrodevices in the aerospace industry has been increasing because of their ability to implement separation missions with a small weight, for example, space launchers, spacecrafts, and missiles. During operation, pyrodevices generate pyroshock, which causes failures of electronic devices. Recently, a pyroshock simulation method using laser shock has been developed to evaluate the risk of pyroshock before flight mission. However, depending on the structure, the laser shock showed some difficulty simulating pyroshock in the low-frequency regime accompanying vibration. Therefore, in this study, we developed a hybrid method of numerical modal analysis and laser shock-based experimental simulation to visualize the pyroshock propagation in all the relevant frequency regimes. For the proof of concept of the proposed method, we performed experiments of explosive bolt-induced shock and pyrolock-induced shock in the open-box-type tension joint and compared the hybrid simulation results with actual pyroshock. From the results, we obtained the simulated time-domain signal with an averaged peak-to-peak acceleration difference (PAD) of 11.2% and the shock response spectrum (SRS) with an averaged mean acceleration difference (MAD) of 28.5%. In addition, we were able to visualize the simulation results in the temporal and spectral domains to compare the pyroshock induced by each pyrodevice. A comparison of the simulations showed that the pyrolock had an impulse level of 1/12 compared to the explosion bolt. In particular, it was confirmed that the pyrolock-induced shock at the near field can cause damage to the electronic equipment despite a smaller impulse than that of the explosive bolt-induced shock. The hybrid method developed in this paper demonstrates that it is possible to simulate pyroshock for all the frequency regimes in complex specimens and to evaluate the risk in the time and frequency domain.

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Biomimetic tough helicoidally structured material through novel electrospinning based additive manufacturing

MRS Advances ◽

10.1557/adv.2019.313 ◽

2019 ◽

Vol 4 (43) ◽

pp. 2345-2354 ◽

Cited By ~ 2

Author(s):

Komal Agarwal ◽

Rahul Sahay ◽

Avinash Baji ◽

Arief S. Budiman

Keyword(s):

Structural Design ◽

Polyvinylidene Fluoride ◽

Architectural Design ◽

Mechanical Characteristics ◽

Near Field ◽

Structural Materials ◽

Electrospinning Technique ◽

Mantis Shrimp ◽

Novel Method ◽

Microstructural Design

ABSTRACTNatural structural materials (NSMs) such as nacre, teeth, bones and crustacean exoskeleton are usually made of weak biomaterials arranged in specific structural design imparting them remarkable mechanical characteristics. Such hierarchical structural layouts found in nature encourage designing of mechanically desirable synthetic structural materials (SSMs). Among variety of natural hierarchical layouts, this paper specifically focuses on helicoidal architectural design found in the tough dactyl club of mantis shrimp. We first decode the mechanics behind helicoidal microstructural design and document the development of impact resistant macroscale helicoidal architectured synthetic structural materials (HA-SSMs). Next, near-field electrospinning technique (NFES)- both melt (polycaprolactone) and solution (polyvinylidene fluoride) type has been discussed in detail, as a novel method for developing lab scale 3D biomimetic HA-SSMs in micro-nanoscale. Further, the effect of the helical arrangement, size of substructures and surface treatment on strength and toughness of NFES fabricated HA-SSMs samples is analysed.

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