scholarly journals Modification of Mechanical and Electromechanical Resonances of Cellular Ferroelectret Films Depending on the External Load

Polymers ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 3239
Author(s):  
Julio Quirce Aguilar ◽  
Tomás Gómez Álvarez-Arenas
Keyword(s):  
Film Thickness ◽  
External Load ◽  
Mechanical Load ◽  
Water Immersion ◽  
Polarization Vector ◽  
Ultrasonic Transducers ◽  
Piezoelectric Response ◽  
Active Elements ◽  
Electromechanical Responses ◽  
Electrically Charged

Ferroelectret films are cellular polymers with electrically charged pores that exhibit piezoelectric response. Among other applications, ferroelectret films have been widely used as active elements in air-coupled ultrasonic transducers. More recently, they have also been tested in water immersion. They show a promising wide frequency band response, but a poor sensitivity produced by the disappearance of the electromechanical resonances. This paper studies in detail the modification of FE films response when put into water immersion, both the mechanical and the electromechanical responses (the latter in transmission and reception modes). The lack of electromechanical thickness resonances when the films are put into water is explained as the result of the different profile of the modification of the polarization vector along the film thickness imposed by the large mechanical load produced by the water. This different electromechanical response can also be the reason for the subtle modification of the mechanical thickness resonances that is also observed and analyzed.

scholarly journals Ferroelectret Ultrasonic Transducers for Pulse-Echo Water Immersion

2020 ◽  
Vol 10 (24) ◽  
pp. 8771
Author(s):  
Julio Quirce ◽  
Linas Svilainis ◽  
Jorge Camacho ◽  
Tomas Gomez Alvarez-Arenas
Keyword(s):  
Short Pulse ◽  
Water Immersion ◽  
Wide Band ◽  
Spot Size ◽  
Ultrasonic Transducers ◽  
Piezoelectric Response ◽  
Radius Of Curvature ◽  
High Porosity ◽  
Technical Problems ◽  
Pulse Echo

Ferroelectrets are thin and porous polymeric films with a cellular microstructure, high porosity, permanent polarization and piezoelectric response. They have been used for different applications, where one of the most interesting ones is for the fabrication of air-coupled ultrasonic transducers. More recently they have been tested as water immersion transducers, showing a promising wide bandwidth but limited sensitivity along with other technical problems. This paper investigates ultrasonic transducers for water immersion and pulse-echo operation based on ferroelectret films. Two different ferroelectret foams with different resonant frequencies, acoustic impedances and cellular structures were tried. Flat and spherically focused prototypes (radius of curvature of 22 and 35 mm) were produced and tested. Finally, different materials and methods were tried to provide a protective surface coating. Acoustic field measurements for the focused transducers confirm the possibility to efficiently focus the ultrasonic beam by the proposed fabrication method, with focal spot size of 1.86 mm at −6 dB. Results show that in spite of the reduced sensitivity (about −115 dB), some of the tried ferroelectret films provide a very wide band response (−6 dB band from 0.29 to 2.7 MHz) and short pulse duration (2–3 us) that can be of interest for different applications.

scholarly journals Giant electromechanical coupling of relaxor ferroelectrics controlled by polar nanoregion vibrations

2016 ◽  
Vol 2 (9) ◽  
pp. e1501814 ◽  
Author(s):  
Michael E. Manley ◽  
Douglas L. Abernathy ◽  
Raffi Sahul ◽  
Daniel E. Parshall ◽  
Jeffrey W. Lynn ◽  
...  
Keyword(s):  
Local Structure ◽  
Electromechanical Coupling ◽  
Collective Motion ◽  
Piezoelectric Materials ◽  
Relaxor Ferroelectrics ◽  
Piezoelectric Response ◽  
Atomic Displacements ◽  
Electromechanical Responses ◽  
Polar Nanoregions ◽  
Ultrasound Applications

Relaxor-based ferroelectrics are prized for their giant electromechanical coupling and have revolutionized sensor and ultrasound applications. A long-standing challenge for piezoelectric materials has been to understand how these ultrahigh electromechanical responses occur when the polar atomic displacements underlying the response are partially broken into polar nanoregions (PNRs) in relaxor-based ferroelectrics. Given the complex inhomogeneous nanostructure of these materials, it has generally been assumed that this enhanced response must involve complicated interactions. By using neutron scattering measurements of lattice dynamics and local structure, we show that the vibrational modes of the PNRs enable giant coupling by softening the underlying macrodomain polarization rotations in relaxor-based ferroelectric PMN-xPT {(1 − x)[Pb(Mg1/3Nb2/3)O3] – xPbTiO3} (x = 30%). The mechanism involves the collective motion of the PNRs with transverse acoustic phonons and results in two hybrid modes, one softer and one stiffer than the bare acoustic phonon. The softer mode is the origin of macroscopic shear softening. Furthermore, a PNR mode and a component of the local structure align in an electric field; this further enhances shear softening, revealing a way to tune the ultrahigh piezoelectric response by engineering elastic shear softening.

scholarly journals Frequency Dependence of Receiving Sensitivity of Ultrasonic Transducers and Acoustic Emission Sensors

Sensors ◽  
2018 ◽  
Vol 18 (11) ◽  
pp. 3861 ◽  
Author(s):  
Kanji Ono
Keyword(s):  
Acoustic Emission ◽  
Frequency Dependence ◽  
Ultrasonic Transducers ◽  
Piezoelectric Response ◽  
Apparent Velocity ◽  
Response Type ◽  
Low Frequencies ◽  
Calibration Methods ◽  
Velocity Response ◽  
Excitation Method

Receiving displacement sensitivities (Rx) of ultrasonic transducers and acoustic emission (AE) sensors are evaluated using sinewave packet excitation method and compared to the corresponding data from pulse excitation method with a particular emphasis on low frequency behavior below 20 kHz, down to 10 Hz. Both methods rely on the determination of transmitter displacement characteristics using a laser interferometric method. Results obtained by two calibration methods are in good agreement, with average spectral differences below 1 dB, indicating that the two calibration methods yield identical receiving sensitivities. At low test frequencies, effects of attenuation increase substantially due to increasing sensor impedance and Rx requires correction in order to evaluate the inherent sensitivity of a sensor, or open-circuit sensitivity. This can differ by more than 20 dB from results that used common preamplifiers with ~10 kΩ input impedance, leading to apparent velocity response below 100 kHz for typical AE sensors. Damped broadband sensors and ultrasonic transducers exhibit inherent velocity response (Type 1) below their main resonance frequency. In sensors with under-damped resonance, a steep sensitivity decrease occurs showing frequency dependence of f2~f5 (Type 2), while mass-loaded sensors exhibit flat displacement response (Type 0). Such behaviors originate from sensor characteristics that can best be described by the damped harmonic oscillator model. This model accounts for the three typical behaviors. At low frequencies, typically below 1 kHz, receiving sensitivity exhibits another Type 0 behavior of frequency independent Rx. Seven of 12 sensors showed this flat region, while three more appear to approach the Type 0 region. This appears to originate from the quasi-static piezoelectric response of a sensing element. In using impulse method, a minimum pulse duration is necessary to obtain spectral fidelity at low frequencies and an approximate rule is given. Various factors for sensitivity improvement are also discussed.

Introduction to Applications of the Raman Spectroscopy to Experimental Mechanics

2015 ◽  
Vol 240 ◽  
pp. 49-54
Author(s):  
Marek Sikoń ◽  
Bogusław Rajchel ◽  
Jadwiga Kwiatkowska ◽  
Alicja Strzała
Keyword(s):  
Raman Spectroscopy ◽  
External Load ◽  
Laser Light ◽  
Mechanical Load ◽  
Experimental Mechanics ◽  
Mechanical State ◽  
State Of Stress ◽  
The Continuum

In this work, the mechanical state of the material is considered in the form of the oscillation of the molecule. The analysis is carried out for material without an external load and for material under the action of the mechanical load. These two states are tested in a Raman spectroscope where oscillations of molecule with modulations are induced by laser light. One should expect that the results of these investigations will confirm the capability of Raman spectroscopy in analysis of molecular mechanical state of material.This research is carried out using photoelastic material, and an analogy to state of stress on the continuum level is presented by photoelastisity.

Piezoelectric Multimaterial Fibers

2011 ◽  
Vol 1312 ◽  
Author(s):  
Noémie Chocat ◽  
Zheng Wang ◽  
Shunji Egusa ◽  
Zachary M. Ruff ◽  
Alexander M. Stolyarov ◽  
...  
Keyword(s):  
Electric Fields ◽  
Water Immersion ◽  
Ultrasonic Transducer ◽  
Piezoelectric Response ◽  
Water Tank ◽  
Ferroelectric Layer ◽  
Fabry Perot ◽  
Fiber Sample ◽  
Piezoelectric Fiber

ABSTRACTHere we report on the design, fabrication, and characterization of fiber containing an internal crystalline non-centrosymmetric phase enabling piezoelectric functionality over extended fiber lengths [1]. A ferroelectric polymer layer of 30 μm thickness is spatially confined and electrically contacted by internal viscous electrodes and encapsulated in an insulating polymer cladding hundreds of microns in diameter. The structure is thermally drawn in its entirety from a macroscopic preform, yielding tens of meters of piezoelectric fiber. Electric fields in excess of 50V/μm are applied through the internal electrodes to the ferroelectric layer leading to effective poling of the structure. To unequivocally establish that the internal copolymer layer is macroscopically poled we adopt a two-step approach. First, we show that the internal piezoelectric modulation indeed translates to a motion of the fiber’s surface using a heterodyne optical vibrometer at kHz frequencies. Second, we proceed to an acoustic wave measurement at MHz frequencies: a water-immersion ultrasonic transducer is coupled to a fiber sample across a water tank, and frequency-domain characterizations are carried out using the fiber successively as an acoustic sensor and actuator. These measurements establish the broadband piezoelectric response and acoustic transduction capability of the fiber. The potential to modulate sophisticated optical devices is illustrated by constructing a single-fiber electricallydriven device containing a high-quality-factor Fabry-Perot optical resonator and a piezoelectric transducer.

Thermomechanical and Hydrophobic Characterization of Shape Memory Polymers

2009 ◽  
Author(s):  
P. Daniel Warren ◽  
Rafael R. Bernal ◽  
John L. Harper ◽  
Rachelann N. Herlihy ◽  
Jonathan P. Vande Geest
Keyword(s):  
Shape Memory ◽  
Crystalline Structure ◽  
Thermal Energy ◽  
External Load ◽  
Mechanical Load ◽  
Shape Memory Polymers ◽  
Direct Result ◽  
Molecular Architecture ◽  
Original Shape ◽  
Chemical Crosslinks

Shape memory polymers (SMPs) have generated a great amount of interest due to their capacity to recover a programmable shape under an applied stimulus, such as temperature change or light irradation [1, 2]. The SMP is initially synthesized with a specific original shape. This shape can be deformed under a mechanical load and at a temperature (TH) greater than the glass transition temperature, Tg. The application of this deformation coupled with subsequent lowering of the temperature (TC) to below the Tg, can fix the polymer in the newly altered formation even after removal of the external load. Increasing the temperature again, to a point above Tg, then activates the shape memory effect, whereby the original shape can be recovered. This shape memory ability is a direct result of specific molecular architecture. Chemical and physical crosslinks and macromolecular chain entanglements are part of this structure. Chemical crosslinks between segments give form to the original shape. Some of these segments are stimuli-sensitive, in other words, segments can become increasingly elastic with the application of thermal energy. This application of energy causes the crystalline structure of these segments to melt and be easily deformed under external load. This temporary shape can now be maintained with the removal of thermal energy leading to re-crystallization. Recoil in this state is prevented by both the new crystalline structure and entanglements of the segments caused by deformation. Physical crosslinks give the architecture permanence, since the linkages do not degrade with stimulus [3]. Different crosslinker formulations can result in varying types of chemical crosslinks. Variations in the structure lead to alterations in the material properties, such as mechanical characteristics and hydrophobicity.

scholarly journals Load-Dependent Assembly of the Bacterial Flagellar Motor

mBio ◽  
2013 ◽  
Vol 4 (4) ◽  
Author(s):  
Murray J. Tipping ◽  
Nicolas J. Delalez ◽  
Ren Lim ◽  
Richard M. Berry ◽  
Judith P. Armitage
Keyword(s):  
External Load ◽  
Mechanical Load ◽  
Life Cycles ◽  
High Load ◽  
Solid Surfaces ◽  
Flagellar Motor ◽  
Essential Factor ◽  
Liquid Media ◽  
External Mechanical Load ◽  
Bacterial Flagellar Motor

ABSTRACTIt is becoming clear that the bacterial flagellar motor output is important not only for bacterial locomotion but also for mediating the transition from liquid to surface living. The output of the flagellar motor changes with the mechanical load placed on it by the external environment: at a higher load, the motor runs more slowly and produces higher torque. Here we show that the number of torque-generating units bound to the flagellar motor also depends on the external mechanical load, with fewer stators at lower loads. Stalled motors contained at least as many stators as rotating motors at high load, indicating that rotation is unnecessary for stator binding. Mutant stators incapable of generating torque could not be detected around the motor. We speculate that a component of the bacterial flagellar motor senses external load and mediates the strength of stator binding to the rest of the motor.IMPORTANCEThe transition between liquid living and surface living is important in the life cycles of many bacteria. In this paper, we describe how the flagellar motor, used by bacteria for locomotion through liquid media and across solid surfaces, is capable of adjusting the number of bound stator units to better suit the external load conditions. By stalling motors using external magnetic fields, we also show that rotation is not required for maintenance of stators around the motor; instead, torque production is the essential factor for motor stability. These new results, in addition to previous data, lead us to hypothesize that the motor stators function as mechanosensors as well as functioning as torque-generating units.

scholarly journals Temperature and frequency dependence of the dielectric and piezoelectric response of P(VDF–TrFE)/CoFe2O4 magnetoelectric composites

2017 ◽  
Vol 57 (2) ◽  
Author(s):  
Šarūnas Svirskas ◽  
Jaroslavas Belovickis ◽  
Daumantas Šemeliovas ◽  
Pedro Martins ◽  
Senentxu Lanceros-Méndez ◽  
...  
Keyword(s):  
Polyvinylidene Fluoride ◽  
Piezoelectric Coefficient ◽  
Piezoelectric Properties ◽  
Piezoelectric Response ◽  
Free Standing ◽  
Host Matrix ◽  
Practical Applications ◽  
Electromechanical Responses ◽  
Different Temperatures ◽  
Multiferroic Films

CoFe2O4 nanoparticles embedded in polyvinylidene fluoride–trifluoroethylene (P(VDF–TrFE)) matrix show suit­able properties for practical applications as piezoelectric and magnetoelectric transducers. The knowledge about the dielectric and electromechanical responses of the multiferroic films in a broad frequency and temperature range is essential for applicability. The purpose of this work is to investigate the dielectric, ferroelectric and piezoelectric properties of multiferroic composites based on P(VDF–TrFE) as a host matrix and CoFe2O4 as a magnetic filler. Free-standing films with a different concentration of the filler were investigated. The polarization switching was demonstrated for all the compositions. The polarization displacement hysteresis was achieved at different temperatures. The piezoelectric coefficient d33 is not affected by different concentration of ferrite. On the other hand, the composition with the largest weight % of CoFe2O4 shows higher coercive fields which is not favourable for applications. This indicates that the optimal content of the filler must be determined and taken into account when optimizing both ferroelectric and magnetoelectric properties.

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