Twenty fungal genera, including 14 Fusarium species, were examined for ice nucleation activity at... more Twenty fungal genera, including 14 Fusarium species, were examined for ice nucleation activity at −5.0°C, and this activity was found only in Fusarium acuminatum and Fusarium avenaceum . This characteristic is unique to these two species. Ice nucleation activity of F. avenaceum was compared with ice nucleation activity of a Pseudomonas sp. strain. Cumulative nucleus spectra are similar for both microorganisms, while the maximum temperatures of ice nucleation were −2.5°C for F. avenaceum and −1.0°C for the bacteria. Ice nucleation activity of F. avenaceum was stable at pH levels from 1 to 13 and tolerated temperature treatments up to 60°C, suggesting that these ice nuclei are more similar to lichen ice nuclei than to bacterial ones. Ice nuclei of F. avenaceum , unlike bacterial ice nuclei, pass through a 0.22-μm-pore-size filter. Fusarial nuclei share some characteristics with the so-called leaf-derived nuclei with which they might be identified: they are cell free and stable up to 6...
1.3 PZT-polymer composites were fabricated using the dice and fill method with various PZT types ... more 1.3 PZT-polymer composites were fabricated using the dice and fill method with various PZT types and volume fractions. These composites were evaluated for power underwater transducer applications with an air backed and no matching layer configuration. Electrical input and acoustical output powers were monitored as a function of the drive level. Total acoustic power densities of 30 W/cm 2 were obtained with a P189/epoxy piezocomposite vibrating at 350 kHz with a low duty cycle (1-5%) and with a 90% efficiency. Power densities up to 20 W/cm 2 were measured with a 50% duty cycle. Evolution and destruction of the transducers were monitored versus increasing averaged power. It was observed that better efficiencies were obtained with low volume fraction configurations allowing natural acoustic impedance matching to water. It was found that hard PZT type (Navy III) are optimal compositions even for piezocomposite transducers. It is shown that, unlike a common belief, the polymer mechanical losses are comparable to those of the active ceramic justifying that 1.3 piezocomposites are suited for low-cost power applications. In fact, the main limitation induced by the polymer phase is a strong thermal breakdown when the temperature of the transducer approaches the glass transition region of the polymer. Measurements of the polymer losses as a function of the temperature were obtained confirming this point and offering interesting new alternatives for future composite power transducers.
In this paper, the performances of a new piezoelectric damping method for vibration control are c... more In this paper, the performances of a new piezoelectric damping method for vibration control are compared to the passive tuned shunt method where the mechanical energy converted with the piezomaterial in electrical energy is simply dissipated in a resistor. This low consumption semi-passive damping technique, called SSDI for Synchronized Switch Damping on Inductor allows enhanced damping performances over a large frequency range. Compared with purely passive control, this method offers several advantages. It is self-adaptive because no tuning parameter is necessary, as in the case of the usual passive shunt network. In other word, the SSDI is a natural broadband method and is not sensitive to environmental changes. For low structural frequencies, the SSDI does not required a very large tuning inductor. A multi-modal damping is easily possible with the SSDI technique without complex circuits. Experimental results are given for a cantilever steel beam and for a clamped steel plate. A broadband and stable control is obtained with SSDI, hence outperforming the passive technique.
This paper presents the combination of periodic structures with nonlinearly interfaced piezoelect... more This paper presents the combination of periodic structures with nonlinearly interfaced piezoelectric elements for vibration control purposes. The nonlinear treatment consists of quickly inverting the piezoelectric voltage when the latter reaches either a maximum or a minimum value, hence shaping a voltage with a higher magnitude and reduced phase with the speed. It is shown that the nonlinear interface not only dramatically increases the damping abilities of periodic structures in stopband, but also permits significantly enlarging the latter, hence providing a very adaptive, efficient vibration damping system. Theoretical and experimental investigations on a clamped–clamped periodic beam are conducted, showing the very good abilities for efficiently damping the mechanical vibrations over a very wide frequency band.
3rd International Conference on Intelligent Materials and 3rd European Conference on Smart Structures and Materials, 1996
The measurement of shear stresses in the hydrodynamic boundary layer required high sensitivity se... more The measurement of shear stresses in the hydrodynamic boundary layer required high sensitivity sensors. A floating element type sensor using the piezoelectric effect is proposed. It is constituted of a composite material with high shear stress sensitivity. The evolution of the sensor characteristics with the PZT volume fraction is analyzed. The experimental results show a good agreement with the Finite Element Modeling predictions.
ISAF 2000. Proceedings of the 2000 12th IEEE International Symposium on Applications of Ferroelectrics (IEEE Cat. No.00CH37076)
The synchronized switch damping (SSD) is a semi-passive damping technique, based on an intermitte... more The synchronized switch damping (SSD) is a semi-passive damping technique, based on an intermittent switching of piezoelements bonded on a mechanical structure. It corresponds to a proper chopping of the voltage across the piezoelements in order to get it in phase with the vibration displacement speed thus resulting in an efficient damping. A 20 dB damping can be obtained with
ISAF '96. Proceedings of the Tenth IEEE International Symposium on Applications of Ferroelectrics
The knowledge of the mean shear stress and of its fluctuations in the hydrodynamic boundary layer... more The knowledge of the mean shear stress and of its fluctuations in the hydrodynamic boundary layer requires high sensitivity sensor. The principle of a floating element type sensor using piezoelectric bimorphs bending has been studied for this application. This transducer can perform direct measurement of shear stresses with a satisfactory accuracy. The transducer has first been embedded for its waterproofing and its behaviour in air has been optimised with the heap of both Finite Element Modelling and experimental calibration. Finally, the influence of normal stresses and hydrodynamic pressure on the embedded transducer have been evaluated
Proceedings of 1994 IEEE International Symposium on Applications of Ferroelectrics
Piezoelectric 1.3 composites of PZT-epoxy and PZT-polyurethane compositions were developed for in... more Piezoelectric 1.3 composites of PZT-epoxy and PZT-polyurethane compositions were developed for investigations in low-frequency acoustic applications. Samples with different PZT volume fractions and varying PZT rod aspect ratios (from 4/spl times/4/spl times/9 to 1/spl times/1/spl times/9 mm/sup 3/) were fabricated by using the "dice and fill" method. Experimental measurement in the 3.3 mode in air was carried out by using a laser-Doppler vibrometry (LDV) technique. Strain profiles of the composite sample driven by a low-frequency ac electric field excitation was obtained. The result showed that PZT rod aspect ratio has a drastic effect on composite performance. A quasi-static model based on an isolated 1.3 composite unit-cell was developed to account for the stress transfer at the PZT-polymer interface. Analysis result showed that an aspect ratio of 20 or higher is necessary for low frequency sensing or projecting application of 1.3 piezocomposites. For use in the 3.3 mode, a soft polymer was shown to be preferred, since the longitudinal clamping of the PZT rod is greater for hard resins.
Active control of smart structures equipped with piezoelectric elements has shown its efficiency ... more Active control of smart structures equipped with piezoelectric elements has shown its efficiency for two decades now. However, the electric power required by amplifiers for driving actuators appeared to be a severe limitation to the development of these techniques. In order to reduce this power requirement, semi-passive techniques developments such as Synchronized Switch Damping control were carried out. These ultra-low power techniques perform very well for monomodal excitation but their performances are limited in the case of multi-modal or complex vibrations. This paper deals with the implementation of an enhanced semi-active technique using methods developed for active control. A new multimodal control technique is proposed. It is based on SSD-Inductance semi-active technique. A Luenberger observer separates the modal variables from the voltage of the piezoelectric sensors. Then, the SSDI control can be targeted separately on each mode to control the vibration. This technique does not need operative power supply. An application of the proposed method on a clamped-free smart beam is proposed. Modal dampings of the controlled smart structure are first of all predicted by simulations. Then experimental results validate the proposed principle. Results obtained show the efficiency of the method and demonstrate its capabilities to control different modes on a broad frequency range.
Active and Passive Smart Structures and Integrated Systems 2014, 2014
ABSTRACT An alternative switching technique for piezoelectric energy harvesting is presented. The... more ABSTRACT An alternative switching technique for piezoelectric energy harvesting is presented. The energy harvester based on piezoelectric elements is a promising method to scavenge ambient energy. Several non-linear techniques such as SSHI have been implemented to improve the global harvested energy. However, these techniques are sensitive to load and should be tuned to obtain optimal power output. This technique, called Series Synchronized Switch Harvesting (S3H), has both the advantage of easy implementation and independence of the harvested power with the load impedance. The harvesting circuit simply consists of a switch in series with the piezoelement and the load. The switch is nearly always open and is triggered-on each time the piezoelectric voltage reaches an extremum. It is opened back after an arbitrary on-time t0. The energy scavenging process happens when switch is closed. Based on linear motion assumption, the harvester structure is modeled as a “Mass-Spring-Damper†system. The analysis of S3H technique is considered with harmonic excitation. An analytical model of S3H is presented and discussed. The main advantage of this approach compared with the usual standard technique is that the extracted power is independent of the load within a wide range of load impedance, and that the useful impedance range is simply related to the defined switch on-time. For constant displacement excitation condition, the optimal power output is more than twice the power extracted by the standard technique as long as the on-time interval is small comparatively with the vibration period. For constant force excitation, an optimal on-time can be defined resulting in an optimally wide load bandwidth. Keywords: piezoelectric; energy harvesting; non-linear harvesting techniques; switching techniques.
Active and Passive Smart Structures and Integrated Systems 2014, 2014
Any piezoelectric generator structure can be modeled close to its resonance by an equivalent circ... more Any piezoelectric generator structure can be modeled close to its resonance by an equivalent circuit derived from the well known Mason equivalent circuit. This equivalent circuit can therefore be used in order to optimize the harvested power using usual electrical impedance matching. The objective of this paper is to illustrate the full process leading to the definition of the proper passive load allowing the optimization of the harvested energy of any harvesting device. First, the electric equivalent circuit of the generator is derived from the Mason equivalent circuit of a seismic harvester. Theoretical ideal impedance matching and optimal load analyze is then given emphasizing the fact that for a given acceleration a constant optimal output power is achievable for any frequency as long as the optimal load is feasible. Identification of the equivalent circuit of an experimental seismic harvester is then derived and matched impedance is defined both theoretically and experimentally. Results demonstrate that an optimal load can always be obtained and that the corresponding output power is constant. However, it is very sensitive to this impedance, and that even if impedance matching is a longtime well known technique, it is not really experimentally and practically achievable.
ISAF '96. Proceedings of the Tenth IEEE International Symposium on Applications of Ferroelectrics
1.3 or 2.2 composites made respectively of PZT rods or lamella embedded in a polymer matrix have ... more 1.3 or 2.2 composites made respectively of PZT rods or lamella embedded in a polymer matrix have been proven to be efficient materials for ultrasonic transducers. A new modelling approach taking into account explicitly the stress-transfer at the PZT rod-matrix interface is proposed. It is based on a simple description of the drag force of the polymer-matrix acting on the ceramic. This drag force is applied as shear stresses at the interface. The dispersion curves relative to the various thickness and lateral periodicity related modes are established. The theoretical results are compared to experimental data obtained on 2.2 composite samples characterized both electrically and with the LDV technique.
Twenty fungal genera, including 14 Fusarium species, were examined for ice nucleation activity at... more Twenty fungal genera, including 14 Fusarium species, were examined for ice nucleation activity at −5.0°C, and this activity was found only in Fusarium acuminatum and Fusarium avenaceum . This characteristic is unique to these two species. Ice nucleation activity of F. avenaceum was compared with ice nucleation activity of a Pseudomonas sp. strain. Cumulative nucleus spectra are similar for both microorganisms, while the maximum temperatures of ice nucleation were −2.5°C for F. avenaceum and −1.0°C for the bacteria. Ice nucleation activity of F. avenaceum was stable at pH levels from 1 to 13 and tolerated temperature treatments up to 60°C, suggesting that these ice nuclei are more similar to lichen ice nuclei than to bacterial ones. Ice nuclei of F. avenaceum , unlike bacterial ice nuclei, pass through a 0.22-μm-pore-size filter. Fusarial nuclei share some characteristics with the so-called leaf-derived nuclei with which they might be identified: they are cell free and stable up to 6...
1.3 PZT-polymer composites were fabricated using the dice and fill method with various PZT types ... more 1.3 PZT-polymer composites were fabricated using the dice and fill method with various PZT types and volume fractions. These composites were evaluated for power underwater transducer applications with an air backed and no matching layer configuration. Electrical input and acoustical output powers were monitored as a function of the drive level. Total acoustic power densities of 30 W/cm 2 were obtained with a P189/epoxy piezocomposite vibrating at 350 kHz with a low duty cycle (1-5%) and with a 90% efficiency. Power densities up to 20 W/cm 2 were measured with a 50% duty cycle. Evolution and destruction of the transducers were monitored versus increasing averaged power. It was observed that better efficiencies were obtained with low volume fraction configurations allowing natural acoustic impedance matching to water. It was found that hard PZT type (Navy III) are optimal compositions even for piezocomposite transducers. It is shown that, unlike a common belief, the polymer mechanical losses are comparable to those of the active ceramic justifying that 1.3 piezocomposites are suited for low-cost power applications. In fact, the main limitation induced by the polymer phase is a strong thermal breakdown when the temperature of the transducer approaches the glass transition region of the polymer. Measurements of the polymer losses as a function of the temperature were obtained confirming this point and offering interesting new alternatives for future composite power transducers.
In this paper, the performances of a new piezoelectric damping method for vibration control are c... more In this paper, the performances of a new piezoelectric damping method for vibration control are compared to the passive tuned shunt method where the mechanical energy converted with the piezomaterial in electrical energy is simply dissipated in a resistor. This low consumption semi-passive damping technique, called SSDI for Synchronized Switch Damping on Inductor allows enhanced damping performances over a large frequency range. Compared with purely passive control, this method offers several advantages. It is self-adaptive because no tuning parameter is necessary, as in the case of the usual passive shunt network. In other word, the SSDI is a natural broadband method and is not sensitive to environmental changes. For low structural frequencies, the SSDI does not required a very large tuning inductor. A multi-modal damping is easily possible with the SSDI technique without complex circuits. Experimental results are given for a cantilever steel beam and for a clamped steel plate. A broadband and stable control is obtained with SSDI, hence outperforming the passive technique.
This paper presents the combination of periodic structures with nonlinearly interfaced piezoelect... more This paper presents the combination of periodic structures with nonlinearly interfaced piezoelectric elements for vibration control purposes. The nonlinear treatment consists of quickly inverting the piezoelectric voltage when the latter reaches either a maximum or a minimum value, hence shaping a voltage with a higher magnitude and reduced phase with the speed. It is shown that the nonlinear interface not only dramatically increases the damping abilities of periodic structures in stopband, but also permits significantly enlarging the latter, hence providing a very adaptive, efficient vibration damping system. Theoretical and experimental investigations on a clamped–clamped periodic beam are conducted, showing the very good abilities for efficiently damping the mechanical vibrations over a very wide frequency band.
3rd International Conference on Intelligent Materials and 3rd European Conference on Smart Structures and Materials, 1996
The measurement of shear stresses in the hydrodynamic boundary layer required high sensitivity se... more The measurement of shear stresses in the hydrodynamic boundary layer required high sensitivity sensors. A floating element type sensor using the piezoelectric effect is proposed. It is constituted of a composite material with high shear stress sensitivity. The evolution of the sensor characteristics with the PZT volume fraction is analyzed. The experimental results show a good agreement with the Finite Element Modeling predictions.
ISAF 2000. Proceedings of the 2000 12th IEEE International Symposium on Applications of Ferroelectrics (IEEE Cat. No.00CH37076)
The synchronized switch damping (SSD) is a semi-passive damping technique, based on an intermitte... more The synchronized switch damping (SSD) is a semi-passive damping technique, based on an intermittent switching of piezoelements bonded on a mechanical structure. It corresponds to a proper chopping of the voltage across the piezoelements in order to get it in phase with the vibration displacement speed thus resulting in an efficient damping. A 20 dB damping can be obtained with
ISAF '96. Proceedings of the Tenth IEEE International Symposium on Applications of Ferroelectrics
The knowledge of the mean shear stress and of its fluctuations in the hydrodynamic boundary layer... more The knowledge of the mean shear stress and of its fluctuations in the hydrodynamic boundary layer requires high sensitivity sensor. The principle of a floating element type sensor using piezoelectric bimorphs bending has been studied for this application. This transducer can perform direct measurement of shear stresses with a satisfactory accuracy. The transducer has first been embedded for its waterproofing and its behaviour in air has been optimised with the heap of both Finite Element Modelling and experimental calibration. Finally, the influence of normal stresses and hydrodynamic pressure on the embedded transducer have been evaluated
Proceedings of 1994 IEEE International Symposium on Applications of Ferroelectrics
Piezoelectric 1.3 composites of PZT-epoxy and PZT-polyurethane compositions were developed for in... more Piezoelectric 1.3 composites of PZT-epoxy and PZT-polyurethane compositions were developed for investigations in low-frequency acoustic applications. Samples with different PZT volume fractions and varying PZT rod aspect ratios (from 4/spl times/4/spl times/9 to 1/spl times/1/spl times/9 mm/sup 3/) were fabricated by using the "dice and fill" method. Experimental measurement in the 3.3 mode in air was carried out by using a laser-Doppler vibrometry (LDV) technique. Strain profiles of the composite sample driven by a low-frequency ac electric field excitation was obtained. The result showed that PZT rod aspect ratio has a drastic effect on composite performance. A quasi-static model based on an isolated 1.3 composite unit-cell was developed to account for the stress transfer at the PZT-polymer interface. Analysis result showed that an aspect ratio of 20 or higher is necessary for low frequency sensing or projecting application of 1.3 piezocomposites. For use in the 3.3 mode, a soft polymer was shown to be preferred, since the longitudinal clamping of the PZT rod is greater for hard resins.
Active control of smart structures equipped with piezoelectric elements has shown its efficiency ... more Active control of smart structures equipped with piezoelectric elements has shown its efficiency for two decades now. However, the electric power required by amplifiers for driving actuators appeared to be a severe limitation to the development of these techniques. In order to reduce this power requirement, semi-passive techniques developments such as Synchronized Switch Damping control were carried out. These ultra-low power techniques perform very well for monomodal excitation but their performances are limited in the case of multi-modal or complex vibrations. This paper deals with the implementation of an enhanced semi-active technique using methods developed for active control. A new multimodal control technique is proposed. It is based on SSD-Inductance semi-active technique. A Luenberger observer separates the modal variables from the voltage of the piezoelectric sensors. Then, the SSDI control can be targeted separately on each mode to control the vibration. This technique does not need operative power supply. An application of the proposed method on a clamped-free smart beam is proposed. Modal dampings of the controlled smart structure are first of all predicted by simulations. Then experimental results validate the proposed principle. Results obtained show the efficiency of the method and demonstrate its capabilities to control different modes on a broad frequency range.
Active and Passive Smart Structures and Integrated Systems 2014, 2014
ABSTRACT An alternative switching technique for piezoelectric energy harvesting is presented. The... more ABSTRACT An alternative switching technique for piezoelectric energy harvesting is presented. The energy harvester based on piezoelectric elements is a promising method to scavenge ambient energy. Several non-linear techniques such as SSHI have been implemented to improve the global harvested energy. However, these techniques are sensitive to load and should be tuned to obtain optimal power output. This technique, called Series Synchronized Switch Harvesting (S3H), has both the advantage of easy implementation and independence of the harvested power with the load impedance. The harvesting circuit simply consists of a switch in series with the piezoelement and the load. The switch is nearly always open and is triggered-on each time the piezoelectric voltage reaches an extremum. It is opened back after an arbitrary on-time t0. The energy scavenging process happens when switch is closed. Based on linear motion assumption, the harvester structure is modeled as a “Mass-Spring-Damper†system. The analysis of S3H technique is considered with harmonic excitation. An analytical model of S3H is presented and discussed. The main advantage of this approach compared with the usual standard technique is that the extracted power is independent of the load within a wide range of load impedance, and that the useful impedance range is simply related to the defined switch on-time. For constant displacement excitation condition, the optimal power output is more than twice the power extracted by the standard technique as long as the on-time interval is small comparatively with the vibration period. For constant force excitation, an optimal on-time can be defined resulting in an optimally wide load bandwidth. Keywords: piezoelectric; energy harvesting; non-linear harvesting techniques; switching techniques.
Active and Passive Smart Structures and Integrated Systems 2014, 2014
Any piezoelectric generator structure can be modeled close to its resonance by an equivalent circ... more Any piezoelectric generator structure can be modeled close to its resonance by an equivalent circuit derived from the well known Mason equivalent circuit. This equivalent circuit can therefore be used in order to optimize the harvested power using usual electrical impedance matching. The objective of this paper is to illustrate the full process leading to the definition of the proper passive load allowing the optimization of the harvested energy of any harvesting device. First, the electric equivalent circuit of the generator is derived from the Mason equivalent circuit of a seismic harvester. Theoretical ideal impedance matching and optimal load analyze is then given emphasizing the fact that for a given acceleration a constant optimal output power is achievable for any frequency as long as the optimal load is feasible. Identification of the equivalent circuit of an experimental seismic harvester is then derived and matched impedance is defined both theoretically and experimentally. Results demonstrate that an optimal load can always be obtained and that the corresponding output power is constant. However, it is very sensitive to this impedance, and that even if impedance matching is a longtime well known technique, it is not really experimentally and practically achievable.
ISAF '96. Proceedings of the Tenth IEEE International Symposium on Applications of Ferroelectrics
1.3 or 2.2 composites made respectively of PZT rods or lamella embedded in a polymer matrix have ... more 1.3 or 2.2 composites made respectively of PZT rods or lamella embedded in a polymer matrix have been proven to be efficient materials for ultrasonic transducers. A new modelling approach taking into account explicitly the stress-transfer at the PZT rod-matrix interface is proposed. It is based on a simple description of the drag force of the polymer-matrix acting on the ceramic. This drag force is applied as shear stresses at the interface. The dispersion curves relative to the various thickness and lateral periodicity related modes are established. The theoretical results are compared to experimental data obtained on 2.2 composite samples characterized both electrically and with the LDV technique.
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Papers by Claude RICHARD