92 research outputs found
Effect of thermal annealing on dielectric and ferroelectric properties of aerosol-deposited thick films
In this work, the effects of thermal annealing at 500 {\deg}C on
aerosol-deposited
thick films on stainless-steel substrates are investigated using two
complementary methods at high and low applied external electric fields. The
first one is Positive Up Negative Down method, which allows us to obtain
information about the switching and non-switching contributions to the
polarization. It shows that the as-deposited film is ferroelectric before
annealing, since it has a switching contribution to the polarization. After
annealing, both the switching and non-switching contributions to polarization
increased by a factor of 1.6 and 2.33, respectively, indicating stronger
ferroelectric behavior. The second method is based on impedance spectroscopy
coupled with Rayleigh analysis. The results show that post-deposition thermal
annealing increases the reversible domain wall contribution to the dielectric
permittivity by a factor 11 while keeping the threshold field similar. This
indicates, after annealing, domain wall density is larger while domain wall
mobility remains similar. These two complementary characterization methods show
that annealing increases the ferroelectric behavior of the thick film by
increasing the domain wall density and its influence is visible both on
polarization versus electric field loop and dielectric permittivity
Fabrication and modeling of piezoelectric transducers for High-Frequency medical imaging
International audienceWe have studied the processing of piezoelectric thick films using electrophoretic deposition (EPD) for high-frequency ultrasound applications. Lead-zirconium-titanate (PZT) particles synthetized by solid states synthesis were dispersed in ethanol using ammonium polyacrylate (PAA). The electrophoretic deposition of PZT particles was performed at a constant-current mode. PZT thick-films deposited at 1 mA for 60 seconds were sintered at 900oC for 2 hours in a PbO-controlled atmosphere. The scanning-electron microscopy (SEM) analysis shows that the thickness of PZT layer is uniform and that the pores are homogeneously distributed within the layer. The complex electrical impedance was measured and fitted by KLM scheme in order to deduce the dielectric, mechanical and piezoelectric parameters of the thick-films. The density and thickness of PZT thick films are used as inputs and the thickness coupling factor kt, dielectric constant at constant strain and resonant frequency are deduced. The results show that homogeneous PZT thick-film structures with tailored thickness and density prepared by EPD and sintering having a resonant frequency around 20 MHz can be used for noninvasive medical ultrasound imaging and diagnostics
Ultrasonic transducers based on curved lead-free piezoelectric thick films for high resolution medical imaging
International audienceKNN-based lead free ferroelectric materials are receiving much attention due to their high electromechanical properties that make them promising candidates to replace the lead-based piezoceramics that will eventually be banned by environmental regulations in many countries over the world. Studies include the development of KNN thick films that are particularly well adapted for high frequency applications due to higher wave velocities and a dielectric constant in an acceptable range for single element transducers. Here, a KNN based thick film is deposited on a curved substrate by pad-printing in order to be used in a focused high frequency transducer. This substrate is a porous lead-free KNN cylinder specifically developed to exhibit the required acoustical properties of a backing (acoustical impedance, high attenuation) and is compatible with the high sintering temperature of the KNN thick film. Electromechanical properties of the piezoelectric thick film in thickness mode were deduced (kt over 35%). This structure was used to fabricate a transducer which was characterized (relative bandwidth over 90%). Finally this transducer was integrated in a high frequency imaging system and its performance allowed skin images to be produced. To conclude, the replacement of lead-based high frequency transducers by green devices is a viable option
Recommended from our members
Non-Planar Pad-Printed Think-Film Focused High-Frequency Ultrasonic Transducers for Imaging and Therapeutic Applications
Pad-printed thick-film transducers have been shown to be an interesting alternative to lapped bulk piezoceramics, because the film is deposited with the required thickness, size, and geometry, thus avoiding any subsequent machining to achieve geometrical focusing. Their electromechanical properties are close to those of bulk ceramics with similar composition despite having a higher porosity. In this paper, padprinted high-frequency transducers based on a low-loss piezoceramic composition are designed and fabricated. High-porosity ceramic cylinders with a spherical top surface are used as the backing substrate. The transducers are characterized in view of imaging applications and their imaging capabilities are evaluated with phantoms containing spherical inclusions and in different biological tissues. In addition, the transducers are evaluated for their capability to produce high-acoustic intensities at frequencies around 20 MHz. High-intensity measurements, obtained with a calibrated hydrophone, show that transducer performance is promising for applications that would require the same device to be used for imaging and for therapy. Nevertheless, the transducer design can be improved, and simulation studies are performed to find a better compromise between low-power and high-power performance. The size, geometry, and constitutive materials of optimized configurations are proposed and their feasibility is discussed
Inkjet-printing-derived lead-zirconate-titanate-based thick films for printed electronics
International audienc
Domain wall evolutions laws of piezoceramic materials under mechanical loading
International audienc
Textured multilayered piezoelectric structures for energy conversion
International audienc
Textured, lead-free piezoelectric ceramics with high figure of merit for energy harvesting
International audienceAbstract Piezoelectrics are key materials for energy conversion, for example in ultrasound transducers and energy harvesters. This work presents the synthesis and characterization of the lead-free piezoelectric composition (Li 0.06 (K 0.52 Na 0.48 ) 0.94 )(Nb 0.71 Ta 0.29 )O 3 doped with 0.25 mol% Mn (KNNLTM) as textured ceramics. Templated grain growth from NaNbO 3 platelet templates aligned by tape casting was used to introduce texture, and after sintering for 14 h at 1100 °C this produced up to 84% (100) pc grain orientation. After high temperature poling, the textured samples exhibit reasonable piezoelectric response with d 33 values up to 171 pC N −1 , and k t values of 0.35, which is 71% of the response obtained in a single crystal of the same composition. The low relative dielectric permittivity of the textured and high temperature-poled KNNLTM ( ϵ 33 T / ϵ 0 down to 182) resulted in record-high piezoelectric voltage constants ( g 33 up to 101 mV m N −1 ), higher than previously reported for lead-free piezoelectric ceramics, as well as very high figure of merit ( d 33 g 33 up to 16 × 10 −12 m 3 J −1 ) for non-resonant energy harvesting in compression. These numbers make the textured KNNLTM materials of this work highly promising for use in thickness mode, non-resonant piezoelectric energy harvesters
High Concentration Sol-Gel Synthesis of BaHf 0.05 Ti 0.95 O 3 to Prepare Ceramics with Significant Piezoelectric Properties
- …