Fabrication, Modelling and Use of Porous Ceramics for Ultrasonic Transducer Applications
Porous ceramics are of interest for ultrasonic transducer applications. Porosity allows to decrease acoustical impedance,
thus improving transfer of acoustical energy to water or biological tissues. For underwater applications, the dhgh figure of merit can also be improved as compared to dense materials. In the case of high frequency transducers, namely for
high resolution medical imaging, thick film technology can be used. The active films are generally porous and this porosity
must be controlled. An unpoled porous PZT substrate is also shown to be an interesting solution since it can be used in a
screen-printing process and as a backing for the transducer. This paper describes the fabrication process to obtain such materials,
presents microstructure analysis as well as functional properties of materials. Modelling is also performed and results are
compared to measurements. Finally, transducer issues are addressed through modelling and design of several configurations.
The key parameters are identified and their effect on transducer performance is discussed. A comparison with dense materials
is performed and results are discussed to highlight in which cases porous piezoceramics can improve transducer performance,
and improvements are quantified.
Available from: Linda K Weavers
- "or 10–12 Â 10 6 V/m ) and results in a more uniform temperature throughout the sample. However, in the present work, samples that were poled in oil exhibited substantial hydrophobicity due to oil penetrating the pore surfaces. "
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ABSTRACT: Membranes utilized for water and wastewater treatment are susceptible to fouling. Fouling leads to gradual flux decline, possible loss of selectivity and increased operational costs. Conventional de-fouling strategies such as backwashing and chemical cleaning can be effective, but have inherent disadvantages. Recently, application of ultrasound was shown to be an effective cleaning method but, thus far, has been applied only with the ultrasonic source in close proximity to the membrane. In this work we demonstrate for the first time, a new membrane design in which ultrasound for de-fouling is generated from within the membrane structure. To test the feasibility of this idea, we fabricated porous, poled and unpoled piezoelectric ceramic microfiltration membranes and performed filtration tests with a fouling dispersion containing 10 mg/L of 500 nm latex particles. To generate ultrasound from within the membrane, an alternating voltage was applied across the membrane with the feed side electrode located 1 mm from the membrane surface. In the absence of voltage, the flux decreased by 420% within 3 h of filtration. Conversely, when an alternating voltage was applied in intermittent pulses, no water flux decrease was observed over 3 h of filtration, demonstrating the feasibility of membranes with built-in de-fouling functionality.
- "Similarly, the planar coupling coefficient k p has the same evolution as k t . Levassort et al.have shown that both electromechanical and dielectric properties are influenced by the porosity volume fraction in ceramics. Indeed, their work has shown that the modelled relative dielectric constant decreases when the open or closed porosity volume fraction enhances while the thickness mode coupling factor increases before vanishing. "
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ABSTRACT: Lead free piezoelectric K0.5Na0.5NbO3 (KNN) is synthesised by the conventional solid state mixed oxide route using dry ball milling. Spark plasma sintering technique (SPS) is an original and fast method which enables the grain growth to be controlled and allows to decrease a potential alkali volatilisation. Undoped KNN are sintered by SPS in the 920-975 degrees C temperature range, for dwell times of 5-15 min. The density range is 93-97%. Density, grain size and composition of samples are comparatively analysed. Electromechanical performances are measured and related to the microstructure. High planar coupling coefficient k(p) of 48%, thickness coupling factor k(t) of 45%, dielectric constant at constant strain epsilon(S)(33)/epsilon(0) of 328, and low mechanical losses delta(m) of 2% are reached for undoped KNN. These results are promising and suitable for transducer applications. (c) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Available from: Erling Ringgaard
- "The backing was made of porous unpoled lead zirconate titanate (PZT) based on Ferroperm Pz37 composition (meggitt a/s) . This porous material offers several advantages for transducer properties (in particular for the center element) . "
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ABSTRACT: Detection of high-order nonlinear components issued from microbubbles has emerged as a sensitive method for contrast agent imaging. Nevertheless, the detection of these high-frequency components, including the third, fourth, and fifth harmonics, remains challenging because of the lack of transducer sensitivity and bandwidth. In this context, we propose a new design of imaging transducer based on a simple fabrication process for high-frequency nonlinear imaging. The transducer is composed of two elements: the outer low-frequency (LF) element was centered at 4 MHz and used in transmit mode, whereas the inner high-frequency (HF) element centered at 14 MHz was used in receive mode. The center element was pad-printed using a lead zirconate titanate (PZT) paste. The outer element was molded using a commercial PZT, and curved porous unpoled PZT was used as backing. Each piezoelectric element was characterized to determine the electromechanical performance with thickness coupling factor around 45%. After the assembly of the two transducer elements, hydrophone measurements (electroacoustic responses and radiation patterns) were carried out and demonstrated a large bandwidth (70% at -3 dB) of the HF transducer. Finally, the transducer was evaluated for contrast agent imaging using contrast agent microbubbles. The results showed that harmonic components (up to the sixth harmonic) of the microbubbles were successfully detected. Moreover, images from a flow phantom were acquired and demonstrated the potential of the transducer for high-frequency nonlinear contrast imaging.
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