Transparent lead lanthanum zirconate titanate (PLZT) ceramic fibers for high-frequency ultrasonic transducer applications

This paper presents fabrication of transparent lanthanum zirconate titanate (PLZT) fibers using extrusion technique. The diameter of the sintered PLZT fiber is about 400-μm, and the fibers exhibit very good transparency. Measured dielectric constant, remnant polarization and coercive field of PLZT fiber were found to be 2340, 22.5-μC/cm², and 9.8-kV/cm, respectively. The transparent piezoelectric materials may exhibit great potential for Photoacoustic (PA) imaging and hybrid intravascular imaging combining OCT and ultrasound imaging by using the transparent fiber as the path of light propagation and ultrasonic transducer material. In our study, these transparent PLZT fibers were designed to fabricate two types of high-frequency ultrasonic transducers: small aperture single PLZT fiber/epoxy composite and large aperture 1–3 PLZT fiber/epoxy composite ultrasonic transducers. Besides, a 20-μm tungsten wire phantom and the cornea of the porcine eye were also imaged with the 1–3 PLZT fiber/epoxy composite ultrasonic transducer to demonstrate its imaging capability.     

Experimental study of continuous ultrasonic reactors for mixing and precipitation of nanoparticles

Nanoparticles can be synthesized by precipitation. State-of-the-art is the precipitation of nanoparticles in stirred tanks or high-pressure T-mixers. The study presents two new reactor concepts for continuous precipitation of nanoparticles. Both of them utilize ultrasonic sound as a mixing accelerator. The first reactor has a conical chamber (10 mL), which is used to study the micromixing quality, the cavitation intensity and the precipitation of barium sulfate nanoparticles. The second reactor has a so-called cavitational chamber (2.5 mL), which is an optimized conical reactor. Both reactors are compared with each other with respect to the properties of the products. Additionally, the influence of the ultrasonic output from the transducer to the liquid and the feed rate are demonstrated.     

Composite Polymers Transducers for Ultrasonic and Biological Applications

Ferrite polymer transducer and copolyesters are being used for ultrasonic generation to be used in technology and in biological applications like orthodontic treatment. The objectives of this study were to introduce a new piezoelectric composite polymers and to evaluate and compare their electric and mechanical properties with the widely used other materials. The resonance and antiresonance frequencies were measured for the materials in the radial mode. It is noticed that the resonance frequency decreased with increasing CoZn ferrite concentrations in polymers. The electromechanical coupling factor was determined to be of value 0.8 which is the highest value of the piezoelectric materials. It is very difficult to produce ceramic transducers in large sizes because they are fragile, thus the composite transducer could be an alternative. The ultrasonic wave velocity of the composite polymer is higher than that of other polymers and piezoelectric ceramics making them more attractive for many applications than ceramics. The Young's modulus of the composite polymer increased with increasing ferrite concentrations.     

Defluoridation performance and mechanism of nano‐scale aluminum oxide hydroxide in aqueous solution

BACKGROUND: The present study has concentrated on investigating the fluoride removal potential of nano‐scale aluminum oxide hydroxide (nano‐AlOOH). A series of batch adsorption experiments were carried out to assess parameters that influence the adsorption process. The different parameters investigated include the effect of contact time, initial fluoride concentration, adsorbent dose, pH of the solution and co‐existing anions. RESULTS: Most of the adsorption took place during the first 30 min and kinetic and equilibrium adsorption data show that the process obeys a pseudo‐second‐order kinetic equation and the Langmuir adsorption model. The fluoride removal efficiency is greater than 90% between pH 6 and 8 and decreases as pH values increase to 11. The presence of SO₄^2? or PO₄^3? in aqueous solution was found to reduce the fluoride uptake. Desorption studies showed that the fluoride can easily be desorbed at pH 13. CONCLUSION: Nano‐AlOOH possesses a maximum fluoride capacity of 3259 mg F^? kg^?1, which is comparable with that of activated alumina. Maximum adsorption occurred at around pH 7, which makes nano‐AlOOH a potential adsorbent for drinking water treatment. Copyright © 2009 Society of Chemical Industry     

Strategies for non‐invasive imaging of polymeric biomaterial in vascular tissue engineering and regenerative medicine using ultrasound and photoacoustic techniques

The ability of new polymeric materials to provide excellent biomechanical properties expanded their potential for biomedical applications enormously. The use of non‐invasive imaging modalities could provide crucial information to monitor the efficacy/effectiveness/efficiency of the new materials employed in ‘regenerative’ approaches, including scaffolds, hydrogels, self‐assembling materials and nanosized structures. The assessment of the morpho‐functional and metabolic changes of treated or implanted tissues, the visualization of sites of drug delivery and the real‐time check of the in vivo efficacy of therapeutics could be achieved by non‐invasive micro‐ and macro‐imaging techniques. The macro‐ and nano‐requirements of these new materials and their behaviour in vivo can be investigated using standard approaches such as computed tomography, MRI and ultrasound techniques and the emerging photoacoustic imaging. This paper presents recent advancements of ultrasonography and the novel photoacoustic technique to monitor the morpho‐functional parameters of synthetic polymeric scaffolds and conduits in experimental models. © 2016 Society of Chemical Industry     

Study of vibratory behavior of interconnected porous PZT by impulse method

Performances in ultrasonic active transducers of interconnected porous lead zirconate titanate (PZT) piezoelectric disks with a porosity ranging from 30 to 70%, and polarized along their axial axis, are investigated. The characterization method used is based on the measurement of the voltage, which appears between the two faces of the piezoelectric element when it is excited by a current impulse. The device used, allows the acquisition of axial and radial vibrations of the transducer, and from these data, electromechanical and acoustic parameters are deduced. One observes that interconnected porosity causes the disappearance of the radial vibrations, and for large porosities the disk vibrates exclusively according to the axial mode. k_t is increased, the acoustic impedance is reduced, and the axial propagation velocity reaches 2500 m s⁻¹ for 30% of porosity. These results show that interconnected porous PZT are suitable for making ultrasonic active transducer, such as biomedical imaging devices.     

换能器结构参数对聚合物超声塑化黏弹生热的影响

为研究超声换能器结构参数对聚合物超声塑化过程黏弹性生热的影响,首先确定超声黏弹性生热系统的组成,进行纵振超声换能器结构设计;然后分析超声黏弹性生热过程及超声黏弹性生热原理;最后采用单一变量法分析超声换能器的主要结构参数对其纵振频率及工具头前端质点最大振幅的影响,将其实际输出的纵振激励加载于熔融聚合物,研究其结构参数对聚合物超声黏弹性生热过程及达到聚合物玻璃化转变温度所用时间的影响。结果表明,随纵振激励作用时间的增加,聚合物温度非线性升高;放大比对聚合物温度变化影响最大,前盖板厚度和工具头长度次之,影响最小的是变幅杆长度。     

Bismuth sodium titanate based lead-free ultrasonic transducer for microelectronics wirebonding applications

Bismuth sodium titanate based lead-free piezoelectric ceramic 0.885(Bi_1/2Na_1/2)TiO₃–0.05(Bi_1/2K_1/2)TiO₃–0.015(Bi_1/2Li_1/2)TiO₃–0.05BaTiO₃ (BNKLBT-1.5) rings (OD = 12.7mm, ID = 5.1 mm and 2.3 mm thick) were fabricated and characterized. Four ceramic rings were sandwiched between front and back metal plates to form a pre-stressed piezoelectric sandwich transducer and used as the driving element of an ultrasonic wirebonding transducer and the performance of the transducer was evaluated. The BNKLBT-1.5 transducer, when fitted with titanium front and back plates, was found to have axial vibration comparable to that of PZT transducer thus showing that BNKLBT-1.5 has the potential to be used in fabricating lead-free ultrasonic wirebonding transducers.     

Ultrasonic in‐line monitoring of polymer extrusion

In‐line ultrasonic monitoring of polymer co‐extrusion and twin‐screw extrusion are presented. Co‐extrusion of high density polyethylene (HDPE) and a thermoplastic elastomer based on polypropylene‐EPDM (ethylene‐propylene‐diene monomer) has been investigated by ultrasonic sensors consisting of piezoelectric transducers and clad buffer rods. One extremity of the rod (probing end) was installed flush with the die surface so as not to disturb the material flow. The other end was air cooled in order to protect the transducer from excessive heating. This approach has been demonstrated to be quite convenient for monitoring and controlling industrial material processes: first, it can work at temperatures up to 1000°C; second, the clad buffer rod probing end can be machined to the same shape as those of commercial temperature and pressure sensors commonly used in the extrusion process. Therefore, no modifications are required for the installation in the original equipment. The information obtained includes the position of the interface between polymers and the stability of the process. The same ultrasonic probe has also been installed on a barrel of a twin‐screw extruder. This study was performed using polyethylene and polystyrene. It has been verified that the ultrasonic sensor can be successfully operated along the extruder screw and that the ultrasound can give access to the material properties while the polymer is being processed. This means that the technique can be exploited to monitor and control in situ the characteristics of the polymer being transformed in operations typically performed on twinscrew extruders, such as compounding, visbreaking or reactive extrusion.     

Macro- and micromixing in a novel sonochemical reactor using high frequency ultrasound

This paper deals with the influence of ultrasound on macro- and micromixing in a new developed sonochemical reactor. Unprecedented piezoelectric transducer arrangement with a high frequency of 1.7 MHz has been used in this novel reactor. Macromixing quality has been investigated visually and the Dushman reaction (iodide-iodate) coupled with a neutralization reaction have been examined in order to characterize micromixing quality. In addition, the effect of liquid viscosity on the segregation index has been studied. The results show that this new developed reactor can establish reasonable macro- and micromixing inside the reactor. Moreover, the performance of this reactor has been compared with a stirred tank reactor equipped with a Rushton turbine impeller. It is found that with the same input electrical power, the obtained segregation index for stirred tank reactor is approximately 10% more than proposed new ultrasound reactor, which means the sonoreactor works more efficiently.     

Real‐time monitoring of injection molding for microfluidic devices using ultrasound

Real‐time process monitoring of the fabrication process of microfluidic devices using a polymer injection molding machine was carried out using miniature ultrasonic probes. A thick piezoelectric lead‐zirconate‐titanate film as an ultrasonic transducer (UT) was fabricated onto one end of a 4‐mm diameter and 12‐mm long steel buffer rods using a sol gel spray technique. The center frequency and 6 dB bandwidth of this UT were 17 MHz and 14 MHz, respectively. A signal‐to‐noise ratio of more than 30 dB for ultrasonic signals reflected at the probing end was achieved. The probe can operate continuously at 200°C without ultrasonic couplant and cooling. Clear ultrasonic signals were obtained during injection molding of a 1‐mm‐thick part having test patterns on its surface. Shrinkage of the molded part and part detachment from the mold were successfully monitored. Surface imperfections of the molded parts due to a lack of the sufficient holding pressure is discussed with regard to the ultrasonic velocity obtained. The presented ultrasonic probes and technique enable on‐line quality control of the molded part by optimizing the holding pressure and improvement of process efficiency by reducing the cycle time. POLYM. ENG. SCI., 45:606–612, 2005. © 2005 Society of Plastics Engineers     

Fine‐Scaled Piezoelectric Ceramic/Polymer 2‐2 Composites for High‐Frequency Transducer

A novel technique was utilized to fabricate fine‐scaled piezoelectric ceramic/polymer 2‐2 composites for high‐frequency ultrasonic transducers. Lead zirconate titanate (PZT) was used as raw material. Tape‐casted acetylene black tapes were used to define kerfs after sintering. A one‐directional supporter was utilized to avoid distortion of PZT elements. PZT elements with 20 ± 2 μm width exhibited good consistency in longitudinal direction. A resonant method was utilized to evaluate the piezoelectric and dielectric properties of the composites. A 72‐μm‐thick composite with an aspect ratio of ~3.6 exhibited a k_t of 0.61 with satisfied piezoelectric and dielectric properties. A prototype high‐frequency ultrasonic transducer was fabricated and evaluated by an underwater pulse‐echo test. The center frequency was found to be 23.75 MHz, with ?6 dB bandwidth of 5.5 MHz.     

Toward Understanding of Two‐Phase Eccentric Helical Reactor Performance

Mass transfer investigations in a two‐phase gas‐liquid Couette‐Taylor flow (CTF) reactor and a numerical flow simulation are reported. The CTF reactor is characterized by high values of the mass transfer parameters. Previous mass transfer investigations have yielded high values of the volumetric mass transfer coefficients (of the order of 10^–1 s^–1) and the specific interfacial area, compared to those obtained in a stirred tank (10³ m² m^–3). In order to intensify mass transfer in the CTF reactor, an eccentric rotor (rotating inner cylinder) was used. In the eccentric annulus with rotating inner cylinder, due to frequent variation of the hydrodynamic flow field parameters, nonlinear hydrodynamic conditions occurred. These conditions can influence the rate of mass transfer. The experimental results of benzaldehyde oxidation in an eccentric CTF reactor confirmed an increase in mass transfer, as against a concentric CTF reactor. Numerical simulation of the Couette‐Taylor (helical) flow was performed in a concentric and in an eccentric annulus. Calculation of parameters such as velocity, static pressure, kinetic energy and energy dissipation rate revealed a significant effect of gap eccentricity on the flow behavior.     

Iodine Pentoxide Nano‐rods for High Density Energetic Materials

The iodine pentoxide is one of the most advanced oxidizers for nanostructured energetic formulations among the thermites due to the highest energy release per volume 25.7 kJ cm⁻³. The size and shape of iodine pentoxide particles have a strong impact on the pressurization rates during the reaction. Although micro‐sized iodine pentoxide particles are commercially available, nano‐sized particles, which are desired for various nano‐energetic applications, are not available on the market. Conventional wet chemical methods are unable to produce iodine pentoxide nanoparticles due to high solubility in water. In this study, we demonstrate fabrication of iodine pentoxide nano‐rods by high energy mechanical treatment of micro‐sized I₂O₅ particles. Tuning the energy dose in high‐energy ball milling is allowing to produce I₂O₅ nano‐rods with diameter of 50–100 nm and length of 300–600 nm. The produced nano‐rods exhibited 10 % smaller decomposition energy compared to the precursor of micro particles. The experiments showed that the nano‐energetic materials prepared with nano‐sized I₂O₅ rods have pressure discharge value of 43.4 MPa g⁻¹ which is two times higher than using commercial iodine pentoxide particles.     

Synthesis and Characterization of CNT Composites for Laser‐Generated Ultrasonic Waves

In the last few years, extensive progress in ultrasonic wave generation by using multiwalled carbon nanotubes (MWCNTs) in combination with polydimethylsiloxane (PDMS), functional composites, has been achieved. Due to high optical absorption of MWCNTs as perfect absorbers for laser beams and the high thermal expansion coefficient of PDMS, a compact transducer for ultrasonic wave generation at higher frequency can be realized. This study reports a novel method to synthesize MWCNT–PDMS composites deposited on a glass substrate by spray coating, which is done in a short time of 2 h. The layers (0.9–32.2 µm) show low optical transmission properties of 13.9–0.0% at a wavelength of 1047 nm. Apart from using a 1% Triton‐X‐100 stock solution and then diluted to a 0.1% relatively nonhazardous solution, no toxic chemicals are used. The Triton‐X‐100 solution is not hazardous for lab handling and is a commonly used lab detergent for the treatment of biological cells. The achieved sound pressure level is 3.4 MPa with a frequency bandwidth of 9.7 MHz. These results show the potential for a fast and nontoxic production of laser‐generated ultrasonic transducers, which can be used well in the field of nondestructive material testing of layered materials or in medicine with an appropriate frequency range.     

Nano‐structured materials with low surface energies formed by polyelectrolytes and fluorinated amphiphiles (PEFA)

Polymer complexes formed by polyelectrolytes and fluorinated amphiphiles (PEFA) represent a new class of materials which can be prepared easily as nano‐structured coatings on a large number of chemically different substrates. The surface energies of PEFA coatings are remarkably low and can be adjusted in the range 6–18 m Jm⁻². Many of their physical properties, such as elastic modulus and mechanical strength, are determined by the nature of the polymer structure. By adjusting charge densities, molecular weights and the content of nonionic comonomers, a great variety of optimizations for a number of applications are possible. The amphiphiles have a decisive influence on the nano‐structure and on the surface energy of these materials. They act as building blocks, which vary in their number of fluorinated chains, their chain lengths and in the ionic head‐groups. Carboxylate, phosphate and sulfonate groups are preferred for the preparation of PEFAs. The scope of this review is to present a discussion of the mesomorphous structures (from columnar discotic to perforated lamellar), the low surface energies and attractive applications of these PEFA materials. Applications are found predominantly in low‐friction and anti‐soiling coatings. © 2000 Society of Chemical Industry     

Matrix influence on the piezoelectric properties of piezoelectric ceramic/polymer composite exhibiting particle alignment

This study was addressed to the influence of an electric field strength applied at fabrication process and matrix properties, such as the dielectric constant and the Young's modulus, on “pseudo‐1‐3 piezoelectric ceramic/polymer composite” in order to further enhance the piezoelectricity of that. The pseudo‐1‐3 piezoelectric ceramic/polymer composite consists of linearly ordered piezoelectric ceramic particles in polymer material. Silicone gel, silicone rubber, urethane rubber, and poly‐methyl‐methacrylate, which exhibit different dielectric constants and Young's modulus, were used as matrices to evaluate the matrix influence. The piezoelectricity of the pseudo‐1‐3 piezoelectric ceramic/polymer composite was evaluated using the piezoelectric strain constant d₃₃. The d₃₃ is one of the indices of the piezoelectric properties for piezoelectric materials. As a result, it was confirmed that d₃₃ of the pseudo‐1‐3 piezoelectric ceramic/polymer composite increased with the increase of the electric filed strength applied at fabrication process, though, it reached a constant value at a certain strength value. Further it was confirmed that dielectric constant of the matrix had a small influence on d₃₃ of the pseudo‐1‐3 piezoelectric ceramic/polymer composite, however, in case of matrix of lower Young's modulus, d₃₃ was increase. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41817.     

纳米吸波材料的研究现状与发展趋势

评述了纳米吸波材料的特性及吸波原理,介绍了纳米铁氧体吸波材料、纳米金属吸波材料、纳米陶瓷吸波材料、纳米导电高分子吸波复合材料、碳纳米管吸波材料、纳米复合吸波材料研究现状及发展情况,指出了纳米复合吸波材料是未来纳米吸波材料的研究重点。     

Ba0.9Ca0.1TiO3: microwave-assisted hydrothermal synthesis and piezoelectric properties

ABSTRACT

This communication reports the microwave-assisted hydrothermal synthesis of the x?=?0.1 member of the solid solution Ba_1–xCa_xTiO₃ (BCT) materials, its structural and microstructural characterisation and the piezoelectric properties. Using this novel – ‘fast chemistry’ – synthetic procedure, this material can be obtained in much shorter periods of time in comparison with conventional solid-state methodologies: just a few minutes instead of days. Under microwave irradiation in aqueous basic solutions, the material produced is a polycrystalline and nanosized powder which was processed as a ceramic disc in order to measure piezoelectric properties. A maximum d₃₃ value of 118?pC/N is obtained for this sample with a poling electric field of 1.5?KV?mm^?1, a value similar to those reported for conventionally made BCT materials.     

The Effect of Nanosized Layered Materials on the Structure-Property Relationship of Poly(aniline)s: An FTIR Kinetic Study

Aniline (ANI) was chemically polymerized in the presence of two different nanosized layered materials, zirconylphosphate (ZP) and molyptic acid (MA) under different experimental conditions with nitrogen purging at 45°C. The effect of nanosized layered materials on the rate of polymerization (R_p) and Fourier transform infra red-relative intensities (FTIR-RI) of benzenoid and quinonoid forms of poly(aniline) (PANI) were tested. The thermal stability and electrical conductivity values were boosted with the help of nanosized materials. High resolution transmission electron microscope (HRTEM) determined the size of nano material and its uniform distribution on the PANI matrix. For the sake of comparison, o-toluidine (OT) was polymerized under the same experimental conditions and its structure-property relationship in the presence of nano materials were also tested and critically compared with PANI systems.