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A Review on preparation of conductive paints with cnts as fillers
Published in Badal Jageshwar Prasad Dewangan, Maheshkumar Narsingrao Yenkie, Novel Applications in Polymers and Waste Management, 2018
Sahithi ravuluri, Mansi khandelwal, Harshit bajpai, G. S. Bajad, R. P. Vijayakumar
Ultrasonication is the act of using ultrasound energy to agitate particles in a solution. It is usually achieved by using an ultrasonic bath or an ultra sonic probe. The principle behind ultrasonication is that when ultrasound waves propagate through series of compression, attenuated waves are induced in the medium through which the waves are passed. The production of such shock waves promotes the peeling of individual nanoparticles (mostly peel off the nanoparticles located at the outer part of the bundle) and thus results in the separation of individual nanoparticles from bundles. After the removal of external shear stress, the dispersed CNTs in solution would reconfigure themselves to a new equilibrium state of low energy through reaggregation (driving force for reaggregation is provided by the van der Waals forces of attraction). This process will take place unless surfactants are added to provide steric hindrance or static charge repulsion in order to stabilize the particles.13 Literature studies show that the appli cation of weak shear subsequent to a wellmixed state can significantly accelerate the reaggregation.14 Sonication at higher rate to be avoided as it may lead to the damage of CNTs. This method is quite suitable to disperse CNTs in liquids having low viscosity.
Chapter 12 Image Production
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
Ultrasound energy is generated by a transducer (a transducer is a device for converting energy from one form into another) which converts electrical energy into ultrasonic energy. The physics of this subject was introduced in Chapter 7 (section 7.3). Piezoelectric materials such as quartz and tourmaline change their shape when subjected to an electric field. The converse effect is also obtained: mechanical deformation of the crystal produces an electric field across it which can be measured. Piezoelectric crystals are therefore suitable both for transmitting and receiving transducers. In practice, at the frequencies which are used for medical diagnosis, an artificial material lead titanium zirconate (PZT) is used. A crystal of a particular thickness has a particular resonant frequency and this determines the frequency at which the transducer can be used. A typical lead titanium zirconate transducer operating at its fundamental resonant frequency would be half a wavelength thick (about 2 mm thick for a 1 MHz transducer).
Role of Photoacoustic and Ultrasound Imaging in Photothermal Therapy
Published in Lihong V. Wang, Photoacoustic Imaging and Spectroscopy, 2017
Shah Jignesh, Suhyun Park, Salavat Aglyamov, Stanislav Emelianov
Ultrasound imaging is a real-time imaging modality where short pulses (typically 2–3 cycles) are transmitted into the body using an ultrasound transducer. As the pressure wave interacts with tissue, some of the ultrasound energy is reflected back to the transducer, which now acts as a receiver and converts the backscattered echo into electric signals. Knowing the time delay between the transmitted pulse and received echo signals, we can determine the axial position or depth of the echo-producing structure. Ultrasound has been utilized to assist thermal cancer therapies, including high intensity focused ultrasound [35], radio frequency ablation [36], and photothermal therapy [11,12] by monitoring temperature elevation and assessing thermal damage.
Nondestructive Testing by Frequency-Domain Continuous-Wave Ultrasound Reflectometry
Published in Research in Nondestructive Evaluation, 2020
Ultrasound testing is one of the nondestructive inspection techniques used to detect, locate, and size discontinuities [1–3]. In this method, an electrical signal is converted to sound/ultrasound energy, which is further coupled into the tested material. Reflected and/or transmitted sound energy is detected and converted into an electrical signal, which is analyzed. Currently, the primary method employed by ultrasound inspection systems is based on applying pulsed sound/ultrasound energy to the inspected part, and detecting reflected/transmitted pulses. After analysis of the received pulses, different properties of the tested sample and/or the discontinuities present inside the sample can be determined. Usually, the most useful information is the time delay between the transmitted and detected pulses. The pulsed ultrasound inspection method has certain deficiencies, such as: (i) distance measurements and distance resolution are limited by the propagation speed and the duration of the pulse; (ii) pulsed signals typically have a low duty-factor, i.e., there is a limit to the amount of energy used to stimulate the object under test; and (iii) achieving acceptable signal-to-noise ratio (SNR) requires increasing the amplitude of the pulses, which would lead to reduced life-expectancy of the transducers. Trying to overcome these limitations was the main motivation for investigating the applicability of modulated continuous-wave stimulus to the classical nondestructive testing (NDT) techniques.
Contact ultrasound strengthened far-infrared radiation drying on pear slices: Effects on drying characteristics, microstructure, and quality attributes
Published in Drying Technology, 2019
Yunhong Liu, Changying Sun, Yuqing Lei, Huichun Yu, Huihan Xi, Xu Duan
In addition, it can be seen from the figures of drying rate curves that the gap between the drying rate curves at different ultrasound powers gradually reduced with the decrease of moisture content during CUFIR drying, which maybe indicated that the strengthening effect of ultrasound decreases with the reduction of moisture content. For example, at FIR power of 100 W, when the moisture content of samples was >600% at the initial phase of drying process, the average drying rates of CUFIR drying at ultrasound powers of 30 and 60 W were 5.89%/min and 6.63%/min, respectively, and were 0.59%/min and 1.33%/min higher than the average drying rate of FIR drying without ultrasound assistance (5.30%/min), with the increasing ratios of 11.13% and 25.09%, respectively. When at the intermediate stage of drying process, and for example, the moisture content ranged from 300 to 500%, the average drying rates of CUFIR drying at ultrasound powers of 30 and 60 W decreased to 2.68%/min and 3.08%/min, respectively, with the increasing ratios of 6.35% and 22.22% comparing with that of FIR drying without ultrasound enhancement (2.52%/min). When the moisture content reduce to <100% at the final stage of drying process, all the three drying rate curves nearly overlapped, which meant that the strengthening effect of ultrasound is very weak at low moisture content during drying. The results above indicated that with the decrease of drying rate during CUFIR drying of pear slices, the strengthening effect of ultrasound on drying rate decreases with the reduction of moisture content as well. Since the attenuation coefficient of ultrasonic propagation in liquid is much less than that in the solid,[32] more water inside the samples represent lower ultrasound attenuation and then better ultrasound penetration and transportation. At the stage of high moisture content, most of the water inside belongs to free water and unbound water, which is beneficial for the spread and transportation of ultrasound waves inside the materials. The increase of ultrasound power could produce greater cavitation effect and mechanical effect, more efficient ultrasound energy and stronger turbulence and vibration inside the materials, causing smaller internal diffusion resistance and better mobility of water molecules.[23] As the moisture content decreased, the content of free water would reduce significantly and then lead to greater internal diffusion resistance and larger attenuation coefficient of ultrasonic propagation. So, the transportation and utilization of ultrasound energy became more difficult and the cavitation and mechanical effects of ultrasound waves became weaker, resulting in the decrease of ultrasound strengthening effect on accelerating moisture diffusion and drying rate with the reduction of moisture content. Moreover, the pear slices started to warp at the latter stage of drying process at low moisture content, and the contact between samples and the ultrasound radiation plate became worse, which was not conducive to the ultrasound strengthening effect on drying process.