Accumulated power. The power P was calculated based on the power dissipated in all of the samples according to the different evaluated amplitude and pulse conditions. The calorimetric method was used for the P calculation using the ratio presented in equation 1 :. The Cp was calculated using the method by Choi and Okos The accumulated power was calculated as the sum of the power that dissipated at each measurement point.
Experimental design. A multilevel categorical factorial design was performed using the statistical software Design Expert Version 9 Statease Inc. The pulsation and amplitude were the two categorical factors that were defined at different levels. Table 1 shows the experimental design in which analysis of variance ANOVA was performed to find significant differences for the pulses and amplitudes in the results of the phase separation. The fit of the model was evaluated using the R2 and adjusted R2 values.
Results and discussion. The selection of parameters as power, frequency and pulse type, helps to define the different effects that are produced by high-power ultrasound when it passes through a medium, which demonstrates their significance depending on the features of the material [6].
Therefore, the density difference between both phases under the influence of gravity leads to phase separation [25]. The following effects are described in our study: 1 the effect of amplitude on the medium temperature and phase separation, 2 the accumulated power during the sonication time, and 3 the effect of the treatment on the phase separation. As stated by Gaikwad and Pandit [26], the use of ultrasonic emulsification can be described using four characteristics: 1 a minimum intensity is required to start the emulsification process, 2 an increase in the power emitted to the matrix enhances the emulsion stability, 3 an increase in the sonication time decreases the dispersed phase droplet size, favouring the formation of microjets, and 4 the forces responsible for the emulsification are the ratio of the force acting on the droplets and the surface tension, which represent the physicochemical properties of the system.
Effect of amplitude and pulse type on temperature. The effect of different amplitudes on the temperature for each ultrasound pulse treatment was evaluated for the three types of pulse. Thus, Fig 3 shows the temperature increase during the 5 minutes of treatment for each type of pulse.
This increase has been widely described by Shanmugam, Chandrapala, and Ashokkumar [26] and Pingret, Fabiano-Tixier, and Chemat [27] as being caused by the cavitation phenomenon. Thus, the ultrasound generates a strong resonance in the pulses that are represented in bubbles in the form of micro-jets, which significantly influences the acoustic environment of the liquid [29].
This allowed some of the acoustic energy to be degraded as heat, leading to an increase in medium temperature due to the direct relation between the temperature and the solubility of water and oil [7,30]. Figure 3 shows that the and pulsed treatments have a lower temperature increase compared to the continuous treatment due to the off period of the pulsed wave effect.
Power accumulated during the sonication time. Table 2 shows the accumulated power, as calculated from equation 1. Anihouvi, Danthine, Kegelaers, Dombree, and Blecker [31] reported that cavitation is the most significant mechanism of power dissipation in a low frequency ultrasound system; thus, changes in cavitation intensity can be related directly to changes in power.
Effect of treatments on phase separation. The homogenization technology in emulsions has a relevant role in the stability of its phase, and this can be measurement as the minima distance of separation. Results of the correlation. Table 3 shows the correlation of the response variables, temperature, accumulated power and separation distance. We observed a high correlation with accumulated power, followed by a correlation with temperature and, finally, with the separation distance.
Transient cavitation that is generated by the pulse that is related to the temperature during the emulsification process is highlighted. The relevance of the cavitation that is generated by low frequency ultrasonic waves contributes to the degradation of the acoustic energy into heat, favouring the increase in the emulsion temperature. However, smaller temperature increases that do not favour emulsion stability were found due to the accumulation of more power; thus, emulsions exhibiting less separation were obtained with continuous pulsing.
These results will allow the application of an advanced and emerging technology with less use of surfactants for low oil-content emulsions that can be the basis for low-fat food products. Displays can be black-and-white or color, depending upon the model of the ultrasound machine. These devices allow the operator to add notes to and take measurements from the data. Typically, a patient's ultrasound scans are stored on a floppy disk and archived with the patient's medical records.
Printers Many ultrasound machines have thermal printers that can be used to capture a hard copy of the image from the display. Different Types of Ultrasound The ultrasound that we have described so far presents a two dimensional image, or "slice," of a three dimensional object fetus, organ.
Two other types of ultrasound are currently in use, 3D ultrasound imaging and Doppler ultrasound. In these machines, several two-dimensional images are acquired by moving the probes across the body surface or rotating inserted probes.
The two-dimensional scans are then combined by specialized computer software to form 3D images. Photo courtesy Philips Research 3D ultrasound images. Doppler Ultrasound Doppler ultrasound is based upon the Doppler Effect. When the object reflecting the ultrasound waves is moving, it changes the frequency of the echoes, creating a higher frequency if it is moving toward the probe and a lower frequency if it is moving away from the probe.
How much the frequency is changed depends upon how fast the object is moving. Doppler ultrasound measures the change in frequency of the echoes to calculate how fast an object is moving. Doppler ultrasound has been used mostly to measure the rate of blood flow through the heart and major arteries.
Photo courtesy Philips Research Doppler ultrasound used to measure blood flow through the heart. The direction of blood flow is shown in different colors on the screen. Major Uses of Ultrasound Ultrasound has been used in a variety of clinical settings, including obstetrics and gynecology, cardiology and cancer detection. The main advantage of ultrasound is that certain structures can be observed without using radiation.
Ultrasound can also be done much faster than X-rays or other radiographic techniques. Here is a short list of some uses for ultrasound:. In addition to these areas, there is a growing use for ultrasound as a rapid imaging tool for diagnosis in emergency rooms. There have been many concerns about the safety of ultrasound. Because ultrasound is energy, the question becomes "What is this energy doing to my tissues or my baby?
The two major possibilities with ultrasound are as follows:. The higher frequency wavelength will have shorter wavelength whereas lower frequency wavelength will have longer wavelength. The wavelength for the 2. Image resolution determines the clarity of the image. Such spatial resolution is dependent of axial and lateral resolution.
Both of these are dependent on the frequency of the ultrasound. Axial resolution is the ability to see the two structures that are side by side as separate and distinct when parallel to the beam. So a higher frequency and short pulse length will provide a better axial image.
Lateral resolution is the image generated when the two structures lying side by side are perpendicular to the beam. This is directly related to the width of the ultrasound beam. Narrower the beam better is the resolution. The width of the beam is inversely related to the frequency. Higher the frequency narrower is the beam. If the beam is wide the echoes from the two adjacent structures will overlap and the image will appear as one.
When the ultrasound beam travels through the tissues there is some energy loss and this is called attenuation. Attenuation of the signal is due to absorption, reflection and scattering. Attenuation is represented by the attenuation coefficient and each tissue ahs its own coefficient. Blood has the lowest coefficient and bone ahs the highest coefficient. Attenuation is also results from reflection and scattering.
Reflection depends on the difference in acoustic impedances of the tissues at the interface. Acoustic impedance is the resistance offered by the tissues to the transmission of the sound. Higher the difference in impedance greater is the reflection of the wave.
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