Diameter of the transducer

We have used several different frequencies between 0.25 and 2 MHz. The use of lower frequencies not only increases the focal spot size but also reduces the number of erythrocyte extravasations per unit area (9). The reduction in the diameter of the transducer, or increase in the radius of curvature, also increases the focal spot size. Examples of the 50% focal spot dimensions for different transducers are given in Table 2. The electrical impedance of the transducer is, typically, matched to the output impedance of the amplifier by an external LC-matching network to allow optimum power transfer. Although, we manufactured our own transducers in-house, custom MRI compatible transducers can be purchased from several manufacturers such as Imasonic, Inc. (Besancon, France). 

The diameter of the buffer rod is set to be larger than the diameter of the transducer. The length of the buffer rod is generally chosen to be longer than the near-field region (i.e., Fresnel zone), which is in turn calculated through the following equation ... 

After input of the mechanical values of the transducer-container arrangement and the transducer data (length of the transmitted wave, diameter) the program calculates automatically all relevant parameters ... 

To accommodate smaller liquid flows of about 10 pl/min, micro-ultrasonic nebulizers have been designed. Although basically similar in operation to standard ultrasonic nebulizers, in these micro varieties, the end of a very-small-diameter capillary, through which is pumped the sample solution, is in contact with the surface of the transducer. This arrangement produces a thin stream of solution that runs down and across the center of the face of the transducer. The stream of sample... 

Because most applications for micro-channel heat sinks deal with liquids, most of the former studies were focused on micro-channel laminar flows. Several investigators obtained friction factors that were greater than those predicted by the standard theory for conventional size channels, and, as the diameter of the channels decreased, the deviation of the friction factor measurements from theory increased. The early transition to turbulence was also reported. These observations may have been due to the fact that the entrance effects were not appropriately accounted for. Losses from change in tube diameter, bends and tees must be determined and must be considered for any piping between the channel plenums and the pressure transducers. It is necessary to account for the loss coefficients associated with singlephase flow in micro-channels, which are comparable to those for large channels with the same area ratio. 

The reactor design in terms of ratio of the diameter of the immersion transducer to reactor diameter, liquid height, position of the transducers and characteristics of the cell plays a important role in deciding the cavitational activity distribution and hence the efficacy of sonochemical reactors for the specific application. Based on a critical analysis of the existing literature, following important design related information can be recommended ... 

With an increase in the diameter of immersion transducer relative to the reactor diameter, the cavitational activity increases till an optimum ratio, usually dependent on the application [51,52], The ratio mainly affects the level of turbulent... 

Having specified the frequency of operation and the aperture diameter of the lens surface, it is now possible to consider the position and size of the transducer. This will be a disc and, ideally, it will operate as a so-called piston source. The amplitude in the far field of such a source can be calculated by... 

The ultrasound fields are generated by a focused, MRI compatible piezoelectric transducer (19). The physical characteristics of the transducer determine the size of the focal spot and can be tailored for the experimental needs. For example, we have performed successful experiments with 100-mm diameter, 80-mm radius of curvature transducers with a frequency of 0.7 MHz (see Note 1). 

To measure left ventricular internal diameter (LVID), the transducers are placed in the same anatomical area as for the epicardial crystals. However, they are pushed through the wall of the left ventricle through stab wound incisions. The crystals are positioned across the greatest transverse diameter of the left ventricle, one on the anterior and the other on the posterior endocardial wall. 

The DOD device produces drops that are approximately equal to the orifice diameter of the droplet generator [12]. As shown in Figure 11-3, a DOD system is conceptually much less complex than continuous mode systems but requires the transducer to deliver three or more orders of... 

A Spring type diaphragm pressure transducer is made of carbon steel to measure a pressure differential of 1000 psi. The diameter of the diaphragm is 0.5 in. Calculate the thickness of the diaphragm, in mm, so that the maximum deflection is less than one third its thickness. 

We have also received and ultrasonically examined 21 silicon nitride tensile specimens. These samples are cylindrical and have a diameter of 6.4 mm in the gage section, which was the only region inspected. The evaluation was conducted using a 75-MHz. spherically focused transducer. As we have mentioned in previous reports, the sharply curved entry surface of small-diameter cylindrical specimens introduces both severe astigmatism and spherical aberration in the ultrasonic beam distribution inside the solid and limits the depth at which critical flaw sizes can be detected to a few hundred microns. Our work has indicated that this limitation could be greatly reduced by aspherical shaping of the transducer lens, but the cost of such a transducer has thus far proved prohibitive. No indications were observed in any of the specimens although we could not perform a 100% inspection on any of the rods because of equipment limitations. 

PZT transducers, 2.5 cm in diameter, are used in this apparatus. The larger the transducer diameter at a given frequency, the better collimated the acoustic beam (170). In this case, at 1 MHz, the diffraction attenuation is negligible and specimen alignment is not critical. The resonant frequency of the transducer is proportional to its thickness, 0.25 cm, and is 0.75 MHz. The maximum output of the transducer is at its resonant frequency, but it can be operated below resonance without much loss, and can be operated at harmonics of the resonant frequency to obtain higher frequency measurements. In this manner, the apparatus has been... 

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