High power transducer

Recent developments in high power transducers now allow the treatment of large amounts of sewage sludge [74,75]. The principal advantages of the sonochemical method are that it can be automated with no moving parts and involves no added chemicals. 

To make a permanent bond for a high power transducer to the curved surface of a flow reactor of cylindrical cross-section is not as easy as to a flat surface but several... 

Lin, S., Zhang, F., 2000. Measurement of ultrasonic power and electro-acoustic efficiency of high power transducers. Ultrasonics 37 549-554. 

Lead zirconate [12060-01 -4] PbZrO, mol wt 346.41, has two colorless crystal stmctures a cubic perovskite form above 230°C (Curie point) and a pseudotetragonal or orthorhombic form below 230°C. It is insoluble in water and aqueous alkaUes, but soluble in strong mineral acids. Lead zirconate is usually prepared by heating together the oxides of lead and zirconium in the proper proportion. It readily forms soHd solutions with other compounds with the ABO stmcture, such as barium zirconate or lead titanate. Mixed lead titanate-zirconates have particularly high piezoelectric properties. They are used in high power acoustic-radiating transducers, hydrophones, and specialty instmments (146). 

Gallego-Juarez JA, Rodriguez Corral G, Riera E et al. (2001) Development of industrial models of high power stepped-plate sonic and ultrasonic transducer for use in fluids. IEEE Ultrasonic Sypoos. Proceedings, pp 571-578... 

A semi-industrial pilot plant has been developed in which air-borne ultrasound has been applied to the reduction of particle emissions in coal combustion fumes [62]. The installation basically consists of an acoustic agglomeration chamber with a rectangular cross-section, driven by four high-power and highly directional acoustic transducers operating at 10 and/or 20 kHz, and an electrostatic precipitator (ESP). In the experiments, a fluidised bed coal combustor was used as fume generator with fume flow rates up to about 2000 m /h, gas temperatures of about 150 °C. and mass concentrations in the range 1-5 gm. The acoustic filter reduced fine particle emissions by about 40 %. 

Fig. 4.6. Transducer assembly for the production of high power air-born ultrasound.

The structure of a typical composite power transducer for ultrasonic cleaning is illustrated in Fig. 6.32. The PZT toroids are kept in compression (stress 25 MPa) by the bolt to reduce the risk of their fracturing under the high drive fields. The PZT will be of the hard variety ( acceptor -doped see Section 6.3.2) so as to minimize the risk of depolarization under the high mechanical stresses experienced. The associated high Qm value and low electrical tan 3 ensure that the losses are kept within acceptable limits. The structure has the added advantage that any heat developed in the ceramic can be dissipated through the massive metal end pieces. 

In pulse-echo-based techniques, the time of flight in a sample cannot be determined simply from the observation of the time span between adjacent echoes in the echo pattern if plane parallel transducers operated at resonant frequencies are employed. Transducers introduce substantial errors if the velocity is derived from such measurements, especially if relatively short samples are used. Various correction approaches have so far been developed in order to consider the influence of resonant transducers and the effects of diffraction [31-33]. The need for corrections can be avoided and a broad operational bandwidth obtained by using short pulses of duration equal to or shorter than the transduction [34] this requires a time resolution better than the transit time in the transducer. This short-pulse excitation (e.g. the maximum for a 10-MHz transducer is 50 ns) requires a high-power wide-band ultra-linear amplifier to ensure the detection of US signals with sufficient resolution under non-resonant conditions. 

To make slender objects for transducing traction forces, as in the case of cantilever force sensors, it is important to have control over the manufacturing dimensions. For this reason, nanotechnology and microfabrication have been used to construct the measurement devices. For example, cantilever beams have been built so thin and slender that although the elastic modulus of the materials are between 1 MPa and 100 GPa, the spring constant of the structure is in the range of 1-100 nN/pm. The structural flexibility allows the beam to deflect a few micrometers under the load of a traction force, which is an amount that is readily measured under a high-powered microscope. 

Acceptors, e.g, replacing Zr"" with Fe with the concomitant formation of oxygen vacancies. Domain reorientation is limited, and hence acceptor additives lead to poorly developed hysteresis loops, lower k, low tan 5, low compliance, and high aging rates. Typical applications are in high-power devices such as sonar and ultrasonic transducers. 

To increase the active zones existing in the reactor, one can easily modify the position of the transducers (if multiple transducers have been used, which is likely to be the case at large-scale operation due to the fact that it is quite difficult to successfully operate a single transducer with very high power and frequency due to limitations in the material of construction of the transducers) so that the wave patterns generated by the individual transducers... 

Frequently, a high-resolution transducer is used to visualize the appendix during graded compression. In many cases, the appendiceal region can be seen with transabdominal 7.5-MHz transducers. The use of colour- or power Doppler may be useful however, use of the Doppler methods is not mandatory. 

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