Process ultrasonic transducers

Another important class of titanates that can be produced by hydrothermal synthesis processes are those in the lead zirconate—lead titanate (PZT) family. These piezoelectric materials are widely used in manufacture of ultrasonic transducers, sensors, and minia ture actuators. The electrical properties of these materials are derived from the formation of a homogeneous soHd solution of the oxide end members. The process consists of preparing a coprecipitated titanium—zirconium hydroxide gel. The gel reacts with lead oxide in water to form crystalline PZT particles having an average size of about 1 ]lni (Eig. 3b). A process has been developed at BatteUe (Columbus, Ohio) to the pilot-scale level (5-kg/h). 

Ultrasonic insertion an ultrasonic transducer (horn) vibrates the insert, which heats by vibrating against the plastic. The advantages and drawbacks of this process are ... 

Solid/liquid flows are commonly found in industrial processes to avoid flow obstruction, nonintrusive flowmeters are generally preferred. Flowmeters based on ultrasonic techniques are ideal nonintrusive instruments because, in most applications, the ultrasonic transducers are simply clamped on the outside pipe wall. In this section, we describe two ultrasonic flowmeters based on the Doppler and cross-correlation methods. Both require an inherent flow tag thus both are directly applicable to solid/liquid flows because of the presence of solid particles. Both flowmeters measure mainly particle velocity liquid-phase velocity, if different from the particle velocity, is not determined. 

The s nethic aperture focusing technique (SAFT) uses a. scanning transducer to collect and process ultrasonic waves into a unit known as an aperture, by shifting adjacent waves with... 

Ultrasonic welding is a sohd-state process in which the actual bonding between the two parts to be welded is obtained through the decaying into heat of the fi-iction forces work. The latter are generated by a vibration induced by an ultrasonic transducer. As it is well known, ultrasonic elastic waves are characterized by frequencies which can reach 10 kHz. To obtain the welding, electromechanical generators are used ... 

Ultrasound. An aqueous formulation of insulin is placed on the skin. An ultrasonic transducer is immersed in the formulation, and the ultrasonic vibrations cause aqueous pathways to form in the stratum comeum by a process called cavitation. Insulin reaches the epidermal vasculature by diffusion (see Tachibana and Tachibana, 1991). 

The optoacoustic properties of plasmon-resonant gold nanoparticles originate from photoinduced cavitation effects. This process can be summarized as follows (i) thermalization of conduction electrons on the subpicosecond timescale/ (ii) electron-phonon relaxation on the picosecond timescale and thermalization of the phonon lattice, with a subsequent rise in temperature by hundreds to thousands of degrees (iii) transient microbubble expansion upon reaching the kinetic spinodal of the superheated medium, initiated on the nanosecond timescale (iv) microbubble collapse, resulting in shockwaves and other forms of acoustic emission. The expansion and collapse of a cavitation bubble takes place on a microsecond timescale, and are easily detected by ultrasonic transducers. 

Figure 2.47 Cumulative Graphical Accounting of the Operating Steps in the Process Using Ultrasonic Transducers of Table 2.10...

In the following, the fabrication and characterization of micromachined high frequency focused polymer ultrasonic transducers in a manner that is compatible with CMOS microelectronics, and MEMS batch fabrication techniques, are described. The specifics of the electronics are not described here, but the interested reader may find more details elsewhere [75, 76, 81-84]. The transducer is capable of being manufactured on silicon wafers after the completion of CMOS electronics. These two key elements enable the eventual creation of a monolithic transducer chip that does not require modification of the standard circuit fabrication process. This type of transducer chip will likely follow the path of other MEMS devices such as accelerometers, gene chips and digital micromirror arrays, where batch production, high yields and... 

Figure 17.4 Process flow used to fabricate the prototype ultrasonic transducers (a) a silicon (Si) wafer is micromachined to create an array of holes with diameters between 0.75 and 2.00 mm, after which the wafer is then thermally oxidized to grow a 1.5 pm thick S1O2 layer (b) the wafer is then diced into 1 cm wide square die (c) the die is laid flat onto a piece of free-standing F DF film in a jig (the die is now viewed in cross-section through the hole) (d) the die and PVDF film are clamped into the jig against an O-ring forming an air-tight seal, and air pressure is applied to the face of the PVDF film to deflect it into the desired spherical shape (e) finally, conductive epoxy is injected into the hole and a 30 gage wire is potted into the epoxy the air pressure is maintained until the epoxy cures, then the transducer chip is removed from the jig.

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