Transducer Fig

To investigate the potential pressure gradients that exist within a laminate during autoclave processing, miniature pressure transducers (Fig. 10.5), which are capable of measuring the hydrostatic resin pressure, were embedded at multiple locations within several laminates to study the effects of vertical and horizontal pressure gradients [9]. 

Note the difference in operation of the inductive transducer (Fig. 6.12) where the core of an inductor is displaced linearly by a distance xs along the axis of the coil and the reluctive sensor (Fig. 6.14) which responds to a small displacement x of the armature.]... 

Pump manufacturers continue to work to reduce pulsing. The first attempt was the two-headed pump, which is connected through an output manifold or pressure transducer (Fig. 9.4). One head delivers solvent while the second refills. This improvement led to the first high-performance FIPLC pumps, but... 

Another possibility is adapting the titanium tip of the US transducer (Fig. 8.16C) for use as a working electrode (a sonotrode ). The simplest case is the use of the titanium tip itself as electrode [175] however, anodic currents are not possible owing to the formation of a Ti02 layer [176]. More recently, sonotrodes have been prepared by directly embedding a platinum electrode into the horn tip this provides extremely high limiting currents for diffusion layer thicknesses of less than 1 pm, even at low US intensities [133]. The operation... 

Mechanical Steering. The simplest method of beam steering is to use a mechanism to reorient a transducer (usually a circular aperture) to a predetermined set of orientations so as to capture the required two-dimensional data set. This approach was dominant at first however, in the last 15 years, electronically steered systems have become, by far, the most popular. Mechanical systems usually use either a single-element transducer or an annular array transducer (Fig. 25.8). Tlie former will have a fixed focus while the latter does allow the focal point to be moved electronically. This will be discussed more fiilly later. 

As mentioned before, AFM can measure surface forces using two different operation modes, DC and AC. In the DC mode, one measures the deflection (AZ) of a cantilever as a function of the tip-sample distance (D) that is varied usually hy a piezoelectric transducer (Fig. 3). The tip-sample force is given by Hooke s law in terms of AZ, F = kAZ, where k is the spring constant of the cantilever. This force clearly depends on the tip-sample distance, D, which is given by D = Z — AZ, in the absence of sample deformation. Z in the expression is the displacement of the piezo and the one that can be controlled in the experiment. When the tip is far away from the sample (large D), the force is zero. When the tip approaches the sample, it experiences various forces, electrostatic, van der Waals, double-layer, solvation forces, and so on. This is the regime of interest in... 

Displacement transducers may be considered according to application as gross (large) displacement transducers or sensitive (small) displacement transducers. The demarcation between gross and sensitive displacement is somewhat arbitrary, but may be conveniently taken as approximately 1 mm for rectilinear displacement and approximately 10 arc (1/6°) for angular displacement. The predominant types of gross displacement transducers (Fig. 18.2) are... 

The predominant types of sensitive (small) displacement transducers (Fig. 18.3) are... 

A third category of velocity transducers. Counter-type velocity transducers (Fig. 18.4(b)), is simple to implement and is directly compatible with digital controllers. 

The acoustic method that has been extensively studied in Paris uses a hemispherical piezoelectric transducer (Fig. 5a) to focus bursts of a 1 MHz sound wave [43]. The high frequency allows to stretch a small volume of liquid (typically (100 (Jtm) ), during a short time (typically 100 ns). The nucleated bubbles can be detected optically, by the audible sound emitted, or by the echo they reflect back to the transducer. The three methods provide perfectly consistent results with respect to one another [49]. The third detection method is easier to use because the transducer itself serves as a detector its voltage changes when the echo reaches its surface. 

Figure 4 shows the received signal when bubbles are generated (pulse generator on). As it can be seen, the harmonics appear clearly when the bubbles reach the overlapping insonating regions both transducers (Fig. 4-b). 

In colour Doppler, similar processing is applied across the image. The colour Doppler signals are shown as an overlay conventionally coded in shades of red for flow towards, and blue for flow away from the transducer (Fig. 1.3). Another way to display flow information depicts only the Doppler signal intensity as a power Doppler scan. It has higher sensitivity than frequency-based colour Doppler but lacks directional information and so is more useful for the small vessels, for example, in tumours, than for the portal vein where flow direction is important. 

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