Voltage piezoelectric transducers

In general, one should be aware that tablet press instrumentation involves the use of strain gauges or piezoelectric transducers to provide a voltage signal proportional to the force applied for the compaction operation. Let us say we can measure forces, such as those applied to the granulation by the punches, that applied to the die wall, that required for tablet ejection, etc. With tlie use of other transducers we can also measure distance. With the measurement of force and distance, we can calculate work, energy, etc. 

Single-mode operation was achieved by closing down the variable iris in front of the output coupling mirror. The mirror itself was mounted on a piezoelectric transducer, which is capable of converting an applied voltage into a proportional extension of the element (Lansing 80-214 Lock-In... 

The PEM is made of a piezoelectric transducer that is glued to a ZnSe crystal. The piezoelement converts a periodic voltage to a periodic mechanical (acoustic) wave, which compresses or expands the crystal. This movement changes the refractive index in the x direction and imposes a periodic retardation (or acceleration) of the fix component of the incident linearly polarized wave. The fiy component remains unchanged. The PEM is operated at its resonant frequency (50 kHz). If the optical element is at rest, the polarization of the radiation remains unchanged. If the optical element undergoes compression or expansion, the component fix has a positive (retardation) or negative (acceleration) phase shift relative to the phase component of the component fiy. 

Polymer electrets can be operated as sensors or actuators. Their operation is very similar to that of a piezoelectric material and their direct piezoelectric transducer coefficient (d33) is higher than that of solid PVDF ferroelectric polymers [97]. If a compressive force is apphed to the film, the pores will deform preferentially with respect to the polymer material. Unlike charges within the polymer will be pushed closer together and the potential measured at the contacts will change accordingly. Similarly, the application of a voltage across the electrodes will yield a change in thickness in the material. 

Clearly, static loads are not faithfully represented in this particular piezoelectric transducer. It is possible to compensate for such dynamics by using an appropriate conditioning circuit. If we rearrange Equation 27.19, we can relate the desired force measurement in terms of the voltage produced at the amplifier input as follows ... 

The simplest application of a piezoelectric transducer is its use as a strain indicator, since the strains applied to a piezoelectric element can be quantified simply by measuring the electrical field which is created across the boundaries of that element. In the case of photoacoustic detectors, pressure pulses, created by the absorption of light from a chopped beam, deform a thin plate and are transformed into a series of voltage pulses. In such applications the electrical signals created are either dc or low-frequency, so that the design of the device and interface electronics is straightforward. 

The self-sensing solid-state actuator concept illustrated in Fig. 6.139b was implemented into a commercially available positioning system driven by a low-voltage piezoelectric stack transducer [332,360]. 

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. 

In contrast, as noted above, the electrical-ultrasonic efficiency of the piezolectric transducer allows energy to be saved when compared to magnetostrictive transducers. This is probably the main reason why the former is more widely used than the latter, regardless of the relatively low levels of acoustic power intensity provided and the short life-span. Additionally, piezoelectric transducers are high-voltage-driven and air-cooled which, for some applications, implies the risk of explosion (Peshkovsky and Peshovsky, 2010). 

In the brewing industry, there is no ideal foam-control method currently in use, although ultrasonics have been tested to suppress foaming in fermenting vessels. The ultrasound generated by ceramic piezoelectric transducers has the unusual property that when an electric voltage is applied across their crystalline ceramic structure, deformation occurs, so that an alternating current thus produces a sinusoidal vibration. The resonance frequency depends on the physical dimensions of the... 

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