Vibrators, piezoelectric

Scientists can fabricate microelectromechanical devices such as the cantilever above, which is a beam of silicon anchored at one end. The beam has a resonant vibrational frequency near 13 X 106 hertz (13 MHz) when stimulated with a piezoelectric vibrator. (A piezoelectric crystal, such as quartz, is one whose dimensions change in response to an electric field.) When 93 attograms (93 X 10, 8g) of an organic compound bind to the gold dot near the end of the cantilever, the vibrational frequency decreases by 3.5 kHz because of the extra mass on the beam. The minimum mass that can be detected is estimated as 0.4 attogram. 

Figure 26-40 Integrated biochip for DNA analysis of biological samples. Dimensions are 100 x 60 x 2 mm. Two bright circles are piezoelectric vibrators for ultrasonic agitation. 

The MicroDose DPI (MicroDose Technologies, United States) is a breath-activated device that includes a piezoelectric vibrator that converts electrical energy from a battery to mechanical motion that is then transferred into the dry powder. The vibration energy deaggregates and aerosolizes the dose. By controlling the energy input, i.e., the amplitude and frequency of the vibration, the DPI is claimed to be usable for various compounds. As with the devices from Nektar and Dura, the MicroDose DPI uses accurately filled unit-dose blisters. 

External energy sources for active mixing are, for example, ultrasound [22], acoustic, bubble-induced vibrations [23,24], electrokinetic instabilities [25], periodic variation of flow rate [26-28], electrowetting induced merging of droplets [29], piezoelectric vibrating membranes [30], magneto-hydrodynamic action [31], small impellers [32], integrated micro valves/pumps [33] and many others, which are listed in detail in Section 1.2. 

Figure 19.10 (a) Piezoelectric hysteresis loops of 256 points (each approx. 30x30nm) obtained by combining phase and amplitude of the induced piezoelectric vibration, (b) Average of the 256 loops [17]. 

Figure 19.12 Amplitude maps A(x, y) of the piezoelectric vibration corresponding to the respective phase maps of Figure 19.11.

A conventional <111> oriented Pb(Zro.45Tio.55)03 (pzt) ferroelectric film, deposited on Pt/Ti02/Si02/Si substrate by sol-gel spin casting and Pt-sputter top electrodes, was used in this study [24], The pzt film thickness was 175 nm. The experimental set-up used for the afm assisted piezoresponse imaging study of the pzt film consisted of a Park Scientific Instrument Autoprobe cp afm combined with a lock-in amplifier to excite and collect the piezoelectric vibration response amplitude and phase. 

Figure 19.20 Piezoelectric vibration maps of phase ((a), (c)) and amplitude ((b), (d)) (3x3 /um2) of a fatigued Pt-PZT-Pt structure after positive ((a), (b)) and negative ((c), (d)) poling. Bright and dark phase areas correspond to bottom-to-top and top-to-bottom polarization orientations, respectively.

IRE Standards on Piezoelectric Crystals the piezoelectric vibrator definitions and methods of measurement, 1957, Proceedings IRE, March 1957, 353-8. 

M Umeda, K Nakamura, S Ueha, Analysis of the transformation of mechanical impact raiergy to electric energy using piezoelectric vibrator , Jpn J Apfd Phys, 1996 35(1,58)3267-3273. 

Next let us introduce the electromechanical couplingfactor k, which corresponds to the rate of electromechanical transduction. The internal energy 1/ of a piezoelectric vibrator is given by summation of the mechanical energy Um (= fxdX) and the electrical energy Ue (= fD dE). U is calculated as follows, when linear relations Eqs 20 and 21 are applicable ... 

The boundary conditions for these piezoelectric equations are important (a) The condition mechanically free stipulates specifically that boundaries of a piezoelectric sample (e.g., a piezoelectric vibrator) can move, i.e., the vibrator vibrates with a variable strain and zero (or constant) stress. Under this condition, the coefficients in these equations carry a superscript T e.g., is the dielectric constant at constant stress, (b) The condition mechanically clamped stipulates specifically that the boundaries of a vibrator cannot move. This condition means that, when the frequency of the applied voltage is much higher than the resonance frequency of the vibrator, the strain is constant (or zero), while the stress varies. In this case, the coefficients in these equations carry a superscript S e.g., is the dielectric constant at constant strain, (c) The condition of electrical short circuit implies specifically that the electric field = 0 (or a constant), while the electric displacement D 0 inside the vibrator. This is the case when the two electrodes on the surface of the crystal sample are electrically connected (or the electric potential on the entire surface of the sample is constant). Under this condition, the coefficients in these equations carry a superscript E e.g., sfj (or c ) is the elastic compliance (or stiffness) coefficient at constant electric field, (d) The condition of electrical open circuit corresponds to the case when aU the free charges are kept on the electrodes of the sample (electrically insulated) and the internal electric field / 0, while = 0 in the sample, hi this case, the coefficients in these equations carry a superscript D e.g., sjj (or c ) is the elastic compliance (or stiffness) coefficient at constant polarization. 

Piezoelectric Vibrators and Determination of Piezoelectric and Elastic Parameters by the Transportation Line Method... 

Based on the vibration equation of the piezoelectric vibrator, the elecnomechanical coupling factor, k, can be calculated ... 

A System using the diaphragm micropump equipped with a piezoelectric vibrator (bimorph oscillator) No data No data <1 Soft drinks 1996 184 ... 

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