Piezoelectric Pumps

Fluids are often pumped hydrodynamically to exert the flow. Various pumps are used, including syringe pumps, peristaltic pumps, piezoelectric pumps, and gas-pressure-driven hydrodynamic pumps. In the case of hydrodynamic pumps, an inert gas is pressurized in the headspace of the vial containing the sample or carrier fluid. The force exerted by the gas on the liquid phase sustains flow of the liquid in the channel. When a liquid moves along the circular cross-section channel, the Poiseuille equation can be used to relate the... 

Mechanical scales, 26 229-236 functionality of, 26 251 Mechanical seals, for pumps, 21 81 Mechanical strength measurement, in tire compounding, 21 811 Mechanical stress, in piezoelectric materials, 22 709... 

There are, of course, noncontact printing devices useful for the construction of microarrays (see Figure 4.2). These are microdispensers that eject droplets by several different mechanisms (solenoid, piezoelectric, heated jet, acoustical wave). Perhaps the best-known commercial dispensers are the syringe driven-solenoid pump (e.g., Cartesian BioDot) and piezo systems (e.g., Packard Biosciences). 

We have to make a distinction here between electric controllers (e.g. PID controllers) with a proportional valve as actuator and mechanical diaphragm controllers. In a regulation system w/ith electric controllers the coordination between controller and actuator (piezoelectric gas inlet valve, inlet valve A/ith motor drive, butterfly control valve, throttle valve) is difficult because of the very different boundary conditions (volume of the vessel, effective pumping speed at the vessel, pressure control range). Such control circuits tend to vibrate easily when process malfunctions occur. It is virtually impossible to specify generally valid standard values. 

Another common method of generating particles with diameters 0.5-50 /rm is the Berglund-Liu (1973) vibrating-orifice generator shown schematically in Fig. 11.77. The solution to be aerosolized is pumped through a small orifice 5-20 /xm in diameter. The orifice is oscillated by a piezoelectric crystal so that the liquid stream is broken on each oscillation, forming a small liquid particle that is carried away in a stream of air. 

Micropumps based on piezoelectrics are made of pumping chambers that are actuated by three piezoelectric lead zirconate titanate disks (PZT). The pump consists of an inlet, pump chambers, three silicon membranes, three normally closed active valves, three bulk PZT actuators, three actuation reservoirs, flow microchannels, and outlet. The actuator is controlled by the peristaltic motion that drives the liquid in the pump. The inlet and outlet of the micropump are made of a Pyrex glass, which makes it biocompatible. Gold is deposited between the actuators and the silicon membrane to act as an upper electrode. Silver functions as a lower electrode and is deposited on the sidewalls of the actuation reservoirs. In this design, three different pump chambers can be actuated separately by each bulk PZT actuator in a peristaltic motion. 

Figure 4.3. Schematic diagram and sectional views of the autoclave of the pressure-jump apparatus of Knoche and Wiese (1974) 1, conductivity cells 2, potentiometer 3, 40-kHz generator for Wheatstone bridge 4, tunable capacitors 5, piezoelectric capacitor 6, thermistor 7, 10-turn helipot for tuning bridge 8, experimental chamber 9, pressure pump 10, rupture diaphragm 11, vacuum pump 12, pressure inlet 13, heat exchanger 14, bayonet socket. [From Knoche and Wiese (1974), with permission.]...

Pulsed-Valve Cl and CID-Exneriments. Chemical Ionization (Cl), self-CI (SCI), and direct or desorption Cl (DCI) experiments in FTMS can be done equally well with the differentially-pumped external ion source described below, or with a pulsed-valve single cell arrangement (5,6). In our experiments, we admit a pulse of reagent gas via a piezoelectric pulsed valve with a minimum opening time of about 2.5 ms (7). Unlike solenoid pulsed valves, the performance of piezoelectric pulsed valves is not disturbed by the strong magnetic field of 4.7 Tesla. 

Piezoelectric pulsed-valve inlet systems are equally useful in collision-induced dissociation (CID) experiments (8) where the CID target gas (usually Argon) is pulsed, and subsequently pumped away to permit high-resolution, high-accuracy acquisition of FTMS spectra. 

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. 

A piezoelectric pump is constructed with two glass plates and a silicon wafer [22]. A pressure chamber and a raised flat surface suspended with a thin diaphragm are formed on the upper glass plate (Fig. 3). The piezoelectric actuator is placed on the raised flat surface. In order to guide the flow of the pumped liquid, two check valves made of poly-silicon are fabricated on the silicon wafer... 

Kar, S., McWhorter, S., Ford, S.M., Soper, S.A., Piezoelectric mechanical pump with nanoliter per minute pulse-free flow delivery for pressure pumping in microchannels. Analyst 1998, 123, 1435-1441. 

Fig. 7.18. Low-pressure interfaces to detectors based on flow injection. (A) Interface to a photometric detector across a membrane. (Reproduced with permission of the American Chemical Society.) (B) Interface to a flow-through photometric sensor with prior derivatization by the modified Griess reaction. (Reproduced with permission of the American Chemical Society.) (C) Interface to a piezoelectric detector. P peristaltic pump, C collector, CUC clean-up column, DB debubbler, SA sulfamic acid, NEDD /V-( 1-naphthyl)ethylenediamine dihydrochloride, SV switching valve, W waste, DF displacement flask, IV injection valve, FC-PZ flow-cell-piezoelectric crystal, OC oscillator circuitry, F frequency counter, PC personal computer. (Reproduced with permission of Elsevier.)...

An additional advantage of the integrated circuit technology is the ability to integrate the various components, such as the transducer, reactor, valve, pump etc., within the electronic system, forming refined flow-analysis systems on silicon wafers. Several approaches, such as electrostatic, electromagnetic, piezoelectric, thermopneumatic and thermoelectric can be employed for force transduction in the microvalves, these are also applicable to micropumps. Based on these approaches, two versions of micropumps have been developed. These are connected in parallel the first pump (dual pump) is activated with periodic two-phase voltage, while the second pump (the buffer pump) is driven by two piezoelectric actuators. Microsensors of two kinds are described below a thermopile based- and a thermistor based microbiosensor. 

FIGURE 6.5 Schematic representation of the operation of a piezoelectric pump. 

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