Piezo actuator

The schematic of synthetic jet is shown in Fig. 2. It consists of a cavity open to the flow through a sUt or orifice. The bottom waU of the cavity is driven by a moving surface, which can be either a piston or a vibrating membrane. The vibration of the membrane can be achieved using electrostatic actuation, piezo-ceramic material, and differential thermal expansion of the electrode material with silicon layer underneath. When the membrane or piston moves inward of the cavity, the fluid is pushed out of the cavity, and when the membrane or piston moves back, the fluid is sucked into the cavity. The namre of flow through the slit opening depends on (a) the... 

In the early years of STM instrumentation, tripod piezoelectric scanners were the predominant choice, as shown in Fig. 9.6. The displacements along the X, y, and z directions are actuated by three independent PZT transducers. Each of them is made of a rectangular piece of PZT, metallized on two sides. Those three PZT transducers are often called x piezo, y piezo, and z piezo, respectively. By applying a voltage on the two metallized surfaces of a piezo, for example, the x piezo, the displacement is... 

Fig. 12.3. STM with a double-action lever. Various parts are shown in (a) (A) The macor block onto which the x, y piezo bars (horizontal) and the z piezo bar (vertical) are mounted, (B) the microscope base plate, (C) carriage rod, actuated by a linear feedthrough and a lead screw, (D) stop, (E) ball bushing assembly, (F) lever, (G) sample and sample holder, (H) catch, the pivot point for coarse motion, (I) foot, the pivot point for fine motion, and (J) the probe tip assembly, (b) Shows the STM in coarse motion. Using the catch as the pivot point, the sample can be removed away from the tip. (c) Shows the STM in fine motion. Using the foot as the pivot point, the linear motion of the carriage rod is reduced by a large factor. (After Demuth et al., 1986a.)...

Fig. 12.4. Single-tube STM. The tube piezo scanner is adhered inside a sturdy metal cylinder, which sits on three screws on the base plate. The two front screws make the coarse approaching. The rear screw makes fine approaching by using the two front screws as the pivot axis. The rear screw is actuated by a stepping motor for automatic approaching. The preamplifier (not shown) is mounted directly on top of the metal cylinder to eliminate the microphone effect of the coaxial cable between the tip and the input of the preamplifier. The entire unit is rigid enough that a mediocre vibration isolation device can provide atomic resolution. (After Hansma et al., 1988.)...

Fig. 3 Spotting tools for non-contact printing a Bubble ink-jet A heating coil locally heats the loaded sample, resulting in a changed viscosity and expansion of fluids. The generated droplet can be easily expelled from delivery nozzles, b Microsolenoid A microsolenoid valve, fitted with the ink-jet nozzle is actuated by an electric pulse transiently opening the channel and dispenses a defined volume of the pressurized sample, c Piezo ink-jet A piezoelectric transducer that is fitted around a flexible capillary confers the piezoelectric effect based on deformation of a ceramic crystal by an electric pulse. An electric pulse to the transducer generates a transient pressure wave inside the capillary, resulting in expulsion of a small volume of sample...

Ejection of an aliquot from an open capillary using a pressure pulse generated by a piezo actuator. 

The Bespak Piezo Electric Actuator is a novel aerosol delivery system based on a piezoelectric crystal combined with an electroformed mesh (Fig. 3). It produces droplets of adjustable size from a single metered drop or fluid reservoir. The mesh hole dimension (as small as 3 pm) determines the size of the droplets produced, whereas the size and density of the holes control the rate of fluid delivery. These can be varied according to the formulation. Although solutions are more readily nebulized, suspensions can be aerosolized if the particle size of the suspended particles is two to three times smaller than the mesh size. 

Fig. 3 Schematic diagram of the sprayhead of the Bespak Piezo Electric Actuator. (Reproduced courtesy of Bespak pic, UK.)...

The prime differences among the different AFM modes, such as CM (discussed above) and intermittent CM, as elucidated in the following section, are the feedback parameters and the choice of the cantilever. For intermittent contact (tapping) mode AFM, a stiff cantilever (k typically 10—50 N/m) with a resonance frequency of 100—400 kHz is chosen. The cantilever, which is inserted in an identical manner as for CM into the cantilever holder, is excited to vibrate by an integrated piezo actuator. Instead of deflection (contact force), the amplitude of the forced oscillating lever is detected, analyzed, and utilized in the feedback loop (Fig. 2.20). 

How can the tunneling barrier width and the lateral position of the tip be controlled so accurately Tire tip is mounted on an actuator consisting of piezoelectric ceramics for reliable and exact positioning in all three dimensions (particular for the scanning). Only the nanometer positioning ability of piezo ceramics (see Tutorial 2 on Piezoelectric Tube Scanners and Translational Stages) made SPM techniques initially possible. 

When a new scan size is actuated with a piezo scanner (e.g. 60 pm), the piezo will further stretch (to 61.8 pm) over time. This effect causes an apparent bending of rows at the beginning of an SPM image. Hence, to avoid piezo creep in an image, the measurement should be restarted after the first 20% of the imaged area, when a new scan range has been selected. 

ECDL External Cavity Diode Laser OI Optical Isolator L Lens AOS Acousto-Optic Switch PZT Piezo-Electric actuator Me Cavity mirror APD Avalanche Photodiode PC Pressure Controller P Pump... 

Two key issues in SECM are speed and resolution. These are tied to the nature of the available tips and the techniques used to move them in the vicinity of the sample. One approach to greater speed is the use of multiple tips. There are a number of approaches to the fabrication of an array of tips. A problem with these arrays is alignment of the array with the sample so that all of the tips are at the same or a known distance from the sample. This can be accomplished by having each tip on its own controllable positioning device, such as an array of cantilevers with individual piezoelectric control (32,33). For example, 50 cantilevers with a 200-/xm period (to cover a span of 1 cm) were fabricated with integrated piezo sensors and zinc oxide actuators. Such an array provided 35 A resolution and a 20 kHz bandwidth. A difficulty with such arrays is the complexity of the instrumentation needed to use them. Each sensor in the array essentially needs its own driver and potentiostat. An alternative would be an array of individually addressable tips on a single chip that all move in the x, y, and z directions in unison. This would require some additional means to orient and align the array chip... 

One of the techniques used is piezo-actuated microinjection, whereby a vibrating needle pierces the donor cell and oocyte plasma membrane. This technique was used to directly inject porcine fetal fibroblast donor nuclei into enucleated oocytes. The injection was followed by activation by means of an electric pulse after nuclear transfer by microinjection. 

Chemical sensitivity can be conferred to AFM by coating the tip with covalently linked monolayers which affect the tip-surface interaction the method is called chemical force microscopy [77]. Additional modulation of the piezo actuator operating in z-direction and evaluation of the force signal can be used to measure the adhesion force between a surface and a chemically modified AFM tip [78]. Metal coated AFM tips can be used in a scanning electrochemical microscopy (SECM, see p. 264) mode [79] in studies of crystal dissolution or growth where surface processes are associated with considerable fluxes of species. 

Instrumentation. A cantilever with a sharp tip interacting with the surface under investigation is used. The actual bending of the cantilever is measured with a laser beam deflected from a mirror-like surface spot on the back of the cantilever towards a position-sensitive photodetector. The measured signal is used to control the piezo actuators. A constant force mode in which the cantilever-surface distance is kept at a preset interaction force and a constant height mode of scanning operation are possible. The principle of operation is schematically outlined in Fig. 7.9. 

The relaxational behaviour of polyvinylidene fluoride (PVDF) is of interest. Its p phase exhibits piezo- and pyroelectric properties and so it is used in various devices, such as sensors, transducers or actuators for different applications. Typically such materials are prepared through a technological process involving stretching and... 

FIGURE 49.6 The spot-on-a-chip platform (a) the piezo-actuated microdispenser (b) heated high-density MALDI-target plate, and (c) antomated MALDI-TOF MS. (Reproduced with permission from Ekstrom, S., Ericsson, D., Onnerfjord, R, Bengtsson, M., Nilsson, J., Marko-Varga, G., and LaureU, T., Analytical Chemistry, 73, 214—219, 2001, copyright 2001, American Chemical Society.)... 

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