Piezoelectric transducer, sample

Photomultiplier lubes (PMTs), 194 Photon, 132, 144 counting, 195, 202, 313,491,957 emission, 148-149 Photons, in photoelectric effect, 146 Photoresist, 184,683, 733 Photosedimentalion, 958-961 Photosedimentation analyzers, 958 Phoioiransduccr, 5,9,81,411 Phototubes, 66,67, 144,191-194 Photovoltaic cell, 192-193 pi. See Isoelectric point Piezoelectric transducer, sample, 618... 

In its most common mode of operation, STM employs a piezoelectric transducer to scan the tip across the sample (Figure 2a). A feedback loop operates on the scanner to maintain a constant separation between the tip and the sample. Monitoring the position of the scanner provides a precise measurement of the tip s position in three dimensions. The precision of the piezoelectric scanning elements, together with the exponential dependence of A upon c/means that STM is able to provide images of individual atoms. 

In piezoreflectance (PzR), modulation is achieved by mounting the sample on a piezoelectric transducer that varies the lattice constant of the material, producing a band gap modulation. Although PzR is contacdess it requires special mounting of the sample, as does thermomodulation. 

Fig. 3. Schematic beam path of a phase-measurement interference microscope (PMIM, Fizeau optics). The beam partially reflected at the reference plane and at the sample surface interfere with each other while the reference plane is moved by the piezoelectric transducer for automatic phase determination. A reflectivity of at least 1% is required for the sample surface...

In situations where absorption of the incident radiation by the transducing gas is troublesome a piezoelectric transducer (made from barium titanate, for example) can be attached to the sample (or sample cuvette in the case of liquids) to detect the thermal wave generated in the sample by the modulated light (8,9). The low frequency, critically damped thermal wave bends the sample and transducer thus producing the piezoelectric response. The piezoelectric transducer will also respond to a sound wave in the solid or liquid but only efficiently at a resonant frequency of the transducer typically of the order of 10 to 100 KHz (see Figure 4). Thus neither in the case of microphonic nor piezoelectric detection is the PA effect strictly an acoustic phenomenon but rather a thermal diffusion phenomenon, and the term "photoacoustic" is a now well established misnomer. 

Figure 4. Photoacoustic signal measured in a sample liquid with an attached piezoelectric transducer having a resonant frequency of several tens of thousands of kilohertz. Note the change in scale of the amplitude and thus the much greater sensitivity of the detector at low light chopping frequencies. Argon ion laser light source, 400 mW, x = 488 nm sample 25 pg/mL BaSO powder suspended in aqueous glycerine. Reproduced with permission from Ref. 21 copyright 1980, American Chemical Society.

Sonication using ultrasonic cleaner baths remains a popular extraction approach particularly for controlled-release products. In sonication, an ultrasonic wave of 20-40 kHz generated by a piezoelectric transducer is used to produce the formation and collapse of thousands of microscopic bubbles (cavitations) in the water bath to facilitate the break up of the solid particles and the subsequent dissolution of the API. Note that parameters such as the wattage power of the sonicator, presence of the perforated tray, depth of the water level, bath temperature and the number of sample flasks sonicated might all affect the extraction rate. For... 

Fig. 13.2. Addition of piezoelectric transducers to an atomic force microscope for acoustically excited probe microscopy. The forces acting between the tip and the sample are measured by the vertical and lateral deflections of the cantilever...

When the experimentalist set an ambitious objective to evaluate micromechanical properties quantitatively, he will predictably encounter a few fundamental problems. At first, the continuum description which is usually used in contact mechanics might be not applicable for contact areas as small as 1 -10 nm [116,117]. Secondly, since most of the polymers demonstrate a combination of elastic and viscous behaviour, an appropriate model is required to derive the contact area and the stress field upon indentation a viscoelastic and adhesive sample [116,120]. In this case, the duration of the contact and the scanning rate are not unimportant parameters. Moreover, bending of the cantilever results in a complicated motion of the tip including compression, shear and friction effects [131,132]. Third, plastic or inelastic deformation has to be taken into account in data interpretation. Concerning experimental conditions, the most important is to perform a set of calibrations procedures which includes the (x,y,z) calibration of the piezoelectric transducers, the determination of the spring constants of the cantilever, and the evaluation of the tip shape. The experimentalist has to eliminate surface contamination s and be certain about the chemical composition of the tip and the sample. 

Ultrasonic nebulizers are unique in that a piezoelectric transducer, powered at frequencies of 200 kHz to 10 MHz, is used to generate aerosol from sample that... 

Fig. 2 Schematic representation of the basic detection elements of the scanning force microscope and of the piezoelectric transducers generating the displacement modulations for purposes of dynamic mechanical measurements. The dynamic components of the tip-sample forces resulting from the normal/lateral displacement modulations are detected via the torsion/bending of the microscopic cantilever and the deflection of the laser beam reflected off the rear side of the cantilever. The positional shift of the latter is registered by means of a segmented photo-diode...

The tip is scanned across the sample surface using a piezoelectric transducer in one of two modes, topographic mode or current mode. In the topographic mode a con-... 

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...

Not only PAHs, pesticides and PCBs, but also other pollutants have been isolated with excellent results by USAL. One case in point is the leaching of total organic pollutants from particulate samples [145] by using a direct ultrasonic leacher, where the transducer was bonded directly to the bottom of the sample vessel (see Fig. 2.6A). The ultrasonic piezoelectric transducer was used at two different power settings (25 and 50 W). The transducer was tightly attached to the glass sample vessel and a condenser... 

Piezoelectric transducers can be of the high contact, two- or one- point contact types. The contact force between the sample and the transducer has been found to affect resonance spectra. Thus, resonant peaks increase with decreasing contact force also, the resonant frequency is dependent on the contact force [8]. Electrical and mechanical cross-talk between... 

It should be noted that many of the former studies on US-based detection were carried out by using piezoelectric transducers in contact with the sample [18,19]. Some, however, used non-contact electromagnetic transducers [20] and eddy current testing [21]. The greatest restrictions of the latter are that they require an electrically conductive sample and highly precise positioning of the transducer near the sample. 

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