Piezoelectric detector

Scheide EP, Guilbault GG. 1972. Piezoelectric detectors for organophosphorus compounds and pesticides. Anal Chem 44(11) 1764-1768. 

In order to gain a direct experimental approach to probe the internal conversion of P, LIOAS was further developed to afford time-resolved measurements. For this purpose / -polyvinylidene difluoride foil was introduced [81] as a broad-frequency band piezoelectric detector—instead of the previously used ceramic transducers—which permitted for the first time the... 

Piezoelectric detectors are one of the most promising solutions to this problem. They can be installed at various locations on the aircraft body where they can constantly monitor the integrity of the materials of which the body is made. If cracks begin to develop at any location on the body, they can be detected because they result in the formation of small-scale shock waves as air passes over the aircraft body. These shock waves cause minute distortions of the aircraft s surface. While these distortions are too small to he noticed by most ordinary procedures, they are large enough to create electrical signals in nearby piezoelectric devices that can he picked up and analyzed by processing units attached to them. 

The fluid oscillations can be detected by shuttle balls, ultrasonic and piezoelectric detectors. In noisy installations, dual piezoelectric elements provide noise compensation. The various detectors can measure one of the following (1) the oscillating flow across the face of the bluff body, (2) the oscillating pressure difference across the sides of the bluff body, (3) the flow through a passage drilled through the bluff body, (4) the oscillating flow or pressure at the rear of the bluff body, or (5) the presence of free vortices downstream to the bluff body. 

Photoacoustic spectroscopy A spectroscopic technique based on the photoacoustic effect. A photoacoustic spectrum consists of a plot of the intensity of the acoustic signal detected by a microphone or a piezoelectric detector, against the excita-... 

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.)...

Immunoassays using piezoelectric detectors coated with antigen or antibody had been devised as early as 1972 (Shons et al., 1972). The mass increase resulting from the immunological complex formation leads to a measurable change of the resonance frequency of the piezoelectric crystal. Effects of temperature and electronic noise can be eliminated by using a pair of crystals. Such sensors are only applicable in the dry state. 

The displacement of the heavy ligand by the lighter molecule HCN yields an increase in the sensitivity, a concept identified as "mass amplification", and was not applied to piezoelectric detectors before. As mass is lost from the coated crystal when exposed to HCN, the frequency increases whereas a decrease in frequency is expected if moisture is absorbed by the coating. The effect of humidity was studied over the range of 40-92% RH, and it was shown that humidity plays a part in the reacation. Since the reaction is irreversible and the nickel complex is prone to hydrolysis, the coated crystal could be used once only. Substitution of other ligands in nickel complexes, including dibenzoylmethane, dipivaloyl-methane, formate and acetate, did not improve the selectivity towards HCN. 

The slight mass increase caused by the absorption of mercury on a gold-plated piezoelectric crystal can be measured as a change in the resonant frequency of the crystal. A piezoelectric detector for mercury in air was described by Scheide and Taylor (1974). Another detector was constructed by Ho and Guilbault (1981), who used it for determination of mercury in water after CV generation. A detection limit of about 1 ng per sample can be deduced, which might also be applied on biological samples. 

The pressure geireration (fcscribed by Eqs. (27) and (28) in solution is finally to be detected by a piezoelectric transducer. Since the detector is not din tly introduced into solution in our expmments [18, 24], the sound wave must be conducted by difierent connecting materials to the piezoelectric detector and thus passes throuj various phase boundaries. The acoustic transition coefficient represents a measure for the crossing of the acoustic wave at these boundary surfaces [%, 97]. For the crossover of the sound wave from medium 1 into medium 2 we have ... 

Fig. 3. Coordination system for cydin-drical piezoelectric detectors...

Since 1975 [63, 115], PZT transducers have often been used for the detection of photoacoustic signals from solutions. Many different piezoelectric detectors have been developed for these experiments [67, 70, 116-121]. Piezoelectric ceramics in tubular form are frequently used. Then the detectors serve simultaneouly as a container for the sample solution. Despite many proposals for the constructicm of a piezoelectric detector, it is necessary to (fcwlop a sf al cell and detector unit to perform photoae>ustk experiments on highly radic ti cotrc ive dilutions. The following requirements had to be taken into special consideration in the d gn ... 

An advantage of polymers is that they have low e and Y values as well as high polarizability. Thus, polymers can provide sensitive piezoelectric detectors with large areas. 

A New Blood Alcohol Breath Analyzer with Piezoelectric Detector. II. Effect of Composition on n-Octa-decanol Solvolysis of Zinc Stearate by Gas Chromatography Univ. Microfilms Int., Order No. 77-17,392, 221 pp. Diss. Abstr. Int. 38B(2) 629 (1977) CA 87 162299c... 

The sensitivity of piezoelectric detectors is directly proportional to the square of resonant frequency, and inversely proportional to the surface area. Therefore, a SAW device is considered to be an excellent transducer of chemical vapor sensor. Besides sensitivity, the SAW device could be made at relatively low cost, and miniaturized with precise and reproducible characteristics using photolithographic techniques. In addition, the lithographic fabrication capability easily permits a complex circuit to be present on the same crystal surface. 

Fig. 4.21 Cell housing. A, mercury head B, powder bed C. hole in powder bed D, O—ring seal E, vacuum port F, vacuum and vent port G, piezoelectric detector.

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