Frequency electric field

Other types of mass spectrometer can use point, array, or both types of ion detection. Ion trap mass spectrometers can detect ions sequentially or simultaneously and in some cases, as with ion cyclotron resonance (ICR), may not use a formal electron multiplier type of ion collector at all the ions can be detected by their different electric field frequencies in flight. 

Let us now turn our attention to the application of the sound wave to a liquid since this is the medium of importance to the practising chemist. The sound wave is usually introduced to the medium by either an ultrasonic bath or an ultrasonic horn (see Chapter 7). In either case, an alternating electrical field (generally in the range 20-50 kHz) produces a mechanical vibration in a transducer, which in turn causes vibration of the probe (or bottom of the bath) at the applied electric field frequency. The horn (or bath bottom) then acts in a similar manner to one prong of a tuning fork. As in the case of air, the molecules of the liquid, under the action of the applied acoustic field, will vibrate about their mean position and an acoustic pressure (P = P sin 2k ft) will be superimposed upon the already ambient pressure (usually hydrostatic, Pjj) present in the liquid. The total pressure, P, in the liquid at any time, t, is given by Eq. 2.4. 

In Table 2, the electrostriction constant is given for various polymer films (Nakamura and Wada, 1971 Kawai (2), 1970). The values by Nakamura and Wada were obtained at the strain frequency f0 —130 Hz and electric field frequency / = 1 MHz. Values by Kawai were measured at /=/0 = 150 Hz. The values are negative because the density decreases during elongation. 

Fig. 26a and b. Influence of the electric field frequency on the electro-optical behaviour of the nematic polymer XII and scheme of mesogenic groups orientation before (A) and after (B) the application of electric field (a) optical transmission as a function of time at different frequencies (U = 30 V T = 75 °C) (b) optical transmission as a function of time upon application of an electric field at U = 85 V (f = 50 Hz) (1) relaxation upon switching the electric field off (2), upon application of an electric field (U = 80 V) of different frequency f = I (3) 5 (4) 7 (5) and 20 kHz (6) during the relaxation process... 

Fig. 29. Tehi of polymer A.4 (Table 9) as a function of electric field frequency (U = 200 V)...

Fig. 30. Regulation of the optical transparency Tr of the films of polymer A.4 (Table 9) via discrete changes of the electric field frequency f, = 400 (1), 200 Hz (2) and f2 = 4 (1 ) and 1 kHz (20. Arrows correspond to switching on the frequency f, and f2...

However, superimposed on this gradual decrease in t] they found a sharp, pronounced minimum in rj at an electric-field frequency of around 200 Hz (again see Fig. 8-9). A similar... 

In an EHD droplet generator, an electric field acts directly oti the surface of an electrically conducting jet after it has been formed and ejected from the nozzle. At proper electric field frequency, it disturbs the jet by inducing compression and expansion of the jet, which will eventually cause the jet to break up into droplets. 

Quasi-static direct methods are both versatile and well suited to investigating fully the piezoelectric response of polymers. Direct methods of this type are especially appropriate for amorphous polymers. TSC measurements (68) are used to measure the remanent polarization imparted to a polymer, and direct strain or charge measurements are used to investigate the piezoelectric coefficients with respect to the electric field, frequency, and stress. 

The dielectric loss constant, e", or its associated tan 5 can be measured by placing the sample between parallel plate capacitors and alternating the electric field. Polar groups on the polymer chain respond to the alternating field. When the average frequency of molecular motion equals the electric field frequency, absorption maxima will occur. 

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