Effect of temperature and frequency

The effects of temperature and frequency on the permittivity and dissipation factor of a high-purity alumina ceramic are shown in Fig. 5.24. The discrepancies between the permittivity levels in Fig. 5.24 and values given elsewhere are probably due to differences in microstructure and measurement technique. Reliable room temperature values for er for single-crystal sapphire at 3.4GHz are 9.39 perpendicular to the c axis and 11.584 parallel to it, which are close to the values measured optically. The average er to be expected for a fully dense ceramic form is therefore 10.12, and values close to this have been determined. Nothwithstanding the uncertainties there is no doubt that the general behavioural pattern indicated by Fig. 5.24 is correct and typical of ceramic dielectrics. 

At high temperatures the isotherms were linear and almost level. Multiple linear regression was used to determine the separate effects of temperature and frequency ... 

The dielectric properties can vary widely between solids and are a function of temperature, frequency of applied field, humidity, crystal structure, and other external factors. Furthermore, the response can be either linear or nonlinear. This chapter examines linear dielectrics from a microscopic point of view as well as the effects of temperature and frequency... 

Resistivity depends oti temperature - for nonmetallic materials it invariably decreases with T. Volume resistivity is markedly more sensitive to temperature than surface resistivity. In any measurement it is important to ensure that temperature is maintained constant during the test. Temperature fluctuations produce changes in measured current and lead to significant errors (Brown 1981 ASTM D257). In the case of power factor or permittivity determinations, the effects of temperature and frequency are interrelated. With nonpolar polymeric materials, the changes in properties with temperature and frequency are small, while with polar materials very large changes may take place. 

The effects of temperature and frequency are given by Figs. 19 and 20. Here, increases in frequency or decreases in temperature give increases in both G and G". This appears to be the classical increase in modulus which occurs as the condition of the sample is moved from the rubbery state to that of the glassy state. 

Cao, M.-S., Song, W.-L., Hou, Z.-L., Wen, B., Yuan, J., 2010. The effects of temperature and frequency on the dielectric properties, electromagnetic interference shielding and microwave-absorption of short carbon fiber/silica composites. Carbon 48, 788—796. 

Makhlouf, K., Jones, J.W. Effect of temperature and frequency on fatigue crack growth in 18 %Cr ferritic stainless steel. Int. J. Fatigue 15, 163-171 (1993)... 

Fig. 12. Effect of temperature and frequency on electric strength of (a) mica-filled phenolic resin (b) glass-silicone Ifiminate (c) polytetrafluoroethylene and (d) polyethylene.

Effects of Temperature and Frequency. According to the theoretical aspects discussed above, a dielectric-loss peak within the range of temperature and frequency in use might adversely Eiffect the performance of a plastic at high voltage stress or in some electronic applications requiring a high impedance (or Q). The a-c electrical properties of plastics may also indirectly assess mechanical properties. 

PTFE is an outstanding insulator over a wide range of temperature and frequency. The volume resistivity (100s value) exceeds lO Gm and it appears that any current measured is a polarisation current rather than a conduction current. The power factor is negligible in the temperature range -60°C to -i-250°C at frequencies up to lO" Flz. The polymer has a low dielectric constant similarly unaffected by frequency. The only effect of temperature is to alter the density which has been found to influence the dielectric constant according to the relationship... 

In Lab 17.1, you learned about the effect of temperature and concentration on reaction rate. Another factor that affects reaction rate is the amount of surface area of the reactants. If a chemical reaction is to take place, the molecules of reactants must collide. Changing the amount of surface area modifies the rate of collision, and, thus, the rate of reaction. If surface area increases, collision frequency increases. If surface area decreases, so does the number of collisions. In this lab, you will examine the effect of surface area on rate of reaction. You will also determine how a combination of factors can affect reaction rate. 

The Kieffer approach uses a harmonic description of the lattice dynamics in which the phonon frequencies are independent of temperature and pressure. A further improvement of the accuracy of the model is achieved by taking the effect of temperature and pressure on the vibrational frequencies explicitly into account. This gives better agreement with experimental heat capacity data that usually are collected at constant pressure [9],... 

These analysers exist in many forms but are essentially relatively small bench instruments, which use small test pieces and can be programmed to measure damping and dynamic moduli as a function of temperature and frequency. Apart from their importance for measuring the dynamic properties where these are relevant to service, they allow the generation of a large quantity of data over ranges of temperature and frequency extremely efficiently. Hence, they can be used effectively to obtain modulus even if the application is not dynamic. Another valuable use is to obtain glass transition temperatures. 

A general model for electronic relaxation of the Gd3+ S = 7/2 ion in various complexes in solution was presented by Rast el al. [86]. Contrary to the usual assumption, the electronic relaxation in their model is not only due to the effects of the transient zero field splitting, but is also strongly influenced by the static crystal field effect which is modulated by the random Brownian rotation of the complex. Experimental peak-to-peak widths of three gadolinium complexes could be well interpreted as a function of temperature and frequency using three static and one transient crystal field parameters. Moreover, their interpretation of experimental data did not require the addition of any field independent contribution to the line width like the spin-rotation mechanism. 

The dielectric constant remains at 2.04 over a wide range of temperature and frequencies (from 100 Hz to 1 GHz). The dissipation factor at low frequencies (from 10 Hz to 10 kHz) decreases with increasing frequency and decreasing temperature. In the range from 10 kHz to 1 MHz, temperature and frequency have little effect while above 1 MHz the dissipation factor increases with the frequency.55... 

Microdielectrometry was introduced as a research method in 1981 14 and became commercially available in 1983 20). The microdielectrometry instrumentation combines the pair of field-effect transistors on the sensor chip (see Sect. 2.2.3) with external electronics to measure the transfer function H(co) of Eq. (2-18). Because the transistors on the sensor chip function as the input amplifier to the meter, cable admittance and shielding problems are greatly reduced. In addition, the use of a charge measurement rather than the admittance measurement allows the measurements to be made at arbitrarily low frequencies. As a matter of practice, reaction rates in cure studies limits the lowest useful frequency to about 0.1 Hz however, pre-cure or post-cure studies can be made to as low as 0.005 Hz. Finally, the differential connection used for the two transistors provides first-order cancellation of the effects of temperature and pressure on the transistor operation. The devices can be used for cure measurements to 300 °C, and at pressures to 200 psi. 

The dielectric behavior of copper-doped and pure KTN crystals were compared over a wide range of temperature and frequency in order to study the effect of such small Cu ion concentrations on the dielectric landscape [179]. The two KTN crystals studied were grown using the top seeded solution growth method [180]. The Ta/Nb ratio in both crystals was estimated by Perry s linear relation [175] linking Tc to the concentration of Nb, T, = 682x + 33.2, and was found to be approximately 62/38 per mole. The first crystal (crystal 1) was... 

Figures 5 and 6 examine the 3M material measurements for consistency of temperature and frequency effects using plot formats...

Solvent reorientation and isomerization of trans-stilbene in alkane solutions has been studied by ps time scale anisotropic absorption and polarization239 Coupling of solute and solvent decreases as the size of the solvent molecules increases. The applicability of currently favoured models for the activated barrier crossing in the photoisomerization of stilbene is discussed, A method for measuring quantum yields in the photoisomerization of trans-stilbene gives high accuracy without use of a chemical actinometer . Evidence has been found for dynamic solvent effects on the photoisomerization of 4,4 -dimethoxystilbene in which the effects of temperature and hydrostatic pressure were made in n-alkane and n-alkyl alcohol. A ps laser time-resolved study fits frequency dependent solvent shifts but gives results inconsistent with the free volume model. Photophysical and theoretical studies of trans and 9-... 

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. 

Mirin is a condiment with almost 40%-50% sugar and is widely used in Japanese cuisine. Dielectric loss factor of mirin is affected by both the dipolar loss component and the ionic conductivity. Ionic conductivity is lower at higher microwave frequencies. The combined effect of temperature, microwave frequency, and sugar content is complex and hard to describe. Nevertheless, the e" increases with frequency and temperature. The penetration depth decreases as the processing temperature increases. The effect of temperature on the is significant at lower processing frequencies at higher frequencies, temperature has only moderate effect on the d. Tanaka et al. (2005) reported similar results for soy sauce. It was noted by Liao et al. (2003) that this trend is distinctive for thick or complex solutions. 

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