Large-Signal Response

Most of the discussion of the transient and frequency-dependent response has been given in terms of the small-signal or linear behavior. This is obviously a significant simplification, which allows, for example, analysis of processes in terms of a perturbation around a well-defined thermodynamic state. However, when larger signals are involved this will not be a good description of the system. This observation is particuiariy important for puise applications of electrochemical devices or in conventionai 

In the last two sections, we have considered in a general way the mechanism of charge storage and the electrical response we might expect for different types of systems. In the next three sections, we will consider the properties of specific materials systems and try to relate those properties to the earlier discussion. 

Electrochemical capacitors, based on high surface-area carbon 

Carbon is available with awide variety of morphologies and physical and chemical properties. The subject is comprehensively reviewed in a recent book by Kinoshita (18). To a large extent, the actual carbon used in commercial electrochemical capacitors has remained proprietary, but most would appear to be carbon blacks (47) and very high-surface-area active carbons. The latter materials are prepared from carbonaceous precursor materials by steam activation. Recent Japanese patents indicate that a carbon obtained by activation of a carbonized phenolic resin is particularly suitable, especially for organic solvent-based systems. This material may have a specific surface area up to 2500 mVg- 

The contribution of surface active groups to the interface capacitance is increased by oxidation, and decreased by a heat treatment in an inert or reducing atmosphere. Kinoshita and Bett (49) have studied the oxidation of carbon black (Vulcan XC72) In chromic acid and found that a reversible peak develops In the cyclic voltammogram at 0.5 - 0.6 volt vs. SHE) with an increasing level of oxidation. This type of reaction is associated with oxidation and reduction of carbonyl/quinone groups. Numerous other studies of the electrochemical activity of species on carbon surfaces have been reported and are collected and summarized by Kinoshita (18). 

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A further approach to separate the reversible and irreversible 90° and non-90° contributions is the investigation of the piezoelectric small and large signal response of the ferroelectric... 

It is really a large-signal response issue. The biggest impact on the undershoot/overshoot observed in this case comes simply from the amount of bulk capacitance (and stored energy) present at the output. Because in the initial instant of sudden application of load, the bulk capacitor (Cqut) alone provides the energy being demanded by the load, until the loop finally kicks in to prop up the falling rail. Note that it takes several cycles for the current to ramp up to the new required level in the inductor. So small inductances tend to help in quick recovery and help achieve a fast loop response (of course provided they don t create full-blown instability in the process). 

The partial derivation or integration with respect to time is a shorthand notation for the convolution with a function that is a power 1-p of the time, as detailed earlier in Section 10.1.4. This model allows one to predict or identify the large signal response of a CPE. 

On-off action provides the highest available gain for large-signal response. So the choice of on-off to operate sequentially with the linear controller is obvious. But the transition from one to another is not obvious. And the boundary between what is considered a small signal and what is considered large, is not at the moment clear. 

Solid-state mass transport and its effect on the electricai response are considered in Section 3.5. Again, the discussion is given in terms of the small-signal response, i.e., the linear behavior of the system, in the final part of this section, consideration is given to some aspects of the large-signal response, which are important for reai applications, and which may be difficult to predict on the basis of linear-response considerations. 

A hidden node that sends a large signal to an output node is more responsible for any error at that node than a hidden node that sends a small signal,... 

In order to assess the dependence of the output signal on changes in the humidity content of the sample gas, an additional series of measurements was carried out. The hotplate temperature was set to 275 °C, and CO measurements were recorded at three different humidity levels (10, 20 and 40% r.h.) The humidifier temperature was set to 23 °C, and the chip temperature was 30 °C. As can be seen in Fig. 5.14, the sensor response increases with increasing humidity. The large sensor response difference between 10% and 20% r.h. shows that this effect is more pronounced at low humid-... 

Figure 1.26 displays the results of the dss coefficient as function of the bias field, the large signal 33 response ( butterfly loop ) as well as constructed x33trev curve of the same pzt... 

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