Sensing electrode capacitance

The use of capacitance measurement is based upon the principle that the concentration changes as particles settle through a suspension and will alter the effective dielectric constant between the sensing electrodes. A complete capacitance transducer consists of capacitance sensing electrodes together with capacitance sensing electronics, which is essentially a capacitance to voltage converter. 

Fig. 10. The proposed structure of the SET-hased readout circuit for THz detector. The quantum detector cell (QDC), which is the triple Q-dot system, is capacitively coupled through the sense electrode to a carbon based nanotubes RF-SET. A bias-electrode is used to control the bias potential on the sense electrode.

To differentiate between the two possible QDC states, i.e. whether QD2 is occupied or not, a reliable value for the capacitive couphng between the quantum dots and the sense electrode is needed. To that end, simulations for the capacitance of the proposed stracture shown in Fig. 10 were performed using the software program FastModel. For simphcity purposes the bias electrode was not included in these simulations because it will have a negligible affect on the results. The relation between the charge and voltage vectors can be written out as a linear set of equations as... 

Fig. 12. A schematic of the proposed read-out circuit for the THz detector showing only the capacitances contacting tiie sense electrode. The capacitance values given were obtained from the simulation study results.

For case (2), when the electron is ejected from the QDC the potential on the sense electrode is 0 V. This yields a AV =1.7 mV between the two cases. At this point, it is possible to determine how much the impedance of the SET will change as a result of a change in the gate voltage of AV =1.7 mV. The capacitance between the CNT-SET and sense electrode has been approximated to be C51 = 40 aF which means the distance between conductance peaks of the SET would be AF = e/Cji = 4mV. Consequently, it is possible to derive the useful approximation,... 

Schematic diagrams of the instrumentation for the ANL capacitive flowmeter are given in Fig. 6.20. A 100-kHz sine-wave oscillator, with stable frequency and amplitude controls, was used to pulse the drive electrode. Each sensing electrode was connected to a current-to-voltage converter preamplifier. The preamplifier outputs were bandpass filtered at 100 kHz 5 Hz and amplitude-demodulated. The demodulated signals were amplified and DC-coupled to a first-order low-pass filter to give density signals.

The cross-correlation technique is used in the ANL capacitive instrument to measure particle velocity. The outputs from the velocity-sensing electrodes were amplitude-modulated capacitor currents. If one assumes that the output capacitance signals vary sinusoidally (Aasincoat), and the applied voltage to the... 

Combinations of detection mechanisms have also been employed in MIP sensors. For example, an electropolymerized film of polyphenol imprinted with phenylalanine was prepared on a gold electrode by Panasyuk et al. [51], who employed surface plasmon resonance and reduction in electrode capacitance to effect recognition sensing. The change in capacitance upon exposure to a mixture of amino acids... 

In all cases a low value of capacitance at the detection node is desirable. This points up the advantages of a CCD with preamplifier electronics integrated on the same chip. Here C2 can be on the order of 0.1-0.2 pF. As will be discussed later, use of a CID tends to lead to more capacitance at the sensing electrode. With more capacitance at the detection node, power dissipation constraints become important for the preamplifier especially if a large number are to be used at cryogenic temperatures (as is often the case with IR imagers). 

Halow and Nicoletti (1992) Capacitance Studies on voidage distribution in the fluidized bed, bed diameter 0.15 m, sensing electrodes installed round the riser in four rings, each containing 32 electrodes... 

The history of the observation of anomalous voltammetry is reviewed and an experimental consensus on the relation between the anomalous behavior and the conditions of measurement (e.g., surface preparation, electrolyte composition) is presented. The behavior is anomalous in the sense that features appear in the voltammetry of well-ordered Pt(lll) surfaces that had never before been observed on any other type of Ft surface, and these features are not easily understood in terms of current theory of electrode processes. A number of possible interpretations for the anomalous features are discussed. A new model for the processes is presented which is based on the observation of long-period icelike structures in the low temperature states of water on metals, including Pt(lll). It is shown that this model can account for the extreme structure sensitivity of the anomalous behavior, and shows that the most probable explanation of the anomalous behavior is based on capacitive processes involving ordered phases in the double-layer, i.e., no new chemistry is required. 

Sodium contamination and drift effects have traditionally been measured using static bias-temperature stress on metal-oxide-silicon (MOS) capacitors (7). This technique depends upon the perfection of the oxidized silicon interface to permit its use as a sensitive detector of charges induced in the silicon surface as a result of the density and distribution of mobile ions in the oxide above it. To measure the sodium ion barrier properties of another insulator by an analogous procedure, oxidized silicon samples would be coated with the film in question, a measured amount of sodium contamination would be placed on the surface, and a top electrode would be affixed to attempt to drift the sodium through the film with an applied dc bias voltage. Resulting inward motion of the sodium would be sensed by shifts in the MOS capacitance-voltage characteristic. 

For the measurement of impedance or capacitance of the MIP material in sensing applications, this material is treated as a capacitor dielectric, which is placed between the electrode and electrolyte pseudo-plates. Any sorption or binding of the analyte disturbs the dielectric characteristics of the interface, which is... 

The effect of too high a scan rate is due to the existence of the interfacial capacitance, whereas the effect of uncompensated ohmic resistance is the result of the solution resistance between the working electrode surface and the point in solution at which the reference electrode senses this potential. These effects are explained in more detail below. 

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