Surface impedance

Staunton S. 1990. A comparison of the surface impedance factors of Ca, Na, Rb and Cs derived from their self-diffusion coefficients in various soils. Journal of Soil Science 41 643-653. 

Figure 5.1 Schematic representation of an electrochemical cell (a) three electrodes (b) equivalent circuit for three-electrode cell (c) equivalent circuit for the working-electrode interphase (d) a solution impedance in series with two parallel surface impedances.

Chemical Microsensors Based on Surface Impedance Changes... 

Sensing chemical species is a much more difficult task than the measurement of mechanical variables such as pressure, temperature, and flow, because in addition to requirements of accuracy, stability, and sensitivity, there is the requirement of specificity. In the search for chemically-specific interactions that an serve as the basis for a chemical sensor, investigators should be aware of a variety of possible sensor structures and transduction principles. This paper adresses one such structure, the charge-flow transistor, and its associated transductive principle, measurement of electrical surface impedance. The basic device and measurement are explained, and are then illustrated with data from moisture sensors based on thin films of hydrated aluminum oxide. Application of the technique to other sensing problems is discussed. 

BSA Selective binding to anti-BSA antibody in electropolymerised polypyrrole film on SPCE surface Impedance... 

The stressed or pulled specimen bonded with photopolymerized adhesive failed as shown in Fig. 3.14 within the bonded area as expected, because porcine skin breaks at a tensile strength several times greater than the adhesive. The thickness and placement of adhesive is importantbecause a barrier between the injured tissue surfaces impedes the healing process. The adhesive is most preferably placed in a very thin layer on matting tissue surfaces and more substantively on exterior surfaces around the bond. 

In case of vacuum (e = e0) the impedance is real and its absolute value is 377 fl (wave impedance of vacuum). In case of a metal an incident wave decays rapidly from the surface, thus the impedance of a metal is called surface impedance Zs = Rs + iXs. The real part of Zs is called surface resistance Rs, the imaginary part surface reactance Xs. 

For a normal metal at microwave frequencies the imaginary part of the conductivity can be neglected and the real part is equal to the dc conductivity a do In this case a simple expression for the surface impedance follows from Maxwell s equations and Ohm s law ... 

Surface impedance of high-temperature superconductor films... 

For bulk dielectrics, a dielectric resonator can be formed by a cylindrically shaped piece of dielectric material. Dielectric thin films are more difficult to investigate, in particular when the loss tangent is very small. Planar resonator techniques as well as specially designed dielectric resonators can be used to examine their properties. For high-temperature superconductors both dielectric resonators and planar resonators represent an ideal tool to examine their surface impedance values. 

Non resonant techniques are only of limited use to determine microwave losses with high precision, in particular when the losses are very small. Flowever, for the investigation of nonlinear absorption phenomena (i.e. rf power dependent on surface impedance or loss tangent) by intermodulation distortion measurements broad-band test devices are more common. Typically, a planar transmission line with an impedance of 50 Ohms can be employed for intermodulation... 

With thermal surface impedance testing, heat is injected into the test objects surface from a hot gas pulse. The resulting surface temperature transient is analyzed to determine the bond quality in nearly real time. The surface temperature transients are sensed using an innovative noncontacting, emissivity-independent infrared sensor.27 This method is not adversely affected by surface blemishes or roughness. 

Hensen, S., Muller, G., Rieck, C. T., and Schamberg, K. (1997). In-plane surface impedance of epitaxial YBa2Cus07 a films Comparison of experimental data taken at 87 GHz with d- and s-wave models of superconductivity. Phys. Rev. B, 56 6237. 

The formation of a rare earth metal oxide on the metal surface, impedes the cathodic reduction of oxygen and thus cathodic inhibition is achieved by the addition of a rare earth metal salt to a system. The surface atom concentration ratio, [Ce/Ce + M], where M is Fe, Al or Zn, is a function of cerium oxide film thickness determined by AES depth profiles as shown in Fig. 12.2. 

The experimental situation is inconclusive and sometimes even the same experimental techniques used by different groups give contrary results. Especially for the compounds k-(ET)2Cu(NCS)2 and K-(ET)2Cu[N(CN)2]Br many different techniques have been employed to measure A(T). Evidence for non BCS-like behavior has been obtained by complex ac susceptibility [220], radio-frequency penetration depth [221], muon spin relaxation (//SR) [222], and microwave surface impedance measurements [223]. In contrast, results consistent with conventional BCS theory, sometimes revealing a tendency towards strong coupling, are reported for measurements of the //SR [224], microwave surface impedance [225, 226], and dc magnetization [227]. 

Yttria thin films can also be deposited on Si substrates from Y(hfac)3 and Y(thd)3 by oxygen plasma-assisted CVD. It is found that with Y(hfac)3 the appropriate thin films were contaminated with fluorine, leading to unexceptional electrical properties. As discussed in Section V.A.4, next to yttrium oxide, SiOi and yttrium silicate are formed on the substrate surface. Pre-nitridation of the silicon surface impedes the reaction with the substrate. 

M. K. Karkkainen, FDTD model of electrically thick frequency-dispersive coatings on metals and semiconductors based on surface impedance boundary conditions, IEEE Trans. Antennas Propag., vol. 53, no. 3, pp. 1174-1186, Mar. 2005. doi 10.1109/TAP.2004.842655... 

In particular, widespread interest has surrounded claims of exceptionally high microwave conductivities in TTF-TCNQ based upon a surface impedance analysis valid for isotropic conductors. We have devoted considerable effort to theoretical and experimental studies of the microwave response of small, strongly anisotropic conductors under skin-depth limited conditions. Our conclusion is that the isotropic analysis does not apply, and that the reported measurements bear no simple relationship to the true microwave conductivity of TTF-TCNQ. 

When the skin depth is much less than the simple thickness, the loss for a small isotropic conductor is proportional to the surface impedance Z =(l/a)ReK, where K = (1 + i)/6, is the wavevector parallel to the surface inside the body. We find that in the anisotropic case the components of Z retain this form, but K is severely modified. For a rectangular parallelopiped of biaxial TTF-TCNQ with dimensions b a c anti e b, we find that the leading Fourier component of the loss... 

The understanding of such a problem is obvious from the example of a metallic plate coated with an homogeneous material receiving a plane wave at normal incidence. The calculation of the reflection coefficient is then simple. The surface impedance is defined by ... 

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