Complex impedance method

The test method is a procedure for estimating in place the density and water content of soils and soil aggregates on the basis of electrical measurements, using a Complex-Impedance Measuring Instrument. 

The electrical properties of a soil are measured using a radiofrequency voltage applied to soil electrical probes driven into the soils and soil aggregates to be tested, in a prescribed pattern and depth. Certain algorithms of these properties are related to wet density and water content. This correlation between electrical measurements and density and water content is accomplished using a calibration methodology. In the calibration methodology, density and 

Although this test method causes minimal disturbance, it may not be applicable to all types of soil. 

More information regarding the test is given in ASTM D 7698 (2011). 

AASHTO. 1993. Guide for design of pavement structures. Washington, DC American Association of State Highway and Transportation Officials. 

---

The ionic conductivity of a solvent is of critical importance in its selection for an electrochemical application. There are a variety of DC and AC methods available for the measurement of ionic conductivity. In the case of ionic liquids, however, the vast majority of data in the literature have been collected by one of two AC techniques the impedance bridge method or the complex impedance method [40]. Both of these methods employ simple two-electrode cells to measure the impedance of the ionic liquid (Z). This impedance arises from resistive (R) and capacitive contributions (C), and can be described by Equation (3.6-1) ... 

So far, the ionic conductivity of most ILs has been measured by the complex impedance method [116], In this method, charge transfer between carrier ions and electrode is not necessary. Therefore platinum and stainless steel are frequently used as blocking electrodes. However, it is often difficult to distinguish the resistance and dielectric properties from Nyquist plots obtained by the impedance measurement. In order to clarify this, additional measurements using non-blocking electrodes or DC polarization measurement are needed. 

The Rb based on the sample cannot be calculated correctly, since the electric charge transfer resistance and the electric double layer in an electrode interface are also detected as a resistance, even if bias voltage is impressed to the measurement cell in order to measure the ionic conductivity. For the ionic conductivity measurement, a dc four-probe method, or the complex-impedance method, is used to separate sample bulk and electrode interface [4]. In particular, the complex-impedance method has the advantage that it can be performed with both nonblocking electrodes (the same element for carrier ion and metal M) and blocking electrodes (usually platinum and stainless steel were used where charge cannot be transferred between the electrode and carrier ions). The two-probe cell, where the sample is sandwiched between two pohshed and washed parallel flat electrodes, is used in the ionic conductivity measurement by complex-impedance method as shown in Figure 6.1. 

The complex impedance method involves the measurement of the cell impedance at frequencies ranging from a few Hz up to several MHz. The impedance data are collected with standard electrochemical impedance hardware (i.e., potentio-stat/impedance analyzer) and are separated out into the real and imaginary components. These data are then graphed in the form of a Nyquist Plot (imaginary vs. real impedance), and the ionic liquid resistance is taken as the point where the data crosses the real axis at high frequency. 

The measurement of electrical properties as a function of frequency and their analysis by complex impedance methods (impedance spectroscopy) allow a separation of contributions to impedance from grains, grain boundaries and electrode polarisation (Jonscher, 1983 MacDonald, 1987). This technique therefore permits the separation of the electrical... 

Compaction density obtained on site is measured in situ by one of the following methods the sand-cone method, the rubber balloon method, nuclear methods or the drive-cylinder method. The complex impedance method may also be used. 

ASTM D 7698-lla. 2011. Standard test method for in-place estimation of density and water content of soil and aggregate by correlation with complex impedance method. West Conshohocken, PA ASTM International. 

Conductivity Measurements. Ion conductivity measurements were carried out by the complex impedance method. The sample was in the form of cold pressed pellets (8 mm dia. and 4-5 mm thick). The pellets were made at room temperature in an evacuable die at 10 tons/sq.in. and the blocking electrodes (Pt paint, Engelhard No. 6042) applied on both faces of the pellets. The pellets were sandwiched between two platinum plates which were spring loaded to ensure good electrode/electrolyte contact. The entire cell was controlled with a Barber-Coleman Controller (Model 520) and a Hewlett-Packard HP-55950 IB programmer. The temperature was measured using an HP-3421 data acquisition unit with internal calibration. Impedance measurements were performed in the frequency region 5Hz to 10 MHz... 

The conductivities of the two components of a composite structure can also, in principle, be analyzed by the complex impedance method. Ceramic samples often show two semicircles, one due to a bulk phase and another due to a less conductive grain boundary phase — the two components are effectively in series." In a semicrystalline polymer, however, the grain boundary phase is the more conductive, so that the continuous (parallel) conduction path is more important. The analysis is more complex in this case, but it has been shown that partial crystallinity leads to depressed and skewed semicircles compared with the impedance diagram of corresponding amorphous material." ... 

---