Basically, an impedance analyzer is an electronic test equipment that measures complex electrical impedance as a function of the test frequency. It is used to evaluate a component’s ability to handle a given frequency range.
High resolution electrical impedance spectroscopy
Among the most popular methods used to characterize particles, cells, and tissue is electrical impedance. It is a powerful technique and has many applications. Electrical impedance spectroscopy can be used to analyze the state of charge and health of batteries, determine corrosion of metals, and determine the quality of foods.
Electrical impedance spectroscopy can also be used to study coated metal surfaces. In addition, it can be used to analyze human body composition and bacterial concentrations.
Typically, impedance measurements are conducted in lower frequencies than visible light. However, this limitation is not a limiting factor for most applications. Moreover, impedance characterization can be conducted in open environments. It is also possible to use miniaturized electrodes to integrate into most experimental setups.
For spatial resolution, scanning probe techniques can be used. These methods use small electrodes to map the impedance above the surface of samples in a conductive liquid. However, the resolution of these techniques is dependent on the conductivity of the liquid, the distance between the electrode and sample, and the dimensions of the electrode.
Bioelectrical impedance equation for wrist-wearable device
Using bioelectrical impedance analysis (BIA), the electrical properties of biological tissues can be determined. These properties are derived from the extracellular fluid (ECF) surrounding the tissues. The electrical properties of the tissues vary, with different tissues having different capacitances and resistivities.
Bioimpedance measurement is commonly used to assess body composition, especially fat, but it can also be used to measure cardiac output. BIA uses weak electric currents to measure impedance of tissue. The real part of the measurement is resistance, while the imaginary part is called reactance.
In order to measure the electrical properties of biological tissues, alternating current with multiple frequencies is used. The most widely used model is the Cole-Cole model, which includes an additional parameter (a) to account for nonideal capacitive behavior of cell membranes.
The Fricke and Morse model is another example. It consists of a resistor in parallel with a capacitor. A small amount of resistance is present on the cell membrane, and this resistance is attributed to capacitance.
Contact resistance compensation circuit
During the measurement of wide-band impedance of electrical equipment, there are many problems that can affect the measurement results. The first one is contact resistance. Contact resistance consists of two parts, namely, surface resistance and shrinkage resistance. These two parts can vary with temperature and skin moisture. In addition, there are some non-standard characteristics of compensation terminals that have an effect on measurements. In this paper, we propose a novel compensation method that can ensure accurate measurements. It is based on a 4-point coordinate conversion, which improves measurement accuracy.
In this method, the measured value of the resistance is converted to the real value of the resistance. This method can be used to calculate the impedance of the DUT. In addition, it can be applied to different types of DUTs. It has been experimentally validated and the simulation also validates the proposed method.
In this method, the electrodes of the device are relatively small, compared with the traditional devices. In addition, the contact resistance is reduced through the use of high-precision reference resistors. This increases the accuracy of the compensation results.
