Open-Source Impedance Analyzer

Abstract

Impedance analysis or impedance spectroscopy is a method or technique in which unknown impedance and its phase is measured over a range of frequencies. Impedance is equivalent to resistance in AC current and it is frequency dependent. Impedance is measured by exciting the material/component with a known frequency and measuring its current response at the output. An impedance analyzer is a device which is used to do impedance spectroscopy. It could measure resistance, capacitance and inductance of components. It could measure impedance of any discrete electrical component or an n-port electrical circuit. It can be used for determination of the electrical properties of the materials, its characterization and for quality assurance of materials. In this project we are using AD5933 chip of Analog Devices to build a impedance analyzer which can measure the complex impedance along with its phase by exciting it with a user settable frequency. It can also perform impedance frequency sweep with a frequency resolution of 0.1Hz. The frequency range of the device is from 1KHz-100kHz and impedance range is from 1kΩ - 1MΩ. The device uses I2C protocol to communicate. We are using Arduino uno as a master to control the slave AD5933. A graphical user interface (GUI) software is also build in python using tkinter module to make it easy for the user to operate the device. The software also calculates the equivalent circuit from the complex impedance and phase data measured with the device. As an application of the impedance analyzer, we are measuring the complex impedance of the piezo-electric material and determining its equivalent circuit to characterize it. To measure it we developed a test fixture for it which holds the piezoelectric material in place and can also resonate at its fundamental frequency. The test fixture includes PCB with tracks of 50Ω impedance, since most signal sources have a 50Ω internal resistance; so that we can connect it with BNC connectors that have also 50Ω impedance so there is no power or energy loss at certain frequencies. The software is made compatible with windows and Linux or Raspberry pi. The software made open source so that other people could benefit from it or make improvements in the software.