Simple-Z: A Low-Cost Portable Impedance Analyzer

The use of electrical impedance spectroscopy in point-of-care systems or for online monitoring has been hampered by the high cost of typical benchtop impedance analyzers. In this article, we introduce a portable, low-cost impedance analyzer, referred to as "Simple-Z," which contains a signal processing unit that allows for a precise generation and reading of the excitation and response signals. Simple-Z is based on the integrated circuit AD5933 in conjunction with peripheral circuits for a fine output amplitude regulation, flexible response amplification, sampling rate control, automatic calibration, and external communication. Software solutions were implemented, including the strategical register overflow to allow decreasing frequency sweeps, the control of the number of acquisition cycles to reduce the spectral leakage of the discrete Fourier transform (DFT), and the iterative approximation for defining proper response amplification and calibration resistances. The software also included a graphical user interface (GUI) with entries, buttons, and graphs that allow for an intuitive usage of the device. Results generated with Simple-Z in equivalent circuits mimicking sensing systems and in aqueous solution of different Na2SO4 concentrations were essentially identical to those obtained with a commercial benchtop impedance analyzer. Since the cost of the circuitry and components to fabricate an instrument is near U.S. $100 and because Simple-Z was designed to allow for easy upscale to mass production, one may expect it to be deployed in pointof-care diagnosis systems. Furthermore, it can also be used in teaching laboratories for training students in electrical impedance spectroscopy.