# Low-Cost, Compact, and Rapid Bio-Impedance Spectrometer with Real-Time Bode and Nyquist Plots
## 1 Introduction  
Bioelectrical impedance spectroscopy (BIS) has been currently used in broad fields of studies, such as biophysics, medical physics, agriculture, and other fields of life-sciences. BIS is a non-invasive method for characterizing biological materials based on their electrical properties, which is expressed in terms of complex electrical impedance dispersion curves over a certain frequency range [1, 2]. In here, there are three regions of bioelectrical impedance dispersion, \(\alpha\), \(\beta\), and \(\gamma\). The \(\alpha\)-dispersion (10 Hz to 10 kHz) is related to the phenomena of ionic diffusion of the cell membrane and the counterion effects, the \(\beta\)-dispersion (10 kHz to 100 MHz) is related to the polarization phenomenon of cell membranes, and the \(\gamma\)-dispersion (in GHz order) is related to the polarization of water molecules [3]. Properties of electrical impedance have been reported to understand the nature and behavior of cell [4, 5, 6, 7, 8], bacteria detection and identification [9, 10], identification of beverages and food ingredients [11, 12, 13, 14, 15, 16], and so on. In the medical field, BIS is used to characterizations of serum and blood [17, 18, 19], identification of body composition and disease [20, 21, 22], and to assist the process of diagnosis and functional electrical stimulation of the body [23, 24, 25]. Research on BIS, as mentioned, mostly covers \(\alpha\) and \(\beta\) dispersion, and is carried out using a frequency of 10 Hz to 1 MHz. In principle, identification of the electrical impedance of biological tissue performed by injecting alternating current, \(\mathbf{I}\), into the sample through a pair of current electrodes, and measuring the voltage, \(\mathbf{V}\), which arises through a pair of voltage electrodes. Then, the impedance, \(\mathbf{Z}\), is calculated by using formula \(\mathbf{Z}=\mathbf{V}\mathbf{I}\). It should be noted that \(\mathbf{V},\mathbf{I}\), and \(\mathbf{Z}\) is complex variables, therefore a BIS instrumentation system must not only be able to measure the magnitudes of current and voltage, but must also be able to measure their phase difference. Therefore, a BIS instrumentation system is at least having three functional units. First is an AC current source, which must be stable within working frequency range; second is a data acquisition system to record voltage, current, and their phase difference; and third is software for computing and displaying the impedance dispersion curves, which is commonly in the Bode plot or Nyquist plot. Furthermore, in an effort to provide a BIS instrumentation system in good performance, some researchers have offered the new design. Starting from precision AC current sources [26], the high accuracy data acquisition system [27; 28], even the whole system device [29; 30; 31; 32; 33]. Commonly, the offered BIS instrumentation system is arranged in modular and work separately. It has weaknesses in compactness and synchronization of the hardware system. Besides that, most of the offered BIS instrumentation cannot perform automatically frequency scans. The measurement process is carried out manually starting from the lowest to the highest frequency, then the measurement results are plotted using MS-Excel or others data processing software by entering the recorded measuring data. These methods will require a long time, so it is inefficient to produce an impedance dispersion curve. In this research, we propose a low-cost, rapid, and compact BIS instrumentation system with Bode and Nyquist plot in real-time. There are several new things we offer:  
* The system contains three main modules in an integrated (compact) ones, so synchronization among modules can be maintained/controlled by PC, and it can work automatically. * The system uses programmable AC current source, so that the value of the current to be injected into biological samples can be selected/regulated through software via PC.