Development of a Multifrequency Bioimpedance Measurement Channel Using STM32

Different tissue and bodies present different impedance values depending on several parameters such as health, composition, and structure. Among the equipment used for morphophysiological analysis is electrical impedance tomography (EIT) as a non-invasive, portable, and low-cost technique. Some authors suggest the usage of more than one frequency could provide more information once cells and tissues have capacitive characteristics. Since there is a lack of multifrequency commercial EIT equipment, this paper aims to develop a multifrequency bioimpedance measurement channel using STM32 microcontrollers. The proposed channel should be composed of an excitation system, electrodes responsible for applying and measuring signals, a measurement circuit, and a supervisory module. Hardware and software were developed altogether and according to the necessities that have arisen specific libraries were created. Efficiency validation regarding the developed channel occurred through performance tests. Three proposed tests were developed to assess different parameters: whether a multiplexer or an adder circuit should be used to combine the multiple frequencies, what would be the fastest way for the developed system to operate, and whether the overall functioning of the system was satisfactory. The results show that using an adder circuit instead of a multiplexer one was the best strategy. Furthermore, the proposed bioimpedance measurement channel may be further ameliorated and replicated to build a low-cost modular multifrequency electrical impedance tomography.