Tallinn University of Technology

6 October 2025 at 11:00 AM
Anar Abdullayev, "Research and Implementation of Electrical Bioimpedance Measurement Solutions"

Supervisor: Senior researcher Dr. Olev Märtens, Thomas Johann Seebeck Department of Electronics Tallinn University of Technology Tallinn, Estonia 

Co-supervisor: Senior researcher Dr. Margus Metshein, Thomas Johann Seebeck Department of Electronics Tallinn University of Technology Tallinn, Estonia

Opponents: 

  • Prof. Dr.-Ing. Olfa Kanoun, Faculty of Electrical Engineering and Information Technology Chemnitz University of Technology Chemnitz, Germany 
  • Prof., Dr.-Ing., Dr. rer. medic. Daniel Teichmann, The Maersk Mc-Kinney Moller Institute University of Southern Denmark Odense, Denmark

Electrical impedance is the opposition that a material or tissue presents when an alternating current flows through it. Since its introduction in the 19th century, this property has become an important tool for characterizing both technical systems and biological tissues. In medicine, bioimpedance measurement has gained special attention because it offers a non-invasive, safe, and low-cost way to monitor vital physiological processes. Applications include estimating body composition, assessing blood flow and respiration, monitoring cardiac function, and even producing medical images of the lungs and other organs using electrical impedance tomography.
Despite this potential, most commercial devices for bioimpedance measurement are expensive and optimized for very specific applications. Researchers and clinicians are often unable to modify the hardware or access low-level signals to test new algorithms. This lack of flexibility limits innovation and makes it difficult to adapt bioimpedance techniques for new medical needs.
This thesis addresses the limitations of current bioimpedance technology by developing a fully custom, open, and portable measurement platform. Three generations of devices were created, each one more advanced than the last. The first prototype laid the groundwork by showing that highly accurate impedance measurements could be achieved. The second device introduced safer connectors, battery power, and the ability to record heart activity (electrocardiography) and blood flow at the skin surface (photoplethysmography) alongside impedance. These combined signals allow, for example, cuffless estimation of blood pressure and improved detection of cardiac and respiratory events. The third and most advanced device added support for electrical impedance tomography, which makes it possible to create two-dimensional biomedical images. This device also features wireless communication, programmable amplifiers for greater accuracy, and flexible measurement modes, making it a powerful tool for both research and healthcare applications.
The work also goes beyond hardware design by introducing two key innovations. The first is a new way of generating the electrical signals used for measurement. This method, based on pulse-width modulation, produces a clean and stable signal while keeping the design simple and energy-efficient. The second innovation is a low-power circuit that can automatically detect important points in the heart’s impedance signal. These points are critical for calculating values such as the amount of blood pumped by the heart in each beat. By detecting them directly in hardware, the system avoids heavy digital processing and saves energy, which is vital for wearable devices.
For the first time using in-house equipment, electrical impedance tomography images of the lungs were successfully produced under ethical approval, showing the promise of this system for continuous bedside monitoring. The results of this research have already been shared widely through scientific publications and patent applications, helping to advance the field of non-invasive medical technology.
In summary, this thesis delivers a complete set of tools, from hardware platforms to signal processing methods, that advance the field of bioimpedance measurement. By making the system portable, low-cost, and reconfigurable, it provides a foundation for new biomedical applications, including improved cardiac monitoring, lung imaging, and wearable health technologies.

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