Date of Award

2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering

Specialization

Biomedical Engineering

Department

Electrical, Computer, and Biomedical Engineering

First Advisor

Godi Fischer

Abstract

The U.S. has 12.3% disabled people based on the American Community Survey (ACS) in 2012. According to this survey, more than half of the disabled population suffers from ambulatory disabilities. Therefore, a system which enables people with disabilities to control their environments is crucially important. Moreover, ubiquitous physiological monitoring will be a key driving force in the upcoming medical revolution. Cardiac and brain signals in the form of electrocardiograms (ECGs) and electroencephalograms (EEGs) are two critical health indicators that directly benefit from long-term monitoring.

Brain-computer interfaces (BCIs) are systems that detect changes in brain signals related to human intentions, typically translating intention into a control signal to communicate between the brain and the external world such as a computer. The tripolar concentric ring electrode (TCRE) has shown to be sensitive enough to visualize the electrical impulses that correspond to a person’s specific thought pattern. Therefore, this electrode has the potential to enable people who are paralyzed to use their thoughts to control their phone, television or other things in their environment.

The TCRE has been built and was successfully tested. However, at this step of its development, long coaxial cables are required to connect the electrodes to the preamplifier. The preamplifier is a big box with 24 channels (for 24 electrodes), although not all channels are always used. Despite technologically advancements and electronic miniaturization, the use of current EEG monitoring is limited by inconvenience and discomfort. Thus, having an active TCRE EEG electrode that can record the signal, digitize it and send the data to the host computer for further processing is helpful. Such a system not only preserves the advantages of the TCRE electrode, but also takes advantage of today’s advancement in microelectronics. This renders the electrode more comfortable and convenient to be used in real life situations. Therefore, the EEG acquisition board has to be miniaturized so that it fits on the electrode. The small board can also be duplicate many times to meet the needs of a specific EEG recording application.

Our approach to build an active TCRE acquisition system (digital TCRE) involves two steps:

Step 1: create a mathematical model of the electrode, electrolyte, and body may contribute to a better understanding of how biomedical signals are obtained by electrodes. Good design starts with clearly understanding and defining interface requirements and developing accurate equivalent circuit models of all components involved.

In order to understand the behavior of the interface, electrochemical impedance spectroscopy (EIS) has been used to measure the impedance on both a TCRE and standard cup electrode. To perform the experiments, Ten20 is used as an electrode paste. The preliminary results have been published in the proceedings of the Engineering in Medicine and Biology Society (EMBC) in 2016. The title of the paper is “Electrode- Electrolyte Interface Model of Tripolar Concentric Ring Electrode and Electrode Paste”. More experiments were carried out with different pastes to measure the characteristics of the electrodes with various electrolyte materials. These findings have been published in the proceedings of the Engineering in Medicine and Biology Society (EMBC) in 2017. The title of the paper is “Impedance Spectroscopy of Tripolar Concentric Ring

Electrode with Ten20 and TD246 Pastes”. In this paper the impedance characteristics of electrode using Ten20 and TD246 as electrolyte material is shown. Finally, more measurements with two electrode setup and three electrode setup were done using EIS. The findings have been submitted to the Transaction on Biomedical Engineering (TBME). The title of the manuscript is “Electrode-Electrolyte Interface Modeling and Impedance Characterization of Tripolar Concentric Ring Electrode”. This paper introduces a model for a tripolar concentric ring electrode (TCRE) derived from impedance measurements using the Ten20 electrode impedance matching paste. It is shown that the model serves well to predict the performance of the electrode-electrolyte interface for TCREs as well as standard cup electrodes. The paper also presents a comparison between the TCRE and the standard cup electrode regarding their impedance characterization and demonstrates the benefit of using TCREs in biomedical applications. We have also conducted auditory evoked potential experiments using both TCRE and standard cup electrodes.

Step 2: design and fabricate a system level circuit for monitoring the TCRE outputs have started with commercial off-the-shelf components (COTS). Subsequently, we will design and fabricate an application specific circuit (ASIC) that digitizes the EEG signatures at the front-end and sends the acquired data to a host PC.

To accomplish this, a delta sigma based data converter has been designed and fabricated. Preamplifier and the data converter have been mounted on two pcb boards with 15mm diameter. The results are under preparation for submission to a peer reviewed journal. The title of the manuscript is “Digital Tripolar Concentric Ring Electrode for Biopotential Signal Recordings”.

Available for download on Saturday, November 30, 2019

Share

COinS