Principles and Applications of Ubiquitous Sensing

Chapter 8Medical Sensing

Prince Hamlet's disdainful yet candid admission that man is endowed with infinite faculties is not merely a poetic hyperbole. When regarded as a measurand, the human body is a remarkable signal generator. The brain, the heart, the eyes, the lungs, the digestive system, the muscles, and different types of tissues in the body generate electrical and electromagnetic signals having various magnitudes and frequencies. These signals may give unique insights into the physical, emotional, cognitive, and psychological conditions of a person. Providing an exhaustive account of these signals is not the purpose of this chapter. Instead, it introduces the most important signals (action potentials) and how they are generated, measured, and processed. Readers interested in gaining more comprehensive insights into biomedical signals and sensors are referred to the following excellent books: (Hall 2015; Kandel et al. 2000; Levick 2013; Webster 2009).

The most important signals that can be measured from the human body are action potentials, which are generated by excitable cells. The media through which the action potentials propagate consist of extracellular fluid, blood, connective tissue, muscle, tendon, and bones containing different ions. Generally, the body can be regarded as an electrolyte solution and interfacing the sensing system with the human body using appropriate electrodes (Figure 8.1) enables the electrodes to chemically interact with the cations and anions ...