A biosignal is any signal in living beings that can be continually measured and monitored. The term biosignal is often used to refer to bioelectrical signals, but it may refer to both electrical and non-electrical signals.
Biosignals provide communication between biosystems and are our primary source of information on their behavior. Interpretation and transformation of signals are major topics of this text. Biosignals, like all signals, must be carried by some form of energy. Biosignals can be measured directly from their biological source, but often external energy is used to measure the interaction between the physiological system and external energy. Measuring a biosignal entails converting it to an electric signal using a device known as a biotransducer. The resultant analog signal is often converted to a digital (discrete-time) signal for processing in a computer.
Biosignals and the systems that produce them have several important properties: they can be stationary or nonstationary, linear or nonlinear, and deterministic or stochastic (i.e., random). Biosignals often contain noise, which is an unwanted signal component.
Biosystems modeling is a powerful analytical tool for investigating living systems. Two very different models have been developed to represent physiological systems: analog models and system models. Each representation has different strengths and weaknesses.
The goal of this book is to present the most important and fundamental of the many powerful signal and systems analysis tools available to biomedical engineers.