信号与系统

One-dimensional signals are single-variable functions, such as air pressure variations in human speech over time. Multi-dimensional signals depend on two or more variables, like monochromatic images that measure light intensity based on horizontal and vertical positioning. Both types convey information about phenomena of interest in engineering applications.

Systems are collections of devices that operate on input signals to produce output signals. A resistor-capacitor network exemplifies this: source voltage serves as input and capacitor voltage as output. The human body demonstrates complex signal processing, where heat exposure triggers nerve signals sent to the central nervous system, which then produces multiple output signals instructing muscles to respond.

A resistor-capacitor network is a single-input, single-output system with one source voltage input and one capacitor voltage output. The human body exemplifies a multi-input, multi-output system: heat exposure at a fingertip generates input signals that the central nervous system processes, producing multiple output signals to various arm muscles. Systems vary widely across electrical, mechanical, computer, and biological domains.

Mathematical modeling of signals and systems facilitates the development of systems to execute specific operations. Models relate input signals to output signals, enabling engineers to analyze and design systems capable of performing desired functions. In electrical systems, signals are currents and voltages; in mechanical systems, they are temperatures, forces, and velocities, allowing systematic engineering across disciplines.

Electrical systems use currents and voltages as signals. Mechanical systems employ temperatures, forces, and velocities. Hydraulic systems use displacements and pressures. These signals represent variables of interest and may carry energy or information. Understanding signal types in each domain is essential for designing systems that process input signals into meaningful output responses.

Basic continuous time signals represent phenomena like atmospheric temperature, humidity, human voice, television images, and animal sounds as time-dependent functions. These signals convey information about physical processes and are fundamental to signal and system analysis. Understanding basic continuous time signals provides the foundation for analyzing more complex signal behaviors and system responses.

The human body responds to stimuli by processing signals through its nervous system. When heat is applied to a fingertip, nerve endings generate input signals transmitted to the central nervous system. This system processes the signals and produces multiple output signals that instruct various arm muscles to retract the finger, demonstrating multi-input, multi-output signal processing.