Lecture Sensors and Measurement Techniques in Biomedicine - Chapter 2: Physical Principles of Sensing

This chapter delves into the fundamental physical principles of sensing, which are crucial for converting various non-electrical stimuli into measurable electrical signals. Understanding these underlying mechanisms is paramount for the design and implementation of effective sensors across diverse applications. The discussion will cover how phenomena like electric charges, electric fields, and electric potentials govern the behavior of materials and how these can be harnessed. Furthermore, the principles of capacitance and magnetism, including Faraday's Law, will be explored to elucidate their roles in detecting physical changes. This foundational knowledge is essential for engineers and researchers developing next-generation sensing technologies.

Students, engineers, and researchers in electrical engineering, sensor technology, physics, and related fields seeking a foundational understanding of physical sensing principles.

This academic content comprehensively explores the physical principles of sensing, detailing how diverse non-electrical effects are transformed into quantifiable electrical signals. It begins by outlining the necessity of conversion steps for various stimuli and introduces fundamental phenomena such as the thermoelectric effect, piezoelectricity, and photo effect as direct generators of electrical signals. A significant portion is dedicated to electric charges, electric fields, and electric potentials, explaining concepts like the triboelectric effect through mechanical charge redistribution and illustrating electric field generation by charged objects. The document then transitions to capacitance, defining it and highlighting its dependence on physical parameters. It thoroughly discusses how varying geometry and the introduction of dielectric materials impact capacitance, explaining molecular polarization. Practical applications are demonstrated through examples like capacitive sensors for measuring distance, force, and specifically, a water level sensor, acknowledging the need for temperature compensation due to the dielectric constant of water. The discussion extends to displacement sensors leveraging capacitance. Finally, the chapter covers magnetism, from its historical discovery to the generation of magnetic fields by magnets and electric currents. It elucidates Faraday's Law, which describes the induced voltage (electromotive force) resulting from changes in magnetic flux, and identifies various factors affecting this induction, including geometric changes and current variance, concluding with a discussion of displacement sensors utilizing magnetic principles. This integrated approach underscores the foundational physics behind modern sensing technologies.