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## Introduction

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Sensors, Actuators, and Their Interfaces: A multidisciplinary introduction — Recommend this title to your library

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The senses: the five senses-vision, hearing, smell, taste, and touch-are universally recognized as the means by which humans and most animals perceive their universe. They do so through optical sensing (vision), acoustic sensing (hearing), chemical sensing (smell and taste), and mechanical (or tactile) sensing (touch). But humans, animals, and even lower-level organisms rely on many other sensors as well as on actuators. Most organisms can sense heat and estimate temperature, can sense pain, and can locate a sensation on and in the body. Any stimulus on the body can be precisely located. Touching of a single hair on the body of an animal is immediately located exactly through the kinesthetic sense. If an organ is affected, the brain knows exactly where it occurred. Some animals such as bats can echolocate using ultrasound, while others, including humans, make use of binaural hearing to locate sounds. Still others, such as sharks and fish (as well as rays and the platypus), sense variations in electric fields for location and hunting. Birds and some other animals can detect magnetic fields and use these for orientation and navigation. Organisms can sense pressure and have a mechanism for balance (the inner ear in humans). Pressure is one of the main mechanisms fish use to detect motion and prey in the water, and vibration sensing is critical to a spider's ability to hunt. Bees use polarized light to orient themselves, as do some species of fish. And these represent only a small selection of the sensing mechanisms used by organisms. Sensing of course is not limited to higher organisms. It exists in all organisms down to the cell level. Some of these can be observed directly such as some that are associated with plants including sensitivity to light, heat, and moisture. Plants have exquisite chemical sensing mechanisms that allow them to detect and often to protect themselves from pests or the effects of cold weather. Even lower on the dimensional scale, some microbes can detect electric and magnetic fields and use these to their advantage. The range of sensing mechanisms and the range of their sensitivities are truly vast. The eye of a hawk, the hearing of a fox, the olfactory sense of a hyena, or the capability of a shark to detect blood in the water has always fascinated us. But, what about the ability of a moth to detect pheromones released by another moth at large distances or the homing of a bat on a single insect without being able to see it? Organisms also have a variety of actuators to interact with their environment. In humans, the hand is an exquisite mechanical actuator capable of a surprising range of motion, but it is also a tactile sensor. The feet, as well as many muscles, allow interaction with the environment. But, here as well there are other mechanisms that can be used to affect actuation. A human can use its mouth to blow away dust or sooth a burn and can close and open its eyelids, a cat can unsheathe its claws, and a chameleon can move each eye independently and shoot its tongue to catch a fly. Other actuators allow for voice communication (vocal chords in humans) or the stunning of prey (ultrasound in dolphins, electrical shock in eels), direct mechanical impact used by some species of shrimp, and many other specialized functions. Some actuation, such as the movement of a sunflower to track the sun or the twisting and turning of an oat seed to insert itself into the soil are more subtle but nevertheless equally important. With respect to the sensory and actuation diversity in organisms, we are still very far behind and our mimicking of natural sensors and actuators is still in its infancy. It has taken the better part of 40 years to develop a working artificial heart, whereas seemingly simple organs, such as the esophagus, do not yet have an artificial implementation. Where are we in comparison with the nose of a dog?

Chapter Contents:

• 1.1 Introduction
• 1.2 A short historical note
• 1.3 Definitions
• 1.4 Classification of sensors and actuators
• 1.5 General requirements for interfacing
• 1.6 Units
• 1.6.1 Base SI units
• 1.6.2 Derived units
• 1.6.3 Supplementary units
• 1.6.4 Customary units
• 1.6.5 Prefixes
• 1.6.6 Other units and measures
• 1.6.6.1 Units of information
• 1.6.6.2 The decibel (dB) and its use
• 1.6.7 Convention for use of units
• 1.7 Problems
• Reference

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