Physics
Sound Sensor
A sound sensor is a device that detects sound waves and converts them into electrical signals. It typically consists of a microphone or transducer that captures the sound and a circuit that processes the signal. Sound sensors are used in various applications, such as noise monitoring, audio recording, and in automated systems for detecting sound-based events.
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7 Key excerpts on "Sound Sensor"
eBook - PDF- Wolfgang Göpel, Joachim Hesse, J. N. Zemel, Wolfgang Göpel, Joachim Hesse, J. N. Zemel(Authors)
- 2008(Publication Date)
- Wiley-VCH(Publisher)
Before concentrating on the sensor itself, we should remind ourselves of the definition of sound first: sound is an alteration in pressure, stress, particle displacement, or particle velocity which is propagated in an elastic medium [l]. The frequency range of sound is extremly wide, since it covers 12 orders of magnitude from a few hertz (iqlrasound) up to the terahertzrange (hypersound). Further, sound propagates in completely different media, namely solids, fluids, or gases. Depending on the above conditions, the transducing mechanisms and sensor designs used are different, and the enormous variety of Sound Sensors resulting therefrom exceeds the scope of this chapter. We have therefore concentrated on Sound Sensors which are commer- cially the most important. Such Sound Sensors are utilized for the detection of airborne sound in the audiofrequency range. Sound Sensors according to these specifications are called micro- phones. In Section 16.2, we review the fundamentals of sound as far as is necessary for an under- standing of Sound Sensors. The characteristic parameters and specifications of the sound sen- sors themselves are reported in Section 16.3. In nearly all types of microphones, there is a membrane of some sort which responds to the pressure or the particle velocity of an impinging sound wave. The motion of this mem- brane is converted into alternating electromotive forces or electric currents by a linear transducing mechanism. The mechanical behavior of membranes, the various operating prin- ciples, and the structures of the devices resulting therefrom are described in Section 16.4. Each subsection starts with a review of the classical designs, followed by a description of interesting and significant innovations during the last decade. These new designs are based on micromechanical, optical waveguide, and polymer transducers. Especially for these new types of microphones, the term acoustic sensor is now frequently used.
eBook - ePub- Paul P.L. Regtien, Edwin Dertien(Authors)
- 2018(Publication Date)
- Elsevier(Publisher)
Unlike light (electromagnetic waves) that can propagate in a vacuum, sound waves need an elastic medium to travel. The most common waves are longitudinal waves and shear waves. In longitudinal waves the particle motion is in the same direction as the propagation; in shear waves the motion is perpendicular to the propagation direction. Some sensors utilize surface acoustic waves (SAWs). An absorbing substance is deposited on the surface of a device on which the waves are travelling: The SAW's velocity is influenced by the concentration of the absorbed matter. Such SAW devices are suitable for chemical sensing. The selectivity is greatly determined by the chemical interface.In this chapter we only discuss acoustic sensors for the measurement of mechanical quantities in mechatronics, where the propagation medium is generally air. Since the quality of an acoustic measurement strongly depends on the acoustic properties of the medium, we present here an overview of the major acoustic characteristics of air. But first we give some definitions of terms commonly in use in acoustics.9.1.1 Sound intensity and pressure
Any piece of vibrating material radiates acoustic energy. The rate at which this energy is radiating is called the acoustical or sound power (W). Sound intensity is the rate of energy flow through a unit surface area; hence intensity is expressed as W/m2 (compare the optical quantity flux ). A sound wave is characterized by two parameters: the sound pressure (a scalar, the local pressure changes with respect to ambient) and the particle velocity (a vector). The intensity is the time-averaged product of these two parameters. It may vary from zero (when the two signals are 90 degrees out of phase) to a maximum (at in-phase signals). The relation between intensity and pressure in the free field (no reflections) is simply given by the equationI =(9.2)p 2ρ v(9.2)where p is the pressure (in root-mean-square or RMS value), ρ the density, and v the speed of sound. This equation is only valid in a free field.Often sound power, pressure, and intensity are expressed in dB, which means relative to a reference value. Common reference values are: P ref =1 pW, I ref =1 pW/m2 , and p ref
- R M MARSTON(Author)
- 2000(Publication Date)
- Newnes(Publisher)
The modern electronics design engineer has ready access to a con-siderable armoury of useful sensors and transducers that enable him to interface his circuits with the outside world. This chapter gives a concise run -down on some of the best known and most useful of these devices. Before looking at these, however, it is necessary to first define a ‘sensor’and a ‘transducer’. A sensor is, in the context of this volume, defined as any device that directly converts some physical quantity (such as heat, light, pres-sure, etc.) into a proportional electrical quantity. A transducer , on the other hand, is defined as any device that directly converts one physical quantity into another physical quantity; thus, any device that (for example) converts electrical current into mechanical move-ment (such as a relay or electric motor) is a transducer. From the above definition it is obvious that although all sensors are transducers, it is not true that all transducers are sensors. Consequently, to tie the two groups of devices together in a logical way, this chapter is split into sections that first categorise the devices by function (electroacoustic, optoelectronic, thermoelectric, or piezoelectric), and then describe the individual sensors and trans-ducers that come under that heading. One major category of trans-ducer, the electromechanical type, has already been described in Chapter 2, and at this point it is worth noting that there is often con-siderable flexibility in the use of generic titles when describing transducers; an electric bell, for example, is undoubtedly an electro-mechanical device, but is most noted for its noise-making qualities and is thus best described as an electroacoustic device. Electroacoustic devices An electroacoustic device is one that converts electrical or electro-mechanical power into acoustic energy, or vice versa .
eBook - PDF- Owen Bishop(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
11 Sensors and transducers Although the words 'sensor' and 'transducer' are often used as if they have the same meaning, their purpose is entirely different. A sensor is a device intended for detecting or measuring a physical quantity such as light, sound, pressure, temperature or magnetic field strength. It has an electrical output (often a varying potential or a current) which varies according to variations in the quantity it is detecting. A transducer is simply a device for converting one form of energy into another form of energy. Some sensors are also transducers. For example, a crystal microphone (p. 107) converts the energy of sound waves into electrical potentials. It con-veniently converts the sound energy into a form that can be handled by an electronic circuit. But some other sensors are not transducers. For example, a platinum resistance thermometer detects change in temperature as a change in the electrical resistance of its sensing element. Resistance is not a form of energy. Conversely, there are many transducers that are not sensors; examples include electric lamps (convert electrical energy to light energy), electric motors (convert electrical energy to motion), cells (convert chemical energy to electri-cal energy). Descriptions of transducers begin on p. 115. Light sensors and transducers are dealt with separately in Chapter 12. Temperature sensors The resistance of metallic conductors increases with increasing temperature. If we measure the resistance of a length of wire, of known length, diameter and composition, we can determine its temperature. A platinum resistance thermo-meter consists of a coil of platinum wire wound on a ceramic former. One of its advantages is that it can be used over a very wide range of temperatures, from -100°C to several hundred degrees Celsius. Unfortunately, the resistance of platinum, like that of all metals is very low, so that a long wire is needed for the coil, which is bulky.
eBook - PDFPassive and Discrete Circuits
Newnes Electronics Circuits Pocket Book, Volume 2
- R M MARSTON(Author)
- 2016(Publication Date)
- Newnes(Publisher)
3 Modem sensors & transducers The modern electronics design engineer has ready access to a consid-erable armoury of useful sensors and transducers that enable him to interface his circuits with the outside world. This chapter gives a concise run-down on some of the best known and most useful of these devices. Before looking at these, however, it is necessary to first define both a 'sensor' and a 'transducer'. A sensor is, in the context of this volume, defined as any device that directly converts some physical quantity (such as heat, light, pressure) into a proportional electrical quantity. A transducer, on the other hand, is defined as any device that directly converts one physical quantity into another physical quantity; thus, any device that (for example) converts electrical current into mechanical movement (such as a relay or electric motor) is a transducer. From the above definition it is obvious that although all sensors are transducers, it is not true that all transducers are sensors. Consequently, to tie the two groups of devices together in a logical way, this chapter is split into sections that first categorise the devices by function (electroacoustic, optoelectronic, thermoelectric, or piezoelectric), and then describe the individual sensors and transducers that come under that heading. One major category of transducer, the electromechanical type, has already been described in Chapter 2, and at this point it is worth noting that there is often considerable flexibility in the use of generic titles when describing transducers; an electric bell, for exam-ple, is undoubtedly an electromechanical device, but is most noted for its noise-making qualities and is thus best described as an electroacoustic device. Electroacoustic devices An electroacoustic device is one that converts electrical or electrome-chanical power into acoustic energy, or vice versa.
- Patrick F. Dunn(Author)
- 2011(Publication Date)
- CRC Press(Publisher)
2 Sensors in Engineering and Science CONTENTS 2.1 Chapter Overview ......................................................... 23 2.2 Physical Principles of Sensors ............................................. 23 2.3 Electric .................................................................... 24 2.3.1 Resistive ........................................................... 26 2.3.2 Capacitive ......................................................... 35 2.3.3 Inductive .......................................................... 39 2.4 Piezoelectric ............................................................... 41 2.5 Fluid Mechanic ............................................................ 45 2.6 Optic ...................................................................... 48 2.7 Photoelastic ............................................................... 63 2.8 Thermoelectric ............................................................ 65 2.9 Electrochemical ........................................................... 66 2.10 Problems .................................................................. 69 2.1 Chapter Overview Sensors can be understood best by examining the basic physical principles upon which they are designed. In this chapter, some sensors involved in the measurement of length, relative displacement, force, pressure, acceleration, sound pressure, velocity, volumetric and mass flow rates, temperature, heat flux, relative humidity, circular frequency, particle diameter, void fraction, density, density gradient, gas concentration, and pH are presented. The fun-damental equations that relate what is sensed to its measurable output are given for each sensor described. 2.2 Physical Principles of Sensors The first step in choosing a sensor is to gain a thorough understanding of the basic physical principle behind its design and operation. The principles of sensors [1] do not change. However, their designs change almost daily.
eBook - PDFThe Haskell School of Music
From Signals to Symphonies
- Paul Hudak, Donya Quick(Authors)
- 2018(Publication Date)
- Cambridge University Press(Publisher)
Sound above our hearing range (i.e., vibration that is too quick to induce any nerve impulses) is called ultrasonic sound, and sound below our hearing range is said to be infrasonic. 262 18.1 The Nature of Sound 263 –1 –0.5 0 0.5 1 0 0.002 0.004 0.006 0.008 0.01 Amplitude Time (seconds) Sine Wave at 1,000 Hz Signal Figure 18.1 A sine wave. Staying within the analog world, sound can also be turned into an electrical signal using a microphone (or “mic” for short). Several common kinds of microphones are: 1. Carbon microphone, based on the resistance of a pocket of carbon particles that are compressed and relaxed by sound waves hitting a diaphram 2. Condenser microphone, based on the capacitance between two diaphrams, one being vibrated by the sound 3. Dynamic microphone, based on the inductance of a coil of wire suspended in a magnetic field (the inverse of a speaker) 4. Piezoelectric microphone, based on the property of certain crystals to induce current when they are bent Perhaps the most common and natural way to represent a wave diagram- matically, either a sound wave or electrical wave, longitudinal or transverse, is as a graph of its amplitude versus time. For example, Figure 18.1 shows a sinusoidal wave of 1,000 cycles per second with an amplitude that varies between +1 and −1. A sinusoidal wave follows precisely the definition of the mathematical sine function, but also relates strongly, as we shall soon see, to the vibration of sound produced by most musical instruments. In the remainder of this text, we will refer to a sinusoidal wave simply as a sine wave. Acoustics is the study of the properties, in particular the propagation and reflection, of sound. Psychoacoustics is the study of the mind’s interpretation of sound, which is not always as tidy as the physical properties that are
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