微电子与微传感器
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10.1 Introduction 10.2 Acoustic wave propagation 10.3 Acoustic wave propagation representation 10.4 Introductiowenku.baidu.com to acoustics 10.5 Acoustic wave propagation
Acoustics is the study of sound or the time-varying deformations, or vibrations, in a gas, liquid, or solid. Some nonconducting crystalline materials become electrically polarised when they are strained. A basic explanation is that the atoms in the crystal lattice are displaced when it is placed under an external load. This microscopic displacement produces electrical dipoles within the crystal and, in some materials, these dipole moments combine to give an average macroscopic moment or electrical polarisation. This phenomenon is approximately linear and is known as the direct piezoelectric (PE) effect (Auld 1973a). The direct PE effect is always accompanied by the inverse PE effect in which the same material will become strained when it is placed in an external electric field.
Figure 10.1 Particle displacement profiles for(a)longitudinal ,and (b ,c)shear uniform plane waves . Particle propagation is in the ydirection
The most general type of acoustic wave is the plane wave that propagates in an infinite homogeneous medium. As briefly summarised at the end of Chapter 9 for those readers omitting that chapter, there are two types of plane waves, longitudinal and shear waves, depending on the polarisation and direction of propagation of the vibrating atoms within the medium. Figure 10.1 shows the particle displacement profiles for these two types of plane waves 1. For longitudinal waves, the particles vibrate in the propagation direction (ydirection in Figure 10.1 (a)), whereas for shear waves, they vibrate in a plane normal to the direction of propagation, that is, the x- and zdirections as seen in Figure 10.1(b) and (c).
Shear, also known as "bump wave," is the particle vibration direction perpendicular to the direction of wave propagation. Transverse wave is characterized by particle vibration direction and the direction of wave propagation perpendicular to each other. In the transverse section of the projections is the peak, concave part called a trough. Wavelength generally refers to the distance between two adjacent peaks or troughs between.
10.4.1 Particle Displacement and Strain
10.4.2 Stress
10.4.3 The Piezoelectric Effect
In a solid, an acoustic wave is the result of a deformation of the material. The deformation occurs when atoms within the material move from their equilibrium positions, resulting in internal restoring forces that return the material back to equilibrium. If we assume that the deformation is timevariant, then these restoring forces together with the inertia of the particles result in the net effect of propagating wave motion, where each atom oscillates about its equilibrium point. Generally, the material is described as being elastic and the associated waves are called elastic or acoustic waves.
Vibration wave is spread, spread by the media. In the same kind of uniform medium, the propagation of vibration is uniform motion, this motion, with velocity V characterization. For uniform motion, constant velocity V (same size, same orientation), so the velocity V is a constant amount. Media molecule and not with the wave propagation and migration, irregular movement of molecules unceasing media is thermal motion, the average speed is zero. Vibration wave is spread, spread by the media. Shear, also known as "bump wave", transverse particle vibration direction perpendicular to the direction of propagation. Pwave vibration direction parallel to the propagation direction of wave particle.
A basic understanding of the generation and propagation of acoustic waves(sound)in PE media is needed to understand the theory of surface acoustic wave(SAW)sensors . Unfortunately , most textbooks on acoustic wave propagation contain advanced mathematics and that makes it harder to comprehend . Therefore , in this chapter , we set out the basic underlying principles that describe the general problem of acoustic wave propagation in solids and derive the basic equations required to describe the propagation of SAWs.
Before a more detailed analysis of the propagation of uniform plane waves in piezoelectric materials in the following sections , a pictorial representation of the concept of shear wave propagation is presented. Figure 10.2 illustrates shear wave propagation in an arbitrary cubic crystal medium . An acoustic wave can be described in terms of both its propagation and polarisation directions . With reference to the X,Y,Z(x , y , z)coordinate system, propagating SAWs are associated with a corresponding polarisation , as illustrated in the figure.
P wave vibration direction parallel to the propagation direction of wave particle. In the longitudinal wave wavelength is the distance between the close parts or rough parts adjacent.
When boundary restrictions are placed on the propagation medium, it is no longer an infinite medium, and the nature of the waves changes. Different types of acoustic waves may be supported within a bounded medium, as the equations given below demonstrate. Surface Acoustic Waves (SAWs) are of great interest here; in these waves, the traveling wave is guided along the surface with its amplitude decaying exponentially away from the surface into the medium. Surface waves were introduced in the last chapter and include the Love wave mode, which is important for one class of IDT microsensor.
Acoustics is the study of sound or the time-varying deformations, or vibrations, in a gas, liquid, or solid. Some nonconducting crystalline materials become electrically polarised when they are strained. A basic explanation is that the atoms in the crystal lattice are displaced when it is placed under an external load. This microscopic displacement produces electrical dipoles within the crystal and, in some materials, these dipole moments combine to give an average macroscopic moment or electrical polarisation. This phenomenon is approximately linear and is known as the direct piezoelectric (PE) effect (Auld 1973a). The direct PE effect is always accompanied by the inverse PE effect in which the same material will become strained when it is placed in an external electric field.
Figure 10.1 Particle displacement profiles for(a)longitudinal ,and (b ,c)shear uniform plane waves . Particle propagation is in the ydirection
The most general type of acoustic wave is the plane wave that propagates in an infinite homogeneous medium. As briefly summarised at the end of Chapter 9 for those readers omitting that chapter, there are two types of plane waves, longitudinal and shear waves, depending on the polarisation and direction of propagation of the vibrating atoms within the medium. Figure 10.1 shows the particle displacement profiles for these two types of plane waves 1. For longitudinal waves, the particles vibrate in the propagation direction (ydirection in Figure 10.1 (a)), whereas for shear waves, they vibrate in a plane normal to the direction of propagation, that is, the x- and zdirections as seen in Figure 10.1(b) and (c).
Shear, also known as "bump wave," is the particle vibration direction perpendicular to the direction of wave propagation. Transverse wave is characterized by particle vibration direction and the direction of wave propagation perpendicular to each other. In the transverse section of the projections is the peak, concave part called a trough. Wavelength generally refers to the distance between two adjacent peaks or troughs between.
10.4.1 Particle Displacement and Strain
10.4.2 Stress
10.4.3 The Piezoelectric Effect
In a solid, an acoustic wave is the result of a deformation of the material. The deformation occurs when atoms within the material move from their equilibrium positions, resulting in internal restoring forces that return the material back to equilibrium. If we assume that the deformation is timevariant, then these restoring forces together with the inertia of the particles result in the net effect of propagating wave motion, where each atom oscillates about its equilibrium point. Generally, the material is described as being elastic and the associated waves are called elastic or acoustic waves.
Vibration wave is spread, spread by the media. In the same kind of uniform medium, the propagation of vibration is uniform motion, this motion, with velocity V characterization. For uniform motion, constant velocity V (same size, same orientation), so the velocity V is a constant amount. Media molecule and not with the wave propagation and migration, irregular movement of molecules unceasing media is thermal motion, the average speed is zero. Vibration wave is spread, spread by the media. Shear, also known as "bump wave", transverse particle vibration direction perpendicular to the direction of propagation. Pwave vibration direction parallel to the propagation direction of wave particle.
A basic understanding of the generation and propagation of acoustic waves(sound)in PE media is needed to understand the theory of surface acoustic wave(SAW)sensors . Unfortunately , most textbooks on acoustic wave propagation contain advanced mathematics and that makes it harder to comprehend . Therefore , in this chapter , we set out the basic underlying principles that describe the general problem of acoustic wave propagation in solids and derive the basic equations required to describe the propagation of SAWs.
Before a more detailed analysis of the propagation of uniform plane waves in piezoelectric materials in the following sections , a pictorial representation of the concept of shear wave propagation is presented. Figure 10.2 illustrates shear wave propagation in an arbitrary cubic crystal medium . An acoustic wave can be described in terms of both its propagation and polarisation directions . With reference to the X,Y,Z(x , y , z)coordinate system, propagating SAWs are associated with a corresponding polarisation , as illustrated in the figure.
P wave vibration direction parallel to the propagation direction of wave particle. In the longitudinal wave wavelength is the distance between the close parts or rough parts adjacent.
When boundary restrictions are placed on the propagation medium, it is no longer an infinite medium, and the nature of the waves changes. Different types of acoustic waves may be supported within a bounded medium, as the equations given below demonstrate. Surface Acoustic Waves (SAWs) are of great interest here; in these waves, the traveling wave is guided along the surface with its amplitude decaying exponentially away from the surface into the medium. Surface waves were introduced in the last chapter and include the Love wave mode, which is important for one class of IDT microsensor.