Chapter 5
Acoustics in Biology and Medicine
Everything I say is sound.
—wcp
Summary Sounds originate from vibrational waves traveling in a material. Animals take advantage of sounds to get and send notice of opportunities and impending
dangers. Within the science of acoustics, we have applied mechanical principles
to study how life forms detect and generate sounds, how these sounds carry
information and energy, and how life utilizes sound, including for communication.
Covered are acoustical analysis, biogeneration, biodetection, music and acoustical
dosimetry.
5.1 The Nature of Sound Waves
The term sound was first used to refer to the physiological sensation accompanying
hearing. Recognizing the origin of this sensation, we now use the term to mean any
coherent vibration propagating in materials. Coherent here refers to a group-like
behavior of numerous elements in a system. In contrast, incoherent microscopic
vibrations occur in all ordinary materials above absolute zero in temperature.
The statistical fluctuations in these incoherent motions produce thermal noise, an
important consideration both in the design of transistors and in the design of your
ear. Acoustics is the study of sound.
Consider a small segment of material of fixed mass δm at the position x in
the material, with adjacent segments in front and back along the x-axis exerting
opposing pressure-forces on the selected segment. Differences between these
pressure-forces account for the acceleration of the segment mass. Suppose, in
response to these variations in the pressure forces, the left surface of the segment
is displaced an amount ξ(x), while the right surface is displaced ξ(x + δx). These
displacements may depend both on the position x where the displacement originated
in the material and on the time t when the displacement is observed. To describe the
© Springer Nature Switzerland AG 2020
W. C. Parke, Biophysics, https://doi.org/10.1007/978-3-030-44146-3_5
113
Acoustics in Biology and Medicine
Everything I say is sound.
—wcp
Summary Sounds originate from vibrational waves traveling in a material. Animals take advantage of sounds to get and send notice of opportunities and impending
dangers. Within the science of acoustics, we have applied mechanical principles
to study how life forms detect and generate sounds, how these sounds carry
information and energy, and how life utilizes sound, including for communication.
Covered are acoustical analysis, biogeneration, biodetection, music and acoustical
dosimetry.
5.1 The Nature of Sound Waves
The term sound was first used to refer to the physiological sensation accompanying
hearing. Recognizing the origin of this sensation, we now use the term to mean any
coherent vibration propagating in materials. Coherent here refers to a group-like
behavior of numerous elements in a system. In contrast, incoherent microscopic
vibrations occur in all ordinary materials above absolute zero in temperature.
The statistical fluctuations in these incoherent motions produce thermal noise, an
important consideration both in the design of transistors and in the design of your
ear. Acoustics is the study of sound.
Consider a small segment of material of fixed mass δm at the position x in
the material, with adjacent segments in front and back along the x-axis exerting
opposing pressure-forces on the selected segment. Differences between these
pressure-forces account for the acceleration of the segment mass. Suppose, in
response to these variations in the pressure forces, the left surface of the segment
is displaced an amount ξ(x), while the right surface is displaced ξ(x + δx). These
displacements may depend both on the position x where the displacement originated
in the material and on the time t when the displacement is observed. To describe the
© Springer Nature Switzerland AG 2020
W. C. Parke, Biophysics, https://doi.org/10.1007/978-3-030-44146-3_5
113