Fundamentals of Acoustics (3rd Ed.)

Abstract

Reviewed by H. Saunders Kensler and Frey have been "household" names in the world of acoustics for the past three decades. Many acousticians and engineers have been weaned and raised on their Fundamentals of Acoustics. The third edition rearranges the contents of the previous editions and puts them in the proper place. This new edition updates some features of acoustics and keeps the more fundamental aspects in its proper perspective. Among the newer phases of acoustics (some mentioned in this book) are noise control, boundary layer acoustics, acoustic emission, and ultrasonics. Understanding the fundamentals propounded in this book will furnish a good foundation in the understanding of the more advanced and newer aspects of acoustics. The book consists of 15 chapters and ten small appendices. Chapter 1 treats the topic of fundamentals of vibrations. This includes the simple oscillator subjected to forced oscillation, transient response, power relationships, mechanical resonance and frequency. It concludes with equivalent electrical circuit for a simple oscillator, transients and Fourier analysis. There is very little change from the previous edition. Chapter 2 considers transverse motion of a vibrating string. This includes transverse waves on a string, one-dimensional wave equation, initial value and boundary conditions applied to wave equation. This continues with forced vibration of a finite and infinite string, normal modes and overtones, and harmonics. Again, this chapter is just a slight rearrangement of the information in the same chapter of the previous edition. Chapter 3 follows the same format of the previous edition and considers vibrations of bars. This encompasses longitudinal vibrations, forced vibration, transverse vibration and transverse wave equation. The clamped and free conditions are applied to the beam equation. Chapter 4 proceeds into the vibration of membranes and plates. The authors examine the wave equation for stretched, rectangular and circular membranes fixed at the rim. The chapter concludes with forced vibration of a membrane and vibrations of thin circular plates. The reviewer feels that the topic of rectangular plate and its associated boundary conditions should have been included. Chapter 5 focuses on the acoustic wave equation. Beginning with equation of state and continuity, this leads into Euler's equation, harmonic plane waves, acoustic intensity, specific acoustic impedance and decibel scales. New additions embrace rays and waves, Snell's law, inhomogeneous wave equation and point source. Again, there is very little change from the previous editions. Chapter 6 examines transmission phenomena. This fundamental chapter treats in a simple manner, transmission from one fluid to another, reflection at the surface of a solid for both normal and oblique incidence. Probing further, we meet absorption and absorption coefficients, molecular thermal relaxation, absorptionphenomena in liquids and attenuation in inhomogeneous fluids. Again, this is a readable chapter. Chapter 8 treats t...

Acoustic streaming in the transducer plane in ultrasonic particle manipulation devices

“…In planar manipulation devices the gradients of the velocity in the z-direction are much greater than in the lateral directions due to the planar geometry 36 , hence the left side of equation (19) can be approximated as Meanwhile, using standard relations between density and pressure in linear acoustics 31 and then exploiting the harmonic nature of the excitation, the right hand side of equation (19) becomes Thus, equation (19) can be written Using this, the product ⁄ can be approximated as where the complex intensity, C x , is given by: 37 Thus the x component of the limiting velocity can be written According to Fahy 37 , the complex intensity (a harmonic representation of the real, instantaneous intensity, which is a function of time) can be decomposed into two parts: (i) the real part, called the active intensity, which gives the time average energy flow; and (ii) the imaginary part (the reactive intensity) which corresponds to local, oscillatory energy flows with zero time average. We see from equation 25 that the limiting velocity is proportional to the active intensity.…”

An ultrasonic pulse-echo technique for monitoring the setting of CaSO4-based bone cement

“…The acoustic impedance, Z ðPa s m À3 ) can be related to an analogue electrical system in a similar way as voltage is related to sound pressure and current is related to particle or volume velocity. The specific acoustic impedance, z; of a material has the unit pressure/particle velocity ðPa sÞ and is very useful in calculations involving transmission and reflection of sound waves [13]. In the rest of this paper the term acoustic impedance is referring to the specific acoustic impedance.…”

Construcción de una cámara anecoica para la caracterización de la pérdida de transmisión sonora

“…donde τ es el coeficiente de transmisiσn sonora, que es propio de cada material o medio de propagación, definido como τ = W t /W i , donde W t y W i son las potencias acústicas transmitida e incidente respectivamente [4,15]. En el montaje propuesto en este trabajo se emplea una cámara anecoica, que se caracteriza por no tener eco y presentar pocas reflexiones en su interior.…”

“…Los sonómetros empleados en este trabajo son integradores, es decir que se pueden ajustar en niveles de ponderación determinados. Dichas curvas de ponderación son redes de filtrado en el aparato que dan a cada frecuencia un "peso" determinado, el cual está relacionado a la sensibilidad del oído humano a dichas frecuencias [3,15].…”