ISO 20998-1:2006 音響法による粒子の測定と特性評価—パート1：超音波減衰分光法の概念と手順 | ページ 5

2.1

absorption

direct reduction of incident ultrasonic energy by means other than scattering

2.2

attenuation

extinction

total reduction of incident ultrasonic energy, including both scattering and absorption.

Note 1 to entry: The recommended measurement unit is the decibel (dB), which is defined as 10 times the common (base 10) logarithm of the ratio of incident intensity to transmitted intensity, or equivalently 20 times the common logarithm of the ratio of incident amplitude to transmitted amplitude. The neper (Np) is a permitted alternative measurement unit based on the natural logarithm, rather than the common logarithm. The conversion factor is 1 Np = 8,686 dB.

2.3

attenuation coefficient

extinction coefficient

attenuation (extinction) per unit length of ultrasonic propagation through a material, measured in units of dB/cm or Np/cm.

Note 1 to entry: Attenuation coefficients are sometimes scaled by frequency, or frequency-squared, to identify the dominant attenuation mechanism. For clarity, in this part of ISO 20998, only the attenuation per unit length (in dB/cm) is considered.

2.4

attenuation spectrum

attenuation coefficient measured as a function of frequency

2.5

bandwidth

range of frequencies contained in an ultrasonic signal, typically measured as the frequency difference between the -3 dB points on a spectrum analyser

2.6

broadband

characterized as having a bandwidth that is equal to at least half of the centre frequency

2.7

digitization

act of generating a digital (quantized) representation of a continuous signal

Note 1 to entry: The number of bits determines the resolution (fidelity), and the sampling rate determines the bandwidth (Nyquist criterion).

2.8

excess attenuation

incremental attenuation caused by the presence of particles in the continuous phase

2.9

Fourier transform

mathematical transform that converts a time-varying signal into its frequency components, which is often implemented in computers as a Fast Fourier Transform (FFT) algorithm

2.10

interference

wave phenomenon of cancellation or enhancement observed when two or more waves overlap

2.11

intrinsic response

frequency-dependent response of the ultrasonic spectrometer itself

Note 1 to entry: This is not to be confused with the intrinsic absorption of the sample component materials.

2.12

path length

distance traversed by the ultrasonic wave between the emitting transducer and the receiver

2.13

pulse

wave of sufficiently short duration to contain broadband Fourier components

2.14

reflection

return of an ultrasonic wave at an interface or surface

2.15

scattering

removal of ultrasonic energy from the incident wave by redirection

2.16

spectrum

frequency components of a signal, typically arranged as magnitude versus frequency

2.17

tone burst

short duration of a few cycles of a sinusoidal wave

Note 1 to entry: Typically, a tone burst consists of 5 to 10 cycles of a sinusoidal wave.

2.18

transducer

device for generating ultrasound from an electrical signal or vice versa

Note 1 to entry: Piezoelectric devices are commonly used for this purpose.

2.19

transmission

passage of ultrasound through a sample

2.20

transmission spectrum

transmission value measured as a function of frequency

2.21

transmission value

amplitude of an ultrasonic signal (or a component thereof) that has been transmitted through a sample, measured in volts or arbitrary units

2.22

ultrasound

high frequency (over 20 kHz) sound waves which propagate through fluids and solids

Note 1 to entry: The range employed in particle characterization is typically 100 kHz to 100 MHz.

2.23

wave

fluctuation, e.g. pressure, shear or thermal, which propagates through a physical medium

2.24

waveform

shape of the wave when seen on an oscilloscope or digitized display

2.25

wavelength

length of a wave, determined by the distance between corresponding points on successive waves