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Appendix A
Decibel scale
The decibel scale allows the large range of values of ultrasound intensities, or signal voltages, to be expressed by a smaller range of numbers, as shown in Table A.1. The decibel scale expresses the ratios of intensities, or voltages, using a logarithmic scale. The decibel scale is used to describe ultrasound attenua- tion and amplifier gain.
Table A.1 Decibel scale applied to intensity and voltage (or echo amplitude)
Intensity ratio (I/I0)
1 000 000 10000 100
10
2
0.5
0.1
0.01 0.0001 0.000001
Decibel (dB)
Amplitude ratio (V/V0)
60 1000 40 100 20 10 10 3
3 1.4 3 0.7 10 0.3 20 0.1 40 0.01 60 0.001
Intensity I (relative to I0) in dB 10 log10 (I/I0). Gain in dB 20 log10(V /V0).