(d B/d t) Definition: The ratio between the amount of change in amplitude of the magnetic field (dB) and the time it takes to make that change (dt). Because changing magnetic fields can induce electrical fields, this is one area of potential concern for safety limits.
The value of dB/dt is measured in Tesla per second (T/s).

See also Directivity Index, Phon, and Decibel.

(dB) A customary logarithmic measure most commonly used (in various ways) for measuring sound. Decibel is a way to express the ratio of two sound intensities: dB=10log10I1/I2 being I1 the reference. If one sound is 1 bel (10 decibel) 'louder' than another, this means the louder sound is 10 times louder than the fainter one. A difference of 20 decibel corresponds to an increase of 10 x 10 or 100 times in intensity.
The intensity of ultrasound decreases during the propagation and is measured in db/cm.
For sound pressure (the pressure exerted by the sound waves) 0 decibel equals 20 microPascal (μPa), and for ultrasonic power 0 decibel sometimes equals 1 picoWatt.

See also dB/dt, Phon, and Logarithms.

(DI) The directivity index is the value in dB of ten times the common logarithm of the directivity factor. The directivity factor is the ratio of the sound intensity produced by a test transducer on a specific axis to that of a point source that is emitting the same acoustic power. Since the specific axis is usually one of maximum radiation, the directivity index is usually greater than zero.

See also dB/dt.