Q-factor is Not Q-value. in Q-factor, the Q is for Quality.

Q-factor is a dimensionless factor for showing the degree of reasonace of a coil or an Oscillator.

Higer value means a better coil. The definition is the resonance frequency over the Full Width Half Maximum (FWHM).

Q = f/\Delta f

High value means:

  1. high sensitivity
  2. noise reduction due to narrow band of absorption.
  3. over damped with long decay time.
  4. higher energy stored
  5. lower energy loss

For complex electric circuit, the Q factor is:

Q = | im Z/ re Z|

It seem that there is a conflict between impedance matching.