Page 441 - Electrical Properties of Materials

Detectors for magnetic resonance imaging 423

(a)

E H
ω

(c)

(b)

Pump
Fig. 15.20
(a) A magnetoinductive wave ring
resonator excited by a rotating
GND
magnetic field. (b) Realization by
rectangular loops made resonant by
V B
inserting capacitors: upper ring for
the pump wave, lower ring for the
signal wave. (c) A prototype detector
consisting of 16 elements. From
Signal
R.R.A. Syms et al., Metamaterials 2,
122 (2008).

parametric amplification is a signal wave, a pump wave in synchronism (trav-
elling at the same phase velocity), and an idler wave. In the actual realization
with rectangular loops (Fig. 15.20(b)), there is both an upper ring and a lower
ring, serving the pump wave and the signal wave, respectively. The idler wave is
obtained by circuit means. A photograph of the complete device shows separate
loops for excitation and detection (Fig. 15.20(c)).