Radio frequency (RF) antenna element with a (de) tuning system

Abstract

A radio frequency (RF) antenna element with a (de)tuning system, with the RF antenna element having a resonant electrically conductive loop and a (de)tuning system including a photosensitive switching element to (de)tune the resonant electrically conductive loop. The (de)tuning system comprises an injection optical source optically coupled to the photosensitive switching element.

Claims

1. A radio frequency (RF) antenna element for magnetic resonance imaging (MRI), wherein the RF antenna element comprises a resonant electrically conductive loop and a detuning system comprising a photosensitive switching element configured to detune the resonant electrically conductive loop, wherein the detuning system comprises; an injection optical source optically coupled to the photosensitive switching element; a photodetector in parallel with the photosensitive switching element; and a bias optical source optically coupled to the photodetector, wherein the photodetector is configured to generate a negative bias voltage over the photosensitive switching element in response to incident radiation from the bias optical source.

2. The radio frequency (RF) antenna element of claim 1, further comprising an electrical interface circuit with at least one inductance in series with the photosensitive switching element and a resistor in parallel to the photodetector.

3. The radio frequency (RF) antenna element of claim 1, wherein the photosensitive switching element is formed by back-to-back circuited photodiodes.

4. The radio frequency (RF) antenna element of claim 1, wherein the injection optical source and the bias optical source are formed by a common optical source with an optically switching system configured to independently optically couple the common optical source to the injection optical source and to the bias optical source, respectively.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic representation of an embodiment of a radio frequency (RF) antenna element with a (de)tuning system of the invention;

(2) FIG. 2 shows a schematic representation of a further embodiment of a radio frequency (RF) antenna element with a (de)tuning system of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(3) FIG. 1 shows a schematic representation of an embodiment of a radio frequency (RF) antenna element with a (de)tuning system of the invention. The radio frequency antenna element is formed as an electrically conductive coil loop 11. The (de)tuning system 12 includes a switchable resonance circuit 111 coupled to the coil loop 11. The switchable resonant circuit includes a capacitance 15 in series with the coil loop 11 and an inductance 16 that is switchable, by the photosensitive switching element 14, in parallel to the capacitance 15 and in series with the inductance 16. By opening/closing the photosensitive switching element (i.e. changing its character between capacitive and resistive) the electrically conductive loop is switched between its non-resonant state and its resonant state. To close the photosensitive switching element, photon from the injection light source 13 are injected via the optical link 112 into the photosensitive switching element. When no photons from the injection light source are incident on the photosensitive switching element, the photosensitive switching element is in its open state. A (de)tune controller 17 is provided to control the injection optical source 17. The switching of the injection light source causes the (de)tuning system to switch the coil loop between its resonant and non-resonant state.

(4) The photosensitive switching element may be a simple pin-(photo)diode or alternatively back-to-back circuited pin-(photo)diodes may be used.

(5) FIG. 2 shows a schematic representation of a further embodiment of a radio frequency (RF) antenna element with a (de)tuning system of the invention. In the embodiment of FIG. 2 a photodetector 22 is circuited parallel to the photosensitive switching element 14. The bias optical source 21 is optically coupled 113 to the photodetector. The bias optical source is switched-on/off by the (de)tune controller. When photons from the bias optical source 21 are incident on the photodetector 22, then the photodetector 22 generates a negative bias voltage applied over the photosensitive switching element. The bias optical source is activated when the injection optical source is switched off. The negative bias voltage is applied over the photosensitive element when the photosensitive element is in its open state.

(6) Instead of switching-off of the injection optical source and the bias optical source, the optical links 112,113 might be interrupted.

(7) The photodetector may be a GaN-based semiconductor laser or a InGaN blue LED which may generate up to 75V negative bias voltage.