JPS6353906A - Radio frequency magnetic field generating detector - Google Patents

Abstract

PURPOSE:To obtain a stable and highly efficient radio frequency magnetic field generating detector by a method wherein 2nd and 3rd variable capacitors are connected to the respective terminals of 1st variable capacitor to form a balanced impedance matching circuit and a balun is connected to the matching circuit. CONSTITUTION:2nd variable capacitor 8b and 3rd variable capacitor 8c are connected to the respective terminals of 1st variable capacitor 8a which provides a capacitive coupling between a pair of adjoining wings 1b to form a balanced impedance matching circuit 8 and a balun 9 is connected to the balanced impedance matching circuit 8. Then the resonance frequency and the impedance matching frequency of a microwave circuit which functions as an equivalent series resonance circuit are adjusted by the 1st variable capacitor 8a. As a result, voltages whose magnitudes are equal and polarities are opposite to each other are applied to electrodes 7a and 7b so that the balanced feeding of the LC series resonance circuit can be completely realized.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a high frequency magnetic field generator/detector, particularly a high frequency magnetic field generator/detector used in the magnetic resonance apparatus [Prior Art] Figure 4 is, for example, the Journal of Magnet (Journal of Magnet).
eticResonance) J, Volume 36, No. 447
This is a perspective view showing a conventional high-frequency magnetic field generator/detector shown in pages 1 to 451 (1979). When configured as above, the coils are arranged symmetrically with respect to a predetermined axis (not shown), and the vertical hand (
The non-protruding part (L
a) and a protrusion Q called a wing
b) has t. (2) is the adjacent wing (1b)
A fixed capacitor inserted between the capacitors (3) and 1 for electric field shielding is installed on the inside of the wing (1b) via an insulator N (not shown) and with the axes mentioned above at the common center. The conductor ring (3a) is called the top guard ring, and the other conductor ring (3b) is a pair of conductor rings.
is called the bottom guard ring.

(4a) and (4b) are the conductor plate (1) and the conductor ring (
3) is an electrode formed integrally with the electrode. (5a), (5
b) is a matching variable capacitor connected in series between these electrodes (4a) and (4b), and (6) is a transmitter/receiver (
Q [(4
The conventional high-frequency magnetic field generator/detector that will be directly connected to
), the conductor ring (3) forms a standing tree circuit that functions equivalently as an LC series resonant circuit, and furthermore, the electrodes (4a), (4b
) are coupled by each amount τ, so the variable capacitor (5a
), (5b) can be added to adjust the resonance frequency. t, variable capacitor (5a),
If the impedance is matched using (5b), it will be possible to connect the transmitter/receiver with a predetermined impedance to the terminal (6).As mentioned above, the conductor ring (3) is used for electric field shielding, i.e., for generating and detecting high frequency magnetic fields. It is used to reduce dielectric loss within the measurement object due to the generated electric field when the measurement object is installed inside the instrument.

[Problem that the invention seeks to solve]

Conventional high-frequency magnetic field generators and detectors do not take into account the balance-unbalance conversion of circuit impedance, so if a common-mode current flows through the coaxial cable connected to the terminal and the operation becomes unstable, the efficiency will decrease. This invention, which had some problems, was made in order to solve these problems.
Aiming to obtain a stable and efficient high-frequency magnetic field generator/detector 6 If the high-frequency coil for the whole body is cylindrical, the efficiency of transmitting magnetic field generation is low, and the reception signal is
There were problems such as a relatively small ratio (to No.1se Ratio).

[Means for solving problems]

The high frequency magnetic field generator/detector according to the present invention includes a first variable capacitor Gt-coupling a pair of adjacent wings, and a second variable capacitor connected to each end of the first variable capacitor.
A mermetal bridge is provided with a balanced impedance matching circuit consisting of a variable capacitor and a third variable capacitor, and a balanced unbalanced converter connected to this balanced impedance matching circuit. To make the shape of the whole body high-frequency coil elliptical [Operation] In the present invention, a balanced impedance matching circuit and a balanced unbalanced converter are balancedly connected to a pair of adjacent wings.

Furthermore, by making the high-frequency coil for the whole body into an elliptical shape, the efficiency of generating the transmitting magnetic field and the S/N of the received signal are improved.

[Real #i same]

FIG. 1 is a perspective view showing a first embodiment of the invention,
This is the case where the high frequency coil is cylindrical, and (1) to (3) and (6) are the same as conventional ones. (7a).

(7b) each has four (1) adjacent wings (lb)
The electrode (8a) formed integrally with the electrode (8a) is the first variable capacitor for the LC series resonant circuit and impedance matching. A pair of wings (1
b) is connected between the electrodes (7a) and (7b). (8b
), (sc) are respectively connected to each end of the first variable capacitor (8a), and together with the first variable capacitor (8a) constitute a balanced impedance matching circuit (8). (9) is a balanced unbalanced converter connected to the second variable capacitor (8b) and the third variable capacitor (8C) of this balanced impedance matching circuit (8),
It is a coaxial cable with an electrical length of wavelength. GO is the bottom guard ring (3b), the first variable capacitor (8
a) and the ground wire connected to terminal (6). Note that the angle θ huff 0° formed by the vertical band (la) is
(preferably 75° x 900).

Figure 2.3 is the second example of this invention. FIG. 7 is a perspective view showing a third embodiment, in which the high-frequency coil has an elliptical cylindrical shape;
) to (11m are the same as in the first embodiment. In Fig. 2, the vertical band is arranged in the short axis direction of the ellipse, and in Fig. 3, the vertical band is arranged in the long axis direction. This is an example.

Alternatively, in this invention, the first variable capacitor (8a) adjusts the resonant frequency and impedance matching frequency of the three-dimensional circuit that functions as an isometric series resonant circuit. In addition to this, 1. By arranging the second variable capacitor (8b) and the third variable capacitor (8C) in a balanced manner and using a balanced-unbalanced converter (9), a coaxial cable and a transmitter/receiver with unbalanced impedance can be connected to the terminal (6). When coupled to , the maximum power can be delivered to the load and the maximum power sensed. In this case, electrodes (7a) and (7
Since voltages of equal magnitude and opposite polarity are applied to b), the LC series resonant circuit will be fed with completely balanced power.This may be the reason why the stability and efficiency of the high frequency magnetic field generator/detector can be increased. Although not shown, the high-frequency magnetic field generator/detector of the present invention reduces the loss of the LC resonant circuit by installing a conductor tube for electromagnetic shielding, that is, a Kinpo cylinder, having a common central axis on the outside of the conductor plate. However, since the spatial uniformity of the generated high frequency magnetic field is in the same direction, the conductor plate is
In addition, the cylindrical high-frequency magnetic field generator/detector for the whole body becomes larger, and the efficiency of transmitting magnetic field generation or the S/N of the received signal becomes smaller. It is almost oval in shape, so
The high-frequency magnetic field generator/detector can be made into an elliptical cylinder whose major axis is the diameter of the cylinder. As a result, the efficiency of magnetic field generation is 2 higher than in the case of a cylinder, and the S/N of the received signal is also decreased. For example, compared to 64MHz or the case of two cylinders, the elliptical case has a transmission power of 60 to 70% for the same transmission power.
Experiments have shown that the transmitted magnetic field increases.Also, when the RF coil is installed so that the major axis of the ellipse is horizontal, the vertical Arrange the punts in the short axis direction and the long axis direction.

〔Effect of the invention〕

As described above, the present invention includes a first variable capacitor that couples a pair of protrusions in different amounts, a second variable capacitor and a third variable capacitor connected to each end of the first variable capacitor, respectively.
A balanced impedance matching circuit consisting of a variable capacitor and a balanced unbalanced converter connected to this balanced impedance matching circuit have the effect of providing a stable and efficient high frequency magnetic field generator/detector. Furthermore, by making the shape of the high-frequency magnetic field generator/detector for the whole body into an ellipse, the efficiency of magnetic field generation is high, and the S/N ratio of the received signal is also improved.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a high-frequency magnetic field generator/detector according to an embodiment of the present invention, FIGS. 2 and 3 are perspective views showing an embodiment of the pond according to the present invention, and FIG. 4 is a conventional high-frequency magnetic field generator/detector. The detector is shown in the figure, fi+ is a conductor plate, (1a) is a vertical capacitor, (lb) is a wing & (2) is a fixed capacitor. 9) is a balanced unbalanced converter. The same reference numerals in each figure indicate the same or equivalent parts. Agent: Masuo Oiwa Variable Container; 'W' 8c: No. J Variable Container Diagram 2 Figure 3 Figure 4

Claims (6)

[Claims] (1) At least one pair of H-shaped conductor plates is arranged symmetrically with respect to a predetermined axis, the protrusions of the conductor plates are brought close to each other, and at least three pairs of these protrusions are fixed capacitors. When capacitively coupled, the pair of protrusions that remain together are called the first
A balanced impedance consisting of a three-dimensional circuit that is capacitively coupled with a variable capacitor to equivalently constitute an LC resonant circuit, and the first variable capacitor, and a second variable capacitor and a third variable capacitor connected to each end of the first variable capacitor. A high-frequency magnetic field generator/detector comprising a matching circuit and a balanced/unbalanced converter connected to the balanced impedance matching circuit. (2) A three-dimensional circuit includes a pair of conductor rings installed inside a protrusion of a conductor plate with an insulating layer in between and a predetermined axis as a common center, and at least one conductor ring is connected to a ground potential. A high-frequency magnetic field generator/detector according to claim 1, characterized in that: (3) The high-frequency magnetic field generator/detector according to claim 1, wherein the three-dimensional circuit is cylindrical. (4) The high-frequency magnetic field generator/detector according to claim 1, wherein the three-dimensional circuit has an elliptical cylinder shape. (5) The high-frequency magnetic field generator/detector according to claim 1 or 2, wherein the three-dimensional circuit has a conductor tube having a predetermined axis as its central axis on the outside of the conductor plate. (6) The high frequency magnetic field generator/detector according to claim 1 or 2, wherein the balanced/unbalanced converter is a coaxial cable having an electrical length of 1/2 wavelength.