JPS62231145A - Generating and detecting device of high frequency magnetic field - Google Patents

Abstract

PURPOSE:To improve the isolation between a transmitter and a receiver and to obtain a DC and AC excitation and detection type high frequency magnetic field generating and detecting device which is highly reliable by composing a 90 deg. hybrid part of only coaxial lines. CONSTITUTION:The 90 deg. hybrid part 15 consists of a closed loop coaxial line 15a formed by coupling three 1/4-wavelength lines and one 3/4-wavelength line in a ring shape and two coaxial lines 15b and 15c. The coaxial lines 15b and 15c have relation ¦L1-L2¦=n/4lambda (n: odd number), where L1 and L2 are their electrical lengths. When the transmitter 10 generates high frequency pulses, high frequency pulses which are 180 deg. out of phase are induced at connection points P3 and P4 to produce 90 deg. out-of-phase high frequency magnetic fields at high frequency coils 1 and 3. Further, the 90 deg. out-of-phase high frequency magnetic fields detected by the 1st and the 2nd high frequency coils 1 and 3 are put together in in-phase relation and inputted to only the receiver 1.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an orthogonal excitation/detection type high frequency magnetic field generation/detection device used in magnetic resonance experiments and the like.

[Conventional technology]

Figure 2 shows, for example, ``Magnetic Resonance in Mezzoiso7''.
1 is a schematic diagram summarizing the high-frequency magnetic field generation and detection device described in Volume 1, page 349 of In Medicinale J. In the figure, (1) is the first high-frequency coil, (2) is the first high-frequency coil + the first
impedance matching i, (3) is a second high-frequency coil disposed coaxially and orthogonally to the first high-frequency coil,
(4) Second impedance matching device for the ldgz high frequency coil (3), (5) is a power combiner/divider called 9d:' hybrid, high frequency transformer (6a)
, (6b), a coil (7
a), (7b) and y f y + (8a), (
8b), DC blocking capacitors (9a), (9b)
It is made up of. The decoy is a transmitter that supplies high-frequency power to high-frequency coils (1) and (3) to generate a high-frequency magnetic field, and (b) is the high-frequency coil (1).

(3) a receiver that amplifies the signal detected by the magnetic field;
(6) is a cross diode in which diodes are connected in parallel and reversely to separate the transmitter (1G) and receiver (11)' in high frequency when receiving,
It is a parallel and reverse connected cross diode to protect the

Next, the high frequency magnetic field generation operation will be explained. Transmitter IJ
When a high frequency pulse is output from I, the cross diode (6) becomes conductive, and the high frequency pulse is applied to the 9o0 hybrid (5). As a result, the high frequency tri-y
connection point A between the first impedance matching device (2) and the 90 hybrid (5), and the second impedance matching device (4) and the 9CP
Connection point B with hybrid (5)! : High-frequency pulses having a phase difference of 90° from each other are induced. This phase difference of 9o0 is especially achieved by setting the coil # (7a) + (7b) and the capacitors (8a) and (8b) to predetermined values.

Therefore, the connection point A and BIC are connected to the first high-frequency coil (1) via the first impedance matching device (2) and the second high-frequency coil via the second impedance matching device (4), respectively. (3) is connected, so the first high frequency coil (1) and the second high frequency coil (3)
A high frequency magnetic field is generated. Furthermore, since the phases of these high-frequency magnetic fields differ by 90°, both high-frequency coils (1
) and (3) are orthogonally arranged, a high-frequency magnetic field of orthogonal excitation type can be generated. Note that the voltage induced at the connection point P between the receiver 01) and the 90° hybrid resistor 5) at this time is due to the configuration of the high frequency transformers (6a) and (6b) (windings W2 and W4 are in opposite directions). ), it is zero.

In addition, even if a finite induced voltage is generated due to imperfections in the high frequency transformers (6a) and (6b), the cross diode □
The voltage applied to the receiver αη is limited to the field of view by □□, and the receiver (b) is captured.

Next, the high frequency magnetic field detection operation will be explained. When high-frequency magnetic fields with different phases of ≦nO0 are detected by the high-frequency coils (1) and (31) of the first and coffin 2 arranged orthogonally,
Detection voltages are applied to the connection points A and B, and are synthesized in phase by the 90° . The transmitter (IQI is separated from the receiver α) [Problem to be solved by the invention] The conventional high-frequency magnetic field generation/detection device is configured as described above, and this @ e-gi : is used in strong quiet flea fields, so
Ferrite, which exhibits high magnetic permeability, cannot be used in the high-frequency coil normally used as a high-frequency transformer (ferrite causes magnetic saturation), and an air-core one is used as the high-frequency transformer. In addition, there were problems such as poor isolation characteristics between the This was done to solve these problems, and the purpose is to replace high-performance high-frequency magnetic field generation/detection equipment with low insertion loss and good isolation characteristics between the transmitter and receiver of the 90° hybrid. shall be.

[Failure to solve the problem]

The high frequency magnetic field generation/detection device according to the present invention includes a first circuit including a transmitter, a receiver, a first high frequency coil and a first impedance matching device, a second high frequency coil and a second impedance matching device.
Shift the phase by 90 degrees between the closed loop coaxial line to which the second circuit consisting of the impedance matching device is connected and the two coaxial lines whose electrical lengths are odd multiples of a quarter wavelength.90゜It is a hybrid configuration.

[Effect]

In this invention, the high frequency magnetic field generation/detection @ position is 90°
By configuring the hybrid with only coaxial lines, the transmitted power from the transmitter is sent to two high-frequency coils with a phase shift of 90F, or the magnetic field detected power from two high-frequency coils arranged orthogonally is combined in phase and sent to the receiver. without waste, improving the isolation characteristics of the transmitter and receiver.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. , In Figure 1, the same symbols as the conventional device are the same or equivalent parts, OfJ is the 9CP/% hybrid that combines and distributes power using a coaxial line, αφ is the 90° hybrid 06I and the receiver α power It is a coaxial line (quarter wavelength line) that has an electrical length of one quarter wavelength. In addition, the 9o hybrid α0 includes a closed loop coaxial line (15a) in which three quarter wavelength lines and one three quarter wavelength line are coupled in a ring shape, a first coil (1), and a first coil (1). A coaxial line (151: I
), the mud 2 circuit consisting of the second coil (3) and the i2 impedance matcher (4), and the closed loop coaxial line (1
5a), and if the electrical lengths of the lines (x5b) and (15c) are Ll and L2, ILI-L21=÷λ (where n is an odd number). It is configured. In addition, a closed loop coaxial line (15
a) On the top, the connection point to which the transmitter α is connected is Pl
, the connection point where the receiver α power is connected is a 22% coaxial line (1
5b), and the connection point with the coaxial line (15c) is P4. From the connection point P1, clockwise, the connection point P3 is located at the point where the electrical length is 1/4 wavelength. There is a connection point P2 at a point of 1 wavelength, and a connection point P4 at a point of 3/4 wavelength. Here, the characteristic impedance of the closed loop coaxial line (15a) is calculated from the expansion of the characteristic impedance of other parts.
It is most efficient to keep it close to double. For example, for the closed loop coaxial line (15a), the commonly used 70~
It is convenient to set the resistance to 75Ω and 50Ω for other parts. When the high-frequency pulse is output, the cross diode 0 becomes conductive, and the high-frequency pulse is applied at 90°...initially. As a result, due to the nature of the transmission line, connection point P3. High-frequency pulses with a phase difference of 180 degrees are induced at P4. This is because, based on the connection point P1, there is a quarter wavelength distance from the connection point Pi to the connection point P3, so the phase at the connection point P3 is is delayed by 90 degrees (5/4 on the route from connection point P1 → P4 → P2 → P3)
Since the wavelengths are different, there is a delay of 900 as well. ), the connection point P1 is separated by three-quarters of a wavelength from the connection point P4, so the phase is delayed by 270 degrees at the connection point P4.

λ Furthermore, since Ll=O and L2=7, the phase is delayed by 90° before reaching the second high frequency coil (3). In this way, the high frequency coils (1) and (3) have a phase of 9
Since high-frequency magnetic fields differing by 0° are generated, the high-frequency coil (
1).

By arranging (3) orthogonally, a high-frequency magnetic field of orthogonal excitation type can be generated.In addition, at this time, the power induced at the connection point P2 is transmitted along the path of the connection point P1 → P3 → P2 and the connection point P
In the path 1→P4→P2, the electrical length differs by a half wavelength, and the mutual phases are canceled by 18♂ difference, so the path is almost zero. Even if a finite induced power is generated, the receiver a:1)
The power applied to is amplitude limited and the receiver α°C is protected.

Next, the operation of receiving a high frequency magnetic field will be explained. 1st
and the second high-frequency coils (1) and (3) are arranged orthogonally, so that the high-frequency magnetic field with a 90° phase difference is applied to the first high-frequency magnetic field.
and the second high-frequency coil (11, (31K), it is transmitted and the detected power λ is applied to the connection points P3 and P4. At this time, since Ll=Or''2=4, the above 90 'The phase difference disappears, and the detected voltages are combined in phase and transmitted to the connection point P2.Also, since the cross diode (2) is non-conducting, the transmitter a [and the receiver αD are separated from each other]. In this way, the high-frequency magnetic field is detected by the high-frequency coils (1) and (3) arranged orthogonally, and the detected magnetic fields are combined in phase and input to only the receiver (1). A detection-type high-frequency magnetic field detection device can be realized.In the above embodiment, a closed-loop coaxial line (15a) with an electrical length of 3/2 wavelength was used, but as shown in FIG. A coaxial line (15a) with an electrical length of 5/4 wavelength is used, and on this closed loop coaxial line (15a), the connection point P1 of the transmitter H is connected to the connection point P3 of the first impedance matching device (2). The electrical length from connection point P1 of transmitter a to connection point P4 of the second impedance matching device (4) is 5/8 wavelength, and the electrical length from connection point P1 of transmitter a to connection point P4 of The electrical length from point P1 to receiver α connection point P2 is 3/8 wavelength,
The electrical length from the connection point P3 of the first impedance device (2) to the connection point P2 of the receiver αυ may be a quarter wavelength.

In addition, as shown in FIG. 3, a closed loop coaxial line (15a) with an electrical length of two wavelengths is used, and on this closed loop coaxial line (15a), a first impedance matching is conducted from the connection point P1 of the transmitter α. The electrical length to the connection point P3 of the device (2) is one wavelength of nutrients, and the transmission! From the connection point P1 of Ql to the second
The electrical length at the connection point P4 f of the impedance matching device (4) is one wavelength, and from the connection point P1 of the transmitter αC to the receiver αυ
The electrical length from the connection point P2 of the first impedance matching device (2) to the connection point P2 of the receiver αυ is 3/8 wavelengths. may be configured. Further, a closed loop coaxial line (15a) of any electrical length may be used as long as it can form an hybrid α9 of 90°.

In addition, in the above embodiment, the cross diode (to) connected to the input point of the receiver αυ and the receiver αη is 1/4 of the electrical length.
Although the wavelength line α is used to connect to the 90°... hybrid (c), it is also possible to directly connect the two using a coaxial connector without using the electrical length quarter wavelength line α [Effects of the invention] As described above, according to the present invention, since the 9CP/' hybrid is configured by a coaxial line, the isolation characteristics of the transmitter and receiver are improved, and a highly reliable orthogonal excitation/detection type high-frequency magnetic field can be generated. 0 that has the effect of providing a generation/detection device

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a high frequency magnetic field generation/detection device according to one embodiment of the present invention, and FIGS. 2 and 3 are block diagrams of a high frequency magnetic field generation/detection device showing other embodiments of the present invention. 4
The figure is a configuration diagram showing a conventional high frequency magnetic field generation/detection device. In the figure, (L) and (3) are high frequency coils, +2
), +4) is the impedance matching device, and the bit is the transmitter.
qη is the receiver, (2) is the 9o0 hybrid, (:L5
a) is a closed loop coaxial line, (15b), (x5c) is a coaxial line. In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (4)

[Claims] (1) A first high-frequency coil, a second high-frequency coil disposed coaxially and orthogonally to the first high-frequency coil, and a first impedance matching device connected to the first high-frequency coil. , a second impedance matching device connected to the second high-frequency coil, a transmitter that supplies high-frequency power to the first high-frequency coil and the second high-frequency coil, and a first high-frequency coil and a second high-frequency coil. a receiver for amplifying the magnetic field signal detected by the high frequency coil;
a closed loop coaxial line to which the impedance matching device, the second impedance matching device, the transmitter and the receiver are connected; a first coaxial line A connecting the closed loop coaxial line and the first impedance matching device; A second coaxial line whose absolute value of the difference in electrical length from the first coaxial line A has a length that is an odd multiple of a quarter wavelength, and which connects the closed loop coaxial line and the second impedance matching box. line B, on the closed loop coaxial line, a signal transmitted clockwise from the connection point P_1 of the transmitter and a signal transmitted counterclockwise from the connection point P_2 of the receiver are in opposite phase to each other, and The connection point P_3 of the first impedance matching device is in the same phase as the connection point P_3 of the second impedance matching device.
_4 is in phase with each other, and the connection points P_3 and P_4 are in opposite phase with each other, and the connection point P
A high frequency magnetic field generation/detection device characterized in that connection points of the transmitter, the receiver, and the first and second impedance matching devices are set so that _1 and P_2 are not adjacent to each other. (2) Using a closed-loop coaxial line with an electrical length of 3/2 wavelength, connect the transmitter to the connection point P on this closed-loop coaxial line.
The electrical length from _1 to the connection point P_3 of the first impedance matching box is 1/4 wavelength, and the connection point P_1 of the above transmitter
The electrical length from the connection point P_4 of the transmitter to the connection point P_4 of the second impedance matching device is three-quarters of a wavelength, the electrical length from the connection point P_1 of the transmitter to the connection point P_2 of the receiver is one-half wavelength, and the electrical length from the connection point P_1 of the transmitter to the connection point P_2 of the receiver is one-half wavelength. 2. The high frequency magnetic field generation/detection device according to claim 1, wherein the electrical length from the connection point P_3 of the impedance matching device to the connection point P_2 of the receiver is a quarter wavelength. (3) Using a closed-loop coaxial line with an electrical length of 5/4 wavelength, connect the transmitter to the connection point P on this closed-loop coaxial line.
The electrical length from _1 to the connection point P_3 of the first impedance matching device is 1/8 wavelength, and the connection point P_1 of the above transmitter
The electrical length from the connection point P_4 of the transmitter to the connection point P_4 of the second impedance matching device is 5/8 wavelength, the electrical length from the connection point P_1 of the transmitter to the connection point P_2 of the receiver is 3/8 wavelength, and the electrical length from the connection point P_1 of the transmitter to the connection point P_2 of the receiver is 3/8 wavelength, 2. The high frequency magnetic field generation/detection device according to claim 1, wherein the electrical length from the connection point P_3 of the impedance matching device to the connection point P_2 of the receiver is a quarter wavelength. (4) A closed loop coaxial line with an electrical length of 2 wavelengths is used, and on this closed loop coaxial line, the electrical length from the transmitter connection point P_1 to the first impedance matching device connection point P_3 is 1/4 wavelength; The electrical length from the connection point P_1 of the transmitter to the connection point P_4 of the second impedance matching device is one wavelength, and the electrical length from the connection point P_1 of the transmitter to the connection point P_2 of the receiver is 5/8 wavelength. , the electrical length from the connection point P_3 of the first impedance matching device to the connection point P_2 of the receiver is three-eighths of a wavelength. Detection device.