JP3100658B2 - Pulsed nuclear quadrupole resonator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nuclear quadrupole resonance.
ances (hereinafter abbreviated as NQR) for analyzing and detecting, especially high-sensitivity and high-efficiency control of substances to be controlled, such as plastic bombs, drugs, stimulants, etc. hidden in aircraft cargo. The present invention relates to a pulse NQR device suitable for remote sensing by using a pulse NQR device.

[0002]

2. Description of the Related Art The pulse NQR method irradiates a sample with a pulsed high-frequency magnetic field having a frequency (resonance frequency) peculiar to the sample (resonance frequency) to excite a nuclear quadrupole, and induces an NQR signal ( This is a method of identifying and analyzing a substance by receiving, amplifying, and analyzing a high-frequency magnetic field) by a receiving coil.

[0003] Conventional pulse NQR devices usually include transmission and reception as described in, for example, "New Experimental Chemistry Course 3 Basic Technology 2 Magnetism", published by Maruzen (1976), pp. 489-492. The "bridge method" and the "single coil method", in which the same method is used with the same coil, have been used.

On the other hand, an example in which the transmission coil and the reception coil are formed as different coils is described in, for example, "Journal of Molecular Structure", Vol. 58 (198).
0), pages 63 to 77 (Journal of
Molecular Structure, 58, (1
980), pp. 63-77). The figure shows an example of a coil design using a “crossed coil method” in which transmission and reception are performed by separate coils whose coil axes are orthogonal to each other.

Further, recently, for example, “Applied
Physics Letters ", Vol. 47 (1985), No. 6
From page 37 to page 639 (Applied Physic)
sLetters, 47 (1985), pp 637-6.
39), a superconducting quantum interference device (Superconducting Quantum I)
interference Device, abbreviation SQUI
In an apparatus using D) as a detector for an NQR signal, there has been reported an example in which the receiving coil and the transmitting coil are separated while keeping their axes parallel. In this example, the receiving coil is arranged coaxially in the transmitting coil, but by connecting a coil of reverse winding to the receiving coil in series to reduce the coupling between the receiving coil and the transmitting coil, the receiving coil and the transmitting coil are connected. The two can be separated while keeping their axes parallel.

[0006]

SUMMARY OF THE INVENTION Free induction decay (Free Induction) used for reception in the pulse NQR method
Decay (hereinafter referred to as FID) signal occurs immediately after the transmission pulse. However, the pulse signal to be transmitted does not immediately return to zero potential due to the inductance and capacitance existing in the circuit or the mutual inductance between the transmission coil and the reception coil, and during this time, the FID signal cannot be received. Therefore, the pulse NQR
In order to increase the sensitivity of the device, the transmission pulse should be cut off so that the signal can be received as soon as possible.
It is necessary to minimize the reception loss of the D signal.
When remote sensing is performed by NQR, the optimum size and shape of the transmission coil are determined mainly by the strength of the high-frequency magnetic field to be transmitted and the volume and input power for distributing it, while the optimum size and shape of the reception coil are Is mainly determined by the sample amount, the volume to detect it, and the sensitivity of the receiving system. Therefore, in order to realize an NQR remote detection device having high transmission efficiency and high reception sensitivity, it is necessary to use a separate coil for the transmission coil and the reception coil, and individually optimize the size and shape of both.

However, in the first conventional example, since the same coil is used for the transmission coil and the reception coil, the transmission pulse is not interrupted, and the sizes and shapes of the transmission coil and the reception coil are individually optimized. NQ
There is a problem that there is a limit in increasing the sensitivity and efficiency of the R remote detection device.

In the coil design of the second conventional example, the "crossing coil method" is used in which the transmitting and receiving coils are separated by making the axes of the transmitting and receiving coils orthogonal to each other to reduce the coupling of the coils. ing. However, in NQR, nuclear magnetic resonance (Nuclear Ma
Unlike a magnetic resonance (abbreviation NMR), most of the components of the received high-frequency magnetic field (NQR signal) are in the same direction as the high-frequency magnetic field to be transmitted.
There is a problem that the QR signal cannot be received efficiently.

In the third conventional example, the transmitting coil and the receiving coil can be separated from each other while keeping the coil axes parallel. However, the size, shape and position of the transmitting coil and the receiving coil are different. Depending on the relationship, the coupling between the coils is increased, the transmission pulse is hardly cut, and the transmission efficiency and the reception sensitivity are reduced. Therefore, there is a problem in that the size, shape, and positional relationship between the transmission coil and the reception coil are limited, and there is a limit in increasing the sensitivity and efficiency of the NQR remote detection device.

[0010] It is an object of the present invention to separate the transmitting coil and the receiving coil while keeping the coil axis parallel, and to improve the cutoff of the transmitting pulse, and to increase the size and shape of the transmitting coil and the receiving coil. Another object of the present invention is to provide a pulse NQR device whose arrangement can be individually optimized and realize a highly sensitive and highly efficient NQR remote sensing device.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a switch or a switch for disconnecting a tuning circuit for a receiving coil when a high-frequency pulse is applied and disconnecting a tuning circuit for a transmitting coil when a high-frequency pulse is not applied. This is achieved by adding an electrical circuit.

[0012]

In the above configuration, when a high-frequency pulse is being applied, for example, the switch added to the tuning circuit for the transmitting coil is closed and the switch added to the tuning circuit for the receiving coil is opened. Thus, the tuning circuit for the transmitting coil operates as a resonance circuit, but does not operate as a resonance circuit because the tuning circuit for the receiving coil is disconnected.
Therefore, even if the axes of the transmission coil and the reception coil are parallel to each other, the coupling between them is small, and the transmission coil can transmit a high-frequency magnetic field without being affected by the reception coil.

Conversely, when no high frequency pulse is applied, the switch added to the tuning circuit for the transmitting coil is opened and the switch added to the tuning circuit for the receiving coil is closed. As a result, the tuning circuit for the receiving coil operates as a normal resonance circuit, but does not operate as a resonance circuit because the tuning circuit for the transmission coil is disconnected. Therefore, even if the axes of the transmission coil and the reception coil are parallel to each other, the coupling between them is small, and the reception coil can receive the NQR signal without being affected by the transmission coil.

According to the present invention, even if the axes of the transmitting coil and the receiving coil are parallel, the coupling is sufficiently small irrespective of the size, shape and positional relationship of both. Therefore, the pulse is improved, and the transmission coil and the reception coil can be individually optimized without deteriorating both the transmission efficiency and the reception sensitivity, thereby realizing a high sensitivity and high efficiency NQR remote sensing device.

In the above description, the added switch or electric circuit has a function of disconnecting the tuning circuit for the receiving coil when a high-frequency pulse is applied, and a function for cutting the transmitting coil when the high-frequency pulse is not applied. Although it has been described as having both functions of disconnecting the tuning circuit, it goes without saying that a device having only one of the functions has a certain effect.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIG.

First, the high frequency generated by the high frequency generator 2 and the rectangular pulse generated by the DC pulse generator 3 in synchronization with the signal of the controller 4 are input to the high frequency power amplifier 5 to generate a high frequency pulse train. . Next, this pulse train is input to the transmission coil 7 through the tuning circuit 6 for the transmission coil, and a pulsed high-frequency magnetic field is applied to the inspection object 9 placed in the shield box 8.

Further, an NQR signal (high-frequency magnetic field) induced in the target substance 1 contained in the inspection object 9 by the irradiated high-frequency magnetic field is received by the receiving coil 10 whose axis is parallel to the transmitting coil 7, and After passing through the tuning circuit 11, the signal is amplified by the low noise amplifier 12. The amplified signal is further phase-detected by a phase detector 13, then the frequency band is narrowed through a frequency filter 14, and a digital adder 15
To obtain a high signal-to-noise ratio. The NQR FID signal obtained in this way is further subjected to Fourier transform by the data processing device 16 and it is determined whether or not the test substance 9 contains the target substance 1 based on whether or not there is a peak due to the target substance 1 in the frequency spectrum. I do.

Here, in the tuning circuit 6 for the transmitting coil,
As shown in FIG. 1B, a switch 19 is added in series to the variable capacitor 18 for adjusting the resonance frequency. The switch 19 is closed by the controller 4 when a high-frequency pulse is applied, and is not applied. Sometimes it is controlled to open. Also, in the tuning circuit 11 for the receiving coil, a switch 20 is added in series to the variable capacitor 21 for adjusting the resonance frequency, and this switch is opened by the controller 4 when a high-frequency pulse is applied, and is applied. If not, control to close. The switches 19 and 20 do not necessarily need to be added in series to the variable capacitors 18 and 21 for adjusting the resonance frequency.
May be added in series. Switch 19, switch 20
Is controlled in this way, even if the axes of the transmission coil 7 and the reception coil 10 are parallel, the coupling between the two is small and does not affect each other. Can be optimized.

Here, a specific example of the apparatus of this embodiment will be described.

The target substance 1 is RDX (hexahydro, 1,3,5-tri), which is a main component of a plastic bomb.
Nitro, 1,3,5-triazine) 600
g, the inspection object 9 is carry-on baggage (volume 50
In the case of about a liter, a solenoid coil having a diameter of about 50 cm and three turns capable of efficiently irradiating the inspection object 9 with a high-frequency magnetic field with small electric power is appropriate as the transmission coil 7. In addition, as the receiving coil 10, RDX6, which is a target substance existing in a space having a volume of 50 liters or more, is used.
It is preferable to use a solenoid coil having a diameter of about 100 cm and a length of about 3 turns, which is capable of detecting 00 g with high sensitivity, and which is arranged coaxially outside the transmission coil. Here, the target substance 1 included in the inspection target 9 does not necessarily have to be in the transmission coil 7 or the reception coil 10.

The above apparatus transmits a high-frequency pulse train having a frequency of 5.2 MHz, a pulse width of 200 μsec, a pulse interval of 30 msec, and a pulse intensity of about 2 gauss, and adds a FID signal after the pulse about 256 times to test a volume of 50 liters. 600 g of the target substance RDX in the target object 9 can be detected.

If the conditions are different from those of the above specific example, the sizes of the transmitting coil and the receiving coil may be changed so as to be optimal. For example, if the power supplied to the transmission coil can be increased, it is better to make the transmission coil larger, and if the target substance is small, it is better to make the reception coil smaller. Therefore, depending on the conditions, the transmitting coil may be larger than the receiving coil.

According to this embodiment, it is possible to improve the cutoff of the transmission pulse and to optimize the transmission coil and the reception coil individually, thereby realizing a high-sensitivity and high-efficiency pulse NQR remote sensing device. effective. Further, in this embodiment, since the opening / closing control of the switch is actively performed by the controller, there is an effect that precise timing control can be performed without being affected by the characteristics of electric components and circuits.

Next, a second embodiment of the present invention will be described with reference to FIG.

In this embodiment, a circuit composed of a capacitor and a coil, and diodes having opposite polarities is used instead of a switch added to the tuning circuit for the transmitting coil and the tuning circuit for the receiving coil. Is different from the first embodiment in that a controller is not required for the control of the first embodiment. FIG. 2B shows an equivalent circuit of the tuning circuit for the transmitting coil and the tuning circuit for the receiving coil used in this embodiment, and the operation will be described below.

When the transmission pulse is being applied, the assembled diodes 23 and 26 become conductive. Therefore, the circuit on the transmitting side is in the same state as when the switch is closed due to the short circuit. On the other hand, in the circuit on the receiving side, the variable capacitor 27, the coil 28, and the capacitor 29 form a parallel resonance circuit, the impedance becomes high, and the circuit is in the same state as when the switch is opened.

Conversely, when no transmission pulse is applied, the assembled diodes 23 and 26 are turned off. Therefore, the circuit on the transmitting side includes the variable capacitor 24, the coil 25
Forms a parallel resonance circuit, and the impedance becomes high, which is the same state as when the switch is opened. On the other hand, in the circuit on the receiving side, the variable capacitor 27 and the coil 28 are disconnected,
Capacitor 29, variable capacitor 2 for adjusting resonance frequency
1. A resonant circuit is formed by the impedance-adjusting variable capacitor 22 and the receiving coil 10, and the same effect as when the switch is closed is obtained. The variable capacitor 21 for adjusting the resonance frequency can be omitted if the capacitor 29 is made a variable capacitor so that it also has the function of the variable capacitor for adjusting the resonance frequency.

As described above, these circuits perform the same operation as the opening and closing of the switch in synchronization with the application and non-application of the transmission pulse, so that the same effects as in the first embodiment can be obtained. Further, in this embodiment, since no controller is required, there is an effect that the device configuration can be simplified.

Further, a third embodiment of the present invention will be described with reference to FIG.

The present embodiment differs from the first embodiment in that the transmitting coil is divided into N coil segments 30, and (N-1) insertion capacitors 31 are connected in series between them. I have. The combined capacitance of the (N-1) insertion capacitors 31 and the frequency adjustment capacitor 18 is made equal to the capacitance of the frequency adjustment capacitor when the transmission coil is not divided so that the tuning frequency does not shift. Thereby, the high voltage applied to both ends of the coil piece and the capacitor is reduced by 1 / N
, Power that can be applied to the transmitting coil without causing discharge can be increased. Note that the division is not necessarily equal, but since the highest voltage is applied to a coil piece having a large inductance and a capacitor having a small capacitance, care must be taken so that discharge does not occur in these parts. . In this embodiment, an example is shown in which a switch is added to the tuning circuit. However, the circuit used in the second embodiment may be used instead of the switch.

According to this embodiment, in addition to the same effects as those of the first and second embodiments, there is an effect that the power that can be applied to the transmission coil without causing discharge can be increased.

Finally, a fourth embodiment of the present invention will be described with reference to FIG.

In this embodiment, two transmitting coils 7 smaller than the receiving coil 10 and connected in series or in parallel are arranged on both sides of the object 9 to be inspected, and these are moved in the direction of the arrow in FIG. It covers the receivable area of the coil. Other points are the same as those of the first to third embodiments. Note that it is not always necessary to move the two transmitting coils together, and any other moving method may be used as long as it covers the receivable area of the receiving coil. Further, for example, when the amount of the target substance is small and the NQR signal is small, the transmitting coil may be fixed and the small receiving coil may be moved.

According to the present embodiment, in addition to the same effects as those of the first to third embodiments, a large test object can be inspected by a low-power high-frequency amplifier that is inexpensive and easily manufactured and available. Even when the amount of the target substance is small, there is an effect that a large inspection target can be inspected, and the NQR remote detection device can have higher sensitivity and higher efficiency.

[0036]

As described above, according to the present invention,
In a pulsed nuclear quadrupole resonator, the transmission coil and the reception coil can be separated while keeping their respective coil axes parallel, and the cutoff of the transmission pulse can be improved, and the size, shape, and arrangement of the transmission coil and the reception coil are individually Therefore, there is a remarkable effect in realizing a pulse NQR remote detection device with high sensitivity and high efficiency.

[Brief description of the drawings]

FIG. 1A is a diagram illustrating an apparatus configuration according to a first embodiment of the present invention;
(B) It is an equivalent circuit diagram of the tuning circuit for transmitting coils and the tuning circuit for receiving coils.

FIG. 2A is a diagram illustrating an apparatus configuration according to a second embodiment of the present invention;
(B) It is an equivalent circuit diagram of the tuning circuit for transmitting coils and the tuning circuit for receiving coils.

FIG. 3 is an equivalent circuit diagram of a transmission coil and a tuning circuit for the transmission coil according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram showing the arrangement and movement of a transmitting coil and a receiving coil according to a fourth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Target substance 2 ... High frequency generator 3 ... DC pulse generator 4 ... Controller 5 ... High frequency power amplifier 6 ... Tuning circuit for transmission coil 7 ... Transmission coil 8 ... Shield box 9 ... Test object 10 ... Reception coil 11 ... Reception Tuning circuit for coil 12 ... Low noise amplifier 13 ... Phase detector 14 ... Frequency filter 15 ... Digital adder 16 ... Data processing device 17,22 ... Variable capacitor for impedance adjustment 18,21 ... Variable capacitor for resonance frequency adjustment 19,20 ... Switches 23, 26 ... Diodes 24, 27 ... Variable capacitors 25, 28 ... Coils 29 ... Capacitors 30 ... Coil fragments 31 ... Insertion capacitors

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Nagasawa 2-1 Shinju Yoyo, Kashiwa-shi, Chiba Pref. Inside the Kashiwa Plant, Hitachi Medical Corporation (56) References Applied Physics Letters, Vol. 47, No. 6, p. 637-639 (1985) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 24/00-24/14 JICST file (JOIS)

Claims (4)

(57) [Claims] 1. A high-frequency pulse generating means, a tuning circuit for a transmitting coil, a transmitting coil, a receiving coil, a tuning circuit for a receiving coil, and means for amplifying and processing a high-frequency signal. And the axis of the receiving coil is parallel to each other, in the pulse nuclear quadrupole resonance apparatus, the function of cutting the tuning circuit for the receiving coil when a high-frequency pulse is applied, and when the high-frequency pulse is not applied A pulse nuclear quadrupole resonance apparatus characterized by adding a switch or an electric circuit having at least one of a function of cutting a tuning circuit for a transmission coil. 2. The pulse nuclear quadrupole resonance apparatus according to claim 1, wherein said electric circuit comprises a parallel resonance circuit including a capacitor and a coil, and a diode group having opposite polarities. . 3. The pulse nuclear quadrupole resonance apparatus according to claim 1, wherein the transmission coil is divided into a plurality of parts, and a capacitor is inserted in series between the divided parts. 4. The pulse nucleus according to claim 1, further comprising a mechanism for moving the transmission coil or the reception coil, wherein a relative position between the two is variable. Polar resonator.