JPH04326051A - Pulse nucleus four-pole resonance device - Google Patents

Abstract

PURPOSE:To enable a transmission pulse to be cut fully and a size, a shape, and a placement of a coil to be optimized by cutting off a tuning circuit for reception coil when a high-frequency pulse is applied to and then cutting off a tuning circuit for transmission coil when a high-frequency pulse is not applied to. CONSTITUTION:A switch 19 is added in series to a variable capacitor 18 for adjusting resonance frequency within a tuning circuit for transmission coil 6 and it is so controlled by a controller 4 that the switch 19 is closed 4 when a high-frequency pulse is applied to and is opened when it is not applied to. Also, a switch 20 is added in series to a variable capacitor for adjusting resonance frequency 21 within a tuning circuit for reception coil 11 and it is so controlled by the controller 4 that the switch 20 is opened when a high-frequency pulse is applied to and is closed when it is not applied to, thus enabling both coupling to be small even if axes of the transmission coil and the reception coil are in parallel each other and a high-frequency magnetic field signal to be received without causing the reception coil to be affected by the transmission coil.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to pulsed nuclear quadrupole resonance (
Nuclear Quadrupole Reso
It is a device that analyzes and detects substances that are subject to control, such as plastic bombs, narcotics, and stimulants hidden in aircraft cargo, etc., with high sensitivity and high efficiency. The present invention relates to a pulsed NQR device suitable for remote detection in the field.

0002

[Prior Art] In the pulsed NQR method, a pulsed high-frequency magnetic field having a frequency (resonance frequency) unique to the sample is applied to the sample from a transmitting coil to excite a nuclear quadrupole, and the NQR signal ( This method identifies and analyzes substances by receiving, amplifying, and analyzing high-frequency magnetic fields (high-frequency magnetic fields) using a receiving coil.

[0003] Conventional pulsed NQR devices usually have transmission and reception functions, as described in, for example, "New Experimental Chemistry Course 3 Basic Technology 2 Magnetism", published by Maruzen (1976), pages 489 to 492. The ``bridge method'' and ``single coil method'' have been used in which both are performed using the same coil.

On the other hand, an example in which the transmitting coil and the receiving coil are separate coils, for example,
"Molecular Structure", Volume 58 (19
80), pp. 63 to 77 (Journal o
f Molecular Structure, 5
8, (1980), pp. 63-77). This document shows an example of a coil design using the "crossed coil method" in which transmission and reception are performed using separate coils whose coil axes are orthogonal to each other.

Furthermore, recently, for example, “applied
Physics Letters, Volume 47 (1985),
Pages 637 to 639 (Applied Phy
sics Letters, 47 (1985), pp63
7-639), a superconducting quantum interference device (Superconducting Quant
Among devices using a umInterference Device (abbreviated as SQUID) as an NQR signal detector, an example has been reported in which the receiving coil and transmitting coil are separated while keeping their axes parallel. In this example, the receiving coil is placed coaxially within the transmitting coil, but by connecting a reversely wound coil in series with the receiving coil to reduce the coupling between the receiving coil and the transmitting coil, This allows the two to be separated while keeping their axes parallel.

[0006]

[Problem to be solved by the invention] Free induction attenuation used for reception in pulsed NQR method
The nDecay (hereinafter referred to as FID) signal is generated immediately after the transmit pulse. However, the pulse signal to be transmitted does not immediately return to zero potential due to inductance and capacitance existing in the circuit, or mutual inductance between the transmitting coil and the receiving coil, and the FID signal cannot be received during this time. Therefore, in order to make the pulse NQR device highly sensitive, it is necessary to improve the sharpness of the transmitted pulse so that the signal can be received as quickly as possible, and the FID
It is necessary to minimize signal reception loss. Furthermore, when performing remote sensing with NQR, the optimal size and shape of the transmitting coil are determined mainly by the strength of the high-frequency magnetic field to be transmitted, the volume in which it is distributed, and the input power, while the optimal size and shape of the receiving coil are , mainly determined by the amount of sample, the volume in which it is detected, and the sensitivity of the receiving system. Therefore, in order to realize an NQR remote sensing device with high transmission efficiency and high reception sensitivity, it is necessary to separate the transmitting coil and the receiving coil, and to individually optimize the size and shape of both coils.

However, in the first conventional example described above, since the same coil is used for the transmitting coil and the receiving coil, the transmitting pulse is difficult to cut, and the size and shape of the transmitting coil and receiving coil are individually optimized. Since it is not possible to do so, NQ
There is a problem in that there is a limit to how high the sensitivity and efficiency of the R remote detection device can be made.

[0008] Furthermore, in the coil design of the second conventional example, a ``crossed coil method'' is used in which the transmitting and receiving coils are separated by making the axes of the transmitting coil and receiving coil orthogonal to each other to reduce coupling between the coils. ing. However, in NQR, nuclear magnetic resonance (Nuclear M
agnetic resonance (abbreviation NMR)
However, most of the components of the received high-frequency magnetic field (NQR signal) are in the same direction as the transmitted high-frequency magnetic field, so there is a problem that the NQR signal cannot be efficiently received.

Furthermore, in the third conventional example, it is possible to separate the transmitting coil and receiving coil while keeping the coil axes parallel; however, the size, shape, and position of the transmitting coil and receiving coil Depending on the relationship, the coupling between the coils becomes large, making it difficult to cut the transmission pulse, and reducing the transmission efficiency and reception sensitivity. Therefore, there are restrictions on the size, shape, and positional relationship of the transmitter coil and the receiver coil, and there is still a problem in that there is a limit to increasing the sensitivity and efficiency of the NQR remote detection device.

An object of the present invention is to be able to separate the transmitter coil and receiver coil while keeping the coil axes parallel, and to improve the sharpness of the transmitter pulse, as well as to improve the size and shape of the transmitter coil and receiver coil. The object of the present invention is to provide a pulsed NQR device whose arrangement can be individually optimized, and to realize a highly sensitive and highly efficient NQR remote sensing device.

[0011]

[Means for Solving the Problems] The above object is to provide a switch or a switch that disconnects a receiving coil tuning circuit when a high frequency pulse is applied and disconnects a transmitting coil tuning circuit when a high frequency pulse is not applied. This is achieved by adding an electric circuit.

0012

[Operation] In the above structure, when a high frequency pulse is applied, for example, a switch added to the tuning circuit for the transmitting coil is closed, and a switch added to the tuning circuit for the receiving coil is opened. As a result, the transmitting coil tuning circuit operates as a resonant circuit, but the receiving coil tuning circuit does not operate as a resonant circuit because it is disconnected. Therefore, even if the axes of the transmitting coil and the receiving coil are parallel to each other, the coupling between the two is small, and the transmitting coil can transmit a high-frequency magnetic field without being influenced by the receiving coil.

Conversely, when no high-frequency pulse is applied, the switch added to the transmitting coil tuning circuit is opened, and the switch added to the receiving coil tuning circuit is closed. As a result, the receiving coil tuning circuit operates as a normal resonant circuit, but since the transmitting coil tuning circuit is disconnected, it does not operate as a resonant circuit. Therefore, even if the axes of the transmitting coil and the receiving coil are parallel to each other, the coupling between the two is small, and the receiving coil can receive the NQR signal without being influenced by the transmitting 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 regardless of their size, shape, and positional relationship. Therefore, the pulse sharpness is improved, and the transmitting coil and receiving coil can be individually optimized without reducing either the transmitting efficiency or the receiving sensitivity, and it is possible to realize a highly sensitive and highly efficient NQR remote sensing device.

[0015] In the above explanation, the added switch or electric circuit has the function of disconnecting the receiving coil tuning circuit when a high frequency pulse is applied, and the function of disconnecting the receiving coil tuning circuit when a high frequency pulse is not applied. Although it has been described as having both the function of cutting off the tuned circuit, it goes without saying that even having only one of the functions has a certain effect.

[0016]

Embodiment 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 from the controller 4 are input to the high frequency power amplifier 5 to create a high frequency pulse train. . Next, this pulse train is input to the transmitting coil 7 through the transmitting coil tuning circuit 6, and a pulsed high-frequency magnetic field is irradiated onto the inspection object 9 placed in the shield box 8.

Furthermore, the 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 a tuning circuit 11, the signal is amplified by a low noise amplifier 12. The amplified signal is further phase-detected by a phase detector 13, then passed through a frequency filter 14 to narrow the frequency band, and then sent to 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 target substance 1 is contained in the inspection target 9, depending on whether there is a peak due to the target substance 1 in the frequency spectrum. do.

Here, in the transmitting coil tuning circuit 6,
As shown in FIG. 1(b), a switch 19 is connected in series to the variable capacitor 18 for adjusting the resonant frequency, and the switch is closed by the controller 4 when a high-frequency pulse is applied, and closed when the high-frequency pulse is not applied. Sometimes it is controlled to open. Also, in the receiver coil tuning circuit 11, a switch 20 is added in series with a variable capacitor 21 for adjusting the resonance frequency, and the switch 20 is opened when a high frequency pulse is applied by the controller 4. control to close when not in use. Note that 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, but may be added in series to the variable capacitors 17 and 22 for adjusting the impedance. By controlling the switches 19 and 20 in this manner, even if the axes of the transmitter coil 7 and the receiver coil 10 are parallel, the coupling between them is small and they do not affect each other, which improves the pulse cutting. , each can be optimized individually.

A specific example of the apparatus of this embodiment will now be described.

Target substance 1 is RDX (hexahydro, 1,3,5-tri), which is the main component of plastic bombs.
nitro, 1,3,5-triazine) 600g
If the object to be inspected 9 is carry-on baggage on an airplane (capacity: about 50 liters), the transmitting coil 7 should be a coil with a diameter of about 50 cm and about 3 turns, which can efficiently irradiate a high-frequency magnetic field into the object to be inspected 9 with low power. A solenoid coil is suitable. In addition, as the receiving coil 10, RDX60, which is a target substance existing in a space with a volume of 50 liters or more, is used.
It is preferable to use a solenoid coil with a diameter of 100 cm and about 3 turns, which can detect 0 g with high sensitivity, and arranged on the outer side on the same axis as the transmitting coil. Here, the target substance 1 contained inside the test object 9 does not necessarily have to be inside the transmitting coil 7 or the receiving coil 10.

[0022] With the above device, if a high-frequency pulse train with a frequency of 5.2 MHz, a pulse width of 200 μsec, a pulse interval of 30 msec, and a pulse strength of about 2 Gauss is transmitted, and the FID signals after the pulses are added about 256 times, a volume of 50 liters can be inspected. 600 g of the target substance RDX in the target object 9 can be detected.

[0023] If the conditions differ from those in the above specific example, the sizes of the transmitting coil and the receiving coil may be changed to be optimal. For example, if the power input to the transmitting coil can be increased, it is better to make the transmitting coil larger, and if there is less target material, it is better to make the receiving coil smaller. Therefore, depending on the conditions, the transmitting coil may be larger than the receiving coil.

According to this embodiment, not only can the transmission pulse be sharply cut, but also the transmitter coil and the receiver coil can be individually optimized, making it possible to realize a highly sensitive and highly efficient pulsed NQR remote sensing device. effective. Furthermore, in this embodiment, since the opening/closing control of the switch is actively performed by the controller, there is an advantage that precise timing control can be performed without being influenced by the characteristics of electrical components or circuits.

Next, a second embodiment of the present invention will be explained using FIG. 2.

In this embodiment, instead of the switches added in the transmitting coil tuning circuit and the receiving coil tuning circuit, a circuit composed of a capacitor, a coil, and a set of diodes with opposite polarities is used. This embodiment differs from the first embodiment in that a controller is not required for control. An equivalent circuit of the transmitting coil tuning circuit and the receiving coil tuning circuit used in this example is shown in FIG. 2(b), and the operation thereof will be described below.

When a transmission pulse is being applied, the set diodes 23 and 26 are in a conductive state. Therefore, the circuit on the transmitting side is in the same state as if the switch had been shorted and closed. On the other hand, in the circuit on the receiving side, the variable capacitor 27, coil 28, and capacitor 29 form a parallel resonant circuit, and the impedance becomes high, resulting in the same state as if the switch were open.

Conversely, when no transmission pulse is applied, the set diodes 23 and 26 are non-conductive. Therefore, the circuit on the transmitting side includes a variable capacitor 24 and a coil 25.
forms a parallel resonant circuit and the impedance becomes high, resulting in the same state as if the switch were open. On the other hand, in the receiving side circuit, the variable capacitor 27 and coil 28 are disconnected.
Capacitor 29, variable capacitor 21 for resonant frequency adjustment
, the variable impedance adjustment capacitor 22, and the receiving coil 10 form a resonant circuit, and the same effect as a closed switch can be obtained. Note that the variable capacitor 21 for adjusting the resonance frequency can be omitted if the capacitor 29 is made into a variable capacitor so that it also functions as a variable capacitor for adjusting the resonance frequency.

As described above, these circuits effectively operate in the same way as opening and closing a switch in synchronization with the application and non-application of transmission pulses, so that the same effects as in the first embodiment can be obtained. Furthermore, since this embodiment does not require a controller, it has the advantage that the device configuration can be simpler.

Further, a third embodiment of the present invention will be explained using FIG. 3.

This embodiment differs from the first embodiment in that the transmitting coil is divided into N coil segments 30, and (N-1) inserted capacitors 31 are connected in series between them. There is. 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 transmitting coil is not divided, so that the tuning frequency does not deviate. This reduces the high voltage applied across the coil piece and capacitor to 1/N.
The power that can be input to the transmitter coil can be increased without causing discharge. Note that the division does not necessarily have to be equal, but since the highest voltage is applied to the coil piece with large inductance and the capacitor with small capacitance, care must be taken to prevent discharge from occurring in these parts. . Furthermore, although this embodiment shows an example in which a switch is added to the tuning circuit, 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 input to the transmitting coil can be increased without causing discharge.

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

In this embodiment, two transmitting coils 7, which are smaller than the receiving coil 10 and connected in series or in parallel, are arranged on both sides of the object to be inspected 9, and by moving them in the direction of the arrow in FIG. Covers the coil's receivable area. Other points are similar to the first to third embodiments. Note that it is not necessary to move the two transmitting coils together, and other methods may be used as long as the method covers the receivable area of the receiving coil. Furthermore, for example, when the amount of target substance is small and the NQR signal is small, the transmitter coil may be fixed and the smaller receiver coil may be moved.

According to this embodiment, in addition to the same effects as those of the first to third embodiments, a large object to be inspected can be inspected with a low-power high-frequency amplifier that is inexpensive, easy to manufacture, and easy to obtain. This has the effect of making it possible to inspect a large object even if the amount of the target substance is small, and making the NQR remote detection device more sensitive and efficient.

[0036]

[Effects of the Invention] As explained above, according to the present invention,
In a pulsed nuclear quadrupole resonator, the transmitting coil and receiving coil can be separated while keeping their respective coil axes parallel, allowing for better cutting of the transmitting pulse, and allowing the size, shape, and arrangement of the transmitting coil and receiving coil to be separated. This has a remarkable effect on realizing a highly sensitive and highly efficient pulsed NQR remote sensing device.

[Brief explanation of drawings]

FIG. 1: (a) Device configuration diagram of 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. 2: (a) Device configuration diagram of 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 transmitting coil and a tuning circuit for the transmitting coil according to a third embodiment of the present invention.

FIG. 4 is an explanatory diagram showing the arrangement and movement of a transmitter coil and a receiver coil in a fourth embodiment of the present invention.

[Explanation of symbols]

1...Target substance 2
...High frequency generator 3...DC pulse generator
4...Controller 5...High frequency power amplifier
6... Tuning circuit for transmitting coil 7... Transmitting coil 8...
Shield box 9...Object to be inspected
10... Receiving coil 11... Tuning circuit for receiving coil 12... Low noise amplifier 13... Phase detector
14...Frequency filter 15...Digital adder 16...Data processing device 1
7, 22... variable capacitor 18 for impedance adjustment,
21... Variable capacitor for resonant frequency adjustment 19, 20... Switch 23, 26... Group diode 24, 27... Variable capacitor 25, 28... Coil 29... Capacitor 30
…Coil fragment 31…Insert capacitor

Claims (4)

[Claims] Claim 1: Consisting of a high-frequency pulse generating means, a transmitting coil tuning circuit, a transmitting coil, a receiving coil, a receiving coil tuning circuit, and a means for amplifying and processing a high-frequency signal, the shaft of the transmitting coil In a pulsed nuclear quadrupole resonance device in which the axes of the receiving coil and the receiving coil are parallel to each other, the tuning circuit for the receiving coil is disconnected when a high-frequency pulse is applied, and the tuned circuit for the receiving coil is disconnected when the high-frequency pulse is not applied. 1. A pulsed nuclear quadrupole resonator comprising a switch or an electric circuit having at least one of the functions of disconnecting a transmission coil tuning circuit. 2. The pulsed nuclear quadrupole resonator according to claim 1, wherein the electric circuit is composed of a parallel resonant circuit including a capacitor and a coil, and a set of diodes having opposite polarities. . 3. The pulsed nuclear quadrupole resonance device according to claim 1, wherein the transmitting coil is divided into a plurality of parts, and a capacitor is inserted in series between the divided parts. 4. The pulse core according to claim 1, further comprising a mechanism for moving the transmitting coil or the receiving coil, so that the relative positions of the two can be varied. Polar resonator.