SU1490480A1 - Device for determining profile of nonmagnetic object surfaces - Google Patents

Abstract

This invention relates to a measurement technique. The aim of the invention is to improve the performance of measurements by eliminating scanning on the third coordinate by automatically keeping the sensitive point on the surface under study. The principle of operation of the device is based on the sensitive point method. A container 10 filled with fluid 9 containing a core with a magnetic moment (for example, water) in which the object 16 is immersed is placed in the measurement zone and exposed to a magnetic field, which is a superposition in the measurement zone of a constant uniform field created by a magnetic system 1, an inhomogeneous low frequency field created by three pairs of gradient coils 2 and 3, 4 and 5, 6 and 7, and a radio frequency coil 8 with nuclear magnetic resonance frequency (NMR) of the dermis. As a result of synchronous detection of the NMR signal at a frequency corresponding to the value of the magnetic induction at the sensitive point, the constant component of the output signal contains only the contribution from the cores located in the region of the sensitive point. Consequently, in any of the coordinates, for example X, the field depends on time for all X, except X = Xo, corresponding to the sensitive point. Contributions to the NMR signal will be made by those cores that are in a layer of thickness ΔX near the X = Xo plane. The position of the sensing plane is determined by the ratio of the currents in the corresponding pair of gradient coils 2 ... 7. The free nuclear induction signal from the radio frequency coil through the matching and protection unit 12 enters the receiving unit 13. The position of the third sensitive plane depends on the control signal coming from the output of the receiving unit 13 to the variable gradient control unit 14, thus feedback is effected with the help of which the sensitive point is kept on the surface under study, which allows avoiding scanning on the third coordinate and thereby reducing the measurement time. 2 Il.

Description

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surface. The principle of deistysil device. Based on the method of sensitive points. A container 10 filled with a liquid 9 containing a core, possessed by a magnetic moment (for example, water) in which the object 16 is immersed, is placed in the measurement zone and is exposed to a magnetic field, which is a superposition in the constant homogeneity measurement zone created by a magnetic system 1, a non-uniform low-frequency field created by three pairs of gradient coils 2 and 3, 4 and 5, 6 and 7, and the field of radio frequency katuiki 8 with nuclear magnetic resonance frequency (NMR) of the liquid. As a result of the synchronous detection of the 5SR signal at the frequency corresponding to the value of the magnetic induction at the sensitive point, the constant composition of the output signal contains only the contribution from the cores located in the region of the sensitive point. Consequently

The invention relates to the field of measurement technology and can be used to determine the profile of the external and internal surfaces of non-magnetic objects.

The aim of the invention is to increase productivity by scans on the third coordinate by automatically keeping the sensitive point on the surface under study.

FIG. 1 shows a functional diagram of the device; in fig. 2 are timing diagrams showing changes in magnetic field gradients.

The device contains a magnetic system 1, which is a source of a constant uniform magnetic FIELD, three pairs of gradient coils 2 and 3, 4 and 5, 6 and 7, the axes of which are mutually perpendicular, being the source of a non-uniform low-frequency magnetic field, radio frequency coil 8, placed in the superposition zone of the magnetic system I and gradient coils 2, ... 7, fluid 9 containing cores with magnetic moment, capacitance 10 filled with fluid 9 and set to any of the coordinates, for example X, the field depends on time for all X kro ie corresponding to the sensitive point. Contributions to the NMR signal will be made by those cores that are in a layer of thickness DX near the plane. The position of the sensing plane is determined by the ratio of the currents in the corresponding pair of gradient coils 2 ... 7. The signal of free nuclear induction from the radio frequency coil through the block 12 of the coordination and protection enters the receiving unit

13. The position of the third sensitive plane depends on the control signal coming from the output of the receiving unit 13 to the block 14 with a variable gradient, thus providing feedback, by means of which the sensitive point is kept at the test surface, thus avoiding scanning third coordinate

and shorten the measurement time. 2 Il.

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A radio frequency impulse generator 11, the output of which is connected to the radio frequency coil 8, connected in series with the radio frequency coil 8 of the matching and protection unit 12, the receiving unit 13 and the variable gradient control unit 14, the first output of which is connected to

The inputs of the gradient coils 2, ... 7, and the recording unit 15, the input of which is connected to the second output of the control unit 14.

The principle of operation of the device is based on the method of a sensitive point, the essence of which is that the entire investigated volume, with the exception of one of its small element — the sensitive point — is subjected

Q action of a pregnant magnetic field of low (sound) frequency. Under these conditions, synchronous detection of nuclear magnetic magneto resonance (NMR) at the QO frequency of the corresponding field E 3 sensitive point is performed. The constant component of the output signal contains only a contribution from the cores located in the region of the sensitive point, since the NMR spectrum from the rest of the volume under study is modulated in frequency. This method is implemented in practice with the help of three time-varying gradients of a magnetic field, the directions of which are mutually orthogonal, and the magnitude oscillates with different frequencies. If the gradient, for example, on the coordinate X, G, (t) has the form

G, (t) G, sinJ2, t. (1) where Q, is the frequency of the oscillations qr {and then the magnetic field in the studied volume changes according to the law

Bp (X, t) (X-X,) G, sinS2, t. (2)

Relationship (2) shows that the field Bd (X, C) depends on the time for all X except (,. Entering the observed NMR signal will give those cores that are in a layer of thickness X near the plane passing through Xp, perpendicular to the X axis. In practice, an oscillating gradient is created by a pair of coaxial katuiek fed by alternating current, the magnetic fields of which are directed towards each other.The position of the sensing plane is determined by the ratio of the currents in these coils.

A device for determining the surface profile of non-magnetic objects works as follows (see Fig. 1).

The object to be measured 16 is placed in a container 10, which is a measurement zone filled with liquid 9 containing a core with a magnetic moment, preferably protocontaining, for example, water. The magnetic system creates a constant uniform magnetic field in the measurement zone, causing polarization

The fluid core 9. At the same time, the 45 ° C of the receiving unit 13 is measured at the point of two-dimensional magnetic field that is characterized by gradients in three mutually perpendicular directions, and the frequency of change of each gradient must be different. A variable inhomogeneous magnetic field is created by three pairs of gradient coils 2 and 3, 4, and 5.6 and 7. The currents causing these gradients are created by a variable gradient control unit 14, which creates alternating currents in each pair of gradient coils 2, 3, 5, 5, and 7, which differ in amplitude and are in antiphase. The ratio of the amplitudes of the currents in each pair of coils determines the positions of the sensing plane; the intersection of the sensitive planes created by each pair of sensitive katuiek determines

position of the sensing point. With the help of the first pair of rollers 2 and 3, a sensitive plane is distinguished, which is perpendicular to one of the axes, na nntiep, Z; similarly, using the second pair of coils 4 and 5, the plane perpendicular to the Y axis is selected; the intersection of these two planes gives a sensitive line parallel to the X axis. And, finally, using the third

a pair of coils 6 and 7 is a sensitive point. Control block 4 forms the control signals dp of the gradient system in such a way that the gradients GX, GU, G when the object 16 is not present in the measurement 16 have the form shown in FIG. 2. When measuring the profile of the surface of an object 16 at each moment of time, the values of the stress control gradients G, (,

GU, G correspond to the X, Y, Z coordinates of the surface points of the object. The RF pulse generator 11 generates pulses arriving at the RF coil 8 and exciting a free nuclear signal in fluid 9, which through the matching and protection unit 12 enters the receiving unit 13 and from its output into the control unit 1A.

The position of the sensitive plane depends on the signal at the output of the receiving unit 13. If the sensitive point is in a liquid, then under the action of the control signal from you

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If the point falls inside the measured object 16, the signal at the output of the receiving unit 13 disappears, and the direction of change of the gradient G automatically changes to the opposite. Thus, the sensitive point is constantly held on the surface of the measured object 16. The signal from the second output of the control unit 14, proportional to the coordinates of the position of the sensitive point, goes to the recording unit 15, in which

Form 1 is the image of the surface profile of the measurement object 16.

Claims (1)

Thus, the operation of holding a sensitive point on the surface of the object being measured, performed automatically, eliminates scanning on the third coordinate and thereby avoiding scanning the sensitive point of the whole object under study and, consequently, improving the measurement performance. It should also be noted that the device allows measurements to be made in hard-to-reach or inaccessible places of an object, for example, to determine the profile inside the product surface. Invention Formula A device for determining the surface profile of non-magnetic objects, containing a source of a constant uniform magnetic field in the form of a magnetic system, a source of a non-uniform low-frequency magnetic field in the form of three pairs of gradient GXX WITH d I | V4VA carcasses, the axes of which are mutually perpendicular, the radio frequency coil, placed in the zone of superposition of magnetic fields and three pairs of gradient coils, the generator of equal frequency pulses, the output of which is connected to the radio frequency coil, the matching unit and connected to a radio frequency coil, a receiving unit whose input is connected to the output of the matching and protection unit, a variable gradient control unit, the first output of which is connected to the inputs of gradient coils, and a recording unit whose input is connected to the second output of the variable gradient control unit, different the fact that, in order to increase productivity, it is provided with a container for placing the object under study, filled with a liquid containing cores, having a magnetic moment, and installed inside the RF coil, and the output of the receiving unit is connected to the input of the variable gradient control unit.