RU2114419C1 - Method of radiation computational vibrotomography - Google Patents

Abstract

FIELD: study of materials and objects by methods of radiation computational tomography. SUBSTANCE: method consists in inspection of at least one layer of examined object by beam of penetrating radiation, in registration of radiation passed through object by detection system, in primary processing of signals of detection system with generation of measurement signals, in processing of measurement signals with generation of set of reconstructive data and in reconstruction of image of layer of examined object. As result of primary processing of signals there is extracted one variable component of mentioned signals as minimum on one frequency of vibrations of examined object and set of reconstructive data is obtained on the basis of extracted variable component. EFFECT: method ensures possibility of study of dynamic periodic processes going on in objects with structures closed for mechanical or optical access. 6 cl, 1 dwg

Description

 The invention relates to the study of materials and objects by methods of radial computational tomography.

 A known method of radial computational tomography, in which obtaining projection data is accompanied by the operation of their double differentiation according to the coordinate of the projection, which allows to more clearly identify the contours of the internal structure of the volume [1].

 The closest technical solution is the method of radiation computed tomography, which consists in illuminating at least one layer of the object under study by a beam of penetrating (x-ray) radiation along the set of trajectories (directions) located in the plane of this layer, which is realized by means of a linearly rotational scanning relative movement of the object under study and transmission beam, registration in each of the directions of radiation transmitted through the studied object by the detection system Hovhan, the primary detection system processing signals to obtain measurement signals, processing the measurement signals of a predetermined algorithm to obtain a set of data reconstruction and restoration of the image layer of the test object based on the obtained set of reconstruction data [2].

 Known methods do not provide the possibility of tomographic study of the processes of dynamic oscillations of objects, since the processing results in an averaged static image of the internal structure of the object with possible artifacts from the oscillatory process, the nature and parameters of which are not disclosed.

 The objective of the invention is to provide the possibility of studying dynamic batch processes occurring in objects with a structure that is closed to mechanical or optical access.

 According to the invention, the problem is solved by the method of radiation computational vibrotomography, which consists in illuminating at least one layer of the object under study by a beam of penetrating radiation in the aggregate of directions located in the plane of the specified layer, registering in each direction of the radiation transmitted through the object under investigation a detection system, primary signal processing of the system detection to receive measuring signals, processing of measuring signals to obtain a set reconstructive data and reconstructing the image of the layer of the investigated object on the basis of the obtained set of reconstructive data, in which (the method) during the primary processing of the signals of the detection system, at least one variable component of these signals is extracted at least at one oscillation frequency of the studied object and a set of reconstructive data is obtained based on the selected variable component.

In particular, the in-phase with the oscillations of the test object and the 90 ^° phase-shifted reactive variable components of the detection system are extracted and sets of reconstructive data for the in-phase and reactive components are obtained.

 Based on the reconstructive data sets for the in-phase and variable components, at least one additional reconstructive data set is formed from the group including the reconstructive data set of the oscillation amplitude module, the reconstructive data set of the oscillation phase and the reconstructive data set of the square of the oscillation phase.

 In particular, the selection of the variable components of the signals of the detection system is performed at the fundamental frequency of the oscillations of the object under study and at least at its one harmonic.

 In one embodiment, the object is driven into forced vibrations with a given frequency.

 In this case, during the study, it is possible to change the oscillation frequency of the investigated object, and at each frequency of forced vibrations, the studied object is translucent and the transmitted radiation is recorded in the entire set of directions, the signal components of the detection system are isolated at each of the forced oscillation frequencies, and the corresponding sets of reconstructive data.

 In another embodiment, when the object’s vibrations have an unknown frequency spectrum, the object’s oscillation spectrum is preliminarily analyzed and one or more variable components of the detection system are extracted at one or more representative frequencies of the specified spectrum.

 The above set of general and private essential features of the claimed invention allows us to identify the interaction zones of the oscillating parts of the internal structure of the studied object with the probe beam during the known tomographic control procedure, which leads to modulation of the intensity of the beam transmitted through the object at the frequency of the corresponding oscillation. The procedure for isolating the modulation components allows us to form a picture of the dynamic behavior of the investigated volume at the selected frequency.

 The invention is illustrated in the drawing, which shows a diagram of an X-ray tomograph, illustrating the principles of the method of radiation computing vibrotomography.

 The X-ray tomograph contains an X-ray emitter 1, which is associated with a collimator 2, forming a narrowly collimated probe beam 3 of x-ray radiation. The object 4 under study is mounted on a vibration platform 5 connected with a vibrator 6 and a scanning system 7, which includes step drives 8 and 9 of linear movement and rotation of the platform 5 with object 4, as well as a timer 10 that sets the time of a single count during linear movement and the interval actuation of the drive 9 rotation. Drives 8 and 9 are equipped with coordinate outputs on which the signals of the current position (linear and angular) of the object 4 are generated. The vibrator 6 is equipped with a synchronizing output on which the frequency and phase signal of the vibrator 6 is generated.

Behind the test object 4, a radiation detector 11 is installed, to which an amplifier-driver 12 is connected. The output of the amplifier-driver 12 is output to the first synchronous detector 13, the second, phase-shifted 90 ^o relative to the first, synchronous detector 14 and processing system 15 for restoring the tomographic Images. Synchronous detectors 13 and 14 have control inputs to which a synchronizing output of the vibrator 6 is connected.

 The processing system 15 contains three input memories 16, 17, 18, which receive signals with the output, respectively, of the amplifier-former 12, the first 13 and second 14 synchronous detectors. The input memories 16, 17, 18 have timer inputs connected to the output of the unit time reference of the timer 10 of the scanning system 7, and coordinate inputs connected to the corresponding outputs of the drives 8 and 9. The input memories 16, 17, 18 are connected to parallel blocks 19, 20, 21 processing in which the same algorithm for generating reconstructive data sets is implemented. The outputs of the processing units 19, 20, 21 are connected to the inputs of the first three output memories 22, 23, 24. In addition, the outputs of the units 20 and 21 are connected to the inputs of the amplitude reconstructive data set generation unit 25 and the oscillation phase reconstructive data set formation unit 26, on the output of which is included in a block 27 for generating a set of reconstructive data of the square of the oscillation phase. The outputs of blocks 25, 26, 27 are connected to the second three output memories 28, 29, 30. The outputs of the memories 22-24, 28-30 through the interface unit 31 (interface) are connected to the video monitoring device 32.

 It should be noted that in the embodiment shown in the drawing, the detector 11 operates in a counting mode, due to which there is no need to use analog-to-digital converters at the inputs of the memory 16-18. When the detector 11 is in analog mode, a conventional amplifier (or a preamplifier-logarithmic amplifier chain) is switched on behind it, and analog-to-digital converters are switched on at the inputs of the memory 16-18.

 The method of radiation computing vibrotomography is as follows.

Using an adjustable collimator 2 form a narrowly collimated probe beam 3 of x-ray radiation. Turn on the vibrator 6, with which the platform 5 with the investigated object 4 is driven into oscillations with a certain frequency ω ₁ and a certain amplitude. Scanning the test object 4 by the probe beam 3 is carried out in a stepped mode by cycles such as linear movement of the platform 5 with the drive 8 - rotation of the platform 5 by a given angle by the drive 9 - linear movement in the opposite direction of the drive 8, etc., i.e. scan mode corresponds to 1st generation topography systems. The stop time of the platform 5 in each position, i.e. single count time, set by timer 10.

, где i и j - обозначения координатных положений объекта 4. На выходе первого синхронного детектора 13 формируется сигнал, величина счета которого во втором входном ЗУ 17 системы обработки 15 за время каждого единичного отсчета соответствует синфазной с колебаниями объекта составляющей

амплитуды модуляции на частоте ω₁ интенсивности прошедшего через объект 4 зондирующего пучка 3. На выходе второго, сдвинутого по фазе на 90^o относительно первого, синхронного детектора 14 формируется сигнал, величина счета которого в третьем входном ЗУ 18 системы 15 обработки за время каждого отсчета соответствует сдвинутой по фазе на 90^o (реактивной) составляющей

амплитуды модуляции на частоте ω₁ интенсивности прошедшего через объект 4 пучка 3.The signals from the output of the amplifier-former 12, which are amplified and generated count pulses of the detector 11, are fed to the input memory 16 of the processing system 15, the first and second synchronous detectors 13, 14. In the memory 16 for each unit in the cells corresponding to the coordinate signals from the corresponding outputs of the drives 8 and 9, a signal is generated that characterizes the constant component of the intensity

, where i and j are the designations of the coordinates of the object 4. At the output of the first synchronous detector 13, a signal is generated whose count in the second input memory 17 of the processing system 15 during each unit reference corresponds to the in-phase component with the oscillations of the object

the modulation amplitude at a frequency ω _{1 of the} intensity of the probe beam 3 transmitted through the object 4. At the output of the second, 90 ^o phase-shifted relative to the first, synchronous detector 14, a signal is generated, the count of which in the third input memory 18 of the processing system 15 during each reading corresponds to 90 ^o phase (reactive) component

modulation amplitudes at a frequency ω _{1 of the} intensity of beam 3 passing through object 4.

, которые подвергаются обработке на основе идентичных алгоритмов восстановления в блоках 19, 20, 21, в которых формируются наборы реконструктивных данных {α(x,y)},{α^A(x,y)},{α^R(x,y)} , где α,α^A,α^R - поставленная, синфазная и реактивная составляющие коэффициента поглощения; x, y - координаты матрицы восстановления. Эти наборы реконструктивных данных записываются в первые три выходных ЗУ 22, 23, 24.Thus, in the input memory 16, 17 18 data sets are formed

, which are processed on the basis of identical recovery algorithms in blocks 19, 20, 21, in which reconstructive data sets {α (x, y)}, {α ^A (x, y)}, {α ^R (x, y) are formed }, where α, α ^A , α ^R are the delivered, in-phase and reactive components of the absorption coefficient; x, y are the coordinates of the reconstruction matrix. These reconstructive data sets are recorded in the first three output memories 22, 23, 24.

соответствующий модулю амплитуды модуляции интенсивности прошедшего через объект 4 зондирующего пучка 3, а в блоке 26 - дополнительный набор реконструктивных данных
{φ(x,y)} = {arctgα^A(x,y)/α^R(x,y)},
соответствующий фазе модуляционных колебаний интенсивности пучка 3 после объекта 4. На основе набора реконструктивных данных {φ(x,y)} блоком 26 формируется вспомогательный набор реконструктивных данных
{φ²(x,y} = {arctg²α^A(x,y)/α^R(x,y)}.
Наборы реконструктивных данных

записываются во вторые три выходные ЗУ 28, 29, 30.In addition, based on the reconstructive data sets {α ^A (x, y)} and {α ^R (x, y)} generated by blocks 20 and 21, an additional set of reconstructive data is generated in block 25

the corresponding modulus of the amplitude of the modulation of the intensity of the probe beam 3 transmitted through the object 4, and in block 26, an additional set of reconstructive data
{φ (x, y)} = {arctanα ^A (x, y) / α ^R (x, y)},
corresponding to the phase of modulation oscillations of the beam intensity 3 after object 4. Based on the set of reconstructive data {φ (x, y)}, block 26 forms an auxiliary set of reconstructive data
{φ ² (x, y} = {arctan ² α ^A (x, y) / α ^R (x, y)}.
Reconstructive Datasets

are recorded in the second three output memories 28, 29, 30.

 A set of reconstructive data {α (x, y)} characterizes the distribution of the absorption coefficient of x-ray radiation over the cross section of the studied object 4.

A set of reconstructive data {α ^A (x, y)} characterizes the distribution of the in-phase variable component of the absorption coefficient over the cross section of the studied object 4. This value is maximum near moving boundaries, increasing at resonance.

A set of reconstructive data {α ^R (x, y)} characterizes the distribution of the reactive variable component of the absorption coefficient over the cross section of the studied object 4. This value is maximum near moving boundaries, turning to zero at resonance.

характеризует распределение амплитуды переменной составляющей коэффициента поглощения по сечению исследуемого объекта 4.Reconstructive dataset

characterizes the distribution of the amplitude of the variable component of the absorption coefficient over the cross section of the investigated object 4.

 A set of reconstructive data {φ (x, y)} characterizes the phase distribution of the variable component of the absorption coefficient over the cross section of the studied object 4.

The reconstructive data set {φ ² (x, y)} is used to more clearly identify the resonance regions, since this value vanishes where resonance vibrations occur and equals ~ (π / 2) ² at the points where the frequency of the exciting force is outside the resonance peak. Moreover, the function φ ² (x, y) has no singularities near the boundaries of regions with different absorption coefficients up to a calculation error.

 The indicated reconstructive data sets from the output memories 22-24, 28-30 through the interface unit 31 are output to the video monitoring device 32 individually or in combination.

For a more detailed description of the oscillatory process in the studied object 4, one can additionally use the variable components of the intensity modulation of the probe beam 3 behind the object 4 at harmonics of the fundamental frequency ω ₁ . In this case, additional processing channels constructed identically to the above can be used. The information obtained in such channels is useful for identifying areas of the object where nonlinear processes take place either due to large oscillation amplitudes or due to nonlinearities of a structure such as cracks.

 In the course of research, platform 5 can be driven into oscillations with different frequencies and receive vibrotomograms at these different frequencies. Such a procedure may be useful in the study of resonant vibrational processes.

 In the case of natural vibrations of object 4 with unknown frequencies, to implement the method, it is necessary to perform the operation of spectral analysis of the vibrations of object 4 and select one or several representative frequencies of this spectrum to construct the vibrotomogram.

 It has been experimentally shown that vibration of metal structures with amplitudes of the order of 1 μm leads to modulation of the x-ray beam intensity to 1%, which is available for measurement by computed tomography methods. With the dimension of the image recovery matrix 320x320 and the thickness of the translucent object up to 30 cm, the spatial resolution in the plane of the studied layer is 0.1-0.3 mm with a vibration detection threshold of 0.45 - 3 μm.

Claims (7)

 1. The method of radiation computational vibrotomography, which consists in illuminating at least one layer of the object under study by a beam of penetrating radiation in the aggregate of directions located in the plane of the specified layer, recording in each direction of the radiation transmitted through the object under study a detection system, primary processing of the signals of the detection system to obtain measurement signals, processing of measuring signals to obtain a set of reconstructive data and image recovery the layer of the object under study on the basis of the obtained set of reconstructive data, characterized in that during the primary processing of the signals of the detection system, at least one variable component of these signals is extracted at least at one oscillation frequency of the object under study and the set of reconstructive data is obtained on the basis of the extracted variable component . 2. The method according to p. 1, characterized in that they produce in-phase with the oscillations of the test object and phase-shifted by 90 ^o reactive variable components of the signals of the detection system and receive sets of reconstructive data for the in-phase and reactive components.  3. The method according to p. 2, characterized in that based on the reconstructive data sets for the in-phase and reactive components, at least one additional reconstructive data set is formed from the group including the reconstructive data set of the oscillation amplitude module, the reconstructive data set of the oscillation phase and the reconstructive set data of the squared phase of the oscillations.  4. The method according to PP. 1 - 3, characterized in that the allocation of the variable components of the signals of the detection system at the fundamental frequency of the oscillations of the investigated object and at least one of its harmonics.  5. The method according to PP. 1 to 4, characterized in that the test object is driven into forced oscillations with a given frequency.  6. The method according to p. 5, characterized in that during the study, the frequency of the forced vibrations of the object under study is changed, at each frequency, the object under study is translucent and the transmitted radiation is recorded in the whole set of directions, the variable components of the detection system signals are isolated at each of the forced oscillation frequencies and generating the corresponding sets of reconstructive data.  7. The method according to PP. 1 to 4, characterized in that they analyze the spectrum of oscillations of the investigated object and the selection of at least one variable component of the signals of the detection system is carried out at least at one representative frequency from the specified spectrum.