RU2530181C1 - Calibration method of ultrasonic antenna array installed on prism - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: ultrasonic signals are emitted by means of a variety of elements of an antenna array to a specimen of known thickness, and ultrasonic signals are received, which are reflected from a side drilling hole of known diameter at the specified depth; a variety of ultrasonic echo signals is recorded for the chosen configuration of emission and reception, which is determined by a list of pairs of emitting and receiving elements; parameters of echo signals are calculated depending on speed of a sound in a prism and its geometrical parameters; measured and calculated echo signals are compared to each other, and such a value of speed of longitudinal ultrasonic wave in the prism and its geometrical parameters are searched, which provide minimum difference and which will be considered as a calibration result; with that, as a result of calibration of an ultrasonic antenna array, time of run in a protector of the antenna array is determined as well.

EFFECT: providing a possibility of determining actual coordinates of centres of piezoelectric elements with an accuracy of one eighth of wave length.

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Description

The invention relates to the field of ultrasonic non-destructive testing.

A known method of calibrating an ultrasonic antenna array mounted on a prism, carried out by measuring the propagation velocity of ultrasonic signals and their travel time in a prism, is implemented in an ultrasonic flaw detector "OmniScan MX2" (See the official website of the company OLYMPUS - http: //www.olympus- ims.com/en/omniscan-mx2/).

The disadvantage of this method is the multi-stage procedures for measuring the propagation velocity of ultrasonic signals and their travel time in a prism, the use of three samples, one of which has a complex structure, and the inability to determine the following parameters of an ultrasonic antenna array mounted on a prism: prism boom, travel distance in a prism along the central beam, the angle of the prism, the delay time in the matching layer of the antenna array.

The closest adopted for the prototype is a method for calibrating an ultrasonic antenna array mounted on a prism, carried out by measuring the propagation velocity of ultrasonic signals and their travel time in a prism, implemented in an OmniScan MX2 ultrasonic flaw detector (See the OLYMPUS official website - http : //www.olympus-ims.com/en/omniscan-mx2/).

The known method does not allow to determine the following parameters of an ultrasonic antenna array mounted on a prism: a prism boom, a distance in the prism along the central beam, the angle of the prism, the delay time in the matching layer of the antenna array.

A method is proposed for calibrating an ultrasonic antenna array mounted on a prism, which consists in emitting ultrasonic signals using a plurality of elements of the antenna array into a sample of known thickness and receiving ultrasonic signals reflected from a side hole of a known diameter at a given depth, recording a number of ultrasonic echo signals for a selected radiation configuration and reception, determined by the list of pairs of emitting and receiving elements, the calculation of the evaluation of echo signals, depending on the speed the sound in the prism and its geometric parameters, comparing the measured and calculated echo signals between each other, and searching for such values of the speed of sound in the prism and its geometric parameters that provide the minimum difference and which will be considered the result of calibration, characterized in that as a result of calibration of the ultrasonic antenna array the values of the longitudinal wave velocity in the prism, its geometric parameters and travel time in the protector of the antenna array are determined.

The proposed method allows you to simultaneously determine the following parameters of an ultrasonic antenna array mounted on a prism: the velocity of a longitudinal wave in the prism, the arrow of the prism, the distance in the prism along the central beam, the angle of the prism, the delay time in the matching layer of the antenna array. The parameters to be determined are necessary for calculating the real coordinates of the centers of the piezoelectric elements with an accuracy of one eighth wavelength in order to further introduce them into the algorithms for image restoration and minimize the coordinate displacement of the reconstructed image from the coordinates of the real position of the reflectors, which makes it possible to increase the efficiency of applying methods of coherent reconstruction of the image from reflectors, and therefore increase the accuracy of determining the coordinates of reflectors.

To clarify the described method:

the figure 1 shows a photograph of a sample with a prism mounted on it without an antenna array,

the figure 2 shows the calibration results of the antenna array PE-5.0M32E0.8P No. 0334 on the prism X-42-R420 No. 1,

the figure 3 shows the images of the side drilling holes in the sample, restored according to the passport data and restored according to the parameters determined by the calibration results.

The proposed calibration method is as follows.

For calibration, you need a special sample with a hole for side drilling. As such a sample, a steel sample (see FIG. 1) with a thickness of 18 mm can be made, in which a side hole with a diameter of 2 mm is drilled at a depth of 12 mm. There is an emphasis to fix the prism on the calibration sample. In order for the distance x _w from the front face of the prism to the center of the hole to be a calibrated value, inserts with a length of 10 mm can be inserted between the sample stop and the prism. The walls of the sample must be parallel with an accuracy of not less than 0.01 mm per 100 mm, and the velocities of the longitudinal and shear waves in the sample must be measured with an accuracy of at least 0.5%.

и их оценки $$\widehat{p}(r_t,r_r,t;v)$$

при вариации таких параметров как стрела призмы а_w, расстояние пробега в призме р_w, скорость звука в призме c_w,l. Вектор, по которому происходит оптимизация, обозначим как v=(a_w,p_w,c_w). Его размеры могут быть увеличены за счет включения дополнительных параметров для оптимизации, например угла наклона призмы β_w, или времени пробега в протекторе t_prot. Критерием максимального совпадения измеренных эхосигналов $$p(r_t,r_r,t)$$

и их оценки $$\widehat{p}(r_t,r_r,t;v)$$

может служить достижение минимума целевой функции D(v)The antenna array on the prism is mounted close to the sample either to the stop or to the edge of the insert. The recommended distance x _w should be approximately equal to the distance at which the central beam hits the bottom under the side hole. Echo signals should be measured with amplification that prevents the occurrence of nonlinear distortion. The calibration method is based on achieving maximum coincidence according to a given criterion of the measured echo signals $$p(r_t,r_r,t)$$

and their assessment $$\widehat{p}(r_t,r_r,t;v)$$

when varying parameters such as the prism boom a _w , the distance in the prism p _w , the speed of sound in the prism c _{w, l} . The vector by which the optimization takes place is denoted by v = (a _w , p _w , c _w ). Its dimensions can be increased by including additional parameters for optimization, for example, the angle of inclination of the prism β _w , or the travel time in the tread t _prot . The criterion for the maximum coincidence of the measured echo signals $$p(r_t,r_r,t)$$

and their assessment $$\widehat{p}(r_t,r_r,t;v)$$

reaching the minimum of the objective function D (v) can serve

. $$v=\underset{v=(a_w,p_w,c_w)}{argmin}D(p(r_t,r_r,t),\widehat{p}(r_t,r_r,t;v))$$

.

будем обозначать как D(v). Если работать с комплексными сигналами, которые можно получить из обычных эхосигналов с помощью преобразования Гильберта, то целевую функцию можно представить в виде величины обратной функции корреляции $$D_c(v)=\frac{1}{\left|\int \int p(x,t){\widehat{p}}^{\ast }(x,t;v)dtdx\right|}$$

, где значок * означает операцию комплексного сопряжения.Next objective function $$D(p(r_t,r_r,t),\widehat{p}(r_t,r_r,t;v))$$

will be denoted by D (v). If you work with complex signals that can be obtained from ordinary echo signals using the Hilbert transform, then the objective function can be represented as the value of the inverse correlation function $$D_c(v)=\frac{\mathrm{one}}{|\; |\; |\int \int p(x,t){\widehat{p}}^{\ast }(x,t;v)dtdx|\; |\; |}$$

where the * indicates a complex pairing operation.

проводилась для прямого луча и однократно отраженного от дна образца. Результаты калибровки приведены (см. Фиг.2.).As an example of the proposed method, we present the results of the calibration of the antenna array PE-5.0M32E0.8P No. 0334 on the prism X-42-R420 No. 1. The antenna array has an operating frequency of 5 MHz, the distance between the elements is 0.8 mm. The prism with an inclination angle β _w = 42 degrees is made of plexiglass. Field Rating $$\widehat{p}(x,t;v)$$

was carried out for a direct beam and once reflected from the bottom of the sample. The calibration results are shown (see Figure 2.).

To evaluate the effectiveness of the proposed calibration procedure, the image of the side drilling hole in the calibration sample was reconstructed using the M-C-SAFT method using six transverse-wave acoustic schemes using the certified parameters Error! The source of the link was not found, and according to the parameters obtained after the calibration procedure. Images restored according to the parameters determined by the calibration results, more precisely correspond to the boundary of the hole (see Figure 3.).

Thus, the proposed method allows to obtain reconstructed images of reflectors with deviations from the actual location of less than a quarter of the wavelength on the effective part of the antenna array.

Claims (1)

A method of calibrating an ultrasonic antenna array mounted on a prism, which consists in emitting ultrasonic signals using a plurality of elements of the antenna array into a sample of known thickness and receiving ultrasonic signals reflected from a side hole of a known diameter at a given depth, recording a plurality of ultrasonic echo signals for a selected radiation configuration and reception, determined by the list of pairs of emitting and receiving elements, calculation of the evaluation of echo signals, depending on the speed of sound in p measurable and its geometrical parameters, the comparison between a measured and calculated echo signals, and search for such sound velocity values in the prism and its geometric parameters that provide the minimum difference, and which would be considered the result of the calibration,
characterized in that as a result of the calibration of the ultrasonic antenna array, the values of the longitudinal wave velocity in the prism, its geometric parameters and travel time in the protector of the antenna array are determined.

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