SU1682779A1 - Method for examination of microspecimens with the aid of focused supersonic waves - Google Patents

Abstract

This invention relates to ultrasound microscopy. The aim of the invention is to increase the reliability of the research results and simplify the hardware implementation of the method by using the harmonic signal as a probing signal and implementing the Doppler shift of the spectrum of the reflected signal, allowing it to be processed by selection in the frequency domain. The generated ultrasound transducer 1, excited by a harmonic signal from generator 4, focuses the ultrasonic wave, reflected from the surface moving in the direction perpendicular to the focal plane of transducer 1, sample 8, is received last, and the information signal enters the processing path to select informative parameters by which the properties of sample 8 are judged. The use of a harmonic probing signal and the processing of an information signal by frequencies selection in the band corresponding to the spectrum of the Doppler biased reflected signal, allows to remove restrictions on the focal length, which allows to increase the level of the useful signal at high operating frequencies, to perform a narrowband, receiving path of the device that implements the method, it is easy to filter the signal direct passage (harmonic), eliminate the incorrectness associated with the dependence of the elastic parameters of the sample on the wavelength (fixed), reduce the effect of nonlinear effects by izheni peak power of the probe signal while maintaining the average power, eliminating the need for complicated processing of the reflected signal at a high frequency, since the information signal is low frequency and contains both informative parameters — amplitude and phase. This ensures the achievement of the stated objectives of the invention. 1 il. sl about 00 th VI VI

Description

The invention relates to ultrasound microscopy and can be used to study and visualize the spatial distribution of the structural and mechanical properties of microsamples of materials, as well as to study

reflective properties of local areas in the ultrasonic range.

The purpose of the invention is to increase the reliability of the research results and to simplify the hardware implementation of the method by using the harmonic signal as a probing signal and by carrying out the Doppler shift of the reflected signal spectrum, which allows its processing by selection in the frequency domain.

The drawing shows an example of the scheme of the device that implements the method.

The device is made on the basis of a scanning acoustic microscope and contains an electro-acoustic transducer 1, a three-coordinate scanning mechanism 2 mounted to the radiation path of the transducer 1, an immersion medium 3 that fills the volume between the transducer 1 and the scanning mechanism 2 providing acoustic contact between them, series-connected generator 4 harmonic signal, the isolating element 5, the second input (output) connected to the electrical output (input) of the converter 1 and intended for separation of probing and reflected signal paths, receiver b, and signal processing and recording unit 7 (processing unit 7), connected to the synchronized output of scanning engine 2 with a second input.

Before the operation of the device, examine the specimen, designated 8, is attached to the scanning mechanism 2.

The method is carried out as follows.

The harmonic signal produced by the generator 4 is supplied to the electro-acoustic transducer 1 via the coupling element 5, which may be, for example, a microwave circulator or a directional coupler. The transducer 1, excited by the generator 4, emits into the immersion medium 3 a focused ultrasonic wave, which is reflected from the surface of the sample 8 moving in the direction perpendicular to the focal plane of the transducer 1 (along the Z axis in the drawing), the scanning mechanism 2 propagates in the opposite direction and is received by the same transducer 1. The received electrical signal is fed to the input of the receiver b through the isolating element 5. This signal of the receiver 6 also receives a forward pass signal This is via the isolating element 5 and the signals corresponding to the reflection from the electrical and acoustic inhomogeneities located on the propagation path of the signal and the ultrasonic wave from the isolating element 5 to sample 8. The sum of these signals and the signal

Reflections from sample 8 are subjected to quadratic detection in receiver 6 and then band-pass filtering. Thus, the Doppler biased signal is reflected, reflected from sample 8. The extracted signal then enters the signal processing and recording unit 7, which may contain, for example, a channel in which the determination is made

0 reflection coefficient depending on the angle of incidence, and the channel of formation of the image. In the first channel, the signal recorded as a function of the displacement of sample 8 from the focal plane in the absence of its

5 scanning on coordinates Xs, Ys, is subjected to spectral analysis, either by analog-digital conversion with ps 1 next digital processing, or, in the case of uniform motion along the Z axis,

0 analog means.

In the imaging channel, the required parameter of the signal to be visualized is determined, for example, the envelope is

5 signals as a function of sample displacement 8 from the focal plane, then this parameter is read for a specific sample displacement value 8, which gives one pixel. A full image is formed by scanning the sample with the scanning mechanism 2 and repeatedly repeating the procedure described for each image element. Thus, the method consists in

5 that is formed by an electroacoustic transducer excited by a harmonic electric signal, a focused ultrasound wave propagating in an immersion medium; directing this wave to the sample surface; carry out the relative movement of the electroacoustic converter and the sample in the direction perpendicular to the focal plane

5 converter; take the electro-acoustic transducer reflected wave; extracted from the received signal, processing it by frequency selection in the band corresponding to the spectrum

0 Doppler components of the angular spectrum of the incident wave reflected from the moving sample reflected from the surface, informative parameters by which the sample properties studied are judged.

In the process of implementing the method to the input of the receiver 6 receives two signals. One of them - the signal of direct transmission and rereflection of the probing signal - can be represented as

Si (t) Aicos (ufet), (1)

where (Do is the frequency of the exciting harmonic signal.

The second signal reflected from sample 8, whose position relative to the acoustic axis of the electroacoustic transducer 1 is determined by the coordinates (Xs, Ys), is a function of the displacement of sample 8 from the Z (t) focal plane: S2 (t) V (Z (t), Xs, Ys) cos (ufe t + / (Z (t), Xs, Ys)},

(2)

where the functions V and p denote the amplitude and phase of the signal reflected from sample 8.

Then the sum of these two signals is subjected, for example, to quadratic detection, and by subsequent filtering a low-frequency useful signal is extracted, which, based on (1) and (2), can be represented as S3 (t) AiV (Z (t), Xs, Ys) ) cos (p (Z (t), Xs, Ys)). (3)

With fixed Xs, Ys, this signal is proportional to the real part of the analytical signal Va (Z (t)), which is associated with the dependence of the reflection coefficient of the ultrasonic wave on the angle of incidence on the surface of the local region of the sample 8 P (E, Xs, Ys) R (Q ) reverse Fourier transform

Va (Z (t)) 7Г / 2 „

 / R (0) P2d (0) exp (i 2k Z (t) cos G) sin в d в,

about

(four)

where k 2 tg / A (A is the ultrasound wavelength in the immersion medium 3); t

PD (0) is the generalized aperture function of an electroacoustic transducer 1.

From formula (4), it follows that the spectrum of the analytical signal Va (Z (t)), and hence also the signal S3 Re {Va (Z (t))}, is the spectrum of the Doppler-shifted the waves. Therefore, in the mode of finding the reflection coefficient depending on the angle of incidence on the surface of the sample 8, the signal S3 (Z (t)) is subjected to spectral analysis. The analysis can be performed numerically, if the signal is represented as a function of the displacement Z, or, provided that the motion Z (t) V0t is uniform, where Vo const is the speed of the sample 8, the spectral density can be found by radio engineering methods.

In the imaging mode, the 5s (x) signal is processed to extract the necessary information, for example, the amplitude of the signal or phase. The values of the converted are then recorded.

the signal at the instants of time when the displacement of the sample 8 from the focal plane takes a certain fixed value, and, producing a mechanical scan of the sample 8 in the plane (Xs, Ys), form an acoustic image.

Thus, the technical advantages of the method are as follows. A harmonic rather than a pulsed signal is used as a probing signal, the sample is associated with a movement in the direction perpendicular to the focal plane of the electroacoustic converter, which allows

5 is a useful signal in the background of interference signals due to the Doppler shift of the spectrum of the reflected wave, and not due to the time delay of the reflected signal relative to the probing signal. There are no restrictions on the focal length of the electroacoustic converter, which allows, for example, to increase the level of the useful signal at high operating frequencies. Radio reception of the device,

5 that implements the method may be narrowband, since its bandwidth is determined only by the width of the Doppler spectrum of the reflected signal, which increases its noise immunity.

0 Harmonic sounding signal, penetrating directly to the input of the receiving device, is used as a reference and, being filtered out during further processing, is not a hindrance. Using

5, the harmonic signal also eliminates the incorrectness associated with the dependence of the elastic parameters of the surface under study on the ultrasound wavelength in the immersion medium, since the measurement results

0 correspond to its only value. In addition, the effect of non-linear effects can be reduced by reducing the peak power of the probing signal while maintaining its average power.

5 The implementation of the method can be carried out with much simpler (with respect to the known method) instrumental means, since there is no need for complex processing.

0 of the reflected signal at high frequency, and the selected useful low-frequency signal, which is the result of interference of the reflected and probing signals, contains information about both the amplitude and

5 and the phase of the reflected signal, which in this case are informative parameters.

Claims (1)

The invention of the Method for the study of microsamples using focused ultrasound waves, which form an focused ultrasonic wave using an electro-acoustic transducer, direct this wave to the sample surface through an immersion medium, receive the reflected wave with an electro-acoustic transducer, extract from the received signal by appropriate processing informative parameters, which are judged by microsample properties studied, characterized in that, in order to increase the reliability, 0 microsample and electroacoustic transducer in the direction perpendicular to the focal plane of the electroacoustic transducer, excite an electroacoustic transducer harmonic signal, and the processing of the received signal is performed by selektirovani frequency in the band, the Doppler spectrum sootvetstsvuyuschey ski displaced upon reflection from a moving sample surface constituting the angular spectrum of the incident the waves.