Visualization of defects in thin metal plates by a scanning airborne ultrasound source technique using guided waves of different frequencies

A scanning airborne ultrasound source technique was developed to overcome the riskiness of laser ultrasound, which uses an ultrasound source that has a fixed sound wave focusing point and thus requires mechanical motion for sound source scanning. Therefore, the measurement time becomes longer. To solve this problem, we have proposed a method of simultaneously exciting many measurement points in the target using focused ultrasound sources of different frequencies. In this paper, we investigated the visualization of defects in a thin metal plate by the scanning elastic wave source technique using an airborne ultrasound source driven at two frequencies. When the testing was performed using two frequencies, either frequency visualized the defects.

About the possibility of using physiotherapy in the practice of a surgeon. Literature review

Physiotherapy is a field of medicine based on the study and application of natural and artificially created natural factors on the human body. Physical factors can have both local and systemic effects on the patient’s body. In the postoperative period, physiotherapy helps to solve the most important problems, such as accelerating the processes of tissue regeneration and reducing the risk of infection in the area of surgery. Physical factors, activating fibroblasts, accelerate the synthesis of collagen fibers and increase the regenerative capacity of damaged tissues. In addition, due to bacteriostatic and bactericidal action, microorganisms are destroyed and the risk of postoperative infectious complications is reduced. Understanding the key features of all stages of the wound process allows you to rationally affect the wound. The use of an integrated approach based on drug therapy and the use of physiotherapy procedures significantly increases the effectiveness of treatment and helps the patient to return to their usual level of life as soon as possible. This article is a review of the literature on the most commonly used methods of physiotherapy in the postoperative period. Based on the analysis of publications, the article presents the features and principle of operation of such techniques as electrophoresis, phonophoresis, magnetotherapy, ozone therapy, electrical stimulation, cryotherapy, shock wave therapy, galvanization, darsonvalization, as well as therapy based on the effects of ultraviolet radiation, laser, ultrasound, microcurrents. Examples of physiotherapeutic procedures that should be used at various stages of the wound process, depending on the impact, are given. It is the use of various methods of influence in combination with each other that helps to achieve the maximum effect of treatment in the postoperative period.

Cloaking, trapping and superlensing of lamb waves with negative refraction

We report on experimental and numerical implementations of devices based on the negative refraction of elastic guided waves, the so-called Lamb waves. Consisting in plates of varying thickness, these devices rely on the concept of complementary media, where a particular layout of negative index media can cloak an object with its anti-object or trap waves around a negative corner. The diffraction cancellation operated by negative refraction is investigated by means of laser ultrasound experiments. However, unlike original theoretical predictions, these intriguing wave phenomena remain, nevertheless, limited to the propagating component of the wave-field. To go beyond the diffraction limit, negative refraction is combined with the concept of metalens, a device converting the evanescent components of an object into propagating waves. The transport of an evanescent wave-field is then possible from an object plane to a far-field imaging plane. Twenty years after Pendry’s initial proposal, this work thus paves the way towards an elastic superlens.

Research on laser ultrasonic surface defect identification based on a support vector machine

To solve the problem of difficult quantitative identification of surface defect depth during laser ultrasonic inspection, a support vector machine-based method for quantitative identification of surface rectangular defect depth is proposed. Based on the thermal-elastic mechanism, the finite element model for laser ultrasound inspection of aluminum materials containing surface defects was developed by using the finite element software COMSOL. The interaction process between laser ultrasound and rectangular defects was simulated, and the reflected wave signals corresponding to defects of different depths under pulsed laser irradiation were obtained. Laser ultrasonic detection experiments were conducted for surface defects of different depths, and multiple sets of ultrasonic signal waveform were collected, and several feature vectors such as time-domain peak, center frequency peak, waveform factor and peak factor were extracted by using MATLAB, the quantitative defect depth identification model based on support vector machine was established. The experimental results show that the laser ultrasonic surface defect identification model based on support vector machine can achieve high accuracy prediction of defect depth, the regression coefficient of determination is kept above 0.95, and the average relative error between the true value and the predicted value is kept below 10%, and the prediction accuracy is better than that of the reflection echo method and BP neural network model.