Air-coupled Ultrasonic Method Research Articles

Investigation of Surface Damages in Composite Materials Using Ultrasonic Lamb Waves

In this research, it was aimed to figure out the damages in composite materials using air-coupled ultrasonic method. The ultrasonic lamb waves were used to obtain C-scan images of damaged materials. A couple of planar air coupled transducers (500 kHz-Ultran Group-USA) and an air-coupled scanning system (MISTRAS-EPA, France) were used for obtaining the data from the surfaces of materials used in this research. These transducers were located in different incidence angles for obtaining the lamb waves. The data obtained as A-scan signals was saved in txt data. This txt data was processed with the MATLAB codes for drawing C-scan images of the surfaces of materials. The results obtained from this research showed that the surface damages in composite materials can be characterized with using ultrasonic lamb waves.

Measurements of the weak bonding interfacial stiffness by using air-coupled ultrasound

An air-coupled ultrasonic method, focusing on the problem that weak bonding interface is difficult to accurately measure using conventional nondestructive testing technique, is proposed to evaluate the bond integrity. Based on the spring model and the potential function theory, a theoretical model is established to predict the through-transmission spectrum in double-layer adhesive structure. The result of a theoretical algorithm shows that all the resonant transmission peaks move towards higher frequency with the increase of the interfacial stiffness. The reason for these movements is related to either the normal stiffness (KN) or the transverse stiffness (KT). A method to optimize the measurement parameters (i.e. the incident angle and testing frequency) is put forward through analyzing the relationship between the resonant transmission peaks and the interfacial spring stiffness at the frequency below 1MHz. The air-coupled ultrasonic testing experiments at the normal and oblique incident angle respectively are carried out to verify the theoretical analysis and to accurately measure the interfacial stiffness of double-layer adhesive composite plate. The experimental results are good agreement with the results from the theoretical algorithm, and the relationship between bonding time and interfacial stiffness is presented at the end of this paper.

The Application and Development of Composite Material Detection Using Dry Coupled Acoustic Technology

This paper focus on the method of composite material detection, and five dry coupled acoustic technologies are introduced, which are dry pressure coupling method, acoustical impedance method, Local percussion method, air-coupled ultrasonic method and ultrasonic fixed spacing pitch-catch method. The principle, character and application of these five methods are discussed, and the development trend of dry coupled acoustic technology is previewed.

Crack Detection in Single-Crystalline Silicon Wafer Using Laser Generated Lamb Wave

In the semiconductor industry, with increasing requirements for high performance, high capacity, high reliability, and compact components, the crack has been one of the most critical issues in accordance with the growing requirement of the wafer-thinning in recent years. Previous researchers presented the crack detection on the silicon wafers with the air-coupled ultrasonic method successfully. However, the high impedance mismatching will be the problem in the industrial field. In this paper, in order to detect the crack, we propose a laser generated Lamb wave method which is not only noncontact, but also reliable for the measurement. The laser-ultrasonic generator and the laser-interferometer are used as a transmitter and a receiver, respectively. We firstly verified the identification of S0 and A0 lamb wave modes and then conducted the crack detection under the thermoelastic regime. The experimental results showed that S0 and A0 modes of lamb wave were clearly generated and detected, and in the case of the crack detection, the estimated crack size by 6 dB drop method was almost equal to the actual crack size. So, the proposed method is expected to make it possible to detect the crack in the silicon wafer in the industrial fields.

Observation of interference effects in air-coupled ultrasonic inspection of wood-based panels

The air-coupled ultrasonic inspection method is a widely applied non-destructive measuring technique in the wood-based panel industry. The technology is mainly applied to detect panel delaminations by analyzing the transmitted signal. Recent research deals with the use of ultrasonic techniques not only for the qualitative but also for the quantitative characterization of wood-based panels. To achieve a fundamental understanding of the behavior of ultrasonic waves in wooden panels, it is necessary to study the mechanisms that affect ultrasonic transmission and velocity during testing. Impedance and attenuation effects have been examined in previous studies. This article focuses on the interferences of ultrasonic waves. The interferences can be detected in experiments where the ultrasonic transmission is tested against the panel thickness. The results are verified with a mathematical model that explains the interferences due to multiple reflections inside the tested panels. By fitting the experimental data to the model predictions, the ultrasonic velocity and attenuation can be determined. So far, interference effects have not been considered for the non-destructive testing of wood-based panels. This research is a contribution to a better understanding of the mechanisms influencing the air-coupled ultrasonic methods.

Online Profiling of Nonplanar Objects by High-Resolution Air-Coupled Ultrasonic Distance Measurements

Ultrasonic measurements are used in product sizing in various industrial technologies. The advantage of such techniques is that measurements can be performed contactless on a conveyer using an air-coupled ultrasonic method. Nevertheless, implementation of such systems is complicated due to temperature variations, a nonconstant movement velocity, and geometry of the object necessary to measure. In this paper, an ultrasonic technique for the measurement of geometric parameters of objects transported by a conveyer is presented. Operation of the system is based on precise measurements of the distance between the transducer and the surface of an object. The measurement technique includes such stages as detection of the object, recognition of a typical profile, using a feature extraction algorithm, and measurement of object dimensions at selected positions. As an example of implementation of such a measurement technique, the ultrasonic air-coupled system for the measurement of the thickness of chocolate during the production process is presented.