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Ultrasonic testing using arrays is becoming widely used to test composite structures in the Aerospace industry. In recent years, the Full Matrix Capture (FMC) technique has been implemented to extract the signals for post-processing to form an image. The inherent anisotropy and the layering of the structure pose challenges for the interpretation of this FMC data. To overcome this challenge, modeling techniques are required that take into account the diffraction caused by finite-size transducers and the response of the structure to these bounded beams. Existing models either homogenize the entire structure, use computationally expensive finite difference time domain (FDTD) methods, or do not consider the shape of the bounded beam, which is used to test such structures. This paper proposes a modeling technique based on combining the Multi-Gaussian beam model with the recursive stiffness matrix method to simulate the FMC signals for layered anisotropic media. The paper provides the steps required for the modeling technique, the extraction of the system efficiency factor, and validation of the model with experimentally determined signals for aluminum as an isotropic material such as aluminum and Carbon Fiber Reinforced Plastic (CFRP) laminate as a layered material. The proposed method is computationally inexpensive, shows good agreement with the experimentally determined FMC data, and enables us to understand the effects of various transducer and material parameters on the extracted FMC signals., Structural Integrity & Composites

Herein, we present a novel approach to the spec-radiation method (a method of acoustical holography) for determining the sound distribution on a tilted particleboard by calculating a single plane and rotation in the frequency domain. The tilted particleboard allows testing without standing waves between the transmitter and the particleboard. This eliminates the need to evaluate several parallel planes and to search for values belonging to the tilted particleboard. The numerical requirements can be optimally exploited through a combination with a flaw detectability enhancement method. The results are supported by experiments on a wooden particleboard with flaw imitations. Finally, we showed, through a comparison with the usual procedure of identifying a flaw (calculating many parallel planes and then selecting the data belonging to the tilted plane), that the calculation of the tilted plane is up to 98.5% faster and improves the detectability of flaws in a tilted particleboard.

For real-time evaluation of non-destructive air-coupled ultrasonic testing of wood-based materials, efficient and reliable calculation methods from ultrasonic holography are essential. Presented here is the spec-radiation method as a fast alternative to the re-radiation method. The spec-radiation method offers a more accurate and up to 88% faster evaluation than the re-radiation method for the determination of flaws in particleboards. Flaws of sub-wavelength sizes can be identified and their shape and location can be determined with this method. The spec-radiation method produces a better reproduction of the sound field than the re-radiation method, especially in the area of the measuring plane.

Ultrasonic testing using arrays is becoming widely used to test composite structures in the Aerospace industry. In recent years, the Full Matrix Capture (FMC) technique has been implemented to extract the signals for post-processing to form an image. The inherent anisotropy and the layering of the structure pose challenges for the interpretation of this FMC data. To overcome this challenge, modeling techniques are required that take into account the diffraction caused by finite-size transducers and the response of the structure to these bounded beams. Existing models either homogenize the entire structure, use computationally expensive finite difference time domain (FDTD) methods, or do not consider the shape of the bounded beam, which is used to test such structures. This paper proposes a modeling technique based on combining the Multi-Gaussian beam model with the recursive stiffness matrix method to simulate the FMC signals for layered anisotropic media. The paper provides the steps required for the modeling technique, the extraction of the system efficiency factor, and validation of the model with experimentally determined signals for aluminum as an isotropic material such as aluminum and Carbon Fiber Reinforced Plastic (CFRP) laminate as a layered material. The proposed method is computationally inexpensive, shows good agreement with the experimentally determined FMC data, and enables us to understand the effects of various transducer and material parameters on the extracted FMC signals., Structural Integrity & Composites

In this paper results from a non-linear AS (angular spectrum) based ultrasound simulation program are compared to water-tank measurements. A circular concave transducer with a diameter of 1 inch (25.4 mm) is used as the emitting source. The measured pulses are rst compared with the linear simulation program Field II, which will be used to generate the source for the AS simulation. The generated non-linear ultrasound eld is measured by a hydrophone in the focal plane. The second harmonic component from the measurement is compared with the AS simulation, which is used to calculate both fundamental and second harmonic elds. The focused piston transducer with a center frequency of 5 MHz is excited by a waveform generator emitting a 6-cycle sine wave. The hydrophone is mounted in the focal plane 118 mm from the transducer. The point spread functions at the focal depth from Field II and measurements are illustrated. The FWHM (full width at half maximum) values are 1.96 mm for the measurement and 1.84 mm for the Field II simulation. The fundamental and second harmonic components of the experimental results are plotted compared with the AS simulations. The RMS (root mean square) errors of the AS simulations are 7.19% and 10.3% compared with the fundamental and second harmonic components of the measurements.

In this paper results from a non-linear AS (angular spectrum) based ultrasound simulation program are compared to water-tank measurements. A circular concave transducer with a diameter of 1 inch (25.4 mm) is used as the emitting source. The measured pulses are rst compared with the linear simulation program Field II, which will be used to generate the source for the AS simulation. The generated non-linear ultrasound eld is measured by a hydrophone in the focal plane. The second harmonic component from the measurement is compared with the AS simulation, which is used to calculate both fundamental and second harmonic elds. The focused piston transducer with a center frequency of 5 MHz is excited by a waveform generator emitting a 6-cycle sine wave. The hydrophone is mounted in the focal plane 118 mm from the transducer. The point spread functions at the focal depth from Field II and measurements are illustrated. The FWHM (full width at half maximum) values are 1.96 mm for the measurement and 1.84 mm for the Field II simulation. The fundamental and second harmonic components of the experimental results are plotted compared with the AS simulations. The RMS (root mean square) errors of the AS simulations are 7.19% and 10.3% compared with the fundamental and second harmonic components of the measurements.

A quantum mechanical model for the description of the alpha-decay of heavy nuclei with accompanying photons emission is presented. The model is based on a quantum mechanical one-particle model of alpha-decay through a decay barrier. The bremsstrahlung spectrum calculation employs multipole expansion of the vector potential of the Coulomb field of the daughter nucleus and takes into account the dependence on the angle between the directions of the alpha-particle propagation and the photon emission. Spectra of 210Po are obtained for the angles 25 and 90, and the best agreement with the experimental data in the 90 case in a comparison with other existing models is achieved. From the angular analysis, the model gives monotonic behavior of the bremsstrahlung spectrum for any value of the angle. We find that sub-barrier photon emission (i.e. bremsstrahlung photon emission during alpha-particle tunneling through decay barrier) exists but gives a small contribution to the total bremsstrahlung spectrum.

Experimental verification of the stochastic power-spectral-density theory of radio propagation, as applied to a mobile receiver in a forested environment, is presented. Using a novel technique to achieve fractional-hertz resolution of the diffuse and direct wave components of the Doppler-spread received spectrum, the resultant data taken at 432 MHz shows that the angle of arrival of the diffuse component of the incident energy at the receive antenna is described by an uniform probability density function for both vertical and horizontal polarizations. Given an 8.8 km transmission path with the signal penetrating 1.3 km of forest just before reaching the receiver, the ratio of coherent (direct wave) intensity to total received signal power is 42% for horizontal polarization and 5% for vertical polarization. The results of the research indicate that long transmission paths in foliage are better characterized by a forward-scattering mechanism than by a lateral wave model. (Author), Masters theses.