Pulsed Wave Excitation Research Articles

Nonlinear Ultrasonic C-Scan Imaging for Contact-Type Defects in Diffusion-Bonded Joints-A Case Study.

Diffusion bonding technology is widely used in the connection of precision components, yet accurately and reliably detecting contact-type defects on the bond interface still remains a significant problem. Nonlinear ultrasonic methods have been proven to be sensitive to contact-type defects; however, the use of continuous wave or tone burst wave excitation limits its wider application. In this paper, dual-probe nonlinear ultrasonic testing with pulse wave excitation is proposed to detect contact-type defects in diffusion-bonded joints. A titanium alloy diffusion-bonded specimen with artificial defects was fabricated, and the corresponding detection device was designed based on the existing ultrasonic C-scan testing system. A C-scan imaging program based on nonlinear parameters was developed by extracting the fundamental and second harmonic waves of the reflection echo on the bond interface. The results demonstrated that the proposed detection scheme can obtain the nonlinear parameters of diffusion-bonded interfaces, and the nonlinear ultrasonic C-scan image of the bond interface is also obtained. The nonlinear parameter in the contact-type defects areas calculated from the bond interface echo is about 10 times (20 dB) higher than that in macro defects areas, whose gap is about 10 μm. The results indicate that the nonlinear ultrasonic methods seem to be more sensitive to contact-type defects and have a great potential to complement the insufficient detection capability of linear ultrasound for diffusion-bonded joints.

Deep Tissue Characterization with Optical Coherence Elastography: A Comparison of Different Methods

The measurement of the biomechanical properties of the skin is of great interest since these properties play an important role in the development of several diseases such as skin cancer and systemic sclerosis. In this direction, several diagnostic tools have been developed to analyze the mechanical properties of the skin. Optical coherence elastography (OCE) is one of the emerging imaging techniques used for the characterization of the mechanical properties of the tissue quantitatively. In systemic sclerosis patients, the measurement of the mechanical properties of the deeper skin layers is desirable compared to the superficial layers. There are several variants of OCE that exist, but it is still not clear which method is more suitable for the measurement of the mechanical properties of the deeper tissue. In this work, we tested three common methods, the pulsed excitation method, the continuous wave excitation method, and the resonant frequency method, for the measurement of the mechanical properties of the deeper layers in the tissue. We found out that the pulsed wave excitation method provides the most reliable measurements in the shortest possible time compared to the other two methods.

Nondestructive Approach for Complex-Shaped Cracks in Concrete Structures by Electromagnetic Waves with FDTD Technique

Concrete cracks have no specific shape and do not show linearity. Since the natural occurrences of concrete cracks make simulation identification difficult, rectangular step function and a dynamic geometry are used to define a concrete surface crack in the natural process. A novel interior crack expression is obtained by accepting the area between two curves as a crack filled by air in concrete and modeling this area like a Riemann integral domain. Taking the partition of this integral domain, the most realistic definition of the crack is made. Electromagnetic (EM) waves are utilized for numerical simulation after identifying the defects, cracks, rebars, and geometry of concrete. Three different simulation setups with complex geometries with two different surface cracks and one internal crack are simulated using a finite-difference time-domain (FDTD) method with Gaussian pulse wave excitation. Simulations are obtained using both transverse electric (TEz) waves and transverse magnetic (TMz) waves and the results are compared with each other. Air-dried concrete specimens are molded following simulation setups with surface cracks and measurements are made nondestructively with a Vivaldi antenna array in the frequency range of 0.4–4.0 GHz. The reflection and transmission coefficients are validated by comparing the data obtained using the measurement with the results obtained from numerical simulation.

A pulsed wave excitation system to characterize micron-scale magnetoelastic biosensors

This paper describes the design of a resonant frequency measurement system based on a pulsed wave excitation technique that can be used to resonate and measure micron-size Magnetoelastic (ME) biosensors. Current measurement techniques can only detect millimeter and above size ME biosensors. By using a specially designed, dedicated coil and low noise cascade amplifier, the system described in this paper is capable of measuring micron-size (ME) biosensors as small as 200μm in length (200×40×15μm). In the system, a square pulse current is applied to an excitation coil to excite the ME sensors, and a pick-up coil senses its mechanical vibration and converts it to an electrical output signal. The output signal is amplified by a signal amplification circuit and the output waveform is shown on an oscilloscope. Based on the acquired damped oscillating signal, the frequency change due to the mass change on the surface of the ME biosensor can be calculated. The impact of signal amplification on the resonant frequency, amplitude, and Q-factor of the resonant frequency peak, has been studied. The average resonant frequency of a 200μm sensor was found to be 10.8283±0.0027MHz. As a proof-in-concept experiment, the detection system was used in combination with JRB7 phage-coated ME biosensors to detect different concentrations of Bacillus anthracis spores. A statistically significant difference for all concentrations of 5×102spore/ml and higher can be reached by the system.

Inkjet Printed All-Polymer Flexural Plate Wave Sensors

We discuss the fabrication and performance of an all-polymer, flexural plate wave gravimetric sensor using flexible, piezoelectric Polyvinylidene fluoride as the substrate and an inkjet-printed interdigital transducer (IDT) employing conductive poly(3, 4-ethylenedioxythiophene) poly(styrenesulfonate) to excite Lamb waves within the film. Lamb waves are measured both electronically, using a second IDT, and mapped directly using a scanning laser Doppler vibrometer. Pulsed wave excitation is utilized to isolate the weak acoustic signal from the electromagnetic crosstalk, enabling the measurement of relative changes in the resonant frequency, Δf/f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , in response to added mass, Δm, to the sensing area. A gravimetric mass sensitivity equivalent to Δf/(f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> Δm)=-153 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /g is measured by mass loading the sensor with printed polymer layers. It is found that the low stiffness of the substrate contributes significantly to the response of the sensor, yielding a measured overall sensitivity of Δf/(f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> Δm)=-83 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /g.

Composite Scattering of a Plasma-Coated Target Above Dispersive Sea Surface by the ADE-FDTD Method

In this letter, the composite scattering of a plasma-coated target above a randomly rough sea surface is investigated by the finite-difference time-domain (FDTD) method with pulsed wave excitation. Both sea water and plasma layer are regarded as isotropic and dispersive media, and they satisfy the Debye model and the Drude model, respectively. The auxiliary differential equation (ADE) technique is incorporated into the FDTD scheme to deal with the dispersive media. To ensure the feasibility of our present method, the scattering of a perfect electrically conducting target without coating above dispersive sea surface by the ADE-FDTD method is compared with the result obtained by the parallel method of moments, which requires an individual run for every frequency of interest. Finally, the normalized radar cross section of a plasma-coated target above rough sea surface is calculated and analyzed for different parameters in detail.

Wide-band scattering of 1-D dispersive soil surface by the ADE-FDTD algorithm

In this paper, a wide-band scattering of one-dimensional (1-D) soil surface with exponential spectrum is investigated by the finite-difference time-domain (FDTD) algorithm with pulsed wave excitation. Soil is regarded as isotropic and dispersive media, and it satisfies the two-pole Debye model. And the auxiliary differential equation (ADE) technique is incorporated into the FDTD scheme to deal with the dispersive soil. To ensure the validity of our present method, the wide-band scattering of dispersive soil surface by the ADE-FDTD method is computed and compared with the result by the conventional method of moments (MOM), which requires an individual calculation for every frequency point of interest. Finally, the scattering characteristic of dispersive soil surface is analyzed for different parameters in detail.

Frequency response of 1D dispersive sea surface by the ADE-FDTD algorithm

The frequency response of a one-dimensional (1D) sea surface was investigated using the finite-difference time-domain (FDTD) algorithm with pulsed wave excitation. Where the sea water is regarded as an isotropic and dispersive medium, it satisfies the single-pole Debye model. The auxiliary differential equation (ADE) technique is incorporated into the FDTD scheme to deal with the dispersive sea surface. To ensure the feasibility of our present method, the frequency response of dispersive sea surface by the ADE-FDTD method is compared with the result by the conventional method of moments (MOM), which requires an individual calculation for every frequency point of interest. Finally, the scattering characteristic of dispersive sea water is investigated for different wind speed, temperature, and salinity. The representative far zone scattered field versus time is also analyzed.

Simulation-based microwave imaging of plain and reinforced concrete for nondestructive evaluation

The focus of this paper is the implementation of a backpropagation algorithm as a potential solution for the inverse source problem for microwave imaging of plain and reinforced concrete targets. The data used in imaging was obtained from numerical simulation of far-field microwave scattering by concrete targets using typical frequency bandwidth of commercially available radar systems. A finite difference-time domain (FD-TD) technique was used for the simulations. Electromagnetic (EM) properties of concrete for various moisture conditions were obtained from a previous study. A total of four simulations were performed using a Gaussian pulse wave excitation for dry and moisture saturated concrete cylinders with and without a rebar at the center. The reflected and transmitted fields were recorded along two measurement lines. Images reconstructed using the backpropagation algorithm showed the potential of the method for concrete non destructive testing (NDT) while drawing attention to its limitations mainly due to the linearizing assumptions made in the algorithm’s formulation. Key words: Nondestructive testing (NDT), microwave, imaging, concrete, ground penetrating radar (GPR), finite difference-time domain (FD-TD), simulation, backpropagation.

Investigation on wide-band scattering of a 2-D target above 1-D randomly rough surface by FDTD method

Finite-difference time-domain (FDTD) algorithm with a pulse wave excitation is used to investigate the wide-band composite scattering from a two-dimensional(2-D) infinitely long target with arbitrary cross section located above a one-dimensional(1-D) randomly rough surface. The FDTD calculation is performed with a pulse wave incidence, and the 2-D representative time-domain scattered field in the far zone is obtained directly by extrapolating the currently calculated data on the output boundary. Then the 2-D wide-band scattering result is acquired by transforming the representative time-domain field to the frequency domain with a Fourier transform. Taking the composite scattering of an infinitely long cylinder above rough surface as an example, the wide-band response in the far zone by FDTD with the pulsed excitation is computed and it shows a good agreement with the numerical result by FDTD with the sinusoidal illumination. Finally, the normalized radar cross section (NRCS) from a 2-D target above 1-D rough surface versus the incident frequency, and the representative scattered fields in the far zone versus the time are analyzed in detail.

Low-noise second-harmonic-type magnetic modulator excited with a pulse wave at a temperature near the Curie point

In order to reduce the noise level of the second-harmonictype magnetic modulator, the authors propose a new method of modulation employing pulse-wave excitation at a temperature slightly below the Curie point. It is verified experimentally that the equivalent input noise could be reduced to 0.026 µAT/cm.