Ultrafast laser-enabled optoacoustic characterization of three-dimensional, nanoscopic interior features of microchips.

The recent advances in micromanufacturing have been pushing boundaries of the new generation of semiconductor devices, which, in the meantime, brings new challenges in the material and structural characterization - a key step to ensure the device quality through the micromanufacturing process. An ultrafast laser-enable optoacoustic characterization methodology is developed, targeting in situ calibration and delineation of the three-dimensional (3-D), nanoscopic interior features of opaque semiconductor chips. With the guidance of ultrafast electron-phonon coupling effect and velocity-perturbated optical interference, a femtosecond-laser pump-probe set-up based on Sagnac interferometer is configured to generate and acquire picosecond ultrasonic bulk waves (P-UBWs) traversing the microchips.

Full-range stress-strain curve estimation of aluminum alloys using machine learning-aided ultrasound.

Full-range stress-strain (SS) curves are crucial in understanding mechanical properties of a material such as the yield strength, ultimate tensile strength, and elongation. In this study, a full-range SS-curve was nondestructively estimated by applying machine learning to the ultrasonic amplitude-scan signal propagated through the material. The performance of the developed technique was validated using five-hundred aluminum alloy specimens with a wide spectrum of mechanical properties.

Optical polarization perturbed by shear strains of ultrasonic bulk waves in anisotropic semiconductors: Multiphysics modeling and optoacoustic validation.

Characterization of lattice properties of monocrystalline semiconductors (MS) has been rapidly advanced. Of particular interest is the use of shear strains induced by optoacoustic-bulk-waves. However, this technique has been hindered owing to the lack of quantitative correlations between optoacoustic-bulk-waves-induced shear strains and anisotropic photoelasticity of MS.

The Unknown Abnormal Condition Monitoring Method for Pumped-Storage Hydroelectricity.

Pumped-storage hydroelectricity (PSH) is a facility that stores energy in the form of the gravitational potential energy of water by pumping water from a lower to a higher elevation reservoir in a hydroelectric power plant. The operation of PSH can be divided into two states: the turbine state, during which electric energy is generated, and the pump state, during which this generated electric energy is stored as potential energy. Additionally, the condition monitoring of PSH is generally challenging because the hydropower turbine, which is one of the primary components of PSH, is immersed in water and continuously rotates.

Continuous Structural Displacement Monitoring Using Accelerometer, Vision, and Infrared (IR) Cameras.

With the rapid development of computer vision, vision cameras have been used as noncontact sensors for structural displacement measurements. However, vision-based techniques are limited to short-term displacement measurements because of their degraded performance under varying illumination and inability to operate at night. To overcome these limitations, this study developed a continuous structural displacement estimation technique by combining measurements from an accelerometer with vision and infrared (IR) cameras collocated at the displacement estimation point of a target structure.

Pulsed laser-assisted additive manufacturing of Ti-6Al-4V for in-situ grain refinement.

Metal additive manufacturing (AM) enables rapid customization of complex parts. However, it leads to forming of columnar grain structures which give the AM parts anisotropic properties. In this study, we propose a pulsed laser-assisted AM (PLAAM) technique for in-situ grain refinement of Ti-6Al-4V parts.

Spectral noise and data reduction using a long short-term memory network for nonlinear ultrasonic modulation-based fatigue crack detection.

This paper presents a spectral noise and data reduction technique based on long short-term memory (LSTM) network for nonlinear ultrasonic modulation-based fatigue crack detection. The amplitudes of the nonlinear modulation components created by a micro fatigue crack are often very small and masked by noise. In addition, the collection of large amounts of data is often undesirable owing to the limited power, data storage, and data transmission bandwidth of monitoring systems.

Cubic nonlinearity parameter measurement and material degradation detection using nonlinear ultrasonic three-wave mixing.

Early detection of accumulated damage or material degradation in structures is important to ensure their structural safety. Nonlinear ultrasonic techniques are widely used to measure the quadratic nonlinearity parameter that represents the third-order elastic constants of materials for material degradation detection. In addition, there are ongoing efforts to exploit both the third- and fourth-order elastic constants that describe the cubic nonlinearity parameter to detect material degradation.

Dynamic Displacement Estimation for Long-Span Bridges Using Acceleration and Heuristically Enhanced Displacement Measurements of Real-Time Kinematic Global Navigation System.

In this paper, we propose a dynamic displacement estimation method for large-scale civil infrastructures based on a two-stage Kalman filter and modified heuristic drift reduction method. When measuring displacement at large-scale infrastructures, a non-contact displacement sensor is placed on a limited number of spots such as foundations of the structures, and the sensor must have a very long measurement distance (typically longer than 100 m). RTK-GNSS, therefore, has been widely used in displacement measurement on civil infrastructures.

Multifunctional Smart Ball Sensor for Wireless Structural Health Monitoring in a Fire Situation.

A variety of sensor systems have been developed to monitor the structural health status of buildings and infrastructures. However, most sensor systems for structural health monitoring (SHM) are difficult to use in extreme conditions, such as a fire situation, because of their vulnerability to high temperature and physical shocks, as well as time-consuming installation process. Here, we present a smart ball sensor (SBS) that can be immediately installed on surfaces of structures, stably measure vital SHM data in real time and wirelessly transmit the data in a high-temperature fire situation.

A Real-Time, Non-Contact Method for In-Line Inspection of Oil and Gas Pipelines Using Optical Sensor Array.

Corrosion is considered as one of the most predominant causes of pipeline failures in the oil and gas industry and normally cannot be easily detected at the inner surface of pipelines without service disruption. The real-time inspection of oil and gas pipelines is extremely vital to mitigate accidents and maintenance cost as well as to improve the oil and gas transport efficiency. In this paper, a new, non-contact optical sensor array method for real-time inspection and non-destructive evaluation (NDE) of pipelines is presented.

Analysis of complications and clinical outcomes in the treatment of segmental tibial fractures according to the method of internal fixation.

Background/objective: We compared and analysed not only the clinical and radiological results of surgery but also the complications according to the definitive fixation method.

Methods: We retrospectively reviewed the medical records and radiographs of all segmental tibial fracture patients treated with either intramedullary nailing or minimally invasive plate osteosynthesis between 2010 and 2017. We enrolled 69 patients.

Study on effect of laser-induced ablation for Lamb waves in a thin plate.

In this paper, the effect of ablation on the shape of elastic waves generated by laser excitation is studied numerically and experimentally. Laser-induced ultrasound has been widely used in the nondestructive testing (NDT) field because it has the advantage that the sensor does not have to be directly attached to the target structure. In the safety assessment process, low energy excitation is used, and thus the structure is not damaged.

An Overview of Non-Destructive Testing Methods for Integrated Circuit Packaging Inspection.

The article provides a review of the state-of-art non-destructive testing (NDT) methods used for evaluation of integrated circuit (IC) packaging. The review identifies various types of the defects and the capabilities of most common NDT methods employed for defect detection. The main aim of this paper is to provide a detailed review on the common NDT methods for IC packaging addressing their principles of operation, advantages, limitations and suggestions for improvement.

A Reference-Free and Non-Contact Method for Detecting and Imaging Damage in Adhesive-Bonded Structures Using Air-Coupled Ultrasonic Transducers.

Adhesive bonded structures have been widely used in aerospace, automobile, and marine industries. Due to the complex nature of the failure mechanisms of bonded structures, cost-effective and reliable damage detection is crucial for these industries. Most of the common damage detection methods are not adequately sensitive to the presence of weakened bonding.

Development of a High Precision Displacement Measurement System by Fusing a Low Cost RTK-GPS Sensor and a Force Feedback Accelerometer for Infrastructure Monitoring.

A displacement measurement system fusing a low cost real-time kinematic global positioning system (RTK-GPS) receiver and a force feedback accelerometer is proposed for infrastructure monitoring. The proposed system is composed of a sensor module, a base module and a computation module. The sensor module consists of a RTK-GPS rover and a force feedback accelerometer, and is installed on a target structure like conventional RTK-GPS sensors.

Necessary Conditions for Nonlinear Ultrasonic Modulation Generation Given a Localized Fatigue Crack in a Plate-Like Structure.

It has been shown that nonlinear ultrasonics can be more sensitive to local incipient defects, such as a fatigue crack, than conventional linear ultrasonics. Therefore, there is an increasing interest in utilizing nonlinear ultrasonics for structural health monitoring and nondestructive testing applications. While the conditions, which are the necessary conditions that should be satisfied for the generation of nonlinear harmonic components, are extensively studied for distributed material nonlinearity, little work has been done to understand the necessary conditions at the presence of a localized nonlinear source such as a fatigue crack.

Numerical simulation of damage detection using laser-generated ultrasound.

Laser ultrasonic techniques have been widely investigated due to its high spatial resolution and capacity for remote and noncontact measurement. In this study, the laser induced ultrasonic wave on an aluminum plate is simulated, and a nonlinear feature is used to detect a micro crack introduced in the plate model. A multi-physics simulation is conducted and optimized considering the effect of thermal diffusion.

Fatigue crack localization using noncontact laser ultrasonics and state space attractors.

A fatigue crack and its precursor often serves as a source of nonlinear mechanism for ultrasonic waves, and the resulting nonlinear features are often much more sensitive to the fatigue crack than their linear counterparts. Among various nonlinear ultrasonic techniques, the proposed laser nonlinear wave modulation spectroscopy (LNWMS) is unique in that (1) it utilizes a pulse laser to exert a single broadband input instead of conventional two distinctive sinusoidal waves, and (2) a complete noncontact measurement can be realized based on LNWMS. Under a broadband excitation, a nonlinear source exhibits modulations due to interactions among various input frequency components.

Mechanical impedance measurement and damage detection using noncontact laser ultrasound.

This Letter proposes a mechanical impedance (MI) measurement technique using noncontact laser ultrasound. The ultrasound is generated by shooting a pulse laser beam onto a target structure, and its response is measured using a laser vibrometer. Once ultrasound propagation converges to structural vibration, MI is formed over the entire structure.

Reference-free damage detection, localization, and quantification in composites.

In this study, a reference-free damage characterization technique is developed not only to identify but also to locate and quantify damage in composite structures subject to varying temperature conditions. First, damage is characterized in terms of a damage index (m-value) defined as the ratio of damage size to the wavelength of the A0 mode within the damage. Then, a feasible solution space defining all possible combinations of the damage location and size are estimated without using any prior baseline data obtained from the pristine condition of a structure or different paths.

Duration of in vitro storage affects the key stem cell features of human bone marrow-derived mesenchymal stromal cells for clinical transplantation.

Background Aims: Mesenchymal stromal cells (MSCs) have the ability to self-renew and differentiate into various cell types. Their plasticity and easy availability make them promising candidates for regenerative medicine. However, for successful clinical application, MSCs need to be expanded under a Good Manufacturing Practices-compliant system to obtain a large quantity of these cells.

Piezoelectric transducer self-diagnosis under changing environmental and structural conditions.

Surface-mountable wafer-type piezoelectric transducers using lead zirconate titanate (PZT) are widely used to generate and sense guided waves for nondestructive evaluation and structural health monitoring applications. However, little attention has been paid to monitoring PZT transducer integrity, despite possibly being the weakest link in the entire monitoring system. In this study, PZT transducer self-diagnostic techniques, which enable a single PZT transducer to examine its own integrity, are developed based on a time-reversal process; the effects of temperature and structural condition variations are explicitly considered.

Development of dual PZT transducers for reference-free crack detection in thin plate structures.

A new Lamb-wave-based nondestructive testing (NDT) technique, which does not rely on previously stored baseline data, is developed for crack monitoring in plate structures. Commonly, the presence of damage is identified by comparing "current data" measured from a potentially damaged stage of a structure with "baseline data" previously obtained at the intact condition of the structure. In practice, structural defects typically take place long after collection of the baseline data, and the baseline data can be also affected by external loading, temperature variations, and changing boundary conditions.