Noncontact Laser Interferometer Research Articles

Non-contact Laser Interferometer Method to Characterize Tablet Punches: New Methodology to Assess Surface Roughness.

Sticking to tablet punches is a major issue during drug product manufacturing. Research has shown that sticking involves the interrelationship of powder properties, compression force, length of manufacturing runs and punch quality. Here, we present a novel non-destructive methodology to study the surface metrology of punches to monitor them over their lifetime.This investigation used a non-contact laser interferometer to characterise roughness of commercial standard S7 steel punches coated with chrome that were originally used for commercial scale production that developed a sticking issue. During the development, this phenomenon had not been observed and was not considered a scale-up risk. The profilometer was used to examine the complete surface of these punches to investigate whether they met the acceptability criteria based on BS_ISO_18804 tooling standard. To improve data analysis during changeover, a 3D-printed holder was designed to enable analysis with minimal set-up requirements.Upon investigation, the punches were found to be of an unacceptable roughness and, particularly rough areas of the punch surface profiled, correlated well with areas of visually pronounced sticking.This non-destructive method can be used to produce a more detailed characterisation of punch roughness toensure surfaces are of an acceptable quality after treatment with coatings.

High-Frequency Guided Wave Propagation and Scattering in Silicon Wafers

Abstract Thin monocrystalline silicon wafers are employed for the manufacturing of solar cells with high conversion efficiency. Micro-cracks can be induced by the wafer cutting process, leading to breakage of the fragile wafers. High-frequency guided waves allow for the monitoring of wafers and detection and characterization of surface defects. The material anisotropy of the monocrystalline silicon leads to variations of the guided wave characteristics, depending on the guided wave mode and propagation direction relative to the crystal orientation. Selective excitation of the first antisymmetric A0 wave mode at 5 MHz center frequency was achieved experimentally using a custom-made wedge transducer. Strong wave pulses with limited beam skewing and widening were measured using noncontact laser interferometer measurements. This allowed the accurate characterization of the Lamb wave propagation and scattering at small artificial surface defects with a size of less than 100 µm. The surface extent of the defects of varying size was characterized using an optical microscope. The scattered guided wave field was evaluated, and characteristic parameters were extracted and correlated with the defect size, allowing in principle detection of small defects. Further investigations are required to explain the systematic asymmetry of the guided wave field in the vicinity of the indents.

High-Frequency Guided Waves for Corrosion Thickness Loss Monitoring

Abstract Adverse environmental conditions result in corrosion during the life cycle of marine structures such as pipelines, offshore oil platforms, and ships. Generalized corrosion leading to the loss of wall thickness can cause the degradation of the integrity, strength, and load bearing capacity of the structure. Nondestructive detection and monitoring of corrosion damage in difficult to access areas can be achieved using high-frequency guided waves propagating along the structure. Using standard ultrasonic wedge transducers with single-sided access to the structure, specific high-frequency guided wave modes (overlap of both fundamental Lamb wave modes) were generated that penetrate through the complete thickness of the structure. The wave propagation and interference of the guided wave modes depend on the thickness of the structure and were measured using a noncontact laser interferometer. Numerical simulations using a two-dimensional finite element model were performed to visualize and predict the guided wave propagation and energy transfer across the plate thickness. During laboratory experiments, the wall thickness was reduced uniformly by milling of one steel plate specimen. In a second step, wall thickness reduction was induced using accelerated corrosion for two mild steel plates. The corrosion damage was monitored based on the effect on the wave propagation and interference (beating effect) of the Lamb wave modes in the frequency domain. Good agreement of the measured beatlengths with theoretical predictions was achieved, and the sensitivity of the methodology was ascertained, showing that high-frequency guided waves have the potential for corrosion damage monitoring at critical and difficult to access locations.

Upgrading of The Single Point Laser Vibrometer into a Laser Scanning Vibrometer

The paper proposes a construction design of measuring device for fast and reliable non-contact modal analysis of object surfaces which cannot be measured using classical methods. The design combines conventional non-contact laser interferometer with an active optics module to be able to measure multiple points in a rapid sequence. The paper briefly discusses all the key constructional components and describes in detail the system functional layout. It also introduces the experimental measurement of a HV transformer under operation to demonstrate the system functionality.

Propagation and scattering of guided waves in composite plates with defects

Failure in aerospace composites owing to low-velocity impact raises a significant maintenance concern because it can lead to invisible damage. For the aerospace industry, such defects pose a potential danger to the structural integrity of aircraft. This in turn jeopardises passenger safety and incurs high repair costs. Hence, it is important to efficiently monitor composite structures during the service life. In this study, the potential of low-frequency guided ultrasonic waves for health monitoring in laminated composite plates is investigated. This study focuses on the use of the first antisymmetric guided wave mode (A0). The first part of this study is to investigate the propagation of the A0 mode in three different undamaged composite plates experimentally. The dispersive and anisotropic behaviour are in agreement with the results of finite element simulations and semi-analytical analysis. The final part of this study presents the scattering of guided waves at the impact damage using a non-contact laser interferometer. Significant scattering activities were observed and the impact damage size can be estimated to be about 10 × 25 mm. In conclusion, these results demonstrate the potential of guided ultrasonic waves for the inspection of aerospace composite structures.

Scattering of guided waves at delaminations in composite plates.

Carbon fiber laminate composites are increasingly employed for aerospace structures as they offer advantages, such as a good strength to weight ratio. However, impact during the operation and servicing of the aircraft can lead to barely visible and difficult to detect damage. Depending on the severity of the impact, fiber and matrix breakage or delaminations can occur, reducing the load carrying capacity of the structure. Efficient nondestructive testing and structural health monitoring of composite panels can be achieved using guided ultrasonic waves propagating along the structure. The scattering of the A0 Lamb wave mode at delaminations was investigated using a full three-dimensional (3D) finite element (FE) analysis. The influence of the delamination geometry (size and depth) was systematically evaluated. In addition to the depth dependency, a significant influence of the delamination width due to sideways reflection of the guided waves within the delamination area was found. Mixed-mode defects were simulated using a combined model of delamination with localized material degradation. The guided wave scattering at cross-ply composite plates with impact damage was measured experimentally using a non-contact laser interferometer. Good agreement between experiments and FE predictions using the mixed-mode model for an approximation of the impact damage was found.

Evaluation of vibration on technological devices

Research paper discuss the possibility of vibration detection on production machine and also presents devices and methodology for evaluation of vibration amplitude using non-contact laser interferometer and contact piezoelectric vibration sensors. Experimentally determines the influence of technological conditions on the quality of functional surfaces. Furthermore, paper evaluates the influence of technological conditions during planar grinding on the vibration amplitude of the grinding spindle and presents correlation between grinder vibration amplitude and quality of the product.

Fatigue crack growth monitoring using high-frequency guided waves

A common problem in aircraft maintenance is the development of fatigue cracks at fastener holes due to stress concentration. High-frequency guided ultrasonic waves allow for the structural health monitoring of critical areas of a structure and can be measured with high accuracy using a noncontact laser interferometer. The use of a specific type of high-frequency guided ultrasonic wave that has good sensitivity for the detection of small defects, excited using a standard Rayleigh wedge transducer and propagating along the structure, has been investigated. Fatigue crack growth at the side of a fastener hole in a tensile, aluminum specimen was induced by cyclic loading of the structure. The crack length was monitored optically and showed good correlation with fracture mechanics calculations of the expected growth rate. The changes in the guided wave signal due to the fatigue damage were monitored using a noncontact laser interferometer and quantified. The measurements show a good sensitivity for the early detection of fatigue damage and for the monitoring of fatigue crack growth at a fastener hole. The propagation and scattering of the high-frequency guided ultrasonic wave has been simulated numerically using a three-dimensional finite difference code. Good agreement was found between the measured and predicted changes of the ultrasonic signal for the increasing fatigue crack area, allowing in principle for the approximate sizing of the defect.

Method of accurately measuring silicon sphere density difference based on hydrostatic suspension principls

The micro density difference between silicon single crystal spheres is not only important for the research on the redefinition of Avogadro constant based on quantum standard, but also a key solution for quality control for the production of silicon single crystal with ultra-high purity in semi-conductor industry. To overcome the complexity of non-contact laser interferometer method and improve the accuracy of hydro-weight method, a method based on the hydrostatic suspension principle is realized. The silicon single spheres to be measured are immersed into mixture liquid including 1,2,3-tribromopropane and 1,2-dibromoethane, and floated freely by adjusting the temperature and pressure of the liquid. The micro density difference between two silicon single crystal spheres is calculated based on a mathematical model by using liquid temperature, pressure, and central floatation height difference in the floatation condition. The stable constant temperature liquid with maximal error ± 100 μ K is realized by two-cycle water bath and PID control system. The floatation height of silicon single crystal sphere is determined by binary image and iterative algorithm. The stable suspension is achieved by the PID pressure control system, and the temperature fluctuation due to Joule-Thomson effect is reduced. By means of linearity between changes of temperature and pressure in hydrostatic suspension model, the compressibility of mixture liquid is measured. The experimental results show that the influence from liquid surface tension is avoided by using the hydrostatic suspension method, and accurate measurement of density difference between silicon single crystal spheres can be achieved with an uncertainty of 2.1× 10-7 (expand factor k=1).

Vibration characteristics of the capillary in ultrasonic wire bonders

Currently ultrasonic wire bonders with precision capillary tips are widely used in the packaging industry for bonding wires to ICs and circuits. However, the quality and strength of a bond are affected significantly by the vibration of the bonding capillary. It is, therefore, necessary to study the vibration characteristics of the capillary for better understanding and for developing a non-perturbative and low-cost monitoring device for improving bonding quality control. In this paper, the vibration characteristics of the capillary are presented in terms of natural frequency and vibration modes using finite-element models. The predicted displacement profile along the capillary is compared with the measurement using a non-contact laser interferometer. In general, a good agreement between the prediction and measurement is obtained, and it shows that the interferometer may be a good monitoring tool for characterization of capillary tip vibration, as well as providing a reference for other monitoring devices.