Holographic Nondestructive Testing Research Articles

Design and Implementation of 3D Hologram using Machine Learning

Holographic means “entire recording” and originates from the Greek words “holo” (“whole”) and “graphic” (“message”). “Entire” refers to the recording of both the intensity and the phase of the object, as opposed to conventional photography, where only the intensity profile of the object is recorded. In a new stage in the organisation and control of the industrial value chain, interchangeably with the fourth industrial revolution. It has a broad vision with well-defined frameworks and reference designs, focusing on bridging physical infrastructure and digital technology in so- called cyber-physical systems. Apart from the other essential technologies, Holography is considered a new innovative technology that can completely transform the vision of Industry 4.0. In industrial applications, holographic technology is used for quality control in manufacturing and fracture testing, such as holographic nondestructive testing. Holography has a wide range of applications in medicine, the military, weather forecasting, virtual reality, digital art, and security. The fourth industrial revolution aims to provide automated asset monitoring, decision-making for corporate operations, and real-time network connectivity. This paper explores holography and its significant benefits through various development processes, features, and applications, where the focus is on ‘holography for Industry 4.0'. Hologram technology is a new industry trend and can impact multiple domains of Industry 4.0. Furthermore, the adoption of holographic technologies may improve the efficiency of existing products and services in other technology sectors such as architecture, 3D modelling, mechatronics, robotics, and healthcare and medical engineering

Holography and its applications for industry 4.0: An overview

Industry 4.0 is a new stage in the organisation and control of the industrial value chain, interchangeably with the fourth industrial revolution. It has a broad vision with well-defined frameworks and reference designs, focusing on bridging physical infrastructure and digital technology in so-called cyber-physical systems. Apart from the other essential technologies, Holography is considered a new innovative technology that can completely transform the vision of Industry 4.0. In industrial applications, holographic technology is used for quality control in manufacturing and fracture testing, such as holographic nondestructive testing. Holography has a wide range of applications in medicine, the military, weather forecasting, virtual reality, digital art, and security. The fourth industrial revolution aims to provide automated asset monitoring, decision-making for corporate operations, and real-time network connectivity. This paper explores holography and its significant benefits through various development processes, features, and applications, where the focus is on ‘holography for Industry 4.0'. Hologram technology is a new industry trend and can impact multiple domains of Industry 4.0. Furthermore, the adoption of holographic technologies may improve the efficiency of existing products and services in other technology sectors such as architecture, 3D modelling, mechatronics, robotics, and healthcare and medical engineering.

Holography in the invisible. From the thermal infrared to the terahertz waves: outstanding applications and fundamental limits

Since its invention, holography has been mostly applied at visible wavelengths in a variety of applications. Specifically, non-destructive testing of manufactured objects was a driver for developing holographic methods and all related ones based on the speckle pattern recording. One substantial limitation of holographic non-destructive testing is the setup stability requirements directly related to the laser wavelength. This observation has driven some works for 15 years: developing holography at wavelengths much longer than visible ones. In this paper, we will first review researches carried out in the infrared, mostly digital holography at thermal infrared wavelengths around 10 micrometers. We will discuss the advantages of using such wavelengths and show different examples of applications. In nondestructive testing, large wavelengths allow using digital holography in perturbed environments on large objects and measure large deformations, typical of the aerospace domain. Other astonishing applications such as reconstructing scenes through smoke and flames were proposed. When moving further in the spectrum, digital holography with so-called Terahertz waves (up to 3 millimeters wavelength) has also been studied. The main advantage here is that these waves easily penetrate some materials. Therefore, one can envisage Terahertz digital holography to reconstruct the amplitude and phase of visually opaque objects. We review some cases in which Terahertz digital holography has shown potential in biomedical and industrial applications. We will also address some fundamental bottlenecks that prevent fully benefiting from the advantages of digital holography when increasing the wavelength.

55 Years of Holographic Non-Destructive Testing and Experimental Stress Analysis: Is there still Progress to be expected?

Holographic methods for non-destructive testing, shape measurement, and experimental stress analysis have shown to be versatile tools for the solution of many inspection problems. Their main advantages are the non-contact nature, the non-destructive and areal working principle, the fast response, high sensitivity, resolution and precision. In contrast to conventional optical techniques such as classical interferometry, the holographic principle of wavefront storage and reconstruction makes it possible to investigate objects with rough surfaces. Consequently, the response of various classes of products on operational or artificial load can be examined very elegantly. The paper looks back to the history of holographic metrology, honors the inventors of the main principles, discusses criteria for the selection of a proper inspection method, and shows exemplary applications. However, the main focus is on modern developments that are inspired by the rapid technological process in sensing technology and digitization, on current applications and future challenges.

Delamination testing of polyurethane pads adhered to polishing tool using a digital holographic nondestructive testing method

We demonstrate an application of digital holography for detection of a new type of defect, i.e., delamination of polyurethane pads on a polishing tool used on a high-speed computerized numerical control machine for production of precision optics. The method enabled us to acquire both qualitative and quantitative information about the delaminated region in the polishing pad. A delaminated region of 13.6 mm × 10.8 mm is detected and measured on the surface of the polishing pad. An increase in the delaminated region by 30% is noticed after completion of the polishing process with the delaminated polishing pad. The effect of delamination of the polishing pad on an optical surface is experimentally demonstrated using it for polishing a BK-7 glass substrate. These investigations may enable production of improved quality precision optics at the commercial level.

Determinación de parámetros para el diseño y construcción de una mesa antivibratoria

Este artículo se presenta los resultados de un estudio empírico para la obtención de los parámetros más relevantes que se deben tener en cuenta en el momento de diseñar y construir una mesa que aísle y amortigüe las vibraciones externas a la misma. La necesidad de un sistema aislado de vibraciones para el desarrollo de estudios holográficos y de ensayos no destructivos por métodos ópticos, se debe a que la sensibilidad de los efectos de difracción en un holograma o en un fenómeno de interferencia está en el orden de las décimas y centésimas de micrómetro. Aquí se analiza la ecuación de resonancia para un sistema con un grado de libertad en frecuencias bajas y altas para luego analizar una extrapolación de la misma. Los coeficientes de amortiguación de las diferentes láminas con la que se construye la mesa, son calculados experimentalmente a través de un acelerómetro

Experimental Research on Measuring Two-Dimensional Stress Field Using Digital Holographic Photo-Elastic Method

According to the holographic optical theory, based on the method of rotating reference light polarization plane, through the simultaneous solution of light intensity equations transformed by the hologram, the digital holographic nondestructive testing of two-dimensional stress field is introduced. This technology does not require additional experimental means and numerical method for separate fringes, determining fringe order and solving stress. It is a convenient, accurate and non-destructive measurement of two-dimensional stress field. The paper first introduces the basic theory of digital holographic photo-elastic method, and then verifies it by experiments and simulation. Light intensity images are obtained through the comparative experiments and theoretical solutions. The results prove the strong feasibility of the method in experiments, and lay the foundation for further experimental study.

Special Section Guest Editorial: Digital Holography and Holographic Displays

Holography is now more than 60 years old since the time when Dennis Gabor published his first paper in 1948, introducing the new coherent imaging technique. Holography had to wait for its first practical applications a little over 10 years until the laser was invented and laser light could be used for recording the first holograms. This happened almost simultaneously in both the USA and the former USSR. Since that time, interest in holography has been growing at an increasing rate, and has given rise to numerous applications of holographic techniques in science, industry, medicine, and art. During the first decades mainly analog holograms were recorded, using continuous-wave and pulsed lasers. Display holograms, holographic optical elements (HOE), holographic interferometry, and holographic nondestructive testing (HNDT) used different types of recording materials, often combined with wet processing. It was a time-consuming technique and required special expertise to obtain good results. When computers became faster and their storage capacity increased, very simple computer-generated holograms (CGHs) were introduced to show the potential of generating holograms and HOEs without having to record a real object. Very soon computer programs were introduced for the evaluation of interference fringes in metrology and nondestructive testing. Since the beginning of the new millennium, there has been a dramatic progress in computer technology in regard to computer storage capacity, speed, and graphics, which has made applications of CGHs and holographic displays an important part of current holographic techniques. HNDT and speckle interferometry are now only performed with the help of computers, images being recorded on electronic holographic recording devices. For example, CGHs are also used as null elements in optical testing. Today computers and electronic recording devices are used in different ways. The possibility of recording very high spatial frequencies employing electronic devices is, however, still very limited. For ultrahigh-resolution holographic recording, spatial frequencies of up to 10,000 line pairs/mm are required. For example, to display a full-parallax hologram in real time on a 40-in. wide screen with 30-deg horizontal and 10deg vertical field of view, a bandwidth of 10 Hz is required. The ultimate goal is to computer generate the interference fringe structure which is necessary to generate a holographic image for display. For a large-sized hologram, it is not possible to generate the necessary data fast enough to get a refreshment rate of 25 to 30 Hz. If we compare this with the analogue technique, using a pulsed laser to record a very large hologram of a complex object or scene, the interference structure is created and stored in a high-resolution photographic material in 20 ns, provided the pulsed laser energy is sufficient. Holographic microscopy using in-line holography combined with charge-coupled device (CCD) recording devices is common practice today. Some CCDs have sufficient spatial frequency resolution and can be used for holographic particle studies in real time, using fast Fourier transform programs. CGHs are also used to generate small holographic optical variable devices for important security document applications. Today a combination of techniques is used in order to obtain various types of CGHs. A technique for recording large, color display holograms is to print them pixel by pixel on a high-resolution holographic material. Each pixel hologram, or hogel, is computer generated and displayed on a LCD or liquid crystal on silicon (LCOS) device. Using this technique to obtain a large one-square-meter color display hologram, the printing of the entire hologram can take many hours, depending of the RGB laser’s pulse repetition rate. Using this type of hologram printing technique, both completely computer-generated three-dimensional (3D) images can be recorded, as well as a combination of a large number of photographically recorded images, such as those captured by a digital camera moving along a horizontal rail, for example. The two-dimensional images are then transformed and used to create the printed hologram. For holographic displays, HOEs can be used as a stereo projection screen generating autostereoscopic moving 3D images. There is a lot of research going on in these fields, aiming to create 3D images in real time for potential 3D television techniques. In the future, when computers become even faster, and when nanotechnology-based electronic display devices have sufficient spatial frequency resolution to display full parallax real-time color holograms directly, electronic ultrarealistic 3D images could become a reality. This special section contains state-of-the-art papers on the applications mentioned above. The papers are ordered according to the date of acceptance. I would like to thank all the authors for providing the papers for this issue, as well as the peer reviewers for their comments and meticulous work, the SPIE staff, and finally Ron Diggers, the Optical Engineering editor, for giving me the opportunity to edit this special section.

What Optical Metrology Can Do for Experimental Mechanics ?

Optical metrology has shown to be a versatile tool for the solution of many measurement and inspection problems. The main advantages of optical methods are the non-contact nature, the non-destructive and areal working principle, the fast response, high sensitivity, resolution and accuracy. Consequently, optical principles are increasingly being considered in many areas where reliable data about the shape, the surface properties, the state of stress and the strength of the object under test have to be acquired. However, these advantages have to be paid with some serious disadvantages that are mainly connected with the poor features of identification problems. In this article several examples are presented where optical metrology is helpful for experimental mechanics. The presentation is mainly focused on two topics: the acquisition of quantitative data for experimental stress analysis and the solution of inspection problems by holographic non-destructive testing. Some current aspects such as modern approaches for the solution of identification problems, the installation of remote laboratories and the calibration of measurement set-ups by specially engineered calibration samples are discussed finally.

High-speed generation of digital holographic interferograms and shearograms for non-destructive testing

Digital holographic interferometry is the state-of-the-art technique in holography having applications in the fields of non-destructive testing, flow analysis and vibration measurement covering a wide range from huge aerospace structures to micro objects such as MEMS [1,2,3] In holographic non-destructive testing (HNDT), transient thermal loading is an extensively used method of stressing the objects for defect detection [4] . Test objects are stressed thermally using infrared lamps, flat heater or hot-water tanks depending on the object configuration and geometry, defect type and nature and the safety aspects. Holograms at different stress states of the object are recorded continuously, either during heating or during cooling after the removal of the heating element, to obtain interferograms. However, in order to capture and analyse the fast transient response of the structures upon thermal stressing, a system that records holograms and generates holographic interferograms in high speed is essential. Added to this, if the system can simultaneously generate shearograms, which provide a displacement derivative fringe pattern, this would increase its defect detection capability during NDT. In this paper the development of a digital hologram processing system which can record a digital hologram in high speed and generate holographic interferograms and shearograms simultaneously is reported. The design of the high-speed image processing system and selection of digital camera is also explained. The paper also gives details of the software developed and its features. The need for the high-speed system to record and generate interferograms during NDT of highly porous materials is also demonstrated in this paper.

Non-divestment laser applications in art conservation

Just as lasers have found applications in entertainment, science, industry, and medicine, numerous real and potential uses for lasers in art-conservation analyses and practice have been investigated over the past three decades. Initially, these included archival holographic recording, holographic non-destructive testing (NDT) of statues and paintings, laser-induced ultrasonic imaging of frescos and paintings, laser scattering for surface characterization of paint layers, photoacoustic spectroscopy (PAS) of pigments and varnishes, atomic and molecular microprobe analyses of artwork surfaces (e.g., LIBS), surface modification of stone, laser-induced chemistry (LIC), and surface divestment of art materials from leather to stone. In recent years, this list has been extended considerably. It now includes 3D replication, Raman spectroscopy and mapping, laser-induced fluorescence (LIF) detection and imaging, object repair through laser cutting and welding, laser-doppler techniques for the study of surface motion in order to discern internal features, and laser ranging for contour mapping. Twenty-five years ago, laser divestment/cleaning was, by widespread consensus of the conservation community, the least plausible laser application in art conservation. This attitude was fostered by several circumstances. Foremost, was a general ignorance of laser technology and its potential. Second, were genuine problems with laser reliability, cost, and maintenance. Third, were technology limitations in available wavelengths and beam director options. However, after 20 years of research and development, laser divestment (principally for stone) emerged to dominate all the other initial and latter applications noted above. In light of the current widespread acceptance of radiation-induced divestment (brought about by its practical successes), it is a propitious time to revisit and review those that overshadowed early alternative laser applications in terms of their histories, status, and prognoses. Subsequent advances in laser science and technology (as well as in associated computer systems for digital signal processing and laser control) will enhance and facilitate the practical uses of those other early opportunities for lasers in art conservation. Toward this end, the initial endeavors in exploring and assessing the utility of these tools for art conservation are recounted. Together with the manifest success of laser cleaning, both in the conservation laboratory and in the field, this review may serve to reinvigorate interest in these powerful scientifically established technologies and extend their application and acceptance to the broader art-conservation community.

Dual vacuum stressing technique for holographic nondestructive testing of honeycomb sandwich panels : Rao, MY.; Samuel, R.; Ramesh, K. NDT International, Vol. 23, No. 5, pp. 267–270 (5 Oct. 1990)

Dual vacuum stressing technique for holographic nondestructive testing of honeycomb sandwich panels : Rao, MY.; Samuel, R.; Ramesh, K. NDT International, Vol. 23, No. 5, pp. 267–270 (5 Oct. 1990)

Specialized techniques in holographic non-destructive testing of composites

Holographic interferometry is a very efficient technique used in non-destructive testing and characterizing of composites. Many kinds of defects may be simultaneously detected over large areas, without any contact with the tested material. All the defects appear as local distortions of a regular fringe pattern covering the holographic image of the tested object. Seeing a complicated fringe pattern with a large number of local distortions in a single image might be confusing for the operator, who is often interested in detecting a particular type of defect. In such cases, in order to apply the holographic technique, specialized testing techniques have to be established. This paper describes two such techniques, one for testing the metallic insertions in the belt area of rubber tyres, the other for testing pasteboard-epoxy composites, and detecting fiber direction and interactions.

The method of parameter estimation in holographic structural analysis

Holographic non-destructive testing (HNDT) techniques for structural analysis began in the 1960s. The first fringe patterns showed exciting information about the deformation of structures and other systems. The deformation was small and required minimal force to show interesting changes in the structure. The interest in using holographic techniques to perform structural analysis declined in the 1970s due to the inability to easily quantify the fringe information. The amount of time required to make one test, and the inability to really explain the response of the structure from the fringe information, also contributed to its decline. Interest revived in the 1980s with the advent of ‘TV’ holography. This brought CCD cameras, diode lasers and personal computers to the mainstream of holographic structural analysis. Automatic fringe analysis provided by these systems showed that information about the structure could be acquired in real-time and stored on video tape or storage disks. From these media the structure can be studied in detail. The industrial applications of HNDT have not grown at the rate expected by many, despite these many advancements. Fringes and fringe analysis alone do not provide information in a useful format for industry's growing and automated high technology needs. Inspection is becoming less important as Total Quality Control and other advanced manufacturing and management procedures replace the conventional ways of producing goods and service. New approaches to using HNDT techniques are needed. Additional improvements can also add to the attractiveness for industrial uses of HNDT. With the use of parameter estimation, this paper provides an alternative approach to using fringe information from existing systems. The goal is to provide industry with accurate results that describe, in quantifiable terms, the performance of the structure when varying loads are applied.

Application of laser, holographic, nondestructive testing by impact loading

A description of research on holographic, nondestructive testing (HNDT) with impact loading is presented to demonstrate the technique as a practical HNDT method. The advantages of impact, or impulse, loading coupled with pulsed-laser illumination for HNDT away from the laboratory are discussed. The effect of the loading position, exposure timing, and prestressing on test results is discussed in detail. Experimental verification of the appropriateness of pulsed-laser HNDT in the testing of honeycomb materials by using impact loading is discussed.

Neural network approach to holographic nondestructive testing

A neural network approach for the automatic detection of defects by evaluation of holographic interference patterns of the loaded technical components is described. Translation- as well as rotation-invariant features are defined based on the maximal local slope of the intensity and a partition of the interference pattern into nonoverlapping areas. The training sample set is generated by computer simulation of interferograms directed by a few typical experimentally measured samples. Practical results show the feasibility of the method. A strategy for application of neural networks to any holographic nondestructive testing task is outlined.

Applications of holographic interferometry for spacecraft structural components

An overview of the applications of holographic interferometry for spacecraft structural components at ISRO Satellite Centre, Bangalore, India, is presented. The details of the development of a dual vacuum stressing technique and its application for holographic nondestructive testing (HNDT) of honeycomb panels are presented. Results of some calibration studies conducted for HNDT of propellant tanks are also presented. It is found that holographic interferometry is quite useful, particularly for HNDT of honeycomb panels and propellant tanks used for spacecraft structural components.

Holographic nondestructive testing in bone growth disturbance studies

We used isolated radioulnar bones (fused radial and ulnar bones) of subadult European moose collected in various environmentally polluted areas of Finland. The bones were radiographed and holographic interference pictures, for holographic nondestructive testing (HNDT), were produced by using small caudocranial bending forces. The cortical index values were measured in the diaphyses and samples were taken for mineral studies from the mandibles of the same animals. Results indicated that the bones obtained from the heavily polluted area showed biomechanical response comparable to the bones developed partially without mothers milk. Differences were also seen in morphometrical and radiological studies. The mineral contents studied did not differ significantly from randomly collected samples of the same age category. We therefore conclude that environmental factors may influence the bone matrix development.

Bone structure studies with holographic interferometric nondestructive testing and x-ray methods

Changes in the biomechanics and in the molecular texture and structure of isolated radioulnar bones of subadult European moose (Alces alces L.) collected in various environmentally polluted areas of Finland were investigated by means of holographic interferometric nondestructive testing (HNDT), radiological, morphometrical, and x-ray diffraction methods. By means of small caudal-cranial bending forces, the surface movements of the lower end (distal epiphysis) of the radial bone were recorded with the HNDT method. To study bone molecular texture and structure changes under external compressing forces, the samples for x-ray diffraction analysis were taken from the upper end of the ulnar bone (olecranon tip). Results showed that the bones obtained from the Harjavalta area and those of North Karelian moose showing malnutrition and healing femoral fractures produced different HNDT pictures compared with the four normally developed North Karelian moose. In the x-ray diffraction, the Harjavalta samples showed changes in molecular texture and structure compared with the samples from the apparently normal North Karelian animals.

Biomechanical testing of isolated bones: holographic study

Holographic nondestructive testing (HNDT) is used to investigate the complex structures of bones of various shapes and sizes subjected to forces. Three antlered deer skulls of different species were investigated and significant species-specific differences were observed. The HNDT method was also used to verify the advanced healing of an osteosynthetized sheep jawbone. Radioulnar bones of a normal and an orphaned moose calf were subjected to a bending test. The undernourished calf showed torsio displacement combined with the bending of the bone, which was not seen in the normal calf. The effects ofthe masticatory forces on the moose skull surface were studied by simulating masseter muscle contractions with jawbones in occlusion. The fringe patterns showed fast-moving bone surfaces on the naso-maxillo-lacrimal region.