Three-dimensional imaging using a frequency-domain synthetic aperture focusing technique

Busse, L.J.

doi:10.1109/58.139112

Cited by 112 publications

(57 citation statements)

References 14 publications

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“…The same PSF can be reconstructed from a point source by using our recently published two-stage image reconstruction method. 24 First, the measured signals are converted into virtual acoustic waves, and then, any available ultrasound reconstruction method, such as the frequency domain synthetic aperture focusing technique (F-SAFT), 25 can be used for reconstruction. This gives the similar PSF only if the measurement time is long enough to allow the signals up to h % 45 to be measured and used for the reconstruction.…”

Section: (A)]mentioning

confidence: 99%

Super-resolution thermographic imaging using blind structured illumination

Burgholzer

Berer

Gruber

et al. 2017

Applied Physics Letters

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Using an infrared camera for thermographic imaging allows the contactless temperature measurement of many surface pixels simultaneously. From the measured surface data, the structure below the surface, embedded inside a sample or tissue, can be reconstructed and imaged, if heated by an excitation light pulse. The main drawback in active thermographic imaging is the degradation of the spatial resolution with the imaging depth, which results in blurred images for deeper lying structures. We circumvent this degradation by using blind structured illumination combined with a non-linear joint sparsity reconstruction algorithm. We demonstrate imaging of a line pattern and a star-shaped structure through a 3 mm thick steel sheet with a resolution four times better than the width of the thermal point-spread-function. The structured illumination is realized by parallel slits cut in an aluminum foil, where the excitation coming from a flashlight can penetrate. This realization of super-resolution thermographic imaging demonstrates that blind structured illumination allows thermographic imaging without high degradation of the spatial resolution for deeper lying structures. The groundbreaking concept of super-resolution can be transferred from optics to diffusive imaging by defining a thermal point-spread-function, which gives the principle resolution limit for a certain signal-to-noise ratio, similar to the Abbe limit for a certain optical wavelength. In future work, the unknown illumination pattern could be the speckle pattern generated by a short laser pulse inside a light scattering sample or tissue.

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Section: (A)]mentioning

confidence: 99%

Super-resolution thermographic imaging using blind structured illumination

Burgholzer

Berer

Gruber

et al. 2017

Applied Physics Letters

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“…Today, the F-SAFT method is investigated for imaging simulated and real defects in several applications such as the detection of inclusions in steel slabs, visualization cracks and delaminations along curved interfaces. One method is the frequency domain SAFT (F-SAFT), whereby data processing is performed in a 3-D Fourier space using the angular spectrum method [13,14] (Fig. 7).…”

Section: The F-saft Proceduresmentioning

confidence: 99%

A New Diagnosing Method of the Internal Structure of the Titanium Fan of a Jet Engine with Laser Ultrasonics

Swornowski¹

2011

Metrology and Measurement Systems

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Advanced metallic material processes (titanium) are used or developed for the production of heavily loaded flying components (in fan blade construction). The article presents one process for diagnosing the blade interior by means of laser ultrasonography. The inspection of these parts, which are mainly made of titanium, requires the determination of the percentage of bonded grain sizes from around 10 to 30 m. This is primarily due to the advantages of a high signal-to-noise ratio and good detection sensitivity. The results of the research into the internal blade structure are attached.

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“…One reconstruction method which directly uses the time invariance of the virtual wave signal is time-reversal reconstruction, 14,21,22 and another one which works well for planar sample surfaces is the frequency domain synthetic aperture focusing technique (F-SAFT). [23][24][25] In this work, we introduce the concept of virtual waves for thermographic image reconstruction for the case of short excitation pulses. However, the introduced concept can be easily transferred to other temporal excitation schemes.…”

Section: Introductionmentioning

confidence: 99%

Three-dimensional thermographic imaging using a virtual wave concept

Burgholzer

Thor

Gruber

et al. 2017

Journal of Applied Physics

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In this work, it is shown that image reconstruction methods from ultrasonic imaging can be employed for thermographic signals. Before using these imaging methods, a virtual signal is calculated by applying a local transformation to the temperature evolution measured on a sample surface. The introduced transformation describes all the irreversibility of the heat diffusion process and can be used for every sample shape. To date, one-dimensional methods have been primarily used in thermographic imaging. The proposed two-stage algorithm enables reconstruction in two and three dimensions. The feasibility of this approach is demonstrated through simulations and experiments. For the latter, small steel beads embedded in an epoxy resin are imaged. The resolution limit is found to be proportional to the depth of the structures and to be inversely proportional to the logarithm of the signal-to-noise ratio. Limited-view artefacts can arise if the measurement is performed on a single planar detection surface. These artifacts can be reduced by measuring the thermographic signals from multiple planes, which is demonstrated by numerical simulations and by experiments performed on an epoxy cube.Comment: 22 pages, 8 figures, 1 appendix, acceapted by JA

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Three-dimensional imaging using a frequency-domain synthetic aperture focusing technique

Cited by 112 publications

References 14 publications

Super-resolution thermographic imaging using blind structured illumination

Super-resolution thermographic imaging using blind structured illumination

A New Diagnosing Method of the Internal Structure of the Titanium Fan of a Jet Engine with Laser Ultrasonics

Three-dimensional thermographic imaging using a virtual wave concept

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