Anti Crime Design

Aan de Universiteit Twente is in 2009 de onderzoekgroep Crime Science Twente (CST) opgericht, waarin diverse faculteiten samenwerken. Inmiddels zijn verschillende onderzoekprojecten tot stand gebracht en is er een minor ontwikkeld waaraan studenten hebben deelgenomen. Vanuit de faculteit Constructieve Technische Wetenschappen (CTW) maakt Wim Poelman deel uit van de CST. De inbreng van CTW richt zich hoofdzakelijk op de rol die de ontwerper kan spelen bij het voorkomen van misdaad

Exploring Community Building with an Awareness Display

In this paper, we present a field trial of a pervasive system called Panorama that is aimed at supporting social awareness in work environments. Panorama is an intelligent situated display in the staff room of an academic department. It artistically represents non-critical user generated content such as images from holidays, conferences and other social gatherings, as well as textual messages on its display. It also captures images and videos from different public spaces of the department and streams them onto the Panorama screen, using appropriate abstraction techniques. We studied the use of Panorama for two weeks and observed how Panorama affected staff members’ social awareness and community building. We report that Panorama simulated curiosity and learning, initiated new interactions and provided a mechanism for cherishing old memories

Frequency-phase modulated thermal wave radar : stepping beyond state-of-the-art infrared thermography

Thermal wave radar is a state-of-the-art non-destructive testing method inspired by radio wave radar systems. The underlying principle of the technique is the application of a modulated excitation waveform by which the total energy of the response signal can be compressed in time-domain through cross-correlation. This leads to an enhanced depth resolution and increased signal to noise ratio in optical infrared thermography. Frequency sweep and Barker binary phase modulation are the two popular and widely researched excitation waveforms of the technique. In this research, a novel frequency-phase modulated waveform is introduced, which is designed for optimized performance of thermal wave radar

Backside delamination detection in composites through local defect resonance induced nonlinear source behavior

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Multi-scale gapped smoothing algorithm for robust baseline-free damage detection in optical infrared thermography

Flash thermography is a promising technique to perform rapid non-destructive testing of composite materials. However, it is well known that several difficulties are inherently paired with this approach, such as non-uniform heating, measurement noise and lateral heat diffusion effects. Hence, advanced signal-processing techniques are indispensable in order to analyze the recorded dataset. One such processing technique is Gapped Smoothing Algorithm, which predicts a gapped pixel’s value in its sound state from a measurement in the defected state by evaluating only its neighboring pixels. However, the standard Gapped Smoothing Algorithm uses a fixed spatial gap size, which induces issues to detect variable defect sizes in a noisy dataset. In this paper, a Multi-Scale Gapped Smoothing Algorithm (MSGSA) is introduced as a baseline-free image processing technique and an extension to the standard Gapped Smoothing Algorithm. The MSGSA makes use of the evaluation of a wide range of spatial gap sizes so that defects of highly different dimensions are identified. Moreover, it is shown that a weighted combination of all assessed spatial gap sizes significantly improves the detectability of defects and results in an (almost) zero-reference background. The technique thus effectively suppresses the measurement noise and excitation non-uniformity. The efficiency of the MSGSA technique is evaluated and confirmed through numerical simulation and an experimental procedure of flash thermography on carbon fiber reinforced polymers with various defect sizes

Flash thermography of composites : evaluation of advanced post-processing approaches

Carbon fiber reinforced polymers (CFRP) are composite materials that offer a high stiffness-to-weight ratio in comparison to traditional metals, which explains their increasing use in many high-end applications (e.g. aerospace). However, composites are prone to internal damage that may deteriorate the structural integrity, and thus require reliable and non-destructive testing (NDT) approaches. Infrared thermography (IRT) is a promising NDT technique which provides fast, full-field measurements, and in which hidden defects are detectable based on their thermal signatures. In flash thermography (FT), which is the thermographic technique of interest for this contribution, the component’s surface temperature is rapidly elevated through the application of an intense optical flash. Subsequent recording of the cooling down of the stimulated surface, by means of a high-end infrared camera, allows to detect defects by searching for anomalies in the surface temperature (due to heat build-up above the defect). Considering the anisotropic diffusivity and high damping of thermal waves in CFRP, advanced post-processing techniques are indispensable to detect deep defects (> 2 mm in CFRP). In this paper, FT is performed on several CFRPs with various defects (flat bottom holes, Teflon inserts and barely visible impact damage). This thermographic dataset is then analyzed using various post-processing techniques, including pulsed phase thermography (PPT), principal component thermography (PCT), thermographic signal reconstruction (TSR) and dynamic thermal tomography (DTT), in order to improve the defect detectability and assessment. The performance of the employed processing techniques is critically evaluated

Enhanced detectability of barely visible impact damage in CFRPs : vibrothermography of in-plane local defect resonances

This paper demonstrates the enhanced detectability of barely visible impact damage in CFRPs through low power vibrothermography of in-plane local defect resonances (LDR). In-plane LDR (LDRxy), with a higher cut-off frequency than out-of-plane LDR (LDRz), generally enhances the rubbing interaction and viscoelastic damping of defects and leads to higher vibration-induced heating. The most prominent LDRz and LDRxy frequencies of an impacted CFRP are extracted from its vibrational spectra under a broadband sweep excitation, measured by a 3D infrared laser Doppler vibrometer. The sample is then inspected through lock-in vibrothermography at the extracted LDR frequencies and the distintively higher detectability of LDRxy compared to LDRz is evidenced. Moreover, it is observed that the thermal contrast induced by LDRxy is so high, that it allows for easy detection of impact damage by live monitoring of infrared thermal images during a single broadband sweep vibration excitation