FlexStylus, a flexible stylus, detects deformation of the barrel as a vector with both a rotational and an absolute value, providing two degrees of freedom with the goal of improving the expressivity of digital art using a stylus device. We outline the construction of the prototype and the principles behind the sensing method, which uses a cluster of four fibreoptic based deformation sensors. We propose interaction techniques using the FlexStylus to improve menu navigation and tool selection. Finally, we describe a study comparing users' ability to match a changing target value using a commercial pressure stylus and the FlexStylus' absolute deformation. When using the FlexStylus, users had a significantly higher accuracy overall. This suggests that deformation may be a useful input method for future work considering stylus augmentation.

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Structurally integrated sensors which are capable of continuous structural health monitoring represent an attractive option in view of their potential for providing real-time assessment/ warning of structural damage. In recent years, optical fiber systems have attracted a considerable amount of attention and have been shown to be a very attractive option for health monitoring in advanced composite materials. These sensors have either been embedded or surfacebonded to the host material thereby allowing continuous assessment of the health of the structure. Structural health assessment takes the form of damage detection and/or monitoring of specific health indicators. In the former approach, the optical fiber systems are generally optimized to increase their sensitivity to the presence of damage in the composite structure, while the latter approach relies on the examination of characteristic changes in the monitored parameter to infer a loss in structural integrity. To this end, many investigators have demonstrated the potential of optical fiber sensors, most particularly intensity-based optical fiber systems and fiber Bragg grating sensors for structural health monitoring of advanced composite materials. The initial part of this paper provides an up-to-date review of the applications of optical fiber sensors in composite materials, focussing particularly on the use of intensitybased optical fiber systems and fiber Bragg grating sensors for damage detection. These optical fiber systems have been shown to be capable of detecting impact damage, transverse cracking, and delamination, and have the ability to monitor strain in structures. The introduction of optical fiber sensors into a composite material can inadvertently produce a geometrical discontinuity in the vicinity of the sensor. Numerous experimental investigations have also been performed to assess the possible reduction in the properties of the host structure. A review of the findings of these investigations reported in the literature is also given. This review article cites 161 references.

While a number of literature reviews have been published in recent times on the applications of optical fibre sensors in smart structures research, these have mainly focused on the use of conventional glass-based fibres. The availability of inexpensive, rugged, and large-core plastic-based optical fibres has resulted in growing interest amongst researchers in their use as low-cost sensors in a variety of areas including chemical sensing, biomedicine, and the measurement of a range of physical parameters. The sensing principles used in plastic optical fibres are often similar to those developed in glass-based fibres, but the advantages associated with plastic fibres render them attractive as an alternative to conventional glass fibres, and their ability to detect and measure physical parameters such as strain, stress, load, temperature, displacement, and pressure makes them suitable for structural health monitoring (SHM) applications. Increasingly their applications as sensors in the field of structural engineering are being studied and reported in literature. This article will provide a concise review of the applications of plastic optical fibre sensors for monitoring the integrity of engineering structures in the context of SHM.

Plastic optical fibres have been employed to detect initial cracks, monitor post-crack vertical deflection and detect failure cracks in concrete beams subjected to flexural loading conditions. The intensity-based sensor system relies on monitoring the modulation of light intensity within the optical fibre as the sensor is loaded. The sensor design offers good signal stability and sensitivity to the monitored parameter and represents a cost-effective alternative to other more sophisticated health-monitoring systems currently used in civil engineering structures.Here, a series of three-and four-point bend tests was conducted on a range of structures. Initially, the optical fibres were attached to scale-model concrete samples (without reinforcement) to evaluate their ability to monitor beam deflection and detect cracks. Similar tests were subsequently conducted on life-size concrete beams containing reinforcing steel bars. The location and subsequent trajectory of cracks during the loading regime were marked and then compared to the sensor signal to assess the sensor's ability to monitor crack development.The results demonstrate the possibility of using optical fibres to detect hairline cracks and ultimate failure crack in civil engineering structures and highlight their ability to monitor crack propagation up to ultimate failure. In addition to detecting the initiation of a crack, good agreement between the sensor output and crack progression during loading was also obtained in these concrete beams.

Plastic optical fibre sensors offer remarkable ease of handling, and recent research has shown their potential as a low-cost sensor for damage detection and structural health monitoring applications. This paper presents details of a novel extrinsic polymer-based optical fibre sensor and the results of a series of mechanical tests conducted to assess its potential for structural health monitoring. The intensity-based optical fibre sensor proposed in this study relies on the modulation of light intensity as a function of a physical parameter (typically strain) as a means to monitor the response of the host structure to an applied load. Initially, the paper will reveal the design of the sensor and provide an outline of the sensor fabrication procedure followed by a brief description of its basic measurement principle. Two types of sensor design (fluid type and air type) will be evaluated in terms of their strain sensitivity, linearity and signal repeatability. Results from a series of quasi-static tensile tests conducted on an aluminium specimen with four surface-attached optical fibre sensors showed that these sensors offer excellent linear strain response over the range of the applied load. A comparison of the strain response of these sensors highlights the significant improvement in strain sensitivity of the liquid-filled-type sensor over the air-filled-type sensor. The specimens were also loaded repeatedly over a number of cycles and the findings exhibited a high degree of repeatability in all the sensors. Free vibration tests based on a cantilever beam configuration (where the optical fibre sensor was surface bonded) were also conducted to assess the dynamic response of the sensor. The results demonstrate excellent agreement with electrical strain gauge readings. An impulse-type loading test was also performed to assess the ability of the POF sensor to detect the various modes of vibration. The results of the sensor were compared and validated by a collocated piezofilm sensor highlighting the potential of the POF sensor in detecting the various eigen-frequencies of the vibration. Finally, preliminary results of a loading-unloading test of the same sensor design encased within a metal tube will be presented. The results obtained were encouraging offering the possibilities of employing the proposed device as an embedded sensor for damage detection in concrete beams.

Recently, optical fibre Bragg gratings have attracted a significant amount of attention as optical fibre sensors for measuring strain in composite structures. Indeed, the growth of optical fibre technology has spurred the development of smart composites capable of measuring real-time internal strain within structures and an assortment of measurands such as temperature, pressure and chemical. In this paper, optical fibre Bragg grating sensors are embedded in a novel fibre-metal laminate composite, to demonstrate the potential of fibre Bragg grating sensors in measuring post-processing residual strain within a multimaterial structure. Repeated impact tests in the region of the grating have been performed to investigate the survivability of the sensor. In addition, post-impact sensor linearity tests have then been carried out to evaluate the sensor response to load.

The acoustic emission (AE) technique is a promising approach for detecting and locating fatigue cracks in metallic structures such as rail tracks. However, it is still a challenge to quantify the crack size accurately using this technique. AE waves can be generated by either crack propagation (CP) or crack closure (CC) processes and classification of these two types of AE waves is necessary to obtain more reliable crack sizing results. As the pre-processing step, an index based on wavelet power (WP) of AE signal is initially established in this paper in order to distinguish between the CC-induced AE waves and their CP-induced counterparts. Here, information embedded within the AE signal was used to perform the AE wave classification, which is preferred to the use of real-time load information, typically adopted in other studies. With the proposed approach, it renders the AE technique more amenable to practical implementation. Following the AE wave classification, a novel method to quantify the fatigue crack length was developed by taking advantage of the CC-induced AE waves, the count rate of which was observed to be positively correlated with the crack length. The crack length was subsequently determined using an empirical model derived from the AE data acquired during the fatigue tests of the rail steel specimens. The performance of the proposed method was validated by experimental data and compared with that of the traditional crack sizing method, which is based on CP-induced AE waves. As a significant advantage over other AE crack sizing methods, the proposed novel method is able to estimate the crack length without prior knowledge of the initial crack length, integration of AE data or real-time load amplitude. It is thus applicable to the health monitoring of both new and existing structures.