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Piezoelectric sensor arrays and sensor networks have been suggested as a mean to monitor the integrity of composite structures throughout the service life for instance of an aircraft. Complex sensor systems will require significant additional expenditures with respect to cabling and electronics, with the added weight and effort possibly outweighing any benefits. Sensor positions in remote locations of an aircraft will often necessitate accessibility to these locations for maintenance purposes. For these reasons wireless, integrated sensors have recently become an object of increasing interest.Within the framework of a feasibility study various aspects of integrated wireless sensor systems were investigated in detail.Particular emphasis was thereby laid on issues that are essential from a practical point of view, but that have not been discussed in the literature extensively.As a starting point a trade-off study between different sensor network configurations was conducted, from passive, remotely queried sensors without power supply to fully functional active sensor pads with integrated power supply and electronics. Various concepts for the on-board energy supply of remotely queried sensor pads were studied and a comparison between rechargeable, and single-use batteries was performed. The suitability of different electronic components for integration into carbon fiber composites (CFC) was investigated with particular emphasis on their survivability under typical temperatufe cycles experienced in autoclave runs.Finally a crackwire sensor as an example of a passive remotely queried sensor system was pursued further in order to show the feasibility of such a wireless system for composite health monitoring purposes.

Between 1985 and 1990, 517 patients were treated for colorectal malignancies at our department of surgery. Nd:YAG laser therapy was used in 37 cases (7.1%). The mean age of these 22 men and 15 women was 71.4 years (range: 22-96 years). One hundred-twenty-nine Nd:YAG laser treatments were performed. Indications for laser treatment were (1) palliative tumor reduction (n = 21), (2) preresectional laser recanalization for obstructing carcinoma (n = 6), and (3) curative treatment (n = 10). Laser related complications included one perforation of the rectum and one rectovaginal fistula. One fatal pulmonary embolism occurred. After palliative treatment, five patients died because of tumor progression (mean survival time: 16 months), two because of other reasons. All patients with obstructing tumors could be recanalized successfully. After curative treatment, eight patients are still alive without tumor recurrence (mean survival time: 25.5 months), and two died of other causes. Palliative Nd:YAG laser treatment of colorectal malignancies is a competitive alternative to conventional surgery. Recanalization of obstructing tumors is an excellent treatment for large bowel obstruction, making one-stage resections possible. Curative treatment should be reserved for special cases only.

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