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Thermal analysis of PDMS light bulbs with a luminophore DOI:10.15199/48.2018.12.02

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1. Introduction Polydimethylsiloxane (hereinafter referred to as PDMS) has been primarily designed to encapsulate photovoltaic cells, printed circuit boards, transformers, current sources, thermally stressed cables, optical connectors, etc. [1-3]. Later, it also began to be used for other purposes because it conveniently combines mechanical, electrical and optical properties. In the 3D printing technology using the method of DPL (Digital Light Processing), it is used for the production of a printing base and is also widely used for fine lithography techniques, especially for the creation of microfluidic and microengineering systems - MEMS (Micro Electro Mechanical Systems). For example, the authors of the publication [4] describe an optical biopsy microsystem technology that has smaller dimensions (11.2 x 18.6 mm) compared to other systems and reduced power consumption. The microsystem includes an image magnification optical microsystem (IMOM) and light emitting diodes (LED). Microlenses made from PDMS are integrated into the IMOM subsystem to achieve image magnification and to improve LED illumination. Other interesting solutions in the field of MEMS systems are described by authors of publications [5-10]. Publication [11] describes a new construction of a hybrid multichannel optical sensor system designed to monitor patient's vital functions. The noninvasive measuring probe is based on two FBGs encapsulated in the polymer; the authors selected the PDMS polymer because it is inert. There was no deformation of the FBG sensors in the vulcanization process; after the vulcanization, a fourfold increase in temperature sensitivity was observed compared to the nonencapsulated FBG. The probe and the associated multichannel system offer the ability to monitor the basic vital functions (body temperature, heart rate and respiratory rate) in up to 128 patients. The same issue is addressed by the authors of publications [12-15]. Ot[...]

Micro-bending sensor made from polydimethylsiloxane DOI:10.15199/48.2019.06.02

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Polydimethylsiloxane (PDMS) is a polymeric material on the basis of silicone, which is used in many scientific fields for various applications. One of the key characteristics is the excellent heat resistance of the material, under long term heat exposure PDMS resists temperatures of 200 °C and for short term exposure temperatures up to 350 °C. This is why it is very often used in electronics for pouring plates of wide connectors, transformers, power sources and so on. The authors of publication [1] concentrate on one concrete type of polydimethylsiloxane identified as Sylgard 184 and check its mechanical characteristics at various hardening temperatures (25 - 200 °C). The results show that the hardening temperature can change certain mechanical characteristics of PDMS. Samples prepared at a hardening temperature of 25 °C showed a hardness value of 43.8 Shore A, whereas samples prepared at a temperature of 200 °C showed a hardness value of 54 Shore A. In the construction of sensors (particularly pressure sensors) this information is very important because the hardness of the material undoubtedly affects the resulting behaviour of the sensor. Publication [2] describes a magnetic pole sensor which is constructed from two types of PDMS and a multimodal optical fibre with iron nano-particles. The cover of the sensor is formed by hard polydimethylsiloxane and the internal part of the sensor is filled with a soft silicon gel based on PDMS, so that it is possible using a magnetic field to deflect the first optical fibre with the iron nano-particles. The deviation of the optical fibre has an output of lowering the optical performance. A sensor set up like this can detect a magnetic field up to 0.3 T. A slightly altered sensor can also for instance detect vibrations up to 100 Hz, as is shown in publication [3]. A simple form of pressure sensor made from PDMS is shown in publication [4]. When manufacturing the sensor it is very impo[...]

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