Optical smoke detector: an approach to semiconductors field for high level education students

Abstract

Nowadays, it is undeniable that the amount of technological devices is having a sharp increase all around us, with important benefits and repercussions for the society. Despite this, students are not used to knowing the basic principles of its operations. Hence, it is of utmost importance to approach undergraduate students to a practical example of a device they can find in their daily life.

It is a fact that science is interconnected with multiple disciplines, such as Physics and Solid State Chemistry, Materials Science and Engineering. A good example of it is a smoke detector because it combines both optical and electrical behaviour. Such a device contains a chamber inside which there is an infrared LED (light-emitting diode) and a photodiode (light detector). When the path of light is interrupted by the smoke, according to the principle of light scattering, the smoke will scatter a fraction of light into the photodiode, activating the detector. Thus, detecting low levels of smoke is vital for preventing the fire expansion and occupants can get more time to escape from the premises.

The main purpose of this work is to help students to understand the work mechanism of the LED and photodiode in basis of their material composition. In order to do that, a smoke detector is disassembled and its different parts are observed. After that, the microstructure and composition of them are fully analysed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX) techniques. With these experiments, students have gained knowledge about semiconductors materials and got a more accurate understanding of their role in these devices.

All in all, this experience has allowed them to keep in contact during the whole study with three main concepts of Materials Science: composition, structure and properties. This fact make the work interesting not only from the point of view of students, but also for teachers of Inorganic Chemistry and Materials Science owing to its pedagogical character employing a Problem Based Learning.