Fiber-optic sensors in explosion and detonation experiments

At TNO, considerable effort has been invested into explosion and detonation experiments for energetic materials research. These investigations are required for both the development of new materials and the control optimization of existing materials. Typical measurements include detonation speed, response to high temperature and impact, and shock wave propagation in materials. It is obvious that the measurement systems must be designed with great care to minimize risk. They also need to be protected from the test environment. Furthermore, highspeed measurement is also required to record experimental phenomena. TNO has developed a number of measurement systems based on fiber optic technology. Relative to conventional electrical measurement technology, they offer significant advantages in terms of safety and/or cost. Fiber optic (FO) sensors are currently generating significant interest for special applications. This is because they basically have no electrical components at the measurement location and can be used without risk of interaction with the explosive materials under investigation. Furthermore, since an optical fiber has a typical diameter of 0.25mm, measurements can also be done at locations that are not accessible to other type of sensors. An example is the measurement of shock waves in explosives using a fiber Bragg grating (FBG). The loss in an optical fiber is generally extremely low. This allows placement of the detection unit and its electronics at a safe distance from the experiment without requiring expensive protection and shielding. These advantages allows these sensors to outperform their conventional electrical counterparts. We now describe some of our FO sensor systems developed for explosion or detonation experiments. The fiber optic probe (FOP) shown in Figure 1 is designed to detect the shockwave of detonation velocity in explosivematerials. It consists of a 1mm-diameter polymer fiber in which several holes are drilled at predetermined distances. It is designed for Figure 1. The fiber optic probe (FOP) in an experimental setup.