The silicon-glass MEMS high dose radiation sensor with the optical read-out, acting above 10 kGy has been presented. The sensor consists of a microchamber filled with small portion of high density polyethylene (HDPE) and thin silicon membrane. The principle of operation of the sensor is based on radiolysis effect of the HDPE which, upon radiation exposure, releases the hydrogen. The hydrogen increases the pressure inside the microchamber causing the deflection of the membrane, which is proportional to the pressure, thus to radiation dose. The sensor has been irradiated with high energy electron beam with dose 5÷40 kGy. The displacement of the membrane has been detected by optical interferometer. The relative generated pressure inside the sensor chamber has been found very high (up to 180 kPa). It shows that response of a micro-scaled MEMS sensor is much more effective in comparison to macro-scaled solutions.
We present a miniature silicon–glass MEMS sensor for measurement of high doses of ionizing radiation (above 10 kGy) using a novel wireless optical detection method. The radiation sensor is a miniaturized version of the so-called hydrogen dosimeter. An amount of high-density polyethylene, located inside the MEMS sensor, degrades under ionizing radiation, releasing gaseous hydrogen. The increasing pressure deflects the thin silicon membrane. The sensor’s destructive and proportional modes of work are also proposed. In the destructive mode, sensors provide in situ information on excessive and discrete levels of radiation.
The optical detection method is based on an optical head consisting of a moving membrane and a silicon screen with a matrix of micro-holes. Laser light is reflected from the membrane and scattered when the membrane is deflected, in the process illuminating the holes on the silicon screen. The number of illuminated holes is a function of the degree of membrane deflection; the transformation of the holes to the deflection allows for the calculation of pressure and eventually the dose of ionizing radiation.
In this paper a special optical detection system designed for a MEMS-type (micro-electro-mechanical system) silicon pressure sensor is presented. The main part of the optical system—a detection unit with a perforated membrane—is bonded to the silicon sensor, and placed in a measuring system. An external light source illuminates the membrane of the pressure sensor. Owing to the light reflected from the deflected membrane sensor, the optical pattern consisting of light points is visible, and pressure can be estimated. The optical detection unit (20 × 20 × 20.4 mm3) is fabricated using microengineering techniques. Its dimensions are adjusted to the dimensions of the pressure sensor (5 × 5 mm2 silicon membrane). Preliminary tests of the optical detection unit integrated with the silicon pressure sensor are carried out. For the membrane sensor from 15 to 60 µm thick, a repeatable detection of the differential pressure in the range of 0 to 280 kPa is achieved. The presented optical microsystem is especially suitable for the pressure measurements in a high radiation environment.
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