A passive optical proximity sensor

TLDR: In this paper, a 3D printed model is used for proving the concept and subsequent experiments prove that it is possible to determine the distance between a light source and the sensor by measuring the light intensity and the angle at which the light is incident towards the sensor.

Abstract: A new optical proximity sensor was developed and studied in this project. A 3D printed model is used for proving the concept. An integrated model with a new geometry was then microfabricated to further improve the sensor model’s performance. The sensing operation is based on measurement of light intensity falling on photodiodes placed at an inclined angle with respect to the base surface of the sensor. A mathematical model and subsequent experiments prove that it is possible to determine the distance between a light source and the sensor. This sensor is operated passively which means it does not need an active emission for range sensing. The sensor shows reliable operation for short range proximity detection in the range of 5-15 cm. The sensor structure is pyramidal placed flat on the surface with a fixed base angle. Two independent photodiodes are formed on two of the opposite sides of the pyramid. One such pyramid pixel is able to measure the light intensity and the angle at which the light is incident towards the sensor. Using the intensity measured by micro-fabricated test pyramids structures, the distance to the light source is measured. The experimental values demonstrate that the measurements are accurate and repeatable, more so, the device utilizes no active emission to attain proximity measurements. The discussed device can be used for close and continuous proximity detection in mobile devices with low power consumption.