| Popis: |
The ultimate aim of the work described here is to explore miniaturised electrical tomography systems. The initial target, described in this paper, has been to implement a sensor, integrated on silicon, and able to detect particles as small as 10 pm in diameter from changes in capacitance. 3D finite element modelling has been used to determine the capacitance changes due to the presence of small particles and to explore electrode geometries to give optimum sensitivity. Interdigitated electrodes, measuring 25µm on a side, have been integrated alongside measurement circuitry using a 0.8µm CMOS process. The measurement circuitry is able to detect changes in capacitance down to tens of attofarads. Computational fluid dynamics has been used to determine the likely trajectories of particles in the vicinity of the sensor and confirm that they are likely to hit the surface. Static tests verify the sensitivity of the sensor to horizontal and vertical displacement of small particles. Dynamic tests show that the sensor is able to detect the presence of plastic particles, as small as 20µm diameter, conveyed in an air stream moving at up to 10 m/s. Time resolution is currently 2 µs. Recent work has yielded high speed video images of the particles as they hit the surface of the chip and these are to be used to verify correct operation of the sensors. |
