By using RFMicron's innovative Chameleon technology, the Magnus family of chips can be used either as a proximity sensor or as a pressure sensor.
I. Position Sensor (relative to metal)
A position sensor is mounted on a label, which is then mounted on a surface. A metal sticker is mounted on another surface, moving relative to the label. As the metal sticker gets closer to the label, the inductive reactance of the tuning ring decreases. The chameleon engine compensates for the low inductive reactance with high capacitance, resulting in a higher sensor code. The sensor then reports a closer proximity value using this higher sensor code.
Image: Sensing tuning ring, metallized pattern for a proximity/pressure sensor, MagnusS
II. Pressure Sensor
By using a pressure-sensitive spring between the metal plate and the sensor, a proximity sensor can be converted into a pressure sensor. A simple spring is a small block of closed-cell foam that changes its thickness with pressure. High pressure compresses the foam and then brings the metal plate close to the sensor, reducing its impedance. Just like with proximity sensors, the chameleon engine uses high capacitance to compensate for low impedance, resulting in a larger sensor code. The sensor reports high pressure for a high sensor code. Pressure sensors can use inexpensive, closed-cell foam to perform very low-cost sensing; however, the foam will age or degrade over time. High-precision pressure sensors can also use steel springs.
Figure: Average sensor code, pressure PSi, rising pressure (blue), falling pressure (red)
The performance of a sensor with a pressure chamber is shown below. Note that the pressure chamber resolution is 0.5 psi. The sensor achieves a very linear response to pressure with low latency. A simple linear correction can be applied to directly convert the sensor code reading value to psi (pounds per square inch).
For more information, please follow the Sensor Channel.
