Through the innovative use of RFMicron’s Chameleon™ technology the Magnus family of ICs can be used as either a proximity sensor or a pressure sensor.
Positioning Sensor (relative to metal)
A positioning sensor mounts the tag onto one surface and a metal patch onto another surface that moves relative to the tag. As the patch moves closer to the tag, the inductance of the tuning loop decreases. The Chameleon Engine compensates for the lower inductance with higher capacitance which is then readable as a SENSOR CODE with higher value. The sensor reports closer proximity with higher sensor codes.
The proximity sensor can be converted into a pressure sensor by using a pressure-sensitive spring between the sheet (metal patch) and the inductor. A simple spring is a small block of closed cell foam, which changes its thickness with pressure. Higher pressures compress the foam and brings the metal sheet closer to the inductor, lowering its inductance. Just as for the proximity sensor, the Chameleon engine compensates for the lower inductance with higher capacitance leading to a larger SENSOR CODE. The sensor reports higher pressure as higher sensor codes. Pressure sensors can use inexpensive, closed-cell foams to implement very low-cost sensors; however, foams can wear out or degrade over time. Higher precision pressure sensors using steel springs are also possible.
The performance of the sensor in a pressure chamber is shown below. Note that the resolution of the pressure chamber is 0.5 psi. The sensor achieves very linear response to pressure with low hysteresis. A simple linear calibration can be applied to convert the SENSOR CODE reading directly to psi.