I am using a microchip MTCH101 IC as a proximity detector (based on a self-capacitance electrode) and i have some trouble in detection because of a floating local ground (i guess). The sensor is power supplied by a battery and is a wearable device.
I have read many times that mutual-capacitance is less dependant from grounding issue than self-capacitance, is it true? why ? (but never seen equation to prove it) ?
Is any fundamental detecting methods (CTMU, CVD, CSM,...) better than an other for grounding issue?
For self-capacitance, the grounding issue is comming from the fact the wearable battery power supplied device has an unfix and sometime low capacitance between its local ground and the earth. There is 2 cases: when it's handled by the second hand of the user and when the device is laid on a table. When there is a good coupling (high capacitance), its negligible and only the sensing electrode is measured. When it's not, the ground to earth coupling is taking part to the measurement as parasitic. I have found that the following way would help to improve this coupling :
Big ground plane at the device back, to increase surface which will be seen by the second hand or the table.
connexion from the device local ground to the device casing to let the human hand which hold the device have a contact with local ground and a better coupling.
Heating pipe (which i do not know)
"Use human finger to modify an electrical field between the electrode and the system ground, working as a dielectric constant modified". I interpret that as mutual-capacitance, is that correct ?
Finally, why the mutual capacitance would have less that kind of issue since that the charge exchanged with the finger are still flowing throught the earth and the device ground ?
