Sensing over a shared physical channel
In one aspect the invention provides a sensing apparatus comprising a set of N capacitive sensors connected over a single physical channel provided by two terminals, the apparatus comprising: a sensing array having a first capacitive sensor and N−1 parallel capacitive sensors each connected in parallel with first capacitive sensor, each capacitive sensor having electrodes separated by a dielectric to provide a capacitance which is able to vary with deformation to provide sensing, the array having a set of N−1 resistances each being in series with a respective one of the N−1 parallel capacitive sensors; a solution module operable to determine the capacitance of each capacitive sensor by finding solutions for a vector function equating reactance measured at the two terminals to an analytical model for impedance and/or reactance of the circuit seen at the two terminals, wherein the analytical model comprises N capacitances, each connected in parallel with each other, and comprises N series resistances each connected in series with a respective capacitance.
1. An apparatus, comprising:
an array of sensors comprising N resistor and capacitor pairs, wherein each resistor and capacitor pair is connected:
in parallel with the capacitor of a preceding N−1 resistor and capacitor pair, and
in series with the resistor of the preceding N−1 resistor and capacitor pair; and
a device operable to measure capacitances and/or resistances in the array of sensors, the device being adapted to connect to the array of sensors over a single physical channel provided by two terminals and being operable to provide at the two terminals an excitation signal for the array of sensors, the excitation signal having N frequency components, and operable on data carrying information on a vector function to determine values of capacitance and/or resistances for the array of sensors, the vector function operable to equate at each of the N frequency components:
a) impedance measured at the two terminals;
b) an analytical expression approximating the circuit impedance ZN provided in combination by the array of sensors defined as:
Z
N
=
R
N
+
1
jω
i
C
N
+
1
R
N
-
1
+
1
jω
i
C
N
-
1
+
1
⋮
R
2
+
1
jω
i
C
2
+
1
R
1
+
1
jω
i
C
1
ω i =2πf i where i=1 . . . N, where i=1 . . . N, where C 1 is the first capacitance, C 2 is the second capacitance, where C N−1 is the N−1 th capacitance, Cn is the n th capacitance, R 1 is the series resistance of the first capacitance, R 2 is the resistance of the second capacitance, R N−1 is the series resistance of the N−1 th capacitance, and R N is the series resistance of the N th capacitance, where w, is the angular frequency of the excitation signal, f i is the frequency of the excitation frequency component applied to the circuit described by the impedance ZN, f 1 is the first frequency, f 2 is the second frequency, f N−1 is the N−1 th frequency, and f N is the N th frequency.
2. The apparatus of claim 1 wherein the array of sensors, in combination with the device, comprises N resistances of selected and known value, each resistance being in series with a respective capacitance.
3. The apparatus of claim 1 wherein the array of sensors in combination with the device comprises a set of M resistances of selected and known value and N-M capacitances of selected and known value.
4. The apparatus of claim 1 wherein the array of sensors in combination with the device comprises any number of N or less capacitances to be determined and N or less resistances to be determined and the device is configured to equate both the real components and imaginary components of impedance measured at the two terminals and the analytical expression approximating the circuit.
5. The apparatus of claim 4 wherein the N or less resistances are circuit equivalent resistances to resistances of deformable leads of the array which vary in resistance with deformation.