Patent ID: 7113179

Claim:
A force sensing resistor comprising: first and second substrates each having inner surfaces, wherein at least one of the substrates is flexible in order to move towards the other one of the substrates in response to an applied force; a plurality of electrically conductive traces on the inner surface of the first substrate, the traces including a first finger, a common finger, and a calibration finger which together define a contact area on the inner surface of the first substrate; wherein the first finger, the common finger, and the calibration finger are electrically separated from one another; a spacer substantially surrounding the contact area and attaching the substrates together such that a cavity separates the inner surfaces of the substrates in the contact area; a first resistive layer on the inner surface of the second substrate such that the first resistive layer is arranged within the cavity, wherein the common finger and the calibration finger are physically distinct from the first finger and the first resistive layer; wherein, in response to a force applied to a flexible substrates, the first resistive layer contacts and electrically connects the first finger and the common finger together with a resistance dependent upon resistivity of the first resistive layer and the applied force in order to produce an electrical signal indicative of the applied force; and a second resistive layer arranged within the cavity such that the second resistive layer contacts and electrically connects the calibration finger and the common finger together with a resistance dependent upon resistivity of the second resistive layer in order to produce an electrical signal indicative of the resistivity of the second resistive layer.