Abstract: A capacitive strain gage includes a housing attachable to a test specimen at a first location and a ground plane attachable to the test specimen at a second location. The housing and the ground plane are movable relative to each other. A passage extends through the housing between opposing spaced-apart surfaces. First and second excitation electrodes are located on one of the surface, and a third signal electrode is located on the other of the surfaces. The electrodes each have fixed positions on the housing. Each of the first and second electrodes is positioned for capacitive coupling to the third electrode. The ground plane includes an arm that extends into the passage in the housing. The arm includes an aperture for electric fields that is aligned with the electrodes in a quiescent position.