A New Capacitive Displacement Sensor With Nanometer Accuracy and Long Range

Abstract

A highly stable motion with orthogonally alternating electric field is established to build the relationship between spatial displacement and time standards. Displacement is measured by counting the time pulses that serve as measurement standards. Thus, a displacement method is called time grating. An orthogonally alternating electric field is generated using two rows of differential capacitive sensing electrodes excited by four sinusoidal voltages. Sine-shaped grating planes rather than hyperfine grating lines are used to pick up the displacement signals. Electrode lead wires are designed below the middle of the electrodes and fabricated using multilayer thin-film technology to suppress the cross-sensitivity effect. A time-grating sensor has been fabricated to evaluate the proposed method. The range of measurement is 200 mm, the width of the electrode is 0.2 mm, the interval between two adjacent electrodes is 20 $\mu \text{m}$ , and the gap for capacitive sensing is 0.3 mm. Experimental results indicate that the measurement accuracy reaches ±200 nm with 1-nm resolution. Nanometer accuracy and resolution are achieved using sensing units with sub-millimeter periods. So, the cost for manufacturing the time-grating sensor can be decreased effectively in comparison to traditional nanometrology displacement sensors, and it may be a suitable low-cost alternative to long-range nanometrology.