Literature references to earliest Fully Differential capacitive sensors:
(1) R. D. Peters, "Linear rotary differential capacitance transducer", Rev. Sci. Instr. 60, 2789 (1989)--U.S. Patent No. 5,028,875 (Figure 2 of the patent document shows the fully differential character of the LRDCT.).
The LRDCT was used in both driving and sensing modes by British researchers S. Atalay and P. T. Squire. Details are indicated in their article, "Torsional pendulum system for measuring the shear modulus and internal friction of magnetoelastic amorphous wires", Meas. Sci. Technol. 3, 735-9 (1992).
The LRDCT is mentioned in the electronic engineering reference book, Sensors and Signal Conditioning, by R. Pallas Areny and J. Webster, John Wiley and Sons, 1991 (ISBN 0-471-54565-1-398) --Chapter 4.1.2 describing differential capacitors.
(2) R. D. Peters et al, "Capacitive servo-device for microrobotic applications", Journal of micromechanics and microengineering 1991; VOL. 1; NO. 2; PP. 103-112
(3) R. Peters and Peter J. Seibt, "An inexpensive synchronous detector and its application to differential capacitance sensors, Rev. Sci. Instrum. 63, 3989 (1992).
(4) R. D. Peters, "Symmetric differential capacitive pressure sensor", Rev. Sci. Instr. 64, 2256 (1993).
(5) R. D. Peters, "Full-bridge capacitive extensometer", Rev Sci. Instr. 64, 2250 (1993).
(6) R. D. Peters, "Capacitive angle sensor with infinite range", Rev. Sci. Inst. 64, 810 (1993).
Concerning (3) - (6):
Researchers Kolb et al (Laboratory for Physical Sciences, College Park, Maryland) used the physics of the SDC sensor (c.f. ref. 10) to develop their "Capacitive sensor for micropositioning in two dimensions", Rev. Sci. Instrum., Vol. 69, No. 1, 312 (1998).
(7) R. D. Peters, "Remote Respiratory Monitor", Eighth IEEE Symposium on Computer-Based Medical Systems, pp. 204-211, 1995.
NOTE: Another equivalent term for 'fully differential' is 'fully active' [bridge]. John Cole published a paper in 1991 on the accelerometer that is at the heart of products marketed by Silicon Designs, Inc.: "A new sense element technology for accelerometer subsystems", Transducers '91, (1991) 93-96.
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