Passive charge modulation for a wireless pressure sensor

• Published in: IEEE sensors journal Vol. 6; no. 1; pp. 47 - 54
• Main Authors: Theurer, C.B., Li Zhang, Kazmer, D.O., Gao, R.X., Jackson, R.W.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-02-2006; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Analog to digital converter; Charge; charge control; Charge measurement; Current measurement; Design engineering; Direct power generation; Energy conversion; Energy measurement; injection molding; Manufacturing processes; Modulators; passive charge modulation; piezoelectric energy harvesting; Piezoelectricity; Pressure control; Pressure sensors; Prototypes; self powered; Sensor phenomena and characterization; Sensors; Signal processing; threshold modulator; Thresholds; Transmitters; wireless pressure sensor; wireless sensor; Wireless sensor networks
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2005.859785

A wireless pressure sensor is described for use in a high-pressure manufacturing process with three major subsystems: energy conversion by a stack of piezoelectric disks, energy measurement and control by a threshold modulator, and ultrasonic signal transmission by a piezoelectric transmitter. The second system, the threshold modulator, is the focus of this paper. The charge, proportional to pressure, on a capacitive element is measured and controlled through the use of a two-transistor modulator. Standard NPN and PNP transistors are used to passively control the flow of charge between a piezoelectric stack and an ultrasonic transmitter. The basis for the design is discussed, from which a simulation is developed and compared to a bench top prototype. The results of this comparison indicate the appropriateness of the assumptions used to produce an analytical model of the design and the limiting conditions under which the modulator will effectively measure charge. Finally, the prototype device is optimized with respect to sensitivity, gain, and operating range for use in real-time process monitoring and control.