This method enables sensing and quantization of analog strain gauges. By manufacturing a piezoelectric sensor stack in parallel (physical) with a piezoelectric actuator stack, the capacitance of the sensor stack varies in exact proportion to the exertion applied by the actuator stack. This, in turn, varies the output frequency of the local sensor oscillator. The output, Fout, is fed to a phase detector, which is driven by a stable reference, Fref.
The output of the phase detector is a square waveform, Dout, whose duty cycle, tW, varies in exact proportion according to whether Fout is higher or lower than Fref. In this design, should Fout be precisely equal to Fref, then the waveform has an exact 50/50 duty cycle.
The waveform, Dout, is of generally very low frequency suitable for safe transmission over long distances without corruption. The active portion of the waveform, tW, gates a remotely located counter, which is driven by a stable oscillator (source) of such frequency as to give sufficient digitization of tW to the resolution required by the application.
The advantage to this scheme is that it negates the most-common, present method of sending either very low level signals (viz. direct output from the sensors) across great distances (anything over one-half meter) or the need to transmit widely varying higher frequencies over significant distances thereby eliminating interference [both in terms of beat frequency generation and in-situ EMI (electromagnetic interference)] caused by ineffective shielding. It also results in a significant reduction in shielding mass.
This work was done by Karl F. Strauss of Caltech for NASA’s Jet Propulsion Laboratory.
In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:
Innovative Technology Assets Management JPL Mail Stop 202-233 4800 Oak Grove Drive
Refer to NPO-46665, volume and number of this NASA Tech Briefs issue, and the page number.