Passive Wireless Direct Shear Stress Measurement

TitlePassive Wireless Direct Shear Stress Measurement
Publication TypeConference Paper
Year of Publication2010
AuthorsSells, J., V. Chandrasekharan, H. Zmuda, M. Sheplak, and D. P. Arnold
Conference NameSolid-State Sensors, Actuators, and Microsystems Workshop
Date Published06/2010
Conference LocationHilton Head, SC


This paper presents a passive-wireless interrogation strategy for shear stress measurement.  The wireless system is realized via a hybrid packaging approach that combines a floating-element-type MEMS capacitive shear stress sensor die flush-mounted in a printed circuit board (PCB) substrate.  The sensor die is wire-bonded to a 5-turn inductor on the PCB to form an LC tank circuit with a nominal resonant frequency of 258 MHz and a Q of ~6.  A change in input shear leads to a change in the sensor capacitance and a corresponding shift in the resonant frequency.  A single-turn loop antenna, fabricated on a second PCB substrate and placed in proximity to the sensor is used for wireless interrogation.  The sensor displayed a linear sensitivity of 219 kHz/Pa (849 ppm/Pa) up to the testing limit of 1.6 Pa with a resolution of 45 mPa (limited by instrumentation).  The sensor showed superb stability, with drift variations of only ±0.1% over 3 hrs.  A wireless range of 8 mm was also achieved at 3.4 mW RF source power.