Moving forward with the four main direct transduction methods commonly employed with floating element shear stress sensors (piezoresistive, piezoelectric, capacitive, and optical), this section centers on piezoelectric technologies.
Sensors based on piezoelectric transduction  employ piezoelectric materials that exhibit a relationship between mechanical stress/strain and electrical voltage/charge. For shear stress sensing, the piezoelectric material is typically coupled to a floating element to transduce floating element displacement into deformation within the piezoelectric material. This deformation is either in the shear mode, as with Goyne et al. – and Williams et al. , or in the tensile/compressive mode, through use of a bimorph beam below the floating element, as with Kim et al. . Piezoelectric transduction offers the advantage of inherently low power operation; however, it cannot measure mean shear stress due to a low-frequency roll-off in sensitivity arising from inherent dielectric losses in the material. Further, inherent limitations in device sensitivity and noise floor generally limit application to either high shear stress levels or low bandwidths. Some piezoelectric based shear stress sensors are still in active development , ; however, no commercial devices currently exist.
Table of Contents
- Comparing Techniques – Indirect Measurements
- Comparing Techniques – Direct Measurements
- Transduction Method – Piezoresistive
- Transduction Method – Piezoelectric
- Transduction Method – Capacitive
- Transduction Method – Optical
- Transduction Method – Summary and Guidelines
- Sensor Construction – Conventional
- Sensor Construction – MEMS
- Summary and References
 W. G. Cady, “Piezoelectricity : an introduction to the theory and applications of electromechanical phenomena in crystals.” McGraw-Hill, 1946.
 C. P. Goyne, A. Paull, and R. J. Stalker, “A Skin Friction Gauge for Impulsive Flows,” in 31st AIAA/ASME/SAE/ASEE Joint Propulsion Conference, 1995, p. AIAA 95-3152.
 C. P. Goyne, R. J. Stalker, and A. Paull, “Transducer for Direct Measurement of Skin Friction in Hypervelocity Impulse Facilities,” AIAA J., vol. 40, no. 1, pp. 42–49, Jan. 2002.
 C. P. GOYNE, R. J. STALKER, and A. PAULL, “Skin-friction measurements in high-enthalpy hypersonic boundary layers,” J. Fluid Mech., vol. 485, p. S0022112003003975, May 2003.
 R. P. Williams, D. Kim, D. P. Gawalt, and N. A. Hall, “Surface Micromachined Differential Piezoelectric Shear-Stress Sensors.”
 T. Kim et al., “Piezoelectric Floating Element Shear Stress Sensor for the Wind Tunnel Flow Measurement,” IEEE Trans. Ind. Electron., vol. 64, no. 9, 2017.