Pulsed interrogation of the SAW torque sensor for electrical power assisted steering

P1K-3 Contactless Torque and Temperature Sensor Based on SAW Resonators

“…Two identical one-port SAW resonators, M1SAW and M2SAW, with SAW propagation directions inclined at ±45° to the X axis (parallel or perpendicular to the shaft axis) have nominal resonant frequencies f 1 = 437 and f 2 = 435 MHz respectively and are connected in parallel. The difference frequency F m = f 1 -f 2 is used to measure torque as it is described in [3,8]. Selection of the substrate material and SAW propagation directions for M1SAW and M2SAW is dictated by (a) ability to put two orthogonal resonators with identical temperature characteristics (and small thermal variation of the resonant frequencies) on a single substrate, (b) relatively high strain sensitivity S s = (F m -F m0 )/s ≈ 2.8 kHz/microstrain (for the packaged sensor), and (c) minimization of its thermal variation [3,8].…”

“…The difference frequency F m = f 1 -f 2 is used to measure torque as it is described in [3,8]. Selection of the substrate material and SAW propagation directions for M1SAW and M2SAW is dictated by (a) ability to put two orthogonal resonators with identical temperature characteristics (and small thermal variation of the resonant frequencies) on a single substrate, (b) relatively high strain sensitivity S s = (F m -F m0 )/s ≈ 2.8 kHz/microstrain (for the packaged sensor), and (c) minimization of its thermal variation [3,8]. Here s is the strain along the resonator length and F m0 is the difference frequency at s = 0.…”

“…Interrogation of the sensor was annular microstrip lines with the diameter close to 48 mm [9]. performed by means of RF pulses using a method described in detail in [8]. The RF ASIC MLX11006 and the DSP TMS320F2801 form the basis of the interrogator.…”

A study of wireless torque sensing based on SAW sensors

“…The torsion bar provides mechanical compliance that helps maintain stability of the EPS. However it requires an expensive mechanical overload protection that is not needed in the case of a noncompliant torque sensor [2]. One of the best candidates for this role is a surface acoustic wave (SAW) sensor that has sufficient strain sensitivity to provide good resolution without weakening the steering shaft and ensures sufficient overload protection.…”

“…Several researches developed the SAW sensors for several physical quantities in the last two decades. They are usually divided into two categories, where one is based on resonators [2][3][4][5] and the others are on reflective delay lines. In 1993, A. Lonsdale and N. Schofield [3] utilize SAW technology for shaft torque measurement.…”