A Novel Phase Evaluation Method for Range Detection by Hybrid SAW Sensors

A novel range detection method by phase evaluation of both SAW tag and resonator is proposed. The phase evaluation method has high accuracy for range detection of SAW sensors, while it has the difficulty of phase ambiguity when the range exceed half of the wavelength (called as ruler in phase laser ranging finder). By utilizing several suitable rulers which is in inverse proportion to frequency, unambiguous phases can be derived, which is usually adopted in phase laser ranging finder. Due to that wireless SAW sensors use ISM band, three suitable frequencies of 40MHz, 434MHz and 2.46GHz were calculated, which unambiguous phases were evaluated for range detection. Experiments showed that range accuracy of less than 1cm at 0m-1.4m was accomplished by the above method.