A rate gyroscope based on interaction of sonic waves

Abstract

A new form of rate gyroscope based on interaction between standing sonic waves in solid media is described. One form of the device, using a solid, ring-shaped medium, is analyzed in order to establish the relationship between the modes of the two waves that must exist to produce sensitivity to angular rate. In addition, the analysis establishes estimates for the angular-rate sensitivity in terms of the basic instrument parameters. The theoretical feasibility of the proposed instrument has been confirmed by experiments conducted on a simple laboratory model. The results indicate that strain-induced and mass unbalance cross-coupling between the driving and sensing waves can produce uncertainty in the instrument output signal. These unwanted cross-coupling effects are the practical limitation on the instrument performance at the present time. Methods for their reduction and cancellation are discussed for the ring-shaped transducer. The problem of unwanted cross-coupling seems to be present in sonic gyroscopes, in general, and is not unique to solid media alone. In particular, some preliminary experiments with fluid devices show them to have similar cross-coupling problems. In conclusion, the major advantages over conventional rate gyroscopes of instruments based on interaction of sonic waves appear to be: low power consumption, long life, (potentially) high reliability, ruggedness, and low cost. These advantages must be weighed against the primary disadvantage of the lower precision that is available at the present state of the development.