Determination of Main Bearing Dynamic Clearance in a Shield Tunneling Machine Through a Broadband PMUT Array with a Decreased Blind Area and High Accuracy.

Traditional PMUT ultrasonic ranging systems usually possess a large measurement blind area under the integrated transmit-receive mode, dramatically limiting its distance measurement in confined spaces, such as when determining the clearance of large bearing components. Here, a broadband PMUT rangefinder was designed by integrating six types of different cells with adjacent resonant frequencies into an array. Through overlapping and coupling of the bandwidths from the different cells, the proposed PMUTs showed a wide -6 dB fractional bandwidth of 108% in silicon oil.