Experimental study of mutual acoustic coupling in CMUTs with substrate-embedded springs

The inter-cell and inter-element acoustic crosstalk in capacitive micromachined ultrasonic transducer arrays has been continuously investigated in immersion, since their effects cause significant degradation of the transducer performance. In this paper, experimental measurements of the inter-cell and inter-element acoustic couplings in 2-D capacitive micromachined ultrasonic transducers with substrate-embedded springs (PCMUTs) are demonstrated. The measurements are performed on two different PCMUT configurations by means of optical interferometry. First, a single 2-D PCMUT element composed of four unit cells is used to display the inter-cell acoustic coupling. Second, four 2-D PCMUT elements are positioned on 2×2 array formation in order to measure the inter-element acoustic crosstalk. The inter-cell acoustic coupling in a 2-D PCMUT element results in the cancellation of the average pressure at certain lower frequency than the operating frequency. The symmetric and asymmetric inter-element interactions from the 2×2 2-D PCMUT arrays are also analyzed by means of exciting all the elements simultaneously and applying a bipolar voltage pulse to one element, respectively. In order to reduce the inter-cell acoustic coupling in a 2-D PCMUT element, the effect of a viscoelastic polymer on the mutual acoustic coupling of the PCMUT cells are indirectly evaluated by using the hydrophone measurement.