Piezoelectric micromachined ultrasonic transducer (pMUT) arrays and techniques for frequency shaping in pMUT arrays are described, for example to achieve both high frequency and low frequency operation in a same device. The ability to operate at both high and low frequencies may be tuned during use of the device to adaptively adjust for optimal resolution at a particular penetration depth of interest. In embodiments, various sizes of piezoelectric membranes are fabricated for tuning resonance frequency across the membranes. The variously sized piezoelectric membranes are lumped together by two or more separate electrode rails, enabling independent addressing between the two or more subgroups of sized transducer elements. Signal processing of the drive and/or response signals generated and/or received from each of the two or more electrode rails may achieve a variety of operative modes for the device, such as a near field mode, a far field mode, and an ultra wide bandwidth mode.