Micromachined ultrasonic transducer arrays with multiple harmonic modes
Micromachined ultrasonic transducer (MUT) arrays capable of multiple resonant modes and techniques for operating them are described, for example to achieve both high frequency and low frequency operation in a same device. In embodiments, various sizes of piezoelectric membranes are fabricated for tuning resonance frequency across the membranes. The variously sized piezoelectric membranes are gradually transitioned across a length of the substrate to mitigate destructive interference between membranes oscillating in different modes and frequencies.
1. A method of generating and sensing pressure waves in a medium, the method comprising:
driving an electrode of at least some transducer elements of a micromachined ultrasonic transducer (MUT) array with a first electrical signal wherein, for each transducer element of the MUT array;
a membrane of each transducer element of a plurality of transducer elements of the MUT array is dimensioned to enter a respective first mode of oscillation of a plurality of modes of oscillation, the respective first mode of oscillation corresponding to a solution of a respective Bessel function, wherein the respective first mode of oscillation corresponds to a respective first resonant frequency in a first frequency band; and wherein the membrane of each transducer element of the plurality of transducer elements of the MUT array is dimensioned to enter a respective second mode of oscillation of the plurality of modes of oscillation, the respective second mode of oscillation corresponding to a solution of a respective Bessel function, wherein the respective second mode of oscillation corresponds to a respective second resonant frequency in a second frequency band, wherein the respective first mode of oscillation and the respective second mode of oscillation are different respective modes of oscillation, and wherein the respective second resonant frequency is greater than the respective first resonant frequency, wherein the first electrical signal induces at least the respective first mode of oscillation associated with the first resonant frequency band; and
receiving a second electrical signal from the electrode that includes at least a component corresponding to the respective second mode of oscillation associated with the second resonant frequency band.
2. The method of claim 1 , wherein the driving induces both the first frequency band and the second frequency band; and wherein the second electrical signal includes components from both the first and second frequency bands.
3. The method of claim 2 , wherein the first frequency band is induced on a first channel of the array and the second frequency band is induced on a second channel of the array; and
wherein components from the first frequency band are collected from the first channel and the components from the second frequency band are collected from the second channel.
4. The method of claim 1 , wherein the first electrical signal has a pulse width and shape that preferentially induces the first band more than the second band; and wherein the signal receiver is to filter a component of the second electrical signal associated with the second band from that associated with the first band.