An ultrasonic transducer device typically includes a membrane capable of vibrating in response to a time-varying driving voltage to generate a high frequency pressure wave in a propagation medium (e.g., air, water, or body tissue) in contact with an exposed outer surface of the transducer element. This high frequency pressure wave can propagate into other media. The same membrane can also receive reflected pressure waves from the propagation media and convert the received pressure waves into electrical signals. The electrical signals can be processed in conjunction with the driving voltage signals to obtain information on variations of density or elastic modulus in the propagation media.
Piezoelectric and capacitive transducer devices have proven useful in the imaging field. While many ultrasonic transducer devices that use piezoelectric membranes are formed by mechanically dicing a bulk piezoelectric material or by injection molding a carrier material infused with piezoelectric ceramic crystals, devices can be advantageously fabricated inexpensively to exceedingly high dimensional tolerances using various micromachining techniques (e.g., material deposition, lithographic patterning, feature formation by etching, etc.). As such, large arrays of transducer elements may be employed with individual ones of the arrays driven via beam forming algorithms. Such arrayed devices are known as piezoelectric MUT (pMUT) arrays. Capacitive transducers may also be similarly micromachined as capacitive MUT (cMUT) arrays.
One issue with conventional MUT arrays is that the bandwidth, being a function of the real acoustic pressure exerted from the transmission medium, may be limited. Because ultrasonic transducer applications, such as fetal heart monitoring and arterial monitoring, span a wide range of frequencies (e.g., lower frequencies providing relatively deeper imaging capability and higher frequencies providing shallower imaging capability), axial resolution (i.e. the resolution in the direction parallel to the ultrasound beam) would be advantageously improved by shortening the pulse length via enhancing the bandwidth of a MUT array.
Another issue with conventional pMUT arrays is that the mechanical coupling through the vibration of the substrate and the acoustic coupling between close elements found in a pMUT array can lead to undesirable crosstalk between transducer elements. Signal to noise ratios in the ultrasonic transducer applications would be advantageously improved by reducing undesirable forms of crosstalk within such pMUT arrays.