Capacitive micromachined ultrasonic transducer arrays as tunable acoustic metamaterials

Abstract

Capacitive Micromachined Ultrasonic Transducers (CMUTs) operating in immersion support dispersive evanescent waves due to the subwavelength periodic structure of electrostatically actuated membranes in the array. Evanescent wave characteristics also depend on the membrane resonance which is modified by the externally applied bias voltage, offering a mechanism to tune the CMUT array as an acoustic metamaterial. The dispersion and tunability characteristics are examined using a computationally efficient, mutual radiation impedance based approach to model a finite-size array and realistic parameters of variation. The simulations are verified, and tunability is demonstrated by experiments on a linear CMUT array operating in 2-12 MHz range.

Analysis and Design of High-Frequency 1-D CMUT Imaging Arrays in Noncollapsed Mode

“…Overall, one observes a spurious resonance free range of frequencies between the first mode of the single CMUT membrane on the lower end and either Bragg or a higher order membrane mode resonance on the higher end [37,50]. The effect of Bragg's resonance and crosstalk is also observed in pressure sensitivity.…”

Super broadband acoustic impedance matching by MUT‐type acoustic metamaterial

“…In the field of medical imaging, we, the authors of this study, developed new products, 22‐25 and other companies have also been developing products using CMUTs 26 . Furthermore, recently, there have been studies on acoustic filters whereby the properties of a CMUT‐structure acoustic metamaterial can be made variable by controlling the applied bias voltage 27 …”

“…26 Furthermore, recently, there have been studies on acoustic filters whereby the properties of a CMUT-structure acoustic metamaterial can be made variable by controlling the applied bias voltage. 27 In this study, we focus on MUTs, which are being increasingly put into practical use, and propose a novel acoustic metamaterial-based acoustic impedance matching system that utilizes the structure of MUTs. In Section 2, we present the principle and structure for realizing MUT-type acoustic metamaterial-based acoustic matching, and an evaluation system based on numerical simulation.…”

Nanocontact Tailoring via Microlensing Enables Giant Postfabrication Mesoscopic Tuning in a Self‐Assembled Ultrasonic Metamaterial

“…The ability to tune the response of such materials also remains limited, which is a roadblock for interacting with different devices and phenomena, for device multifunctionality, and for spatially tailoring the materials' effective properties for strategies such as transformation acoustics or topological design . Prior lattices and acoustic metamaterials operating in the MHz–GHz regime have experimentally demonstrated tuning of < to ≈ of the bandgap center and stop band cutoff frequencies, respectively, and prior self‐assembled phononic crystals have demonstrated postassembly tuning of < of the bandgap center frequency. No prior studies have demonstrated the ability to tune a self‐assembled ultrasonic metamaterial in a spatially localized manner after fabrication of the crystal, which is particularly critical due to the sensitivity of most self‐assembly processes to the properties of the particles and the substrate.…”

“…The tunability, which we note is nonreversible (in contrast to refs. ), is achieved through the use of optical‐microlensing to tailor nanocontact features. Our self‐assembled metamaterials mitigate the aforementioned manufacturing scalability challenges, and have been previously demonstrated in the context of, for instance, surface acoustic wave (SAW) filters to have massive attenuations of −0.25 dB µm −1 (similar to recent phononic crystal filters with −0.31 dB µm −1 attenuation).…”