Dual-frequency piezoelectric micromachined ultrasonic transducers

A piezoelectric micromachined ultrasonic transducer (pMUT) operating at dual frequencies (3.75 MHz and 18 MHz) was designed to achieve an ultrasound-on-a-chip solution for next-generation biomedical applications. Optimal electrode configurations for the dual-frequency pMUT were analyzed using finite element methods. It was found that a configuration with two ring electrodes enabled dual-frequency actuations of the diaphragm of the pMUT. Simulations showed that the first two resonances of the diaphragm can be tuned independently, especially with regard to amplitude, by optimizing electrode parameters (e.g., position and dimension) and applied voltage. It was also found that optimized distribution of the R and Z components of the displacement field contributes to near ideal mode superposition in a single diaphragm. Simulations for dual-actuations with both inner and outer ring electrodes showed that the two resonant modes are superimposed without significant vibrational crosstalk and result in high-quality dual-frequency acoustic radiation in water. Unlike transducers using two or more single-frequency ultrasonic resonators to generate dual-frequency ultrasound, every element of dual-frequency pMUTs exhibits dual-resonant response simultaneously.