Search

Capacitive micromachined ultrasonic transducers (CMUTs) have shown great potential to make a strong impact on ultrasound imaging technologies over the years. However, a critical weakness of CMUTs is their relatively low output pressure at transmission. To address this, we present a novel dual-element ultrasonic transducer that incorporates two transducer technologies by using a circular commercial piezoelectric element for ultrasound transmission and an annular CMUT element for reception. The hybrid transducer combines the broad bandwidth and high receive sensitivity of the CMUT and the high output pressure of the piezoelectric transducer to improve the overall sensitivity and axial resolution. The annular CMUT is designed, fabricated, and concentrically aligned with the piezoelectric probe via a custom housing. A through-wafer etching scheme based on deep reactive-ion etching is developed to create the CMUT annulus. Immersion characterization reveals that the CMUT has a center frequency of 2.63 MHz, a −6-dB fractional bandwidth of 131%, and a receive sensitivity of 22.57 mV/kPa, compared with 2.34 MHz, 42%, and 4.28 mV/kPa of the piezoelectric probe. The round-trip measurements show that the hybrid dual-element transducer improves the axial resolution by 25.58% and the signal-to-noise ratio by 8.55 dB over the commercial piezoelectric probe. [2017-0305] [ABSTRACT FROM AUTHOR]

One shortcoming of capacitive micromachined ultrasonic transducers (CMUTs) for commercial use is the weak output power relative to traditional ultrasonic transducers. Recently, we reported an annular CMUT cell with an improved transmit efficiency over a conventional circular cell in air. Extending this paper, we designed and fabricated a nine-element concentric CMUT array to enhance the transmit power and offer depth focusing. The proposed 200-kHz array has an aperture diameter of 2.13 cm and a fill factor of 81%. A pillar-free etching process was developed to create the deep large-area cavities of the proposed wafer-bonded CMUT. The fabricated device was characterized for the static and dynamic performance using a profilometer and a laser Doppler vibrometer, respectively. The average maximum plate dynamic displacements of the CMUT driven by 20-Vpp ac excitation voltage at dc biases of 100 and 150 V were measured to be 1.28 and 1.97 μm, respectively. Accordingly, the surface output power densities were calculated to be 0.40 and 0.96 KW/m2. We investigated the crosstalk between neighboring cells and the plate-cracking phenomenon, and provided relative suggestions for improvement. This paper demonstrates the feasibility of the concentric annular-cell CMUT array design for air-coupled applications. [ABSTRACT FROM PUBLISHER]

Capacitive micromachined ultrasonic transducers (CMUTs) are an alternative to the conventional method of generating ultrasound that increases bandwidths, simplifies fabrication, and facilitates the integration with necessary electronics. We report the fabrication, characterization, and initial-phased array imaging results of a 64-element array CMUT fabricated using a fusion bonding process where both the membrane and insulation layers are user deposited silicon nitride. Individual cells have a diameter of 25 μm and a membrane thickness of 500 nm. The center frequency in immersion is 6.6 MHz with a −6 dB fractional bandwidth of 123%. A 90° phased array sector scan is made of a four-wire target using a 32-element subset of the array. Pressures in excess of 2 MPa are measured. An axial resolution of 130 μm and a lateral resolution of 0.03 rad are obtained from a wire target 15 mm away from the transducer. [ABSTRACT FROM PUBLISHER]