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Capacitive Micromachined Ultrasonic Transducer (CMUT) is a promising ultrasonic transducer in medical diagnosis and therapeutic applications that demand a high output pressure. The concept of a CMUT with an annular embossed pattern on a membrane working in collapse mode is proposed to further improve the output pressure. To evaluate the performance of an embossed CMUT cell, both the embossed and uniform membrane CMUT cells were fabricated in the same die with a customized six-mask sacrificial release process. An annular nickel pattern with the dimension of 3 μ m × 2 μ m (width × height) was formed on a full top electrode CMUT to realize an embossed CMUT cell. Experimental characterization was carried out with optical, electrical, and acoustic instruments on the embossed and uniform CMUT cells. The embossed CMUT cell achieved 27.1% improvement of output pressure in comparison to the uniform CMUT cell biased at 170 V voltage. The fractional bandwidths of the embossed and uniform CMUT cells were 52.5% and 41.8%, respectively. It substantiated that the embossed pattern should be placed at the vibrating center of the membrane for achieving a higher output pressure. The experimental characterization indicated that the embossed CMUT cell has better operational performance than the uniform CMUT cell in collapse region.

A new piezoelectric micromachined ultrasonic transducer (pMUT) with an isolation trench between cells was proposed to improve the output pressure. A 2-D finite-element model was utilized to evaluate and compare the performance of the conventional design with fully clamped boundary and the trench design. It shows that the trench design can improve the membrane displacement or output pressure of pMUTs without a significant change in the resonant frequency; $8\times 8$ aluminum nitride (AlN)-based pMUTs arrays with fully clamped boundary design and the isolation trench were fabricated and characterized. An impulse response of the pMUTs array was first employed to determine the resonant frequency. A 200-cycle burst at the resonant frequency was then delivered to pMUTs and the acoustic output pressure was measured by a hydrophone. The trench design could increase the output pressure by $\sim 76$ % with a shift of its center frequency by only 0.03 MHz. The nonlinear relationship between pressure output and applied high voltage still exists in the trench design. The presence of residual stress in the membrane, and substrate during fabrication was found to have little impact on the displacement and resonant frequency of pMUT. In summary, the presence of isolation trench can reduce the deflection-induced tensile stress on the edge of the membrane and subsequently improve the performance of pMUTs. [2016-0001] [ABSTRACT FROM PUBLISHER]

The initiation capability of a microdetonator 0.9 mm in diameter and 3 mm in height is studied. The critical height of the lead azide explosive is 1.8 mm. The optimal ratio of the heights of the primary and secondary explosives in a microdetonator is determined to be 0.7-2.3. At an identical ratio of the primary and secondary explosive heights, the output pressure changes from the highest to the lowest value in the sequence from CL-20 to HMX and then to RDX. [ABSTRACT FROM AUTHOR]

Capacitive Micromachined Ultrasonic Transducer (CMUT) is a promising ultrasonic transducer in medical diagnosis and therapeutic applications that demand a high output pressure. The concept of a CMUT with an annular embossed pattern on a membrane working in collapse mode is proposed to further improve the output pressure. To evaluate the performance of an embossed CMUT cell, both the embossed and uniform membrane CMUT cells were fabricated in the same die with a customized six-mask sacrificial release process. An annular nickel pattern with the dimension of 3 μ m × 2 μ m (width × height) was formed on a full top electrode CMUT to realize an embossed CMUT cell. Experimental characterization was carried out with optical, electrical, and acoustic instruments on the embossed and uniform CMUT cells. The embossed CMUT cell achieved 27.1% improvement of output pressure in comparison to the uniform CMUT cell biased at 170 V voltage. The fractional bandwidths of the embossed and uniform CMUT cells were 52.5% and 41.8%, respectively. It substantiated that the embossed pattern should be placed at the vibrating center of the membrane for achieving a higher output pressure. The experimental characterization indicated that the embossed CMUT cell has better operational performance than the uniform CMUT cell in collapse region. [ABSTRACT FROM AUTHOR]