The demand for compact power sources with high energy density is increasing. A direct methanol fuel cell (DMFC) is a renewable energy source which works at near room temperature, and allows for easier liquid fuel storage, which makes it a potential candidate. We report the design, fabrication and characterization of a self-driven DMFC made by micromachining techniques and macro-assembly. Several designs were created on the basis of state-of-the-art DMFCs. A simplified mathematical model was used mainly to design the flow channels and verify the polarization curves, which reveal the output power of a cell. Silicon was used as a substrate for the fabrication of electrodes, and the membrane electrode assembly was provided by Ion Power, Inc. A 0.25 cm2 cell showed a performance of 0.29 mW cm−2 and an open circuit voltage of 0.7 V. Ten microliters of 6 M methanol solution is sufficient to operate the cell for more than 1 h.
We demonstrate infrared focal plane arrays utilizing monocrystalline silicon/silicon-germanium (Si/SiGe) quantumwell microbolometers that are heterogeneously integrated on top of CMOS-based electronic read-out integrated circuit substrates. The microbolometers are designed to detect light in the long wavelength infrared (LWIR) range from 8 to 14 μm and are arranged in focal plane arrays consisting of 384 × 288 microbolometer pixels with a pixel pitch of 25 μm × 25 μm. Focal plane arrays with two different microbolometer designs have been implemented. The first is a conventional single-layer microbolometer design and the second is an umbrella design in which the microbolometer legs are placed underneath the microbolometer membrane to achieve an improved pixel fill-factor. The infrared focal plane arrays are vacuum packaged using a CMOS compatible wafer bonding and sealing process. The demonstrated heterogeneous 3-D integration and packaging processes are implemented at wafer-level and enable independent optimization of the CMOS-based integrated circuits and the microbolometer materials. All manufacturing is done using standard semiconductor and MEMS processes, thus offering a generic approach for integrating CMOS-electronics with complex miniaturized transducer elements.Index Terms-Long-wavelength infrared imaging, LWIR, thermal imaging, uncooled microbolometer, Si/SiGe quantum-wells, wafer-level vacuum packaging, very large-scale heterogeneous 3-D integration, MEMS.
Understanding the energy loss in piezoelectric materials is of significant importance for manufacturers of acoustic transducers. The contributions to the power dissipation due to nonzero phase angles of the mechanical, electrical, and piezoelectric constants can be separated in the expression for power dissipation density. However, this division into separate contributions depends on the piezoelectric constitutive equation form used. Thus, it is problematic to identify any of the three terms with a specific physical domain, electric or mechanical, or to a coupling as is common in the discussion of loss in piezoelectric materials. Therefore, assumptions on the phase of the material constants based on this distinction could be erroneous and lead to incorrect piezoelectric models. This study demonstrates the challenge of distinguishing mechanical, electrical, and piezoelectric losses by investigating the power dissipation density and its contributions in a piezoelectric rod for all four piezoelectric constitutive equation forms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.