Person:
Brand,
Oliver
Brand,
Oliver
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ItemCharacteristics of laterally vibrating resonant microcantilevers in viscous liquid media(Georgia Institute of Technology, 2012-01) Cox, Russell ; Josse, Fabien ; Heinrich, Stephen M. ; Brand, Oliver ; Dufour, IsabelleThe characteristics of microcantilevers vibrating laterally in viscous liquid media are investigated and compared to those of similar microcantilevers vibrating in the out-of-plane direction. The hydrodynamic loading on the vibrating beam is first determined using a numerical model. A semi-analytical expression for the hydrodynamic forces in terms of the Reynolds number and the aspect ratio (beam thickness over beam width) is obtained by introducing a correction factor to Stokes’ solution for a vibrating plate of infinite area to account for the effects of the thickness. The results enable the effects of fluid damping and effective fluid mass on the resonant frequency and the quality factor (Q) to be investigated as a function of both the beam’s geometry and liquid medium’s properties and compared to experimentally determined values given in the literature. The resonant frequency and Q are found to be higher for laterally vibrating microcantilevers compared to those of similar geometry experiencing transverse (out-of-plane) vibration. Compared to transversely vibrating beams, the resonant frequency of laterally vibrating beams is shown to decrease at a slower rate (with respect to changes in viscosity) in media having higher viscosities than water. The theoretical results are compared to experimental data obtained for cantilevers completely immersed in solutions of varying aqueous percent glycerol. The increases in resonant frequency and Q are expected to yield much lower limits of detection in liquid-phase chemical sensing applications.
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ItemCancellation of environmental effects in resonant mass sensors based on resonance mode and effective mass(Georgia Institute of Technology, 2009-06) Naeli, Kianoush ; Brand, Olivernovel technique is developed to cancel the effect of environmental parameters, e.g., temperature and humidity, in resonant mass sensing. Utilizing a single resonator, the environmental cancellation is achieved by monitoring a pair of resonant overtones and the effective sensed mass in those overtones. As an eminent advantage, especially compared to dual-mode temperature compensation techniques, the presented technique eliminates any need for previously measured look-up tables or fitting the measurement data. We show that a resonant cantilever beam is an appropriate platform for applying this technique, and derive an analytical expression to relate the actual and effective sensed masses on a cantilever beam. Thereby, it is shown that in applying the presented technique successfully, the effective sensed masses must not be the same in the investigated pair of resonance overtones. To prove the feasibility of the proposed technique, flexural resonance frequencies of a silicon cantilever are measured before and after loading with a strip of photoresist. Applying the presented technique shows significant reductions in influence of environmental parameters, with the temperature and humidity coefficients of frequency being improved from −19.5 to 0.2 ppm °C⁻¹ and from 0.7 to −0.03 ppm %RH⁻¹, respectively.
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ItemDimensional considerations in achieving large quality factors for resonant silicon cantilevers in air(Georgia Institute of Technology, 2009-01) Naeli, Kianoush ; Brand, OliverThis work aims to provide guidelines for designing rectangular silicon cantilever beams to achieve maximum quality factors for the fundamental flexural resonance at atmospheric pressure. The methodology of this work is based on experimental data acquisition of resonance characteristics of silicon cantilevers, combined with modification of analytical damping models to match the captured data. For this purpose, rectangular silicon cantilever beams with thicknesses of 5, 7, 8, 11, and 17 µ m and lengths and widths ranging from 70 to 1050 µ m and 80 to 230 µ m, respectively, have been fabricated and tested. Combining the three dominant damping mechanisms, i.e., the air damping, support loss, and thermoelastic damping, the variation in the measured Q-factors with the cantilever geometrical dimensions is predicted. Also to better describe the experimental data, modified models for air damping have been developed. These modified models can predict the optimum length and thickness of a resonant cantilever to achieve the maximum quality factor at the fundamental flexural resonance mode in air.
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ItemTemperature compensation method for resonant microsensors based on a controlled stiffness modulation(Georgia Institute of Technology, 2008-07-01) Seo, Jae Hyeong ; Demirci, Kemal Safak ; Byun, Albert ; Truax, Stuart ; Brand, OliverA strategy to compensate for frequency drifts caused by temperature changes in resonant microstructures is presented. The proposed compensation method is based on a controlled stiffness modulation of the resonator by an additional feedback loop to extract the frequency changes caused by temperature changes. The feasibility of the suggested method is verified experimentally by compensating for temperature-induced frequency fluctuations of a micromachined resonator. The developed compensation scheme requires only one additional feedback loop and is applicable to any resonant microstructure featuring excitation and detection elements.
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ItemMicrosensor integration into systems-on-chip(Georgia Institute of Technology, 2006-06) Brand, OliverSensing systems-on-chip (SSoCs), combining micromachined sensing structures and microelectronic building blocks on a single chip, are reviewed. While single-chip pressure and inertial sensing systems have been commercially available for more than a decade, the recent expansion of SsoC into new application areas, ranging from chemical and biochemical sensing to atomic force microscopy, demonstrates the full potential of this microsensor integration approach. Available fabrication processes for integrated sensing systems are summarized, categorizing them into pre-, intra-, and post-CMOS approaches depending on the way the micromachining module is merged with the integrated circuit (IC) technology. Examples of SSoCs are presented to highlight the different integration options, ranging from cointegration of micromachined sensors with purely analog signal chains to microsystems with cointegrated digital signal processors and digital interfaces.
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ItemMicrojet cooling devices for thermal management of electronics(Georgia Institute of Technology, 2003-06) Kercher, Dan S. ; Lee, Jeong-Bong ; Brand, Oliver ; Allen, Mark G. ; Glezer, AriThis research is an effort to demonstrate the applicability of miniaturized synthetic jet (microjet) technology to the area of thermal management of microelectronic devices. Synthetic jets are jets which are formed from entrainment and expulsion of the fluid in which they are embedded. Design issues of microjet cooling devices are discussed along with characterization of excitation elements and the turbulent synthetic jets produced thereby. Geometrical parameters of the microjet cooling devices were empirically optimized with regards to cooling performance. The cooling performance of the optimized microjets was compared with previous theoretical and empirical studies of conventional jet impingement. The cooling performance of the microjet devices has been investigated in an open environment as well as in a vented and closed case environment. In such experiments, the synthetic jet impinges normal to the surface of a packaged thermal test die, comprising a heater and a diode-based temperature sensor. This test assembly allows simultaneous heat generation and temperature sensing of the package, thereby enabling assessment of the performance of the synthetic jet. Using microjet cooling devices, a thermal resistance of 30.1 °C/W has been achieved (when unforced cooling is used, thermal resistance is 59.6 °C/W) when the test chip is located at 15 mm spacing from the jet exit plane. In order to more directly compare and scale the cooling results, a preliminary study on heat transfer correlations of the microjet cooling device has been performed. Finally, a comparison of the performance of the microjet cooler with standard cooling fans is given.