On heat transfer at microscale with implications for microactuator design

The dominance of conduction and the negligible effect of gravity, and hence free convection, are verified in the case of microscale heat sources surrounded by air at atmospheric pressure. A list of temperature-dependent heat transfer coefficients is provided. In contrast to previous approaches based on free convection, supplied coefficients converge with increasing temperature. Instead of creating a new external function for the definition of boundary conditions via conductive heat transfer, convective thin film coefficients already embedded in commercial finite element software are utilized under a constant heat flux condition. This facilitates direct implementation of coefficients, i.e. the list supplied in this work can directly be plugged into commercial software. Finally, the following four-step methodology is proposed for modeling: (i) determination of the thermal time constant of a specific microactuator, (ii) determination of the boundary layer size corresponding to this time constant, (iii) extraction of the appropriate heat transfer coefficients from a list provided and (iv) application of these coefficients as boundary conditions in thermomechanical finite element simulations. An experimental procedure is established for the determination of the thermal time constant, the first step of the proposed methodology. Based on conduction, the proposed method provides a physically sound solution to heat transfer issues encountered in the modeling of thermal microactuators

Magnetomotive and Tension-Based Tuning of a Micromechanical Resonator

Bidirectional frequency tuning in microresonators is demonstrated through the simultaneous use of both mechanical (stretching) and magnetomotive approaches. Stretching is employed to increase the resonance frequency, while the magnetomotive method provides actuation and spring softening. The fabrication process is presented for a double-clamped micromechanical nickel resonator. Lorentz Force is used for excitation and flexural deformation of the resonator. A substrate bending method is utilized to introduce uniaxial tension in the resonator. As a result of flexural deformation, up to 13% decrease in the resonance frequency is achieved. An 8% increase in the resonance frequency is obtained by the stretching method. The presented study is the first demonstration of the combination of the aforementioned techniques for the bidirectional and wide-range frequency tuning up to 200 kHz

Reference-Incorporating Microwave Resonator-Based Sensors for Biological Sensing Applications

Use of microwave resonator-based sensors is a relatively new approach for the detection of biological reagents. Sensing mechanism is based on the tracking of the resonant frequency on electromagnetic resonator. Resonant frequency depends on structure geometry and material but is also affected by secondary changes in environment. Addition of a reference resonator to suppress these effects is proposed in this work. Identical sensor structures designed at 2 GHz, fabricated using low-cost processes are used in experiments to demonstrate the use of a resonator pair for sensing of glucose in solutions, yielding a sensitivity of 34.72 MHz/ (mg/mL)

A split-ring resonator-based microwave sensor for biosensing

A split-ring resonator-based microwave sensor comprises a metallic ring with a slit and integrated monopole patch antennas on top of a dielectric substrate. The resonant frequency of the device is measured as 2.12 GHz. The device is demonstrated as a resonant biomolecular sensor where the interactions between heparin and fibroblast growth factor 2 are probed. The sensitivity of the device is obtained as 3.7 kHz/(ng/ml) with respect to changes in concentration of heparin

Loop Antenna Driven Double Microwave Resonator-Based Sensors Incorporating PDMS Microchannels on Glass Substrates

Microwave resonator-based sensors offer low-cost, contactless, label-free sensing solutions in a variety of applications. Sensing is done by the observation of the shifts in resonant frequency of the sensor structure, which depends on resonator geometry, material and physical properties of the environment. It is observed that the readings can be significantly affected by changes in secondary physical parameters or sample localization on resonator. A double microwave resonator sensing system incorporating microchannels on glass substrates are proposed to address these challenges. PDMS microchannels bonded on glass substrates are mounted on split ring resonators fabricated via low-cost processes. Experiments are performed with glucose solutions of 1.4 mg/mL–3.0 mg/mL concentration range. Results confirm that the use of double resonators increase rejection of background noise, whereas microchannel use increases measurement stability. Overall measurement sensitivity is shown to be 0.92 MHz/(mg/mL). Further improvements are aimed with the bonding of microchannels directly on resonators fabricated on glass substrates