Microheater

About: Microheater is a research topic. Over the lifetime, 814 publications have been published within this topic receiving 12478 citations.

Microthermal sensors for determining fluid composition and flow rate in fluidic systems

Abstract: To analyze fluid mixtures a simple and low cost measurement method is realized using a microthermal sensor that introduces a short heat pulse into the fluid under test whilst the resulting temperature increase reflects thermal parameters of the fluid. For methanol in water this principle showed an almost linear dependence of the temperature increase on the methanol content for the volume concentration range 0–20 %. The sensitivity was determined to S = 0.19 K/(% (V/V)) for a heat pulse of 0.5 s duration and a heater power of 30 mW. The accuracy achieved in stopped-flow single pulse measurements is ~0.5 % (V/V). By integrating additional temperature sensors in front and behind the microheater the flow rate of the liquid can also be determined using thermal anemometry. The low cost sensor construction and simple signal analysis make this principle promising for use in low cost mobile applications like DMFC power supplies for laptops.

Highly insulating, fully porous silicon substrates for high temperature micro-hotplates

Abstract: As alternative to established thermal substrates and thin membranes, we have investigated fully porous silicon substrates as highly insulating material for thermal devices. Exhibiting a thermal conductivity similar to silica glass and considerably lower than silicon nitride due to increased phonon scattering, thick mesoporous silicon also offers improved thermal and mechanical stability. Our work has focused on full wafer thickness porosification as a not extensively documented use of porous silicon and its application to thermal devices. Here we present measurement and finite element simulation results for our latest generation thin film microheaters on fully porous silicon substrates as proof of concept devices. Porosity, mass density, and specific heat capacity of porous silicon are deduced from fabrication parameters, thermal conductivity is determined by the so-called 3ω-measurement method, and all material properties are validated by fitting measurement data to our finite element models. For thick fully porous domains we estimated a thermal conductivity of ≈0.9 W/m/K, as well as a density of ≈1200 kg/m3, a specific heat capacity of ≈780 J/kg/K and a corresponding volumetric porosity of ≈50%. Thin film fabrication of nitride passivation and molybdenum meander microheaters on fully porous domains allowed characterization of thermal performance and insulation. For 10 mm2 microheaters we measured a power efficiency of 0.40 K/mW stable up to a maximum temperature of 475 °C, compared to 0.37 K/mW stable up to 440 °C on silica glass. Both static and dynamic heater measurements show superior performance of fully porous silicon substrates compared to reference samples on thin silica glass substrates.

Thermally driven thin film bulk acoustic resonator voltage controlled oscillators integrated with microheater elements

Abstract: In this letter, we report on thermally driven thin film bulk acoustic resonator (TFBAR) voltage-controlled oscillators (VCOs) integrated with a microheater element. The oscillation frequency of TFBAR VCOs is controlled by applying different power (or bias voltage) to the microheaters implemented on the TFBAR membrane. The TFBARs with the microheater elements are fabricated by Si bulk micromachining technology. The series feedback schematic TFBAR VCO has an oscillation frequency of 3.566 GHz, an output power of -21 dBm, and a phase noise of -110 dBc/Hz at an offset frequency of 100 kHz. The measured frequency controllability and the measured temperature coefficient of resistance (TCR) of the heater element are 3.19 MHz/V and 0.24%/°C, respectively, with a resistance of 88.1 Ω at room temperature.

Analysis of local heating of liquid samples in multiparametric capillary sensors

Abstract: The local heating enables liquid classification in multiparametric capillary sensors. The dispersion of capillary and microheater parameters may determine the sensor action. Therefore, this paper focuses on the analysis of a local heating implemented in mentioned sensor. The microheater consist of 4H-SiC volume heating unit, alundum ceramic base and a glass capillary is modeled and simulated using CoventorWare™. We use finite element method (FEM) to determine thermo-mechanical parameters of the designed structure. Obtained results are then compared and verified with experimental research. The influences of a capillary to microheater distance and capillary’s thickness on the output results are examined.

Development of integrated microsystem for hydrogen gas detection

Abstract: A low-power microelectromechanical system-based metal-oxide gas sensor along with integrated signal conditioning unit is presented in this study to detect and quantify the variation of H 2 gas concentrations. The interface circuit controls the sensor operating temperature, measures the H 2 gas concentration, contributes a user-friendly interface and can be used with any suitable sensor network. A PIC16F877A microcontroller has been used for this purpose. The temperature of the sensors was stabilised by controlling the actuating voltage of the microheater. Temperatures of the microheater depend on the output voltage of the digital-to-analogue converter (DAC) and were measured by sampling the heater resistance through the use of a voltage divider and analogue-to-digital converters (ADCs). A microcontroller accordingly adjusts the output of DAC's in order to apply the appropriate steering voltage to the heaters. The method employed to measure the concentration of gases is to sample the voltage drop over the resistances of the sensors by ADCs. Alarming system for safety measure was also implemented in this design. The preventive action was taken by introducing an additional feature of wireless communication by sending short message service via global system for mobile modem to the designated emergency number.