Actuator – sensor technology on “electronic grade” diamond films

 Thermal microheaters as used for example in thermal ink print heads contain a variety of materials, the heater itself is commonly based on refractory metals. Here, a novel concept based on diamond as a multifunctional material is proposed and demonstrated. In this concept, diamond serves as an insulating substrate, a metal-like heater and as a temperature sensor. Superheating of water could be achieved after 7.5 μs heating of a 60×60 μm element. Bubble nucleation was visualized using a high speed stroboscopic technique. The influence of the diamond thermal properties and geometry on the thermal response were investigated by dynamic 3D-simulations. Received: 29 June 1997 / Accepted: 12 November 1997     

Electro-thermal analysis of an embedded boron diffused microheater for thruster applications

One of the important design criteria of micropropulsion systems in particular VLM is the type of microheater, its layout and placement with a view to achieve uniform heating of propellant, fast heat transfer efficiency with minimum input power. Thrust produced by microthruster not only depends on the structural geometry of the thruster and propellant flow rate, but also on the chamber temperature to produce super saturated dry stream at the exit nozzle. Detailed design of microheater in thermal and electrical domains using co-solvers available in MEMS software tools along with material’s thermal property, temperature dependence of electrical resistivity and thermal conductivity have been considered in the present work to achieve precise modeling and experimental accuracy of heater operation. The chamber temperature was analytically calculated and subsequently the required resistance and power were estimated. The boron diffused microheaters of meanderline configuration in silicon substrate has been designed and its finite element based electro-thermal modeling was employed to predict the heater characteristics. The variation of microheater temperature with time, applied voltage and along chamber length has been determined from the modeling. Subsequently the designed microheater was realized on silicon wafer by lithography and boron diffusion process and its detailed testing was evaluated. It was found that boron diffused resistor of 820 Ω can generate 405 K temperature with applied input power 2.4 W. Finally the simulated results were validated by experimental data.     

Measurement technique for the thermal properties of thin-film diaphragms embedded in calorimetric flow sensors

In diaphragm-based micromachined calorimetric flow sensors, convective heat transfer through the test fluid competes with the spurious heat shunt induced by the thin-film diaphragm where heating and temperature sensing elements are embedded. Consequently, accurate knowledge of thermal conductivity, thermal diffusivity, and emissivity of the diaphragm is mandatory for design, simulation, optimization, and characterization of such devices. However, these parameters can differ considerably from those stated for bulk material and they typically depend on the production process. We developed a novel technique to extract the thermal thin-film properties directly from measurements carried out on calorimetric flow sensors. Here, the heat transfer frequency response from the heater to the spatially separated temperature sensors is measured and compared to a theoretically obtained relationship arising from an extensive two-dimensional analytical model. The model covers the heat generation by the resistive heater, the heat conduction within the diaphragm, the radiation loss at the diaphragm’s surface, and the heat sink caused by the supporting silicon frame. This contribution summarizes the analytical heat transfer analysis in the microstructure and its verification by a computer numerical model, the measurement setup, and the associated thermal parameter extraction procedure. Furthermore, we report on measurement results for the thermal conductivity, thermal diffusivity, and effective emissivity obtained from calorimetric flow sensor specimens featuring dielectric thin-film diaphragms made of plasma enhanced chemical vapor deposition silicon nitride.     

中频井口电磁加热器

一种用于油井井口的中频电磁加热器。外表面缠绕电磁感应线圈的导磁钢管做为换热器的主要部件。在导磁钢管靠近出油口设置有管壁温度检测传感器和油温检测传感器,检测到的温度信号经过检测电路处理后,送给控制器,实现控制与保护。该中频电磁加热器加热速度快,热效率高,调温、控温容易。     

Transient thermal characterisation of hot plates

The paper will present the methodology and the results of measuring and simulating the thermal transient behaviour of micro hotplates. The investigated devices were designed for integrated gas sensors of calorimetric operation principle, e.g. micro-pellistors, heat conductivity type sensors or mass flow meters. They consist of a platinum heater filament embedded in silicon-nitride membranes that can be used both for heating and temperature sensing.     

Frequency-Dependent Electrical and Thermal Response of Heated Atomic Force Microscope Cantilevers

This paper investigates the electrical and thermal response of the heated atomic force microscope (AFM) cantilevers in the frequency range from 10 Hz to 1 MHz. Spectrum analysis of the cantilever voltage response to periodic heating distinguishes different thermal behaviors of the cantilever in the frequency domain: the cantilever voltage at low frequencies is modulated by higher-order harmonics, and at high frequencies it oscillates with 1-omega only. A simple model facilitates the understanding of complicated electrical and thermal behaviors in the cantilever, thus, it is possible to determine the cantilever temperature. The calculation predicts that temperature oscillation is restricted to the heater region when the cantilever is operated at about 10 kHz, suggesting that the periodic-heating operation of the cantilever may be employed for highly sensitive thermal metrology     

A nodal analysis model for the out-of-plane beamshape electrothermal microactuator

This paper introduces a nodal analysis model for the out-of-plane beamshaped electrothermal microactuators. The electrothermal microactuator is traditionally simulated with finite element method (FEM) due to the complex coupling of the electrical, thermal and mechanical problem. This complex problem is classified into two parts in this paper: the coupling electrothermal problem and the coupling thermomechanical problem. By utilizing the characteristic of the temperature distribution, the nodal analysis model for the coupling electrothermal behavior of the electrothermal microactuator is built. The model scale is much smaller than the finite element model, which results in less computational consumption. Then the coupling thermomechanical behavior, such as the shift of the heat flow from the bottom of each part of the actuator to the substrate due to its out-of-plane movement, is modeled to make the model more reasonable. Many other effects which remarkably influence the behavior of the actuator are also taken into account. This model is verified by available experimental results, and achieves an agreement.     

MEMS-based microthruster with integrated platinum thin film resistance temperature detector (RTD), heater meander and thermal insulation for operation up to 1,000°C

We have fabricated microthruster chip pairs—one chip with microthruster structures such as injection capillaries, combustion chamber and converging/diverging nozzle machined using the deep reactive ion etching process, the other chip with sputtered platinum (Pt) thin film devices such as resistance temperature detectors (RTDs) and a heater. To our knowledge, this is the first microelectromechanical systems-based microthruster with fully integrated temperature sensors. The effects of anneal up to 1,050°C on the surface morphology of Pt thin films with varied geometry as well as with/without PECVD-SiO₂ coating were investigated in air and N₂ and results will also be presented. It was observed that by reducing the lateral scale of thin films the morphology change can be suppressed and their adhesion on the substrate can be enhanced. Chemical analysis with X-ray photoelectron spectroscopy showed that no diffusion took place between neighboring layers during annealing up to 1?h at 1,050°C in air. Electrical characterization of sensors was carried out between room temperature and 1,000°C with a ramp of ±5?Kmin^?1 in air and N₂. In N₂, the temperature-resistance characteristics of sensors had stabilized to a large extent after the first heating. After stabilization the sensors underwent up to eight further temperature cycles. The maximum drift of the sensor signal was observed for temperatures above 950°C and was less than 8.5?K in N₂. To reduce the loss of combustion heat, chip material around microthruster structures was partially removed with laser ablation. The effects of thermal insulation were investigated with microthruster chip pairs which were clamped together mechanically. The heater was operated with up to 20?W and the temperature distribution in the chip pairs with/without thermal insulation was monitored with seven integrated RTDs. The experiments showed that a thermal insulation allows the maximum temperature as well as the temperature gradient within the microthruster chip pairs to be increased.     

原子磁传感器原子气室无磁控温技术

针对原子磁传感器碱金属原子气室对无磁加热的需求,解决磁力仪共振谱线信号信噪比低的问题,使用了差分对的布线方法,采用微加工膜工艺,在陶瓷基板上制备了方形纯铜材质的无磁加热线圈.使用COMSOL Multiphysics多物理场仿真软件分析了线圈在2.2mA直流条件下产生的附加稳态磁场分布情况,结合Pro/Engineer软件构建的铜质气室固定支架及其热仿真分析结果,得到了比较理想的加热线圈固定位置.进一步分析确定了20kHz交流加热方案,最终制作完成了具有3W加热功率和0.1℃控温精度的无磁加热器.实验结果表明:该加热器瞬时磁扰动为2.24pT,满足原子气室无磁加热要求.其结果对原子磁传感器气室的设计及工作参数的优化改进具有一定的参考意义.     

A study of heat distribution and dissipation in a micromachined chemoresistive gas sensor

A micromachined chemoresistive gas sensor was studied from the point of view of heat distribution and thermal dissipation: this innovative device for environmental pollutant gas monitoring, is based on a sensitive film of semiconductor metal oxides, kept in temperature by a platinum resistor. In order to avoid electrical interactions between the film heater and the contacts for the film reading, the heater is driven by a square wave, and the film is read when no voltage is provided. Since the working temperature of the film is extremely important for its operation, it is crucial to maintain the temperature fluctuations within few degrees; to this end, in this work we study the heat distribution and dissipation of such a device, aiming to set a proper heating frequency, which will assure a right stability of the working temperature.     

Analytical study of resistive MEM gas flow meters

An analytical study for micro-electro mechanical system (MEMS) type gas flow meters is presented. A bulk micromachined structure for the flow meter is proposed. It consists of a micro resistive heater and two temperature sensors situated at the opposite sides of the heater. The silicon substrate is considered to be thermally isolated from the heater by a stacked (SiO₂/Si₃N₄) membrane on a bulk micromachined cavity. The flow meter is considered to work on the bases of displacement of temperature profile around the heating element due to the gas flow. The obtained equation from the analytical model is applied to a specific device dimension. The calculated results show a linear relationship between the gas flow velocity and the device response when the heater and sensing elements separation is about 80 μm. The linearity decreases for increased separation between the heater and the sensing elements as well as the gas flow velocity. The proposed device is also simulated by finite element method using Ansys/Flotran software. The simulation results are in a good agreement with the analytical results. Our analytical results can assist the MEMS gas flow meter designers to define the position of the sensing elements with respect to the heater accurately, depending on the required output signal linearity and gas flow velocity.     

Response time of thermal flow sensors with air as fluid

Due to their fast response time miniaturized thermal flow sensors can be applied well for the measurement of instationary gas flow. For some applications, the response time of the sensor must be known with high accuracy. We investigated three methods for response time determination with air: a jump of temperature induced by electric heating, a gas velocity step made by a membrane burst and acoustic phase shifts between sound velocity and sound pressure (standing and traveling waves). The measurements have shown that the response time of thermal flow sensors is a function of flow velocity. For stagnant flow, the thermal response time is about 4.5 ms for our thermal flow sensors. With increasing flow from the heater to the thermopiles, the heat transfer rises. Thus, the response time is faster and decreases to about 1 ms.     

蓄热地板分散式电采暖负荷协同优化调度系统设计

传统的调度系统在调度蓄热地板分散式电采暖负荷时,调度范围很小,导致采暖效果很差。为了解决这一问题,设计了一种新的蓄热地板分散式电采暖负荷协同优化调度系统,对系统的硬件和软件分别进行设计。硬件部分重点设计了采暖器、控制器和处理器,采暖器选用型号为TSDA-523的新型集热采暖器,提高采暖效果;控制器采用了LPI控制器,能够实现连续控制;处理器选用了型号为AN176的中央集成处理器,在短时间内能够处理大量电采暖负荷。软件由电采暖负荷量确定、电采暖负荷量处理、电采暖负荷量调度三部分组成。为了检测系统效果,与传统系统进行对比,结果表明,系统能够完成大范围调度,有效提高采暖效果。     

A multilayered microfluidic system with functions for local electrical and thermal measurements

Microfluidic systems have been extensively applied in research of chemistry, biology and fluidic dynamics. In these applications, local and precise measurements are often crucial for reliable results. We demonstrate here a multilayered, multifunctional microfluidic platform with embedded electrodes open to the microchannel and thermocouple sensors underneath the microchannel that are suitable for local electrical and thermal measurements, respectively. We demonstrate that precise transport measurements with ac excitation frequency up to 1 MHz can be performed for electrolytes in centimeter-long microchannels. Local temperature sensing of the fluids in the microchannels can also be performed on this system. Such system can be either used to characterize local electrical and thermal properties of fluids, or applied to the study of thermal related electrokinetic phenomena, such as joule heat generation in dc conductance or temperature dependence of electrical transport.     

虚拟实验热触觉再现系统的设计与实现

针对目前虚拟实验热触觉装置缺乏的现状,设计了一种基于PTC（Positive Temperature Coefficient）加热片的热触觉感知复现系统。该系统利用HTC VIVE的红外定位,将虚拟环境下热源的空间位置映射为现实环境下制热模块的空间位置。根据虚拟实验中不同位置和不同温度的热源,使用两个步进电机控制热源的位置和方向,并提供4个自由度的热源定位方法;使用PID控制算法控制PTC加热片产生热风的温度,获得不同的热触觉感知。该系统以一种非接触式的触觉感知来呈现虚拟实验的热触觉,保证了热触觉产生的真实性。通过铝热反应虚拟实验,验证该系统的实用性,结果表明该系统的热触觉再现能够提高虚拟实验的真实感受,补偿触觉上缺失的热反馈。     

Study on the effect of heating plate thickness on the micro induction heater for thermal bubbles generation

This paper designed a micro planar induction heater for thermal bubbles generation. The micro heater which consists of a micro planar coil, a copper heating plate and a glass slide was fabricated with MEMS fabrication process. The relations between the heating performance and the thickness of heating plate were studied in the simulation with the software of COMSOL. The experimental system has been built and the experimental tests for thermal bubble generation have been also carried out with the prototype. The process of thermal bubbles generation was recorded by the video camera. The frequency of AC current applied in the experiment is 100 kHz and the heating time of 1 s. The experimental results indicated that the micro heater has the best heating performance with the heating plate thickness of 12–16 μm, and the minimum power for thermal bubbles generation was only 0.427 W. This micro heater can be applied to a variety of thermal bubble devices, such as micro actuator, micro ejector and micro pump.     

Thermal and Optical Characterization of Silicon-Based Tunable Optical Thin-Film Filters

In this paper, we report on the successful fabrication and comprehensive optical and electrothermal characterization of a silicon-based tunable optical filter. Of particular interest here are the static and transient electrothermal characteristics of the filter membrane. The filter is configured as a Fabry-Perot resonator with dielectric Bragg reflectors and is fabricated as a stress-compensated multilayer of dielectric thin-films. Tunability is achieved by changing the refractive index of the solid-state cavity material through thermal modulation, accomplished by Joule heating in metal thin-film resistors. The filter layers are configured as a membrane to provide good thermal isolation and its electrothermal behavior was characterized in steady-state and dynamically. A maximum stable temperature difference of 450 K and a heating efficiency of 13.4 K mW^-1 were measured with a thermal time constant for the filter hotplate of 3 ms. The filter's spectral width is 0.28 nm at a wavelength of 1550 nm and through thermal modulation it was possible to shift the filter peak over more than 29 nm.     

Numerical simulation of AC electrothermal micropump using a fully coupled model

The classic model by Ramos et al. for numerical simulation of alternating current electrothermal (ACET) flow is a decoupled model based on an electrothermal force derived using a linear perturbation method, which is not appropriate for the applications, where Joule heating is large and the effect of temperature rise on material properties cannot be neglected. An electrically–thermally–hydrodynamically coupled (fully coupled) ACET flow model considering variable electrical and thermophysical properties of the fluids with temperature was developed. The model solves AC electrical equations and is based on a more general electrostatic force expression. Comparisons with the classic decoupled model were conducted through the numerical simulations of an ACET micropump with asymmetric electrode pairs. It was found that when temperature rise is small the fully coupled model has the same results with the classic model, and the difference between the two models becomes larger and larger with the increasing temperature. The classic decoupled model underestimates the maximum temperature rise and pumping velocity, since it cannot consider the increase in electrical conductivity and the decrease in viscosity with temperature. The critical frequencies where the lowest velocity occurs or pumping direction reverses are shifted to higher frequencies with the increasing voltage according to the fully coupled model, while are kept unchanged according to the classic model.     

Design,fabrication, and test of a peristaltic micropump

The design, fabrication, and electrical characterization of a novel peristaltic thermopneumatic microfluidic (PTMF) pump for next-generation implantable medical treatment. To satisfy the demands of an implantable system, the PTMF pump design presented here includes biocompatibility, simple integration with microfluidics, bidirectionality, and particle tolerance. Test devices were fabricated with both silicon micromachining and soft lithography (polydimethylsiloxane micromolding). The effects of process parameters, specifically those related to silicon wet etch and metal deposition, on the performance of the microheaters in a peristaltic microfluidic pump. The thermal resistance of the microheaters is strongly dependent upon the relative thermal isolation, which impacts maximum pumping speed (from a few Hertz to kilo-Hertz). Thermal isolation is shown not to be an issue in the pump design given the spacing of the neighboring microheaters.