Size effect on microscale single-phase flow and heat transfer

Size effect on single-phase channel flow and heat transfer at microscale

The techniques of micromachining silicon are used for the manufacturing of a thermal accelerometer. This sensor requires no solid proof mass and has a low cost production. A heating resistor creates a symmetrical temperature profile and two temperature detectors are placed on both sides. When an acceleration is applied, the temperature profile becomes asymmetric and the two detectors measure the differential temperature. Platinum resistors deposited by electron beam evaporation on a SiN x membrane are used as heater and temperature sensors. This paper presents measurements of temperature profile and sensitivity according to the distance heater–detector, power supplied and room temperature. It shows that the sensitivity is proportional to the heating power and decreases when the room temperature increases. Experimental results in tiltmeter utilization and in a centrifuge are also presented. A 3 dB bandwidth of 20 Hz is measured applying a sinusoidal acceleration and the equivalent acceleration noise is found to be 0.3 mg RMS.

Micromachined thermal accelerometer

Recognition of body posture and motion is an important physiological function that can keep the body in balance. Man-made motion sensors have also been widely applied for a broad array of biomedical applications including diagnosis of balance disorders and evaluation of energy expenditure. This paper reviews the state-of-the-art sensing components utilized for body motion measurement. The anatomy and working principles of a natural body motion sensor, the human vestibular system, are first described. Various man-made inertial sensors are then elaborated based on their distinctive sensing mechanisms. In particular, both the conventional solid-state motion sensors and the emerging non solid-state motion sensors are depicted. With their lower cost and increased intelligence, man-made motion sensors are expected to play an increasingly important role in biomedical systems for basic research as well as clinical diagnostics.

https://www.mdpi.com/1424-8220/11/1/638/pdf

Sensing Movement: Microsensors for Body Motion Measurement

Miniaturization, low cost and high performance of accelerometers have been the topic of extensive research. A kind of convective micromachined accelerometer without proof mass is described in this paper. It consists of a microheater and two temperature sensors which measure the temperature difference between two sides of the microheater caused by the effect of acceleration on free convection. The optimization consideration is conducted before fabrication; some key factors, heater size and power, cavity size, distance between the heater and the sensor and the working medium, are considered. The test for the optimized device shows that the linearity error is smaller than 0.35% under tilt conditions of natural gravity and smaller than 2% under acceleration to 10 g (g = 9.81 m s-2). A sensitivity of 600 µV g-1 is measured for operating power of 87 mW, the response frequency is about 75 Hz and the corresponding noise equivalent acceleration is approximately 1 mg Hz-1/2 at 25 Hz. The dependence of the sensitivity on the heating power is a nearly linear function and the resolution increases with heating power increasing.

https://iopscience.iop.org/article/10.1088/0960-1317/11/5/309/pdf

An optimized micromachined convective accelerometer with no proof mass

This letter describes an implementation of micromachined accelerometers in standard complimentary metal–oxide–semiconductor technology. The devices operate based on heat convection and consist of microheaters and thermocouple or thermistor temperature sensors separated by a gap which measure temperature difference between two sides of the microheater caused by the effect of acceleration on free gas convection. The devices show a small linearity error of <0.5% under tilt conditions (±90°), and <2% under acceleration to 7g(g≡9.81 m/s2). Sensitivity of the devices is a nearly linear function of heater power. For operating power of ∼ 100 mW, a sensitivity of 115 μV/g was measured for thermopile configuration and 25 μV/g for thermistor configurations. Both types of devices are operable up to frequencies of several hundred Hz.

Beverly Payne

Papers

Micromachined convective accelerometers in standard integrated circuits technology