Micromachined Fluid Inertial Sensors

Abstract

Micromachined fluid inertial sensors are an important class of inertial sensors, which mainly includes thermal accelerometers and fluid gyroscopes, which have now been developed since the end of the last century for about 20 years. Compared with conventional silicon or quartz inertial sensors, the fluid inertial sensors use a fluid instead of a solid proof mass as the moving and sensitive element, and thus offer advantages of simple structures, low cost, high shock resistance, and large measurement ranges while the sensitivity and bandwidth are not competitive. Many studies and various designs have been reported in the past two decades. This review firstly introduces the working principles of fluid inertial sensors, followed by the relevant research developments. The micromachined thermal accelerometers based on thermal convection have developed maturely and become commercialized. However, the micromachined fluid gyroscopes, which are based on jet flow or thermal flow, are less mature. The key issues and technologies of the thermal accelerometers, mainly including bandwidth, temperature compensation, monolithic integration of tri-axis accelerometers and strategies for high production yields are also summarized and discussed. For the micromachined fluid gyroscopes, improving integration and sensitivity, reducing thermal errors and cross coupling errors are the issues of most concern.

Fluidic mechanism for dual-axis gyroscope

“…The equivalent mass of air flowing through the driven channel is similarly determined as follows. (16) The last component contributing into the equivalent mass is the air flow through the jet shaping nozzle. Since it flows through the driving channel whose jet nozzle has a uniform cross section, the kinetic energy is computed by .…”

“…With the introduction of circulatory flow, the integration and miniaturization of measuring systems significantly enhance the capability and impact of microfluidic systems [11]- [15]. A majority of applications of circulatory flow in a confined space are in the inertial sensing and particular angular rate sensing where the advantage of a self-contained valveless micropump reduces the risk of damage to mechanical counterparts [16]- [19]. For such applications, many different approaches were developed to generate a jet flow.…”

Novel algorithm for tilt measurements using MEMS accelerometers

“…MEMS gyroscopes are sometimes even integrated with MEMS accelerometers (constituting an IMU), so it is a reasonable option to use both kinds of sensors. Even though gyroscopes do not directly respond to linear acceleration, one of their shortcomings is a cross coupling error caused by linear acceleration [14]. So, if it is expected that possible constant disturbing accelerations may be of a certain value, that can be distinguished in the gyroscope noise and drift, it is an interesting and inexpensive option of verifying the operation conditions of the tilt sensor.…”

“…After the calibration process, the output signals of the accelerometer may be regarded relative component accelerations of gravity, calculated as follows, (13) Uncertainty of the relative component accelerations can be determined on the basis of a maximal width of the aforementioned prediction or confidence interval U x..z of the measured output voltages U x..z , according to the following formula, (14) So, Eq. (10) can be transformed into:…”

Study on Point-to-Ring Corona Based Gyroscope

“…In a confined system the circulatory flow is one of the prerequisites in developing a reliable angular rate sensor in a confined system, so several techniques to generate a jet flow were developed. For example, vibration using a lead zircona-titanate diaphragm [13]- [15], activation by electrohydrodynamics in a high electric field using an electro-conjugate fluid [16] or by the natural convection from a locally heated region where a jet flow moves along the direction of mass diffusion [17].…”