MEMS sensing and control An aerospace perspective

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Temperature
Pressure
Figure 4. Honeywell RIMS Sensors
2.1 MEMS tuning fork gyro
Honeywell is currently developing a tuning fork version inertial gyro to place a functioning gyroscope on a chip. Today's platforms, which require sophisticated guidance and navigation applications, are extremely sensitive to size and weight. A gyro on a chip could greatly expand the tactical uses of the technology. The tuning fork gyro technology could he used in autos for braking and steering, as well as for next-generation airhags. Figure 5 illustrates a block diagram of the gyro design. A performance goal of 1 deg/hr is expected in the near future. The MEMS tuning fork (TFG) mechanism is shown in the optical micrograph of Figure 6. A detailed view of the I'FG is shown in Figure 6.
Honeywell has successfully developed prototype versions of the RIMS that are capable of measuring pressure, vibration, and temperature for environmental control, engine condition monitoring, pump diagnostics, and process control applications. Figure 4 illustrates two packaged RIMS sensors.4 Honeywell has also demonstrated the feasibility of using RIMS to detect wide-bandwidth (>500 kHz) acoustic phenomena, which is useful for structural integrity monitoring applications.
2. AEROSPACE SENSING APPLICATIONS
Honeywell has been developing a family ofMEMS based on a polysilicon resonant transducer design that convers environmental changes to changes in a resonating micromechanical beam ofpolysilicon."2'3 The resonant frequency change can be sensed electronically by resistors fabricated into the resonating beam. The polysilicon resonant design approach is called "resonant integrated micromachined sensor (RIMS)." Figure 1 illustrates the RIMS design. The RIMS microbeam design typically has elements 100 to 400 im long, 46 im wide, and 2 jim thick with characteristic resonance frequencies of 100 kHz to more than 1 MHz. As the sensor flexes, the induced strain is read out as a change in frequency of the microbeam. Figure 2 illustrates the effect of stretching the microbeam by applied stress (i.e., external forces of vibration or AE, which causes a measured shift in resonant frequency. Figure 3 highlights an optical micrograph ofa resonant microbeam structure. The typical mechanical Q factor ofthe RIMS exceeds 20,000, and values of 100,000 have been measured.
Resonating Microbeam
Applied Force
Deflection Stresses
Micro beam
C00073G I
Resulting Axial Force
t Figure 1. RIMS Design
Vacuum Cavity Enclosure
Drive Electrode
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In Smart Structures and Materials 2000: Smart Electronics and MEMS, Vijay K. Varadan, Editor, Proceedings of SPIE Vol. 3990 (2000) • 0277-786X/00/$1 5.00
Microbeam
Sense Resistor
源自文库
CIC73-O2
Figure 2. Effect of Stretching the Microbeam by Applied Stress
Figure 3. High-Q Polysilicon Microbeam Oscillator for Precision Digital Sensors
Keywords: MEMS, optical sensors, acoustic emission, condition-based maintenance (CBM), inertial gyro
1. WHAT IS MEMS?
MEMS (microelectromechanical systems) is a class of physically small systems that have both electrical and mechanical components. Originally, modified integrated circuit (computer chip) fabrication techniques and materials were used to create these very small mechanical devices. Today many more fabrication techniques and materials are available. Sensors and actuators are the two main categories of MEMS. Sensors are typically noninvasive, whereas actuators tend to modify their environment. Microsensors are useful because their small physical size (1 00 jim) allows them to be less invasive and work in smaller areas. Key examples ofmicrosensors include devices that measure pressure, acceleration, strain, temperature, vibration, rotation, proximity, acoustic emission, and many others. Microactuators are useful because the amount of work they perform on the environment is small and precise. Microsensors measure the environmental effects.
Invited Paper
MEMS sensing and control: An aerospace perspective
Jeffrey N. Schoess, David Arch, Wei Yang, Cleopatra Cabuz, Ben Hocker, Burgess Johnson, and Mark Wilson Honeywell Technology Center, Minneapolis, MN
ABSTRACT
Future advanced fixed- and rotary-wing aircraft, launch vehicles, and spacecraft will incorporate smart microsensors to monitor flight integrity and provide flight control inputs. This paper provides an overview ofHoneywell's MEMS technologies for aerospace applications of sensing and control. A unique second-generation polysilicon rsonant microbeam sensor design is described. It incorporates a micron-level vacuum-encapsulated microbeam to optically sense aerodynamic parameters and to optically excite the sensor pickoff Optically excited self-resonant microbeams form the basis for a new class of versatile, high-performance, low-cost MEMS sensors that uniquely combine silicon microfabrication technology with optoelectronic technology that can sense dynamic pressure, acceleration forces, acoustic emission (AE), and many other aerospace parameters of interest. Honeywell's recent work in MEMS tuning fork gyros for inertial sensing and a MEMS freepiston engine are also described.