A low-noise micro-machined servo accelerometer has been developed for use in Unattended Ground Sensors (UGS). Compared to conventional coil-and-magnet based velocity transducers, this Micro-Electro-Mechanical System (MEMS) accelerometer offers several key benefits for battlefield monitoring. Many UGS require a compass to determine deployment orientation with respect to magnetic North. This orientation information is critical for determining the bearing of incoming signals. Conventional sensors with sensing technology based on a permanent magnet can cause interference with a compass when used in close proximity. This problem is solved with a MEMS accelerometer which does not require any magnetic materials. Frequency information below 10 Hz is valuable for identification of signal sources. Conventional seismometers used in UGS are typically limited in frequency response from 20 to 200 Hz. The MEMS accelerometer has a flat frequency response from DC to 5 kHz. The wider spectrum of signals received improves detection, classification and monitoring on the battlefield. The DC-coupled output of the MEMS accelerometer also has the added benefit of providing tilt orientation data for the deployed UGS. Other performance parameters of the MEMS accelerometer that are important to UGS such as size, weight, shock survivability, phase response, distortion, and cross-axis rejection will be discussed. Additionally, field test data from human footsteps recorded with the MEMS accelerometer will be presented.
The use of Laser Doppler Vibrometry (LDV) technology has been at the forefront of Micro-Electro-Mechanical Systems (MEMS) research since the early 1990’s. By its nature as a sensitive laser optical technique, it is well suited for non-contact dynamic response measurements of microscopic structures. The art of the technology has culminated into the latest micro-scanning vibrometer for automated scan measurement and display of deflection shapes with sub-nanometer resolution. To exemplify the use of this technology, Polytec PI presents characterization measurements in collaboration with Applied MEMS on two of their devices used in commercial applications. LDV characterization measurements are used for validating the design of the Applied MEMS two-axis micro mirror. Scan measurements reveal distinct, isolated rotation modes about x- and y- axes that can be used to promote the mirror motion in either direction. Settling time performance is evaluated from impulse response and optimized using Input Shaping techniques. Scan measurements of a low-noise accelerometer device from Applied MEMS reveals spurious high frequency modes of support spring causing unwanted response effects. Further use of a new time domain animation feature shows ringing response of the accelerometer to step motions.
The use of Laser Doppler Vibrometer (LDV) technology has been at the fore front of Micro Electro-Mechanical Systems (MEMS) research since the early 1990's. The art of the technology has culminated in our latest Micro Scanning Vibrometer (MSV) system for automated scan measurements on MEMS. One MEMS application driving our product development is the use for testing optical MEMS devices, such as optical switches used in the telecommunications industry. To exemplify this, we present measurements made in collaboration with Applied MEMS on their MEMS DuraScanTM mirror. For Applied MEMS, LDV characterization was important for validating the design intent for two-axis rotation of a single-gimbaled structure. Scan measurements reveal distinct, isolated rotational modes about x- and y-axes that can be used to constrain mirror motion in either direction. A key feature of the LDV is that it measures real-time transient response in typical operating conditions where both electrical and mechanical effects are present. Characterization of settling time performance shows that the mirror can be optimized for fast, accurate beam steering needed for applications like optical switching.
Micro-Electro-Mechanical Systems (MEMS) devices present many difficult characterization challenges. In an environment where dimensions are measured in microns and mechanical resonant frequencies are measured in kilohertz, conventional measurement and characterization techniques cannot be used. Laser Doppler Vibrometer (LDV) technology offers many unique advantages for MEMS characterization and troubleshooting. One of the key problems in characterizing and troubleshooting MEMS devices is the separation of electrical and mechanical effects. By definition, MEMS devices have integrated electrical and mechanical components to form electro-mechanical systems. When characterizing and troubleshooting these devices it is often difficult to determine whether an observed behavior is purely mechanical, purely electrical, or inherently electro-mechanical. Because LDV measurements are electrically inert and do not introduce mechanical artifacts, they are ideally suited for this application. Applied MEMS and Polytec PT have successfully developed LDV based measurement techniques that allow detailed characterization and rapid troubleshooting of MEMS devices. Three real-world examples of MEMS characterization using a LDV are presented including, an optical micro-mirror, a robust low-noise accelerometer and a hermetic ceramic sensor package.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.