06-04-2013, 04:45 PM
Project Update: Applied Research on Remotely-Queried Embedded Microsensors
Remotely-Queried Embedded.pdf (Size: 391.94 KB / Downloads: 42)
ABSTRACT:
Sensors embedded in structural
composites have been a topic of research in recent years.
Embedded sensors can be used to monitor and optimize
the manufacturing process, to monitor performance during
use, and for structural health monitoring in highperformance
applications. For several years, embedded
optical fibers were the predominant type of sensor. There
are well-known reasons that optical fiber sensors have not
yet been fully embraced in industry including the cost of
equipment and sensors, the fragility of the optical fiber
itself, and the need to provide ingress and egress from the
structure. Recent work by the authors and others has
produced prototype wireless electronic sensors of various
types that address these shortcomings.
INTRODUCTION:
This research is funded by the US Office of Naval Research (ONR), contract number
N00014-97-C-0274, with Mr. James Kelly as program
manager. MTS Systems Corporation is the prime
contractor and systems integrator. Other team members
include the Applied Physics Laboratory of Johns Hopkins
University, Boeing Company, Electronic Identification
Devices, Inc., the Illinois Institute of Technology,
Stanford University, and University of Minnesota, and the
University of Utah.
TECHNICAL CHALLENGES:
As with all research programs, ARRQEM has various technical challenges to overcome. The major challenges unique to this program
include the following:
• The sensor system needs to have an indefinite
lifetime, which precludes the use of batteries. Other
system requirements preclude wire (or other physical)
connections to the sensor from the interrogation
system. The predecessor RQEM program
substantially solved this problem.
• To optimize the interrogation range of an embedded
sensor system, the sensors and signal conditioning
electronics need to be extremely low power. State-ofthe-
art piezoresistive strain sensor (see Figure 7) and
conventional strain-gage technology requires
excitation power at several orders of magnitude above
what can be transferred using wireless systems (also
considering allowable sensor package size and power
densities compatible with the host structure
composites). Therefore, new low-power sensing
methods must be developed.
A basic problem with using a silicon strain sensor in
composites is the difference in bulk modulus between the
silicon substrate and the types of matrix used in aerospace
composites. The matrix is orders of magnitude softer than
the silicon, leading to great difficulty in transferring strain
from the composite to the sensor. The problem is likened
to embedding a rock in bubble gum and then stretching
the rock by pulling on the bubble gum.
ALTERNATIVE SENSOR TECHNOLOGY:
An alternative sensor technology is being pursued in parallel
with the micromachined sensors described above. The
alternative sensor is being developed at the University of
Utah. Its primary application is for monitoring rate and
state of cure, but the same technology can be applied to
strain measurements and in-situ damage assessment as
well. In situ sensing using piezoelectric materials was
used by Dr. Dubow at MIT to monitor both elastomeric
and thermoplastic cure processes.
MICROSENSOR/TRANSPONDER
INTERFACE:
The current implementation has the
microsensor fabricated on a separate substrate from the
transponder chip. Development plans call for these to
eventually be fabricated on the same wafer, but this is
currently not practical given the developmental processes
used for the transponder and microsensors (i.e., it is
technically feasible, but it is difficult to coordinate
electronics development with the micromachining
development). Since the microsensors and transponder are
separate, we must interconnect them to make a complete
embeddable sensor.
CONCLUSIONS AND STATUS:
The Remotely Queried Embedded Microsensor (RQEM) program
developed the basic technology needed for embedded
microsensors [Krantz 96]. RQEM developed working
prototype sensors that have had limited testing.
The ARRQEM research has consolidated the progress
made during RQEM. It has extended the capabilities of
the RQEM design and made the RQEM design robust to
prepare the technology for transition to deployment. A
high-priority objective of this research has been a focus on
near-term applications of this technology. The program
addresses the area of sensors, transponders, calibration,
characterization, miniaturization, integration, and
applications, and addresses sensor networking or arrays of
sensors by providing for the addressability of individual
sensors.