This paper summarizes ongoing work on applying passive magneto-inductive (MI) waveguides as wireless sensor arrays
to monitor corrosion in infrastructure systems. The passive uniformly-spaced sensor array provides a low-cost and quick
method to detect the onset of corrosion in concrete structures using a noninvasive approach. The embedded sensors
communicate with neighboring sensors through inductive coupling. The corrosion information is interpreted based on
both frequency and time domain characteristics. Bandpass characteristics in the frequency domain and received reflected
time domain waves are investigated to locate the defects along the wireless sensor array. Using the relationship between
the relative positions of defects and MI waveguide performances, a new combined technique to determine location of
defects has been developed and proven to provide both improved sensitivity and defect location capability.
A reconfigurable and portable wireless reader has been designed for embedded passive Electronic Structural
Surveillance (ESS) sensors, used to monitor corrosion in infrastructure systems. The passive ESS sensors have been
developed and proven effective in monitoring localized defects in their environment. They are interrogated by
inductively coupled magnetic field of a reader coil. The input impedance of the reader coil is monitored to determine
whether a corrosion threshold has been reached. We have previously used an impedance analyzer to obtain the
impedance data. Such systems have good sensitivity and moderate speed but are bulky and heavy. The new reader
approach presented in this paper is designed addressing the need of portability, sensitivity and read range. The reader
electronics is implemented on a reconfigurable National Instruments (NI) modular transceiver platform, capable of
software defined radio. The design employs a reflectometer, which is implemented using a 3-port directional coupler and
a single coil as both the driver and reader, along with the transceiver. The NI transceiver is used to generate a swept
frequency input signal and analyze reflected signal from the reader, which is related to the input impedance of our ESS
sensor. The configuration of the reader coil is optimized for reader range and sensitivity. We have acquired analog data
using this design, showing that the real-time reader system facilitates especially fast detection and long read ranges for
This paper describes the ongoing research efforts to develop a novel class of low-cost, unpowered, wireless sensors for
detecting corrosion of reinforcement in concrete structures. The sensors are powered through magnetic coupling
between an external reader coil and an embedded sensor. Measured AC impedance is used to interpret the state of the
embedded sensor. The sensors are envisioned to be placed during construction and interrogated as part of routine
The sensor prototype incorporates a sacrificial corroding element that is placed entirely outside the sensor components
and interacts with the resonant circuit by inductive coupling and shielding of the magnetic fields. As the resistance of
the sacrificial element increases due to corrosion, the measured frequency response changes gradually indicating
corrosion initiation within concrete. In this paper the potential for detecting multiple levels of corrosion damage is
A passive, wireless sensor has been developed at the University of Texas at Austin to monitor the insitu conductivity of
concrete within civil infrastructure systems. Electrical conductivity is one possible indicator of corrosion of embedded
reinforcement and thereby provides information on structural performance. The sensors would be attached to the
reinforcement cages before placement of the concrete and interrogated as part of a routine inspection over the service
life. A new sensor design, a non-contact conductivity sensor, is being developed to minimize the likelihood of damage to
the sensor during placement of the concrete; a metal element is positioned above the sensor body but is not connected to
the resonant circuit within the sensor. In order to verify the response of the non-contact conductivity sensors, they were
submerged in liquids of increasing conductivity. Analysis of the measured data demonstrated that the noncontact
conductivity sensors successfully detected conductivity variations in liquids.
We present fabrication and characterization of wavelength selective germanium dielectric supported microbolometers
using a self-alignment technique to help insure a flat microbolometer membrane. The fabricated microbolometer consists
of a resistive absorber sheet on a quarter wavelength germanium layer above a half wavelength air gap, producing
dielectric interference . We use a self-aligned process without a polyimide patterning process that helps eliminate
deformation and stress in the structure membrane. We demonstrated that the fabricated wavelength selective
microbolometers have flat, robust membranes and produce excellent tunable narrowband absorption in MWIR/LWIR
band with efficient multi-color IR spectral response using wavelength selective pixels.
This paper describes ongoing work to develop a low cost, passive wireless chemical sensor using a microfabricated inductor with interdigitated capacitors (IDC). A self-resonant-structure (SRS) is designed by incorporating IDC electrodes in the inter-winding space of the inductor. The distributed IDC capacitance is affected by dielectric constant and conductivity of its environment or material under test (MUT). This serves as a capacitive transducer changing the resonant frequency of the SRS. The SRS is interrogated using a non-contact inductively coupled reader coil. The shift in resonance frequency of the SRS is used to detect material properties of the environment/MUT. The dielectric constant (ε) and conductivity (σ) can be used to provide information about the surrounding environment. The ε and the σ are determined by fitting and extraction from circuit models of the IDC. Relationship between sensor layout and coupling factor between sensor and reader is investigated. Optimizations of the coupling factor based on this relationship are discussed. IDC design trade-offs between the sensor's sensitivity and coupling factor are investigated. The sensor's response to variety of liquid MUTs with a wide range of dielectric constant and conductivity is presented.
A passive, wireless and inexpensive sensor has been developed to monitor the conductivity of concrete and thereby
provide information on the progress of chloride-induced corrosion of the embedded reinforcement in concrete structures.
Sensors are designed to be attached to the reinforcement cages before placement of the concrete in new construction or
in portions of rehabilitated structures. Sensors will then be interrogated intermittently over the service life during routine
inspections. The results of two experimental investigations are discussed in this paper. In the first, conductivity sensors
were submerged in liquids of increasing conductivity. In the second, conductivity sensors were embedded in concrete
cylinders and interrogated over a 25-week period during initial set and curing of the concrete. Analysis of the measured
data shows that the passive conductivity sensors were successful in detecting a variety of conductivity levels in the
A passive sensor platform has been developed at the University of Texas at Austin to monitor corrosion of embedded
reinforcement in concrete structures. The sensors are powered and interrogated in a wireless manner. Initial sensor
designs used a sacrificial corroding steel wire to indicate the risk of corrosion within concrete. The wire was
physically connected to the sensor circuitry and passed through the circuit protection layer. Consequently, it allowed
contaminants to reach the circuit electric components causing corrosion and limiting the service life of the sensor. A
novel sensor configuration that relies on wireless inductive coupling between a resonant circuit and the transducer
element is presented. The non-contact design eliminates the breach concern and enhances the durability of the senor.
Preliminary test results of the new design will be discussed in this paper.
This paper summarizes ongoing work to develop low-cost, wireless, resonant sensor nets that can be used to monitor
corrosion in infrastructure systems. A magnetically coupled sensor array is analyzed using a circuit model. The array
acts as a magneto-inductive waveguide and the impedance discontinuities caused by corrosion (or other defects) lead to
reflection. The relationship between the relative position of defects and pass band ripples is investigated, providing a
technique to determine the location of targets. A configuration for increased sensitivity and a method for defect
localization are presented.
Results from our efforts to improve the performance of low-cost, unpowered, wireless, resistance based Electronic
Structural Surveillance tags (ESS) will be presented. The ESS tags use an unpowered embedded sensor read by an external reader using an inductively coupled impedance measurement. Read range of coupled tags is largely dependent on the strength of inductive coupling which is influenced by the relative shape and size of the coils. Reader coil geometries can be optimized to increase read range. Additionally, an enhanced circuit model, for data extraction, is developed and tested with the corrosion sensor. The model provides increased information about the sensor and its surroundings. Better coil design and circuit model based data extraction methods can improve the reliability in reading the sensor. Recommendations for design and analysis resulting from this study can be extended to optimize other electronic structural surveillance tag sensors.
Results will be reported from efforts to develop a self-contained micromachined microfluidic detection system for the
presence of specific target analytes under the US Office of Naval Research CIED Basic Research Program. Our efforts
emphasize improving/optimizing a dedicated micromachined sensor array with integrated photodetectors that are
coupled to chemically sensitized chemiluminescent receptors. Here we will review our work on the fabrication of
integrated photodiodes within an array of micromachined silicon pyramidal cavities that will contain the
chemiluminescent compounds. One particular advantage of such approach over a conventional planar photodiode would
be its collection efficiency without the use of external optical components. This should allow a more compact and
robust system to be constructed by integrating photodetection and fluidics into a single chip-based platform.
Additionally, overview of accessing the photodiode using wireless coupling to a resonant chemically sensitive tag will