Steve Eugene Watkins

An overview of biomimetic sensor technology

Purpose – The purpose of this paper is to provide an overview of the wide range of biomimetic sensor technology and innovations.Design/methodology/approach – The reader is introduced to biomimetic sensors, their types, their advantages and how they are different from traditional sensors. Background information is also provided regarding sensor design, inspiration and innovation.Findings – There are two approaches to sensor design, which lead to diverse advantages and innovations. Classification of biomimetic sensors indicated which natural senses are underutilized by sensor designers and researchers.Originality/value – The paper provides information of value for those seeking innovative sensor designs and research information for those who want to research in this area.

An experimental UAV system for search and rescue challenge

The overall UAV approach discussed in this article provided satisfactory performance for the avionics systems; however, the design is limited with regard to the wireless link and the image processing. Future development will focus on redesign of the airframe platform, the wireless link, and the image processing. UAV flight characteristics need to be better understood and more thoroughly tested to accommodate less-than-ideal flight conditions. Full analyses of the link margin for spectrum management and of risk assessment to handle flight failure/termination events, e.g., loss of data link, GPS, or autopilot, are needed. Overall, the design experience demonstrated systems trade-offs present in a practical vehicle and UAV capabilities even using off-the-shelf component integration. The prototype UAV could be used for aerial mapping, environmental monitoring, and search and rescue at a cost significantly lower than using traditional full-size aircraft for the same missions.

Measurement and analysis of impact-induced strain using extrinsic Fabry-Pérot fiber optic sensors

In-plane strain responses of surface-mounted extrinsic Fabry-Perot interferometric (EFPI) fiber optic strain sensors are investigated. EFPI fiber optic strain sensors are mounted on three graphite/epoxy laminated composite plates. The plates are impacted with various size steel balls using a drop-weight technique. The impacts did not cause apparent damage. The first impact-induced strain peak was characterized by the rise time, peak value, full width at half maximum and decay time. The transient low-velocity impact response of EFPI fiber optic strain sensors is compared to the response from conventional electrical resistance strain gages and polyvinylidene fluoride (PVDF) piezoelectric film sensors. Orientation dependence and other characteristics of the EFPI fiber optic sensing technique are discussed. An in-house finite element program incorporates geometric nonlinearity and transverse shear deformation for the impact events. The finite element results closely match the experimental strain data for the first peak strain response.

Prediction of Impact Contact Forces of Composite Plates Using Fiber Optic Sensors and Neural Networks

Real-time determination of contact forces due to impact on composite plates is necessary for on-line impact damage detection and identification. We demonstrate the use of fiber optic strain sensor data as inputs to a neural network to obtain contact force history. An experimental and theoretical study is conducted to determine the in-plane strains of a clamped graphite/epoxy composite plate upon low-velocity impacts using surface-mounted extrinsic Fabry-Perot interferometric (EFPI) strain sensors. The plate is impacted with a semispherical impactor with various impact energies using the drop-weight technique. The significant features of the strain and contact force response are contact duration, peak strain, and strain rise time. We have designed and built an instrumented drop-weight impact tower to facilitate the measurement of contact force during an impact event. The impact head assembly incorporates a load cell to measure the contact forces experimentally. An in-house finite-element program is used to establish the validity of the EFPI fiber optic sensor contact force response. The finite-element model is based on a higher-order shear deformation theory and accounts for geometric nonlinearity. Experimental load cell data and finite-element impact-induced contact force responses are in close agreement. The load cell data is used to train a three-layer feed-forward neural network which utilizes the Delta Bar Delta back-propagation algorithm. The output of the neural network simulation is the contact force history and the inputs are fiber optic sensor data in two different locations and time in 10-ms intervals. The efficiency and accuracy of the neural network method is discussed. The neural network scheme recovers the impact contact forces without using any complex signal processing techniques.Real-time determination of contact forces due to impact on composite plates is necessary for on-line impact damage detection and identification. We demonstrate the use of fiber optic strain sensor data as inputs to a neural network to obtain contact force history. An experimental and theoretical study is conducted to determine the in-plane strains of a clamped graphite/epoxy composite plate upon low-velocity impacts using surface-mounted extrinsic Fabry-Perot interferometric (EFPI) strain sensors. The plate is impacted with a semispherical impactor with various impact energies using the drop-weight technique. The significant features of the strain and contact force response are contact duration, peak strain, and strain rise time. We have designed and built an instrumented drop-weight impact tower to facilitate the measurement of contact force during an impact event. The impact head assembly incorporates a load cell to measure the contact forces experimentally. An in-house finite-element program is used to...

UAV Autopilot Integration and Testing

The development of an unmanned aerial vehicle (UAV) platform and the integration of avionics for a search and rescue UAV is examined. The project follows the guidelines for the UAV Challenge - Outback Rescue which is an international aerospace competition. The selection process for a commercial autopilot and avionics package is described. The selected system is integrated into a standard hobby remote control aircraft and configured for autonomous flight and navigation. The autopilot system must be tuned to the aircraft platform and flight characteristics. Flight tests are described for a GPS-based grid search pattern.

Assessment of an instrumented reinforced- concrete bridge with fiber-reinforced- polymer strengthening

Field instrumentation is investigated on an in-service highway bridge over a 2-year period. Extrinsic Fabry-Perot interferometric EFPI strain sensors provide a permanent health-monitoring capability. The bridge is a reinforced-concrete RC structure that was repaired and strengthened using fiber-reinforced-polymer FRP wraps. A sensor net- work monitors the load-induced strain in the FRP reinforcement and the steel rebar. Colocated electrical resistance strain gauges and a finite element analysis are used for comparison. Both dynamic and static load characteristics are analyzed for a near-capacity truck. The fiber optic measurements are generally consistent with the comparison measure- ments and the analytical results; and they show no failure or degradation as opposed to the electrical resistance gauges. We demonstrate the implementation and the performance of in situ EFPI sensors in a long- term field environment. Embedded fiber optic sensors can provide the required information for the intelligent management of a transportation infrastructure.

Smart fiber-reinforced polymer rods featuring improved ductility and health monitoring capabilities

The strain-measuring capability of fiber optic strain gages in fiber-reinforced polymer (FRP) rebars was investigated for failure-inducing loads. Fiber optic interferometric sensors were embedded in a pultruded carbon fiber core and then another layer of carbon fibers were filament wound around the core to form a shell. Pultrusion and filament winding techniques protect the fiber optic strain gages from the concrete environment while providing a secure bond to the core and additional ductility to the overall FRP rebar. Tests of coupon FRP rebar and of FRP-rebar-reinforced concrete beams show that the fiber optic strain gages can read internal strain through failure and can duplicate data from conventional linear variable differential transformers and electrical resistance strain gages. Also, the shell of the FRP rebar inside the concrete beams failed before the rebar core providing pseudo-ductility.

Impact-induced Damage Characterization of Composite Plates Using Neural Networks

Impact-induced damage in fiber-reinforced laminated composite plates is characterized. An instrumented impact tower was used to carry out low-velocity impacts on thirteen clamped glass/epoxy composite plates. A range of impact energies was experimentally investigated by progressively varying impactor masses (holding the impact height constant) and varying impact heights (holding the impactor mass constant). The in-plane strain profiles as measured by polyvinylidene fluoride (PVDF) piezoelectric sensors are shown to indicate damage initiation and to correlate to impact energy. Plate damage included matrix cracking, fiber breakage, and delamination. Electronic shearography validated the existence of the impact damage and demonstrated an actual damage area larger than visible indications. The strain profiles that are associated with damage were replicated using an in-house finite element code. Using these simulated strain signatures and the shearography results, a backpropagation artificial neural network (ANN) is shown to detect and classify the type and severity of damage.

Instrumentation and manufacture of a smart composite bridge for short-span applications

A smart composite bridge is described that features an all-composite design and an integral sensor network. This short-span structure is nine meters in length and is designed for an AASHTO H20 highway load rating. The prototype bridge, the first full-composite bridge in Missouri, was installed on the University of Missouri-Rolla campus as a field laboratory for smart structures courses and a demonstration of composite technology. It was designed, analyzed, and manufactured as a cooperative product development among university, industry, and government partners. It has a modular construction based on a pultruded 76-mm-square composite tube. The cross section of the overall structural element is an I-beam formed by seven layers of bonded tubes. The top and bottom layers are carbon/vinyl-ester tubes for strength and the other layers are glass/vinyl-ester tubes for economy. Extrinsic Fabry-Perot interferometric fiber-optic sensors were embedded throughout to measure temperature, flexure strain, and shear strain. Also, radio-frequency identification tags were co-located with sensors to aid in determining load placement during field tests. This paper gives an overview of the project emphasizing the smart instrumentation. In particular, the installation of the integral sensors, the plan for the sensor network, and preliminary strain results for vehicle loading are discussed.

Performance of a Quaternary Logic Design

This paper analyzes the performance of a quaternary logic circuit and its components. The multi-valued logic design consisting of two drivers and a transistor matrix is simulated using Mentor Graphic software. Functional operation of the circuit is shown and propagation delay and power consumption are determined. The design is dependent on the voltage values for the multi-valued logic. Three logic cases are investigated. The performance of the logic circuit as a quaternary difference calculator is described.