Future flight vehicles may comprise complex flight surfaces requiring coordinated in-situ sensing and actuation.
Inspired by the complexity of the flight surfaces on the wings and tail of a bird, it is argued that increasing the number of
interdependent flight surfaces from just a few, as is normal in an airplane, to many, as in the feathers of a bird, can
significantly enlarge the flight envelope. To enable elements of an eco-inspired Dynamic Servo-Elastic (DSE) flight
control system, IFOS is developing a multiple functionality-sensing element analogous to a feather, consisting of a very
thin tube with optical fiber based strain sensors and algorithms for deducing the shape of the “feather” by measuring
strain at multiple points. It is envisaged that the “feather” will act as a unit of sensing and/or actuation for establishing
shape, position, static and dynamic loads on flight surfaces and in critical parts. Advanced sensing hardware and
software control algorithms will enable the proposed DSE flight control concept. The hardware development involves
an array of optical fiber based sensorized needle tubes for attachment to key parts for dynamic flight surface
measurement. Once installed the optical fiber sensors, which can be interrogated over a wide frequency range, also allow
damage detection and structural health monitoring.
Electromechanical impedance is a popular diagnostic method for assessing structural conditions at high frequencies. It has been utilized, and shown utility, in aeronautic, space, naval, civil, mechanical, and other types of structures. By contrast, fiber optic sensing initially found its niche in static strain measurement and low frequency structural dynamic testing. Any low frequency limitations of the fiber optic sensing, however, are mainly governed by its hardware elements. As hardware improves, so does the bandwidth (frequency range * number of sensors) provided by the appropriate enabling fiber optic sensor interrogation system. In this contribution we demonstrate simultaneous high frequency measurements using fiber optic and electromechanical impedance structural health monitoring technologies. A laboratory specimen imitating an aircraft wing structure, incorporating surfaces with adjustable boundary conditions, was instrumented with piezoelectric and fiber optic sensors. Experiments were conducted at different structural boundary conditions associated with deterioration of structural health. High frequency dynamic responses were collected at multiple locations on a laboratory wing specimen and conclusions were drawn about correspondence between structural damage and dynamic signatures as well as correlation between electromechanical impedance and fiber optic sensors spectra. Theoretical investigation of the effect of boundary conditions on electromechanical impedance spectra is presented and connection to low frequency structural dynamics is suggested. It is envisioned that acquisition of high frequency structural dynamic responses with multiple fiber optic sensors may open new diagnostic capabilities for fiber optic sensing technologies.
Structural dynamic characterization is important for ensuring reliability and operability of spacecraft payloads in harsh
environments. During the launch, a structure experiences dynamic loads, including acoustic excitation. Conventional
sensors are used to infer structural dynamic characteristics. Limitations of conventional strain sensors include low
frequency band, susceptibility to electro-magnetic interference, and use of multiple wires. To mitigate these deficiencies,
an innovative fiber optic strain measurement system is considered to obtain strain distribution at specific locations on a
payload. Theoretical models are suggested and compared with results of experimental testing. Limitations of analytical
models are discussed and comparisons with numerical models are presented. The research addresses the usability of
presented models in determining the dynamic response of a payload and variation due to distribution of components. It is
proposed that discussed experimental and theoretical procedures can be used in determining structural performance for a
variety of missions.