Jeffrey N. Schoess

Rotor acoustic monitoring system (RAMS): a fatigue crack detection system

The Rotor Acoustic Monitoring System (RAMS) is an embedded structural health monitoring system to demonstrate the ability to detect rotor head fatigue cracks and provide early warning of propagating fatigue cracks in rotor components of Navy helicopters. The concept definition effort was performed to assess the feasibility of detecting rotor head fatigue cracks using bulk- wave wide-bandwidth acoustic emission technology. A wireless piezo-based transducer system is being designed to capture rotor fatigue data in real time and perform acoustic emission (AE) event detection, feature extraction, and classification. A flight test effort will be performed to characterize rotor acoustic background noise and flight environment characteristics. The long- term payoff of the RAMS technology includes structural integrity verification and leak detection for large industrial tanks, and nuclear plant cooling towers could be performed using the RAMS AE technology. A summary of the RAMS concept, bench-level AE fatigue testing, and results are presented.

Smart aircraft fastener evaluation (SAFE) system: a condition-based corrosion detection system for aging aircraft

The smart aircraft fastener evaluation (SAFE) system is an advanced structural health monitoring effort to detect and characterize corrosion in hidden and inaccessible locations of aircraft structures. Hidden corrosion is the number one logistics problem for the U.S. Air Force, with an estimated maintenance cost of

Optically resonant microbeams

700M per year in 1990 dollars. The SAFE system incorporates a solid-state electrochemical microsensor and smart sensor electronics in the body of a Hi-Lok aircraft fastener to process and autonomously report corrosion status to aircraft maintenance personnel. The long-term payoff for using SAFE technology will be in predictive maintenance for aging aircraft and rotorcraft systems, fugitive emissions applications such as control valves, chemical pipeline vessels, and industrial boilers. Predictive maintenance capability, service, and repair will replace the current practice of scheduled maintenance to substantially reduce operational costs. A summary of the SAFE concept, laboratory test results, and future field test plans is presented.

Test Results of Resonant Integrated Microbeam Sensor (RIMS) for Acoustic Emission Monitoring

Polysilicon microbeams in integral vacuum enclosures on silicon substrates have optical and mechanical properties that provide excellent opportunities for fiber-optic sensors. The microbeam, shell, and silicon substrate form a structure with Fabry-Perot-like properties that functions as an optomechanical modulator. When the beam vibrates incident light is modulated and reflected light is used to sense vibration of the beam. Thus, the structure can be used as a mechanical vibration or acoustic emission sensor. Microbeams attached to the substrate at both ends are highly strain sensitive and form the basis of a variety of sensors, including pressure sensors, accelerometers, strain, vibration, and temperature sensors. Excitation at the wafer level by a polymer film piezoelectric transducer provides a simple non-contact optical method for testing the microbeams before the water is cut into sensor die. Modulated light from a laser diode can also be use to excite the microbeams into resonance. The test results suggest that optically resonant microbeams can be used for low-cost precision fiber-optic sensors. Fiber-optic sensors are especially attractive for aerospace applications because optical fibers provide wide-bandwidth communication capability while eliminating electromagnetic interference (EMI), ground loops, and shielding requirements.

Smart fastener for KC-135 structural integrity monitoring

The feasibility of detecting stress-wave acoustic phenomena with Honeywells resonant microbeam-based MEMS sensor technology is presented. The baseline technical approach described here incorporates an integrated silicon microstructure and a resonant microbeam with micron-level feature size, and features frequency sensitivity up to 500 kHz. The stress-wave acoustic MEMS concept has been demonstrated successfully in the laboratory test environment to sense simulated acoustic emission (AE) events for structural fatigue crack monitoring applications. The technical design approach and laboratory test results are presented.

MEMS sensing and control : An aerospace perspective

Hidden and inaccessible corrosion in aircraft structures is the number-one logistics problem for the U.S. Air Force, with an estimated maintenance cost in excess of

Surface-conforming MEMS: a new approach for vehicle dynamics monitoring

DOL1.0 billion per year in 1990-equivalent dollars. The Smart Aircraft Fastener Evaluation (SAFE) system is being developed to provide early warning detection of corrosion- related symptoms in hidden locations of aircraft structures. The SAFE incorporates an in situ measurement approach that measures and autonomously records several environmental conditions (i.e., pH, temperature, chloride, free potential, time-of-wetness) within a Hi-Lok aircraft fastener that could cause corrosion to occur. The SAFE system integrates a miniature electrochemical microsensor array and a time-of- wetness sensor with an ultra-low-power 8-bit microcontroller and 5-Mbyte solid-state FLASH archival memory to measure the evidence of active corrosion. A summary of the technical approach, system design definition, software architecture, and future field test plans will be presented.

CH-46 Sea Knight flight test results for the Rotor Acoustic Monitoring System (RAMS)

Future advanced fixed- and rotary-wing aircraft, launch vehicles, and spacecraft will incorporate smart microsensors to monitor flight integrity and provide flight control inputs. This paper provides an overview of Honeywells MEMS technologies for aerospace applications of sensing and control. A unique second-generation polysilicon resonant microbeam sensor design is described. It incorporates a micron-level vacuum-encapsulated microbeam to optically sense aerodynamic parameters and to optically excite the sensor pick off: optically excited self-resonant microbeams form the basis for a new class of versatile, high- performance, low-cost MEMS sensors that uniquely combine silicon microfabrication technology with optoelectronic technology that can sense dynamic pressure, acceleration forces, acoustic emission, and many other aerospace parameters of interest. Honeywells recent work in MEMS tuning fork gyros for inertial sensing and a MEMS free- piston engine are also described.

Resonant integrated micromachined (RIMS) acoustic sensor development

Future advanced fixed- and rotary-wing aircraft, launch vehicles, and spacecraft will incorporate smart microsensors to provide vehicle dynamics monitoring. Qualitative measurement of vehicle aerodynamics properties, including airflow, surface pressure distribution, and thermal profiling, are becoming increasingly important. This paper presents a new packaging concept for integrating MEMS sensors into aircraft coating protectant systems to perform conformal sensing and characterize vehicle aerodynamics. A low profile 0.1-in. elastomeric packaging technique will be presented that enables assessment of vehicle low-speed air data parameters and structural integrity.

Smart MEMS for smart structures

From August 28 to September 18, 1997, Honeywells Rotor Acoustic Monitoring System was successfully flight-tested at Patuxent River Naval Base. This flight-test was the culmination of an ambitious, 40-month, proof-of-concept effort to demonstrate the feasibility of detecting crack propagation in helicopter rotor components. During the three weeks of flight-testing, the system was operated on 12 flights plus one ground test and accumulated more than 16 hours of flight data recorder data and about 25 Gbyte of digital data from eight on-rotor acoustic sensors. The flight-test showed that rotor head acoustic monitoring could be uniquely valuable not only for rotor crack and fault detection but also for monitoring the general health of the entire rotor assembly. This paper presents preliminary results from that flight-test.