The Train of Frozen Boxcars (TFB) model has been developed for a continuous piezoelectric cantilever fluidic harvester to simplify the effective one-way interaction between the fluid and the structure for certain flows. The TFB model treats the force due to vortex or turbulent flow as a series of boxcars of different amplitudes, widths and separations advected with a constant velocity over a piezoelectric beam. In this paper, the effect of five parameters, namely the number, amplitude, width, spatial separation and advection speed of the boxcars in the TFB forcing model, is studied for four different forcing scenarios. It has been observed that an increase in the amplitude or advection velocity of the boxcars leads to an increase in the power output, whereas a saturation limit in the power output is observed with an increase in the width or number of boxcars. More importantly, however, it is concluded that the separation between boxcars is the determining factor in maximizing or minimizing the power output from the harvester.
Fatigue and overload of mechanical, civil and aerospace structures remains a major problem that can lead to costly repair
and catastrophic failure. Long term monitoring of mechanical loading for these structures could reduce maintenance
cost, improve longevity and enhance safety. However, the powering of these sensors during the lifetime of the
monitored structure remains a major problem. In this paper we describe an implementation of a novel self-powered
fatigue monitoring sensor. The sensor is based on the integration of piezoelectric transduction with floating gate
avalanche injection. The miniaturized sensor enables self-powered continuous battery free monitoring and time-to-failure
predictions of mechanical and civil structures. Measured results from a fabricated prototype in a 0.5&mgr;m CMOS
process indicate that the device can compute cumulative statistics of electrical signals generated by the piezoelectric
transducer, while consuming less that one microwatt of power. Furthermore, the sensor is capable of storing this
information in non-volatile memory which makes it an attractive alternative when the converted electrical energy levels
are low due to small mechanical force inputs. The current microchip is less than 2 square millimeters in area. The non
volatile memory storage is coupled to a radio frequency (RF) identification microchip which allows the sensor to be
interrogated asynchronously through a RF reader. We are currently developing a state vector machine (SVM), neural
network based hardware to be included on the microchip. The SVM hardware will enable low-power processing and
computation of the incoming mechanical loading cycle data.
Mide Technology Corporation, under the supervision of the U.S. Army, is developing fast hydraulic valve technologies for fuel injection systems. Mide aims to address the Army's 21st Century Vehicle programs by providing the flexibility to achieve economic, environmentally friendly, and power dense diesel operation from a single platform. The technology couples a highly efficient gained piezoelectric actuator to a diesel unit injector's control valve spool. Piezoelectric actuation enables proportional authority over the injector's control valve, as opposed to traditional digital (on/off) operation. This authority allows the integrated device to provide electronically controlled fuel injection rate shaping capability. Each injection event profile may be independently shaped to govern diesel engine operation in one of three selectable modes: Lean, for fuel efficiency; Clean, for reduced emissions; Mean, for improved battlefield performance. To date, Mide has shown injection rate shaping capability in the laboratory using the industry standard "rate tube test" to measure injection profiles. Future development will focus on an engine demonstration of Lean, Clean, and Mean operating mode flexibility using rate shaping technology.
The condition of concrete structures can be assessed through the monitoring of crack openings. Researchers at MIT and Brown University have recently developed a novel concept for the sensing of cracks in concrete structures. The sensing capability is based on the light loss as microbending occurs in a fiber bridging the crack. To use the sensor, only the crack plane orientation in the structure (rather than the exact crack locations) needs to be known. With the use of OTDR, distributed sensing is possible. In this paper, the novel crack sensing concept is first introduced. To guide the design of sensors for various performance requirements, a theoretical model is developed to relate signal loss and crack opening. Prediction from the mold is compared with experimental results. Using laboratory-sized specimens, the detection of both surface and interior cracks are demonstrated.
The detection of delamination damage is important in ensuring the safety of composite structures. In this paper, a novel approach for delamination detection is described. The new approach involves (1) the application of a moving load on the composite member, and (2) measurement of total extension in embedded optical fiber(s). A theoretical study indicates that with the new approach, a single loading test can provide sufficient information to deduce the delamination location (in both the length and thickness directions) as well as the delamination size. Multiple delaminations can also be easily detected if there is no significant interaction between them. While further analysis and experimental work are necessary, the feasibility and potential of the proposed delamination detection technique has been established.
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