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Acceleration Strain Transducer Containing Cantilever Flaps

Sensitivity is maximized along one direction.

A recently invented acceleration strain transducer is based on the principle of a conventional spring-and-mass acceleration transducer combined with a linear strain sensor that measures the acceleration-induced deflection of the spring. The invention is compatible with any of a variety of linear strain sensors, including conventional foil resistance strain gauges, fiber-optic and fiber-laser strain sensors, and electrically-conductive-liquid strain sensors.

This Acceleration Strain Transducer is configured to maximize strain response to acceleration along the y axis and minimize strain response to acceleration along the x and z axes.
The invention encompasses numerous versions; the figure depicts a basic version to illustrate the principle of operation. The transducer includes a linear strain sensor stretched and bent over the tops of an array of angled polymeric cantilever flaps extending from a base. The strain sensor is bonded to the outermost two flaps (but not bonded to any of the other flaps) by an adhesive. The flaps closer to the middle are longer than the flaps closer to the ends; this configuration, in combination with the tension in the stretched strain sensor, keeps the strain sensor in contact with the tips of the flaps.

The flaps on opposite sides are set at opposite angles in a quasi-truss arrangement designed to maximize the strain response to acceleration along the y axis and to suppress or at least minimize the strain response to acceleration along the x axis. The flaps and the strain sensor act as both inertial masses and springs such that in acceleration along the -y or +y direction, the tension (and thus the longitudinal strain) in the linear strain sensor increases or decreases, respectively. The change in measured strain is taken as the indication of y-axis acceleration. On the other hand, because of the opposite tilts of the flaps on opposite sides, acceleration along the x axis causes the flaps on one side to move upward and outward and the flaps on the opposite side to move downward and inward. The strain contributions of these opposing motions tend to cancel, so that the net strain applied to the strain sensor (and, hence, the x-axis acceleration strain response) is close to zero. In addition, the flaps are made sufficiently wide along the z axis to impart insensitivity to acceleration along that axis.

An important consideration affecting the design of such an accelerometer is the need to prevent or at least minimize vibration of the strain sensor in a string mode, which vibration would yield spurious oscillating strain readings and could be excited by acceleration along the x or z axis. Such vibration can be minimized by mounting the strain sensor in enough tension to push the vibrational resonance to a frequency well above the maximum frequency of acceleration that one seeks to measure.

This work was done by Jason M. Maguire of the Naval Under sea Warfare Center.

NUWC-0004

Topics:
Adhesives and sealants Aircraft structures Fiber optics Flaps Physical Sciences Sensors and actuators Springs Suspension systems Vibration
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Acceleration Strain Transducer Containing Cantilever Flaps

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    Defense Tech Briefs Magazine

    This article first appeared in the April, 2009 issue of Defense Tech Briefs Magazine (Vol. 3 No. 2).

    Read more articles from this issue here.

    Read more articles from the archives here.

    Overview

    The document pertains to a patent application for an innovative accelerometer that incorporates a strain sensor designed for measuring acceleration. The accelerometer features a unique transducer configuration that enhances its performance and sensitivity.

    The accelerometer includes a strain sensor that is mounted in a substantially linear configuration across a transducer. This transducer consists of a base and multiple flaps that are joined at one end to the base and support the strain sensor at the other end. The design allows the flaps to translate acceleration into strain, which the strain sensor can then measure. This configuration is particularly effective in capturing acceleration in a predefined direction.

    The document describes various embodiments of the accelerometer, including different designs of the transducer and the arrangement of the flaps. Some embodiments feature flaps that create an interrupted surface, with a greater height at the center, which can enhance the strain experienced by the sensor due to acceleration. This design consideration aims to improve the sensitivity and accuracy of the accelerometer.

    Additionally, the document discusses the use of fiber laser sensors in the accelerometer. It mentions two types of fiber lasers: Fabry-Perot type and distributed feedback fiber lasers. The Fabry-Perot type utilizes a length of erbium-doped optical fiber with Bragg gratings at both ends, while the distributed feedback type has a grating written along the entire length of the fiber. A pump laser is employed to transmit coherent light through the optical fiber, which can be a diode laser operating at specific wavelengths (980 nm or 1480 nm).

    Overall, the accelerometer described in the document represents a significant advancement in sensor technology, particularly for applications requiring precise measurement of acceleration. The innovative design of the transducer and the integration of fiber laser technology suggest potential for enhanced performance in various governmental and industrial applications. The document emphasizes the potential for licensing this technology without royalty fees, indicating its availability for broader use in relevant fields.

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