USA As Represented by Secretary of the Navy

Andrew J Hull

Norman Lee Owsley

Benjamin A Cray

Stephen A Austin

Lee E Estes

Mark S Peloquin

David A Hurdis

Stephen E Forsythe

John R Welch

Walter H Boober

Kent D Kasper

Shawn M Amorino

A method is provided for increasing accuracy in measuring complex Young's modulus and complex shear modulus of a material using a processing system. The material is tested to obtain an experimental frequency response transfer function of normal displacement to input force. A model panel is developed in the processing system as a modeled frequency response transfer function. The modeled transfer function is used at a range of fixed frequencies to calculate displacements of the model panel divided by the input force while varying material parameters. The modeled frequency response transfer function is compared with the experimental frequency response transfer function to compute error function values. These values indicate the most accurate material property values as those minimizing the computed error function values.

Method of estimating material properties of an elastic plate

Using a mechanical shaker test the shear wavespeed in a plate is estimated by applying a cyclical point force to the plate, measuring normal velocity of waves caused by the force, transforming temporal domain measurements with a Fourier transform into a frequency domain, transforming spatial domain measurements into a {k,k} wavevector domain spectra using Fourier transforms, determining propagation wavenumbers for given Lamb waves from peaks within the {k,k} spectra, and determining shear wavespeed by applying a Newton-Raphson gradient method using the propagation wavenumbers to Raleigh-Lamb dispersion curve equations.

Method for measuring shear wavespeed in an isotropic plate

An acoustic sensing device includes a housing having an internal cavity filled with a vibration decoupling medium. An acoustic window formed of an acoustically transparent material is mounted in the housing. This mounting can be by antivibration mounts to prevent housing noise from affecting the acoustic window. A scanning laser vibrometer is positioned within the housing and directed to detect vibrations of the acoustic window. Antivibration mounts are joined between said scanning laser vibrometer and said housing. In further embodiments, the scanning laser vibrometer detects vibrations at a plurality of locations on the acoustic window forming a virtual array.

Adaptive high frequency laser sonar system

A method for calculating material properties of a material includes determining a dilatational wavespeed and a shear wave speed. The dilatational wavespeed is determined by conducting vertical vibration tests of two specimens of the material, one specimen being twice as thick as the other. Transfer functions are obtained from these tests and used to calculate the dilatational wavespeed. The shear wavespeed is determined by conducting horizontal vibration tests of two specimens with one specimen being twice as thick as the other. The shear wavespeed can be calculated from transfer functions obtained from these tests and the dilatational wavespeed. Other material properties can be calculated from the dilatational and shear wavespeeds. Frequency dependence of the properties can be determined by conducting the tests at different frequencies.

Inverse method to calculate material properties using a non-resonant technique

A method for calculating material properties of a material includes conducting two insertion loss tests of the material having a single thickness and a double thickness. These tests are conducted at a zero wavenumber. Utilizing these insertion loss tests, a dilatational wavespeed is computed. The method continues by calculating a shear wavespeed by performing three insertion loss tests of the material at single, double and triple thicknesses. These tests are conducted at a non-zero wavenumber. A shear wavespeed can be calculated from the dilatational wavespeed and these insertion loss tests. Lam&#xe9; constants, Young's modulus, Poisson's ratio, and the shear modulus for the material of interest can then be calculated using the dilatational and shear wavespeeds.

Inverse method to calculate material properties using an insertion loss test

A software system and method is presented that calculates the sensor directivity at all spatial angles, and stores these values in a two dimensional matrix. These values are then used as additional 'weighting' coefficients in the equation for the pressure detected by an array of directive sensors. The azimuthal and polar angles of a particular sensor normal vector are used to 'rotate' the sensor directivity matrix to account for the angular orientation of each sensor within the array. The software system receives as input sensor and array geometry, shading functions, sensor shape, array structure baffling, steering, and shading. A sensor can have the shape of a point, line, plane, volume, baffled ring, or circular plane piston. The sensors within the array can either be baffled by the array structure or retain their free field directivity response, and array as a whole can have steering or no steering.

System and method for calculating the directivity index of a passive acoustic array

A method for measuring the complex frequency-dependent dilatational and shear wavespeeds of a slab of material subjected to insonification. Transfer functions that are obtained by insonifying the material at different angles. Once this is accomplished, the transfer functions are manipulated with an inverse method to yield closed form values of dilatational and shear wavespeeds at any test frequency. The wavespeeds can be combined to determine complex Lam&#xe9; constants, complex Young's modulus, complex shear modulus, and complex Poisson's ratio.

Method to estimate the mechanical properties of a solid material subjected to isonification

A method is provided to distinguish two blended but different waves in a structure, such as compressional and shear waves, by measuring their corresponding wavenumbers and wave speeds. Other characteristics of the two waves may also be measured such as the propagation coefficients of both waves. All measurements can be calculated at every frequency for which a transfer function measurement is made. The measurements do not depend on the resonance frequencies of the structure and do not require curve fitting to the transfer functions.

Inverse method for estimating the wave propagation parameters of two dissimilar wave types

A method to measure the complex frequency-dependent dilatational and shear wavenumbers of a material under a static compressional force. The material is first vibrated in a vertical and horizontal directions while obtaining transfer functions in each direction. The two transfer functions are combined with a theoretical model to estimate a dilatational wavenumber and a shear wavenumber. The wavenumbers can be utilized to give the complex dilatational wavespeed, complex shear wavespeed, complex Lam&#xe9; constants, complex Young's modulus, complex shear modulus, and complex Poisson's ratio.

Method for estimating the properties of a solid material subjected to compressional forces

A system and method is used for estimating the properties of a flexural beam. The beam is shaken transverse to its longitudinal axis. Seven frequency domain transfer functions of displacement are measured at spaced apart locations along the beam. The seven transfer functions are combined to yield closed form values of the flexural wavenumber in propagation coefficients at any test frequency.

Inverse method to estimate the properties of a flexural beam and the corresponding boundary parameters

A method for estimating the real and imaginary Young's modulus, shear modulus and Poisson's ratio of a specimen at an excitation frequency. The specimen is first joined to a reciprocating test apparatus at one end with a mass positioned at the other end. The test apparatus reciprocates at the excitation frequency and accelerations are recorded at each end of the specimen. The Young's modulus is calculated from the recorded accelerations. The specimen is then joined to a reciprocating rotational test apparatus at one end with a rotational inertial mass positioned at the other end. Accelerations are recorded upon subjecting the specimen to rotational reciprocations at the excitation frequency. The shear modulus is calculated from these accelerations. Poisson's ration can be calculated from the Young's modulus and the shear modulus at the excitation frequency. All of the calculations may be performed giving both real and imaginary values.

Nonresonant technique for estimation of the mechanical properties of viscoelastic materials

In accordance with the present invention, a device for acquiring contoured human body surface vibration signals is provided. The device comprises a first component for sensing the displacements of a skin surface as a function of time at multiple points on the human body, with the first component having a plurality of sensing elements, a second component for measuring time average displacements of the skin surface at nominal locations of the sensing elements in the first component; and a third component for correcting for the effect of positional error from a set of nominal displacement sensor locations.

Device for the acquisition of contoured human body surface vibration signals

A device for noninvasively measuring energy emissions in the human chest. This device includes first and second spaced longitudinal flexible supports. At least one transverse support means extends between the said first and second spaced longitudinal supports. A plurality of sensor means positioned in a spaced transverse array on the transverse support. This device is an array based measurement system that minimizes the effect of rib interaction on the space-time field of the human thorax. This array-based measurement system is noninvasive so there is almost no patient risk.

Reconfigurable array for positioning medical sensors

A method for determining whether a hydrophone being tested is being prope responding to a pressure field is described. The method comprises the steps of providing a shell filled with a liquid and having impedance heads attached to a first end and a second end of the shell and a number of pressure sensors or hydrophones positioned between the first and second ends within the liquid filled shell; developing a model of the pressure field within the liquid-filled shell; and comparing the response of at least one of the pressure sensors to the pressure field described by the model. The model of developing the step involves modeling the extensional wave contribution and the breathing wave contribution in the pressure field.

Laboratory test method to measure towed array hydrophone response

Disclosed is an inverse method for measuring the breathing wave speed in a iquid-filled cylindrical shell. The model used with this method is based on an experimental configuration where a shell is attached to a mechanical shaker at the forward end, which initiates longitudinal wave propagation. The resulting spatial field in the shell consists of extensional and breathing waves. End-mounted accelerometers and force transducers are used to measure the extensional wave speed. Once this is accomplished, transfer functions between five equally spaced hydrophones that are in the fluid and a forward accelerometer are recorded. These data are then combined to yield a closed form value of the complex, frequency-dependent breathing wave speed. The experiment included to validate this method is extremely easy to implement and can be executed in a short period of time.

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Portsmouth, RI, United States of America

Andrew J Hull