&lt;title&gt;Ultrasonic displacement sensor for the seismic detection of buried land mines&lt;/title&gt;

An experiment was conducted to determine the response of the human lung to water-borne sound in the range of 20 to 500 Hz. A small pool inside a hyperbaric chamber was used to simulate four ambient pressure conditions spanning the range of recreational diving depths. Ten subjects were tested on two occasions each using three separate measures to evaluate the response of the subjects' lungs. With some notable exceptions, results were consistent between subjects and between measures. These indicate that human lungs can be reasonably modeled as a lumped single-degree-of-freedom system over the lower portion of the band of interest. Here, the surrounding fluid provides the dominant mass and the dominant stiffness is provided by the entrapped air with a small additional contribution from tissue elasticity. Measured resonances increase with the square root of ambient pressure from an average of 40 Hz with a quality factor of 1.8 at near-surface pressure to 73 Hz with a quality factor of 2.6 at an equivalent depth of 36.4 m. There is evidence of other resonances within or near the band of interest that may be attributable to nonvolumetric chest/lung modes, Helmholtz resonance, and/or resonance of gastrointestinal bubbles.

Section: Experimental Methodsmentioning

confidence: 99%

Measurement of the depth-dependent resonance of water-loaded human lungs

Martin

Rogers

Cudahy

2005

“…Cross correlation of the transmitted and received signals [Eqs. (2) and (3)] is the special case where B n V and u n À/ n . Here,…”

Section: Comparison With Other Techniquesmentioning

confidence: 99%

“…1 In that work, the signal processing involved measuring relative sidelobe levels on a spectrum analyzer to determine the amplitude of a pure-tone LF vibration. The technique was later expanded by Martin et al 2 and by Finneran and Hastings 3 to include LF phase measurement and real-time measurement of broadband LF vibration by a variety of different demodulation techniques. These included passive mixers, 3 active analog multipliers, 2 phase-locked loops 4 and direct digitization of the modulated carrier signal.…”

mentioning

confidence: 99%

Range discrimination in ultrasonic vibrometry: Theory and experiment

Martin

Rogers

Gray

2011

A technique has been developed to demodulate periodic broadband ultrasonic interrogation signals that are returned from multiple scattering sites to simultaneously determine the low-frequency displacement time histories of each individual site. The technique employs a broadband periodic transmit signal. The motions of scattering sites are separately determined from the echoed receive signal by an algorithm involving comb filtering and pulse synthesis. This algorithm permits spatial resolution comparable to pulse-echo techniques and displacement sensitivities comparable to pure-tone techniques. A system based on this technique was used to image transient audio-frequency displacements on the order of 1-10 μm peak (≥ 50 nm/√Hz) that were produced by propagating shear waves in a tissue phantom. The system used concentric transmitting and receiving transducers and a carrier signal centered at 2.5 MHz with an 800 kHz bandwidth. The system was self-noise-limited and capable of detecting motions of strongly reflecting regions on the order of 1 nm/√Hz. System performance is limited by several factors including signal selection, component hardware, and ultrasonic propagation within the media of interest.

“…In acoustic landmine detection, [3][4][5] ultrasound vibrometers are being investigated as an imaging sensor that measures displacement and velocity of ground excited to vibrate at low acoustic or seismic frequencies in order to confirm the presence or absence of mine-like targets. [6][7][8] In many applications, it is desirable for the vibrometer to be used in a continuous scan mode to rapidly comb through large areas of the surface or object under investigation. The presence of undulations or roughness on the surface often degrades the performance of the vibrometer for measuring surface displacements.…”

Section: Introductionmentioning

confidence: 99%

Model for continuously scanning ultrasound vibrometer sensing displacements of randomly rough vibrating surfaces

Ratilal

Andrews

Donabed

et al. 2007

An analytic model is developed for the time-dependent ultrasound field reflected off a randomly rough vibrating surface for a continuously scanning ultrasound vibrometer system in bistatic configuration. Kirchhoff's approximation to Green's theorem is applied to model the three-dimensional scattering interaction of the ultrasound wave field with the vibrating rough surface. The model incorporates the beam patterns of both the transmitting and receiving ultrasound transducers and the statistical properties of the rough surface. Two methods are applied to the ultrasound system for estimating displacement and velocity amplitudes of an oscillating surface: incoherent Doppler shift spectra and coherent interferometry. Motion of the vibrometer over the randomly rough surface leads to time-dependent scattering noise that causes a randomization of the received signal spectrum. Simulations with the model indicate that surface displacement and velocity estimation are highly dependent upon the scan velocity and projected wavelength of the ultrasound vibrometer relative to the roughness height standard deviation and correlation length scales of the rough surface. The model is applied to determine limiting scan speeds for ultrasound vibrometer measuring ground displacements arising from acoustic or seismic excitation to be used in acoustic landmine confirmation sensing.