An experimental and theoretical study of a system utilizes two polarization modes of a single cavity to improve the scale factor stability of a passive atomic gyroscope.

We present an entirely linear all-optical method of dispersion enhancement that relies on mode coupling between the orthogonal polarization modes of a single optical cavity, eliminating the necessity of using an atomic medium to produce the required anomalous dispersion, which decreases the dependence of the scale factor on temperature and increases signal-to-noise by reducing absorption and nonlinear effects. The use of a single cavity results in common mode rejection of the noise and drift that would be present in a system of two coupled cavities. We show that the scale-factor-to-mode-width ratio is increased above unity for this system and demonstrate tuning of the scale factor by (i) directly varying the mode coupling via rotation of an intracavity half wave plate, and (ii) coherent control of the cavity reflectance which is achieved simply by varying the incident polarization superposition. These tuning methods allow us to achieve unprecedented enhancements in the scale factor and in the scale-factor-to-mode-width ratio by closely approaching the critical anomalous dispersion condition.

In this paper, the development and use of acoustic energy harvesting technology as a source of local power for aeroacoustic sensing and control applications is discussed. As an example, the application of acoustic energy harvesting as a primary local power source for aircraft engine noise reduction technology is addressed. Noise generated in turbofan engine nacelles can easily exceed 150 dBSPL, presenting a primary motivation for aircraft noise reduction technologies. Adaptive noise control approaches require less power than active methods and can outperform passive techniques (e.g., by actively tuning an otherwise passive system to a changing noise spectrum). Locally sourced power is highly desirable in this application to eliminate cabling in a difficult to access, harsh environment. The low power requirements can be reasonably supplied with harvested acoustic energy, particularly given the large acoustic intensities in and around aircraft engine nacelles. The detailed development approach and experimental results of acoustic energy harvesting using an electromechanical Helmholtz resonator will be presented. Additionally, alternative Helmholtz resonator variants and other aeroacoustic applications of acoustic energy harvesting will be reviewed.

The work described herein discusses the application of a frequency-wavenumber signal processing technique to signals from rectangular infrasound arrays for detection and estimation of the direction of travel of infrasound. Arrays of 100 sensors were arranged in square configurations with sensor spacing of 2 m. Wind noise data were collected at one site. Synthetic infrasound signals were superposed on top of the wind noise to determine the accuracy and sensitivity of the technique with respect to signal-to-noise ratio. The technique was then applied to an impulsive event recorded at a different site. Preliminary results demonstrated the feasibility of this approach.

We present an entirely linear all-optical method of dispersion enhancement using coupled cavities that leads to a substantial increase in system transmission in comparison with atom-cavity systems. This is achieved by tuning the system to an anomalous dispersion condition by under-coupling at least one of the cavities to the other. The intracavity anomalous dispersion is then associated with a dip in reflection (and in turn with a peak in transmission) rather than with an absorption resonance as in the case of the atomic vapor. We find that in contrast with the atom-cavity system where mode reshaping always contributes to the mode pushing, in coupled cavity systems reshaping of the mode profile can either contribute to or oppose the mode pushing, and even reverse it under appropriate conditions leading to a reduced scale factor in transmission. We demonstrate a method for further optimizing the transmission of both atom-cavity and coupled-cavity systems, but show that this leads to a more rectangular mode profile and a reduction in the scale factor bandwidth. We also derive the cavity scale factor in reflection for both atom-cavity and coupled cavity systems and show that in reflection the reshaping of the mode profile can either contribute to or oppose the mode pushing, but cannot reverse it.

This paper addresses the design, fabrication and characterization of a first-generation, low frequency MEMS vibration sensor. The sensor is designed specifically for applications requiring extremely low power vibration detection at only targeted frequencies. For development, lumped element and finite element modeling was performed, driving the design towards a realizable geometry that addresses the targeted performance specs. The sensors were microfabricated using conventional surface micromachining, sol-gel PZT (lead zirconate titanate) thin films, and bulk silicon etching techniques. The completed sensors were then characterized to determine electrical, mechanical and piezoelectric properties at the material and device level. Results demonstrate functional operation with performance close to predicted specifications.

April 25-28, 2011 has been identified by many as the most significant and severe single-system outbreak of tornadoes in recorded history. One day in particular, the 27th of April, has been classified by the National Oceanic and Atmospheric Administration (NOAA) as the fourth deadliest tornado outbreak in US history. Severe tornadic activity on this day levied catastrophic damage to life and property across areas of Mississippi, Alabama, Georgia and Tennessee. During this outbreak, multiple Ducommun Miltec-developed infrasound sensors collecting continuous, high resolution data were deployed in two-dimensional array configurations in Northern Alabama. Prior research on the collection and analysis of infrasonic emissions from severe weather phenomenon has provided much insight on the nature of tornado-generated infrasound. Our effort focuses on the application of novel bearing estimation algorithms using closely spaced (4-6 m) array elements. Direction of Arrival (DOA) estimates, derived from Blind Source Separation (BSS) techniques, will be presented for at least two significant tornadoes: the long-track EF5 that impacted Hackleburg and Phil Campbell, AL and the large multi-vortex EF4 that struck Cullman, AL. Correlation of infrasound detection and bearing estimate initiation and termination with NOAA Storm Prediction Center (SPC) Storm Reports will also be reviewed.

Pipe arrays have conventionally been used to detect infrasound. The advantage of this approach is that the arrays have a large aperture over which wind noise can be averaged. In recent years, distributed arrays have been used for the same effect. In addition to reducing wind noise via spatial averaging, these arrays have the ability to process the individual signals from each sensor to estimate direction of arrival (DOA) of acoustic signals and, potentially, the direction of the wind flow. This is especially true for infrasound and low frequency acoustic sources of tactical interest, in the 1–100 Hz range. A frequency‐wavenumber (F‐K) processing technique has been applied to signals from rectangular infrasound arrays to estimate DOA. This approach will be discussed as well as the dependence of accuracy on signal‐to‐noise ratio.

Two modeling techniques are employed to study two automation goals for a manufacturing process; automation of the design of custom-engineered dies and automation of the manufacturing process that uses them. In both cases the objective is to improve energy efficiency and throughput of a manufacturing process known as “Hotsizing”. Finite Element Modeling (FEM) is used to study the surface temperature distribution of dies used to form titanium blanks into finished parts. First-order analytical modeling is used to study the heat transfer mechanisms at work in heating the blanks and moving them through air from a preheat oven to a forming press. FEM results show that contrary to our hypotheses, die surface temperatures are quite uniform and model-based design of the dies to guide sensor placement so as to minimize surface temperature variation is not justifiable. Analytical modeling reveals unforeseen, potentially substantial energy and throughput improvement and justifiable manufacturing process automation.

A number of security threats and interdiction problems in shallow waterways and the very shallow littorals involve small vessels, which offer difficult detection problems. In water depths on the order of a wavelength, sound propagates with considerable involvement of the bottom, whose bulk and shear moduli, as well as velocities and attenuation vary with depth into the sediment. This problem has been studied with a two dimensional finite-element code, to illustrate the consequences of computational assumptions pertinent to these parameters and their gradients with depth into the sediment. Both time harmonic (steady state) and transient (animated pulse) sequences are treated in two dimensional depictions.