Current Seminars

Modeling and Design of Diffraction Gratings for Optically-Read Vibration Sensors

Friday, September 23, 2016
4:00 p.m. in ETC 4.150

Randall P. Williams, PE

Department of Mechanical Engineering, and
Microelectronics Research Center
The University of Texas at Austin

Displacement detection using optical interferometric techniques allows for high sensitivity and low sensor self-noise which are unmatched by other displacement measurement methods. However, diffraction gratings commonly used in such applications can generate zeroth-order reflected beams which result in reduced sensor performance and packaging limitations. A new grating concept has been designed, fabricated, and tested at the UT Microelectronics Research Center which has a reduced zeroth-order reflected beam, opening the doors for new sensor integration approaches. The design criteria for zeroth-order beam elimination is illustrated using a simple model based on phasor arithmetic, and Fourier propagation techniques are used to model the optical field for realistic grating geometries and incident beam profiles. Important insight into the behavior of the sensor is gained for a range of different operating conditions, which commonly used grating models often fail to capture. Finally, comparisons between the models and experimental measurements on prototypes gratings will be presented and discussed.

“Great Place to Stay. Beware the Train!”

Friday, September 16, 2016
4:00 p.m. in ETC 4.150

David A. Nelson, INCE Bd. Cert., PE
Nelson Acoustics
Elgin, Texas

It’s a nice hotel, convenient to everything, comfortable, nice staff, etc. But one-third of the online reviews mention its only drawback: the train. A freight train passes behind the hotel roughly once per hour. Guests are being awakened, sometimes several times per night. The economics of the situation are equally unpleasant: regular refunds given and clientele potentially lost through unhappy internet reviews significantly affect the bottom line. Audible sound and vibration entering through windows, air conditioners, and even the ground, combine to produce a 2-in-5 chance of being awakened. Evaluation of the relative contribution of the various sound paths was challenging because of the (acoustically) tight quarters. The benefit of noise control options were compared in terms of their potential to reduce awakenings, which is far more meaningful to the client than decibel values.

Optimizing Acoustical Parameter-Extraction Methods

Friday, September 9, 2016
4:00 p.m. in ETC 4.150

Dr. Daniel R. Tengelsen
Bose Corporation
Framingham, Massachusetts

The impedance tube has long been used as an acoustical parameter-extraction device due to the fact that, under certain assumptions, it can be modelled using a one-dimensional wave equation. Since the 1980’s, several techniques have been proposed in the literature to use this device to obtain values for the acoustic properties of various materials. However, most of the methods proposed in the literature fail to pose the problem in a statistically-robust manner. Thus, extracted parameters may vary highly from sample to sample, depending on the material under test. In this talk, we reframe one of the more common extraction methods as an optimization problem and show that more stable parameters are obtained.

Brief Historical Highlights of Underwater Acoustics and the Defense Research Laboratory and Applied Research Laboratories of the University of Texas at Austin

Thursday, September 1, 2016
4:00 p.m. in ETC 5.132

Dr. Thomas G. Muir
Applied Research Laboratories
The University of Texas at Austin

Man’s involvement with sound in the ocean has been motivated by intellectual curiosity as well as by necessity, in response to threats. These have included navigational hazards, catastrophes, and world events including shipwrecks and many problem areas associated with naval warfare. In this short talk, the general historical timeline as well as a few illustrative examples will addressed, through the end of WWII. The subsequent founding and early days of the Defense Research Laboratory, now Applied Research Laboratories, will then be summarized through 1980. Examples will be given of early underwater acoustics research and development at this organization, which is closely allied with the academic program in acoustics at UT Austin.