At Brigham Young University, acoustic time reversal experiments are conducted in solids and fluid media. The experimental setup involves synchronized generation and acquisition hardware. The synchronized hardware allows for multi-channel generation, and in some cases, multi-channel acquisition of time reversal focusing. A LabVIEW application has been compiled to increase ease of use and repeatability for the students conducting experiments. Forward and backward steps of time reversal are conducted through this simple user interface. The software is also able to control a 2D positioning system that allows for the measurement of the spatial extent of a time reversal focus. Modifications to traditional time reversal processing, such as inverse filtering and one-bit processing, may be easily implemented in the software. This presentation describes the hardware and software that help to facilitate time reversal research. Ideas from this presentation may help others develop time reversal data acquisition systems.

A new underwater acoustics laboratory has been created at Brigham Young University. Care was taken to design the lab that can take high precision measurements and yet provide an optimal environment for training undergraduate student researchers. The laboratory water tank is a rectangular acrylic tank of 3.6 m long by 1.2 m wide with 0.91 m as the maximum depth. This paper provides details about the custom-built water treatment and sanitizer with bubble removal column. The measurement chain for signal transmission and recording and the automated positioning system are explained. Sound absorbing tiles acquired to line the side walls are also described. The in situ calibration method for obtaining a through-the-sensor frequency response of the entire measurement chain is presented. Limitations are mentioned along with a discussion of how this design maintains potential for a wide variety of underwater acoustic laboratory measurements.

In recent years, a great deal of attention has been given to the passive detection of fissile material by detecting spontaneously emitted neutrons. Neutron detection schemes generally rely on low-density detection media with high neutron-gamma discrimination capability. However, such detectors generally suffer from low efficiency for high energy (>1.00 MeV) neutrons and usually are constructed with moderating material built into the detector package to compensate for that. But when the source is highly shielded by hydrogenous materials, the moderating material surrounding the detector actually decreases the detector efficiency (Rees and Czirr, 2012). This problem is further compounded if the source is shielded with borated material, significantly reducing the number of emerging neutrons. We have built, tested, and modeled a simple neutron detector that uses a large block of plastic scintillator fitted with a removable cadmium foil. This detector is sensitive to fission gammas, gammas emitted from neutron capture in shielding, gammas emitted from neutron capture in the plastic scintillator, and gammas produced by neutron capture in the cadmium foil. We demonstrate that by applying suitable data analysis, we can detect a shielded californium source with a very small chance of false positives from typical gamma sources. When boron is added to the shielding, we also use the 477 keV gammas emitted when neutrons capture in boron. This process is enhanced by using an auxiliary NaI gamma detector. Although the detection method flies in the face of currently promoted detectors, it is a simple technique that could be applied to a variety of detection applications.

A 1 μm diameter platinum wire resistance thermometer has been used to measure temperature fluctuations generated during a static GEM-60 rocket motor test. Exact and small-signal relationships between acoustic pressure and acoustic temperature are derived in order to compare the temperature probe output with that of a 3.18 mm diameter condenser microphone. After preliminary plane wave tests yielded good agreement between the transducers within the temperature probe's ∼2 kHz bandwidth, comparison between the temperature probe and microphone data during the motor firing show that the ±∼3 K acoustic temperature fluctuations are a significant contributor to the total temperature variations.

Acoustic pressure measurements in high-amplitude sound fields are common, but acoustic temperature measurements are relatively rare. This is primarily because thermometers exhibit thermal lag and, consequently, a limited frequency range. In this study, a 1 μ diam platinum wire resistance thermometer was used to measure temperature fluctuations generated by propagating noise produced by a horizontally fired, static GEM-60 solid rocket motor. The data are compared with those calculated from the pressure data of a nearby 3.18 mm condenser microphone by assuming an ideal adiabatic process.