Browsing by Subject "Transducer"

Now showing 1 - 5 of 5

Design and comparison of single crystal and ceramic Tonpilz transducers
(2010-08) Nguyen, Kenneth Khai; Haberman, Michael R. (Michael Richard), 1977-; Wilson, Preston S.; Hall, Neal A.
Transducers utilizing single crystal piezoelectrics as the active elements have been shown to exhibit broader operating bands, higher response levels, and higher power efficiency than transducers using piezoceramics while also reducing the size and mass of the transducer (Moffett et al., J. Acoust. Soc. Am., 2007). The key to these high performance characteristics is the piezocrystal's inherent high electromechanical coupling coefficient. One potential application is to replace multiple narrowband piezoceramic transducers with a single broadband piezocrystal transducer which reduces the system's weight and size. This is very important for the new generation of smaller and power efficient unmanned underwater vehicles (UUVs). A third application is for use in very broadband communication networks. The work presented here focuses specifically on the design, modeling, and construction of Tonpilz transducers using piezoelectrics as the active material. The modeling includes lumped element and finite element analysis to approximate the performance of these transducers. These models serve as the main structure of an overall iterative design process. The objective of this research is to compare the performance characteristics of a piezocrystal and a piezoceramic Tonpilz transducer and to validate the models by comparing the model predictions with experimental results.
Methodology for the design of hydrophone acoustic baffles and supporting materials
(2011-08) Embleton, Steven Thomas; Wilson, Preston S.; Haberman, Michael R.
One key element of underwater transducer design is the acoustic baffle. Acoustic baffles isolate a structure, such as a submarine hull, from noise and vibration produced by the active elements of the transducer and vice versa. Baffle materials must meet many conflicting requirements such as the need to be lightweight while providing high acoustic isolation. Currently Syntactic Acoustic Damping Material (SADM) is widely used as the primary acoustic baffle material. However, SADM baffles have many undesirable characteristics such as high density, poor machinability, high lead content and depth dependent acoustical behavior. The study of baffle materials is an under-represented area of sonar design. Most sonar transducer research focuses on the electrically active materials and their response to a variety of conditions. Relatively fewer studies have been devoted to understanding the effects of the supporting and baffle materials. This work considers the effects of the entire hydrophone system on the response while developing a method for aiding in proper system material selection. This was accomplished by first developing a model for a transducer's response in a variety of conditions. The response was validated with numerical finite-element models and experiments. Next, a generic model was developed that allows any number of layers with any material to be analyzed. This generic model is applied in concert with a material optimization method to aid in the selection of materials that will improve the transducer's response. The tools are finally applied to a simple real world problem to illustrate its strengths and weaknesses.
Micromachined in-plane acoustic pressure gradient sensors
(2014-05) Kuntzman, Michael Louis; Hall, Neal A.; Champlin, Craig A; Driga, Mircea D; Hamilton, Mark F; Neikirk, Dean P
This work presents the fabrication, modeling, and characterization of two first-generation acoustic in-plane pressure gradient sensors. The first is a micromachined piezoelectric microphone. The microphone structure consists of a semi-rigid beam structure that rotates about torsional pivots in response to in-plane pressure gradients across the length of the beam. The rotation of the beam structure is transduced by piezoelectric cantilevers, which deflect when the beam structure rotates. Sensors with both 10 and 20-μm-thick beam structures are presented. An analytical model and multi-mode, multi-port network model utilizing finite-element analysis for parameter extraction are presented and compared to acoustic sensitivity measurements. Directivity measurements are interpreted in terms of the multi-mode model. A noise model for the sensor and readout electronics is presented and compared to measurements. The second sensor is a capacitive sensor which is comprised of two vacuum-sealed, pistons coupled to each other by a pivoting beam. The use of a pivoting beam can, in principle, enable high rotational compliance to in-plane small-signal acoustic pressure gradients, while resisting piston collapse against large background atmospheric pressure. A design path towards vacuum-sealed, surface micromachined broadband microphones is a motivation to explore the sensor concept. Fabrication of surface micromachined prototypes is presented, followed by finite element modeling and experimental confirmation of successful vacuum-sealing. Dynamic frequency response measurements are obtained using broadband electrostatic actuation and confirm a first fundamental rocking mode near 250 kHz. Successful reception of airborne ultrasound in air at 130 kHz is also demonstrated, and followed by a discussion of design paths toward improve signal-to-noise ratio beyond that of the initial prototypes presented. A method of localizing sound sources is demonstrated using the piezoelectric sensor. The localization method utilizes the multiple-port nature of the sensor to simultaneously extract the pressure gradient and pressure magnitude components of the incoming acoustic signal. An algorithm for calculating the sound source location from the pressure gradient and pressure magnitude measurement is developed. The method is verified by acoustic measurements performed at 2 kHz.
Sediment characterization using in situ measurements of acoustic properties
(2018-08-17) Dubin, Justin Thomas; Wilson, Preston S.; Ballard, Megan S.; Lee, Kevin Michael, 1977-
Three related studies associated with the acoustics of marine sediments were performed and described here. The first study was a direct exploration of the microscopic properties of marine sediment collected in the field. High-resolution images, acquired through scanning electron microscopy, are presented alongside sediment analysis and in situ sound speed data in order to better understand the affect microscopic geometries have on acoustic propagation in naturally occurring marine sediment. This microscopy work is followed by a description of the apparatus, methodology, and results from a field experiment conducted in a shallow water seagrass-bearing environment in which the acoustic properties of both the seagrass canopy and underlying sediment were measured in situ. The results are compared to predictions from several effective medium models to help explain the observed propagation behavior. The final study in this thesis describes acoustic directivity characterization for the compressional wave transducer probes used to collect in situ data presented in the previous studies as well as for a re-designed pair of prototype probes. These laboratory measurements are compared to both analytical and finite element models.
Study of liquid-coupled ultrasonic techniques to evaluate elastic wave propagation in rocks
(2017-08) McMullen, Adam James; Torres-Verdín, Carlos
The development of new methods to measure core acoustic properties will improve understanding of reservoir geomechanical properties. Conventional acoustic analysis under triaxial press is often infeasible or impractical to perform along the entire core. Unconsolidated core samples in liners or cores extracted with pressure coring techniques present additional challenges. This work explores ultrasonic analysis of core samples subject to the previously mentioned constraints by immersing samples in liquid (water) and placing transducers adjacent to the sample at a given distance. Modern pressure-coring ultrasonic sensors are capable of measuring P-wave velocity across the core diameter. This research explores this type of analysis with a focus on quality control effects of transducer-sample alignment. Further, this report studies a dual transducer array adjacent to the core sample to measure refracted P and S-wave velocities simultaneously. The methods are corroborated with forward models assuming a simplified 2D geometry to better understand the constraints of both systems and assist in data analysis. Experiments are performed on cylindrical samples of aluminum, Berea sandstone, and Texas Cream limestone, with the rock samples studied while dry and fully water saturated. The data for the cross-diameter P-wave analysis suggest that there is a minimum amount of fluid required to couple the energy to the sample and highlight the need to use transducers with small effective measurement areas to reduce the effects of sample curvature. Measurements on both dry and fully water saturated core samples agree with Gassmann’s fluid substitution theory within a 2% error margin. Results from the refracted wave tests agree with the forward model, with all P and S-wave velocity estimates below 6% error. A second receiver spaced further away from the source simplifies isolation of relevant wave modes. Overall, forward model predictions agree with experimental results and show the potential of simultaneous P and S-wave measurement in the laboratory.