Browsing by Subject "Transducers"

Now showing 1 - 4 of 4

A novel fabrication process for CMUTs in air
(2017-12) Hord, Samuel Kay; Hall, Neal A.; Wilson, Preston S
A novel fabrication method for producing capacitive micromachined ultrasonic transducers (CMUTs) is presented. The process uses conductive silicon on insulator (SOI) substrates to produce an unstressed transducer diaphragm. By etching release holes through the device layer and selectively removing the underlying buffered oxide (BOX) layer, an ultrasonic transducer can be made using only two photolithography steps. The process is described in detail, including models predicting the modal behavior and the collapse voltage of the device. The acoustical behavior of a perforated plate over a sealed cavity is modeled using mechano-acoustical circuit analysis. The device is found to produce sound despite the perforations so long as the holes are sufficiently small and the frequency of operation is sufficiently high. A pitch-catch measurement verifies the transduction of the device. To the author’s knowledge, this is the simplest method for CMUT fabrication to date.
A comparison of models for a piezoelectric 31-mode segmented cylindrical transducer
(2013-12) Joseph, Nicholas John; Wilson, Preston S.; Haberman, Michael R. (Michael Richard), 1977-
Piezoelectric transducers with cylindrical geometry are often designed to operate in a radial “breathing” mode. In order to tune their performance in a cost effective way, cylinders can be constructed of alternating active (piezoelectric) and inactive (non-piezoelectric) staves. Existing lumped parameter models for such a ring are based on effective piezoelectric properties of the composite ring which reduce the system to a single degree of freedom corresponding to the breathing motion. Unfortunately, if the length of the staves is a sufficiently large percentage of the circumference, the transducer may demonstrate a detrimental higher frequency resonance within the desired bandwidth of operation even when all staves are uniformly excited by an electrical field. This parasitic resonance results from bending motion of the staves associated with stiffness and mass discontinuities of the constituent material properties and can significantly decrease the radiated acoustic pressure and generate distortion of the radiated acoustic waveform. This work presents a multiple-degree-of-freedom lumped parameter model that captures both the breathing and bending resonances of the transducer and provides a more accurate prediction of its effective coupling coefficient. Results are compared with a one-degree-of-freedom model, finite element models, and experimental data. Modifications to account for internal volumes, nonlinearities, and other effects are also presented and discussed.
Electromechanical coupling behavior of dielectric elastomer composites
(2016-12) Scurlock, Ryan Steven; Landis, Chad M.
Dielectric elastomers have gained substantial interest in the past few decades under research efforts aimed to improve electromechanical transducer technology. This material is often termed a “smart material” due to its intrinsic transduction properties, allowing the elastomer to deform in response to electric stimulation. High mechanical compliance, lightweight, low cost, and the ability to achieve enormous voltage induced strains make dielectric elastomers excellent candidates to serve as electromechanical transducers, both as high efficiency actuators and energy harvesters. This work is focused on increasing the transduction efficiency of dielectric elastomers, strengthening their potential effectiveness as a transducer. To enhance the electrostriction of the material, a composite concept is introduced where rigid conducting fibrous electrodes are embedded into the dielectric. A combined theoretical and numerical modeling framework is developed to analyze the electromechanical behavior of several different composite arrangements. In order to examine the large mechanical deformations of the elastomer, a finite deformation theory is required for the description of the material behavior. To describe the material free energy, a compressible Neo-Hookean model is utilized. The finite element method is used for the numerical solution technique to the boundary value problem.
On the propagation of longitudinal stress waves in finite solid elastic horns
(1966) Martin, Gordon Eugene, 1925-; Hixson, Elmer L.
This dissertation consists of an investigation of the propagation of longitudinal stress waves in finite solid elastic horns or tapered bars. A large number of publications during the last several decades have reported improved theories for other structures such as rods of uniform cross section. However, there appears to have been no publication wherein the effects of lateral inertia and/or shear have been included in a theory of longitudinal waves in horns. These effects are included in the results presented here. A new wave equation and appropriate boundary conditions are obtained, and the special case of the conical horn is discussed in detail including theoretical and experimental results. The historical progress in the study of fluid as well as solid horns is surveyed. A previously-unpublished duality principle is derived which shows that the results from fluid horn theory have a one-to-one correspondence with the one-dimensional theory of solid horns. The major advances in the theory of longitudinal waves in rods of uniform cross section are reviewed also. The engineering method for the derivation of improved theories of wave propagation is applied to horns. Namely, assumed forms for the components of particle displacement are used to form the Lagrangian and incorporate it into Hamilton's Principle. The solution of the resultant integral equation leads to an (Euler) wave equation and the corresponding boundary conditions. It is shown that the horn theory satisfies the reciprocity conditions for a physical system only if the appropriate boundary conditions are used. The conical horn is discussed as a special case of a horn with lateral inertia effects only. It is shown that the solution of the wave equation is a linear combination of the two Legendre functions divided by the axial coordinate. The theory of the finite conical horn with arbitrary end conditions is derived. The new theory is compared with the one-dimensional theory with the conclusion that small but significant lateral effects are present if the horn is long and thin. Comparison of theoretical results with experimental data published three decades ago indicated that the previous experimental results were not sufficiently accurate to test the theory. Therefore, an experimental study is reported wherein two identical horns are cemented with a thin ferroelectric disc between them to provide excitation. Measured values of critical frequencies of resonances are compared with results from theory incorporating the effects of the cement joint and the disc as a linear piezoelectric device. A separate experiment for the evaluation of the dynamic compliance of cement joints is described. The comparison of theoretical and experimental frequencies of resonances of conical horns shows that the relative error is reasonably small (.01 - 1.%). Possible causes for the error due to experimental aspects are given. It is concluded further that the theory should be extended with higher order representations of particle displacement used to include more correctly the effects of lateral inertia and shear.