Communications – electrical: acoustic wave systems and devices – Transmitter systems – With beam forming – shaping – steering – or scanning
Reexamination Certificate
1999-09-02
2001-08-21
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Transmitter systems
With beam forming, shaping, steering, or scanning
Reexamination Certificate
active
06278656
ABSTRACT:
TECHNICAL FIELD
The present invention is generally directed to the manipulation (e.g., focusing, dispersing, steering, waveguiding, etc.) of acoustic (sound) waves, and, more particularly to the use of materials having a gradient in acoustic velocities (transverse and longitudinal). These velocity gradients are obtained by generating a gradient in one or more of the following properties: elastic modulus, Poisson's ratio, and density.
BACKGROUND ART
Acoustic waves, e.g., ultrasonic waves, find use in a variety of applications. In many such applications, it is desired to manipulate the acoustic waves in order to focus, disperse, steer, waveguide, or otherwise alter them. There are several different techniques used to fabricate materials with gradients in material properties, such as ion exchange, chemical vapor deposition (CVD), sol-gel, etc.
Chemical vapor deposition techniques can be used to fabricate a gradient in material properties. CVD requires that the reactants be present in the gaseous phase and that the reactants are able to react with each other. This places a restriction on the choice of chemicals that can be used in the fabrication of the final gradient profile, thereby reducing the ability to generate specific property gradients as a function of thickness. Also, this technique is typically used when impurity levels in the material need to be restricted to part per billion (ppb) levels. Due to this fact, this technique is highly capital intensive and time-consuming. Although, the use of CVD can be extended to acoustoelectronics, acoustooptics, and other ultrasonic engineering applications, its use is primarily constrained to fiber optics, photonics, and the semiconductor industry.
Sol-gel processes can also be used to fabricate a gradient in material properties. Unlike CVD, this technique involves the reaction of constituents in the liquid phase. The formation of the gel is restricted by the kinetics of the chemical reaction, which limits the available reactants for production of the gradient profile. Furthermore, failure due to drying shrinkage places a limitation on the dimensions of the final product and is an inherent disadvantage to this technology.
Surface modification for the generation of property gradients in crystals and glasses can be achieved by diffusion of ionic species into or out of the substrate material. The case where the inward diffusing species (ions) replaces the outward moving species, is referred to as ion exchange. A recent publication by A. Abramovich entitled “Acoustic Properties of Gradient Glasses”, published in the proceedings of the 18
th
International Congress on Glass, discloses the use of optical glasses having a gradient in the optical index of refraction and formed by ion-exchange for acoustoelectronics, acoustooptics, and other ultrasonic applications. In glasses, the diffusion of ions occurs through the interstitial volume of the glass structure, whereas in crystals, the diffusion occurs through the interstitial lattice. The diffusion of ions into glass or crystalline materials usually follows Fick's laws of diffusion. According to Fick's laws, the rate of ion diffusion decreases with time and increases with temperature. In glasses, the maximum diffusion temperature is determined by the glass transformation temperature (T
g
) of the substrate glass. Thus, obtaining large diffusion depths at a temperature below T
g
becomes difficult for reasonable amounts of time. In crystals, the diffusion mechanisms are more complex and their description is outside the scope of this invention. However, it will suffice to say that the time and temperature relationships in regard to the depth of ion penetration are similar to that of glasses.
Surface modification of the material substrates using ion exchange or solid state diffusion imposes several limitations with regards to obtaining a particular property gradient. Firstly, the maximum total change in a particular property is dependent upon the diffusing species and does not result in any major structural changes in the material. Therefore, the total change is typically very small. The propagating wave would not see a large difference in acoustic velocity (transverse or longitudinal); therefore, there exists only a limited ability to manipulate the acoustic waves. Secondly, this technique offers the ability to create a variety of functional distributions of a material property, but does not offer the flexibility to tailor a specific material property profile. Thirdly, the total distance across which the material property gradient exists is limited due to the nature of ion exchange phenomena and solid state diffusion. This does not allow for the fabrication of material property gradients across a large thickness.
Therefore, there is a need to provide a tailored element for manipulating acoustic waves, with a gradient throughout its thickness and the flexibility to obtain this gradient across a large thickness. By “large thickness” herein is meant a thickness on the order of about 6 to 30 mm, which is to be compared to the gradient thickness achieved by ion exchange, which is at most only a few mm.
DISCLOSURE OF INVENTION
In accordance with the present invention, a device for manipulation of acoustic waves is provided, comprising a functionally-graded material for interposing between a source of the acoustic waves and a target. The target may be an object upon which the acoustic waves are incident, such as a detector for measuring the intensity of the manipulated acoustic waves across the thickness, an imaging sensor, a specimen under non-destructive testing, or a recipient of focused acoustic energy, such as kidney or gall stones. The functionally-graded material has a gradient in one or both of the acoustic velocities (transverse or longitudinal) across the thickness. The gradient in acoustic velocities is achieved by creating a gradient in at least one of the following material properties: elastic modulus, Poisson's ratio, and density, that is perpendicular to a direction of propagation of the acoustic waves. The gradient is axial, as opposed to radial. Axial gradients having a parabolic or gaussian types of acoustic velocity gradients, such that the highest acoustic velocity is at the surfaces and the lowest acoustic velocity is in the center (positive), may be used for focusing. A negative axial gradient having a parabolic or guassian type acoustic velocity gradient, such that the lowest acoustic velocity is at the surfaces and the highest acoustic velocity is in the center, may be used for dispersing acoustic waves. These types of profiles can be fabricated by gluing or fusing two halves of a specific acoustic velocity profile at the high or low acoustic velocity faces, in subsequent text herein referred to as a biaxial. A continuously increasing, continuously decreasing, or any other special function of acoustic wave velocities may be used for wave steering.
Also in accordance with the present invention, a method of making the device is provided, comprising:
(a) providing the source of acoustic waves;
(b) providing the target for acoustic waves, such as the detector for measuring the acoustic wave intensity across the thickness;
(c) providing the functionally-graded material having a gradient in one or both of the acoustic properties (transverse or longitudinal) across the thickness, the gradient in acoustic properties being achieved by creating a gradient in at least one of elastic modulus, Poisson's ratio, and density; and
(d) interposing the functionally-graded material between the source of acoustic waves and the target for acoustic waves such that the gradient is perpendicular to a direction of propagation of the acoustic waves.
The process of the present invention provides a functionally-graded material with a gradient in properties such as elastic modulus, Poisson's ratio, and density for the purpose of obtaining a gradient in acoustic velocity.
The functionally-graded material so provided can be used to manipulate, i.e., focus, disperse, steer, or w
Tinch David A.
Tyagi Vineet
Collins David W.
LightPath Technologies, Inc.
Pihulic Daniel T.
LandOfFree
Manipulation of acoustic waves using a functionally graded... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Manipulation of acoustic waves using a functionally graded..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Manipulation of acoustic waves using a functionally graded... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2473471