A parameter indicative of the status of fluid flow is remotely monitored in a vessel, a natural graft, or a synthetic graft (106). One or more conformal array transducers (44-46) comprising a plurality of elements that curve around the graft (106) or vessel, are excited with an input signal provided by one of various implantable electronic circuits. The implantable electronic circuits enable a selected transducer to be driven, and to receive an ultrasonic signal or pressure signal indicative of the status of fluid flow monitored by the transducer. The implanted electronic circuit is connected to an implanted radio frequency (RF) coil. An external coil that is connected to a power supply (32), receive data signals from the transducer that are indicative of the parameter being monitored.

Ultrasonic sensors for monitoring the condition of a vascular graft

Surface acoustic wave (SAW) device coverage includes delay lines and filters operating at selected frequencies in the range from about 10 MHz to 11 GHz; modeling with single-crystal piezoelectrics and layered structures; resonators and low-loss filters; comb filters and multiplexers; antenna duplexers; harmonic devices; chirp filters for pulse compression; coding with fixed and programmable transversal filters; Barker and quadraphase coding; adaptive filters; acoustic and acoustoelectric convolvers and correlators for radar, spread spectrum, and packet radio; acoustooptic processors for Bragg modulation and spectrum analysis; real-time Fourier-transform and cepstrum processors for radar and sonar; compressive receivers; Nyquist filters for microwave digital radio; clock-recovery filters for fiber communications; fixed-, tunable-, and multimode oscillators and frequency synthesizers; acoustic charge transport (ACT); and other SAW devices for signal processing on gallium arsenide. Shallow bulk acoustic wave (SBAW) device applications include gigahertz delay lines, surface-transverse-wave resonators employing energy-trapping gratings and oscillators with enhanced performance and capability. >

Applications of surface acoustic and shallow bulk acoustic wave devices

Utilizing a shear horizontal displacement of a leaky SAW mode, SAW sensors to be used in liquid can be realized. Theoretical and experimental works showed that 36O-rotated Y-cut X-propagation LiTaOj is a promising substrate for a biosensor and a viscosity sensor.

New Sensor in Liquid Using Leaky SAW

A method for measuring physical properties or characteristics of liquids uses an acoustic transfer system that utilizes Rayleigh waves. A wave guide with at least one test section formed from a solid surface made from non-piezo-electric material, contacts the liquid medium to be measured and/or a transfer system. A sender sends acoustic wave energy that includes at least one Rayleigh wave, and at least part of the acoustic wave energy leaving the sender passes at least once through a mode converter on its way to the receiver, whereby this part of its wave energy is converted at least partly from a Rayleigh wave (RW) into a volume sound wave (VW) or vice versa. The physical characteristics or physical properties of the liquid are then determined using changes of at least a parameter of the Rayleigh wave.

Measurement of physical characsteristics or physical properties of viscous media by means of Rayleigh waves

The method uses an acoustic transfer system (5) with at least one measurement path (100) formed by a solid state surface of non-piezoelectric material which can be at least partially brought into contact with the medium to be measured. At least part of the acoustic energy of the measurement path is available in the form of Rayleigh waves (RW) which propagate over the measurement path over at least one-eighth of a wavelength and pref. more than two wavelengths. The acoustic transfer path operates as a waveguide at least between the beginning of the measurement path and the receiver. Only variations of at least one characteristic of the Rayleigh waves are used to determine the measurement parameter.

Measuring physical or technical parameters of liquids, including highly viscous, doughy or pasty material

Abstmt-Methods of measuring the acoustic properties of solids using acoustic beams in a liquid generated by interdigital transducers (IDT) are described. An IDT can radiate acoustic waves into a liquid in oblique directions with respect to the substrate, and the wave fronts can be arbitrarily controlled by designing the IDT shape. When the acoustic beam is incident on the solid sample-water interface near the Rayleigh angle, the reflection field is equal to the superposed fields of the specular reflection and the reradiation from the leaky surface acoustic wave (SAW) excited on the sample. One normal IDT pair on a piezoelectric substrate is used to measure the acoustic properties of a solid sample. The velocity and the attenuation of the leaky SAW on the sample can be obtained by measuring the trailing field due to the reradiation. A new method for focusing the beam from an IDT and mapping a leaky SAW velocity on a solid sample surface is shown. An interdigital electrode is divided into several sections, each of which is positioned to form a one-dimensional Fresnelphase-plate interdigital transducer (FPP IDT) on a piezoelectric substrate. It has been found that the FPP IDT generates a converging beam onto a focal plane, and the present system is suitable for measuring the two-dimensional variation of the leaky SAW phase velocity on a sample surface. T

Measurement and Mapping of Elastic Anisotropy of Solids Using a Leaky SAW Excited by an Interdigital Transducer

A method of measuring the acoustic properties of materials using an interdigita1 transducer (IDT) for nondestructive evaluation (NDE) is described. An IDT can efficiently radiate acoustic waves directly into a liquid so that it is used as the acoutic wave transducer in the NDE system. In this paper, a new method for the measuring of SAW velocity by using the IDT is described. The output voltage is measured as a function of the frequency of the acoustic wave in the NDE system using an IDT. The SAW velocity is obtained from the frequency dependence. Measurement are made for an anisotropic materials at frequencies from 15 to 25 I'IIJz. The experimental results obtained in this manner agreed well with the theoretical ones.

https://ieeexplore.ieee.org/iel5/10286/32719/01535682.pdf

T. Nomura

Papers

Measurement and Mapping of Elastic Anisotropy of Solids Using a Leaky SAW Excited by an Interdigital Transducer

Precise keasurement of saw velocity wit11 an interdigital transducer