Abstract: A method and an apparatus are provided for measuring the pressure of a gas within a sealed vessel. A sonic transducer is used to apply an oscillating force to the surface of the vessel. The frequency of the ultrasonic wave is swept through a range which causes resonant vibration of the gas in the vessel. A receiving transducer measures the amplitude of the resultant vibration at the vessel surface and reveals the resonant frequency of the gas as peaks in the amplitude of the sweep. The resonant frequency obtained depends upon the composition of the gas, its pressure and temperature, and the shape of the confining vessel. These relationships can be predetermined empirically so that the pressure inside the vessel can be calculated when the composition of the gas, its temperature, and shape of the confining vessel are known. The output of the receiver is fed into a computer which is programmed to calculate the pressure based upon these predetermined relationships which are stored in the computer.

Abstract: The dynamic viscosity of a viscous medium is measured by positioning an acoustic transducer in the temperature and pressure environment of the medium and spaced from the medium, then measuring a first resonant frequency and bandwidth for acoustic shear wave propagation within the transducer. The transducer is then positioned in surface contact with the medium, and a second resonant frequency and bandwidth are measured. The viscosity of the medium is calculated from the difference between the first and second resonant frequencies and bandwidths. The step of measuring a first resonant frequency and bandwidth involves applying a first input signal to the transducer to generate acoustic shear waves within the transducer, measuring the frequency and amplitude of the output signal produced by the transducer in response to the acoustic shear waves, and repeating the steps of applying and measuring for a range of first input signal frequencies to determine a first resonant frequency and bandwidth for the transducer.

Abstract: An ultrasonic viscometer is described which is particularly designed for monitoring the viscosity of a thermally curing resin or composite, such as a fiber-reinforced epoxy composite, in an autoclave at high temperature. According to a preferred embodiment, the viscometer comprises a piezoelectric element of lithium niobate crystals bonded to a first buffer of copper, which is bonded on the other side to a second buffer of aluminum. The resin or composite is in contact with the second buffer. When the transducer emits a short ultrasonic pulse, two echoes are reflected back, the first echo being generated by the copper-aluminum interface, the second by the aluminum-resin interface. The signals from the two echoes are processed to obtain the complex reflection coefficient at the interface of the second buffer and the resin, from which the viscosity of the resin can be calculated and the cure state of the resin determined.

Abstract: Vibration is conveyed to the proximal orifices of an indwelling catheter to disintegrate accumulated clogging deposits, large suspended particles and contaminating bacteria, viruses, fungi, etc. Orifices may be recessed, hooded or enclosed, and in some cases the catheter tip should be of absorptive material, to deter propagation of the vibration to the parts of the patient's body outside the catheter. Vibration may be conveyed to the orifices by (1) a solid fiber embedded in the catheter walls or positioned in an auxiliary lumen of the catheter; or (2) by a liquid in an auxiliary lumen--which may be formed as an annular space surrounding the main lumen. Preferably the apparatus measures the amount of vibration absorbed by the deposits or bacteria, etc., as a function of frequency, and automatically concentrates the vibration at frequencies where absorption is particularly high, to maximize the disintegration of deposits, particles, bacteria or other bioactive objects.

Abstract: Disclosed is a method for determining the dispersion of a surface acoustic wave in an object, including the steps of generating a broadband acoustic wave in a surface of the object, detecting the wave at first location on the surface, and detecting the wave at a second location on the surface. Fourier transforms of the first and second detected waves are calculated, then the change in phase .DELTA..phi.(f) of the frequency component f of the detected wave, between the first and second locations, is computed from the phase components of the quotient of the two transforms. The dispersion of the wave in the surface is given by the formulav(f)=(2.pi.f .DELTA.l/.DELTA..phi.(f))In a pulse-echo version of the method, the wave is generated and detected at the first location, and generated and detected at the second location, the dispersion then being according to the formulav(f)=4.pi.f .DELTA.l/.DELTA..phi.(f)).

Abstract: Disclosed is a method for measuring the depth a of a surface flaw in an object, including the steps of irradiating the flaw with an incident acoustic surface wave signal, detecting a reflected acoustic surface wave signal, including a first portion reflected from the surface edge of the flaw and a second portion reflected from the bottom of the flaw, and analyzing the interference between the first and second portions of the reflected signal to determine the depth of the flaw. The analysis may be carried out by Fourier transforming the reflected signals from the time domain to the frequency domain, selecting a frequency f.sub.n for which a maximum or minimum amplitude is detected independent of the angle of detection, and calculating the depth a from the formula a=nV.sub.r /2f.sub.n, where n is an integer, and V.sub.r is the speed of an acoustic surface wave in the object.