Abstract: An apparatus and method for changing the optical and/or physical properties of a fluid composition employ an electric field applied across the fluid for controlling the fluid properties. The fluid consists of a dielectric liquid and an electrically conductive, elongated, fibrous particulate material. The fibrous material has a length between approximately 1000 angstroms and five millimeters, a diameter less than about 700 angstroms, and an aspect ratio of length to diameter greater than about five. The particulate material is in colloidal suspension in the liquid. Generally, when the particles are dispersed in the liquid by Brownian movement forces, the fluid composition has an average separation between particles of approximately three to ten or more times the average length of the particulate material.

Abstract: A method and apparatus for measuring fluid characteristics use a non-invasive ultrasonic system for generating spatially extended signals into a volume of a fluid and detecting said signals for measuring the characteristic of the fluid. The generated waves are Rayleigh-like surface waves creating, in effect, an extended aperture transducer from which the waves leak into the fluid. The Rayleigh-like surface wave operates in an environment wherein the plate or other structure on which the surface wave is generated has a thickness, normal to the primary direction of propagation of the wave, of less than four Rayleigh wavelengths and greater than approximately one-half of a Rayleigh wavelength. The extended aperture has a length of at least about ten Rayleigh wavelengths. The excitation for the system is generally a short pulse interrogation in order to avoid those interferences which may cause Lamb waves to be set up in the solid material.

Abstract: An apparatus and method for measuring fluid flow parameters operate under conditions wherein the composition of the fluid flow can change rapidly thereby changing the speed of sound within the fluid and wherein the actual flow rate can change rapidly thereby further changing the transit time of acoustic energy traversing an interrogation path within the fluid. The apparatus determines the speed of sound in the fluid and the fluid flow velocity by measuring an upstream and a downstream transit time of acoustic energy within the fluid. The fluid is typically flowing within a conduit, and the transducers for transmitting and receiving the acoustic energy are precisely and carefully installed in the conduit. The measurements also allow an estimate to be made of the average molecular weight of gases passing through the conduit and hence of the mass flow rate of a gas.

Abstract: An intervalometer for determining the arrival time of a bandwidth limited energy pulse employs an integrated threshold arming apparatus and method for conditioning an event recognition circuit. The event recognition circuit, which is typically a zero crossing detector, responds to the conditioning signal for detecting a predetermined event after occurrence of said conditioning signal. The integrated threshold arming circuit employs a signal integration circuit responsive preferably to a rectified signal input, and comparison means for determining when the integrated value crosses a predetermined threshold. A dual threshold implementation can also be employed to further discriminate against false noise signals. The apparatus and method are preferably employed in connection with volumetric flow measurements of turbulent and time-varying fluids by ultrasonic pulse interrogation.

Abstract: An intervalometer for determining the transit time of an ultrasonic energy pulse through a fluid medium employs an automatic gain control amplifier circuit for amplitude stabilizing the electrical signal derived at a receiving transducer. The automatic gain control circuit tracks both a rapidly increasing and a rapidly decreasing signal amplitude. In various embodiments, synchronous switching can be employed in conjunction with a single amplifier and a plurality of storage elements to rapidly scan a plurality of signal paths and for providing automatic gain control capability on each path. The intervalometer further has a "slipped cycle" capability for accurately determining arrival time when is is known that the signal pulse will be within a certain range of times. In addition, the relative time difference between two arriving signal pulses can be accurately determined using this method so long as the range of time difference is sufficiently small.

Abstract: A photometric detection method and apparatus employ a variable beam modulation device, such as a planar oscillating disk whose reflectance and transmittance with respect an incident beam of electromagnetic radiation vary with disk angular position, to form, from an incident beam of radiation, two amplitude modulated correlated component beams. Preferably the amplitudes of the component beams vary sinusoidally, 180.degree. out of phase. In one illustrative embodiment, one of the component beams passes through a sample fluid, which absorbs a portion of the radiation at a wavelength characteristic of a selected component. The second component beam passes through a reference path and provides a reference signal relative to which changes in the sample fluid are measured. A feedback mechanism is provided to automatically adjust for variations which can occur while the apparatus is operating.

Abstract: An acoustic burst with a predetermined amplitude envelope is triggered by a square wave signal and transmitted upstream or downstream to a transducer connected to an adaptive control system which tracks the midpoint of the received envelope. The received signal is rectified and fed via a polarity reversing circuit controlled by the square wave to an integrator whose output level controls the frequency of the square wave. The burst transit time is measured to the next zero crossing of the received signal following the half cycle transition point of the square wave.

Abstract: An amplifier, responsive to a photosensitive element operating in a high intensity ambient level, and a method for selecting circuit parameters of the amplifier, take into account differing dynamic mechanisms to provide an optimum tradeoff between signal and noise. The dynamic mechanisms, manifested as electrical noise, affect and are particularly noticeable in the output of the photosensitive element operating in a high energy level environment. The method provides steps for selecting an optimum circuit element for enabling a receiving apparatus to achieve a superior signal to noise figure and hence superior sensitivity to a small AC signal level "riding" on a high DC ambient signal.

Abstract: A photometric detection method and apparatus employ a variable beam modulation device, such as a planar rotating disk whose reflectance and transmittance with respect an incident beam of electromagnetic radiation vary with disk angular position, to form, from an incident beam of radiation, two amplitude modulated correlated component beams. Preferably the amplitudes of the component beams vary sinusoidally, 180.degree. out of phase. In one embodiment, one of the component beams passes through a sample fluid, which absorbs a portion of the radiation at a wavelength characteristic of a selected component. The second component beam passes through a reference path and provides a reference relative to which changes in the sample fluid are measured. The component beams are combined and are directed onto a detector which produces an output proportional to the intensity of the combined beam.

Abstract: Waveguide antennas for ultrasonic flowmeters are described in which at least one pair of antennas is used to interrogate a flowing fluid. The waveguides are parallel, each pair defining a plane of interrogation which is parallel or nearly parallel to the flow.Some preferred embodiments use elongated waveguides which effectively interrogate the flow simultaneously along a sufficiently large number of parallel paths so that non-axial components of flow tend to be cancelled. Non-axial components are thereby suppressed or eliminated as significant error sources. The large number of effective paths, over a distributed planar area, also contributes to reliable operation even when the fluid is not single phase, especially if interrogating wavelengths are used which are large compared to scatterer dimensions. Several configurations are disclosed wherein the waveguides or their shields may be maintained clean and free of deposits without interrupting their use in the measurement of flow.

Abstract: An ultrasonic system that measures either the impedance of a fluid or liquid level utilizes moderately directional, bulk SV mode sound waves generated by a transducer and propagated in a homogeneous, flaw-free solid member. The SV wave propagates in the solid along a zigzag path that reflects at a solid-fluid interface in at least two areas and at an angle of incidence that exceeds the first critical angle by at least five degrees and is less than the second critical angle by at least ten degrees. The attenuated amplitude of the wave due to acoustic coupling between the solid and the fluid measures the impedance or an impedance related parameter of the fluid. The system preferably includes a second acoustic path that serves as a reference to compensate for changes in parameters such as temperature, the nature of the fluid, the transducer, the transducer coupling, and residues or corrosion at the solid-fluid interface.

Abstract: An ultrasonic flowmeter for determining fluid flow velocity within a conduit by determining the difference in transit time between interrogating ultrasonic pulses transmitted upstream between a pair of transducers and transmitted downstream between them. A high frequency clock pulse operating for one or more cycles of interrogation allows for accurate digital computation.

Abstract: A method and apparatus for determining volumetric fluid flow rate in an arbitrarily shaped fluid conveyance are disclosed. A plurality of functions, f.sub.j (p,m.sub.k) (where p is a position in the conveyance and m.sub.k depends upon the Reynolds number of the fluid flow), each function being approximately representative of the fluid flow velocity across the conveyance, are linearly combined to approximate the velocity, P(p), of the fluid flow at any point in a plane normal to fluid flow. The scalar constants A.sub.j,k, of the linear combination ##EQU1## are estimated by solving a system of linear equations, ##EQU2## in which acoustical measurements along the paths y.sub.i through the conveyance provide an estimate, v.sub.meas(i), of the actual average velocity v.sub.i at paths y.sub.i.

Abstract: An ultrasonic transducer assembly for making measurements within a fluid, the assembly including a transducer, a backing member and a matching member all supported within a cylindrical metal housing with the transmitting face of the housing being sealed with a thin sealing element formed of a non-resilient relatively high impedance material encasing a matching layer having an acoustic impedance intermediate between that of the transducer element and the fluid. The thickness of the sealing element is between 1/10 and 1/1000th of a wavelength at the center frequency of the wave emitted by the transducer.

Abstract: Disclosed are humidity sensor structures, and fabrication techniques, which result in uniform and reliable humidity sensing, reliable electrical connections in small sensors, and simplified and inexpensive manufacture.

Abstract: Disclosed are humidity sensor structures, and fabrication techniques, which result in uniform and reliable humidity sensing, reliable electrical connections in small sensors, and simplified and inexpensive manufacture.

Abstract: An ultrasonic densitometer for measuring the density or a density related parameter of a fluid has at least one transducer assembly that transmits and receives torsional waves guided in an axially extending sensor that is at least partially immersed in the fluid. The sensor has a noncircular cross section, typically rectangular, with dimensions, aspect ratio, frequency and bandwidth selected to limit dispersion. This non-circularity creates an inverse and substantially linear relation between the density of the fluid and the velocity of the torsional wave in the sensor. To meet special requirements, the sensor can take a variety of forms including axially curved, axially profiled, segmented or longitudinally composite. This densitometer, alone or in combination with conventional auxiliary ultrasonic measuring systems, can measure fluid density, density profiles, liquid level, viscosity, mass flow rate, gas pressure, and boiling or condensation, including measurements of flowing fluids in small conduits.

Abstract: A transducer for an ultrasonic thickness gauge of the pitch and catch type has transmitting and receiving transducer elements on adjoining blocks of delay material separated by an acoustic barrier is calibrated by operating the receiving transducer element in pulse-echo mode. The lengths of the two delay blocks differ by an amount calculated to make the pulse-echo travel time in the longer delay block greater than pitch and catch travel time by an amount at least equal to the geometric delay of the transducer to provide an unambiguous readout during pulse-echo operation when the gauge is adjusted to the proper zero point calibration for the transducer.

Abstract: An apparatus and method for examining the structure of and in particular detecting flaws within a solid are disclosed. The transmitting source directs pseudo-random coded, phase modulated, interrogation signals, at a plurality of frequencies, toward the object being examined. At the receiver, the returning interrogation signals, reflected by structure within the solid object, are demodulated, employing a delayed replica of the pseudo-random code, and are thereafter processed to provide, preferably, both the phase and magnitude of the returning signals relative to the transmitted interrogation signals. The delayed replica of the pseudo-random code provided to the receiver is delayed by selected time increments to provide a range gate. Thus, the data provided by the receiver represents the amplitude and phase of returning signals as a function of both transit time and frequency.

Abstract: Disclosed are humidity sensor structures, and fabrication techniques, which result in uniform and reliable humidity sensing, reliable electrical connections in small sensors, and simplified and inexpensive manufacture.