Abstract: This invention relates to apparatus and method for measurement and monitoring of physical properties of materials, such as liquids, and more particularly to acoustic instruments, methods, and systems that automatically measure air content in real-time within liquids, including concrete, mortar, or other hydratable cementitious mix suspensions using resonant electroacoustic transducers that have their radiating surfaces in contact with the liquid.

Abstract: The bearing accuracy and long-range sonar target detection capability of a multi-cardioid directional receiving hydrophone array is improved by electronically producing mirror images of the cardioid directional patterns of each directional hydrophone in the array whereby the number of receiving channels are effectively doubled by this invention which in turn results in higher signal-to-noise ratios especially when receiving distant relatively weaker sonar signals. As a result, the accuracy of measurement of target range and bearing by the improved directional hydrophone array will be significantly increased.

Abstract: A deep-water low-frequency transducer employs a collapsible air chamber to equalize the internal transducer air pressure with the external hydrostatic pressure at the submerged operating depth. A capsule containing a highly pressurized gas is mounted inside the collapsible air chamber and an automatic valve mechanism releases the gas to inflate the collapsed air chamber at a predetermined depth, beyond which any further reduction in the air volume would impair the operation of the transducer. With the collapsed air chamber restored to its original full volume, the transducer will operate satisfactorily at increased water depths.

Abstract: The insulation resistance between the electroded surfaces of an underwater transducer and the water within which the transducer is immersed is greatly improved by coating the electroded surface of the transducer with a layer of air-free, high-resistance waterproof material before bonding an elastomer covering over the assembly to serve as the outer housing.

Abstract: The insulation resistance between the electroded surfaces of an underwater transducer and the water within which the transducer is immersed is greatly improved by coating the electroded surface of the transducer with a layer of air-free, high-resistance waterproof material before bonding an elastomer covering over the assembly to serve as the outer housing.

Abstract: A novel configuration of a low-frequency lightweight sonar system is described comprising a coaxial assembly of a transmitting transducer and a directional receiving array contained within a cigar-shaped streamlined cylindrical housing less than 1 ft. diameter which operates in the 3 to 4 kHz frequency region and achieves submarine target detection ranges in the order of 20,000 meters with a bearing accuracy within 2.degree.. The small cylindrical streamlined structural assembly results in a very great reduction in drag resistance while it is being towed underwater at high speeds as compared to conventional sonar domes which must be an order of magnitude larger in diameter to accommodate the larger conventional scanning sonar transducers which are several wavelengths in diameter at the operating frequency.

Abstract: An acoustic alarm repeater system detects a coded alarm signal such as might be produced by a smoke detector or burglar alarm. The alarm signal can vary over a wide dynamic range since the signal will usually be greatly attenuated by intervening walls or floors. The system includes an electroacoustic transducer for converting the coded audible alarm signal into an electrical signal; an amplifier; and an autocorrelator for recognizing the presence of the repetitive characteristic of the coded acoustic alarm signal. Upon detecting the presence of the coded alarm signal, the system generates a new loud warning signal. The processing system may be designed to detect a wide variety of differently coded alarm signals. A dual repeater system recognizes the presence of two differently coded alarm signals, such as one produced by a smoke detector and the other produced by an intrusion alarm, and responds differently to each.

Abstract: An intrusion alarm system includes a microcomputer and keyboard for providing control functions for the alarm system with greater reliability and with greatly increased security as compared with prior art systems. The disclosed system provides a positive means for deactivating the alarm system only by authorized personnel by the use of a multi-digit code which must be correctly entered on the keyboard within a prescribed short period of time after entry into the protected zone. Upon entry into the protected zone, the system goes immediately into a preliminary alarm stage which, for example, may be the lighting of a floor lamp in the room. The person entering the premises then has thirty seconds to enter the correct code on the keyboard attached to the front panel of the alarm unit to deactivate the system.

Abstract: A mathematical analysis reveals the existence of circular motion in the head of a rotating phasor which represents the received signal in a Doppler intrusion alarm system in the presence of a moving target. The circular motion is virtually nonexistent when a moving target is absent regardless of the presence of environmental disturbances such as air turbulence and noise transients. The mathematical revelations are confirmed by a considerable amount of experimental data representing hundreds of thousands of measurements under various environmental conditions. The invention makes use of these new findings in combination with a new signal processing system which incorporates a circle detector for recognizing the presence of circular motion in the head of a rotating phasor when it occurs in the received signal, thus permitting absolute detection of a moving target even in the presence of environmental disturbances, such as air turbulence, while the system remains immune to false alarms due to these disturbances.

Abstract: A comprehensive analysis of the effect of air turbulence on the acoustic performance of an ultrasonic intruder alarm system indicates that air turbulence does not cause Doppler frequency shifts in the received signal in the frequency region 2 - 100 Hz, as has been universally assumed in prior art systems but that air turbulence can only produce amplitude modulations in the received signal over this frequency region. It is also disclosed that changes in air velocity, or accelerations of the air flow, cause only very low Doppler frequency shifts in the signal, below 2 Hz for a 20 kHz carrier, and only moving targets can produce higher Doppler frequency shifts. A processing system is disclosed which is immune to false alarms in the presence of air turbulence without sacrificing threshold sensitivity and without introducing long time delays in the signal processing circuit as has been necessary in prior art systems.

Abstract: Electroacoustic transducers are nested to provide a centrally vibrating portion and a peripherally vibrating portion. The phases of the two transducers may be adjusted with respect to each other in order to provide a variety of beam patterns.

Abstract: This invention provides an expendable velocimeter probe. High frequency transmitting and receiving transducers are mounted opposite to one another in axial alignment on the probe body and on a frame in front of the body. The mounting includes means for accurately adjusting the distance between the transducers in order to provide low cost, but highly reliable, means for calibrating the velocimeter during large scale manufacture of the instruments.