Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Patent
1990-07-18
1992-07-14
Howell, Janice A.
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
342432, G01S 504, G01S 328
Patent
active
051305437
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to direction-sensitive energy detecting apparatus, for detecting at least the direction of an object or other matter positioned in space.
BACKGROUND OF THE INVENTION
Numerous kinds of apparatus for detecting the position of something positioned in space are known.
Known methods to determine the direction of a beam of, for instance, electromagnetic energy often employ moving parts, which can be costly, complex and not always reliable. One example is the rotating antenna used in radar, in which the distance to a remote reflector is a calculated by measuring the time taken for the radar beam to travel from the transmitter to the reflector and back. Since the propagation speed is known, this time interval can be converted to a distance measurement. The actual position of the object can then be determined, the antenna direction at the time of measurement being known.
Many devices acting as transmitters and/or receivers of acoustic and electromagnetic energy have respectively an output power or input sensitivity which varies with the angular displacement relative to some datum direction in space. This property will be referred to as a polar characteristic. Examples of devices which exhibit a polar characteristic are radio or radar transmitting and receiving antennae, ultrasonic transducers, microphones, light emitting diodes (LED's), and photoelectric receivers. In many instances it is possible to control the polar characteristics of the device during manufacture.
Optical direction finding equipment is also well known in various forms, such as those used in navigation, surveying etc.
There is a need to establish the direction of an object from an observer who wishes to determine other factors such as the position of an object, or whether it is moving (and in that case, possibly also its direction of movement). Position finding apparatus is for example used in many forms in gunnery and navigation. Movement detectors are also important in security systems, for example for detecting an intruder.
Movement detectors, using the Doppler effect, are widely used in security systems to detect entry of intruders and initiate alarms or control other actions.
These detectors operate by transmitting energy of a specific wavelength into the space in their vicinity. The transmitted energy (or some of it) is reflected back, by objects in the space, to a receiver sensitive to this energy. The reflected signal is then mixed with a reference signal having identical wavelength to that of the transmitted energy. Any difference in frequency between the reflected signal and the reference signal causes low frequency amplitude modulation at the mixer output. If the reflecting objects in the vicinity of the device are stationary, then the transmitted and reflected signal frequencies are identical; but if the objects are moving there is a frequency differential between the received signals. This is proportional to the velocity of the moving objects (s), resulting in amplitude modulation of the mixed signal. By detecting the presence of this amplitude modulation it is therefore possible to determine that there is a moving object within the vicinity. This information may be used tot rigger an alarm sequence or any other desired control action. If the transmitter and receiver are located together, the speed of the object in a radial direction can also be measured by determining the frequency of the resultant amplitude modulation at the output of the mixer.
Since any number of energy waves, simultaneously present in the medium in which they propagate, will mix together to form an additive signal, it is possible to use this property as a ready=made mixing stage. It is therefore quite common in the design of movement detectors to supply the reference signal by causing a proportion of the transmitted energy to "leak" directly into the receiving device. The reflected energy then mixes with the reference signal and the receiver receives the resulting added signal. By demodulating (rectifying) the re
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patent: 1820571 (1931-04-01), Krulsi
patent: 3370293 (1968-02-01), Green
patent: 3495249 (1970-02-01), Downie
patent: 3665481 (1972-05-01), Low et al.
patent: 3893120 (1975-07-01), Trenam
patent: 4833478 (1984-05-01), Nossen
Hanig Richard
Howell Janice A.
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