Mirror used as microwave antenna for motion sensor

Apparatus is provided including a microwave transceiver, a microwave antenna coupled to the microwave transmitter that transmits microwave energy into a secured area and receives reflected microwave signals from the secured area, a passive infrared detector that receives infrared energy from the secured area and a reflector having a focal point, the reflector reflects both microwave and infrared radiation received from the secured area onto the focal point, the microwave antenna and passive infrared detectors both located proximate the focal point of the reflector.

FIELD

The field of the invention relates to security systems and more particularly to motion sensors used in security systems.

BACKGROUND

Passive infrared (PIR) sensors or passive infrared detectors (PIDs) are generally known. Such devices find ready use as intrusion detectors in security systems.

A PID device detects intrusion via the infrared radiation emitted by humans. However, PID devices suffer from the difficulty of not being able to differentiate between humans and animals and in not being able to detect humans against hot background surfaces.

One particular type of PID devices is a PID motion detector. A PID motion detector uses a pair of infrared detectors arranged to scan adjacent areas. In this regard, the pair of detectors may be connected in series so that when both areas have the same background temperature, the signal from the one will cancel the signal from the other.

PID motion detectors have been found to be considerably more reliable than when PID devices are used individually and especially when combined and used with a microwave motion detector. Since the PIDs are connected to cancel one another, PID motion detectors are less vulnerable to transients, e.g., flashes of light (e.g., lightning) detected by the pair of detectors. When combined with a microwave transceiver the two devices can be logically ANDed to provide an even more reliable device.

While a combined PID motion detector and microwave motion detector is a significant improvement, it is bulky and expensive. Accordingly, a need exists for improved motion detection devices.

DETAILED DESCRIPTION OF AN ILLUSTRATED EMBODIMENT

FIG. 1is a simplified block diagram of a motion detection device10shown in a context of use generally in accordance with an illustrated embodiment. In this regard, the motion detection device10may be installed within a secured area12and electrically connected to a control panel14of a security system for the area12.

In use, the motion detection device10may monitor a portion of the secured area12for intruders. Upon detecting an intruder, the motion detection device10may send an intruder alert to the control panel14. The control panel14may respond by activating a local audible alarm and/or by notifying a local police department.

FIG. 2is a block diagram of the motion detector10. Included within the motion detector10is a pyroelectric detector200and a microwave module202that receive signals originating from intruders within the secured area12. In this regard, the microwave module202transmits and receives (transceives) a microwave signal into a portion of the secured area12via an antenna204and reflector206that also operates as a lens because it focuses energy into a focal point. The transmitted microwave signal may be continuous wave (CW) or pulsed (PW).

Objects within the secured area (e.g., a person)208reflect a portion of the transmitted microwave signal back to the microwave module202through the reflector206and antenna204. If the person208is moving, then the reflected signal with have a Doppler phase (or frequency shift) that is proportional to the speed, the size and the direction of movement of the moving person.

The microwave module202and a signal processing module210are hardware devices that are constructed to receive the reflected signal and recover the Doppler signal by filtering the signal and downshifting the signal to baseband. In this case, the processing module210may include one or more mixers and filtering sections that operate to mix the reflected signal with a portion of the transmitted signal to reduce the Doppler signal to baseband. Once at baseband, the Doppler signal is sampled by a microwave analog to digital (ND) converter214at an appropriate sampling rate (e.g., 3 kHz) for processing within another appropriate hardware device (e.g., a microprocessor)212.

Similarly, the pyro device200includes two side-by-side infrared detectors200a,200bthat receive infrared energy from the portion of the secured area12via the reflector206. It should be noted in this regard that the detectors200a,200btogether receive infrared energy from the portion of the secured area12that is substantially coincident with the area that reflects microwave from the microwave module202.

In this regard, the pair of detectors200a,200band the optics of the reflector206are designed so that the pair of detectors200a,200breceive infrared energy from directly adjacent subparts of the portion covered by the microwave module202.

The infrared signals from the pair of detectors200a,200bmay be filtered and amplified within a PIR processing device216and provided as an input to an analog to digital (ND) converter218. Within the processing device212, the infrared signals from the respective infrared detectors200a,200bmay be processed separately to confirm the presence of an intruder.

In general, the reflector206is comprised of a number of reflector elements. Each lens element “casts” a positive and negative finger pair into the secured area12. Each finger of the finger pair of each lens of the reflector receives energy from a small area of the secured area12and delivers that energy on one of the two infrared detectors200a,200b.

The infrared detectors200a,200bmay be connected in an anti-phase relationship (i.e., the positive pole of one device200ais connected to the positive pole of the other device200bor vice versa). This causes common signals detected by both devices200a,200bto be canceled. The net result is that when the person208passes in front on one device200aof the pair of devices200a,200b, the output of the pyro device200will respond with a signal excursion of a first polarity, but when the person208walks further so that they are in front of the second device200b, the excursion will reverse. The direction of the signal excursion from the pyro device200provides a direct indication of the direction that the person208was walking when he/she passes in front of the device200.

The signal from the pyro device200is processed within a first hardware device216and provided as an input to a PIR analog to digital (ND) converter218. The signal is sampled at an appropriate sampling rate (e.g., 3 kHz) for processing within the processing device212.

In the regard, one or more signal processors220operating under control of software222loaded from a non-transitory computer readable medium (memory)224may process the signals. For example, a microwave signal processor220may compare a level of the Doppler signal with a threshold value to confirm the actual presence of an intruder.

Similarly, one or more infrared signal processors220may process the signal from the pyro device200to confirm the presence of the intruder. In a first step, the processor220may compare the signal with a threshold value to confirm that the presence of the intruder. Similarly, the same or a different direction processor220may determine the direction of the signal transition to determine the direction of the intruder passing in front of the detectors200a,200b.

In addition, a confirmation processor220within the device212may logically AND the microwave and infrared signals before an output is transferred through an output226to the control panel14. In addition, one or more encoding processors220may be provided that operate to encode the output signal with source information that identifies the motion detector10to the control panel14.

FIG. 3depicts further details of the reflector206and a detector assembly300. In this case, the detector assembly300may include the pyro device200and antenna204.

Under one preferred embodiment, the detector assembly300is mounted on the reflector206as shown inFIG. 3. In this regard, the pyro device200and antenna204are both located at a focal point of the reflector where the infrared energy and microwave energy is concentrated via operation of the reflector.

Under some embodiments, the pyro device200and antenna204are disposed directly adjacent one another. This is possible because the index of refraction of infrared energy and microwave energy is slightly different thereby allowing the antenna204and device200to be placed directly adjacent one another while both still remain substantially within the focal point of the reflector206, as shown inFIG. 3.

FIG. 4depicts another example of the reflector206. It should be specifically noted in this case, that the segmented nature of the reflector206allows two separate images to be formed on the two different infrared detectors200a,200b.

In one preferred embodiment, the reflector206may be created by selecting a reflector that was previously useable with the pyro device200alone and coating the reflector with a conductive metal. The coating of the reflective metal (and possibly some polishing of the coating) allows the reflector to also reflect microwave energy onto a focal point determined by a frequency of the microwaves.

In this regard, the reflector206has a common reflective surface that receives microwave and infrared energy from the secured area and focuses that microwave and infrared energy from the common reflective surface onto the antenna204and infrared detectors200a,200b. Similarly, the reflector206receives microwave energy from the antenna204and focuses that microwave energy into the secured area.

FIGS. 5-7depict additional examples of the detector assembly300. As shown inFIG. 5, the antenna204is a dipole and is coincident with the pyro device200. In this case, the antenna204is located parallel to and between the two infrared detectors200a,200b. This particular configuration causes the least inference between the functionality of the antenna204and infrared detectors200a,200band is useful in minimizing the space required by the detector assembly300.

As shown inFIGS. 6 and 7, the antenna204positioned perpendicular to the longitudinal axis of the infrared detectors200a,200b. InFIG. 6, the antenna204is located beneath the infrared detectors200a,200b. In this case, the partial shadowing of the antenna204by the infrared detectors200a,200bmay be compensated with a longer antenna204. This may be useful where the reflector is particularly well focused along the axis of the antenna204.

InFIG. 7, the antenna204is placed over the infrared detectors200a,200b. In this case, the partial shadowing of the infrared detectors200a,200bis minimized by the greater diffraction of infrared energy, a relatively thin antenna204and an increased area of the infrared detectors200a,200b.

In general, the motion detection device10includes a microwave transceiver, a microwave antenna coupled to the microwave transmitter that transmits microwave energy into a secured area and receives reflected microwave signals from the secured area, a passive infrared detector that receives infrared energy from the secured area and a reflector having a focal point, the reflector reflects both microwave and infrared radiation received from the secured area onto the focal point, the microwave antenna and passive infrared detectors both located proximate the focal point of the reflector.

In another embodiment, the motion detection device includes a housing, a microwave transceiver, an antenna that transmits microwave energy from the microwave transceiver into a secured area and receives reflected energy from the secured area, a pyroelectric device that receives infrared energy from the secured area, a reflector supported by the housing that receives reflected microwave energy and infrared energy from the secured space on a common reflective surface and focuses the microwave energy and infrared energy from the common reflective surface onto the antenna and pyroelectric device.

In still another embodiment, the motion detector includes a housing disposed within a secure area, a microwave transceiver, an antenna that transmits microwave energy from the microwave transceiver into a portion of the secured area and receives reflected energy from the portion of the secured area, first and second infrared detectors that receives infrared energy from the directly adjacent halves of the portion of the secured area, a reflector supported by the housing that, in turn, supports the antenna and first and second infrared detectors, the reflector receives microwave energy from the antenna on a common reflective surface and transmits the microwave energy into the portion of the secured area, the reflector also receives reflected microwave energy and infrared energy from the portion of the secured area on the common reflective surface and focuses the microwave energy and infrared energy from the common reflective surface onto the antenna and first and second infrared detectors and a processor that provides an intruder detected signal through an output to a security system of the secured area in response to a signal indicating detection of the intruder from the microwave transceiver and first and from the second infrared detectors