RADIO FREQUENCY DETECTOR

Abstract: A microwave detector includes two detector elements (10), preferably microwave diodes, situated at right angles so as to detect radiation in any polarisation. The detector elements (10) are connected to amplifier (12) and warning (21, 22) means, which are actuated when perceived radiation exceeds a predetermined level.

Description: RADIO FREQUENCY DETECTOR The present invention relates to radio frequency detectors for giving warning of excessive electro-magnetic radiation. Many modern activities involve the production of electro¬ magnetic radiation - for example ' radio, radar and television transmission, many manufacturing processes, and even the household micro-wave oven which is " becoming increasingly popular. Excessive electro-magnetic radiation can be extremely harmful to the human body and there is a legal limit to exposure of lOmW/sq.cm. The nature of electro-magnetic radiation is such that there is no physiological response in the human frame to its presence. Fortunately sources of potentially damaging levels of radiation are readily identifiable and harmful effects can be avoided by suitable safety procedures such as, for example screening between a radiation source and personnel. However accidents do happen as a result, for example, of incorrect positioning of screening, faulty equipment, incorrect operation of equipment, and non-realisation that equipment is currently in operation. Devices have been proposed for sensing radio frequencies. For example Patent GB 9916** * *6 describes a coil or loop antenna with its ends connected by a diode detection circuit, the output of which is amplified and used-to provide an audio or visual response. Although portable, this device requires positioning and rotation to concentrate on a set direction. Patent GB 1288750 describes a device for testing the operation of AC electrical equipment. This has to be held whilst a search coil is maneouvred. Patents GB 1166977, 1^5θ6i7 and 1523731 describe devices which can be carried or worn on the person. However these have not become readily available, perhaps because they can only, in use, detect polarised radio frequencies. GB Patent 1*421365 describes an antenna arrangement which will detect radio frequencies of anypolarisation. It requires, however, three mutually - orthoganol antennas and these cannot be arranged such that they can be carried, or worn by an operator without considerable inconvenience. There is, therefore, a requirement for a device which can be worn on the person in such a way as to not interfere with the persons activities and which will give warning of dangerous levels of non- io ising electro-magnetic radiation in any polarisation. According to the present invention a radio frequency detector adapted to detect electro-magnetic radiation in any polarisation is characterised in having two detector elements siutated at right angles, an amplifier and warning means, the detector being tuned such that the warning means is actuated when the intensity of electro- magnetic radiation exceeds a predetermined level. The detector elements are preferably microwave diodes, which are particularly suitable for detecting radiation in the 2-l6 Gigahertz range. The warning means preferably include a buzzer, a warning light or both. In a preferred form of the invention the device also includes means for indicating that it is functioning correctly. The device is preferably powered by a rechargeable battery. One embodiment of the invention, suitable for detecting radiation in the range 2-l6 Gigahertz, will now be described, by way of example only, with reference to the accompanying diagrammatic drawings of which: Figure 1 is a circuit diagram and Figures 2 and 3 are component layout diagrams. A radio frequency detector suitable for detecting microwaves (Figs 1 and 2) has 2 microwave diodes 10 mounted at right angles to one another. The diodes 10 are connected to an amplifier circuit having amongst other components, a high impedance input amplifier 11 and a booster amplifier 12, and links 13- The device has a driver unit shown generally at 1-- which includes a test point 15, and a 4.8 volt battery 16. A first switch 17 connects the battery into the circuit (as shown in Fig l) or to a power input line lδ. A green light emitting diode 19 is included in the circuit at all times when the battery is in circuit, and a second switch 20 is moveable between an off position (as indicated in Fig l) and an on position, in which current passes through a red light emitting diode 21 and a piezo electric buzzer 22 in response to signals from the microwave diodes 10. In use the device is adjusted using the links 13 such that the second switch 20 is operated when the microwave diodes 10 detect electro-magnetic radiation in excess of a predetermined value such as, for example, the legal limit of lOmW/sq.cm. The first switch 17 connects the battery lβ to a power source through the connection 18 until the battery l6 is fully charged. The first switch 17 is then moved to the operative position switching the device on, as will be indicated by the green light emitting diode 19. The device is then attached to a suitable portion of a person's clothing such as a lapel or a breast pocket. Should the wearer enter a electro-magnetic radiation field in excess of the predetermined level this will be detected by the microwave diodes 10 which will actuate the second switch 20 causing the red light emitting diode 21 to light and the buzzer 22 to sound giving warning to the wearer that he is in danger. It will be realised that as a r*esultof the microwave diodes 10 being positioned at right angles polarised radiation will be detected whatever the direction of the polarisation relative to the device. Details of the circuitry will be readily apparent to those skilled in the art and will therefore not be discussed in detail herein. It will be realised that many variations of the device are possible within the scope of the invention. For example whilst the device described above with reference to Figs 1 to 3 is suitable for detecting signals in the range of 2-l6 Gigahertz a device capable of detecting signals at a frequency as low as 100kHz may be obtained by substituting broad band untuned circuits for the microwave diodes 10.

Claims: CLAIMS " What is claimed is: 1. A radio frequency detector adapted to detect electro¬ magnetic radiation in any polarisation characterised in having two detector elements situated at right angles, an amplifier and warning means, the detector being tuned such that the warning means is actuated when the intensity of electro-magnetic radiation exceeds a predetermined level. 2. A radio frequency detector as claimed in Claim 1 characterised in that the detector elements are microwave diodes 3. A radio frequency detector as claimed in Claim 1 characterised in that the detector means are broad band untuned circuits. k. A radio frequency detector as claimed in any one of Claims 1 to 3 characterised in that the warning means includes a bell. 5. A radio frequency detector as claimed in any one of Claims 1 to h characterised in that the warning means includes a light. 6. A radio frequency detector as claimed in any one of Claims 1 to 5 characterised in that the predetermined level is lOmW/sq.cm.

Inventors: FENNELL JOHN REGINALD, FENNELL, JOHN, REGINALD
Applicants: SECR DEFENCE BRIT, THE SECRETARY OF STATE FOR DEFENCE IN HER BRITANNI
Application year: 1988
Main classification: G01R29
IPC codes: G01R29, G08B21