GB2031167A

GB2031167A - Microwave detecting device

Info

Publication number: GB2031167A
Application number: GB7932099A
Authority: GB
Original assignee: MEYED ALUMINIUM Ltd
Current assignee: MEYED ALUMINIUM Ltd
Priority date: 1978-09-18
Filing date: 1979-09-17
Publication date: 1980-04-16

Abstract

A microwave detecting device is provided for detecting and displaying potentially dangerous leakages of microwave radiation, e.g. from a microwave oven. It has a diode detector 14 which either rectifies a signal from a loop antenna 12 for receiving any microwave radiation or itself both receives and rectifies any microwave radiation, so providing a rectified electrical output corresponding in strength to the intensity of the microwave radiation detected. A capacitor 16 is provided to smooth the rectified signal received. The rectified signal is also passed through a resistance load 18 and a display means 20 is used to indicate any output signal developed across the load. This display has a dangerous level indication which is shown when the level of microwave radiation is at or above a harmful level. Such a device can be very simple and needs no external power source. Its sensitivity can also be made variable by providing the resistance load with a variable tap. <IMAGE>

Description

SPECIFICATION Improvements in and relating to microwave detecting device This invention relates to the detection of dangerous microwave radiation and to a microwave detecting device and in particular one which is particularly suitable for detecting leakage of microwave from cooking ovens.

Because of the advantages of time-saving and convenience, microwave ovens are becoming increasingly popular items in kitchens, both commerical and domestic. Microwave ovens use short electromagnetic waves usuaily of a frequency around 2450 MHzto penetrate, heat up and cook food.

The microwave radiation has a high energy and can pass through materials such as paper, china, glass and most plastics materials and it can penetrate through living tissues to a depth of about 3 cm.

Therefore exposure of the human body to microwave radiation from an oven can result in harmful damage, especially to human fetus, nerve tissue, white blood cells and to the lens of the eye.

Despite the close attention paid by microwave oven manufacturers in trying to contain the microwaves inside the oven, leakage is likely to occur and to increase over the life of the oven due to damage or wear of sealing surfaces, the door, the door hinges, and the door latches. It is therefore of benefit to the user to check for leakage periodically.

According to the invention there is provided a method of testing for potentially harmful microwave radiation in which a hand-held testing device is moved over a region suspected of emitting microwave radiation with one end of the device in close proximity to the suspected source, the device including means activated by any microwave radiation to produce an electrical signal which is rectified, a resistance load through which the rectified signal is passed, means for smoothing the rectified signal and a display in which the magnitude of the rectified and smoothed signal is displayed, the display including a dangerous level indication which is shown when the level of microwave radiation is at or above a harmful level, and in which the user looks for a dangerous level indication given by the display.

Also according to the invention there is provided a microwave detecting device comprising a hand holdable housing having an output display at one end thereof and means activated by microwave radiation to produce an electrical signal adjacent the other end thereof, a rectifier for rectifying the electrical signal, a capacitor for smoothing the rectified signal which is displayed by the output display to give an indication of the magnitude of the rectified and smoothed signal, the display including a dangerous level indication which is shown when the level of microwave radiation received by the means activated by microwave radiation is at or above a harmful level.

Such a detecting device can be very simple and need have no external power supply. However, this is not essential and instead an external power supply can be provided to drive the display means which could be a simple volt-meter or an alpha numeric display including for example signal strength and detecting circuits and light emitting diode indicators.

Because the device is simple, it can be small and so readily contain within a hand held housing so that the user can place the housing close to a suspected leakage of microwave radiation, e.g. close to the join between the door and housing of a microwave oven.

The said one end of the housing can then be placed against the microwave oven so that it is at a reasonably predetermined distance from the leakage and the said other end containing the output display will still be visible to the user who can watch for a dangerous level indication as he moves the device around the join between the door and housing of a microwave oven.

A resistance load is preferably provided in series with the rectifier so that any electrical signal passes through the resistance load and devlopes a voltage across at least part of the load which can be sensed by the ouput display to give an indication of the magnitude of the rectified signal.

In a simple embodiment of the invention, the display means is a volt-meter with a dial having a portion marked, for example, in red to correspond to a dangerous level of detected microwave radiation.

Desirably, the sensitivity of the microwave detecting device is made adjustable by providing the resistance load with a variable tap so that the proportion of the output developed across the load and applied to the volt-meter or other display means can be adjusted.

The rectifier means can be a microwave detector or a microwave mixer diode. Provided a good quality microwave detector is provided it will itself pick up microwave signals and develop across it a rectified electrical output signal. Thus, the rectifier can act both to detect emitted microwave radiation and to rectify the electrical signal produced. In an alternative embodiment, the loop antenna can be provided to receive and detect microwave radiation and this loop antenna is desirably placed in series with the rectifier and the smoothing capacitor.

We have found that the use of a loop antenna in place of other possible types of antenna gives the microwave detecting device of the invention a high sensitivity which is important for the detection of small leakages of microwaves. In use, the plane containing the loop antenna is preferably oriented so that it faces the source of microwave radiation and so the plane containing the loop antenna is preferably oriented at right angles to the said other end of the housing.

The loop antenna can be in the form of a length of metal wire and for best sensitivity it should be about 6 cm in length or a multiple of 6 cm in length, i.e. a half wavelength of the microwave radiation frequency conventionally used by the microwave ovens.

The invention will now be described, byway of example, with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram of one microwave detecting device according to the invention; Figure 2 is a circuit diagram of another microwave detecting device according to the invention; and Figure 3 is a perspective view of a device showing the output meter.

The microwave detecting device 10 shown in Figure 1 has a loop antenna 12 of metal wire attached to, standing up in the form of an inverted U from a printed circuit board. In series with the antenna 12 is a microwave detector diode or a mixer diode 14for rectifying any signal received in the antenna 12. Also in series with the antenna 12, is a smoothing capacitor 16 to smooth any fluctuations in output from the antenna. The output of the antenna is applied to a resistance load 18 to develop an output. This load has a variable tap and the variable output is applied to a volt-meter 20 having an indicator dial to show an output in response to microwave radiation received by the antenna 12.In particular the indicator dial has a dangerous level indication, e.g. a portion of the dial marked in red at the higher output and of the dial, corresponding to a dangerous level of microwave radiation detected by the antenna 12. The variable tap can be adjusted to vary the sensitivity of the device.

As can be seen this device is very simple and sensitive but needs no external power supply.

The circuit 30 for an alternative form of microwave detecting device according to the invention is shown in Figure 2. The circuit includes a high quality microwave detector diode 32 positioned in a loop containing a fixed resistance load 34 and a variable resistance load 36. Positioned in parallel across the variable resistance load 36 is a smoothing capacitor 38 for smoothing the voltage developed across the variable resistance load 36. Also, in parallel with the capacitor 38 is a volt-meter 40.

Microwave radiation is detected and rectified by the diode 32 and the resulting rectified electrical signal passes around the circuit formed by the diode and resistance loads 34 and 36. The voltage developed across the variable resistance load 36 is smoothed by the capacitor 38 and displayed in the volt-meter 40. The variable tap of the resistance load 36 can be used to adjust the sensitivity of the arrangement.

Figure 3 shows a suitable housing 42 for a microwave detecting device according to the invention. The housing has one end 44 near which the diode 32 is positioned and this end 44 is arranged to be placed close to a possible source of leaking microwave radiation. At the other end of the housing can be seen the volt-meter 40 which has a scale including a portion 46 marked in red to indicate when a dangerous level of radiation is being detected and which has an output needle 48 which moves across the scale to display the output of the volt-meter 40. The intermediate portion 50 of the housing between the ends 44 and 45 can be conveniently held in the hand of a user so that he can place the end 44 against the microwave oven and still observe the scale of the volt-meter 40.

Claims

1. A method of testing for potentially harmful microwaves radiation in which a hand-held testing device is moved over a region suspected of emitting microwave radiation with one end of the device in close proximity to the suspected source, the device including means activated by any microwave radiation to produce an electrical signal which is rectified, a resistance load through which the rectified signal is passed, means for smoothing the rectified signal and a display in which the magnitude of the rectified and smoothed signal is displayed, the display including a dangerous level indication which is shown when the level of microwave radiation is at or above a harmful level, and in which the user looks for a dangerous level indication given by the display.

2. A method as claimed in Claim 1 in which the meter includes a scale past which a needle is moved and the dangerous level indication is a portion of the scale marked in red.

3. A method as claimed in Claim 1 or Claim 2 in which the means activated by microwave radiation comprise a loop antenna tuned to or substantially to the frequency of the radiation.

4. A method of testing for potentially harmful microwave radiation substantially as herein de scribedwith reference to Figure 1 oftheaccompany- ing drawings.

5. A method of testing for potentially harmful microwave radiation substantially as herein described with reference to Figures 2 and 3 of the accompanying drawings.

6. A microwave detecting device comprising a hand holdable housing having an output display at one end thereof and means activated by microwave radiation to produce an electrical signal adjacent the other end thereof, a rectifier for rectifying the electrical signal, a capacitor for smoothing the rectified signal which is displayed by the output display to give an indication of the magnitude of the rectified and smoothed signal, the display including a dangerous level indication which is shown when the level of microwave radiation received by the means activated by microwave radiation is at or above a harmful level.

7. A device as claimed in Claim 6 in which the rectifier is a diode detector which is capable both of being activated by microwave radiation to produce an electrical signal and of rectifying that electrical signal.

8. A device as claimed in Claim 7 in which a resistance load is provided in series with the diode detector and the capacitor is in parallel with at least part of the load, the display giving an indication of the voltage developed across at least part of the resistance load.

9. A device as claimed in Claim 6 in which the means activated by microwave radiation are a loop antenna tuned to or substantially to the frequency of the microwave radiation.

10. A device as claimed in Claim 9 in which the plane containing the loop antenna is oriented at right angles to the said other end of the housing so that in use the loop antenna is oriented so that it faces the source of microwave radiation.

11. A device as claimed in Claim 9 or Claim 10 in which a resistance load is provided in series with the rectifier and the capacitor is in parallel with at least part of the load, the display giving an indication of the voltage developed across at at least part of the resistance load.

12. A device as claimed in any of Claims 6 to 11 in which the output display comprises a volt-meter having a scale past which a needle is moved to display the output level, the scale including a portion marked in red to indicate a dangerous level of detected microwave radiation.

13. A microwave detecting device substantially as herein described with reference to Figure 1 of the accompanying drawings.

14. A microwave detecting device substantially as herein described with reference to Figures 2 and 3 of the accompanying drawings.