CN115812158A

CN115812158A - Magnetic field detector

Info

Publication number: CN115812158A
Application number: CN202180047155.9A
Authority: CN
Inventors: 休-彼得·格兰维尔·凯利
Original assignee: Direct Thrust Design Co ltd
Current assignee: Direct Thrust Design Co ltd
Priority date: 2020-03-25
Filing date: 2021-05-05
Publication date: 2023-03-17
Also published as: WO2021224621A1; GB2593550A; GB202004314D0; GB202006662D0

Abstract

The invention relates to a magnetic field detector comprising a magnetic antenna for obtaining a magnetic field around the magnetic antenna; and an electronic magnetic field sensor arranged near or at an end of the magnetic antenna to detect a magnetic field obtained by the magnetic antenna.

Description

Magnetic field detector

The present invention relates to improvements in the detection of weak magnetic fields and the use of such improvements in the form of personal alarms. For example, the present invention relates to a device for reducing the likelihood of a human being infected with a virus.

A commonly used device for detecting magnetic fields is a device called a Hall Effect detector. This is typically in the form of a compact electronic component, typically several square millimeters by one millimeter thick in size. They are used extensively throughout the industry, with a typical application being to detect the steel teeth of a rotating gear passing through them, and thereby determine the rate of rotation of the gear by an electrical circuit. Another current application is their integration into mobile phones, both as electronic compasses and as devices for measuring local magnetic field strength.

Hall Effect sensors (Hall Effect sensors) typically comprise a planar layer of doped (typically p-type) semiconductor with a sensing region through which a constant current flows. The hall voltage over the detection area is measured in a direction perpendicular to the direction of current flow. When the device is placed within a magnetic field, the magnetic flux lines exert a force on the semiconductor material that deflects the charge carriers, electrons and holes to either side of the detection region (i.e., in a direction perpendicular to the current flow in the semiconductor plane). This movement of charge carriers is a result of the magnetic forces they experience through the semiconductor material. When these electrons and holes move laterally, a potential difference (hall voltage) is generated between the two sides of the semiconductor material by the accumulation of these charge carriers. The magnitude of the potential difference is indicative of the strength of the magnetic field.

However, the sensing element area (i.e., the magnetic field sensing area) of such devices is typically small, e.g., a circular area of only one millimeter in diameter at the center of the element. Their magnetic "field of view" is limited in extent away from this region (which is typically conical).

Thus, the hall detector cannot register a magnetic field that deviates significantly from the field of view, or in the case of a magnetic field to be detected that is exactly orthogonal to the plane of the detection area. Items to be detected and which emit or disturb magnetic field lines must be present within the window. Furthermore, it is well known that the strength of any magnetic field decreases exponentially with distance, and therefore any hall effect detector must be positioned relatively close to the magnetic article to be detected.

When detecting magnetic fields at a distance or distributed over a large area, a way to circumvent this limitation is to use an array of such devices, which are dispersed and at different viewing angles from each other, so that their effective combined field of view can be enhanced as a whole. Each connected to its own response electronic circuit so that if any one or more of the detectors is activated, the item entering its entire field of view is recorded.

However, this solution is complex and relatively expensive. Preferred alternative devices enable a truly wide field of view, but use only one or a minimal number of detectors.

The present invention provides a magnetic field detector comprising a magnetic antenna for obtaining a magnetic field in the region of the antenna and an electronic magnetic field sensor arranged (e.g. at or adjacent to an end of the magnetic antenna) to detect the magnetic field obtained by the magnetic antenna. The magnetic antenna of the magnetic field detector is composed of a material having a remanence of less than 2 gauss and/or a permeability of 8000H/m or higher.

Apparatus for enhancing the field of view of a single or multiple hall effect detector includes placing the detector at or near one or more portions (e.g., ends) of a magnetic antenna so that the detector can respond to any magnetic field falling on the antenna, which is preferably shaped in such a way as to be able to collect encroaching and surrounding magnetic fields that would otherwise not be detected by the individual hall effect itself, the antenna being formed of a magnetic material having virtually zero or very substantially zero remanence so that when the magnetic field leaves the vicinity of the antenna, no magnetic field remains therein that would otherwise keep the hall effect detector in an active or substantially active state.

It is self-evident that the surface area of any antenna can be many times (hundreds of times, even thousands of times) the 1mm detection area of a hall effect detector alone, thus providing significant advantages for magnetic field detection.

As can be appreciated from the foregoing, a desirable characteristic of any antenna used to collect a magnetic field (particularly a weak magnetic field) for detection by a hall effect device placed thereagainst is that it does not retain any degree of magnetization after the magnetic field has exited. Otherwise, the Hall effect detector itself will remain activated.

Ordinary ferromagnetic steel or mild steel cannot meet this characteristic because a certain degree of magnetism remains in the object, however small, due to its inherent remanence when a permanent magnet is placed thereon or adjacent thereto.

A suitable material that can be used to achieve the described properties is mu metal. It consists of a nickel-iron soft ferromagnetic alloy and has a very high magnetic permeability and has been widely used in magnetically sensitive devices to protect such devices from stray magnetic fields. A very advantageous additional property of such a material is that its remanence is practically zero or close to zero. Thus, according to one aspect of the present invention, any residual magnetic field within any antenna does not remain after any residual magnetic field is removed, which can be achieved by using mu metal or equivalent materials for the aforementioned antenna.

Most hall effect detectors are characterized by their being magnetically sensitive on both sides (meaning each side of the detector).

According to another aspect of the invention, the antenna may be placed on either side of the detector. With each antenna extending out and away from either side of the detector, the field of view is thereby increased. Thus, in an embodiment, the magnetic field detector further comprises a second magnetic antenna for obtaining a magnetic field around the second magnetic antenna, an end of the second magnetic antenna being arranged at the electronic magnetic field sensor such that the electronic magnetic field sensor is capable of detecting the magnetic field obtained by the second magnetic antenna.

According to yet another aspect of the invention, for certain applications, particularly those where it is desirable to detect a magnetic field that occurs randomly over a portion of a large area, it may be advantageous for the antenna to take the form of a split ring. Each end of the loop is placed against each opposing face of the hall effect detector. Thus, in one embodiment, one end of the magnetic antenna is located on the opposite side of the electronic magnetic field sensor from the other end of the magnetic antenna.

However, for this arrangement to be optimally advantageous, the loop itself is preferably not of continuous form between its ends (meaning those ends adjacent to the face of the hall effect detector), i.e. not in a long length of material having only two ends. Instead, the discontinuity, preferably a complete split (which means a gap), is located at some point along its length, ideally in the middle. This splitting is provided to ensure that the value of the aggregate strength of the magnetic polarities presented to the respective faces of the hall effect detector is optimized. And thus the maximum signal from the detector. All of the reasons for this are elusive and will be explained in detail below. Thus, in one embodiment, the magnetic antenna and the second magnetic antenna together form a loop, the loop having a discontinuity at the electronic magnetic field sensor and a discontinuity at an end of the magnetic antenna and the second magnetic antenna opposite to the end at the electronic magnetic field sensor.

An ideal antenna for collecting the ambient magnetic field from the permanent magnet may be in the form of an extended flat strip (i.e. an elongated flat strip). The magnetic field falling on the strip effectively turns it into a bar magnet, one end becoming south and the other north. The strip is highly effective for this purpose if the magnetic field reaching it is generally directed at its surface. This can be best considered from the point that the permanent magnets pass the edges of the strip so that the magnetic field emanating from the surface of the permanent magnets can be collected onto the flat surface of the strip. If the magnets pass through the strip such that the lines of force presented by the permanent magnets are orthogonal and orthogonal to the sides of the surface of the strip, there is less likelihood that they will be attracted to the surface of the strip.

According to yet another aspect of the invention, the antenna may be in the form of an angled strip, in fact having two faces operating in different planes, for collecting the dominant magnetic field. Thus, in one embodiment, the magnetic antenna comprises two elongated flat strips attached to each other in different planes and along elongated sides. An alternative may be that the antenna is in the form of a helical tube or film, in which theoretically an infinite number of planes are covered.

It is well known that people most often infect by inadvertent ingestion or inhalation. This may be through the nose, mouth and even eyes. Certain strains of virus may be lethal to a population. In the practice of the present invention, this malignant virus, known as COVID-19, is prevalent worldwide, causing thousands of deaths.

It has also been found that an average person touches his or her face at least two hundred times a day, which often results in viral infections. For example, once the hand is lifted to contact the face for any purpose, infections picked up from the arm rests or other similar places are easily transmitted to the facial orifice by the hand or fingers.

Thus, knowing this, medical authorities require that people actively and frequently wash or disinfect their hands to remove any traces of virus thereon. However, this is a secondary operation. The main operation is to help prevent hand-to-face contact in the first place, thereby avoiding accidental ingestion and infection by viruses.

A solution that helps to avoid such contact is to provide an alarm that alerts the person to avoid hand-to-face contact before it occurs, thereby preventing viral infection. There are several other applications of such alerts, such as helping people overcome Obsessive Compulsive Disorder (OCD), such as pica. Therefore, cognitive behavioral therapy is feasible.

A form of alarm that can be used for this purpose is the use of a magnetic field detector and permanent magnet combination. The magnetic field detector, preferably a hall effect sensor, is carried on the body of the person, for example the chest, and the permanent magnet is worn on the wrist or hand. When the hand is lifted to contact the face, the magnetic field emanating from the permanent magnet is detected by the hall effect sensor and an alarm sound is emitted in response to the electronic circuit.

In all such devices, a problem arises in that the circuit responsive to a single hall effect detector must be tuned to detect the minimum magnetic field, taking into account the infinite variety of random movements of the hand towards the person's face in terms of location and proximity. In doing so, however, the detector will also react to the earth's magnetic field and may issue false alarms. Strategies to avoid this include wearing a separate hall effect detector on the body to record the earth's magnetic field, but at a location well beyond the range of motion of the hand holding the permanent magnet. The output of the individual hall effect detectors is then compared electronically to the output of the actual hall effect detector, which is positioned to detect the expected magnetic field when the hand is lifted up on the face. The intention is to register only one real signal.

However, this arrangement is complex and only effective for certain positions of the wearer, since it is clear that the earth's magnetic field has a defined direction.

According to the invention, the inventive magnetic field detector disclosed herein is used in an apparatus for warning a person's hand in proximity to the person's face before contact occurs.

With such a device, it is possible to warn a person who intends (without thinking) to scratch his or her face or drown into any other such contact before an action occurs, thereby avoiding accidental infection.

According to one feature of the invention, the personal alarm comprises the use of the arrangement disclosed herein, wherein one or more antennas are placed on a suitable area of the body and used to collect the magnetic field from the proximate permanent magnet onto a single or multiple hall effect detectors which are themselves connected to a response electronic circuit to provide an alarm signal.

For the antennas used in the present invention, since they have a highly effective large surface area in any collection of magnetic fields, even at a distance, the electronic magnetic field sensor response circuit can be substantially detuned, detecting only magnetic fields larger than those provided by the earth's magnetic field. The warning means is therefore arranged to issue a warning signal if the magnitude of the magnetic field picked up by the magnetic antenna detected by the electronic magnetic field sensor is greater than a threshold value. Thus, with this device, it is only possible to respond to movements that truly indicate the presence of an invasive magnetic field, for example, provided to the wrist by a permanent magnet on the wrist. The threshold is adjustable to allow tuning of performance to a particular situation.

The means for powering the electronic circuit in response to the hall effect output and thereby providing an alarm signal may be in the form of a dry cell battery. However, the choice of battery can affect performance. Typically, the housing of many modern dry cell batteries is made of mild steel. This distorts any magnetic field present and interferes with the antenna's collection action. To this end, according to one aspect of the invention, lithium ion batteries are the preferred choice, preferably those that are housed within plastic and therefore do not interfere with any existing magnetic fields.

As mentioned above, the alarm signal may be in the form of an audible tone. In order to suit the user of the device, a volume control may be provided to adjust the sound level to suit local conditions. For those periods when the user does not wish the device to be activated, for example when a beverage is being inhaled, a controller may be provided for temporarily deactivating the alarm.

It will be appreciated that the larger the magnetic field emitted by the permanent magnets carried by the wrist, the better. . According to another feature of the invention, the magnet comprises two planar halves, each half being held together in a repelling manner. With such an apparatus, the magnetic field provided by the combination is made to travel further than a single piece of magnet of the same size. In one option, the two planar halves may be separated by a mild steel disc.

An apparatus for alerting a person that a body or body part of another person is close to the face of the first person is also provided, the apparatus comprising a magnetic field detector.

According to a first aspect of the invention, the detector for providing the warning signal may be placed on the body of the person to be protected.

The warning may be in the form of: an audible signal, a visual signal, vibration, a noticeable scent, a bluetooth connection (or other wireless transmission device) to a headset worn by the user, or a combination of the above, or any other means that can alert the person to their intended action for a sufficient time to avoid any hand contact with the face.

According to a first feature of the invention, the proximity detector may be in the form of a detector worn or mounted on or around the body or neck of the person to be protected, or within a hat or other fashion accessory worn by said person, such that the electronic signal provided thereby effectively provides a warning signal.

As mentioned above, the warning may be in the form of: an audible signal, a visual signal, vibration, a noticeable scent, a bluetooth connection (or other wireless transmission device) to a headset worn by the user and the person, or a combination of the foregoing, or any other means capable of alerting the person of their intended action in sufficient time to avoid any hand contact with the face. Preferred warning devices include simple buzzers and flashing light emitting diodes.

Alternatively, or in combination with proximity detectors worn on or around the body, the proximity detectors may be worn on the person's arm in a suitable position, such as his/her wrist, or on the finger, even with appropriate miniaturization.

Ideally, power consumption should be kept at an absolute minimum. This is particularly important in situations where the virus is so toxic that authorities restrict citizens from moving from home to, for example, stores to purchase replacement batteries.

According to another feature of the invention, proximity detection is provided by using a permanent magnet as part of the device and as another part of the magnetic field detector of the invention. The permanent magnet may for example be accommodated in a watch-like container mounted on the wrist in the manner of a watch and an electronic magnetic field detector, on or around the body of the person to be protected, and provided with suitable sound-emitting electronics, such as a buzzer. Alternatively, the permanent magnet may be worn on or around the body, and the magnetic field detector together with the buzzer is arranged inside the watch-like container. A practical advantage of the latter arrangement is that accidental degaussing of credit cards and other magnetic media operated by the person wearing the device is avoided. In one embodiment, the electronic magnetic field sensor comprises a hall effect detector.

By using a permanent static field provided by a permanent magnet, no power is consumed in illuminating the field, as is the case in active devices (such as doppler detectors, software inertial algorithms, or other devices for detecting hand movement), and battery power is conserved. The static power required to feed an electronic magnetic field sensor, such as a hall effect device component, is minimal.

Although the static magnetic field does not actually have any adverse effect on body tissue or function, to alleviate any anxiety, the rear portion of the magnet (e.g. facing the body or wrist) may be mounted on a high permeability material, such as soft iron or better high permeability material, to effectively disperse the magnetic field.

A person using a device according to the invention may wish to train himself to reduce the number of attempts to make facial contact during waking hours. To this end, the device may be equipped with a visual counter that can be reset by a person (e.g., reset every day) to indicate progress.

With any of the foregoing implementations of the invention, the sensitivity of the detection device may be adjusted, for example by a simple potentiometer, to suit the person wearing the apparatus. An on/off switch may also be provided.

The use of the devices disclosed herein is not necessarily limited to protection against lethal viruses. Many citizens have general habits of facial contact such as skin sucking, nose sucking and other obsessive-compulsive disorders, and even smoking, which may benefit from the use of the device. Therefore, cognitive Behavioral Therapy (CBT) may be feasible.

The invention will now be described with reference to the accompanying drawings, in which:

fig. 1a shows a single electronic magnetic field sensor (e.g. a hall effect detector) and fig. 1b shows such a detector placed adjacent to a magnetic field antenna.

Fig. 2 shows an edge view of a single electronic magnetic field sensor (e.g., a hall effect detector) sandwiched between two antennas.

Figure 3a shows an edge view of a dual split ring antenna sandwiching an electronic magnetic field sensor (e.g. a hall effect detector), and the resulting magnetic field pattern.

Fig. 3b shows the same arrangement, but with only a single split.

Fig. 4 shows various forms of antennas configured to receive magnetic fields that reach different planes.

FIG. 5 illustrates an arrangement for detecting hand movement using the invention disclosed herein.

Fig. 6 shows an arrangement for repulsion of two permanent magnets to provide an enhanced magnetic field.

Fig. 7a and 7b illustrate the general principle of operation of the present invention.

Figure 8 shows the detector device and the permanent magnets carried by the wrist.

Fig. 9a shows an improved magnetic detection device according to the present invention as shown in fig. 9 b.

Fig. 10 shows the magnetic field pattern on the antenna.

Fig. 11 shows a housing, antenna and lanyard device.

FIG. 12 shows a detailed positioning of the Hall effect detector adjacent to the antenna.

Fig. 13 shows various options for improving the facilities provided by the detector.

FIG. 14 shows a magnetic stripe device for emitting a magnetic field.

Fig. 15 shows a circuit used in association with a warning device.

Referring to fig. 1, a common form of electronic field strength sensor (e.g., a hall effect detector, hereinafter HED for convenience) and its approximate dimensions are shown at 10. An electronic magnetic field sensor is a sensor that generates an electronic signal when a magnetic field is sensed. Either of the

flat sides

11 and 12 of the HED must face the magnetic field to be detected. The central circle 13 represents the area receiving the magnetic field and may be only one millimeter in diameter. It is clear that any object to be detected by the HED must fall within its detection area, which is generally nearly conical in shape, as shown in FIG. 14.

It is an object of the present invention to substantially enhance the magnetic field, and thus the detection area covered by such an HED, so that a far and weak magnetic field can be detected. A method of doing so is now shown with reference to fig. 1 b.

When the material is placed in a magnetic field, magnetic poles will form at opposite ends, depending on the geometry of the material. The magnetic field emanating from the material is strongest near the poles. In the present invention, the magnetic antenna is used to acquire a magnetic field around the magnetic antenna, and the electric field sensor is used to detect the magnetic field acquired by the magnetic antenna. One way to do this is to place the magnetic field sensor (at least the detection area of the magnetic field sensor) near the location where the magnetic pole is formed when the magnetic antenna is in a magnetic field.

For an elongated antenna, the magnetic poles formed when the magnetic antenna is in a magnetic field are typically located at opposite elongated ends. It is therefore advantageous to locate the detection area of the magnetic field sensor at or near the end of the elongated antenna, since this is where the maximum magnetic field will be present, thus increasing the sensitivity of the magnetic field detector. An elongated antenna is also preferred because the likelihood of forming a magnetic pole at the end (i.e., reliably forming a magnetic pole at a known, predetermined location within the antenna) is greatly increased. For this reason, it is desirable that the magnetic antenna is elongated, and preferably the dimension in the elongated direction is at least four times larger than the dimension in the direction orthogonal to the elongated direction. Preferably, the elongate dimension is six or even eight times the maximum dimension in the other two orthogonal directions, which further improves the reliability of any magnetic field that results in the formation of a pole at the end.

Regardless of the orientation of the detection area relative to the poles of the antenna, a detectable magnetic field may be present on the detection area. However, if the detection area has a plane orthogonal to the magnetic flux lines leaving the magnetic poles of the antenna, this increases the influence on the electrons in the detection area, thereby improving the sensitivity of the magnetic field sensor. The plane of the detection area is not necessarily the same as the plane of the housing of the hall effect sensor (but this is assumed in the figures). Thus, in the first case, preferably, the detection area has a plane which is offset by a maximum of 45 degrees or preferably faces directly towards one side of the antenna (because the magnetic flux leaves the side of the antenna) if the plane is placed adjacent to that side of the antenna, or in the second case, if the plane is located at the extreme end of the antenna, i.e. its cut end, offset by a maximum of 45 degrees or preferably a maximum of 30 degrees or more preferably faces directly towards the cut end, so that the plane of the detection area (and the body of the detector) is orthogonal to the longitudinal length of the antenna. The second case is preferred because the magnetic flux density at the location is greatest here.

For the same reason, it is preferable that the detection area is within one eighth of the size of the elongated direction of the end of the elongated antenna (the magnetic field lines are most dense in the vicinity of the pole). Experiments have shown that the maximum concentration of magnetic flux is located in the end region of the antenna, and at most at its cutting end, and therefore most preferably the magnetic field sensor should be located as close as mechanically possible to the extreme end of the antenna, for example within 10mm of the extreme end. Preferably, the detection region is located at the center of the width of the magnetic antenna (i.e. on the centerline (longitudinal direction) of the elongated magnetic antenna).

In all cases, the hall effect sensor is preferably within 1.5mm or 1.0mm of the antenna.

In one embodiment, the antenna 15 is a strip antenna. In one embodiment, the ends of the strip antenna 15 are placed on the receiving surface of the HED. In one embodiment, the extreme end 16 of the antenna is placed in contact with the HED, or at least within 1.5mm or 1mm or 1.0mm from the HED. The magnetic field 17 emanating from the permanent magnet 18 is shown as being collected by the antenna on its surface, thus transforming the antenna into a direct bar magnet. Magnetic poles are formed at each end of the strip, with north poles shown facing the HED as an example. The antenna may be really long, e.g. 10, 50 or even 100mm. It is clear that the magnetic field of the HED is thus greatly increased by the presence of the antenna, with the receiving area of its magnetic field being hundreds or thousands of an individual HED.

The output of the HED is connected to electronic circuitry (not shown, but one example is described with reference to fig. 15 below) for recording the presence of the magnetic field and providing a signal of the desired form.

The strip antenna is formed of a material having an effective zero remanence (e.g., 2 gauss or less) to ensure that no residual magnetic field remains therein after the permanent magnet 18 (or any other magnetic source) is removed, otherwise the HED will remain activated. Materials meeting these requirements are commercially available and are known as permalloys.

Lower remanence is preferred. Preferably, a material having a magnetic remanence less than the earth's magnetic field strength (i.e., 0.3 gauss or less) is used. Mu-metal (available from Magnetic Shields Limited of kentuck header, uk) easily achieves this with a remanence of less than 0.1 gauss (1-5 n tesla), and such low levels are preferred. The permeability of the mu-metal is 470000H/m (at 5mOe = 0.4A/m).

Figure 2 shows another arrangement which further enlarges the area in which detection can be performed. Here, the two

antennas

19 and 20 sandwich the HED, with the edges shown at 21. Either or both may collect magnetic fields as schematically shown at 22 and 23.

Still another arrangement is shown with reference to figure 3a. Here, a split rectangular antenna loop 24 (which may, for example, cover a substantial area to detect an invading magnetic field) sandwiches the HED 25. However, for this arrangement to work well, at some point along the length of the strip, ideally in the middle, as shown at 26, there is a further split (which means a gap). The reason is difficult to understand, as follows.

The HED responds to magnetic polarity fields of the same polarity on either side thereof according to its voltage output swing. Thus, if the north pole is brought to the left hand face of the detector, its voltage output will increase from a quiescent value, and if the north pole is brought to the right hand face, the voltage output will increase from a quiescent value. If the north pole is brought to both surfaces, the signal increases further. If the south pole is brought to either or both surfaces, the output voltage will drop from a quiescent value. Either voltage change provides a reasonably detectable signal. However, if a north pole appears on one surface and a south pole of equal strength appears on the opposite surface, substantially no signal is generated. Alternatively, if a particular polarity (e.g., north) of a certain intensity (e.g., +40 gauss) is brought to one face and a weak south pole (e.g., -3 gauss) is brought to the opposite face, then the 37 gauss net north pole effect dominates. The hall effect will then still provide a corresponding increased voltage signal, the magnitude of which is determined by the relative strengths of the polarities prevailing on either side thereof, as shown.

The ideal solution is one in which the hall effect detector provides a maximized signal for any magnetic field that is intended to be collected and detected by the loop antenna, regardless of its orientation. This ensures that even the weakest field can be detected.

It will be appreciated that the manner in which the magnetic fields surround the antenna and how they are acquired, and the corresponding polarities formed on them, are complex and virtually infinitely variable.

Experiments have shown that the aforementioned arrangement of the second split results in an average maximization of the total intensity values of the magnetic polarities present on the various faces of the hall-effect detector, irrespective of the direction and position of the dominant magnetic field. It is this value that determines the swing of the output voltage of the hall effect detector and therefore its sensitivity.

One example of the function of the second split is shown in fig. 3a. The field pattern induced by the magnet 27 is shown. This is shown facing the second split 26 end of the antenna, resulting in the same polarization in both sections of the antenna end facing it. These polarities turn each of the two antennas into a bar magnet, thus creating the same polarity (here shown as south) at the distal end of the antenna that holds the HED. These similar poles combine together to increase the output of the HED. Depending on the exact geometry of the antenna and the positioning of the magnetic field detector, more splits can be used.

A less efficient arrangement is shown in figure 3 b. In the presence of an external magnetic field, the continuous strip antenna effectively becomes a single strip magnet, and thus can form more equal opposite polarities on either side of the HED, thereby reducing its output.

As shown in fig. 1b, the flat strip antenna is well suited to collect magnetic fields towards its edges, which reach a maximum when they are orthogonal to its flat surface. Ideally, however, the antenna arrangement should be able to respond to magnetic fields of any direction. This may be achieved by the arrangement shown in fig. 4, in which the antenna 28 is shown as a right angle strip. The antenna can then collect the magnetic field passing through it in any direction. In this case, two HEDs can be used at the ends of the strip, as shown at 29 and 30, to obtain between them the maximum effect of the field induced on one or both of its two surfaces. Other geometries may benefit from more than one HED.

Instead of a right-angled strip, an annular strip may be used, as shown at 31, but still provided with a second split 32. Its free ends 33 and 34 are sandwiched as before the HED 35, but are flattened to become flattened so that they can be pressed against the corresponding surfaces of the HED, as shown in the inset at 36. By means of the circular surface of the toroidal coil, a magnetic field approaching from any direction is obtained thereon.

Referring now to fig. 5, another aspect of the present invention is shown. This shows the use of an antenna/hall effect detector combination in a personal alarm.

The person 37 is equipped with a watch-like band 38 carrying magnets (this can be worn on both wrists). The housing 39 is supported by a lanyard 40 and rests generally on the chest of the person. The housing accommodates

antennas

41 and 42 of the type shown in fig. 3a. As with the arrangement of fig. 3a, the antenna holds the HED 43. The electronic circuitry and alarm 44, which is responsive to the output of the HED, are located within the antenna.

When a person lifts their hand towards their face, which necessarily results in the magnetic field provided by the magnet being captured by the antenna, the circuit provides a warning signal. This may be an audible alarm, vibration or other form of signal. The intensity of the warning signal (e.g., its loudness) may be adjusted, as well as enabling the user to pause the operation of the device for a given period of time to calmly drink the beverage.

By using such a device, accidental ingestion of other forms of infected viruses, such as those previously picked up by a person's fingers, can be avoided.

The circuit may be battery powered, the preferred form of battery being a lithium ion battery, as these are commercially available without any internal or external ferromagnetic material that might otherwise interfere with the action of the antenna.

Referring to fig. 6, an arrangement of magnets to provide an enhanced magnetic field is depicted. A one-piece magnet is shown at 45. Magnetic field lines of opposite polarity are naturally connected around the sides of the magnet as shown at 46. Alternative arrangements are shown at 47 and 48. In this case, the magnet 50 comprises two planar halves, but remains repulsive. Thus, the force lines propagate further, as shown at 49, thereby increasing the effective range of the force lines. To further improve performance, a soft steel disc (not shown) may be inserted between the two planar halves.

Referring to fig. 7a, the body of a person using the warning device of the present invention is shown at 110, and the arms and hands of the person are shown at 111 and 112 when at rest. A proximity detection device containing an alarm 113 is shown at 114. Fig. 7b shows the arms and hands in a raised position 115 in front of the person's face, and the alarm 113 now rings. It goes without saying that the operation method is to simply lift the hand of the person toward his/her face, thereby causing the proximity detection device to approach, thereby sounding the alarm.

Acceptance of the device may be facilitated for a person of a smaller age and wearing the detector of the present invention by providing a more "user friendly" warning signal that the user's hand is close to his/her face. According to a further feature of the invention, a small speaker is housed within the housing containing the electronic circuitry of the device, and the programming apparatus is used to emit an audible friendly warning, such as "do you wash their hands".

In many cases, the hand is raised towards the face for legitimate reasons, for example when drinking coffee. This facilitates the approach of the hand to the face and thus within the reach of the detection device. For example, the buzzer may be activated each time the beverage is sipped, which may be annoying.

According to a further feature of the invention, the electronic circuit is equipped with a switching device that allows the user of the device to deactivate his circuit for a predefined period of time (for example ten minutes). A warning LED may be used to indicate a deactivated state. After the predetermined period of time has elapsed, a series of recognizable signals can be emitted, indicating that the device is again set to be detectable. The device therefore comprises a switching means which allows a user of the device to prevent the emission of a warning signal for a predetermined period of time. The apparatus further includes a visual indicator to indicate to a user that transmission of the warning signal is prevented during a predetermined time.

Referring to fig. 8, a general apparatus for detecting the presence of a magnetic field carried on one body part when adjacent to a detector worn on another body part is shown at 210. The wrist is shown at 211 and carries a permanent magnet 212 thereon. A magnetic field detector and alarm system housing is shown at 213 which includes an electronic magnetic field sensor 214 (e.g., a hall sensor) for detecting a magnetic field 215 emanating from the permanent magnet 212 and circuitry (not shown) responsive to an output thereof. The circuit is used to sound the sound player 216 which emits an alarm signal when the magnetic field emitted from the magnet is detected.

However, as mentioned above, the response field from such an arrangement is limited. An indication of the detection area of the hall effect detector is shown symbolically at 217. It goes without saying that the magnetic field of 215 must fall within said region 217 to be detected. If the hand-to-face movement is made outside the region, it will not be recorded.

It is obvious that the path taken by the hand when approaching the face is highly variable and does not necessarily pass within the detection field of an electronic magnetic field sensor, such as a hall effect sensor. A typical hall effect integrated circuit has a small receiving area of only one or two square millimeters and cannot cover a wide area even if its magnetic field sensing spatial envelope expands with distance. Thus, when the hand carrying the magnet is raised towards the face, the field from the wrist mounted magnet may be missed. As mentioned above, one way to deal with this is to use a series of such detectors on the chest. However, this is electronically complex and consumes a significant amount of power from the battery used by the device. A device that achieves reliable magnetic detection is preferred.

According to the invention, the magnetic field detector detects the magnetic field over the extended area in that it comprises the use of one or more magnetic antennas arranged over all or most of the area in which magnetism is to be detected, said antennas collecting at least part of the magnetic field present on themselves, and one or more magnetic field sensors arranged in the vicinity of said one or more antennas for responding to the magnetic field collected thereon.

According to one aspect of the invention, the magnetic antenna and the magnetic field sensor are used in combination to detect the presence of a first human body part in proximity to a second human body part.

According to another aspect, the first body part is a hand or both hands and the second body part is a face.

According to yet another aspect, the first body part may be the body of one or more second persons.

In a feature of the invention, the magnetic field sensor may be a Hall Effect integrated circuit (ic).

Any antenna may be used for the purposes of the present invention. In one embodiment, the magnetic antenna is at least partially ferromagnetic so as to obtain any ambient magnetic field thereon. However, for high sensitivity detection, it is desirable for such components to have a remanence of zero or near zero (e.g., a remanence of less than 1 to 2 gauss). The presence of residual magnetism after physical departure of the magnetic field is undesirable as it can compromise the sensitivity of the electronics used to detect the output of the hall effect sensor.

According to another characteristic of the invention, the antenna is made of a particular type of magnetic material, which is more commonly used for magnetic shielding, i.e. high permeability alloys. This exhibits an almost zero remanence and has a particularly high permeability and is therefore highly desirable when attracting ambient magnetic fields. Mu-metal alloys typically have a relative permeability in the range of 80000-100000H/m, so a relative permeability higher than 80000H/m is desirable. The mu-metal may be of the type specified in ASTM A753-08 (2013) alloy 4.

A practical realization of the invention may be to use a housing resting on the upper part of the chest, said housing being held in place and supported by a lanyard. The magnetic antenna may be in the form of one or two wings emanating from either side of the housing, extending through and optionally bent to fit the chest (e.g., fig. 9 a), or a split ring contained within or around the housing (e.g., fig. 9 b). A typical effective dimension of each wing (each magnetic antenna) (for adults) is a length of at least 100mm, for example 160mm. A typical width of the antenna is 15mm, a preferred overall length is 300mm and the thickness is 1mm.

In an alternative arrangement, the antenna may (optionally additionally) be wound as a helix formed from a film. Preferably enclosed within a tube. Experimental evidence suggests that effective detection of the antenna magnetic field by the hall effect sensor is best achieved by placing the sensor at one longitudinal end of the magnetic antenna (e.g., at the longitudinal end of each antenna).

An apparatus for achieving the requirements is shown with reference to fig. 9. Here, two

magnetic antennas

218 and 219 are mounted on either side of the housing 213 (fig. 9 a) or within the housing 213 (fig. 9 b). Their width and (magnetic) field of view greatly extend the possible range of magnetic field detection. Any field 215 emanating from the magnet 212 is picked up by them and falls upon them. The inner end of the antenna is brought to a hall effect sensor 214 for detecting the field that has fallen on the antenna.

This effect is shown more clearly in figure 10. In this case, the field 220, represented by the lower case letter n, is shown to reside on

antennas

218 and 219.

A useful property of any such antenna (or indeed strip of ferromagnetic material) is that when such a magnetic field is present, it becomes a bar magnet no matter how small the magnetic field is. That is, a magnetic pole is formed at each end. This is shown by the capital letter N at 221.

This magnetic concentration is then detected by a hall effect sensor placed at the end of the strip.

Referring to fig. 11, an alternative arrangement of an antenna and lanyard is shown at 222. A housing holding the hall effect sensor and other components is shown at 213. In arrangement 222, the antenna is not housed in a housing, but is shown extending outwardly and terminating in lanyard portions 222a and 223a. The choice of either of the methods shown in fig. 9 or fig. 11 depends on the size/age of the person wearing the device. At B is shown an indication of the body area to be covered when the wrist carrying its permanent magnet is lifted towards the face. The antenna is sized and positioned so as to be able to acquire any magnetic field generated within said defined area.

One aspect to improve the detector function is that the ends of the antennas meet in the center and face the flat opposing planes of the hall effect sensor. That is, the ends of the antenna are positioned as close as possible and as centered as possible, and the surfaces are as close as parallel as possible to the flat surface of the hall element of the hall effect sensor. As shown in fig. 12. Ideally, the distance "d" is zero (i.e., touching), but in practice it is found sufficient to be at most one millimeter. If, for mechanical reasons, the antennas are subtended at an angle

Less than 180 deg., the ends of the antennas 224 and 225 are optimally cut to still meet flat on the hall effect sensor as shown.

Referring to fig. 13, to avoid the use of dry cells which need to be replaced from time to time, the housing 213 is instead provided with a rechargeable battery as shown at 226. These may be charged by a conventional mains charger or by a USB connector as shown at 227. A warning LED 228 may be provided for indicating a battery condition, or any other device capable of warning a user. The battery used is preferably of the lithium-ion type and can be housed in a plastic container, thus avoiding any interference of the magnetic field falling on the antenna.

For younger users, a small speaker 229 may be mounted within the housing in order to make the device more acceptable and "user friendly". Instead of issuing a warning as in, for example, a buzzer, an internal programming device may be used to issue a message, such as "handle down" or "do you wash their hands", etc.

To avoid activation of the device during expected activities, such as drinking a hot cup of coffee and requiring multiple sips, a timer switch facility 230 is provided. Upon pressing the button, the device will mute for a preset period of time, for example five minutes. At the end of the period, a special beep may be emitted to indicate that the device is running again.

To implement the present invention in which the permanent magnet is mounted on the body and the detection device is mounted on the wrist, a magnetic strip as shown in fig. 14 may be used. Here, a ferromagnetic strip 231 is used to hold the magnets 232 in line (and all with the same outward facing polarity). Alternatively, a single long magnet may be used, but magnetized face-to-face, rather than end-to-end.

FIG. 15 outlines the circuitry associated with the electronic magnetic field detector. Assuming a supply voltage of 5 volts, a typical quiescent or static voltage output by the Hall effect detector 138 in the absence of any magnetic field is at half 5 volts, i.e., 2.5 volts, as shown. (the voltage increases or decreases, depending on the overall polarity of the magnetic field, i.e., north or south presented to it.) the voltage is optionally first rectified and then fed into a comparison op amp 139, as shown at 138 b. Note that rectification has the following advantages: the circuit is operable regardless of the polarity of the wrist-bearing magnet providing the field to be detected. Thus, the wrist magnet may be worn under the wrist, which will assume one polarity, or over the wrist, which will assume the opposite polarity to suit the wearer's preference.

The comparison voltage at the time of amplifier triggering, and the strength of the dominant magnetic field indicating the distance from the permanent magnet carried by the person, are provided by the sensitivity-adjusting potentiometer 139 a. Preferably, the minimum is safely set above the level resulting from the detection of the earth's magnetic field. Note that the potentiometer may be logarithmic, reflecting the exponential decay of the magnetic field with distance, thus providing better regulation. The gain of the amplifier is set during manufacturing. The output from the operational amplifier is used to drive a sounding buzzer 141 and a vibrator and a blinking LED 142 via an electronic switch 140. As described above, the output may increment counter 141a as described above.

The following are some aspects of the invention:

1) Apparatus for reducing the likelihood of a person becoming infected with a virus comprising providing a warning signal indicating that a person's hand is in proximity to the face of the person.

2) Apparatus for reducing the likelihood of a person becoming infected with a virus comprising providing a warning signal indicating the approach of another person or persons to the face of the first person.

3) The apparatus of aspects 1 and/or 2, the apparatus being positioned in a manner that specifically detects a position of a hand of a person relative to the face of the person.

4) The apparatus of any preceding aspect, wherein the means for detecting the position of a person's hand relative to the person's face is carried on or around the person's body.

5) The apparatus of any preceding aspect, wherein the device of aspect 4 provides a warning signal regarding the proximity of a human hand relative to his/her face.

6) The device of aspect 5, wherein the warning signal is in the form of an audible signal, a visual signal, a vibration, a distinctive smell, a bluetooth connection to a headset worn by the person (or other wireless transmission device), or a combination of the foregoing, or any other means capable of warning the person of their intended action and avoiding any hand-to-face contact for a sufficient period of time.

7) The apparatus of aspect 4 wherein the detector for indicating proximity of a person's hand to the person's face may be in the form of a detector worn or mounted on or around the body or neck of the person to be protected, or worn or mounted within a hat or other fashion accessory worn by the person, or worn or mounted on the person's clothing, such that the electronic signal provided thereby effectively provides a warning signal.

The device may comprise a plurality of detectors, for example distributed over the body or on each hand.

8) The device of aspect 4, wherein the detector is alternatively worn on a suitable location on the person's arm, such as his/her wrist and/or finger.

9) The apparatus of aspects 4) to 8), wherein the detector for indicating proximity is in the form of a doppler detector.

10 The apparatus of aspect 9), wherein an infrared sensor is used in conjunction with the doppler detector to ensure that no inanimate object is detected.

11 The apparatus according to aspects 4) to 8), wherein the detector for indicating proximity utilizes capacitance or inductance variation according to a position of a hand of a person relative to the detector.

12 The device of aspect 11), wherein the ferromagnetic object is worn on a human hand or wrist for modulating the inductive coupling required for operation.

13 The device according to aspects 4) to 8), wherein the proximity of the hand of the person to the face of the person is detected by using a wireless transmitter mounted on either the wrist or the body of the person and a wireless receiver mounted on the wrist or the body, respectively.

14 4) to 8), wherein the detector is a Hall effect sensor mounted on the person's body or wrist, and the device for providing a magnetic field detected by the sensor is in the form of one or more permanent magnets mounted on the person's wrist or body, respectively.

15 The apparatus according to any one of aspects 4) to 14), wherein the sensitivity of the detector arrangement is manually adjustable by a person using it.

16 The device according to any of aspects 4) to 14), wherein a resettable electronic counter is provided for maintaining a count of the number of attempted facial contacts made over any given period of time.

Other aspects are as follows:

1. a warning device configured to emit a warning signal indicating that a human body part is close to a head of a user.

2. The warning device according to aspect 1, wherein the human body part is a face or a hand.

3. The warning device of

aspect

1 or 2, wherein the warning device is configured to emit a warning signal indicating that the human body part is in proximity to the face of the user.

4. The warning device of

aspect

1, 2 or 3 wherein the human body part is a hand of the user.

5. The warning device of any one of the preceding aspects adapted to be positioned to detect the position of the human body part relative to the face of the user.

6. The warning device of any one of the preceding aspects, adapted to be carried around the user.

7. The warning device of any one of the preceding aspects, wherein the warning signal is in the form of an audible signal, a visual signal, a vibration, a distinctive smell, a wireless transmission signal to a headset worn by the user, or a combination of the above, or any other means, preferably capable of warning the person for a sufficient time to avoid any body part coming into contact with the head.

8. The warning device of any one of the preceding aspects comprising a detector for detecting proximity of an object to the user's head and assuming that the object is the human body part and thereby causing the device to emit the warning signal if the detected proximity of the object is less than a predetermined minimum.

9. The warning device of any one of aspects 8 wherein the detector is adapted to be worn or mounted on or around the body or neck of the user, or within a hat or other fashion accessory worn by the user, or on the clothing of the user, such that the electronic signal provided thereby effectively provides a warning signal.

10. The warning device of aspect 8 wherein the detector is adapted to be worn on an arm of the user, preferably on a wrist, hand or finger of the user.

11. The warning device according to aspect 8, 9 or 10 wherein the detector comprises a doppler detector.

12. The warning apparatus according to

aspect

8, 9, 10 or 11, further comprising an infrared sensor, and the detector is configured to assume that the object whose proximity is smaller than the predetermined minimum value is detected only if the infrared sensor detects an infrared signal within a predetermined range indicating that the object is a human body part.

13. The warning device of any one of aspects 8 to 12 wherein the detector comprises a capacitive or inductive sensor.

14. The warning device of aspect 13 further comprising a ferromagnetic member adapted to be worn, preferably wherein the ferromagnetic member is adapted to be worn on an arm of the user, preferably on a wrist, hand or finger of the user.

15. The warning device according to any one of aspects 8-14, wherein the detector is a detector of wireless electromagnetic waves, and the warning device further comprises an electromagnetic wave emitter, one of the detector and emitter being adapted to be worn near the head of the user and the other of the detector and emitter being adapted to be worn on the arm of the user.

16. The warning device of any one of aspects 8 to 15 wherein the detector comprises a hall effect sensor.

17. The warning device of aspect 16 further comprising a magnetic antenna for obtaining a magnetic field around the magnetic antenna.

18. The warning device of aspect 17 wherein the hall effect sensor is disposed at an end of the magnetic antenna to detect a magnetic field acquired by the magnetic antenna.

19. The warning device of aspect 18 wherein the hall effect sensor is within 1mm of a longitudinal end of the magnetic antenna, and/or wherein the longitudinal end of the magnetic antenna is located proximate to a flat surface of a hall element of the hall sensor.

20. The warning device of any of aspects 17-19 wherein the magnetic antenna comprises a ferromagnetic material.

21. The warning device of any one of aspects 17 to 20 wherein the magnetic antenna comprises a material having a magnetic remanence of less than 2 gauss and/or a magnetic permeability of 80000H/m or higher.

22. The warning device of any one of aspects 17-21 wherein the magnetic antenna is comprised of mu metal.

23. The warning device of any one of aspects 17-22 wherein the magnetic antenna is elongated, the elongated length being at least 100mm.

24. The alarm device of any of aspects 17-23, wherein the magnetic antenna comprises a helically wound film.

25. The warning apparatus according to any one of aspects 16 to 24 further comprising means for providing a magnetic field for detection by the hall effect sensor, preferably in the form of one or more permanent magnets, preferably adapted to be mounted on the arm of the user.

26. The warning apparatus according to any one of aspects 16 to 24 further comprising means for providing a magnetic field for detection by the hall effect sensor, preferably in the form of one or more permanent magnets, preferably adapted to be mounted on the body of the user.

27. The warning device of aspect 26 further comprising an elongate ferromagnetic strip along which a plurality of the permanent magnets are attached, preferably with the same outward facing polarity.

28. The warning device of any one of

aspects

26 and 27 wherein each permanent magnet is comprised of two planar halves that are held together repulsively.

29. The warning device of any one of aspects 8-28 wherein the predetermined minimum value is adjustable by the user.

30. The warning device of any one of the preceding aspects, further comprising a counter for counting the number of warning signals emitted by the warning device, preferably wherein the counter is user-resettable.

31. The warning device of any one of the preceding aspects, wherein the warning signal is an audible signal, preferably a human voice.

32. The warning device of any preceding aspect, further comprising a switching arrangement that allows a user of the device to prevent the warning signal from being emitted for a predetermined period of time.

33. The warning device of aspect 32 further comprising a visual indicator for indicating to the user that the warning signal is prevented from being emitted during the predetermined time.

34. A method of reducing the chance of a user becoming infected with a virus, comprising:

mounting a warning device according to any one of the preceding aspects on the user.

35. A method of reducing the chance of a user becoming infected with a virus, the method comprising:

a warning device is mounted on the user, the warning device being adapted to issue a warning signal when it detects that a body part is close to the user's head.

36. The method of aspect 34, wherein the warning device is the warning device of any one of aspects 1-33.

Many variations will be apparent to those skilled in the art.

Claims

1. A magnetic field detector, comprising:

a magnetic antenna for obtaining a magnetic field surrounding the magnetic antenna; and an electronic magnetic field sensor arranged to detect a magnetic field obtained by the magnetic antenna, wherein the magnetic antenna is composed of a material having a remanence of less than 2 gauss and/or a permeability of 8000H/m or higher.

2. The magnetic field detector of claim 1, wherein the electronic magnetic field sensor is arranged to generate an electrical signal in response to the presence of a magnetic field present within a detection region, and the detection region is adjacent to a location on the antenna where a magnetic pole is formed when the antenna is in a magnetic field.

3. The magnetic field detector according to claim 1 or 2, wherein the magnetic antenna is elongate and has a length in its elongate direction that is at least four times the length in either direction orthogonal to the elongate direction, preferably wherein the magnetic antenna is elongate and has a length in its elongate direction that is at least six or eight times the length in either direction orthogonal to the elongate direction.

4. The magnetic field detector according to claim 3, wherein the face of the electronic magnetic field sensor is located within a distance equal to 1/8 or less of the elongated dimension from the elongated end of the magnetic antenna, preferably wherein the electronic magnetic field sensor is within 1.5mm, more preferably within 1.0mm of the magnetic antenna.

5. The magnetic field detector of claim 4, wherein the electronic magnetic field sensor is located at the cutting end of the elongated sensor and the detection region of the electronic magnetic field sensor has a plane within 45 degrees orthogonal to the elongated direction of the magnetic antenna, preferably wherein the detection region of the electronic magnetic field sensor has a plane within 30 degrees orthogonal to the elongated direction of the magnetic antenna, more preferably wherein the detection region of the electronic magnetic field sensor has a plane orthogonal to the elongated direction of the magnetic antenna.

6. The magnetic field detector according to any of claims 1-3, wherein an end of the magnetic antenna is positioned adjacent to the electronic magnetic field sensor, preferably within 1mm.

7. The magnetic field detector according to any of claims 1-4, wherein the magnetic antenna is comprised of mu metal.

8. The magnetic field detector according to any of claims 1-5, wherein the magnetic antenna is elongated, preferably having an elongated length of at least 100mm.

9. The magnetic field detector according to any of claims 1-6, wherein the electronic magnetic field sensor is a Hall effect sensor.

10. The magnetic field detector according to any of claims 1-7, further comprising a second magnetic antenna for obtaining a magnetic field around the second magnetic antenna, an end of the second magnetic antenna being arranged at the electronic magnetic field sensor such that the electronic magnetic field sensor can detect the magnetic field obtained by the second magnetic antenna.

11. The magnetic field detector of claim 8, wherein an end of the second magnetic antenna is located on an opposite side of the electronic magnetic field sensor from the end of the magnetic antenna.

12. The magnetic field detector of claim 8 or 9, wherein the magnetic antenna and the second magnetic antenna together form a loop having a discontinuity at the electronic magnetic field sensor and a discontinuity at an end of the magnetic antenna and the second magnetic antenna opposite or substantially opposite to the end at the electronic magnetic field sensor.

13. The magnetic field detector of any of claims 1-10, wherein the magnetic antenna comprises an elongated flat strip.

14. The magnetic field detector according to any one of claims 1-11, wherein the magnetic antenna comprises a helically wound thin film.

15. The magnetic field detector according to any of claims 1-11, wherein the magnetic antenna comprises two elongated flat strips attached to each other in different planes and along elongated sides.

16. The magnetic field detector of any of claims 1-10, wherein the magnetic antenna comprises a tube.

17. The magnetic field detector according to any of claims 1-14, further comprising at least one further magnetic field sensor to detect a magnetic field obtained by the magnetic antenna.

18. A warning device configured to emit a warning signal indicating that a human body part is in proximity to a user's head, the warning device comprising a magnetic field sensor according to any preceding claim.

19. The warning device of claim 18, wherein the human body part is a face or a hand.

20. A warning device according to claim 18 or 19, wherein the warning device is configured to emit a warning signal indicating that the human body part is in proximity to the user's face.

21. The warning device of claim 18, 19 or 20 wherein the human body part is a hand of the user.

22. A warning device according to any of claims 18-21 adapted to be positioned to detect the position of the human body part relative to the face of the user.

23. A warning device according to any of claims 18-22, adapted to be carried around the user.

24. A warning device according to any of claims 18-23, wherein said warning signal is in the form of an audible signal, a visual signal, a vibration, a distinctive smell, a wireless transmission signal to a headset worn by the user, or a combination of the above, or any other means, preferably capable of warning the person for a sufficient time to avoid any body part coming into contact with the head.

25. A warning device according to any of claims 18-24 and including a detector for detecting the proximity of an object to the user's head and assuming that the object is the human body part, and thereby causing the device to emit the warning signal if the detected proximity of the object is less than a predetermined minimum.

26. The warning device of any one of claims 25 wherein the detector is adapted to be worn or mounted on or around the body or neck of the user, or within a hat or other fashion accessory worn by the user, or on clothing of the user, such that the electronic signal provided thereby is effective to provide a warning signal.

27. A warning device according to any one of claims 18-26 further including a magnet for providing a magnetic field for detection by said electronic magnetic field sensor, said magnet for providing a magnetic field preferably being in the form of one or more permanent magnets, said magnet for providing a magnetic field preferably being adapted to be mounted on the arm of the user.

28. A warning device according to claim 27 wherein the permanent magnet is comprised of two planar halves which are held together repulsively.

29. A warning device according to claim 28 wherein the two planar halves are separated by a mild steel disc.

30. A warning device according to any one of claims 18 to 29, wherein the device is adapted to allow a user of the device to prevent transmission of the warning signal for a predetermined period of time.

31. The warning device of claim 30 further comprising a visual indicator for indicating to the user that the warning signal is prevented from being emitted during the predetermined time.

32. A warning device according to any one of claims 18 to 31 wherein the warning device allows a user to adjust the strength of the warning signal.

33. The warning device of any one of claims 18-32, further comprising a lithium ion battery.

34. A warning device according to any of claims 18-33, wherein the warning device is arranged such that the warning signal is emitted if the magnitude of the magnetic field picked up by the magnetic antenna, detected by the electronic magnetic field sensor, is greater than a threshold value.

35. A warning device according to claim 34 wherein the selected threshold value exceeds the strength of the earth's magnetic field.

36. A warning device according to claim 34 or 35, wherein said threshold value is adjustable.

37. A warning device according to any preceding claim wherein the electronic circuit responsive to the output of the hall effect detector operates irrespective of the polarity of the magnetic field picked up by the antenna.