DE69230585T2 - Device for monitoring electromagnetic radiation - Google Patents

Description

The present invention relates to a radiation monitoring device and, more particularly, to an electromagnetic radiation monitoring device which can either be carried by a person exposed to potentially harmful levels of electromagnetic energy or strategically located at a fixed location so that persons can be alerted to the presence of potentially harmful levels of electromagnetic radiation. Even more particularly, the invention relates to a personal or area (fixed position) electromagnetic radiation monitoring device, the device having broadband frequency sensitivity and independence of polarization.

Attempts have been made to produce an electromagnetic radiation monitor that can be carried by a person working in areas where potentially harmful electromagnetic radiation may be present, or that can be placed in a fixed position at a strategic point to detect excessive leakage of radio frequency radiation and alert persons to the leakage. Early studies, such as those reported by Beischer in his article Microwave Reflection, Diffraction and Transmission By Man, Department of Naval Aerospace Medical Research Lab, Pensacola, Florida, June 1973, have shown that scattering from a body can cause errors greater than 2 dB. This scattering becomes even more significant when broadband frequency response and independence from polarization are desired characteristics of the monitor. To the inventor's knowledge, no practical device that has broadband frequency response and independence from polarization has been successfully commercialized to date.

Furthermore, from the document GB-A-803792 a device for measuring high frequency is known, which comprises a transmitter and a receiver in a chamber The transmitter is placed at the focus of a curved reflecting wall and walls with wave absorbing layers are placed along the side walls of the chamber so as to ensure that only the direct wave from the transmitter and the reflected waves from the curved reflecting wall can reach the receiver. The device also has a support made of increasingly lossy material.

Furthermore, a portable measuring device for detecting high-frequency electromagnetic radiation is known from the document GB-A-998779. The device contains a round housing with two pairs of slot antennas of different lengths, so that the device can detect the presence of electromagnetic radiation over a wide frequency range.

A conductive surface can be placed behind the low frequency antennas to provide a capacitive effect to reduce their response to high frequency components of the radiation, and the device can be supported by material with significant dielectric loss at higher frequencies to reduce the response of the high frequency antennas at lower frequencies where the lossy material appears reactive.

It is an object of the present invention to provide an electromagnetic radiation monitoring device that can be carried by a person who may be exposed to harmful levels of electromagnetic energy.

Another object of the present invention is to provide a device for monitoring electromagnetic radiation which has a broadband frequency response and is independent of polarization.

Another object of the present invention is to provide a non-obstructive pocket device for monitoring electromagnetic radiation, which precisely detects high frequency radiation and sends out a warning the moment it detects that the wearer is moving into a dangerous zone.

Yet another object of the present invention is to provide an electromagnetic radiation monitoring device that provides an audible and visual alarm indicating that an area must be urgently evacuated.

It is a further object of the present invention to provide a personal electromagnetic radiation monitoring device that includes a dual battery system and provides a battery depletion warning when battery replacement is necessary.

Another object of the invention is to provide a personal electromagnetic radiation monitoring device having a structure that allows sensitive electronic circuitry in the device to function properly while virtually surrounded by high levels of radio frequency radiation, so that a minimum false alarm rate is achieved within or outside the specific frequency range of the device.

Furthermore, it is an object of the present invention to provide a device for monitoring electromagnetic radiation intended for persons, the properties of which remain essentially unaffected by scattering phenomena when carried by a person.

It is yet another object of the present invention to provide a fixed position area electromagnetic radiation monitoring device by which an area near a source of radio frequency power or microwave energy can be monitored.

It is a further object of the present invention to provide an area (fixed position) electromagnetic radiation monitoring device that accurately detects radio frequency energy or microwave energy within a wide frequency band range independent of polarization and issues a warning when struck by a power exceeding a certain threshold.

It is yet another object of the present invention to provide an area monitoring device (in fixed position) of electromagnetic radiation which includes an audible and a visual alarm device and has a structure which allows sensitive electronic circuitry contained in the device to operate properly while radiation is being received.

According to the present invention as defined in claim 1, a personal electromagnetic radiation monitoring device includes an electromagnetic radiation sensor, a graded lossy material holder, and a conductive shield spaced from the sensor. The electromagnetic radiation sensor may include thin film thermocouples. The radiation sensor is positioned proximate the graded lossy material holder so that the holder is between the radiation sensor and one side of the conductive shield. The holder is progressively more conductive across its thickness from the front surface of the holder facing the sensor to the back surface facing the conductive shield.

The radiation monitoring device also includes an acoustic alarm transducer or sonic alarm transducer connected to the electromagnetic radiation sensor and an earplug assembly connected to the sonic alarm transducer, the earplug assembly being electrically non-conductive to prevent radio frequency energy from being received by the assembly and radiated to the wearer's head.

According to a preferred embodiment, the radiation sensor, the holder made of lossy material and the conductive shield are all arranged in a housing of the device. On the inside of one of the housing sides is mounted a sonic alarm transducer which is aligned with an opening which extends through the thickness of the housing half. The first Velcro fastening arrangement is arranged on the outer surface of the respective housing side and surrounds the mentioned opening.

Preferably, the earplug assembly of the device comprises an elongated pneumatic tube or hose having two opposite ends, with a pneumatic earplug disposed at one end of the hose and a housing cavity defining an internal chamber disposed at the other end. The chamber housing has an opening extending through the wall thickness and includes a second Velcro fastening arrangement surrounding the opening.

The second Velcro fastening arrangement is designed to mate with the first Velcro fastening arrangement of the device housing so that the chamber housing of the earplug assembly can be attached directly to the transducer. In this way, the non-conductive earplug assembly can be quickly and easily attached to the housing of the monitor so that the wearer of the monitor can wear it in high noise environments.

According to another preferred embodiment, the monitor includes an alarm circuit and a dual battery system and a battery discharge sensor. When a low battery voltage is detected on one battery, the sonic alarm transducer chirps at predetermined intervals. At extremely low battery charge levels, the sonic alarm emits a continuous tone. The second battery is used essentially independently of the first battery to power a warning lamp in hazardous radiation environments. If the warning lamp circuit fails, the sonic alarm circuit remains operational.

In another preferred embodiment, the sensitive electronic circuitry of the monitor is protected from high levels of radio frequency radiation by providing a second section of graded lossy material disposed within the housing and at least partially surrounding the batteries of the monitor. In this manner, radio frequency energy entering the monitor is absorbed by this second section before the radio frequency energy can be captured by the battery leads between the circuitry and the battery.

According to yet another embodiment, an electromagnetic radiation area monitor is provided. The electromagnetic radiation area monitor includes a radiation sensor disposed adjacent a graded lossy material holder, a sensor, and an extruded housing structure of non-conductive material attached to a conductive shield and enclosing the radiation sensor and the graded lossy material.

According to another preferred solution, the graded lossy material holder includes a laminate formed of at least a first, a second and a third layer of lossy material having different resistivities, the first layer having greater resistance than the second layer and the second layer having greater resistance than the third layer. The third layer is located closest to the conductive shield and the first layer is tapered to minimize field distortion.

These and other objects, features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments, which description should be read in conjunction with the accompanying drawings, in which:

Fig. 1 is a perspective front view of a personal monitoring device for electromagnetic radiation, which is designed in the manner according to the invention;

Fig. 2 is a rear view of the radiation monitor according to the present invention;

Fig. 3 is an exploded view of a preferred embodiment of a radiation sensor for use in the monitoring device according to the present invention;

Fig. 4 is a front view of a preferred embodiment of a radiation sensor for use in the monitoring device according to the present invention;

Figure 5 is a cross-sectional view of an earplug assembly for use in the monitoring device according to the present invention;

Fig. 6 is a graphical representation of the operating characteristics of the radiation monitor according to the present invention plotted against frequency, in free space and when carried by a user;

Figure 7 shows a preferred form of electronic circuit for use in the monitoring device according to the present invention;

Fig. 8 is a perspective view from above of an area monitoring device for electromagnetic radiation in accordance with a second embodiment of the present invention; and

Fig. 9 is a cross-sectional view of the area monitoring device for electromagnetic radiation according to Fig. 8.

A first embodiment of the electromagnetic radiation monitor according to the present invention is shown in Figures 1 and 2 of the drawings. It can be seen that a personal electromagnetic radiation monitor according to an embodiment of the present invention comprises a two-part housing 2. Mounted on the inner surface of the front wall 4 of the two-part housing is an acoustic alarm transducer 6 (see Figure 3), such as a piezoelectric ceramic transducer, which, as will be explained, provides a warning of high level radio frequency radiation or provides a warning that the battery used in the monitor has a low voltage. During an initial power-up test, the acoustic alarm transducer 6 preferably provides a one-second beep. Above a preset threshold of detected radio frequency energy, the alarm provides periodic one-second beeps at a repetition rate that increases with the level of radiation exposure. When the monitor battery is at a low voltage, the sonic alarm transducer 6 will provide an audible chirp every 40 seconds to a continuous trill (as the battery voltage drops). When the battery voltage is so low that the electromagnetic radiation sensor used in the device fails, the sonic alarm transducer will provide a continuous tone.

The personal electromagnetic radiation monitor of the present invention further includes a visual indicator in the form of a light emitting diode (LED) 8. The light emitting diode 8 is mounted on the top wall 10 of the assembled housing. During an initial power-up test, circuitry within the monitor causes the light emitting diode 8 to turn on. When a certain amount of radio frequency energy is detected by the monitor, the electronic circuit causes the light emitting diode 8 to illuminate and the sound alarm 6 to beep, thereby indicating to the wearer of the monitor to quickly leave the area in question.

The monitor further includes an ON/OFF switch 12 mounted on a side wall 14 of the assembled housing and a spring clip 16 attached to the rear wall 18 of the housing so that the monitor can be carried by the wearer on the belt or in a pocket on the shirt.

The radiation monitor of the present invention also includes an earplug assembly 20 so that the monitor can be used in high noise environments. As shown in Figures 1 and 5 of the drawings, a Velcro® (Velcro is a trademark) patch 22 is attached to the outer surface of the housing wall 4 to which the transducer 6 is attached. The Velcro® patch is positioned to surround an opening 23 in the wall and to align with the transducer. The earplug assembly 20 includes an elongated tube 24. A pneumatic earpiece or earplug 26 is positioned at one end of the tube 24 and a housing 28 enclosing an internal chamber 30 is provided at the other end. The housing 28 has an opening 32 extending through the housing wall and includes a second Velcro patch 34 surrounding the opening 32 and which cooperates with the Velcro patch 22 of the monitor housing. This allows the housing 28 to be mounted in proximity to the transducer 6 so that the sound emanating from the transducer passes through the tube to the pneumatic earplug 26 as air pressure fluctuations.

An advantage of the earplug assembly 20 of the invention is that it is completely electrically non-conductive. Thus, the earplug assembly does not pick up radio frequency energy that would otherwise affect the electronic circuitry in the monitor, as would be the case with a conventional electrical transducer, and furthermore, this earplug assembly provides a safety feature in that the user of the monitor does not wear an electrically conductive device on his head, so preventing electrical shock and further preventing radio frequency energy from being picked up by the earplug assembly and radiated toward the user's head. The cooperating Velcro fastener patches 34 and 32 on the earplug assembly and the monitor housing, respectively, allow the earplug assembly to be quickly and easily and non-electrically connected to the radiation monitor.

From consideration of Figure 3 of the drawings, it will be seen that a preferred embodiment of the personal electromagnetic radiation monitor of the invention includes a first housing half 36 to which the transducer 6 is mounted as previously set forth, and a second housing half 38 having a battery chamber 40 and to which the ON/OFF switch 12 is mounted. Interposed between the housing halves are an electromagnetic radiation sensor 44, a graduated lossy material holder 46, a conductive shield 48 serving as a base plane or ground plane, and a printed circuit board 50 containing the electronic circuitry for the monitor.

The electromagnetic radiation sensor 44 preferably includes thin film resistance thermocouples. In one embodiment of the present invention, the electromagnetic radiation sensor includes a pair of relatively orthogonally aligned antenna elements 52 lying in a plane, but preferably the sensor includes four interconnected antenna elements 52 with adjacent antenna elements at right angles to each other and all four antenna elements 52 lying in the same plane, as shown in Figure 4. Each antenna element 52 extends along a respective longitudinal axis and includes a series arrangement of thin film resistance thermocouples 54 arranged along the axis and a number of spaced conductor elements 56 of discrete length aligned transverse to the axis of the series arrangement. Each thermocouple 54 of each antenna element is arranged between adjacent conductor elements 56. The antenna arrangement shown in the Radiation monitoring apparatus used in accordance with the present invention is broadly similar to that set forth in U.S. Patent 4,518,912.

The thin film elements function as both an antenna and a detector. Preferably, the hot and cold junctions of the thermocouples are only 0.5 mm apart, thereby avoiding displacement due to changes in the ambient temperature in space or time. The use of thin film resistance thermocouples 54 in the particular arrangement described above results in broadband detection of the true RMS value of the electromagnetic energy.

The electromagnetic radiation sensor 44 is supported by a thin Mylar sheet (Mylar is a trademark) or preferably a Kapton spacer sheet 58 (Kapton is a trademark). The spacer sheet 58 preferably has a thickness of 0.0129 cm and is provided to prevent shorting of the sensor to the lossy material holder 46.

The holder 46 is made of lossy material and is graded in resistivity. More specifically, the holder has a front surface 60 facing the sensor 44 and an opposite back surface 62 facing the conductive shield 48. The holder is progressively more conductive across its thickness from the front surface 60 to the back surface 62. In one embodiment of the invention, the holder may be a laminate or layered material of two or more layers of lossy material having different resistivities, as shown in Figure 3. Alternatively, the holder may be made of a lossy material that becomes progressively more conductive across its thickness from the front surface to the back.

When a holder made of a laminate of two layers of lossy material is used, the first layer 64 closest to the sensor preferably has a thickness of 0.635 cm and has high resistivity, and the Second layer 66, which is closest to the conductive screen, preferably consists of a 0.25 inch thick layer of low resistivity material. First layer 64 preferably has a resistivity of about 15 kilo ohms per cubic centimeter and has a surface resistivity of approximately 20,000 ohms per cubic centimeter. Second layer 66 has a lower resistivity of approximately 600 ohms per cubic centimeter and has a surface resistivity of approximately 2,000 ohms per cubic centimeter.

The side of the lossy material holder with the higher resistivity faces the radiation sensor 44, while the side of the holder with the lower resistivity faces the conductive shield 48, so that the resistive or lossy material becomes increasingly more conductive as the electric field penetrates deeper into the holder. Thus, the lossy material holder is ultimately closed off by the substantially fully reflective shield plate 48. The conductive shield plate 48 also forms part of the shielding of the electronic circuitry of the monitor.

The distributed resistance of the sensor 44, combined with the fact that the sensor is mounted on the lossy material holder 46, whose resistivity gradually decreases toward the conductive shield plate, results in a broadband response. Since the resistance of the sensor is relative to the antenna reactance, a constant sensitivity is maintained across the operating frequency band.

In Fig. 6, the change in the threshold value which triggers the alarm of the monitoring device is compared over the operating frequency, which is preferably between 2 GHz and 18 GHz, both when the device is worn by the user and when the device is in free space. It is clear from Fig. 6 that the broadband personal monitoring device according to the present invention is essentially independent of its operating environment. Scattering by the user's body has little effect on the operation of the monitor. A substantially flat frequency response with less than ± 1.5 dB variation and independence from field disturbances due to scattering by the person's body result from the use of thin film resistance thermocouples 54 in the monitor which are located near the graduated lossy holder 46 which is itself supported on the conductive shield plate 48. The difference in response for the case of irradiation of the monitor with electromagnetic energy when carried and for the case of free space on material lower in dielectric constant is less than 0.5 dB.

The radiation sensor 44 is coupled to the electronic circuitry of the monitor using a flexible transmission line 68 consisting of at least two lines of carbon impregnated TFE material. The two lines of this transmission line 68 carry the DC output from the sensor to the electronic circuitry. These lines have a resistance of approximately 3937 ohms per centimeter. The two DC lines are connected to one of the four antenna elements 52 and in particular to respective conductive elements 56 at the outermost end of the antenna element as shown in Figure 4 of the drawings.

Fig. 7 shows one form of electrical circuit for use in the radiation monitor. The integrated circuit U1 acts as a quasi-regulated voltage source and provides a regulated -3 volts at the circuit terminal E2 (-V) and an unregulated voltage of approximately 9 volts at the circuit terminal E1 (+V). The battery B1, which is preferably a miniature 12 volt battery, is connected between the terminals E1 and E2. A diode CR1 acts as a Zener diode in the deficiency mode and provides approximately 3 volts as a reference voltage for the integrated voltage U1. The potentiometer R28 allows the regulated voltage to be set to -3 volts.

The integrated circuit U4 operated as a comparator. It is triggered by a positive-going pulse from the integrated circuit U3, as will be explained, and is maintained by hysteresis (i.e., feedback resistor R7) to cause the light-emitting diode CR3 (which represents the visual alarm LED 8) to remain on. The output of the circuit U4 is connected to the base of the driver transistor Q1, the collector of which is coupled to the light-emitting diode CR3. The light-emitting diode CR3 is powered by a 3-volt auxiliary battery.

The use of separate 12-volt and 3-volt batteries in the monitor provides a safety measure against failure. Since the light emitting diode has the greatest current requirement, i.e., requires approximately 500mA, if the light emitting diode fails due to low battery voltage, the remainder of the circuitry powered by the 12-volt battery will continue to operate and provide the user with a warning when high levels of radio frequency energy are present. Since the indicator light (i.e., the light emitting diode) is powered by a separate battery, this provides maximum life for the battery that powers the sound alarm. The battery for the sound alarm is designed to last approximately 30 days in sleep mode and 6 hours in continuous alarm. The radiation warning light will last approximately 100 hours of continuous on.

The integrated circuit U2 is an operational amplifier connected as a conditioning amplifier with a gain of approximately 1000. The potentiometer R9 is used to adjust the gain. The amplifier amplifies the signal from the radiation sensor, which is connected to the circuit terminals E7 and E8, and amplifies this signal before passing it on to the integrated circuit U3.

Resistor R10, connected to one side of potentiometer R9, is a sensing resistor (i.e., a thermally sensitive resistor or thermistor) and serves to compensate for temperature changes such that the conditioning amplifier U2 has more or less gain as needed with changes in temperature.

The integrated circuit U3 is a conventional circuit used in smoke detectors. The smoke detector circuit U3 provides a regulated voltage at its pin 1, which in the case of the monitor circuit is a 3 volt reference to ground. Resistors R19 and R20 form a resistor network which provides an alarm threshold voltage of 1 volt at pin 2 of the circuit U3. A conventional piezoelectric transducer 6 is connected to pins 8, 9 and 10 of the circuit U3 through terminals E4, E5 and E6. A suitable transducer which can be used here is a part number PKM 11-6A0 manufactured by Firm Murata-Erie Co.

The resistance circuit shown in dashed outline A, in conjunction with the potentiometer R26, allows an adjustment to correct the offset bias of the conditioning amplifier U2.

The radiation monitor circuit of the present invention operates in the following manner. The radiation sensor 44 produces 1 millivolt voltage for each milliwatt per square centimeter of radio frequency energy radiated thereon. This signal is transmitted through the transmission line 68 described above to the input of the conditioning amplifier U2. The amplifier U2 amplifies the 1 millivolt signal from the radiation sensor (i.e., when the sensor is irradiated with 1 milliwatt per square centimeter of energy) by a factor of 1000 to provide an output signal which is approximately 1 volt. The 1 volt signal is applied to pin 3 of the smoke detector circuit U3. When the amplified signal from the conditioning amplifier U2 is greater than the one volt threshold voltage at pin 2 of the circuit U3, the output the circuit U3 at pin 12 sends a positive-going pulse via the diode CR2 to the non-inverting input (pin 3) of the comparator U4.

In response to this pulse, the output of comparator U4 on pin 6 goes to a positive voltage and biases transistor Q1 in the on direction. Transistor Q1 conducts current through light emitting diode CR3 to illuminate the radiation monitor diode. Hysteresis holds comparator U4 until the circuit is reset. Additionally, smoke detector circuit U3 causes piezoelectric sound alarm 6 (Fig. 3) to sound when the threshold is exceeded. Circuit U3 also monitors battery voltage. When battery voltage drops to approximately 7.5 volts, circuit U3 causes the sound alarm to emit a chirp every 40 seconds. As battery voltage drops further, the chirps emitted by the sound alarm become more frequent until battery voltage reaches a level that causes the alarm to emit a continuous trilling sound.

The monitor of the present invention further provides a power-on self-test. Capacitor C2, connected between the input (pin 3) of conditioning amplifier U2 and the regulated 3-volt output of circuit U3 (at pin 1), is initially uncharged so that a test voltage is applied to the inputs (pins 3 and 2) of conditioning amplifier U2 through the voltage divider of resistors R16 and R17 and input resistor R15. This test voltage is approximately 1 millivolt which is compared to the voltage that would be provided by the radiation sensor if the sensor were irradiated with radio frequency energy of 1 milliwatt per wire centimeter per square centimeter. The test voltage is amplified by the circuit U2 and the smoke detector circuit U3 causes an audible alarm and causes the comparator U4 to go to the positive state at its output, thereby turning on the transistor Q1 and lighting the light emitting diode CR3. The comparator U4 is not held in place under these test conditions. This is because that capacitor C8, which is connected between the regulated -3 volt voltage and the positive supply voltage input (pin 7) of comparator U4 and one side of resistor R8, the other side of which is connected to the unregulated 9 volt supply voltage, is initially uncharged. Capacitor C8 prevents the positive supply voltage from being supplied to pin 7 of comparator U4. Circuit U4 does not hold up under these conditions across hysteresis feedback resistor R7 until capacitor C8 is charged; by this time, however, capacitor C2 has become fully charged and is effectively removing the test voltage from the inputs of conditioning amplifier U2. The output of amplifier U2 therefore falls below the 1 volt threshold and the output from circuit U3 returns to a low level. This in turn causes the output of comparator U4 to return to a low logic signal level, turning off transistor Q1 and extinguishing light emitting diode CR3 as a warning lamp.

To ensure that the various capacitors and other components of the monitor's electronic circuitry are completely discharged when the monitor is turned off, thereby avoiding false alarm indications and preventing latching of comparator U4, a single pole, double throw switch serves as the ON/OFF switch 12. The positive side of battery B1 is connected to one pole (51-1) (Fig. 3) of the switch. The movable terminal (51-2) (Fig. 3) of the switch is connected to terminal E1 of the electronic circuit board. Terminal E2 is connected directly to the negative terminal of the battery and to the other pole or contact (51-3) (Fig. 3) of the switch. Thus, when switch 12 is in the on position, movable contact S-2 is in contact with contact piece 51-1 to supply voltage from battery B1 through terminals E1 and E2. When the switch is in the off position, the movable contact 51-2 is in contact with the opposite contact piece 51-3 and creates a short circuit between the terminals E1 and E2. Since the transistor Q1 remains off, if the light emitting diode CR3 is not lit, a negligible current is drawn from battery B2 when the monitor is turned off.

A partial list of the circuit shown in Fig. 7 is given below. Also, the pin numbers in Fig. 7 for the integrated circuits U1-U4 refer to the parts shown in the list, but it is of course considered that components comparable to those in the list and connected in a different manner from that shown in Fig. 7 may also be suitable for use.

Partial list for the circuit according to Fig. 7

Part description Reference numbers

2N4124 Q1

CONDUCTOR, BUSS W1-2

CAPACITOR 22uF C7-8

CAPACITOR 0.1 1W C2, C3, C6

CAPACITOR 0.01 kE C4, C5

CAPACITOR 0.001uF C1

LIGHT EMITTING DIODE CR3

CR2

ZENER DIODE CR1

IC CHIP-CA3169A U3

IC CHIP-CA3078 U1, U4

IC CHIP-OP22EZ U2

CAPACITOR 1uF C9

POTENTIOMETER 1 MΩ R27, R28

POTENTIOMETER 10 MΩ R26

RESISTANCE 2.4 kΩ R32

RESISTOR 360 kΩ R9

RESISTANCE 62Ω R23

RESISTANCE 3Ω R15, 22

RESISTANCE 200 Ω R8, 18

RESISTANCE 2Ω R17, 31

RESISTANCE 6.2 MΩ R16

RESISTANCE 510 kΩ R13-14, R20

RESISTANCE 10 kΩ R9, R11, R12

RESISTANCE 680 Ω R10

RESISTANCE 2 MΩ R7

RESISTANCE 3.3 MΩ R6

RESISTANCE 5.1 MΩ R21

RESISTANCE 820 kΩ R2, R5

RESISTANCE 1 MΩ R1, 3, 4, 19, 29

RESISTANCE 100 kΩ R24

RESISTANCE 51 kΩ R30

Battery B1 is a 12-volt miniature battery and is housed in a container 70 that is mounted in a battery chamber 40 of the housing. Battery B2, in one embodiment of the invention, takes the form of a pair of 1.5-volt button batteries connected in series and housed in a separate container 72 that contains a spring 74 to bias the batteries against contacts in the housing.

To further ensure that no radio frequency energy will interfere with the proper operation of the monitor, the battery chamber 40 which houses the batteries B1 and B2 is provided with additional lossy material 76 so that the receptacles 70 and 72 which house the batteries B1 and B2 respectively are at least partially enclosed by the material. The material 76 is preferably extended across its thickness from the rear wall 18 of the housing to the conductive shield plate 48 becomes increasingly conductive, as was previously described for the lossy material of the holder 46.

The radiation monitor of the present invention accurately detects radio frequency radiation without being affected by scattering caused by the wearer's body. The compact size of the monitor allows it to be worn on the belt using the spring clip 16 (Fig. 2) or carried in the wearer's pocket. The broad band frequency response and independence from polarization make the monitor eminently suitable for use in a variety of radio frequency environmental conditions. The sound alarm 6 provides a warning of exposure to radio frequency energy and the light emitting diode 8 also provides a visual indication. The light emitting diode remains illuminated so that a record is provided that the wearer has been exposed to radio frequency energy if the wearer did not hear the sound alarm before leaving the danger zone.

The personal electromagnetic radiation monitor of the present invention is also particularly suitable for use in high noise environments. The earplug assembly 20 includes earplugs used in conjunction with headphones and is electrically non-conductive to avoid injury to the wearer and prevent misreading or damage to the electronic circuitry of the monitor. The Velcro® (Velcro® is a trademark) fastener patches used on the earplug assembly and the housing of the monitor allow the wearer to quickly and easily connect the earplug assembly to the transducer on the housing without the need for an electrical connection.

An alternative embodiment of the electromagnetic radiation monitoring device according to the present invention, in particular a A fixed position electromagnetic radiation area monitor 100 is shown in Fig. 8. The monitor includes an electromagnetic radiation sensor 121 (shown in Fig. 9), a conductive shield 101, a housing 102, a conductive electronic housing 103 placed on the conductive shield, and a holder of progressively lossy material in the form of a first layer 118, a second layer 119, and a third layer 120 (see Fig. 9).

The holder made of graded lossy material is arranged between the radiation sensor and the conductive shield. The holder becomes increasingly conductive across its thickness from the first layer 118 to the third layer 120.

The fixed position mounted area electromagnetic radiation monitor 100 is designed to monitor an area near a source of high power radio frequency energy or microwave energy. In the event of a breakage or failure of a component or part, the monitor generates an alarm when the device detects radio frequency power that exceeds a certain threshold. The operating frequency range for the device according to the present invention is 0.5 GHz to 40 GHz.

The electromagnetic radiation area monitor is provided with a holder or base of graded lossy material, 118, 119, 120, which material becomes increasingly more conductive across its thickness with increasing distance from the radiation sensor 121. The holder is made of three layers. The first layer 118, closest to the radiation sensor, has a volume resistivity of approximately 15kΩ per cubic centimeter and a surface resistivity of approximately 20kΩ per square centimeter. The second layer 119, which is immediately adjacent to the first layer 118, and the third layer 120, which is immediately adjacent to the second layer 119, have volume resistivities and surface resistivities of approximately 600Ω per cubic centimeter or 150Ω per cubic centimeter and 2000Ω per square centimeter or 500Ω per square centimeter. The third layer 120, which is the layer with the lowest resistivity, is attached to the conductive screen 101.

The housing 102 is a substantially rectangular, one-piece extruded part with an upper surface area 111, a first side 107, a second side 104, a third side 105 opposite the first side, and a fourth side 106 opposite the second side. The four sides are adjacent to and oriented perpendicular to the edges of the conductive shield 101. The second side 104 is adjoined by an inclined surface 108 which extends upwards at certain angles to then meet the upper surface area 111. In a corresponding manner, inclined surfaces 109 and 110 adjoin the third and fourth sides 105 and 106, respectively, and extend upwards from there at a certain angle to again meet the upper surface area 111. The optimal inclination angle of surfaces 108, 109 and 110 is 45º, so that a minimum field distortion is obtained.

The upper surface area 111 carries a cylindrical extruded part or cap 112 which encloses the electromagnetic radiation sensor 121. The first side 107 of the housing 102 does not have a beveled part similar to the bevels 108, 109 and 110. The first side 107 abuts the conductive electronics housing 103. The electrically conductive housing 103 contains the electronic circuitry similar to that of the personal electromagnetic radiation monitor shown in Figures 1-7 and previously described. However, the conductive electronics housing 103 may also contain a battery 122 (shown in Figure 9) within a battery chamber 113. The battery 122 is surrounded by a second support 114 which may be formed of a graded lossy material similar to that contained in the housing 102. Also shown is an alarm test button 115 which is arranged on the conductive electronics housing 103.

When an alarm threshold of electromagnetic radiation is set and this value is exceeded, a piezoelectric buzzer 117 sounds and a light emitting diode (LED) 116 illuminates. In a safe environment, the light emitting diode 116 can be made to illuminate intermittently so that it indicates to the user that the device is operating and monitoring the environment. The buzzer 117 can also be made to sound intermittently so that it buzzes once every 40 seconds when the battery voltage drops below a preset minimum value, for example 7.5 volts. A safety circuit feature can be incorporated into the electronic circuitry as described above so that an alarm condition occurs if the sensor is disconnected or faulty. The electronic circuit disposed within the electrically conductive electronic housing 103 may be surrounded by a second holding material or support material 114 that also surrounds the battery 122.

Referring now to Figure 9, there is shown a cross-sectional view of the above-described embodiment of the invention. Figure 9 shows an area electromagnetic radiation monitor 100 in fixed position with a conductive shield 101 on which the housing 102 and the conductive electronics housing 103 are mounted. The hood 112, as shown, contains the sensor element 121 which is electrically coupled to the conductive electronics housing 103 via the lead 124. It can be seen from the drawing figure that a holder of graded lossy material 118, 119, 120 extends from the conductive shield 101 to the base or apex of the radiation sensor 121. In an alternative embodiment, a second battery 123 may be attached to the conductive shield 101 and surrounded by the support material. The second battery 123, which is shown in Figure 9, is a backup battery, if desired.

The sensor element 121 consists of orthogonally arranged thin-film resistance thermocouples similar to those used in the US Patents 3,641,439; 3,794,914 and 4,518,912 and similar to the arrangement described with respect to the personal electromagnetic radiation monitor. The higher frequency range of the fixed position area monitor is covered by the series arrangement as described in U.S. Patent 4,629,978. In particular, the apex of the thermocouples is positioned on the outer surface of the highest resistivity holder, which is then beveled or tapered at its outer edges. The bevel results in a wider angle of incidence for the reception of incoming energy, thereby eliminating or minimizing field distortion.

The response of the radiation sensor 121 is relatively independent of polarization or direction of propagation of the electromagnetic radiation, except when the energy propagates from a direction behind the sensor unit and through the conductive shield 101. The monitor 100 acts as an isotropic antenna which receives all electromagnetic energy within the space that lies on the side of the plane of the conductive shield surface occupied by the mount.

Although exemplary embodiments of the present invention have been described with reference to the accompanying drawings, it is to be understood that the invention is not limited to these particular embodiments and that other changes and modifications may be made by those skilled in the art without departing from the basic spirit of the invention.

Claims (23)

1. Device for monitoring electromagnetic radiation, comprising: a sensor of electromagnetic radiation (44; 121); a conductive shield (48; 101) spaced from the sensor from electromagnetic radiation; and a graduated holder made of dissipation material (46; 118, 119, 120), the holder being between the sensor of electromagnetic radiation (44; 121) and is interposed between the conductive shield (48; 101) and has a front surface (60; 118) directed in the direction of the electromagnetic sensor (44) and a rear surface (62; 120) facing away from it and directed in the direction of the conductive shield (48; 101); characterized in that the holder is gradually more conductive along its thickness from the front surface (60; 118) to the rear surface (62; 120), the device for monitoring electromagnetic radiation further comprising: a sound alarm transducer (6) connected to the electromagnetic radiation sensor (44; 121) and an earplug assembly (20) connected to the sound alarm transducer (6; 117) and not electrically conductive to prevent RF energy from being received by the earplug assembly (20) and radiated to the wearer's head. 2. An electromagnetic radiation monitoring device according to claim 1, wherein the electromagnetic radiation sensor (44) comprises a pair of mutually vertically arranged antenna members (52) coplanar with one another, each antenna member extending along a respective longitudinal axis and comprising an array of thin film resistance thermocouples (54) arranged along the axis and a plurality of spaced conductive elements (56) of discrete length arranged transversely to the axis of the array, each thermocouple (54) of each antenna member (52) being arranged between adjacent conductive elements (56). 3. An electromagnetic radiation monitoring device according to claim 1, further comprising a sheet (58) of insulating material disposed between the sensor (44) and the stepped holder of dissipative material (46). 4. An electromagnetic radiation monitoring device according to claim 1, wherein the graduated holder of dissipative material (46) comprises a laminate consisting of at least first (64) and second (66) layers of dissipative material having different resistances, the first layer (64) having a greater resistance than the second layer (66). 5. An electromagnetic radiation monitoring device according to claim 1, wherein the holder (46) is formed from a dissipative material that becomes continuously more conductive through its thickness from the front surface (60) to the rear surface (62). 6. An electromagnetic radiation monitoring device according to claim 1, further comprising a housing (2) in which the electromagnetic radiation sensor (44), the graduated holder made of dissipative material (46) and the conductive shield (48) are installed. 7. Device for monitoring electromagnetic radiation according to claim 6, in which the sound alarm transducer (6) is attached to one side of the housing; in which the housing has an attached fastening piece with elongated holes and hooks (22) which is mounted on the outer surface of the housing and positioned near the transducer (6); and wherein the non-electrically conductive earplug assembly (20) comprises an elongated air tube (24) having first and second ends facing away from each other, a pneumatic earplug (26) attached to the first end of the tube, and a receptacle (28) defining an internal cavity (30) located at the second end of the tube, the receptacle (28) having an opening (32) formed through its thickness and comprising a second attached fastening piece with slots and hooks (34) surrounding the opening (32) and capable of being coupled to the first applied fastening piece with slots and hooks (22) of the housing of the monitoring device to allow the receptacle (28) to be attached adjacent to the transducer (6), the pneumatic earplug (26) being connected to the transducer (6) via the air tube (24), the cavity and the opening as soon as the holder (28) is attached to the converter (6). 8. An electromagnetic radiation monitoring device according to claim 6, wherein the conductive shield (48) comprises first and second opposite sides, the holder made of dissipative material (46) being attached adjacent to the first side of the shield (48); and wherein the monitoring device further comprises an alarm circuit, the alarm circuit being attached to the housing (2) on the second side of the shield (48). 9. An electromagnetic radiation monitoring device according to claim 8, wherein the housing defines a battery compartment (40) located on the second side of the screen (48); and wherein the monitoring device further comprises a battery receptacle (70) located in the battery compartment (40) and a second graduated layer of dissipation material (76) located in the compartment (40) and at least partially surrounding the battery receptacle, the Dissipation material (76) becomes gradually more conductive along its thickness starting from a rear wall (18) of the housing (2) in the direction of the shield (48). 10. Device for monitoring electromagnetic radiation according to claim 9, in which the device for monitoring further comprises a block circuit and a light indicator (8) attached to the housing (2), the block circuit being connected to the alarm circuit and to the light indicator (8), the block circuit being designed such that the light indicator (8) lights up as soon as a predetermined radiation level is detected by the sensor (44), and further such that the light indicator (8) remains illuminated as soon as the radiation detected by the sensor (44) falls below a predetermined level. 11. An electromagnetic radiation monitoring device according to claim 1, wherein: the electromagnetic radiation sensor (44) comprises a pair of antenna members (52) arranged perpendicularly and coplanar to one another, each antenna member extending along a respective longitudinal axis and comprising an array of thin film resistance thermocouples (54) arranged along the axis and a plurality of spaced-apart conductive elements (56) of discrete length arranged transversely to the axis of the array, each thermocouple (54) of each antenna member being arranged between the adjacent conductive elements (56); the conductive shield has first and second opposite sides; the rear surface (62) of the stepped holder made of dissipative material (46) is directed towards the first side of the conductive shield (48); and in which the device for monitoring electromagnetic radiation further comprises: a housing (2), a sensor (44) and, wherein the graduated holder of dissipative material (46) and the conductive shield (48) are contained within the housing; the sound alarm transducer (6) mounted on a side of the housing, the housing (2) having an applied fastening piece with elongated holes and hooks (22) mounted on the outside of the side of the housing and positioned near the transducer (6); the non-electrically conductive earplug assembly (20) comprising an elongated air tube (24) having first and second ends facing away from each other, a pneumatic earplug (26) attached to the first end of the tube, and a receptacle (28) defining an internal cavity (30) provided at the second end of the tube, the receptacle (28) having an opening formed along its thickness and comprising a second applied fastening piece with slots and hooks (34) surrounding the opening, capable of being coupled to the first fastening piece with slots and hooks (22) of the housing of the monitoring device to allow the receptacle (28) to be attached adjacent to the transducer (6), the earplug (20) being in communication with the transducer (6) via the pneumatic tube (24). wherein the cavity and the opening rest against the transducer (6) when the holder (28) is attached; a light indicator (8) mounted on the housing (2); and an alarm circuit and a blocking circuit, the alarm circuit and the blocking circuit being mounted in the housing (2) adjacent to the second side of the screen (48), the alarm circuit being connected to the transducer (6) and being designed such that the transducer (6) emits an audible tone when a predetermined radiation level is detected by the sensor (44) wherein the block circuit is designed such that the indicator light (8) lights up when the predetermined radiation level is detected by the sensor (44), and is further designed such that the indicator light (8) remains illuminated as soon as the radiation detected by the sensor (44) decreases in magnitude to below the predetermined level; wherein the housing defines a battery compartment (40) lying on the second side of the screen (48), the monitoring device further comprising a battery receptacle (70) and a second, graduated holder of dissipative material (76) located in the battery compartment and at least partially surrounding the battery receptacle, the dissipative material (76) becoming gradually more conductive along its thickness from the rear wall (18) of the housing (2) towards the screen (48). 12. An electromagnetic radiation monitoring device according to claim 1, wherein the electromagnetic radiation sensor (121) comprises three mutually perpendicular antenna members (52), each antenna member extending from an apex formed in the region of the front surface of the holder and comprising an array of thin film resistance thermocouples (54) arranged along the axis of each antenna member (52) and a plurality of spaced apart conductive elements (56) of discrete length arranged transversely to the axis of the array, each thermocouple (54) of each antenna member (52) being arranged between adjacent conductive elements (56). 13. An electromagnetic radiation monitoring device according to claim 1, wherein the graduated holder of dissipation material (46; 118, 119, 120) comprises a laminate formed by at least first (118), second (119) and third (120) layers of dissipation material having different resistivities, the first layer (118) having a resistivity greater than that of the second layer (119), the second layer (119) has a specific resistance which is greater than that of the third layer (120). 14. An electromagnetic radiation monitoring device according to claim 13, wherein the first (118), second (119) and third (120) layers have volume resistivities of substantially 15 kΩ per cubic centimeter, 600 kΩ per cubic centimeter and 150 kΩ per cubic centimeter, respectively, and surface resistivities of substantially 20 kΩ per square centimeter, 2 kΩ per square centimeter and 500 kΩ per square centimeter, respectively. 15. An electromagnetic radiation monitoring device according to claim 1, further comprising an electronic monitoring section having an alarm circuit and a housing (102) attached to the conductive shield (101) in which the sensor (121) and the stepped holder (46; 118, 119, 120) of dissipative material are arranged, the electronic monitoring section being contained in an electronically conductive sheath (103) and mounted on the conductive shield (101) adjacent to the housing (102); wherein the monitoring device further comprises a visual alarm transducer (116) and an alarm test button (115), all attached to the electronic conductive sheath (103). 16. An electromagnetic radiation monitoring device according to claim 15, wherein the housing (102) is a continuous cast rectangular shape comprising an upper body portion and four sides, the first side (107) abutting the electronic conductive shell (103), the second (104), third (105) and fourth (106) sides abutting the edges of the conductive shield (101) and being arranged perpendicularly; and wherein the upper housing portion comprises three tapered sections (108, 109, 110) tapering upwardly at an angle from each of the second (104), third (105) and fourth (106) sides each tapered portion being located near a level portion (111) of the upper housing part on which a cylindrical nose (112) is arranged, the level portion (111) of the upper housing part also being located near the first side (107). 17. An electromagnetic radiation monitoring device according to claim 15, wherein the electronically conductive enclosure (103) comprises a battery compartment (113) for mounting a battery (122), and wherein the battery compartment (113) further comprises a battery receptacle located therein and a second stepped holder (114) made of dissipative material arranged in the battery compartment (113) to at least partially surround the battery receptacle. 18. An electromagnetic radiation monitoring device according to claim 17, wherein the monitoring device further comprises a blocking circuit mounted on the housing, the blocking circuit being connected to the alarm circuit and to the visual alarm transducer (116), the blocking circuit being designed such that the visual alarm transducer (116) is activated as soon as a predetermined level of electromagnetic radiation is detected by the sensor (121) and further being designed such that the visual alarm transducer (116) remains activated when the radiation level detected by the sensor (121) falls below a predetermined level. 19. An electromagnetic radiation monitoring device according to claim 1, wherein: the electromagnetic radiation sensor (121) comprises three mutually perpendicular antenna members (52) extending from an apex, each antenna member extending along a respective longitudinal axis and comprising an array of thin film resistance thermocouples (54) arranged along the axis, and a plurality of conductive elements (56) spaced apart by a discrete length and arranged transversely to the axis of the array are arranged, each thermocouple (54) of each antenna member (52) being arranged between the adjacent conductive elements (56); the conductive shield (101) has first and second opposite sides; the rear surface (62) of the stepped holder made of dissipative material (118, 119, 120) is directed towards the first side of the conductive shield (101), and wherein the device for monitoring electromagnetic radiation further comprises: an electronically conductive sheath (103) attached to the conductive shield (101); a housing (102), the sensor (121) and the graduated holder of dissipation material (46; 118, 119, 120) contained in the housing and attached to the conductive shield (101), at least one side of the housing being adjacent to the electronically conductive sheath (103); the sound alarm transducer (117) attached to the electronically conductive sheath; a visual alarm (116) attached to the electronically conductive cover (103); and an alarm circuit and a block circuit, the alarm circuit and the block circuit being incorporated in the electronically conductive casing (113), the alarm circuit being connected to the acoustic alarm transducer (117) and being adapted to cause the acoustic alarm transducer (117) to emit an audible tone when a predetermined radiation level is detected by the sensor, the block circuit being adapted to cause the visual alarm transducer (116) to illuminate when the predetermined radiation level is detected by the sensor (121) is detected, and further designed such that the visual alarm transducer (116) remains illuminated when the radiation level detected by the sensor (121) decreases in magnitude to below the predetermined level; and wherein the electronically conductive casing (103) has a battery compartment (1:13) located therein, and wherein it further has a battery receptacle, and the casing (103) has a second, stepped holder (114) made of dissipative material located in the battery compartment (113) and at least partially surrounding the battery receptacle, wherein the dissipative material gradually becomes more conductive along its thickness in the same manner as in the holder (118, 119, 120). 20. An electromagnetic radiation monitoring device according to claim 15, wherein the alarm circuit provides a low battery warning via the sonic alarm transducer (117) indicating that the battery associated with the monitor is operating at a low level. 21. An electromagnetic radiation monitoring device according to claim 17, further comprising a second battery (B2) for powering the visual alarm transducer (116) attached to the electronically conductive sheath (103). 22. An electromagnetic radiation monitoring device as claimed in claim 1, wherein the electromagnetic radiation sensor (121) comprises a pair of mutually perpendicular antenna members (52), each antenna member extending from an apex formed near the front surface of the holder and comprising an array of thin film resistance thermocouples (54) arranged along the axis of each antenna member (52) and a plurality of spaced apart, discrete length conductive elements (56) arranged transversely to the axis of the array, each thermocouple (54) of each antenna member (52) being arranged between adjacent conductive elements (56). 23. An electromagnetic radiation monitoring device according to claim 1, wherein: the electromagnetic radiation sensor (121) comprises a pair of mutually perpendicular antenna members (52) extending from a vertex, each antenna member extending along a respective longitudinal axis and comprising an array of thin film resistance thermocouples (54) arranged along the axis and a plurality of spaced apart conductive elements (56) of discrete length arranged transversely to the axis of the array, each thermocouple (54) of each antenna member (52) being arranged between the adjacent conductive elements (56); the conductive shield (101) has first and second opposite sides; the rear surface (62) of the stepped holder made of dissipative material (118, 119, 120) is directed towards the first side of the conductive shield (101); and in which the device for monitoring electromagnetic radiation further comprises: an electronically conductive sheath (103) attached to the conductive shield (101); a housing (102), the sensor (121) and the graduated holder of dissipation material (46; 118, 119, 120) contained in the housing and attached to the conductive shield (101), at least one side of the housing being adjacent to the electronically conductive sheath (103); the sound alarm transducer (117) attached to the electronically conductive sheath; a visual alarm (116) attached to the electronically conductive cover (103); and an alarm circuit and a block circuit, the alarm circuit and the block circuit being incorporated in the electronically conductive enclosure (103), the alarm circuit being connected to the acoustic alarm transducer (117) and being arranged such that the acoustic alarm transducer (117) emits an audible tone when a predetermined radiation level is detected by the sensor, the block circuit being arranged such that the visual alarm transducer (116) illuminates when the predetermined radiation level is detected by the sensor (121), and further being arranged such that the visual alarm transducer (116) remains illuminated when the radiation level detected by the sensor (121) decreases in magnitude below the predetermined level; and wherein the electronically conductive casing (103) has a battery compartment (113) located therein and further comprises a battery receptacle, and wherein the casing (103) has a second graduated holder (114) made of dissipative material arranged in the battery compartment (113) and at least partially surrounding the battery receptacle, the dissipative material gradually becoming more conductive along its thickness in the same way as in the holder (118, 119, 120).