EP0346428A1 - Amperemetre haute frequence et dosimetre personnel - Google Patents

Amperemetre haute frequence et dosimetre personnel

Info

Publication number
EP0346428A1
EP0346428A1 EP89900711A EP89900711A EP0346428A1 EP 0346428 A1 EP0346428 A1 EP 0346428A1 EP 89900711 A EP89900711 A EP 89900711A EP 89900711 A EP89900711 A EP 89900711A EP 0346428 A1 EP0346428 A1 EP 0346428A1
Authority
EP
European Patent Office
Prior art keywords
coil
invention according
current
shield
conductor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP89900711A
Other languages
German (de)
English (en)
Other versions
EP0346428A4 (en
Inventor
Mark J. Hagmann
Tadeusz M. Babij
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Florida International University FIU
Original Assignee
Florida International University FIU
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from US07/120,076 external-priority patent/US4913153A/en
Priority claimed from US07/122,201 external-priority patent/US4897600A/en
Application filed by Florida International University FIU filed Critical Florida International University FIU
Publication of EP0346428A1 publication Critical patent/EP0346428A1/fr
Publication of EP0346428A4 publication Critical patent/EP0346428A4/en
Withdrawn legal-status Critical Current

Links

Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/05—Detecting, measuring or recording for diagnosis by means of electric currents or magnetic fields; Measuring using microwaves or radio waves 

Definitions

  • This invention relates to apparatus for detecting a high frequency current in a conductor. and more particularly to such apparatus which is placed around the conductor and uses the magnetic field produced by the high frequency current to measure the current without perturb ing the ambient electric and magnetic fields.
  • Dosimetry is determining the amount of energy absorbed under various conditions. Dosimetry is much more difficult for nonionizing electromagnetic energy than it is for ionizing radiation because, unlike ionizing radiation, the absorbed dose is not simply related to the incident flux. The absorption of electromagnetic energy is dependent upon the dimensions, composition and posture of the body, as well as the frequency, polarization, and other properties of the radiations. Generally the most intense exposure occurs under near-field conditions, where the electric and magnetic fields are not simply related and where it is often difficult to accurately characterize the source.
  • a ferromagnetic core having cross-sectional area A and permeability ⁇ may be formed to make a closed loop of length L. If the core has a high permeability, the flux within the core at any part of the loop is related to the current passing through the aperture enclosed by the loop, according to the following equation:
  • a coil consisting of N turns may be wound around the core at any location on the loop and the potential induced on the coil is given by the equation:
  • Equation 3 can be used to determine the current I from the potential V measured across the coil. This principle has been used in clamp-on ammeter instruments for many years. These devices allow the measurement of a . c . current in power circuits without cutting the lines and interrupting service. Current probes are also commercially available, which serve as transducers to be used with separate meters, oscilloscopes, or other measuring instruments. These probes have either a clamp-on design, which opens for placement around the conductor, or a fixed configuration which requires that the conductor be passed through the central aperture.
  • Active microwave imaging methods have also been used to obtain approximate images of inhomogene ⁇ us dielectric objects. For example, see Pichot et al "Active Microwave Imaging of Inhomogene ⁇ us Bodies", IEEE Transactions on Antennas and Propagation, Vol. AP-33 pages 416-425 (April 1985). Related methods could be used to determine the distribution of current within the body from non-invasive measurements. Other procedures based on moment method calculations, have also been considered for use in non-invasive measurements of the human body, and results of mathematical modeling suggest that it would be possible to use them to determine the specific absorption rate (SAR) of energy dis position. Each of these methods is quite complex, requiring computations based upon accurate measurements with special purpose probes. They do not appear suitable for use as a personal dosimeter at the present time.
  • SAR absorption rate
  • a current detector for detecting high frequency currents flowing through an object.
  • the detector includes a conductor wound in multiple turns around a substantially closed loop core and has a loop having an aperture greater than the corresponding dimensions of the object to be measured.
  • the detector is characterized by the conductor being a high resistivity material, by the core being non-ferromagnetic and by the ratio of the turns spacing to the core cross-sectional area being constant at any given point along the loop.
  • a detector for non-invasively determining the specific absorption rate of high frequency electromagnetic energy in an animal body subjected to such radiation by measuring the electric current flowing through the body as a manifestation of the specific absorption rate.
  • the detector is characterized by current detector means, including a helical coil of electrical conductor material having two ends and a lead extending from each end, by flexible means for containing the current detector means and for being affixed around a portion of the body so that the two ends are substantially juxtaposed to one another to form a closed loop coil around the body portion, and by means coupled to the leads for detecting the voltage induced in the coil by the current flowing through the body.
  • a method for detecting aberrant heating in an animal body undergoing an application of electromagnetic energy is characterized by the steps of placing a current detecting probe, which does not significantly perturb the electromagnetic energy, around at least one portion of the body, by monitoring the probe for an indication of voltage induced in the probe in excess of a certain threshold as manifestation of aberrant heating, and by affecting the application of the energy to reduce the aberrant heating, in response to the indication.
  • Figure 1 shows a patient undergoing a hyperthermic treatment for cancer
  • Figure 2 shows a personal dosimeter device useful for measuring the current through the patient shown in Figure 1;
  • Figure 2A is a cross-section taken across lines 2A-2A of Figure 2;
  • FIG. 3 shows another embodiment of the personal dosimeter device of the subject invention.
  • Figure 4 shows a general manner in which the personal dosimeter device, shown in Figure 3, can be affixed around an object for measuring high frequency current flowing therein; and Figure 5 shows yet another embodiment of the personal dosimeter device of the subject invention.
  • a solenoidal winding having N uniformly spaced turns with crass-sectional area A may be formed into a closed loop of length L . If the coil is formed around a non-ferromagnetic core, such as air (permeability H ⁇ ), then the flux within the core at any point along the coil is given by (4) The potential induced in this coil is then (5) Using Ampere's law, the potential is (6) Equation (6) may be use to determine the current I from the potential V measured across the coil.
  • a non-ferromagnetic core such as air (permeability H ⁇ )
  • the ANSI committee has not yet made recommendations for frequencies below 0.3 MHz, but it appears that the hazard from shock or burns at the lower frequencies is directly related to the electric current, rather than the SAR.
  • the present invention appears especially appropriate for use at these lower frequencies because the measured parameter is electric current.
  • Another possible application, of the present invention would be a personal dosimeter device that could be fabricated as a part of a belt to be affixed over the clothing of utility workers, in order to quantify the intensity of possible electrical shock.
  • Values of the "let-go" current have been specified as safety criteria for use at power-line frequencies.
  • Values of the SAR can be calculated from non-invasive measurements of current and published values for the dielectric proper ties of tissue. The ANSI recommended limit of peak SAR could be enforced if local values were approximated in this manner.
  • both modeling experiments and computer simulations have show that, when a pet son 10 is exposed to electromagnetic energy, such as from a high frequency applicator device 12, the energy absorbed by the body is greatest when the electric field vector is parallel to the length of the body; this is known as E-polarization.
  • E-polarization there is an electric current I that follows vertically through the body such that the current at one location is related to the current at other locations.
  • the dosimeter 14 of the present invention may be used to determine the current I at a convenient location, such as a leg or an ankle.
  • a larger dosimeter 15 may be attached around the area of a person 10 receiving treatment, such as the abdomen. Published values of the dielectric properties of tissue can be used with these measurements to determine the approximate SAR in the treated area, as well as other parts of the body.
  • the dosimeter 14 of the present invention may be effectively used to determine the longitudinal flow of current I through vari g ous parts of the body, since it is insensitive to azimuthal or other circulating current. Since the aberrant heating during hyperthermia treatment is generally due to the axial flow of current in various narrow bodily regions (e.g. the neck, arms, and legs), dosimeter 14 is useful as a tool for indicating such aberrant heating.
  • a personal dosimeter such as dosimeter 14 in Fiqure 1
  • dosimeter 14 in Fiqure 1 may be used to determine and store the currents induced as a result of the exposure. Later the stored values may be retrieved and used to approximate the SAR throughout the body for that worker. If the approximate SAR exceeds a threshold, corrective action will be required. Local values of SAR determined for the leg or ankle are particularly of interest, since the peak value often occurs in these regions.
  • several personal dosimeter devices 14 may be used at different parts of the body.
  • the principle of the present invention is related to that used in commercial clamp-on a . c . ammeters and current probes. However, these instruments have not been used in dosimetry and it appears that they do not satisfy some of the requirements which are essential for proper implementations of the present invention.
  • the most siqnificant difference between the present invention and the available devices is that the available devices all perturb the field which induce the current being measured, thereby rendering inaccurate any reading obtained.
  • Another difference between the present invention end the prior art is that the present invention permits a significantly larger apertures so that the device can surround the body at the waist, or another location, instead of only enclosing a wire.
  • the larqe size required for the winding of a conventional clamp-on ammeter can cause increased problems from self resonance of the device. These problems have been overcome in dosimeters 14 and 15 by reducing the Q-factor through loading. Another difference is that existing clamp-on ammeters require a ferromagnetic core, which should be avoided in order to reduce the weight of the dosimeter, as well as to avoid the errors caused by saturation and dependence of permeability on frequency. The use of ferromagnetic cores must further be limited to use with low frequencies, where the added gain from large relative permeability is desirable. Even in these applications, such as a shock-hazard monitor for utility workers, a dosimeter device should have low weight and be flexible and adjustable so that it can be incorporated and easily affixed around the body without undue discomfort.
  • a personal dosimeter 20 including in a transducer 22 and a detector 24, is shown, which can measure the current I, shown in Figure 1.
  • the detector 24 may be any conventional high impedance voltage detector, and any digital readout or storage devices desirably attached thereto.
  • Transducer 22 includes a coil 26 surrounding a central aperture 28 through which an abject 30 passes.
  • Object 30 may be a body limb or other conductor through which current passes.
  • Coil 26 is formed by winding a high resistance conductor 32 around a non-ferromagnetic material, such as air core 34. Because the air core 34 has a low permeability, at each point of coil 26 the ratio of the turn spacing between adjacent turns of conductor 32 and the cross- sectional area of air core 34, at that point, should be constant. This constant ratio of turn spacing to cross sectional area is desirably maintained over the entire length of coil 26. The reason for this is to permit equal sensitivity at any, position within aperture 28. In other words, object 30 may be positioned anywhere in aperture 28 and the same results will be obtained.
  • the requirement for a constant turns spacing to area ratio is not necessary if a ferromagnetic core is used, because a constant flux is maintained at all points in the ferromagnetic core.
  • the core 34 must have a low permeability, such as air, in order to allow measurement of the induced high frequency currants normally associated with diathermy and hyperthermic treatments, so as not to perturb the inducing field.
  • An air, or other flexible low permeability material, core further has the advantage that the coil 26 is flexible and can fit around the conductor 30 in an non- circular fashion.
  • the dosimeter 20 is positioned around the ankle area of the person.
  • the coil 26 would tend to be more elliptical than circular. This is particularly advantageous so that the length of the coil 26 can be made greater than the circumference around the ankle, or other location of measurement, which vary substantially from patient to patient.
  • High resistivity conductor 32 should have a volume resistivity such that the ratio of the volume resistivity to the thickness or diameter of conductor is in the range of 1000 ohms to 1,000,000 ohms and preferable about 100,000 ohms.
  • the material of conductor 32 may be, for example, carbon loaded Teflon or conductive rubber materials.
  • the purpose for using a high resistivity conductor 32 is to prevent or inhibit the perturbance of any existing electric fields which are in the area. Ideally, the windings 32 over the air core 34 will only respond to the magnetic field from the conductor 30 in the aperture 28. This magnetic field will be generated due to the current I flowing through conductor 30, and as previously discussed, relates to the SAR from applicator 12.
  • the high resistivity of the windings formed by conductor 32 also prevents false readings due to perturbance of the current inducing fields.
  • an electrostatic a shield 36 of a high resistivity material is wrapped around the coil 26.
  • a gap 38 in shield 36 extends entirely along the closed loop of coil 26.
  • the purpose of gap 38 is to permit only magnetic coupling through the shield. It may be one millimeter in width.
  • shield 36 may be made of carbon loaded Teflon material or conductive rubber material.
  • the ratio of the volume resistively to the thickness of the material of shield 36 ideally should be 100,000 ohms, but may be within the range of 1,000 ohms to 1,000,000 ohms.
  • the presence of shield 36 as well as the constant ratio of turns spacing to cross sectional area, previously discussed, permits object 30 to be positioned at any point within the aperture 28 of coil 26 and still obtain substantially the same reading.
  • a space 40 is left between the inner surface of shield 36 and the outer surface of the conductors 32 forming coil 26.
  • the space 40 is required to reduce the self-capacitance of the coil 26, thereby increasing the sensitivity and frequency responses of device 22.
  • a distance of between two and three millimeter may be used for space 40.
  • leads 46 and 48 are coupled to the high impedance voltage detector 24 by high resistivity leads 46 and 48, which are also contained in a shield 50.
  • Device 22 includes inductance due to the winding of coil 26, capacitance due to the coupling of coil 26 to shield 36 and the coil 26 self capacitance and resistance from conductor 32, thereby creating and RLC resonant circuit.
  • the sensitivity of device 22, as a result of this resonant circuit, is strongly dependent an frequency, unless the quality factor (Q) is reduced to ten or less.
  • Reduction of Q may be accomplished by adding a register 52, which may be 1000 ohms, in parallel with coil 26. Alternatively, a resister of typically ten ohms may be added in series with coil 26.
  • the high resistivity material of conductor 32 which is preferably used, may reduce the Q factor sufficiently to permit stable operation without the use of additional resistors. However, for certain application, a further reduction in Q may be required and a resister, such as resistor 52, will be required.
  • a diode 53 may be added to rectify the coil 26 output voltage.
  • the external circuit capacitances act as a smoothing capacitor, thereby providing a d.c. voltage, which is attenuated much less, to be provided over leads 46 and 48 to detector 24.
  • the siqnal to noise ratio may be improved when it is possible to modulate the source of the radiation, and add a filter to detector 24.
  • a belt dosimeter 60 is shown, in which the structure, described in detail above with respect to Figure 2, is fabricated into a belt arrangement adapted to be strapped around an object, such as the ankle or knee of a person, for use in either Figure 1 type environment or for use as a personal dosimeter by a person working in a potentially hazardous electromagnetic enerqy environment.
  • the belt dosimeter 60 device may also be strapped around any other type conductors, where the current therethrough is desired to be measured.
  • Belt dosimeter 60 includes a high resistivity coil 62 surrounding an air core 64 in the manner described above in respect to Figure 2. Extending from one end of dosimeter 60 is a portion 66 of a connector, such as the hooks side of hook and loop type fastener, such as Velcro. The other portion 68 of the connector is shown in dash lines as being on the opposite end of coil 62 and may be the loop portion of the hook and loop type fastener. Connector portion 68 may be positioned above the shield material 70 surrounding coil 62 and aligned to mate with portion 66 when the two coil 62 ends are fastened together to form a closed coil 62.
  • a connector such as the hooks side of hook and loop type fastener, such as Velcro.
  • the other portion 68 of the connector is shown in dash lines as being on the opposite end of coil 62 and may be the loop portion of the hook and loop type fastener.
  • Connector portion 68 may be positioned above the shield material 70 surrounding coil 62 and aligned to
  • each end of coil 62 Extending from each end of coil 62 is respective leads 72 and 74, which are adapted to be inserted along a lead shield 76 when portion 66 is affixed to portion 68 of the fastener.
  • Means may be including for attaching a shield 76 to the assembled closed loop forming dosimeter 60 when portion 66 is affixed to portion 68.
  • the two portions of the connector 66 and 68 should be arranged so that when portions 66 is affixed to portions 68, leads 72 and 74 are separated from one another by the same spacing as between turns forming coil 62.
  • shield 70 In order to make coil 62 sufficiently flexible for being formed into a closed loop around a conductor, shield 70 should be a flexible material, such as conductive rubber.
  • the circumference of coil 62 should be less than the wavelength of the frequency being measured, but experiments have shown that it is usable with acceptable error up to three times the wavelength frequency.
  • clamp-on ammeter 90 operating according to the principals of the subject invention is shown.
  • Ammeter 90 includes a coil 92 and a pair of leads 94 and 96 extending back from the ends 98 and 100 of coil 92.
  • the ends 98 and 100 should be spaced apart so that the exiting point for leads 94 and 96 are spaced from one another by an amount substantially the same as the distance between adjacent turns on coil 92.
  • Leads 92 and 94 may be buried beneath the flexible shield 99 of coil 92 and extend through a main handle 102 from which they exit and are applied to a detector, such as the high impedance voltage detector 24 shown in Figure 2.
  • a second handle 104 is also provided and angularly spaced apart from main handle 102. When handle 104 is rotated toward handle 102, the ends 98 and 100 of coil 92 are separated, as shown in the dashed lines, and the conductor to be tested may be inserted into the aperture 106 defined by coil 92. When handle 104 is released, the spring tension of coil 92 reposi tions dosimeter 92 to the configuration shown by the solid lines of in Figure 5.
  • Additional springs may be positioned between handles 102 and 104 to assist in the closure of clamp-on ammeter 90.
  • one may use any of the dosimeters described with respect to Figures 2 through 5 to measure the current I flowing through the leg of patient 10. It can be expected that the current I through the leg of patient 10 will manifest the aberrant heating caused by the energy from applicator 12.
  • a dosimeter 14 is placed at various places along the extremities of person 10. As seen in Figure 1, dosimeter 14 is placed around the ankle of person 10. Other similar dosimeters may be placed at other places along the legs, arms or neck of person 10 to monitor the aberrant heating.
  • the physician or technician may adjust the position of the limbs, or change the frequency of energy from applicator 12 or change the focal point of the applicator 12, energy.
  • the clamp-on dosimeter 90 shown in Figure 5 may be moved along each limb to monitor for aberrant heating. Dosimeter 15 is placed around the abdomen of person
  • Dosimeter 15 is intended to monitor the SAR in the region being treated rather than monitor aberrant heating. Where the reading on detector 24 is to low, it may indicate insufficient energy is being applied or that applicator 12 is not properly focused. If the reading from dosimeter is too high, the energy applied by the applicator 12 should be reduced.

Abstract

Un détecteur (14, 15, 22, 60 ou 90) permettant de détecter un courant haute fréquence (I) comporte une bobine à résistivité élevée (26) enroulée autour d'un noyau non ferromagnétique (34). Le rapport de l'espacement de la bobine (26) à la superficie de section de celle-ci est maintenu constant sur la longueur de ladite bobine. Un blindage (36) en matériau de haute résistivité entoure la bobine (26) dont il est espacé et présente un entrefer (38) orienté le long d'un azimut de l'enroulement en boucle fermée et dirigé de manière orthogonale par rapport au sens courant de réseau du courant induit dans la bobine (26). Les extrémités de cette dernière sont couplées à un détecteur de tension à impédance élevée (24) par l'intermédiaire de fils à haute résistivité (46 et 48), et une résistance (52) est couplée entre les fils (46 et 48) afin de réduire le facteur de surtension. Le détecteur de courant (14, 15, 22, 60 ou 90) peut être utilisé pour détecter du courant (I) circulant dans un corps humain (10) par suite de l'absorption d'un rayonnement incident haute fréquence, en vue d'indiquer le taux d'absorption spécifique d'un tel rayonnement.
EP19890900711 1987-11-13 1988-11-08 High frequency ammeter and personal dosimeter Withdrawn EP0346428A4 (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US120076 1987-11-13
US07/120,076 US4913153A (en) 1987-11-13 1987-11-13 Personal dosimeter
US07/122,201 US4897600A (en) 1987-11-13 1987-11-13 High frequency ammeter
US122201 1987-11-13

Publications (2)

Publication Number Publication Date
EP0346428A1 true EP0346428A1 (fr) 1989-12-20
EP0346428A4 EP0346428A4 (en) 1991-06-05

Family

ID=26818037

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19890900711 Withdrawn EP0346428A4 (en) 1987-11-13 1988-11-08 High frequency ammeter and personal dosimeter

Country Status (2)

Country Link
EP (1) EP0346428A4 (fr)
WO (1) WO1989004632A1 (fr)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20190021958A (ko) * 2017-08-24 2019-03-06 한국표준과학연구원 인체모사 팬텀 및 mri 스캐너의 sar 값을 획득하기 위한 방법

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2737661B2 (ja) * 1994-09-21 1998-04-08 日本電気株式会社 Ｓａｒ測定方法およびｓａｒ測定装置
WO1996035371A1 (fr) * 1995-05-10 1996-11-14 Ackermann Patent Gmbh Systeme de mesure et procede permettant de mesurer les tensions alternatives induites au niveau du corps humain par electrosmog
JP2790103B2 (ja) * 1995-12-15 1998-08-27 日本電気株式会社 比吸収率測定装置及び比吸収率測定方法

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GB2088568A (en) * 1980-11-14 1982-06-09 Central Electr Generat Board A transducer for an alternating current measuring device
EP0165835A1 (fr) * 1984-05-21 1985-12-27 Merlin Gerin Capteur de courant à noyau amagnétique
EP0207729A2 (fr) * 1985-06-28 1987-01-07 Bsd Medical Corporation Antenne pour une disposition interstitielle
US4659984A (en) * 1984-12-06 1987-04-21 Doss James D Passive integrating electromagnetic field dosimeter

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FR2167392B1 (fr) * 1972-01-14 1974-06-21 Anvar
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Publication number Priority date Publication date Assignee Title
GB2088568A (en) * 1980-11-14 1982-06-09 Central Electr Generat Board A transducer for an alternating current measuring device
EP0165835A1 (fr) * 1984-05-21 1985-12-27 Merlin Gerin Capteur de courant à noyau amagnétique
US4659984A (en) * 1984-12-06 1987-04-21 Doss James D Passive integrating electromagnetic field dosimeter
EP0207729A2 (fr) * 1985-06-28 1987-01-07 Bsd Medical Corporation Antenne pour une disposition interstitielle

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See also references of WO8904632A1 *

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20190021958A (ko) * 2017-08-24 2019-03-06 한국표준과학연구원 인체모사 팬텀 및 mri 스캐너의 sar 값을 획득하기 위한 방법

Also Published As

Publication number Publication date
WO1989004632A1 (fr) 1989-06-01
EP0346428A4 (en) 1991-06-05

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