Triaxial Induction (Search-coil) Magnetic Field Sensor of an Ultimate Sensitivity for Measurement of the Environmental, Industrial, and Biological Signals
ABSTRACT- An object of the present proposal provide an improvement in search-coil type sensors. It is a further object of the present proposal to provide lightweight metallic glass antenna (pickup coil- PC) for detecting AC magnetic fields both generated by natural- and man-made sources including outer space wave activity (ionospheric noise signals). The sensor has an improved effective height characteristic in the frequency range from 0.2 Hz to 16 kHz. An induction sensor is a device that measures fluctuating magnetic fields (MFs) and comprises a magnetic antenna and associated electronics therefor. When used on sounding rockets or on spacecraft, search-coils are typically mounted on a boom in order to escape the electronic noise generated by other scientific instruments and/or subsystems in the immediate vicinity.
A lightweight search-coil antenna or sensor assembly for detecting magnetic fields and including a multi-turn electromagnetic induction coil wound on a spool type coil form through which is inserted an elongated coil loading member comprised of mu-metal rod or metallic glass material stripes wrapped around a dielectric rod. The stripes have a special shape which allows the reduction of eddy currents twice. This leads to rising the sensor’s sensitivity to the same degree. The maiden core has a length which is relatively larger than its thickness, so as to provide a large length-to-diameter ratio for its considerable relative permeability.
It is necessary to lay down the fundamentals of non-contact passive FMs. It is based on the effect of creating the vortical MF by ionized particles of the substances. This MF is transduced into the measurable voltage by the torus-like PC of the induction (search-coil) sensor/transducer (IS). Non-contact passive measuring of the said substances and tissues is possible by using the induction sensor with solenoidal and/or toroidal PC which will embrace the flow. These coil(s) can be both room-temperature and superconducting with connection to either common or superconducting FET. The measured quantities are: 1) vortical MF of gasiform stream for the toroidal PC, and 2) variation of the surrounding (natural) MF according to the magnetohydrodynamical effect for the solenoidal PC.
Most brain–computer interfaces (BCIs) for human subjects rely on non-invasive MEG signals; i.e., the electrical brain activity recorded from PCs placed above the scalp. These principles include the development of hybrid BCI architectures, the design of user–machine adaptation algorithms, the exploitation of users’ mental states for BCI reliability and confidence measures, the incorporation of principles in human–computer interaction to improve BCI usability, and the development of novel BCI technology including better MEG devices. The measuring method and necessary performance data of the sensor for the driver’s monitoring according to the emanating MF with BMI in order to obtain output signals from brain to the measurement system and coverting monitoring results into information for machine operation or environmental control.
I. An IS configuration according to a first version of the device which is comprised of induction coil (PC) inserted into casing. PC consists of many turns of electrically conductive wire wound on a dielectric coil form which is in the form of a spool of a circular cross section and having a central circular aperture or opening. Through this aperture is inserted an elongated sensor coil loading device. The coil is connected
parallel to the PA. The loading device has a length which is greater than the width of the spool so that it projects through the circular opening and extends a predetermined distance outward from each side.
Typically the width of the induction coil is in the order of 8.0 in., and comprises twenty- thousand turns of wire providing a diameter of 0.06 in. The loading
device, for example, is at least 10 in. long and has a diameter of 0.4 in. A relatively high length to diameter ratio structure is provided thereby and it may be of any
length as long as it accords with design. The amplifier typically comprises some instrument amplifier which has high common mode rejection characteristics for enhanced signal to noise performance. The flat transfer function is created by current or magnetic flux feedback loops.
The three ISs compose one vector device. The MF parallel to the coil axis is detected with this sensor. The integrated sensor consists of a 20 thousand turns PCs through which is inserted an elongated sensor coil loading device. The mechanical design of the base enables it to endure all the g-loads during starting. The overall size of the IS is 210×210×210 mm3. The device is mounted on a triangle base made of dielectrical composition materials. Three devices are attached to three adjacent surfaces of the
mount cut from a cube in order to keep the sensors perpendicular to each other.
A second version of the device comprised of a triaxial metal1ic glass search-coil assembly for measuring field strength
along three mutually perpendicular X, Y and Z axes (Cartesian coordinates). As shown, the assembly includes three substantially identical magnetic antenna structures: 1x, 1y and 1z. They are oriented in an orthogonal configuration, comprising a triangle base including three dielectrical boxes 2x, 2y and 2z with PAs. Three head sensors are attached to the surfaces of a corner cut from a cube so that they are located perpendicular to each other.
II. Among the variety of MF sensors/transducers there are two passive ones of high sensitivity: IS and SQUID devices. Non-contact passive measuring of the said substances and tissues is possible by using only the IS with solenoidal and/or torus-like PCs which will embrace the flow. These coil(s) can be both room temperature and superconducting with connection to either common or superconducting FET. The measured quantities are: 1) vortical MF of gasiform stream for the torus-like PC, and 2) variation of the surrounding MF according to the magnetohydrodynamical (MGD) effect for the solenoidal PC. The said measured quantities caused by the electrogaseodynamical jet or MGD flow. The invented transducer can be applied in the flowmeters (FMs) of gasiform and friable substances and liquid mediums. Measured MF interferes with the surrounding one. The variations of measured MF strength Hfl 1 of the stream or flow as a result of subtraction which corresponds linearly to the difference of the respective output voltages of the transducer(s).
The method of measuring the volume flow of liquids and gaseous or friable substances by defining their interaction with only ambient natural MF. The first device based on such method is a passive and non-contact FM gaseous or friable substances includes a resistive or superconducting torus-like PC of an IS which is PC-placed around the jet-flow. The second one is a FM of liquids and organic tissues (a blood) or a counter of the ferromagnetic particles into this mediums, consists of the same IS, but with solenoidal-shape PC. As a result of such arrangement, the measuring device is setting up without a failure of the communications pipes and interrupting in their functioning. The absence of a measuring device or any moving members will considerably raise the safety factor in service due to isolation of the flows from potentially combustible substances. Also, gives us the possibility to avoid any influence on the measuring substance, including the danger of changing its chemical or physical composition.
One of the main mechanisms of gases ionization is their interaction with the surface of the solid body, i.e. surface ionization. As a result of such interaction arouses an electrogaseodynamical flow. This flow absorbs by the torus-like PC of an IS. It is necessary to notice, that an acquired value of MF strength will be generated outside the pipe only when it is made of the paramagnetic material. In the case of diamagnetical, and especially ferromagnetical metal or alloy, it is measuring of some residual value occurs.
The performance of the FM of volume movement of these liquid substances and tissues laid down on measuring the variations of ambient MF strength will cause to pull it along with a moving medium which the strength crosses. Let us consider the MGD foundations of this phenomenon. For the liquid that moving between two nonconducting walls in the direction of this motion the partial of the MF induction is arise: It is possible to do counting/registration of the changes of the volumes by summation of the momentum, relative to B0, values of Bx (MF strength) without having a contact with them: Moreover, the gradiometrical configuration connection of PCs makes it possible to define the direction of the flow (B0-Bx > 0 or < 0) and dynamic nature of its’ pulsations (B0-Bx > or < B0-Bx).
Let us proceed explaining this technique on the example of the advancing counting/measuring device of hemoglobinum level in the blood flow (BF). This level is influence the paramagnetic susceptibility of the flow due to variation of the density of ferrum molecules into it. Such variations dH=H-Hfl in the ambient MF H is absorbing by a solenoidal PC which embrace the BF. As a result the output voltage Uout of IS defines both the absolute value of hemoglobinum content and variations of it density in respect to some optimal value.
This give us possibility to define the magnetic susceptibility of a blood according to a formula. By employing of some substance as a core of PC is expected to define an effective magnetic permeabillity muef of the formed physical body. As a big veines and arteries is possible to consider as a long cylinders, in consequence for them is valid the expression. As a result a formula for PC's core which formed by big BF vessels is written down.
III. Real sensors detect unwanted signals, referred to as noise. Noise is broadly divided into two categories— uncorrelated noise and correlated noise. Uncorrelated noise is induced by the sensors, thermal fluctuations in conductors (Johnson noise) or by thermal fluctuations in magnetic susceptibility of nearby materials within shielded parts of the sensors. Correlated noise which appears in all or most of the sensors can be due to environmental disturbances such as moving vehicles, elevators and power lines, or from near-field biological disturbances such as MF of the heart and muscles or displacement of the body tissue in the local MF. Even unwanted brain signals (i.e. signals from parts of the brain that are of no interest to a study) can be considered to be noise. We refer to this as ‘brain noise’. In addition, correlated noise can be caused by Johnson noise and magnetic susceptibility of nearby materials which are exposed to all flux transformers (e.g., dewar materials).
The EM sensors are surface PCs, which are used in regular configuration where PCs with a small distance between each other are positioned within the helmet type surface to pick up the local signals within the place of interest. The problem of sensing the EM signal for amplification/switching/memory it with a speed of light in a single (passive) solid-state device EM transistor/memristor (EMTM) has been advanced. The said problem in the advanced method is solving by application of ferroelectric or ferroelectromagnetic (FE or FEM) crystals which are controlled by an electric or magnetic fields (EF or MF) respectively.
The term ‘MEG sensor array’ will mean the collection of EMTMs. Rejection of environmental noise can be improved by measuring a MF difference, rather than the field itself. Such flux transformers are referred to as gradiometers (i.e. the field difference approximates a component of the field gradient tensor). The radial gradiometer detects the radial gradient of a radial MF (radial with respect to the surface of the head). The 20 cm2 array W for sheathing of the heart or brain consists of 40 thous. EMTMs which could be produced by printed electronics processes. These elements are set out into the square or rectangular matrices and are included in further mathematical operations. Control (and interaction) signals can be both in the current and voltage form to create MF or EF respectively.
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