Apparatus and system for measuring magnetic fields

Abstract

The present invention relates to a measurement device for measuring weak magnetic fields, such as those in the sub-picotesla range (e.g., below a few nanotesla). The measurement device includes an ultrasensitive magnetic sensor (or an array of ultrasensitive magnetic sensors) coupled to a low-noise processing circuit. The processing circuit includes a two-stage design including a low-noise amplifier and an analog filter. The present invention is suitable for magnetic cardiovascular (MCV) applications thanks to its ability to measure very small magnetic fields with good precision and very little noise.

Description

[Technical field]

[0001] The present invention relates to the measurement of magnetic fields and signals. [Background technology]

[0002] Magnetocardiography has recently emerged as a promising technique for analyzing and monitoring the cardiovascular system of a living subject.

[0003] This non-invasive technique is based on the measurement of the electrical activity of the heart, for example the magnetic fields and signals generated by the electrical currents flowing through the myocardial fibers during cardiac activity.

[0004] However, such magnetic fields are typically weak (e.g., less than a few nanoteslas) and therefore difficult to measure accurately.

[0005] Measurement devices based on superconducting sensors, such as SQUID (Superconducting QUantum Interference Devices) magnetometers, have been proposed; such sensors are very sensitive and can measure weak magnetic fields with sufficient accuracy.

[0006] However, these SQUID-based systems are often cumbersome to use because, among other reasons, they require constant cooling.

[0007] Therefore, there is a need for a magnetic measurement system for measuring small magnetic fields, especially for medical applications such as magnetocardiography, that can overcome the drawbacks associated with existing measurement systems such as SQUID-based measurement systems. Such a system also holds promise for measuring small amounts of magnetic materials such as magnetic nanoparticles, or for non-destructive detection of microcracks in ferrous metal materials. Summary of the Invention

[0008] It is therefore an object of the present invention to provide a measuring device for measuring magnetic signals, comprising: The measuring device comprises: A magnetic sensor; an electronic processing circuit connected to an output of the magnetic sensor; Including, The electronic processing circuitry includes: a first amplifier and filter stage connected in series with an output of the magnetic sensor; a second amplifier and filter stage connected in series with the first amplifier and filter stage; an analog-to-digital converter connected to the output of the second amplifier and filter stage; Including, the magnetic sensor is a highly sensitive magnetoresistive sensor having high thermal stability; The first amplifier and filter stage includes a first low noise amplifier and at least a first linear analog and / or a first non-linear analog filter, the second filter stage includes a second low noise amplifier, a second linear analog filter and a second non-linear analog filter, and the analog-to-digital converter is further connected to an output interface of the processing circuit.

[0009] According to advantageous optional aspects, alternative embodiments of the invention may include one or more of the following features, taken alone or according to all possible technical combinations:

[0010] The first amplifier and filter stage includes a first low noise amplifier and a first linear analog filter, and the second amplifier and filter stage includes a second low noise amplifier and a second non-linear analog filter.

[0011] The second linear filter includes a Butterworth band pass filter, the filter preferably having a frequency range of 0.01 Hz to 1000 Hz.

[0012] The first and second non-linear analog filters are used to remove frequency components of 50 Hz or 60 Hz and / or their harmonics.

[0013] The magnetic sensor and the electronic processing circuit are integrated on the same substrate, such as an embedded application specific integrated circuit system on a chip or an embedded system in a package.

[0014] The measurement device further includes an integrated low noise power supply, the low noise power supply comprising at least: an electric battery for powering the low noise amplifier, the linear analog filter, and the non-linear analog filter; a power conversion module including a low noise current limiter for powering at least the magnetic sensor, the power conversion module being configured to be powered by an external power source; Includes.

[0015] The measurement device further includes an electromagnetic shielding structure, for example made of mu-metal and / or including a Faraday cage, that houses the magnetic sensor and the electronic processing circuitry.

[0016] A measurement system comprising a measurement device as briefly described above and a processor, such as a programmable microcontroller, connected to an output of the electronic processing circuit, the processor configured to implement digital filters including at least a linear filter, a non-linear filter and a Kalman filter.

[0017] A measurement system including a computer system and a device for measuring a magnetic signal, the computer system being connected to an output of the measurement device, the computer system being configured to implement digital filters including at least a linear filter, a non-linear filter, and a Kalman filter.

[0018] The computer system is connected to the measurement device by a high speed data link.

[0019] The high-speed data link is a wired high-speed data link, such as an Ethernet connection, or a wireless high-speed data link, such as a 5G telephone network connection.

[0020] The measurement system includes a built-in self-test feature configured to monitor the functionality of the magnetic sensor and to allow calibration of the sensitivity of the magnetic sensor.

[0021] The measurement system is configured to measure magnetic fields generated by the cardiovascular system of a living subject and / or the electrical activity of the living subject and / or the vascular network of the living subject.

[0022] The magnetic sensors are a sensor matrix configured to measure, either in series or in parallel, a magnetic field generated from a portion of a vascular network of a living subject with a spatial resolution comprised between 0.1 μm and 10 mm.

[0023] The measurement system is configured to extract at least one of the following data to determine the state of the subject's vascular system: - a flow direction of at least a part of a vascular system, such as a blood vessel or a number of blood vessels; -pulsation rate, - pulsatility and resistivity indices of at least a part of the vascular system, - the capacitance of the wall compliance of at least a portion of the vascular system; - inductance of blood flow in at least a part of the vascular system, - pressure in at least part of the vascular system, - the rate of blood flow in at least a part of the vascular system, - the velocity of pulse wave propagation in at least a part of the vascular system, - Stiffness of at least part of the blood vessel wall.

[0024] The measurement system is configured to measure the presence of a magnetic field due to a magnetic material or to measure the magnetic properties of small amounts of magnetic material, such as ferrous metal, magnetic nanoparticles, or spin crossover materials.

[0025] The measurement system is configured for non-destructive detection of cracks or thickness reduction in walls containing ferrous compounds and / or magnetic impurities, such as any structure of an oil or gas pipeline, an oil and gas tanker, or an oil or gas container. [Brief description of the drawings]

[0026] The invention will be understood on reading the following description, given by way of example only and made with reference to the accompanying drawings, in which:

[0027] [Figure 1] FIG. 1 is a schematic diagram of a measurement system for measuring a magnetic field, the measurement system including an apparatus for measuring a magnetic signal according to an embodiment of the invention. [Diagram 2] FIG. 2 is a schematic diagram of the measurement system of FIG. 1, with the electromagnetic shielding elements visible. [Diagram 3] FIG. 3 is a number of graphs illustrating exemplary performance of the measurement system of FIG. [Figure 4] FIG. 4 shows first and second embodiments of a magnetic sensor array that can be used in the measurement system of FIG. [Diagram 5] FIG. 5 shows third and fourth embodiments of a magnetic sensor array that can be used in the measurement system of FIG. [Figure 6] FIG. 6 shows a comparison of experimental measurement results between Doppler ultrasound and a method using the measurement system of FIG. [Figure 7] FIG. 7 shows another comparison of experimental measurement results between Doppler ultrasound testing and a method using the measurement system of FIG. [Figure 8] FIG. 8 shows a block diagram of one embodiment of an electronic circuit for implementing the measurement system of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Description of Some Embodiments 1 and 2 show a measurement system 2 for measuring magnetic fields.

[0029] Preferably, the measurement system 2 is configured to measure the magnetic fields generated by the cardiovascular system of a living subject, such as a human patient, although many other applications are possible.

[0030] The measurement system 2 comprises a device 4 for measuring magnetic signals and a computer system 6 connected to the measurement device 4 .

[0031] The measurement device 4 includes a magnetic sensor 10 and an electronic processing circuit 12 connected to the output of the magnetic sensor 10 .

[0032] In a preferred embodiment, the magnetic sensor 10 comprises a highly sensitive magnetoresistive sensor, for example a planar Hall effect magnetic sensor.

[0033] In some embodiments, the magnetic sensor 10 can include one or more sensing elements, each of which includes multiple layers of magnetic thin films configured to form a microstructure having a particular shape.

[0034] In the illustrated example, the microstructure has a central circular shape including four identical or similar radial arms regularly spaced around the central circle and extending outside the central circle.

[0035] The sensing elements can be connected to electrical contact pads to allow for wired connection to the electronic processing circuitry 12 .

[0036] For example, magnetic sensor 10 includes a first output terminal and a second output terminal and is configured to provide an output signal, such as a voltage, between the first output terminal and the second output terminal.

[0037] In a non-limiting example provided for illustrative purposes, the magnetic material stack can include an exchange biased multilayer structure of Ta / Py / Cu / IrMn / Ta layers (permalloy, copper, iridium-manganese alloy, and a tantalum buffer layer), each layer having a thickness of less than 10 nanometers.

[0038] To improve the temperature stability of the magnetic properties of the multi-layer structure, the multi-layer structure can be annealed during fabrication at high temperatures under a uniform magnetic field.

[0039] The shape and materials can produce magnetoresistive and / or planar Hall effect properties that are used by the sensor to detect magnetic fields.

[0040] An example of this magnetic sensor is described in International Application WO2017 / 207640A1, the contents of which are incorporated by reference into this application.

[0041] 2, the arrows V and H indicate the direction of the bias voltage applied to the sensor and the magnetic field sensitivity direction during several measurements, respectively. A bias voltage V can be applied between a bias voltage input and a ground input (seen as the leftmost and rightmost electrodes of the magnetic sensor 10 in FIGS. 1 and 2, respectively).

[0042] For example, the magnetic sensor 10 has a high sensitivity of greater than 10 V / T.

[0043] In many embodiments, the magnetic sensor 10 is a highly sensitive magnetoresistive sensor that has high thermal stability with a variation of less than 10 ppm / °C.

[0044] Preferably, the magnetic sensor 10 has a small size.

[0045] For example, the minimum size of the sensing element is less than 50 μm, and preferably 10 μm or less. In the illustrated example, the magnetic sensor 10 is 2×2 mm 2 dicing area of ​​1000 .ANG.. Nevertheless, other embodiments are possible.

[0046] The electronic processing circuitry 12 is more specifically designed to quickly and efficiently process the signals measured by the magnetic sensor 10 (e.g., signal filtering and amplification) while maintaining a good signal-to-noise ratio. This is important because the signals representing very weak magnetic fields measured by the magnetic sensor 10 are very weak and can easily be drowned out by noise.

[0047] For example, in vascular networks, magnetic fields are in the picotesla to nanotesla range.

[0048] For example, the electronic processing circuit 12 is a low noise processing circuit.

[0049] In many embodiments, electronic processing circuitry 12 includes a first amplifier and filter stage (i.e., the “first stage” including elements 20, 22, and 24) and a second amplifier and filter stage (the “second stage” including elements 26, 28, and 30).

[0050] The first stage and the second stage are connected in series with the output of the magnetic sensor 10. More precisely, the first stage is connected to the output of the magnetic sensor 10. The second stage is connected to the output of the first stage.

[0051] The electronic processing circuit 12 also includes an analog-to-digital converter 32 connected to the output of the second filter stage.

[0052] The first stage includes a first low noise amplifier (LNA) 20 and at least a linear analog filter 22 and / or a non-linear analog filter 24. The first linear analog filter 22 is configured to remove continuous parasitic components of the signal, such as geomagnetic signatures.

[0053] In this example, the first stage includes a first linear analog filter 22 and a first non-linear analog filter 24 connected together in series at the output of a first low noise amplifier 20 .

[0054] In an illustrative example, the first low noise amplifier 20 has a 0.25 nVHz -1 / 2 It has a nominal noise of 0.01 and a fixed gain of 2000.

[0055] In a non-limiting example given for illustrative purposes, the first linear analog filter 22 is a 0.01 Hz high pass filter configured to remove a DC offset component.

[0056] According to one embodiment, the first linear analog filter 22 is a Butterworth filter having a preferred frequency range of 0.01 Hz to 1000 Hz.

[0057] The first nonlinear analog filter 24 may be a 50 Hz or 60 Hz nonlinear filter configured to remove noise from the electrical network (because the measurement system 2 may be at least partially powered by an electrical network grid having a mains frequency of 50 Hz or 60 Hz), and may more generally be configured to further remove peak attenuation of 50 Hz or 60 Hz and / or their harmonics.

[0058] The second stage includes a second low noise amplifier 26 and at least a second linear analog filter 28 and / or a second non-linear analog filter 30. Preferably, the second stage includes at least both the second low noise amplifier 26 and the linear analog filter 28.

[0059] In this example, the second stage includes a second linear analog filter 28 and a second non-linear analog filter 30 connected together in series to the output of the second low noise amplifier 26 .

[0060] For example, the second linear analog filter 28 is a 150 Hz low-pass Butterworth filter with a selectable filtering order, e.g., from 1st to 3rd order. In another embodiment, the second linear analog filter 28 is a Butterworth filter, preferably with a frequency range from 0.01 Hz to 1000 Hz.

[0061] The second nonlinear analog filter 30 may be a 50 / 60 Hz filter, such as a notch filter, configured to remove DC offset components and noise from the electrical network, and more generally configured to further remove peak attenuation of 50 Hz and / or 60 Hz and / or their harmonics.

[0062] In a non-limiting example given for illustrative purposes, the second low noise amplifier 26 has a 3 nVHz -1 / 2 It has a nominal noise of 0.01 and a gain of 90.

[0063] In another non-limiting example given for illustrative purposes, the second low noise amplifier 26 may have a 3 nVHz -1 / 2 It has a nominal noise of 0.01 and a gain of 180.

[0064] The analog-to-digital converter 32 is further connected to an output interface of the processing circuit 12. In this example, the analog-to-digital converter 32 is a 4-channel, 16-bit analog-to-digital converter, although other embodiments are possible.

[0065] For example, the processing circuitry 12 includes a processor 34, such as a programmable microcontroller (MC).

[0066] The term "processor" as used herein refers not only to electronic controller devices including processors or microprocessors, but also to other equivalent elements such as application specific integrated (ASIC) circuits, field programmable gate array (FGPA) circuits, logic circuits, analog circuits, their equivalents, and any other circuits or processors capable of performing the functions described herein.

[0067] The processor 34 may be coupled to a communications interface configured to be coupled to the computer system 6, as described below. The processor 34 may be part of the communications interface.

[0068] Preferably, the measuring device 4 is connected to the computer system 6 by a high speed data link 40. The communication interface is adapted accordingly.

[0069] In some embodiments, the high speed data link 40 is a wired high speed data link, such as an Ethernet connection. For example, the processor 34 is a 32-bit microcontroller that implements a high speed Ethernet data transmission protocol.

[0070] In some embodiments, the high speed data link 40 is a wireless high speed data link, such as a 5G telephone network connection.

[0071] In an optional but nevertheless advantageous embodiment, the measuring device 4 further comprises an integrated low noise power supply and power conversion module.

[0072] The low noise power supply includes at least an electric battery for powering the low noise amplifiers 20 and 26 , the linear analog filter 22 , and the linear analog filter 28 .

[0073] The power conversion module includes a low noise current limiter for powering at least the magnetic sensor 10. The power conversion module may be configured to be powered from an external power source, such as the electrical mains grid.

[0074] In a preferred embodiment, the magnetic sensor 10 and the electronic processing circuitry 12 are integrated on the same substrate, for example the substrate being a printed circuit board, nevertheless in alternative embodiments other configurations are possible.

[0075] For example, the magnetic sensor 10 may be integrated into an application specific integrated circuit (ASIC) embedded in a system on chip (SoC) system or an application specific integrated circuit (ASIC) embedded in a package (SiP).

[0076] The magnetic sensor elements can be implemented in advanced CMOS silicon-based technologies taking advantage of the latest packaging solutions (fan-in / fan-out Wafer Level Chip Scale Package (WLCSP) and Semiconductor Embedded in Substrate (SESUB) or any suitable technology).

[0077] As shown in FIG. 2, in a preferred embodiment, the measurement device 4 further comprises an electromagnetic shielding structure housing the magnetic sensor and electronic processing circuitry.

[0078] The electromagnetic shielding structure is configured to protect the measurement device 4 from high and low frequency noise from the surrounding environment.

[0079] For example, a first portion 60 of the electromagnetic shielding structure surrounds a first portion of the measuring device 4 including the magnetic sensor 10 .

[0080] A second portion 62 of the electromagnetic shielding structure surrounds a second portion of the measuring device 4 , which includes the electronic processing circuitry 12 .

[0081] According to some embodiments, the electromagnetic shielding structure is made of mu-metal.

[0082] In some other embodiments, the electromagnetic shielding structure includes a Faraday cage.

[0083] Shielded connectors 64 and 66, respectively, can be used to protect the wired connectors used to connect the magnetic sensor 10 to the electronic processing circuit 12 and to connect the electronic processing circuit 12 to the processor 34. The shielded connectors 64 and / or 66 can be connected to ground GND of the measurement device 4. Preferably, the shielded connectors 64 and / or 66 are low loss cables.

[0084] Furthermore, to minimize interference noise from high speed data processing by the processor 34 into the analog signals, the electronic processing circuitry 12 may be constructed according to certain design considerations, such as shielding all signal lines or having different ground planes for the analog and digital portions of the electronic processing circuitry 12. In Figure 2, ground is represented by the symbol GND.

[0085] The computer system 6 is configured to further analyze and filter the acquired signals to remove noise. The computer system 6, also called a control system, includes electronic circuitry capable of executing algorithms and software code.

[0086] For example, computer system 6 may include a processor and one or more computer memory elements.

[0087] The computer memory stores computer code and / or executable instructions for causing the processor and electronic control unit to perform a method for processing received measurement signals when the computer code and / or executable instructions are executed by the processor.

[0088] In some embodiments, the computer system 6 may also be configured to control the operation of the ultrasound emission system.

[0089] The computer system 6 includes a communication interface that is coupled to the communication interface of the electronic processing circuit 12 and is capable of exchanging data with it.

[0090] The computer system 6 may further include a user interface, which may include one or more interface elements, such as a graphical display, a wireless interface allowing remote control and / or exchange of data with a mobile terminal, data input means such as a keyboard, a mouse, a pointer device, a touch-sensitive screen, or any equivalent interface element, or any combination of such interface elements.

[0091] In a preferred embodiment, computer system 6 includes a digital filter module 50 and a digital algorithm module 52 .

[0092] For example, the digital filter module 50 of the computer system 6 is configured to implement digital filters including at least a linear filter, a non-linear filter, such as a notch filter, to improve noise reduction.

[0093] The digital filter is implemented by a filtering algorithm including high-pass, low-pass and notch filters, which may be a Butterworth filter.

[0094] For example, a low-pass digital filter has a cutoff frequency value ω c may be a low-pass Butterworth filter to block the input voltage Vin(jω) having a frequency higher than

number

[0095] The high-pass digital filter may be a subsequent high-pass Butterworth filter to block voltage signals having frequencies lower than the expected value.

number

[0096] The notch filter may be a notch Butterworth filter, which is used to remove unwanted noise at a defined frequency value, for example noise from the power 50 / 60 Hz and its harmonics.

number

[0097] In these equations, ω is the angular frequency (ω = 2πf; f is the frequency at the measurement time), and ω c is the cutoff value (f=f c ), W is the angular frequency at the cutoff bandwidth, n is the number of filter orders, and j is an imaginary number.

[0098] Increasing the number of filter orders improves the filter quality.

[0099] Module 52 is configured to implement one or more advanced digital filters with the aim of further extracting useful information from the filtered digital signal.

[0100] This is particularly useful in medical applications such as magnetocardiovascular systems, where an automatic classifier can be used to provide a clinical conclusion and / or an automatic diagnosis based on the collected signals.

[0101] For example, module 52 may be configured to implement a Kalman filter to remove unwanted noisy signals and generate a clean signal that can be used in an automated diagnostic system.

[0102] However, in some embodiments, the processor 34 may be configured to implement digital filters including at least a linear filter, a non-linear filter, and a Kalman filter, for example when the computer system 6 is not connected to the measurement device 4.

[0103] According to one embodiment, the filters implemented by module 50 are adaptive, in other words their parameters are automatically updated to adapt to the application, such as the cut-off frequency and cut-off bandwidth of the notch filter, the cut-off frequency, bandwidth and order of the low-pass and high-pass filters.

[0104] Similarly, according to one embodiment, module 52 is configured to implement an adaptive advanced filter, for example to learn and update parameters such as the estimation noise and measurement noise of a Kalman filter.

[0105] In conclusion, the measurement system 2 has the advantage of being able to measure low magnetic fields (e.g., magnetic fields of a few nanoteslas or less) with high sensitivity (up to 10-15 emu) in a wide frequency range (e.g., from 10 mHz to 10 GHz).

[0106] This is primarily due to the association of the magnetic sensor 10 with the electronic processing circuitry 12, which is designed to match the magnetic sensor 10 and to ensure that the measured signal is processed (e.g., amplified, filtered, converted to a digital signal) by the electronic processing circuitry 12 with as little added noise as possible.

[0107] Furthermore, the digital filters implemented by the computer 6 or processor 34 achieve further filtering of the noise, allowing filtering of a quality better than -105 dB. Advantageously, the first and second stage analog filters and the digital filter work together to achieve the desired quality of noise filtering.

[0108] Thus, the present invention is particularly suitable for use in medical applications, such as magnetic cardiovascular (MCV) applications, as the measurement system has the ability to measure very small magnetic fields with good accuracy and very little noise.

[0109] For example, the measurement system 2 can measure weak magnetic fields, such as magnetic fields in the sub-picotesla range (less than a few nanotesla).

[0110] More specifically, measurement system 2 can reliably measure weak magnetic fields with accuracy comparable to existing measurement systems based on superconducting magnetometers, but without the practical drawbacks commonly associated with superconducting magnetometers, such as SQUID magnetometers.

[0111] According to the invention, measurements can be performed at ambient temperature and do not require complex and energy intensive cooling systems.

[0112] Furthermore, in contrast to other methods, according to the present invention magnetic measurements can be performed non-invasively, without direct contact with the patient's skin and without the use of contrast agents inside the patient's body.

[0113] Due to the small size of the magnetic sensor 10, the measurement system 2 can be more easily miniaturized.

[0114] FIG. 3 illustrates an exemplary performance of the measurement system.

[0115] In the leftmost portion (part a) of Figure 3, a first curve 80 shows the output voltage response of the measurement device (PHMR voltage, y-axis, in volts) when increasing or decreasing the magnetic field (x-axis) from 0 nT to 150 nT. In this example, measurements are made for a frequency of 13 Hz.

[0116] The inset graph corresponds to the estimated sensitivity of the measurement device (curve 82), which is defined as equal to the derivative of the bias voltage V with respect to the magnetic excitation field H, and is estimated in this example to be equal to about 771.5 kV / T.

[0117] In the rightmost portion of FIG. 3 (portion b), a third curve 84 shows the noise (THz) as a function of frequency (y-axis). -1 / 2 The equivalent magnetic noise floor of the device is 100 pTHz at 0.1 Hz. -1 / 2 and above 100 Hz it is equal to 2 pTHz.-1 / 2 The magnetic field detectability of the system as a function of frequency for a designed frequency bandwidth of 150 Hz can be estimated by multiplying the noise level by the square root of 150.

[0118] FIG. 8 is a block diagram of an exemplary embodiment of electronic circuitry used in measurement device 4 and is provided for illustrative purposes.

[0119] In this example, the measurement device 4 is implemented by an application specific integrated circuit 300 including a magnetic sensor similar to the magnetic sensor previously described.

[0120] In this example, the magnetic sensor includes a number of magnetic sensor elements 302 arranged to form a sensor array 304 .

[0121] The sensor array 304 is connected to an analog front-end module (block 306) which includes the filter and amplifier stages mentioned above.

[0122] The analog front-end module 306 includes a switched front-end module 308 that can operate in a transmit mode (TX-signal generation) or a receiver mode (RX).

[0123] For example, the magnetic sensor element 302 can operate bidirectionally in either a transmit mode (TX) or a receiver mode (RX). In the transmit mode, a pulse signal can be generated by the magnetic sensor element 302 using an on-chip oscillator.

[0124] The analog front-end module 306 includes a sensor load conditioning module 310 for wideband impedance matching.

[0125] The analog front-end module 306 includes built-in self-test functionality configured to monitor the functionality of the magnetic sensor (i.e., the array 304 in this case) and enable calibration of the sensitivity of the magnetic sensor.

[0126] The signal conditioning module (block 312 ) is connected to the output of the analog front-end module 306 .

[0127] The signal conditioning module 312 is configured to condition the measured signal, for example by filtering the signal. For example, the signal conditioning module 312 may implement a filter bank and / or a digital filter 50.

[0128] The signal conditioning module 312 can be configured for potential downconversion to baseband processing with calibration of the sensor. This module 312 can also control bias and sensitivity adjustments.

[0129] An advanced signal processing stage 314 is connected to the output of the signal conditioning module 312 .

[0130] For example, the signal processing stage 314 is configured to operate at baseband frequencies and handle all algorithmic calculations required to extract the signals required for the end application. The signal processing stage 314 coordinates and coordinates the control and regulation of the sensors, for example using modules 316, 318 and 320.

[0131] The signal processing stage 314 includes functionality (module 324) for implementing modulation schemes and communication protocols for high speed data transmission.

[0132] This implementation is preferred over existing solutions that are based on separate solutions with separate analog and digital signal processing blocks: since the measurement system is designed from the ground up as an ASIC-based implementation, it is easy to combine analog detection with real-time signal processing while properly considering the correlation between noise sources.

[0133] Many other embodiments are possible.

[0134] Figures 4 and 5 show another embodiment of the magnetic sensor 10. The single magnetic sensor 10 described with reference to the embodiment of Figure 1 is replaced by a sensor array or sensor matrix in order to perform measurements at multiple positions in space.

[0135] In this specification, the term "magnetic sensor 10" may be used to refer to a single magnetic sensor element as described above, or a combination of multiple magnetic sensor elements, such as a sensor array or sensor matrix.

[0136] Next, an example of an array or matrix of magnetic sensors will be described.

[0137] FIG. 4(a) shows a sensor array 100 including a number of individual magnetic sensors 10 aligned along a longitudinal direction.

[0138] The sensor array 100 allows for precise measurements along a defined geometric direction, for example, the sensors 10 of the sensor array 100 are periodically spaced along the longitudinal direction, and the individual sensors 10 are preferably identical or at least similar in characteristics.

[0139] In the illustrated example, five sensors 10 are connected together in an array, this number being given as a non-limiting example only.

[0140] For example, a first output terminal of each sensor 10 is connected to a main first output V1. A second output terminal of each sensor 10 is connected to a main second output V2. The sensors 10 are connected to a main voltage bias input V1 by their voltage bias input and ground input. bias and the main electrical ground GND.

[0141] 4(b) shows a sensor matrix 110 that includes a plurality of individual sensors 10. The sensor matrix 110 is constructed in a similar manner to the sensor array 100, except that the sensors 10 are connected to form a pattern along two dimensions, such as a square, instead of in a single direction.

[0142] The sensor matrix 110 allows for accurate measurements along two directions.

[0143] For example, the sensors 10 of the sensor matrix 110 are periodically spaced along the two longitudinal directions. The individual sensors 10 are preferably identical or at least similar in characteristics.

[0144] The sensors 10 are connected in series between the primary first output V1 and the primary second output V2 by their respective first and second output terminals. The sensors 10 are connected in series to the primary voltage bias input V by their voltage bias input and ground input. bias and the main electrical ground GND.

[0145] FIG. 5(a) shows a first main output V1, a second main output V2, and a first main voltage bias input V bias 1 shows a sensor matrix 120 including four individual sensors 10 connected in a bridge-like pattern between a main electrical ground GND and a main electrical ground GND. The sensors 10 are connected by their respective first and second outputs to the main outputs V1, V2, V bias and may be connected to GND.

[0146] FIG. 5(b) shows a first main output V1, a second main output V2, and a first main voltage bias input V bias 5(a) and a main electrical ground GND. Each sensor module 132 is similar or identical to the sensor matrix 120. The sensor modules 132 each have primary outputs V1, V2, V3, V4, V5, V6, V7, V8, V9, V10, V11, V12, V13, V14, V15, V16, V17, V18, V19, V20, V21, V22, V23, V24, V25, V26, V27, V28, V29, V30, V31, V32, V32, V33, V34, V35, V36, V37, V38, V39, V40, V41, V42, V43, V44, V45, V46, V47, V48, V49, V50, V51, V52, V53, V54, V55, V56, V57, V58, V59, V60, V61, V62, V63, V64, V65, V66, V67, V68, V69, V70, V71, V72, V73, V74, V75, V76, V77, V78, V79, V80, V81, V82, V83, V84, V85, V86, V87, V88, V89, V90, V91, V92, V93, V94, V95, V96, V97, V98, V99, V100, V99, V111, V99, V120, V131, V141, V151, V162, V170, V171, V182, V190, V191, V192, V10 bias and GND.

[0147] These configurations allow for more accurate measurements along two directions. Due to the small size of the magnetic sensor 10, the sensor matrices 100, 110, 120 and 130 can be more easily miniaturized for low spatial resolution measurements.

[0148] In a preferred embodiment, the magnetic sensor 10 is configured to measure, in series or parallel, the magnetic field generated from a portion of a vascular network of a biological subject with a spatial resolution in the range of 10 mm down to the micrometer (μm) range or sub-micrometer range, for example, 1 mm, or 100 μm, or 10 μm, or 1 μm, or 0.1 μm.

[0149] For example, the spatial resolution is comprised between 0.1 μm and 10 mm.

[0150] In many embodiments, the magnetic sensor 10 is part of a sensing probe.

[0151] By way of example, some possible applications of the measuring device 4 and the measuring system 2 will now be described.

[0152] For example, the measurement system 2 is configured to extract at least one of the following information data in order to investigate the conditioning state of the subject's vascular system: - a flow direction of at least a part of a vascular system, such as a blood vessel or a number of blood vessels; -pulsation rate, - a pulsatility index and a resistivity index of at least a part of a vascular system, - the capacitance of the wall compliance of at least a portion of the vascular system; - inductance of blood flow in at least a part of the vascular system, - pressure in at least part of the vascular system, - the rate of blood flow in at least a part of the vascular system, - the velocity of pulse wave propagation in at least a part of the vascular system, - Stiffness of at least part of the blood vessel wall.

[0153] In FIG. 6, reference numeral 200 shows the results of a magnetic cardiovascular system performed using measurement system 2 on the radial artery (graph 202) and femoral artery (graph 204) of a subject (such as a human subject) to determine circulatory impedance / resistance.

[0154] In either case, the measured signal is given as a function of time (x-axis expressed in arbitrary units) and represented as a voltage (given as output by the magnetic sensor 10).

[0155] The results obtained with the present measurement system 2 (shown as a solid line) are shown in both graphs 202 and 204, along with measurements obtained with known techniques such as Doppler ultrasound (shown as a dashed area and expressed in velocity in cm / s).

[0156] It can be seen that the data obtained with the measurement system 2 are in good experimental agreement with the reference data obtained from Doppler ultrasonography. This means that the measurement system 2 is able to provide magnetocardiac cardiovascular data that are as reliable as known techniques such as Doppler ultrasonography, despite being much easier to use and implement.

[0157] In FIG. 7, reference number 250 indicates the results of magnetic cardiovascular measurements performed with the measurement system 2 on the lower limb of a human subject to determine the velocity of pulse wave propagation in the femoral artery.

[0158] For example, arterial waves generated by the systolic ejection of a subject's heart propagate along the aorta and then through the arteries of the vascular system at a velocity that depends on the elasticity of the arterial walls, and measuring this velocity therefore provides reliable information about the elasticity of the arterial walls in at least a portion of the subject's vascular system.

[0159] The three graphs, labeled 252, 254 and 256, correspond to the output of three repeated measurements at two separate points spaced apart longitudinally along the leg.

[0160] The magnetic cardiovascular data measured by the measurement system 2 from two measurement probes with similar sensitivity and phase in detecting the alternative magnetic signals are represented as voltage ("measured signal" on the y-axis) as a function of time (x-axis in seconds) and are represented by the solid and dotted lines. The solid and dotted lines correspond to two measurements at the posterior tibial artery and the femoral artery along the lower leg with the legend "PTA". For example, the data may be collected using multiple sensors 10 spaced apart from each other or using a sensor array similar to the sensor array 100 with lower spatial resolution.

[0161] The magnetic cardiovascular data allows the analysis of the velocity of the pulse wave propagation by dividing the distance between the two measurement points by the difference in the different times of the two measurements at the systolic peak. In an example measurement of a healthy volunteer, the pulse wave propagation velocity in the lower limbs is about 10 m / s, which is in good agreement with reference data obtained using known measurement methods such as a combination of Doppler ultrasound and photoplethysmography (PPG) measurements. The reference data can be obtained by correlation of two sets of measurements of separate Doppler / PPG probes.

[0162] The experimental results again show that the magnetic cardiovascular data obtained by the measurement system 2 are in good experimental agreement with the reference data.

[0163] This means that the measurement system 2 is just as reliable as known techniques such as methods based on Doppler ultrasound, despite being much simpler to use and implement.

[0164] Many other embodiments are possible. The above embodiments and alternatives can be combined with each other to create new embodiments of the invention, within the scope of the claims.

[0165] Advantageously, the measurement device comprises a highly sensitive magnetoresistive sensor with high thermal stability, for accurately measuring small magnetic fields, for example in the patient's vascular network.

[0166] Advantageously, by cascading a first amplifier and filter stage with a second amplifier and filter stage, the gain-bandwidth tradeoff of the amplifier can be overcome.

[0167] Advantageously, an electromagnetic shielding structure surrounding the magnetic sensor 10 and the electronic processing circuitry 12 helps to avoid high and low frequency noise from the surrounding environment.

[0168] The invention is illustrated in its application for the measurement of magnetic fields and signals in the field of magnetocardiography.

[0169] The application of the present invention is not limited to this field.

[0170] For example, the measurement system 2 is advantageously configured to measure the presence of a magnetic field due to a magnetic material or to measure the magnetic properties of small amounts of magnetic material such as ferrous metal, or magnetic nanoparticles, or spin crossover materials.

[0171] For example, advantageously, the measurement system 2 is configured to non-destructively detect cracks or thickness reductions in walls containing ferrous compounds and / or magnetic impurities, such as any structure of an oil or gas pipeline, an oil and gas tanker, or an oil or gas container. Thus, advantageously, the present invention may find application for monitoring pipeline systems in the oil and gas industry.

Claims

1. A measuring device (4) for measuring magnetic signals, comprising: The measuring device (4) A magnetic sensor (10); an electronic processing circuit (12) connected to the output of the magnetic sensor; Including, The electronic processing circuit (12) a first amplifier and filter stage (20, 22, 24) connected in series with the output of the magnetic sensor (10); a second amplifier and filter stage (26, 28, 30) connected in series with said first amplifier and filter stage (20, 22, 24); an analog-to-digital converter (32) connected to the output of the second amplifier and filter stage (26, 28, 30); Including, The magnetic sensor (10) is a highly sensitive magnetoresistive sensor with high thermal stability, the first amplifier and filter stage (20, 22, 24) includes a first low noise amplifier (20) and at least a first linear analog (22) and / or a first non-linear analog (24) filter; the second amplifier and filter stage (26, 28, 30) includes a second low noise amplifier (26), a second linear analog filter (28), and a second non-linear analog filter (30); The measurement device (4) is further connected to the output interface of the processing circuit, wherein the analog-to-digital converter (32) is connected to the output interface of the processing circuit.

2. 2. The measurement device (4) of claim 1, wherein the first amplifier and filter stage includes a first low noise amplifier (20) and a first linear analog filter (22), and the second amplifier and filter stage includes a second low noise amplifier (26) and a second non-linear analog filter (30).

3. 3. The measuring device (4) of claim 1 or 2, wherein each of the first and second linear filters (28) comprises a Butterworth bandpass filter, the bandpass filters preferably having a frequency range of 0.01 Hz to 1000 Hz.

4. 3. The measuring device (4) according to claim 1 or 2, wherein the first and second non-linear analog filters (24, 30) are used to remove frequency components of 50 Hz or 60 Hz and / or their harmonics.

5. 3. The measuring device (4) according to claim 1 or 2, wherein the magnetic sensor (10) and the electronic processing circuit (12) are integrated on the same substrate, such as an embedded application specific integrated circuit system on a chip or an embedded system in a package.

6. the measuring device (4) further comprises an integrated low noise power supply; The low noise power supply comprises at least an electric battery for powering the low noise amplifier, the linear analog filter, and the non-linear analog filter; a power conversion module including a low noise current limiter for supplying power to at least the magnetic sensor, the power conversion module being configured to be powered by an external power source; 3. The measuring device (4) according to claim 1 or 2, comprising:

7. 3. The measuring device (4) according to claim 1 or 2, further comprising an electromagnetic shielding structure (60, 62), e.g. made of mu metal and / or comprising a Faraday cage, that houses the magnetic sensor (10) and the electronic processing circuit (12).

8. 10. A measurement system (2) including a measurement device (4) for measuring magnetic signals as claimed in claim 1, wherein a processor (34), such as a programmable microcontroller, connected to the output of the electronic processing circuit (12) is configured to implement digital filters including at least a linear filter, a non-linear filter, and a Kalman filter.

9. 1. A measurement system (2) comprising a computer system (6) and a measurement device (4) for measuring magnetic signals according to claim 1, wherein the computer system (6) is connected to an output of the measurement device (4), and the computer system (6) is configured to implement digital filters including at least a linear filter, a nonlinear filter, and a Kalman filter (50).

10. 10. The measurement system (2) according to claim 9, wherein the computer system (6) is connected to the measurement device (4) by a high-speed data link (40).

11. The measurement system (2) of claim 10, wherein the high-speed data link (40) is a wired high-speed data link, such as an Ethernet connection, or a wireless high-speed data link, such as a 5G telephone network connection.

12. 10. The measurement system (2) of claim 8 or 9, wherein the measurement system (2) includes a built-in self-test function (306) configured to monitor the functionality of the magnetic sensor and enable calibration of the sensitivity of the magnetic sensor.

13. 10. The measurement system (2) according to claim 8 or 9, wherein the measurement system (2) is configured to measure magnetic fields generated by the cardiovascular system of a living subject and / or generated by the electrical activity of a living subject and / or the vascular network of a living organism.

14. 10. The measurement system (2) according to claim 8 or 9, wherein the magnetic sensor (10) is a sensor matrix (100, 110, 120, 130) configured to measure, either in series or in parallel, the magnetic field generated by a portion of the vascular network of a living subject with a spatial resolution comprised between 0.1 μm and 10 mm.

15. The measurement system (2) is configured to examine the state of the subject's vascular system, - the direction of flow in at least a part of a vascular system, such as a blood vessel or vessels; - pulsation rate, - pulsatility index and resistivity index of at least a part of the vascular system, - the capacitance of the wall compliance of at least part of the vascular system; - the inductance of the blood flow in at least part of the vascular system, - pressure in at least part of the vascular system, - the rate of blood flow in at least part of the vascular system; - the velocity of pulse wave propagation in at least part of the vascular system, - stiffness of at least a part of the vessel wall, 10. The measurement system (2) according to claim 8 or 9, configured to extract at least one of the following data:

16. 10. The measurement system (2) according to claim 8 or 9, wherein the measurement system (2) is configured to measure the presence of a magnetic field due to a magnetic material or to measure the magnetic properties of a small amount of magnetic material.

17. 10. The measurement system (2) according to claim 8 or 9, configured for the non-destructive detection of cracks or thickness reduction in walls containing iron compounds and / or magnetic impurities, such as any structure of an oil or gas pipeline, an oil and gas tanker or an oil or gas container.

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