System and method for acquiring biosignal from living subject

Abstract

The system can have a circuit including an output, an electrical signal source electrically connected to the output, and a meter electrically connected to the output, the circuit having a characteristic impedance being fixed; and an antenna electrically connected to the output of the circuit for receiving the source signal, the antenna having a near field and an antenna impedance, the antenna impedance matching with the characteristic impedance of the circuit when driven by the source signal, when a region of interest of the living subject is within a near field of the antenna and when the antenna is electrically insulated from the region of interest.

Description

SYSTEM AND METHOD FOR ACQUIRING BIOSIGNAL FROM LIVING SUBJECTBACKGROUND

[0001] The Respiratory Rate (RR) and associated time constants and patterns are critical parameters in diagnosing certain diseases and are important indicators used to monitor the evolution of a disease in adults, children, and even animals. For humans, an abnormal RR is an important predictor of severe events such as respiratory and cardiac arrest and admission to an intensive care unit.

[0002] In addition, this parameter is fundamental in monitoring patients with sleep apnea, infections (like COVID-19), and respiratory depression after surgery, for example. It is reported in some studies that an RR > 27 bpm in adults is the main predictor of cardiac arrest in a hospital setting. Additionally, it is shown that the continuous monitoring of RR is essential to study the effects of heroin administration in addicted individuals to prevent heroin-induced respiratory depression during drug administration. However, although RR is of paramount importance in assessing a patient’s health and / or disease state, it is still often clinically measured manually or using cumbersome monitoring systems such as a flow meter built into a mouthpiece (spirometry), a mask, or measurement of end-tidal CO2, rather than portable, reliable, non-invasive devices with demonstrated continuous monitoring capability. Recently, many portable sensors and devices for monitoring the patient’s breathing have appeared on the market or proposed in the literature. Nevertheless, most of these sensors only allow punctual measurements with reliability disputed by clinicians, which implies the urgent need for mobile, non-invasive, medically accurate, and comfortable technology for monitoring respiration, whether for newborns or older adults, at home or in hospitals. Such a system can be a significant advancement in monitoring patients and at-risk people in both at-home and incare settings.SUMMARY

[0003] One possible approach to acquiring a biosignal such as respiratory rate is to drive a stretchable antenna mechanically coupled to the chest of a user with an electrical signal, and to monitor the change in the emission strength or the emission frequency of the antenna whichstems from the periodic stretching and relaxing of the antenna which occurs due to the inflation and deflation of the lungs. Such an approach can involve using a second antenna to receive the signal emitted by the first antenna, and an additional circuit associated to the second antenna, which may be inconvenient. Further, such an approach may be subject to noise, which may stem from electromagnetic interference, as well as motion artifacts, which may arise from relative displacements between the two antennas or changes in the environment between them, which may affect the transmission of the signal between the first antenna and the second antenna.

[0004] Another possible approach to acquiring a biosignal such as respiratory rate is to harness the phenomenon of impedance mismatch between the antenna and the circuit to intentionally cause reflection of a portion of the source electrical signal by the antenna, back into the electric circuit having the electrical signal source. By including a meter as part of the electrical circuit, an indication of how much of the source electrical signal is reflected back can be acquired. The degree of impedance mismatch directly affects the proportion in which the source electrical signal is reflected back, and can be affected by either one, or both, of two significant factors : a) a change in the dielectric permittivity of the matter (such as the presence of the subject) in the near field of the antenna and b) mechanical deformation of the antenna such as stretching and relaxing which may stem from inflation and deflation of a chest, back, or abdomen mechanically coupled to the antenna and experiencing respiration. Indeed, the antenna impedance of the antenna can be significantly affected by the dielectric permittivity of the matter in its near field, and the changes in the portion of the subject which are within the near field of the antenna can thus change the antenna impedance of the antenna and, in turn, change the extent to which the source signal is reflected back into the circuit. Accordingly, in this context, a biosignal may be acquired either by acquiring an absolute measurement indicative of a variation over time of how much source signal is reflected back into the circuit, or by acquiring a relative measurement indicative of a variation over time of how the reflected portion of the signal compares to the source signal.

[0005] In particular, a significant change in dielectric permittivity of lungs may occur between an inflated state, e.g., immediately after a complete inspiration, and a deflated state, e.g., immediately after a complete expiration. In the context of an adult human being, forinstance, the relative dielectric permittivity in the deflated state may be of the order of 50, whereas the relative dielectric permittivity in the inflated state may be of the order of 22. Significant changes in dielectric permittivity of lungs during inspiration and expiration also occur in different sizes of human beings and in animals.

[0006] Moreover, a significant change in dielectric permittivity of the heart of a living subject may occur during regular heartbeats, and heart rate may thus also be a potential biosignal captured using the technique referred to above. Other biosignals may also be acquired using such techniques, such as potentially muscular activity which may be a source of change in dielectric permittivity and / or a source of mechanical deformation of an antenna mechanically coupled to the source of muscular activity. In some embodiments, an antenna may be non- stretchable and the technique may be used to acquire a biosignal purely based on changes in dielectric permittivity for instance, or the region of interest of the living subject may not exhibit a significant change of dielectric permittivity during movement, and the technique may be used to acquire a biosignal purely based on a mechanical deformation of the region of interest of the living subject.

[0007] The near field of an antenna is affected by the type of antenna and also by the wavelength of the signal emitted by the antenna. In particular, an omnidirectional antenna may radiate electromagnetic energy over a wider range of dimensions, whereas a directional antenna may focus the radiation of electromagnetic energy over a narrower range of directions. The distance to which the near field extends relative the antenna is closely tied to the wavelength (e.g., dominant wavelength) or wavelengths of the signal which are emitted by the antenna. Indeed, the near field is a geometrical region defined relative the antenna in which electromagnetic waves may deviate significantly from those found in free space, wherein changes in dielectric permittivity affect the antenna impedance of the antenna, and this region is typically considered to extend roughly to within 1 wavelength. The wavelength is inversely proportional to the frequency. In some embodiments, it can be preferred for specifically for the area of interest of the living subject to be within the radiative near field of the antenna. The radiative near field of the antenna can be defined as a region extending between 1 / 6thof a wavelength and 1 wavelength.

[0008] While offering potential, the technique presented above may also, in some embodiments, bear a challenge. Indeed, different individuals of a same species, particularly when they are of different sizes for instance, may have significantly different effects on the antenna impedance, and while the phenomena harnessed in the proposed technique is referred to as “impedance mismatch”, the label may be to a certain extent confusing, because a relatively high degree of matching between the antenna impedance of the antenna and the impedance of the electrical circuit may be required to avoid a scenario where the proportion of the signal reflected back into the circuit vs emitted by the antenna is so high so as to make it difficult or impossible to extract a biosignal from it. Impedance mismatch may thus refer to relatively minute degrees of impedance mismatch in a general context where the impedance generally matches. Accordingly, in many embodiments, while the phenomenon of impedance mismatch is indeed the phenomenon which is harnessed in the acquisition of the biosignal, when designing the system, it may nonetheless be desired to achieve as good a match as feasible between the antenna impedance of the antenna when in its condition of use, and the impedance of the electrical circuit. Even if the match is in theory perfect, variations in the dielectric permittivity in the near field of the antenna, and / or variations in the mechanical deformation of the antenna, as can be expected to stem from natural biological changes in a living subject, can lead to varying degrees of impedance mismatch which can be harnessed as a source of biological signal. Henceforth the expression “matching the impedance” should not be construed as contrary to, or excluding the presence of impedance mismatch in this specification.

[0009] One approach to matching the antenna impedance of the antenna (in its condition of use with a region of interest of the living subject in its near field) to the impedance of the electrical circuit is to include variable impedance elements in the electrical circuit itself, and to change the configuration of the variable impedance element(s) in a manner to achieve a sufficiently close match between the impedance of the circuit and the antenna impedance of the antenna to allow harnessing the phenomenon of impedance mismatch to acquire a biosignal. Variable impedance elements are circuit components which can have more than one configuration, and for which the configuration can be changed (adjusted) to change the impedance of the electrical circuit. In other words, in a specific condition of use, e.g., while the antenna is electromagnetically engaged with a subject having a specific set of biologicalcharacteristics positioned within its near field, the impedance of the variable impedance element can be adjusted to bring the impedance of the circuit closer to or farther away from the antenna impedance of the antenna. In this manner, the impedance of the electrical circuit can be matched to the antenna impedance of the antenna in its condition of use by changing the configuration of the one or more variable impedance elements of the electrical circuit. While this approach can offer flexibility to adapt to changes of antenna impedance which could stem from applying the system to subjects having different biological characteristics and thus different geometrical configurations of dielectric permittivity, it does so at the cost of using variable impedance elements in the electrical circuit, which may be undesired. In particular, variable impedance elements are relatively costly and may significantly complexify the electrical circuit, as they require a processor for adjustment, which often involves complex algorithms. This makes them less interesting as a solution in many embodiments, and particularly when targeting consumer electronics to be mass marketed and where price point and power efficiency may be significant factors in commercial success or failure.

[0010] Another approach is to, rather than performing the matching of the impedance by adjusting the configuration of one or more variable impedance element forming part of the circuit, perform the matching based on the selection or design of the antenna itself, taking into consideration the effect that the presence of a region of interest of the subject within its near field can be expected to have on the antenna impedance in the intended conditions of use. In this case, the electrical circuit can be devoid of variable impedance elements, and rather have a characteristic impedance. The characteristic impedance being fixed and not being dynamically tuned by a controller during use of the system. This approach can require to design the antenna with specialized software which can simulate the antenna impedance in a modelized condition of use. Moreover, it was found that, while it was preferred to target a theoretically perfect match between the antenna impedance and the characteristic impedance of the circuit, there could be some degree of tolerance in some embodiments, which could be harnessed in using a single antenna for acquiring a biological signal from different users having biological characteristics which vary, within a certain extent. For instance, a single antenna size may be able to accommodate significant differences in weight between different users, e.g. adult human users. Accordingly, a limited number of different antenna sizes may be used for a limited number of different user types, and a system may be provided with asingle antenna adapted to a given user type, or with a single electrical circuit, but with a set of different antennae, with each antenna targeting a different user type. The degree of tolerance in differences between the antenna impedance and the characteristic impedance of the circuit, and conversely, the targeted degree of precision expected by the expression “matching”, can depend on a number of additional factors, such as the power of the source signal, and the degree of matching between a main frequency of the source signal and a resonance frequency of the antenna for instance. In several contexts, such as in the case of consumer electronics in particular, it can be desired to limit the power of the source signal, such as for reasons including cost considerations and health and safety considerations.

[0011] In a context where the frequency is inversely proportional to wavelength, and wavelength affects the distance to which the near field extends from the antenna, and thus the penetration depth of biological signal acquisition, it can be desired to select a main frequency as a function of the nature of the biosignal which is targeted. Indeed, if heart rate acquisition is targeted for instance, a penetration depth reaching the heart of the subject can be targeted. Since some antennae are more efficient when operating at their resonance frequency, it can be desired to design or select an antenna having a resonance frequency which corresponds to the intended penetration depth for biosignal acquisition. It is to be noted moreover that stretching of the antenna can affect its resonance frequency, can affect the emission frequency, and can affect antenna impedance, and that such factors may need to be taken into account in the context of the latter approach.

[0012] In accordance with one aspect, there is provided a system for acquiring a biosignal from a living subject, the system comprising : a circuit including an output, an electrical signal source electrically connected to the output, configured for generating a source signal, and a meter electrically connected to the output, the circuit having a characteristic impedance, the characteristic impedance being fixed; and an antenna electrically connected to the output of the circuit for receiving the source signal, the antenna having a near field and an antenna impedance, the antenna impedance matching with the characteristic impedance of the circuit when driven by the source signal, when a region of interest of the living subject is within a near field of the antenna and when the antenna is electrically insulated from the region of interest

[0013] In accordance with another aspect, there is a method of acquiring a biosignal from a living subject, the method comprising : generating a source signal with an electrical circuit having a characteristic impedance; driving an antenna with the source signal while i) maintaining a region of interest of the living subject within a near field of the antenna, and ii) maintaining the antenna electrically insulated from the region of interest, the antenna exhibiting an antenna impedance matching the characteristic impedance of the electrical circuit during said driving; a portion of the source signal reflecting back from the antenna into the electrical circuit during said driving; and performing a measurement of the portion of the source signal reflecting back.

[0014] Many further features and combinations thereof concerning the present improvements will appear to those skilled in the art following a reading of the instant disclosure.

[0015] DESCRIPTION OF THE FIGURES

[0016] In the figures,

[0017] Fig. 1 is an oblique view of an example of a system for acquiring a biosignal from a living subject, worn by an example living subject;

[0018] Fig. 2 is a block diagram of an example of a system for acquiring a biosignal from a living subject;

[0019] Figs 3A, 3B and 3C are examples of biosignals;

[0020] Fig. 4 is a schematic representation of yet another example of a system for acquiring a biosignal from a living subject;

[0021] Figs 5A and 5B are block diagrams of examples of systems for acquiring a biosignal from a living subject;

[0022] Fig. 6A is a graph representing an example of sample extracted respiration signal with the example system of Fig. 1 and with a reference medical system;

[0023] Figs 6B and 6C are graphs presenting results of a Bland-Altman analysis based on comparisons such as exemplified in Fig. 6A;

[0024] Fig. 7A is a graph representing an example of sample extracted heart signal with the example system of Fig. 1 and with a reference medical system;

[0025] Fig. 7B is a graph presenting results of a Bland-Altman analysis based on comparisons such as exemplified in Fig. 7A; and

[0026] Fig. 8 is a block diagram representation of a computer.DETAILED DESCRIPTION

[0027] Fig. 1 shows an example of a system 10 for acquiring a biosignal from a living subject. In this example, the system 10 includes an antenna 12 which is worn by the subject, and a circuit which is electrically connected to the antenna 12. In this example, the circuit is housed in a circuit housing 14 which is shown, and is selectively connectable and disconnectable from the antenna 12 via a connector 16. The presence of a connector(s) offering selective connectability is optional as alternate embodiments may be more permanently connected (e.g., welded), but can nonetheless be an interesting feature of the system. The circuit may or may not include a cable. The output 18 of the circuit can correspond to the point of connection of the antenna 12.

[0028] Fig. 2 shows a block diagram of a system 10 for acquiring a biosignal from a living subject. As depicted in this diagram, the circuit 14 can have a source 20 configured to generate a source signal. The source signal can be an oscillatory electrical signal having a main frequency. The source 20 can be electrically connected to an output 18 of the circuit 14, to which the antenna 12 can also be connected in a manner to be driven by the source signal. The circuit 14 can further include a meter 22 also connected to the output 18. The circuit 14 can have a characteristic impedance. This characteristic impedance is a characteristic impedance of the circuit 14, i.e., at the output 18, not to be confused with the characteristic impedance of any transmission line between the output 18 and the antenna 12. The characteristic impedance is fixed, e.g., which is not variable or more specifically not dynamically tunable during use of the system 10. Otherwise said, the circuit does not includea variable impedance-matching element at the output 18. The circuit 14 can thus be devoid of variable impedance elements. An antenna impedance, as seen from the output 18, can depend on a plurality of factors, including the antenna 12, the presence of matter in a near field of the antenna 12, and the presence of any transmission line between the output 18 and the antenna 12. The antenna 12 can be selected in a manner for its antenna impedance to match the characteristic impedance of the circuit 14 when the system is in an intended configuration of use. In the example presented in Fig. 1 , the intended configuration of use is illustrated, and includes a region of interest of a living subject, in this case a chest of an adult human, being within the near field of the antenna 12. The region of interest of the living subject can have a dielectric permittivity which is different from the dielectric permittivity of air or of empty space, and its presence in the near field of the antenna 12 can thus affect the antenna impedance of the antenna 12.

[0029] The source 20 can generate a source signal which drives the antenna 12. Variations in the biological configuration of the region of the living subject which is in the near field of the antenna 12 cause somewhat minor, but detectable, variations in the antenna impedance of the antenna 12. Such variations in the biological configuration can be caused, for instance, by respiration and / or by the beating of a heart of the subject for instance. The variations in the antenna impedance of the antenna cause variations in the impedance mismatch between the antenna impedance of the antenna and the characteristic impedance of the circuit 14, and these variations in the impedance mismatch affect, in real time, the degree of signal reflection between the circuit 14 and the antenna 12. Since an oscillatory electrical signal can be represented with complex numbers, the oscillatory electrical signal can have an imaginary component and a real component, or a phase as well as a magnitude. Reflection can affect the phase and / or magnitude (real or imaginary component) (Ph / Mag) of the source signal. Henceforth, a time-varying portion of the source signal can be said to be reflected based on the time-varying impedance mismatch. The meter 22 can be configured to acquire a measurement indicative of this time-varying portion of the source signal which is reflected, and which can be referred to as the reflected signal. In practice, this measurement can be indirect as will be detailed below.

[0030] An example of a raw signal which can be acquired by the meter 22 is presented in Fig. 3A. As will be explained in greater detail below, this raw signal may be processed at a given point in time using a computer and associated software. In the case of a raw signal such as shown in Fig. 3A, which was acquired using an antenna 12 for which both lungs and the heart of a subject was present in the near field, processing of the raw signal can allow to extract a respiration signal, such as presented in Fig. 3B for instance, and a heart rate signal, such as presented in Fig. 3C. The type of biosignal which can be extracted from the raw signal will depend on the context of a given embodiment or application.

[0031] Moreover, in the example presented in Fig. 1 , the antenna 12 is a stretchable antenna which is integrated to a wearable item 24 tightly fitted, and thus mechanically coupled, to the area of interest of the living subject. The mechanical coupling affects the stretching of the antenna 12, and thus the resonance frequency of the antenna 12 and the antenna impedance of the antenna 12. The mechanical coupling is such that geometrical changes in the living subject, such as may occur during respiration for instance, can affect the degree of stretching and thus the resonance frequency of the antenna 12 and the antenna impedance 12. It was found that harnessing the stretchability of the antenna 12 in obtaining biosignals such as the respiration signal for instance, could in some embodiments, contribute to amplify the effect of the variations in dielectric permittivity and lead to a higher quality signal. It will be noted however here that the stretchability of the antenna 12 is an optional feature which may be omitted in alternate embodiments.

[0032] Indeed, impedance of an antenna is a function of geometrical factors and the effective relative permittivity of the dielectric surrounding the antenna’s radiating elements in the near field range. Considering a dipole antenna as an example of an antenna used for obtaining the biosignals, the dipole antenna having a length d in free space and a resonating frequency f,[L0033] J

[0034] where c is the speed of light in vacuum. In a medium with effective relative dielectric permittivity erefr, the equation can be written as:

[0036] Therefore, a change in the effective relative dielectric permittivity causes a shift in the resonance frequency of the dipole antenna. The resonance frequency is a frequency where the imaginary part of the impedance is zero. A similar behavior may be observed with other antenna types such monopole antennas, patch antennas, and loop antennas, to give some alternate examples.

[0037] On the other hand, in a case where the antenna 12 is a flexible antenna such as in the example presented in Fig. 1 , changes in the dimension d of the antenna 12 also affects the resonance frequency f in light of the equation presented above.

[0038] It will be noted that using a flexible antenna 12 which stretches via mechanical coupling with the user can allow detecting a respiration signal when the antenna 12 is positioned on a region of interest which moves with respiration, even if the relative permittivity remains relatively constant, such as positioning the flexible antenna on the abdomen of a subject, in which case only the second contribution, that of the mechanical deformation of the flexible antenna, may constitute a significant contribution to the biosignal.

[0039] Referring back to Fig. 2, the system 10 may further include an optional controller 26. The controller 26 may or may not include a computer. The controller 26 can have relatively simple functions, such as storing or transmitting the raw signal in a raw or partially processed form, to be later analyzed with a more elaborate computer or more elaborate software. Alternately, the controller 26 can directly provide more elaborate functions such a processing the signal in a more elaborate manner, and or display the data. Examples of basic processing functions can include compressing the data, for instance. Examples of more elaborate processing functions can include extracting a respiration signal and / or a heartbeat signal from the raw signals, or extracting higher level parameters from such signals, such as respiration rate, respiration amplitude, inspiration / expiration time, respiration period, heartbeat rate and / or heartbeat rate variability for instance.

[0040] In the example embodiment presented in Fig. 4, for instance, a controller 26 included as part of the on-body sensor system 10 includes a transmitter which can transmit the rawsignal over a short-range data stream, such as via Bluetooth™, for instance, to a local computer such as a smartphone. The local computer can be provided with capabilities of transmitting data over a telecommunications network such as the Internet, e.g., via WiFi™, over additional devices, possibly through a cloud computer. A remote computer such as a clinic server may access the data via Internet communication, e.g., by logging into the cloud to retrieve the data. Processing may occur at any one of such computers, e.g., local computer, cloud computer, remote computer.

[0041] As presented above, two example signal acquisition schemes will now be presented in relation with Figs. 5A and 5B. In the embodiment presented in Fig. 5A, the meter includes a sampler which branches off a portion of the reflection signal incoming from the output to the detector, away from the source (the detector remains electrically insulated from the source). In this configuration, the detector performs an absolute measurement on the reflection signal (or more specifically, on the portion of the reflection signal which is branched off, which is indicative of the reflection signal). In one embodiment, in accordance with this approach, the detector can be an absolute power detector such as a root mean square (RMS) detector, an envelope detector, or another detector which can perform a measurement of a single signal. The detection signal communicated from the meter to the controller can be an absolute power of the reflection sample.

[0042] In the embodiment presented in Fig. 5B, the meter includes a sampler which branches off a portion of the reflection signal incoming from the output to the detector, and also branches off a portion of the source signal emitted by the source, between the source and the output, to the detector. The detector can be configured to perform a differential measurement between the branched off portion of the source signal and the branched off portion of the reflected signal. A differential measurement may allow to provide more information than an absolute measurement, as it can provide information on the imaginary part, or phase. The detector can be a phase and magnitude detector (Ph / Mag detector), or an IQ detector, for example. The detection signal communicated from the meter to the controller can be magnitude, phase, I, Q or any combination thereof.

[0043] Indeed, the detector can receive a sample of the antenna’s reflection signal as input and provide a raw signal as output, based on the absolute power of the input signal.Alternately, the detector can receive a sample of the antenna’s reflection signal as a first input and a sample of the source signal as a second input and provide a relative coefficient as output. For instance, the detector can provide one or more one detection signal as output, based on the relative magnitude or the relative phase of the first input signal compared to the second input signal or based on the in-phase (I) component and / or the quadrature (Q) component of the first input signal compared to the second input signal.

[0044] The expression sampler is used to refer to a circuit element, or to a combination of circuit elements, which perform(s) the above-identified branching off function(s). Such circuit element(s) can include a directional coupler, a circulator, a power splitter, a Y splitter, a power splitter with electrical insulation, a Wilkinson divider, to name some examples. The sampler can be a distribution circuit, for instance.

[0045] In some embodiments such as the ones shown in Fig. 5A and 5B, the source can be a signal generator producing a monotonic, continuous wave (CW), radiofrequency (RF) signal to be fed to the antenna. The sampler can be a subcircuit configured to capture the signal reflected from the antenna back to the circuit, which can be implemented using a directional coupler placed between the RF generator and the antenna. A detector can be a RF detector subsystem for measuring the reflected signal’s phase, magnitude, or both, or an IQ detector for measuring in-phase and quadrature components of the signal. An example of an RF detector is the AD8302 (Analog Devices Inc., Wilmington, MA, US), which can measure the phase and magnitude of the reflected signal compared to a reference RF signal sampled from the signal generator.

[0046] The measured values can then be passed to an onboard processor or transferred to an external system for real-time signal processing, long-term storage, and telemetry to medical professionals.

[0047] The operation frequency of the antenna and the circuit can be selected according to the respective wavelength. A too low frequency may lead to an inconveniently large antenna dimension, which may be hard to integrate with wearables. On the contrary, a too high frequency may shrink the antenna and the signal penetration, and may reduce the signal quality due to limited chest area coverage and reduced penetration depth. The frequencies inthe range of 450 MHz up to 2.8 GHz (equalling wavelengths 66 cm down to 10cm) were investigated in the laboratory, and vital signals could be acquired. The circuit does not necessarily need to operate precisely over the antenna’s resonance frequency, but operating closer to the antenna’s resonance frequency can provide better sensitivity. Another parameter can be the choice of the RF signal’s power level, which may depend on the sensitivity of the power detector utilized in the circuit design. For example, for the AD8302 power detector, a signal power of -30 dBm can be enough to provide a confident reading with limited noise.

[0048] In some embodiments, it can be preferred for the return loss to be below -3 dB, below -6 dB or below -10 dB. The return loss being defined as I ),wherein Z is the antenna impedance, as defined above, which is the impedance seen looking toward the antenna 12 from the output 18 of the circuit, including the effects of any transmission line or cable in between and the antenna 12 at the end, while Zcis the characteristic impedance of the circuit. Impedance is a complex number which can be expressed as Z = R + jX, where R is resistance, X is reactance, and j is the imaginary unit. In some embodiments, it can be preferred to adapt the system for the antenna impedance in the 7 conditions of operation to respect 73 < Re{ } < 3ZCand -2ZC< Im{Z} < 2ZCor to respectZc / ^ < Re{Z} < 3ZCand -Zc< Im{Z} < Zcwhere Re{Z} denotes the real part and lm{Z} denotes the imaginary part of Z. In some embodiments, it can be preferred for the frequency to be around 850-950 MHz for instance. In some embodiments, it can be preferred for the frequency to be below 850 MHz or above 950 MHz, such as around 424 MHz, or such as around 2.45 GHz, to name some examples.

[0049] A controller may be onboard or external may include one or more data input interface to read the output(s) provided by the detector circuit. Example of data input interfaces include analog to digital converters (ADCs), digital inputs (SPI, Serial, GPIO, etc.), etc. In one example, a switch is provided to toggle the output of the source on and off in specific time periods. In one example, the output power level and frequency the source signal can be changed. Raw or processed data can be displayed to a user or medical units using appropriate computer hardware and software.

[0050] In one example, an on-board controller transmits or exports data from the biosignal (e.g., via Bluetooth, BLE, LoRaWAN, Wifi, LTE, 5G via wired, wireless, or both connectivity methods to another system for processing, storage, or displaying to the user or medical units (e.g., by directly saving data to internal or USB flash disks, HDDs, SSDs, MicroSD cards, etc.)

[0051] The antenna can be sewn on a T-shirt with a regular comfortable fit and does not require a tight fitting. When the change in dielectric permittivity is a significant biosignal source, the system can operate even if the T-shirt is loose or there is a gap or extra clothing layers between the antenna and the chest surface. In another embodiment, the antenna can be more tightly mechanically coupled to the subject, such as via a band, a belt, or bandage, and can further be harnessed to use stretchability of the antenna as a significant biosignal source. The antenna sensor can be placed over or embedded in a wearable item such as garment, a bandage, a band, a necklace, or a skin patch wherein the whole or a part of the circuit can also be placed over or embedded in the wearable item.

[0052] The acquired signals can be processed to extract various vital information, including respiratory and cardiac activity waveforms and parameters such as respiratory rate, respiratory amplitude, inspiration time, expiration time, respiratory period, heart rate, and heart rate variability. This list is not exhaustive, since we might be able to extract more hidden info and parameters from the signals in future steps of the project, and not all waveforms and parameters would be necessarily available for all configurations and embodiments.

[0053] In one example mode of operation, the antenna conductors are insulated from the subject’s skin by a layer of non-conductor material, such as by introducing an insulating sheet of material therebetween or coating the antenna within a plastic cover or patch, etc.

[0054] Depending on the embodiment, the system can be provided with a plurality of different antennae each specifically adapted to a specific type of subject. The associated method of operation can include selecting the antenna from the plurality of antennas based on the specific type of subject, for the antenna to exhibit the antenna impedance matching the characteristic impedance of the electrical circuit during operation, and connecting the antenna to the electrical circuit prior to operation. The type of subject can depend on characteristics ofsubjects of a given specie, such as different size groups of a human beings for instance (e.g. small, medium, large, baby, adult, etc.), or can depend on the species of the subject.

[0055] Several different types of antennae can be used depending on the embodiment, and in some embodiments, the antenna can be rigid (non-flexible). Examples of antennae include wire antennae such as different variants of dipole, monopole, loop, or helix antennae, planar antennae such as different variants of patch, printed dipole, printed monopole, and chip antennae, and perhaps other forms of antennae such as an aperture antenna. Specific examples of rigid antennae having been successfully tested include a circular pin-fed patch antenna operating at 960 MHz, monopole PCB trace antenna (KYOCERA AVX 1002089) at 727MHz, and ceramic chip antenna (Abracon ACAG1204-915-T) at 902 MHz. Another example of antennae is a rigid sinusoidal dipole antenna.

[0056] The characteristic impedance of the circuit can vary from one embodiment to another. For the sole purpose or providing examples, 50 ohms or 75 ohms are relatively common values.

[0057] It will be understood that the source can have different configurations, such being operable at different frequencies, and / or different power levels, including potentially to be selectively switchable on or off during use, such as to account for intermittent power cycling. The changes of configuration of the source may have an effect on impedance, but are not considered to define the characteristic impedance of the circuit. For example, the impedance at the output might change if the frequency or power of the signal generator changes, but the characteristic impedance may nonetheless be considered to be fixed and defined by the absence of variable-impedance (or impedance-matching) element in the circuit and the fact that it is not dynamically tunable during operation specifically to this end by a controller.

[0058] To validate the medical efficiency of using a system 10 such as presented in Fig. 1 to acquire a respiratory signal and / or to acquire a heart signal, Bland-Altman analyses were made using “gold standard” reference systems, namely a spirometer for respiration and a pulse oximeter for cardiac monitoring. The Bland-Altman method creates a scatter plot with y- axis showing the difference between the two readings, and the x-axis showing their average. The mean of difference (MoD) reveals the systematic bias, the spread of the datapointsreflects agreement between the methods, and the limits of agreement (LoA) are ±1.96 x standard deviation, representing the 95% percentile confidence range. Agreement was demonstrated, as will now be detailed.

[0059] Fig. 6A presents two respiration signals. The first one, at the top, shown as a solid line, shows the extracted respiratory signal from the antenna reflection magnitude using the system 10 such as presented in Fig. 1. The second one, at the bottom, presents the spirometer exchanged volume acquired from the spirometer, which is considered a gold standard, medical-grade reference system for respiration signals.

[0060] Fig. 6B and 6C show the scatter plots acquired with the Bland-Altman analysis for respiratory signal acquisition. The dashed lines show ±LoA and the solid line shows MoD. The parameters mentioned in these figures are defined as follows:Table 1 : Parameters used in the Bland-Altman analysis for respiratory signal acquisition for male and female volunteers

[0061] The calculated Bland-Altman parameters for respiratory signal acquisition are as follows:Table 2: Calculated B and-Altman parameters for respiratory signal acquisition (MoD ± LoA)

[0062] These very low MoD and LoA values show the great agreement between the results obtained from the system 10 and those obtained from the reference medical device (spirometer).

[0063] Fig. 7A presents two cardiac signals. The first one, at the top, shown as a solid line, shows the extracted cardiac signal from the antenna reflection magnitude using the system 10 such as presented in Fig. 1. The second one, at the bottom, presents the photoplethysmogram (PPG) amplitude acquired from the pulse oximeter as the medical reference system for cardiac signals.

[0064] Fig. 7B shows the scatter plots acquired with the Bland-Altman analysis for cardiac signal acquisition. The dashed lines show ±LoA and the solid line shows MoD. The parameters mentioned in the Fig. 7B are defined as follows:

[0065] The calculated Bland-Altman parameters for cardiac signal acquisition are as follows:Table 4: Calculated B and-Altman parameters for cardiac signal acquisition (MoD ± LoA)

[0066] These very low MoD and LoA values show the great agreement between the results obtained from the system 10 and those obtained from the reference medical device (pulse oximeter).

[0067] Referring to Fig. 8, it will be understood that the expression “computer” 400 as used herein is not to be interpreted in a limiting manner. It is rather used in a broad sense to generally refer to the combination of some form of one or more processing units 412 and some form of memory system 414 accessible by the processing unit(s). The memory system can be of the non-transitory type. The use of the expression “computer” in its singular form as used herein includes within its scope the combination of a two or more computers working collaboratively to perform a given function. Moreover, the expression “computer” as used herein includes within its scope the use of partial capabilities of a given processing unit.

[0068] A processing unit can be embodied in the form of a general-purpose micro-processor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a fieldprogrammable gate array (FPGA), a reconfigurable processor, and a programmable read-only memory (PROM), to name a few examples.

[0069] The memory system can include a suitable combination of any suitable type of computer-readable memory located either internally, externally, and accessible by the processor in a wired or wireless manner, either directly or over a network such as the Internet. A computer-readable memory can be embodied in the form of random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) to name a few examples.

[0070] A computer can have one or more input / output (I / O) interface to allow communication with a human user and / or with another computer via an associated input, output, or input / output device such as a keyboard, a mouse, a touchscreen, an antenna, a port, etc. Each I / O interface can enable the computer to communicate and / or exchange data with other components, to access and connect to network resources, to serve applications, and / or perform other computing applications by connecting to a network (or multiple networks) capable of carrying data including the Internet, Ethernet, plain old telephone service (POTS) line, public switch telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fiber optics, satellite, mobile, wireless (e.g. Wi-Fi, Bluetooth, WiMAX), SS7 signaling network, fixed line, local area network, wide area network, to name a few examples.

[0071] It will be understood that a computer can perform functions or processes via hardware or a combination of both hardware and software. For example, hardware can include logic gates included as part of a silicon chip of a processor. Software (e.g. application, process) can be in the form of data such as computer-readable instructions stored in a non-transitory computer-readable memory accessible by one or more processing units. With respect to a computer or a processing unit, the expression “configured to” relates to the presence of hardware or a combination of hardware and software which is operable to perform the associated functions. Different elements of a computer, such as processor and / or memory, can be local, or in part or in whole remote and / or distributed and / or virtual.

[0072] As can be understood, the examples described above and illustrated are intended to be exemplary only. Indeed, the system and method described herein can be adapted for use on other types of living beings than humans, such as cattle for instance, and can be used to measure biosignals other than respiration-based or heartbeat- based, such as biosignals indicative of muscular activity for instance. The scope is indicated by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A system for acquiring a biosignal from a living subject, the system comprising : a circuit including an output, a source electrically connected to the output, configured for generating a source signal, and a meter electrically connected to the output, the circuit having a characteristic impedance, the characteristic impedance being fixed; and an antenna electrically connected to the output of the circuit for receiving the source signal, the antenna having a near field and an antenna impedance, the antenna impedance matching with the characteristic impedance of the circuit when driven by the source signal, when in a configuration of use, in which configuration of use a region of interest of the living subject is within a near field of the antenna, the antenna is electrically insulated from the region of interest, and the antenna is driven by the source signal.

2. The system of claim 1 wherein the antenna is a stretchable antenna integrated to a wearable item configured for being worn by the living subject in a manner which mechanically couples the stretchable antenna to geometrical changes in the living subject, the antenna impedance of the antenna changing with the stretching of the antenna.

3. The system of claim 2 wherein the wearable item is a garment.

4. The system of any one of claims 1 to 3 wherein a return loss is below -3 dB, the return loss being defined as RL = I ), wherein Z is the antenna impedance andZcis the characteristic impedance.

5. The system of claim 4 wherein the return loss is below -6 dB.

6. The system of claim 5 wherein the return loss is below -10 dB.

7. The system of any one of claims 1 to 6 wherein the near field extends to within 1 wavelength of the resonance frequency.

8. The system of any one of claims 1 to 7 wherein the source has different configurations corresponding to source signals having different main frequencies and is adjustable between the different configurations during use.

9. The system of any one of claims 1 to 8 wherein the source has different configurations corresponding to source signals having different power levels, and is adjustable between the different configurations during use.

10. The system of any one of claims 1 to 9 wherein the source is operable to be selectively activated or deactivated during operation.11 . The system of claim 1 wherein a portion of the source signal reflects back from the antenna into the circuit due to impedance mismatch between the antenna impedance and the characteristic impedance, forming a reflection signal, the meter includes a sampler and a detector, the sampler branching off a portion of the reflection signal to detector, away from the source, the detector performing a measurement based on the portion of the reflection signal.

12. The system of claim 11 wherein the detector is an absolute power detector.

13. The system of claim 11 wherein the sample further branches off a portion of the source signal to the detector, and the detector measures a difference between the portion of the reflection signal and the portion of the source signal.

14. The system of claim 13 wherein the detector is a phase and magnitude detector.

15. The system of claim 13 wherein the detector is a phase or magnitude detector.

16. The system of claim 13 wherein the detector is an in-phase and quadrature (IQ) component detector.

17. The system of claim 13 wherein the detector is an in-phase (I) or quadrature (Q) component detector.

18. The system of claim 11 further comprising a controller electrically connected to the detector, the controller performing at least one of storing values stemming from the measurement in a non-transitory computer readable memory and transmitting the values stemming from the measurement.

19. A method of acquiring a biosignal from a living subject, the method comprising : generating a source signal with an electrical circuit having a characteristic impedance; driving an antenna with the source signal while i) maintaining a region of interest of the living subject within a near field of the antenna, and ii) maintaining the antenna electrically insulated from the region of interest, the antenna exhibiting an antenna impedance matching the characteristic impedance of the electrical circuit during said driving; a portion of the source signal reflecting back from the antenna into the electrical circuit during said driving; and performing a measurement of the portion of the source signal reflecting back.

20. The method of claim 19 wherein the antenna is a stretchable antenna integrated to an item worn by the living subject during said driving, the method further comprising stretching the antenna based on geometrical changes in the living subject, and changing the antenna impedance of the antenna based on the stretching of the antenna during said driving.

21. The method of claim 19 or 20 further comprising branching off a portion of the portion of the source signal reflecting back away from a source of the source electrical signal, said performing the measurement including performing a measurement of the branched off portion.

22. The method of any one of claims 19 to 21 wherein said performing the measurement includes measuring variations in absolute power over time.

23. The method of claim 21 further comprising branching off a portion of the source signal away from the antenna, wherein said performing the measurement includes measuring variations in differences between the portion of the source signal and the portion of the portion of the source signal reflected back.

24. The method of any one of claims 19 to 23 further comprising storing values stemming from said performing the measurement over time into a non-transitory computer readable memory.

25. The method of any one of claims 19 to 23 further comprising transmitting values stemming from said performing the measurement over time in a wireless manner.

26. The method of any one of claims 19 to 25 further comprising selecting the antenna from a plurality of antennas having different features, for the antenna to exhibit said antenna impedance matching the characteristic impedance of the electrical circuit during said driving, and connecting the antenna to the electrical circuit.

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