Near-field measurement device

Abstract

One example discloses a near-field measurement device comprising: a near-field antenna; a tuning circuit electrically coupled to the near-field antenna and configured to set a resonant frequency and / or a quality factor of the measurement device; and a current sensor inductively coupled to the near-field antenna and configured to generate a signal in response to a current flowing through the electrical coupling between the near-field antenna and the tuning circuit; wherein the signal is representative of a measurement of a non-propagating quasi-static near-field signal received by the near-field antenna.

Description

TECHNICAL FIELD

[0001] This specification relates to systems, methods, devices, apparatus, articles of manufacture, and instructions for near-field measurements. BACKGROUND

[0002] Discussed herein are near-field devices based on near-field electromagnetic induction (NFEMI) that can interact with other conductive surfaces and / or other wireless networking devices (e.g., Internet of Things (IoT) devices, wearables, earbuds, body area networks, gaming products, and medical products such as continuous glucose monitoring, etc.) on or near a user's body, where both transmitter and receiver couple through both magnetic (H) and electric (E) fields. While RF wireless communication is achieved by propagating RF plane waves through free space, NFEMI communication utilizes non-propagating quasi-static H and E fields.

[0003] H-field antennas (i.e., magnetic antennas) are primarily sensitive to magnetic fields and / or primarily induce magnetic fields when driven by a current. Any E-field component from an H-field antenna is greatly reduced (e.g., by -20 to -60 dB, a factor of 0.1 to 0.0008 (10% to 0.08%), depending on the antenna design).

[0004] Small loop antennas are example H-field antennas and include loop antennas that are much smaller in size than the wavelength they use. Small loop antennas do not resonate at the NFEMI carrier frequency, but instead are tuned to a resonant state by an external reactance. In some example embodiments, the current in a small loop antenna has the same value in each location around the loop.

[0005] E-field antennas (i.e., electric antennas) are primarily sensitive to electric fields and / or primarily induce electric fields when driven by a voltage. Any H-field component from an E-field antenna is greatly reduced (e.g., by -20 to -60 dB, a factor of 0.1 to 0.0008 (10% to 0.08%), depending on the antenna design). SUMMARY

[0006] According to an example embodiment, a near-field measurement device, comprising: a near-field antenna; a tuning circuit, the tuning circuit galvanically coupled to the near-field antenna and configured to set a resonant frequency and / or a quality factor of the measurement device; and a current sensor, the current sensor inductively coupled to the near-field antenna and configured to generate a signal in response to a current flowing through the galvanic coupling between the near-field antenna and the tuning circuit; wherein the signal represents a measurement of a non-propagating quasi-static near-field signal received by the near-field antenna.

[0007] In another example embodiment, the current sensor is a transformer or a toroidal coil.

[0008] In another example embodiment, the current sensor is configured to amplify the current flowing in the current coupling.

[0009] In another example embodiment, the tuning circuit includes a capacitance and a resistance.

[0010] In another example embodiment, the near-field antenna includes a set of conductive surfaces configured to respond to an electric near-field signal; the conductive surfaces together form a capacitance; the tuning circuit capacitance is greater than the conductive surfaces capacitance, such that a greater portion of the current flowing through the near-field antenna flows through the tuning circuit capacitance; and the current sensor is inductively coupled in series with the tuning circuit capacitance and in parallel with the tuning circuit resistance.

[0011] In another example embodiment, additionally comprising a sensing element; wherein the current sensor includes a primary winding and a secondary winding; wherein the primary winding is galvanically coupled to the near-field antenna; and wherein the secondary winding is inductively coupled to the primary winding and galvanically coupled to the sensing element.

[0012] In another example embodiment, the sensing element includes a resistance; the signal is a voltage; and the resistance is configured to generate the voltage in response to the current flowing through the primary winding.

[0013] In another example embodiment, the sensing element includes a low-noise amplifier; the signal is a voltage; and the low-noise amplifier is configured to generate an amplified output signal in response to the current flowing through the primary winding.

[0014] In another example embodiment, the sensing element is configured to be coupled to a measurement instrument; and the measurement instrument is configured to output a magnetic near-field strength signal and / or an electric near-field strength signal in response to the current flowing through the primary winding.

[0015] In another example embodiment, the sensing element is configured to be coupled to a baseband communication circuit; and the communication circuit is configured to output a communication signal in response to the current flowing through the primary winding.

[0016] In another example embodiment, the tuning circuit includes a variable tuning capacitance bank configured to set a resonant frequency of the near-field antenna in response to a control line.

[0017] In another example embodiment, the tuning circuit includes a variable tuning resistance bank configured to set a quality factor or a bandwidth of the near-field antenna in response to a control line.

[0018] In another example embodiment, the tuning circuit includes a fixed tuning capacitance configured to set a fixed resonant frequency of the near-field antenna, and a fixed tuning resistance configured to set a fixed quality factor or bandwidth of the near-field antenna.

[0019] In another example embodiment, the current flowing in the galvanic coupling between the near-field antenna and the tuning circuit is generated solely by the non-propagating quasi-static near-field signal received by the near-field antenna.

[0020] In another example embodiment, the near-field antenna is a near-field magnetic antenna responsive to a non-propagating quasi-static near-field magnetic signal.

[0021] In another example embodiment, the near-field antenna is a near-field electric antenna responsive to a non-propagating quasi-static near-field electric signal.

[0022] In another example embodiment, the near-field antenna is a near-field electromagnetic antenna responsive to a non-propagating quasi-static near-field electric and magnetic signals.

[0023] In another example embodiment, the near-field measurement device is configured to capacitively couple to an external conductive surface from which the measurement of the non-propagating quasi-static near-field signal is made.

[0024] In another example embodiment, the near-field measurement device is embedded in at least one of: a wearable device, a smart watch, a smart watch housing, an earbud, a hearing aid, a medical device, an activity tracker, or a heart rate monitor.

[0025] The above discussion is not intended as an example embodiment or an example implementation of every example embodiment or example implementation within the scope of the current or future claims. The following figures and detailed description further illustrate various example embodiments.

[0026] Various example embodiments can be more fully understood from the following detailed description, taken in connection with the accompanying drawings, in which: BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is an example near-field antenna.

[0028] Figure 2 is an example of a first near-field measurement device.

[0029] Figure 3 is an example application of a second near-field measurement device.

[0030] Figure 4 is an example application of a third near-field measurement device.

[0031] While the disclosure is susceptible to various modifications and alternative forms, the disclosure has been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that there is no intent to limit the disclosure to the particular, exemplary embodiments described. Modifications, equivalents, and alternatives are intended to be encompassed within the spirit and scope of the appended claims. DETAILED DESCRIPTION

[0032] Short load dipole antennas are example E-field antennas and include short dipoles that are much smaller in size than the NFEMI carrier frequency and in some example embodiments have additional capacitive surfaces at both ends.

[0033] The quasi-static nature of these fields is a result of the combination of the NFEMI antenna size and the NFEMI carrier frequency. Most of the near-field energy is stored in the form of magnetic and electric fields, while a small amount of RF energy inevitably propagates in free space. The small antenna geometry minimizes the radiated wave in free space.

[0034] Some wearables, such as hearing aids and wireless earbuds, use near-field magnetic induction (NFMI) as a wireless communication method. In NFMI wireless communication, two loosely coupled coils enable signal transfer. No radio wave radiation occurs. The current flowing in the transmitting coil generates an H-field, which in turn induces a current in the receiving coil. Wireless communication is achieved in this way. Disadvantageously, H-field based NFMI systems with small antenna coils have limited range, which can be much smaller than the entire wearable range of a user's body. Such H-field communication is sensitive to coil orientation. In the case of a hearing aid form factor, H-field induction based systems cannot cover the entire human body. However, since the two coils in a hearing aid are always aligned with each other, a hearing aid is not affected by body movement.

[0035] Other wearables use near-field electric induction (NFEI) as a wireless communication method. NFEI allows electronic devices on and near a conductive surface, such as a human body, to exchange information through E-field coupling, for example, at 21 MHz. NFEI is also sometimes referred to as body coupled communication (BCC). While E-field based NFEI signals can have a greater range than H-field based NFMI signals, E-field signal strength can vary with respect to body posture and is sensitive to body movement. The body can even partially block the capacitive return path, thereby increasing E-field channel loss and failing to enable reliable and robust wireless communication.

[0036] However, ensuring robust near-field communication can require careful measurement and characterization of the near-field environment around such devices (e.g., normal fields generated by the body, noise, other devices, etc.). Since such near-field signals are very close to a user's body and have a relatively low amplitude, such near-field signals can be difficult to measure.

[0037] Existing electric and magnetic field measurement instruments are designed to measure stronger and more distant far-field signals (e.g., for electromagnetic compatibility (EMC) and radiated field patterns, etc.). Such instruments can only be able to measure electromagnetic field strengths down to 500 mV / m.

[0038] Now discussed are example embodiments of near-field measurement apparatuses tailored to measure these concentrated, low-level near-field signals in the vicinity and / or surrounding of a conductive body surface. These example embodiments are able to measure electromagnetic field strengths down to 10 mV / m. Once captured, these near-field signals can then be recorded and characterized by additional diagnostic apparatuses such as spectrum analyzers or oscilloscopes.

[0039] Figure 1 is an example near-field antenna 100. In some example embodiments, the antenna 100 includes a coil (H-field) antenna 105 for magnetic fields, and a short loaded dipole (E-field) antenna 120 for electric fields. The H-field antenna 105 includes a ferrite core 110 wound with wire 115. The E-field antenna 120 includes two conductive load structures 125 and 130. The antenna 100 feed points 135, 140 are coupled to various tuning, measurement, and / or transceiver circuitry, such as downstream resonance frequency and bandwidth tuning sets, current sensors, and radio transmitter and receiver integrated circuits (RF-ICs).

[0040] When the NFEMI antenna 100 is in close proximity to a structure (e.g., a conductive structure, a body, a person, an object, etc.), in some example embodiments, the magnetic and electric fields that are generally confined to the structure and do not radiate strongly in free space can be measured with much greater sensitivity.

[0041] In various example embodiments, the antenna 100 operates at 50 MHz or below (e.g., at 30 MHz) to ensure that the fields follow the structure contours and to ensure that far-field radiation is greatly reduced.

[0042] While the near-field antenna 100 shown is a NFEMI antenna, in other example embodiments, only the coil (H-field) antenna 105 or the short loaded dipole (E-field) antenna 120 can be used alone if only the magnetic (H) field or electric field (E) is to be sensed and measured, respectively.

[0043] Figure 2 is an example of a first near-field measurement apparatus 200. The first near-field measurement apparatus 200 includes the near-field antenna 100, support circuitry 202, and is configured to receive non-propagating quasi-static near-field signals. The near-field measurement apparatus 200 is configured to receive and measure the non-propagating quasi-static near-field signals. It should be noted that in some example embodiments, the near-field antenna 100 can also be coupled to a transmitter circuit (not shown) for bidirectional communication.

[0044] The example idealized antenna 100 includes a magnetic (H-field) antenna 105 having a resistance (R3) and an inductance (LI), an electric (E-field) antenna 120 having a conductive structure formed by two load plates 125 and 130 and a resistance (R4), and two feed points 135, 140.

[0045] The support circuit 202 includes a tuning circuit 204, a current sensor 206, and a controller 216.

[0046] The tuning circuit 204 is coupled to the first feed point 135 and the second feed point 140. The tuning circuit 204 includes a first variable tuning capacitor bank (Cl), a second variable tuning capacitor bank (C2), a first variable tuning resistor bank (Rl), and a second variable tuning resistor bank (R2). The capacitor banks and the resistor banks are coupled to a ground 224. The capacitor banks are coupled to the controller 216 through control lines 218, and the resistor banks are coupled to the controller 216 through control lines 220.

[0047] The controller 216 adjusts the first capacitor bank (Cl) and the second capacitor bank (C2) to adjust the resonant frequency of the magnetic antenna 105 and the electric antenna 120 (e.g., to 10.6 MHz). The controller 216 adjusts the first resistor bank (Rl) and the second resistor bank (R2) to adjust the bandwidth of the magnetic antenna 105 and the electric antenna 120 (e.g., to 400 KHz) sufficient to allow reception of non-propagating quasi-static near-field signals from the antennas 105, 120.

[0048] The capacitor banks (Cl), (C2) are equally tuned using control lines 218 from the controller 216, and the resistor banks (Rl), (R2) are equally tuned using control lines 220 from the controller 216.

[0049] The current sensor 206 includes a primary winding 208 galvanically coupled to the near-field antenna 100 and the tuning circuit 204. The current sensor 206 also includes a secondary winding 210 inductively coupled to the primary winding 208 via an optional ferrite core 212 and coupled to a sensing element 214 (e.g., a resistor). In some example embodiments, the current sensor 206 is a transformer or a toroidal coil.

[0050] The current sensor 206 inductively couples the near-field antenna 100 to the sensing element 214 to help reduce current draw, enable greater sensitivity, and minimize loading of the near-field antenna 100 to improve near-field sensitivity. The inductively sensed resonant current is converted to a voltage across the sensing element 214 for additional instrumentation capture and analysis.

[0051] The controller 216 is then coupled to receive a signal (e.g., a voltage) from the sensing element 214 through a measurement line 222.

[0052] When the near-field measurement device 200 is receiving a non-propagating quasi-static near-field signal, the signal generated across the sensing element 214 can be measured by the controller 216. In some example embodiments, the generated voltage can be used as a front-end for a baseband receiver in a body communication device.

[0053] Figure 3 is an example application 300 of a second near-field measurement device 302. This second near-field measurement device 302 used in this example application 300 is a modified version of the first near-field measurement device 200.

[0054] The coil (H-field) antenna 105, the conductive surfaces 125, 130, and the current sensor 206 are the same as for the first near-field measurement device 200; however, the second near-field measurement device 302 includes a different tuning circuit 304 that instead includes a fixed tuning capacitance 306 and a fixed tuning resistance 308.

[0055] These fixed tuning parameters result in a more compact device 302 that is tuned to a specific resonance frequency and bandwidth for a specific set of applications. For example, if measurements need to be taken at 400 MHz with a 10 kHz bandwidth, the tuning capacitor 306 can be 60 pF and the tuning resistance 308 can be 12 kOhms.

[0056] The second near-field measurement device 302 is positioned in proximity to a conductive structure 310 (e.g., a human body). The conductive structure 310 forms a capacitance 312 (e.g., 100 pF) with the ground 224.

[0057] The conductive surface 130 is positioned in proximity to the conductive structure 310 and at a location where the electric and / or magnetic field is to be measured. The conductive surface 125 is positioned further away from the conductive structure 310 than the conductive surface 130. The conductive surfaces 125, 130 together form their own capacitance. The capacitance value depends on the dimensions, but a realistic value can be approximately 5 pF.

[0058] When both conductive surfaces 125, 130 are in the presence of an electric field (E-field) 316, a voltage is induced between them, and since the conductive surface 130 is in proximity to the conductive structure 310, the electric field (E-field) 316 present on the conductive structure 310 will induce a voltage between the two surfaces 125, 130. A magnetic field (H-field) 314 that is not affected by the conductive structure 310 in the case that the conductive structure 310 is a living body will also induce a voltage in the magnetic coil antenna 105.

[0059] In some example embodiments, the tuning capacitor 306 of the near-field measurement device 302 is much larger than the capacitance between the conductive surfaces 125, 130. In such embodiments, most of the resonant current of the second near-field measurement device 302 flows through the tuning capacitor 306, and thus the primary winding 208 of the current sensor 206 is positioned between the tuning capacitor 306 and the tuning resistor 308, as shown in FIG. 3. Figure 3

[0060] The controller 212 is not shown in this figure, but would be coupled to the sense element 214 of the current sensor 206 as discussed in Figure 2

[0061] Figure 4 is an example application 400 of a third near-field measurement device 402. The third near-field measurement device 402 is similar to the second near-field measurement device 302, however, a different current sensor 404 is included. The current sensor 404 includes the primary winding 208, the secondary winding 210, and the optional ferrite core 212; however, a new sense element 406 is included.

[0062] The sense element 406 includes a first LNA 408, a filter 410, a second LNA 412, and an output 414. The first LNA 408 is connected to the secondary winding 210 and converts the secondary winding 210 current to an amplified voltage. This amplified voltage can be coupled directly to a measurement instrument or baseband communication circuitry for further processing.

[0063] However, if the filter 410 is included, the second LNA 412 can be used to provide sufficient output voltage so that the measurement instrument or baseband communication circuitry has sufficient signal strength.

[0064] Furthermore, the output 414 can be connected to the measurement instrument or baseband communication circuitry through a coaxial cable. The measurement instrument or baseband communication circuitry can be capacitively coupled to the ground 224 via its mains power supply.

[0065] The ground 224 of the mains power supply enables a more accurate sensing of the electric field so that the measurement instrument or baseband communication circuitry is not itself part of the antenna and thus overestimates the measured current.

[0066] Therefore, the capacitive currents on the cables and conductive parts of the LNAs 408, 412 and the measurement instrument or baseband communication circuitry must be reduced as much as possible. This is achieved by using a current sensor 404 configured in series with the tuning capacitor 306 and by reducing any stray capacitance between the primary winding and the secondary winding of the current sensor, and all device 402 elements are coupled to the ground 224.

[0067] ​​Various applications of these near field measurement devices 200, 302, 402 include monitoring the quality of a human body link, use as a new front end for applications with industrial interference, as a measurement device for human exposure to wireless body area devices, or for regular near field (e.g., NFEMI, NFEI, NFMI, etc.) communication.

[0068] Unless a specific order is required, the various instructions and / or operational steps discussed above with regard to the figures can be performed in any order. Moreover, one skilled in the art will appreciate that, although some example sets of instructions / steps have been discussed, the material in this specification can be combined in a variety of ways to produce additional examples, and should be understood to be within the scope of the present disclosure.

[0069] In some example embodiments, the instructions / steps are implemented as functional and software instructions. In other embodiments, the instructions can be implemented using logic gates, application specific chips, firmware, and other hardware forms.

[0070] When the instructions are implemented as executable instructions in a non-transitory computer readable or computer usable medium, the instructions are implemented on a computer or machine programmed with and controlled by the executable instructions. The instructions are loaded to execute on a processor (e.g., one or more CPUs). The processor includes a microprocessor, a microcontroller, a processor module or subsystem (including one or more microprocessors or microcontrollers), or other control or computing devices. A processor can refer to a single component or multiple components. The computer readable or computer usable storage medium is considered a part of an article (or article of manufacture). An article or article of manufacture can refer to any manufactured single component or multiple components. A non-transitory machine or computer usable medium, as defined herein, does not include signals but can be capable of receiving and processing information from signals and / or other transitory media.

[0071] It should be readily understood that the components of the embodiments, as generally described herein and illustrated in the drawings, can be arranged and designed in a wide variety of different configurations. Thus, the specific

[0072] The application can be implemented in other specific forms without departing from the spirit or essential characteristics thereof. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the application is, therefore, indicated by the appended claims rather than by the foregoing description. All changes that come within the meaning of and equivalency of the claims are intended to be embraced therein.

[0073] Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that can be achieved with the present application should be or are in any single embodiment of the application. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the application. Thus, appearances of the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0074] Furthermore, the described features, advantages, and characteristics of the application can be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize, in light of the description herein, that the application can be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages can be recognized in certain embodiments that can not be present in all embodiments of the application.

[0075] Reference throughout this specification to "one embodiment," "an embodiment," or similar language means that a particular feature, structure, or characteristic described in connection with the indicated embodiment is included in at least one embodiment of the application. Thus, appearances of the phrases "in one embodiment," "in an embodiment," and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

Claims

1. A near-field measurement device, characterized in that, include: Near-field antenna; A tuning circuit, the tuning circuit being current-coupled to the near-field antenna, and configured to set the resonant frequency and / or quality factor of the measuring device; as well as A current sensor, which is inductively coupled to the near-field antenna and configured to generate a signal in response to a current flowing through a current coupler between the near-field antenna and the tuning circuit; The signal referred to here represents a measurement of a non-propagating quasi-static near-field signal received by the near-field antenna; The tuning circuit includes a fixed tuning capacitor configured to set a fixed resonant frequency of the near-field antenna, and a fixed tuning resistor configured to set a fixed quality factor or bandwidth of the near-field antenna.

2. The apparatus according to claim 1: Its features are, The current sensor is a transformer or a toroidal coil.

3. The apparatus according to claim 1: Its features are, The current sensor is configured to amplify the current flowing in the current coupler.

4. The apparatus according to claim 1: Its features are, The tuning circuit includes capacitors and resistors.

5. The apparatus according to claim 4: Its features are, The near-field antenna includes a set of conductive surfaces configured to respond to an electric near-field signal; The conductive surfaces together form a capacitor; The tuning circuit capacitor is larger than the conductive surface capacitor, such that a larger portion of the current flowing through the near-field antenna flows through the tuning circuit capacitor; and The current sensor is in series with the capacitor of the tuning circuit and inductor-coupled with the resistor of the tuning circuit in parallel.

6. The apparatus according to claim 1, characterized in that: Additionally, it includes sensing elements; The current sensor includes a primary winding and a secondary winding; The primary winding current is coupled to the near-field antenna; and The secondary winding is inductively coupled to the primary winding, and the current is coupled to the sensing element.

7. The apparatus according to claim 6: Its features are, The sensing element includes a resistor; The signal is a voltage; and The resistor is configured to generate the voltage in response to the current flowing through the primary winding.

8. The apparatus according to claim 6: Its features are, The sensing element includes a low-noise amplifier; The signal is a voltage; and The low-noise amplifier is configured to generate an amplified output signal in response to the current flowing through the primary winding.

9. The apparatus according to claim 6: Its features are, The sensing element is configured to be coupled to a measuring instrument; and The measuring instrument is configured to output a magnetic near-field strength signal and / or an electric near-field strength signal in response to the current flowing through the primary winding.

10. The apparatus according to claim 6: Its features are, The sensing element is configured to be coupled to a baseband communication circuit; and The communication circuit is configured to output a communication signal in response to the current flowing through the primary winding.

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