Patent Description:
A sensor, such as an inductive position sensor, may generate electromagnetic energy. The electromagnetic energy may couple to a portion of the sensor to create conducted emissions or radiate in an associated environment to create radiated emissions. Various industry specifications may advise or require a limited amount of conducted and/or radiated emissions for corresponding industry applications.

<CIT> describes a system that can be used for supplying electrical power to proximity sensors that are mounted on moving machine components.

The invention is defined by independent device claim <NUM> and independent method claim <NUM>. Further optional features are defined in the dependent claims.

The details of one or more example implementations are set forth in the accompanying drawings and the description below. Other possible example features and/or possible example advantages will become apparent from the description, the drawings, and the claims. Some implementations may not have those possible example features and/or possible example advantages, and such possible example features and/or possible example advantages may not necessarily be required of some implementations.

Embodiments of the present disclosure are described with reference to the following figures.

Like reference symbols in the various drawings may indicate like elements.

The discussion below is directed to certain implementations.

It is specifically intended that the claimed combinations of features not be limited to the embodiments and/or implementations and illustrations contained herein, but include modified forms of those implementations including portions of the implementations and combinations of elements of different implementations as come within the scope of the following claims. Nothing in this application is considered critical or essential to the claimed invention unless explicitly indicated as being "critical" or "essential.

For example, a first object or step could be termed a second object or step, and, similarly, a second object or step could be termed a first object or step, without departing from the scope of the invention. The first object or step, and the second object or step, are both objects or steps, respectively, but they are not to be considered a same object or step.

Embodiments of the present disclosure may include a sensor. The embodiments may include one or more coils or sets of coils. For example, the embodiments may include a set of transmit coils and a set of receive coils on a multi-layer printed circuit board (PCB). According to the invention transmit coils are configured in parallel, and the parallel configuration of transmit coils reduces electromagnetic emissions from the sensor (e.g., an inductive position sensor), while maintaining a signal amplitude associated with the sensor. Such a configuration of transmit coils provides optimal emissions performance which benefits accuracy of the sensor.

Referring to <FIG>, a diagram illustrating example components of a sensor <NUM> is shown. In some embodiments, one or more coils (e.g., transmit ("Tx") coils), may be configured with a discrete arrangement of capacitor(s) (e.g., capacitors <NUM> and <NUM>) to form an inductor-capacitor ("LC") oscillator or oscillating circuit, which may also include an oscillator <NUM>. The LC oscillating circuit shown may be typical for automotive applications and may be driven by an integrated circuit ("IC") <NUM> and may operate in a range of <NUM>-<NUM> megahertz (MHz). Further, the LC oscillating circuit may generate a magnetic field of varying strength around windings of the transmit coils. The transmit coils may couple onto one or more receive coils (e.g., receive coils <NUM> and <NUM>) via mutual inductance coupling. For example, receive coils <NUM> and <NUM> may be two discrete receive ("Rx") coils corresponding to sine and cosine respectively, and may be arranged on the PCB with a <NUM> (electrical) degree phase-shift. A sinusoidal output may be generated as a function of a rotor angle because the receive coils <NUM> and <NUM> may be geometrically designed as sine and cosine waveforms which have been wrapped around the device by a polar transform.

The LC oscillating circuit formed by the transmit coils and the one or more discrete capacitor may generate electromagnetic energy at a resonance frequency and its harmonics. The electromagnetic energy may couple to a sensor harness, which may be referred to as conducted emissions, or may or radiate in the environment, which may be referred to as radiated emissions. The sensors described herein may be used in automotive applications and various automotive specifications may require or advise that the conducted and/or radiated emissions should be below a required threshold. Some sensor designs, when tested for conducted and/or radiated emissions, may yield results that are above an acceptable threshold.

Referring now to <FIG>, a plot <NUM> showing example conducted emissions test results is shown. The plot <NUM> may show example conducted emissions test results for a typical LC oscillating circuit formed by transmit coils and a discrete capacitor. The maximum conducted emissions line <NUM> located at or near <NUM> and <NUM> decibels relative to one micro-amp (dBuA) may represent, for example, maximum conducted emissions for an automotive specification. Thus, a typical LC oscillating circuit may generate conducted emissions (e.g., as indicated by values <NUM>) above the required automotive specification.

Referring now to <FIG>, a plot <NUM>, illustrating example values of field strength vs. frequency of radiated emissions corresponding to a sensor having a typical LC oscillating circuit, is shown. The plot <NUM> may show field strength measured in decibel microvolts per meter (dBuV/m) and frequency in MHz. The values <NUM> may represent peak limit, the values <NUM> may represent average limit, the values <NUM> may represent quasi-peak limit, the values <NUM> may represent peak trace, the values <NUM> may represent average trace, and the values <NUM> may represent quasi-peak trace associated with the radiated emissions. In some situations, the radiated emissions of a sensor having a typical LC oscillating circuit may exceed levels required by an automotive specification for automotive applications.

Techniques to reduce conducted and/or radiated emissions may include filtering and/or attenuation of a corresponding transmit signal. Filtering transmit signal harmonics may be accomplished by increasing a resistance or capacitance value. The capacitance value may be inversely proportional to the transmit resonance frequency, and thus the capacitance value may only be increased to a certain extent before the transmit frequency falls below a resonance frequency minimum of <NUM> (e.g., as may be required by various automotive specifications). Further, the transmit signal amplitude may be reduced by adjusting an oscillator current setting. However, these techniques to reduce conducted and/or radiated emissions (e.g., reducing transmit signal amplitude) may result in unintended consequences such as directly attenuating the receive signal and/or an output analog signal amplitude, which may lead to a reduction in sensor accuracy.

Referring to <FIG>, plots illustrating example conducted emissions results which may be achieved by three designs for reducing conducted emissions (one for each of <FIG>, respectively) that may incorporate filtering techniques, and resultant amplitude signal strength, are shown. Referring also to <FIG>, the difficult trade-off of reducing emissions versus achieving output signal strength is illustrated.

Referring to <FIG>, a first design for reducing conducted emissions, which may be referred to as Design A, may yield the results shown in the plot <NUM>. Design A may be for an LC oscillating circuit and may include a <NUM> microamp (uA) signal, <NUM> transmit loops (e.g., corresponding to an inductor(s) and equaling or providing <NUM> micro-Henrys (uH)) of inductance), transmit capacitors = <NUM> pico-Farads (pF), no output ferrites, no R2 (e.g., second resistor) ferrite, wire terminal ferrites (supply and ground), transmit ferrites, and <NUM> spacer added between the sensor and a target plate. The maximum conducted emissions line <NUM> located at about <NUM> and <NUM> dBuA as shown may represent, for example, maximum conducted emissions for an automotive specification at corresponding signal frequencies. Design A may generate conducted emissions (e.g., as indicated by values <NUM>) near or below the automotive specification limit.

Referring to <FIG>, a second design for reducing conducted emissions, which may be referred to as Design B, may yield the results shown in the plot <NUM>. Design B may be for an LC oscillating circuit and may include a <NUM> uA signal, <NUM> transmit loops, transmit capacitors = <NUM> pF, supply and ground terminal ferrites, and transmit ferrites. The maximum conducted emissions line <NUM> located at about <NUM> and <NUM> dBuA as shown may represent, for example, maximum conducted emissions for an automotive specification at corresponding signal frequencies. Design B may generate conducted emissions (e.g., as indicated by values <NUM>) at above the automotive specification limit.

Referring to <FIG>, a third design for reducing conducted emissions, which may be referred to as Design C, may yield the results shown in the plot <NUM>. Design C may be for an LC oscillating circuit and may include a <NUM> uA signal, <NUM> transmit loops, transmit capacitors = <NUM> pF, supply and ground terminal ferrites, and a transmit <NUM> ohm resistor(s). The maximum conducted emissions line <NUM> located at about <NUM> and <NUM> dBuA as shown may represent, for example, maximum conducted emissions for an automotive specification at corresponding signal frequencies. Design C may generate conducted emissions (e.g., as indicated by values <NUM>) at above the automotive specification limit.

Referring to <FIG>, a conducted emissions solution tradeoff is illustrated in the plot <NUM>. The plot <NUM> shows peak to peak voltage for each of Designs A, B, and C. The dashed line <NUM> may represent a desired (or required) threshold for signal amplitude corresponding to output signal strength and the values <NUM> may represent a signal amplitude for each of Designs A, B, and C on the X-axis. As discussed above, Design A uses multiple techniques (including implementing higher capacitance than Designs B or C, e.g., at <NUM> pF) to reduce conducted emissions. As shown in <FIG>, the techniques used in Design A yield results below the maximum conducted emissions line <NUM>, but also as shown in <FIG>, Design A leaves a resulting signal amplitude corresponding to output signal strength below the desired (or required) threshold.

Further, Design B uses a different set of techniques (including transmit ferrites but lower capacitance than Design A, e.g., at <NUM> pF) to reduce conducted emissions. As shown in <FIG>, the techniques used in Design B yield results closer to (but often over) the maximum conducted emissions line <NUM> than Design A, but also as shown in <FIG>, Design B leaves a resulting signal amplitude corresponding to output signal strength at or near the desired (or required) threshold.

Additionally, Design C uses a another set of techniques (including transmit <NUM> ohm resistor(s) and lower capacitance than Design A, e.g., at <NUM> pF) to reduce conducted emissions. As shown in <FIG>, the techniques used in Design C yield results over the maximum conducted emissions line, but also as shown in <FIG>, Design C leaves a resulting signal amplitude corresponding to output signal strength above the desired (or required) threshold. Thus, when viewed together, <FIG> illustrate the difficult trade-off of reducing emissions versus achieving output signal strength.

Embodiments included herein may address the difficult trade-off by using a parallel transmit coil configuration as is discussed in further detail below. Referring to <FIG>, example components of a sensor are shown. The components of <FIG> may form an LC oscillating circuit <NUM>. An example design technique that may be used for LC oscillating circuits (e.g., for Designs A, B, or C as discussed above) may include two coils (e.g., inductors) <NUM> and <NUM> (e.g., L1, and L2, respectively). The LC oscillating circuit <NUM> may also include one or more capacitors (e.g., capacitors <NUM> and <NUM>) and one or more resistors (e.g., resistors <NUM> and <NUM>). Further, the LC oscillating circuit <NUM> may include an oscillator <NUM>.

The coil <NUM> may be a transmit coil and may be positioned on a first layer (e.g., layer <NUM>) of a printed circuit board (PCB). Further, the coil <NUM> may also be a transmit coil and may be positioned on a second layer (e.g., layer <NUM>) of the PCB. Coils <NUM> and <NUM> may be arranged in series, which may result in a total inductance = L1+L2. If L1=L2=L, total inductance may be calculated as Ll+L2=<NUM>*L or <NUM>. For example, if L1=L2= <NUM> uH, then L=<NUM> uH. For the configuration shown in <FIG>, the maximum value of capacitance that may be used may be <NUM> pF in order to meet an application-specific integrated circuit (ASIC) limit for a resonance frequency of <NUM>. The relationship of frequency to capacitance is provided by equation <NUM> below: <MAT>.

For LC oscillating circuits such as the configuration shown in <FIG>, larger capacitance values may allow for increased filtering of harmonic frequencies. Due to the limited capacitance (e.g., <NUM> pF) of the configuration of <FIG>, with coils <NUM> and <NUM> arranged in series, the configuration of <FIG> may not provide sufficient ability to reduce emissions. Thus, higher capacitance may allow for increased filtering, which in turn may allow for greater ability to reduce emissions.

Referring to <FIG>, example components of a sensor are shown. The components of <FIG> may form an LC oscillating circuit <NUM> which may allow for higher capacitance than the LC oscillating circuit <NUM>. The higher capacitance may allow for increased filtering, which in turn may allow for greater ability to reduce emissions. An example design technique that may be used for LC oscillating circuits may include two coils (e.g., inductors) <NUM> and <NUM> (e.g., also shown as L1 and L2, respectively). The LC oscillating circuit <NUM> may also include one or more capacitors (e.g., capacitors <NUM> and <NUM>) and one or more resistors (e.g., resistors <NUM> and <NUM>). Further, the LC oscillating circuit <NUM> may include an oscillator <NUM>, which may be in electronic communication with the coils <NUM> and <NUM>. At least one of the capacitors <NUM> and <NUM> may be positioned between the oscillator <NUM> and at least one of the coils <NUM> and <NUM>. Further, at least one of the resistors <NUM> and <NUM> may be positioned between the oscillator <NUM> and at least one of the coils <NUM> and <NUM>.

The coil <NUM> may be a transmit coil and may be positioned on a first layer (e.g., layer <NUM>) of a PCB. Further, the coil <NUM> may be a transmit coil and may be positioned on a second layer (e.g., layer <NUM>) of the PCB. Coils <NUM> and <NUM> may be arranged in parallel, which may result in a total inductance = L1*L2/(L1+L2); L/<NUM>= <NUM> uH. For the configuration shown in <FIG>, the maximum value of capacitance that may be used may be <NUM> pF in order to meet an ASIC limit for the resonance frequency of <NUM>. As discussed above, the larger capacitance value for LC oscillating circuit <NUM> of <FIG> (e.g., <NUM> pF) may allow for increased filtering of the harmonic frequencies generated by the oscillator (e.g., oscillator <NUM>) than the lower capacitance value for LC oscillating circuit <NUM> of <FIG> (e.g., <NUM> pF). Thus, arranging the inductors <NUM> and <NUM> in parallel (e.g., as shown for the LC oscillating circuit <NUM> of <FIG>) may allow for a greater reduction in emissions as compared to arranging the inductors <NUM> and <NUM> in series (e.g., as shown for the LC oscillating circuit <NUM> of <FIG>).

Accordingly, in some embodiments, the design technique shown in <FIG> may include an inductive transmit coil configuration that achieves optimal emissions performance. The coil configuration shown in <FIG> may meet functional requirements (e.g., automotive specifications and/or ASIC limitations) and may not cause degradation in sensor signal strength to achieve optimal emissions performance. The parallel transmit coil configuration of <FIG> may achieve a low inductance and equivalent series resistance (ESR) value, which may enable use of higher transmit capacitor values (e.g., for capacitors <NUM> and/or <NUM>) which, in turn, may filter electromagnetic emissions from an inductive position sensor (e.g., comprising the LC oscillating circuit <NUM> of <FIG>) while maintaining signal strength.

Referring to <FIG>, a plot <NUM> illustrating example conducted emissions results corresponding to the LC oscillating circuit <NUM> of <FIG> is shown. The maximum conducted emissions line <NUM> located at about <NUM> and <NUM> dBuA as shown may represent, for example, maximum conducted emissions for an automotive specification at corresponding signal frequencies. The LC oscillating circuit <NUM> of <FIG> may generate conducted emissions (e.g., as indicated by values <NUM>) at above the automotive specification limit.

Referring to <FIG>, a plot <NUM> illustrating example conducted emissions results, corresponding to the LC oscillating circuit <NUM> of <FIG>, in accordance with embodiments of the present disclosure, is shown. The maximum conducted emissions line <NUM> located at about <NUM> and <NUM> dBuA as shown may represent, for example, maximum conducted emissions for an automotive specification at corresponding signal frequencies. The LC oscillating circuit <NUM> of <FIG> may generate conducted emissions (e.g., as indicated by values <NUM>) that are generally at or below the automotive specification limit. For example, while most of the values <NUM> fall below the automotive specification limit, one value (e.g., <NUM> dBuA) may fall at or slightly above the automotive specification limit.

Referring to <FIG>, a plot <NUM> associated with example coil configurations in accordance with embodiments of the present disclosure is shown. The plot <NUM> illustrates peak to peak voltage of a coil configuration with inductors in series (e.g., the LC oscillating circuit <NUM> of <FIG>) and of a coil configuration with inductors in parallel (e.g., the LC oscillating circuit <NUM> of <FIG>). The dashed line <NUM> may represent a desired (or required) threshold for output voltage which may correspond to signal amplitude or output signal strength and the values <NUM> may represent a signal amplitude for each of the coil configurations (e.g., inductors in series and parallel). As can be seen in <FIG>, in some embodiments, signal amplitude or signal strength may not be reduced as much in the coil configuration with the inductors in parallel as compared to the coil configuration with the inductors in series. Further, as shown in <FIG>, the coil configuration with the inductors in parallel (e.g., the LC oscillating circuit <NUM> of <FIG>) also generally keeps the conducted emissions below the required maximum conducted emissions level. Thus, when viewed together, <FIG> illustrate a significant improvement in reducing conducted emissions when using the coil configuration with the inductors in parallel (e.g., the LC oscillating circuit <NUM> of <FIG>) as compared to the coil configuration with the inductors in series (e.g., the LC oscillating circuit <NUM> of <FIG>), while maintaining signal amplitude or signal strength.

Referring to <FIG>, a first portion of a schematic <NUM> illustrating example components of a sensor in accordance with embodiments of the present disclosure is shown. <FIG> illustrates an IC <NUM> of the sensor and components on one side of the IC <NUM>. For example, an inductive position sensor (e.g., for use in various automotive applications) may include an LC oscillating circuit. The LC oscillating circuit may include a first transmit coil (e.g., transmit coil <NUM>) of a first layer of a printed circuit board (not shown) arranged in parallel with a second transmit coil (e.g., transmit coil <NUM>) of a second layer of the printed circuit board. The LC oscillating circuit may further include an oscillator (not shown) implemented via an IC (e.g., IC <NUM>). The oscillator may be in electronic communication with the first transmit coil (e.g., transmit coil <NUM>) and the second transmit coil (e.g., transmit coil <NUM>). The LC oscillating circuit may also include at least one capacitor (e.g., one or more of capacitors <NUM> and <NUM>) and at least one resistor (not shown) positioned between the oscillator (which may be implemented via, e.g., the IC <NUM>) and the first transmit coil (e.g., transmit coil <NUM>) and the second transmit coil (e.g., transmit coil <NUM>).

The sensor may further include a first receive coil (e.g., one or more of receive coils <NUM> and <NUM>) and a second receive coil (e.g., one or more of receive coils <NUM> and <NUM>). The first receive coil (e.g., one or more of receive coils <NUM> and <NUM>) and the second receive coil (e.g., one or more of receive coils <NUM> and <NUM>) may be positioned proximate to at least one of the first transmit coil (e.g., transmit coil <NUM>) and the second transmit coil (e.g., transmit coil <NUM>). The positioning of the coils may be such that upon introduction of current to at least one of the first transmit coil (e.g., transmit coil <NUM>) and the second transmit coil (e.g., transmit coil <NUM>), at least one of the first receive coil (e.g., one or more of receive coils <NUM> and <NUM>) and the second receive coil (e.g., one or more of receive coils <NUM> and <NUM>) becomes coupled to at least one of the first transmit coil (e.g., transmit coil <NUM>) and the second transmit coil (e.g., transmit coil <NUM>) by mutual inductance coupling. Arranging the first transmit coil (e.g., transmit coil <NUM>) in parallel with the second transmit coil (e.g., transmit coil <NUM>) may allow, at least in part, maintaining or increasing accuracy of the inductive position sensor as compared to arranging the first transmit coil in series with the second transmit coil (e.g., a discussed above with respect to <FIG>).

Referring to <FIG>, a second portion of the schematic <NUM> illustrating example components of the sensor in accordance with embodiments of the present disclosure is shown. <FIG> illustrates the IC <NUM> of the sensor and components on an opposite side of the IC <NUM> as compared to <FIG>. For example, various grounds and capacitors are shown. The components of <FIG> and <FIG> are shown for illustrative purposes only and are not intended to limit the present disclosure.

Referring to <FIG> a flow chart illustrating example operations in accordance with embodiments of the present disclosure is shown. A process <NUM> (e.g., for reducing emissions of a sensor and/or increasing sensor accuracy) may include arranging (<NUM>), in a first circuit (e.g., the LC oscillating circuit <NUM> of <FIG>), a first coil (e.g., the coil <NUM> of <FIG>) in parallel with a second coil (e.g., the coil <NUM> of <FIG>). The method may further include providing (<NUM>) an oscillator (e.g., the oscillator <NUM>) in electronic communication with the first coil (e.g., coil <NUM>) and the second coil (e.g., coil <NUM>). The process <NUM> may also include positioning (<NUM>) at least one capacitor (e.g., one or more of the capacitors <NUM> and <NUM> of <FIG>) between the oscillator (e.g., oscillator <NUM>) and at least one of the first coil (e.g., coil <NUM>) and the second coil (e.g., coil <NUM>).

In embodiments, the process <NUM> may include positioning (<NUM>) at least one resistor (e.g., one or more of resistors <NUM> and <NUM> of <FIG>) between the oscillator (e.g., oscillator <NUM>) and at least one of the first coil (e.g., coil <NUM>) and the second coil (e.g., coil <NUM>). The process <NUM> may further include positioning (<NUM>) a third coil (e.g., one or more of coils <NUM> and <NUM> of <FIG>) proximate to at least one of the first coil (e.g., coil <NUM>) and the second coil (e.g., coil <NUM>). The coils may be positioned such that upon introduction of current to at least one of the first coil (e.g., coil <NUM>) and the second coil (e.g., coil <NUM>), the third coil (e.g., one or more of the coils <NUM> and <NUM>) becomes coupled to at least one of the first coil (e.g., coil <NUM>) and the second coil (e.g., coil <NUM>) by mutual inductance coupling. The process <NUM> may also include positioning (<NUM>) a fourth coil (e.g., one or more of coils <NUM> and <NUM> of <FIG>) proximate to at least one of the first coil (e.g., coil <NUM>) and the second coil (e.g., coil <NUM>). The coils may be positioned such that upon introduction of current to at least one of the first coil (e.g., coil <NUM>) and the second coil (e.g., coil <NUM>), the fourth coil (e.g., one or more of the coils <NUM> and <NUM>) becomes coupled to at least one of the first coil (e.g., coil <NUM>) and the second coil (e.g., coil <NUM>) by mutual inductance coupling.

As discussed above with regard to <FIG> and <FIG>, arranging the first coil (e.g., coil <NUM>) in parallel with the second coil (e.g., coil <NUM>) may decrease a corresponding inductance of the coils as compared to arranging the first coil (e.g., coil <NUM>) in series with the second coil (e.g., coil <NUM>). Further, decreasing the corresponding inductance may allow for increasing a capacitance of the at least one capacitor (e.g., one or more of the capacitors <NUM> and <NUM> of <FIG>) without falling below an associated resonance frequency threshold (e.g., <NUM> as described above). Meeting or exceeding the associated resonance frequency threshold (e.g., <NUM> as described above) may allow for increased filtering of a harmonic frequency produced, at least in part, by the oscillator (e.g., oscillator <NUM>). Increasing the filtering of the harmonic frequency produced, at least in part, by the oscillator (e.g., oscillator <NUM>) may reduce at least one of a conducted emission associated with the oscillator (e.g., oscillator <NUM>) and a radiated emission associated with the oscillator (e.g., oscillator <NUM>). Reducing at least one of the conducted emission and the radiated emission may allow for maintaining or increasing a signal strength associated with the first circuit (e.g., LC oscillating circuit <NUM> of <FIG>). Maintaining or increasing the signal strength may allow for maintaining or increasing accuracy of a sensor (e.g., an inductive position sensor) comprising the first circuit (e.g., LC oscillating circuit of <FIG>).

As discussed above, using the techniques and features described herein, embodiments of the present disclosure may include a transmit coil configuration for an inductive position sensor that allows for achieving optimal emissions performance. The transmit coil configuration (e.g., coils in parallel) may meet functional requirements (e.g., automotive specifications and/or ASIC limitations) as well as maintain sensor signal strength (i.e., without causing signal strength degradation). For example, parallel configuration of transmit coils described herein may achieve low inductance and ESR values, thus allowing use of higher transmit capacitor values. The higher transmit capacitor values may in turn filter or facilitate filtering of electromagnetic emissions from the inductive position sensor while maintaining signal strength.

The terminology used herein is for the purpose of describing particular embodiments and is not intended to be limiting of the disclosure.

The corresponding structures, materials, acts, and equivalents of means or step plus function elements in the claims below are intended to include any structure, material, or act for performing the function in combination with other claimed elements as specifically claimed. The description of the present disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope of the disclosure. The embodiments were chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure for various embodiments with various modifications as are suited to the particular use contemplated.

Although a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the scope of the present disclosure, described herein. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the following claims.

Claim 1:
A sensor comprising:
an inductance-capacitance oscillating circuit (<NUM>) comprising: a printed circuit board; and
a first transmit coil (<NUM>; <NUM>) on a first layer of the printed circuit board arranged in parallel with a second transmit coil (<NUM>; <NUM>) on a second layer of the printed circuit board;
an oscillator (<NUM>) implemented via an integrated circuit (<NUM>), the oscillator (<NUM>) in electronic communication with the first transmit coil (<NUM>; <NUM>) and the second transmit coil (<NUM>; <NUM>); and
at least one capacitor (<NUM>, <NUM>; <NUM>, <NUM>) and at least one resistor (<NUM>, <NUM>) positioned between the oscillator (<NUM>) and the first transmit coil (<NUM>; <NUM>) and the second transmit coil (<NUM>; <NUM>).