Antenna coupling for sensing and dynamic transmission

A wireless transmission system disclosed herein includes a transmitter-receiver pair. When a dielectric object approaches the transmitter-receiver pair, a signal strength of a transmitted carrier wave increases at the receiver. In response, transmission power of the transmitter can be dynamically reduced. When the dielectric object moves away from the transmitter-receiver pair, a signal strength of the carrier wave decreases at the receiver. In response, the transmission power of the transmitter can be dynamically increased.

BACKGROUND

Consumer electronic devices may be equipped with wireless communication circuitry that makes use of radio frequency (RF) electromagnetic fields. For example, the wireless communications circuitry may transmit and receive RF signals in mobile telephone RF bands, WiFi network RF bands, GPS RF bands, etc. To protect humans from harmful levels of RF radiation when using such devices, government agencies have imposed regulations limiting RF transmission power from some wireless electronic devices, such as tablet computers and mobile phones. However, reducing RF transmission power can appreciably decrease performance of device features in some electronic devices.

SUMMARY

Implementations described and claimed herein address the foregoing by providing a wireless transmission system that adjusts transmission power of a carrier wave responsive to a detected change in signal strength of the carrier wave at a receiver. To satisfy government-imposed RF transmission limitations without significantly compromising device performance, electronic devices can include sensors that allow for adjustable signal strength of a transmitted RF carrier wave. For example, the signal strength of a transmitted RF carrier may be dynamically reduced when a proximity sensor detects a human or other dielectric body in close proximity of the carrier wave transmission source.

DETAILED DESCRIPTIONS

In some jurisdictions, specific absorption rate (SAR) standards are in place that impose maximum energy absorption limits on electronic device manufacturers. These standards impose restrictions on the amount of electromagnetic radiation that may be emitted at any particular point within a given distance of a transmitting radio frequency (RF) antenna. Particular attention is given to radiation limits at distances within a few centimeters from the device (e.g., 0-3 centimeters), where users are likely to place a human body part near the transmitting antenna. Such restrictions may be satisfied by reducing transmitted carrier signal strength when a dielectric body (e.g., a human body part) is detected in the proximity of the transmitter.

Implementations of the disclosed technology provide an electronic device that dynamically alters the power of a transmitted carrier wave responsive to detected changes in the signal strength of the carrier wave received at a nearby receiver. A user in proximity of the electronic device influences the transmitted carrier wave in a detectable manner, allowing for the dynamic power alteration that ensures compliance with SAR standards without significantly compromising performance of the electronic device.

FIG. 1illustrates an example electronic device100that provides for dynamic power adjustment of a transmitted carrier wave responsive to a detected change in signal strength of the carrier wave at a receiver. The electronic device100may be without limitation a tablet computer, laptop, mobile phone, personal data assistant, cell phone, smart phone, Blu-Ray player, gaming system, wearable computer, or any other device including wireless communications circuitry for transmission of an RF carrier wave. The electronic device100includes an RF transmitter102(including a transmitting antenna) that transmits a carrier wave. In one implementation, the carrier wave has a frequency in the range of a mobile telephone RF transmission (e.g., several hundred megahertz (MHz)). Other implementations are also contemplated. In the illustrated implementation, the electronic device100represents a tablet computer having mobile telephone RF capabilities.

The electronic device also includes a RF receiver104(including a receiving antenna) that is capable of detecting wireless transmissions in a frequency range that includes the carrier wave transmitted by the RF transmitter102. In one implementation, the RF transmitter102represents an active antenna radiating at a mobile telephone RF frequency, and the RF receiver104represents a parasitic antenna positioned relative to the RF transmitter102. For example, the RF receiver104may be positioned between the RF transmitter102and an exterior surface of the electronic device100, positioned at the surface of the electronic device100, and/or positioned in close proximity to the RF transmitter102). In this manner, the RF receiver104is excited in the presence of the RF signal (e.g., the carrier wave) emanating from the RF transmitter102. Other frequencies may be employed in a similar configuration.

The reception of the signal from the RF transmitter102by the RF receiver104may be influenced by the proximity of a dielectric body (e.g., a human body part) to the RF receiver104. This influence results from the presence of the dielectric body within the RF field emanating from the RF transmitter102, wherein the dielectric body alters the coupling between the RF receiver104and RF transmitter102. By setting a baseline signal strength level for the carrier wave transmitted by the RF transmitter102and received by the RF receiver104(e.g., in the absence of any external dielectric body in the proximity of the RF transmitter102), changes in received carrier wave signal strength received by the RF receiver104can be detected, referred to herein as a “carrier wave signal strength delta.” The carrier wave signal strength delta may be caused by the encroachment of a dielectric body108within the coupling distance110of the RF transmitter102. In one implementation, the RF receiver104measures a moving threshold that is proportional to the current and active transmission power.

The RF receiver104is connected to an RF power detector106that provides an electrical feedback path between the RF receiver104and the RF transmitter102. If the carrier wave signal strength delta exceeds a predetermined threshold, the RF power detector106can determine that a dielectric body108is in proximity to the RF transmitter102. In addition, the RF power detector106includes control circuitry to vary behavior (e.g., output power level, output wave frequency, etc.) of the RF transmitter102in response to changes in the carrier wave signal (e.g., signal strength) detected by the RF receiver104. Therefore, if the RF power detector106determines that a dielectric body108is in proximity to the RF transmitter102, the RF power detector106can signal the RF transmitter102to reduce its transmission power in an effort to comply with SAR standards.

The RF power detector106may be configured to adjust other characteristics of the signal transmitted by the RF transmitter102, such as decreasing the carrier signal frequency of the transmitted signal. A reduced carrier frequency may result in a decreased SAR. The RF power detector106may be configured to detect other characteristics in the signal received by the RF receiver104as compared to the signal transmitted by the RF transmitter102. For example, the RF power detector106may detect the other frequency components and/or sinusoids having different phases in the signal received by the RF receiver104that may differ from those of the signal transmitted by the RF transmitter102. The RF power detector106may use this information to perform SAR-related functions, such as determining SAR due to the combined power of the RF transmitter102and the power of a nearby transmitter in the same device104or one or more different devices. In this manner, SAR-related transmission power reductions may be based on a detection of overall SAR attributed to the device100and/or neighboring devices. Alternatively, the RF power detector104may filter spurious signal components at frequencies differing from the frequencies of the carrier signal transmitted by the RF transmitter104.

After altering a behavior of the RF transmitter102, the RF power detector106continues to monitor the carrier wave signal strength received by the RF receiver104. If the dielectric body108begins to move away from the electronic device100, the energy coupling between the RF transmitter102and the RF receiver104is changes to return the received carrier wave signal strength to the baseline carrier signal strength.

In the above manner, a behavior of the RF transmitter102(e.g., output power) is altered responsive to detection of a dielectric body within the coupling distance110of the RF transmitter102. Because the RF receiver104detects the transmitted carrier wave of the electronic device100rather than a secondary signal, proximity sensing is achieved without supplying power to a secondary sensing source, thereby reducing total power consumption of the electronic device100.

Additionally, the RF receiver104may be physically smaller than a proximity sensor based on self-capacitance because the disclosed sensing technology may rely less on between the surface areas of components in the electronic device100. Therefore, the electronic device100provides for a reduction in component size and increased design flexibility (e.g., antenna placement options).

FIG. 2illustrates example electrical components and data flows for a wireless transmission system200with a mechanism for dynamic transmission power adjustment. The wireless transmission system200includes an RF transmitter202that generates a carrier wave, such as a mobile telephone RF signal. The RF transmitter202is coupled to a transmitting antenna204that wirelessly transmits the carrier wave. The transmitting antenna204may be embedded within, positioned beneath, or located on a surface of an electronic device. Other implementations may also be employed.

The wireless transmission system200includes a parasitic receiving antenna212coupled to an RF power detector206. The parasitic receiving antenna212receives an RF carrier signal transmitted by the transmitting antenna204. The parasitic receiving antenna212conducts the received carrier signal to the RF power detector206, which provides an electrical feedback path to the RF transmitter202, allowing for dynamic modification of behavior of the RF transmitter202to reduce a human health risk posed by the carrier wave signal strength. This behavior modification of the RF transmitter202may be achieved in a number of ways, such as through a digital logic control line, a communication signal over a digital communication interface bus, or analog feedback mechanisms.

When a dielectric body, such as a human, approaches within a coupling distance of the transmitting antenna204, the dielectric body influences an energy coupling between the transmitting antenna204and the parasitic receiving antenna212. Consequently, the signal strength of the carrier wave changes at the parasitic receiving antenna212. The RF power detector206detects this change in carrier wave signal strength from the baseline carrier wave signal strength. The change is referred to as the “carrier wave signal strength delta.” If the carrier wave signal strength delta detected by the parasitic receiving antenna and communicated to the RF power detector206exceeds a threshold power change condition, the RF power detector206signals the RF transmitter202to reduce its transmission power in order to reduce a radiation health risk posed by the carrier wave.

When the dielectric body begins to move away from the transmitting antenna204, the energy coupling between the transmitting antenna204and the parasitic receiving antenna212begins to return to the base line carrier wave signal strength (i.e., reducing the carrier wave signal strength delta). If the carrier wave signal strength delta of the received carrier wave drops back below the threshold power change condition, the RF power detector206increases the transmission power of the RF transmitter202to the original transmission power level. The original transmission power may be determined based on standard operating procedures and protocols defined in wireless standard and/or based on communications received by the wireless transmission system200from a base station or other control entity in communication with the wireless transmission system200. The wireless transmission system200may advantageously maintain a modification signal that results in a reduced impact on the transmitted signal, such that only the minimum amount of reduction from the original transmission power level is needed to comply with given SAR requirements.

The RF power detector206may store or have access to a number of different threshold power change conditions. Depending on the particular threshold power change condition satisfied, the RF power detector206may modify behavior of the RF transmitter202differently. For example, the RF power detector206may be capable of increasing or decreasing transmission power of the RF transmitter202by a variety of different magnitudes, depending on the carrier wave signal strength delta of the received carrier wave.

In some implementations, multiple parasitic receiving antennas may be placed in pre-defined locations around the transmitting antenna204to improve detection of a proximal object.

FIG. 3illustrates example electrical components and data flows for a wireless transmission system300with dynamic transmission power adjustment. The wireless transmission system300includes an RF transmitter302that generates a carrier wave, such as a mobile telephone RF signal. The RF transmitter302is coupled to a transmitting antenna304that wirelessly transmits the carrier wave. The wireless transmission system300further includes a parasitic receiving antenna312coupled to an RF power detector306. The RF power detector306provides an electrical feedback path to the RF transmitter302, which allows for modification of behavior of the RF transmitter302to reduce a human health risk posed by the carrier wave.

One or both of the RF transmitter302and the transmitting antenna304may be positioned on an external surface of an electronic device or embedded within or below the casing of the electronic device. InFIG. 3, the parasitic receiving antenna312substantially overlies the transmitting antenna304such that the parasitic receiving antenna312is closer to a device exterior than the transmitting antenna304. In this implementation, the carrier wave is transmitted away from the transmitting antenna304in a direction through the parasitic receiving antenna312. In another implementation, the parasitic receiving antenna312and the transmitting antenna304are side-by-side on the surface of an electronic device. In yet another implementation, the parasitic receiving antenna312and the transmitting antenna304are embedded within the electronic device and relatively equidistant from the device exterior. Many other configurations of RF transmitter and one or more parasitic receiving antennas may be employed. The transmitting antenna304and the parasitic receiving antenna312may be arranged relative to each other such that a bulk of electric field lines flowing from the transmitting antenna304to the parasitic receiving antenna312flow through a space through which a dielectric body, such as a human hand, may pass during use of the wireless transmission system300. Such an arrangement may advantageously provide proximity sensing system with a higher dynamic range and/or increased sensitivity. For example, a wireless transmission system range may have a proximity sensing range of 0.2 meters or more.

When a dielectric body308, such as a human body part, comes within a coupling distance of the transmitting antenna304, the dielectric body308changes the signal strength of the carrier wave received by the parasitic receiving antenna312. The RF power detector306detects this increase in signal strength and provides a comparator314with data associated with the received carrier wave (“carrier wave data”). In various implementations, the comparator314is hardware, software, and/or firmware of an electronic device communicatively coupled to the wireless transmission system300. For example, the RF power detector306may provide the comparator314with a waveform, or data represented by waveform, for comparison to the signal received by the parasitic receiving antenna312.

In one implementation, the comparator314uses a signal strength change detected by the RF power detector306to determine a change in proximity between the dielectric body308and the wireless transmission system300. The comparator314compares the signal strength changes of the received carrier wave with a number of stored threshold power change conditions associated with dielectric objects having different proximities to the wireless transmission system300. For example, one threshold power change condition may be associated with a human body part within a first distance of the wireless transmission system300. Another threshold power change condition may be associated with a human body part within a second distance of the wireless transmission system. Still other threshold power change conditions may be associated with non-human dielectric objects at one or more distances from the wireless transmission system300. The various threshold power change conditions may be stored in volatile or non-volatile memory of an electronic device communicatively coupled to the wireless transmission system300.

The comparator314returns a value to the RF power detector305that indicates which, if any, threshold power change condition is satisfied and/or a responsive action to be taken. Based on the value provided by the comparator314, the RF power detector306modifies a transmission power level of the RF transmitter302.

In another implementation, the comparator314determines one or more object characteristics (e.g., object type, object distance, object size, etc.) of the dielectric body308based on an analysis of waveform data stored in memory of a communicatively coupled electronic device. For example, the comparator314may compare a waveform of a signal received by the parasitic receiving antenna312with a plurality of stored carrier wave signatures, including pre-generated RF curves and/or pre-generated Fast Fourier Transform (FFT) curves. This analysis may be performed each time the RF power detector306detects a change in signal strength, or conditionally, if it is determined that the received signal strength satisfies a threshold power change condition.

The RF transmitter302may also transmit SAR-specific signatures and modulations that are sensitive to proximal objects to increase object-detection accuracy. Signatures may be embedded in actual transmission data (e.g., within gaps between data packets) as deemed appropriate by the transmission conditions.

Pre-generated RF or FFT curves associated with a variety of different dielectric objects with different object characteristics can be stored memory accessible by the comparator314. For example, one pre-generated RF curve may be associated with a signal that is expected when the energy coupling between the transmitting antenna304and the parasitic receiving antenna312is influenced by a human body part. Another pre-generated RF curve may be associated with a signal that is expected when the energy coupling between the transmitting antenna304and the parasitic receiving antenna312is influenced by a table or other inanimate object.

If a system is capable of operating at two or more frequencies or frequency bands, the RF power detector306may select one frequency or band over another. For example, one frequency band may provide a greater risk to humans whereas another frequency band provides a lesser risk to humans. In this configuration, if the characteristics of humans and inanimate objects differ between different frequency bands, a scan of frequency bands or two or more frequency bands might be able to reduce the number of transmission adjustments for non-human events (e.g., one objective is to minimize or eliminate non-human transmission adjustments to optimize wireless user experience while maintaining legal compliance). Expanding this concept further, one can employ to RADAR techniques for methods of improving range resolution to targets (dielectric bodies) in the disclosed technology. In RADAR, a chirp pulse (where the frequency of a transmit pulse is altered in a linear or exponential manner) is often used to improve range resolution to the target. If the sensing transmitter were to utilize the RADAR technique (essentially making a very short range RADAR), in one or more frequency bands, the system may improve the detection (of humans) by enhancing range resolution to avoid triggering a transmitter power back off techniques or other transmission adjustment unnecessarily early.

In yet another implementation, the comparator314uses an auto-correlation function to measure similarity between a received waveform and one or more pre-generated waveforms. For example, an auto-correlation function may be used to compute a value for the transmitted carrier wave. The function may also be used to compute a pre-generated RF or FFT curve. If these computed values lie within a pre-defined error margin of one another, one or more object characteristics of the dielectric body308can be identified. In this manner, auto-correlation functions can be utilized to discern randomness (e.g., false positives) from actual objects and/or to determine one or more of an object type (e.g., a human), object distance, object size, etc. Correlation values for various pre-generated RF and FFT curves may be stored in tuning tables or other device memory accessible by the comparator314.

In one implementation, the comparator314derives a correlation value rkusing the auto-correlation function given by Equation 1, below:

rk=∑i=1N-k⁢⁢(Yi-Y)⁢(Yi+k-Y)∑i=1N⁢⁢(Yi-Y)2(1)
where Y is the mean function; k is an auto correlation lag; and N is a total number of data points used in the comparison. In another implementation, the auto correlation lag (k) is equal to 1. In Equation (1), the correlation value rkcan be used to discern an object type when rough object detection occurs. For example, rough object detection may occur when the RF power detector306detects a discernable increase in signal strength of the carrier wave. When “rough” object detection occurs, the auto-correlation function (e.g., Equation 1) can be used to identify a pre-generated RF curve that is most closely correlated with the received carrier wave. From this correlation, the comparator314can determine one or more object characteristics of the dielectric body and/or determine an appropriate response action.

In the above-described implementation, the comparator314returns a value to the RF power detector306that indicates which object characteristic is satisfied and/or a responsive action to be taken. Based on the value provided by the comparator314, the RF power detector306modifies a transmission power level of the RF transmitter302.

Alternatively, the comparator314can use an auto-correlation function to measure for similarity or correlation between a transmitted carrier waveform (e.g., received from the RF transmitter302) and a received waveform (e.g., detected by the parasitic receiving antenna312). For example, such measure may be used to determine whether a signal strength change results from the carrier wave signal itself or from a combination of other external signals detected by the parasitic receiving antenna312.

In the event that the auto-correlation function results are inconclusive, then the wireless transmission system300may prompt the user to provide input as to which type of object is proximate to the RF receiving antenna312. The user input may be stored in memory so that a more conclusive auto-correlation result may be determined when a similar object is proximate to the RF receiving antenna312. An inconclusive auto-correlation result may be based on a high error output from the correlation function. The most closely correlating pre-generated curve may be accepted even where correlation error is high to avoid the need for user input. In the case of a correlation tie between two pre-generated curves, a tie-breaker may be selected based on the achievement of a higher power reduction to err on the side of safety.

FIG. 4illustrates example operations400for a wireless transmission system with dynamic transmission power adjustment. A transmission operation402transmits an RF carrier wave, such as a mobile telephone RF signal. A receiving operation404receives the RF carrier wave. In one implementation, the receiving operation404is performed by an RF receiving antenna positioned proximal to an RF transmitting antenna that performs the transmission operation402. A detection operation406detects a change in the signal strength of the received RF carrier wave. In one implementation, the detection operation406is performed by an RF power detector coupled to a parasitic receiving antenna. Other implementations may also be employed.

A determination operation408determines whether the detected change in signal strength of the received RF carrier wave satisfies at least one threshold power change condition. Threshold power change conditions may be stored in memory locations accessible by an RF power detector of the wireless transmission system.

If the detected change in signal strength satisfies a threshold power change condition, additional analysis may be performed to determine an appropriate responsive action. For example, waveform data of the received RF carrier wave may be compared with a plurality of stored carrier wave signatures, including pre-generated RF curves and/or pre-generated Fast Fourier Transform (FFT) curves. Each of the stored carrier wave signatures may be associated with the carrier wave when influenced by a dielectric object having one or more different object characteristics. By measuring a correlation between the received carrier wave and the stored wave signatures, one or more object characteristics of the dielectric object can be determined. Based on this analysis, a responsive action can be identified and implemented.

If the determination operation408determines that the detected change in signal strength satisfies at least one threshold power change condition, an adjustment operation410adjusts the power of the transmitted RF carrier wave. The degree of the power adjustment may depend on the magnitude of the detected change in signal strength and/or one or more object characteristics associated with stored RF and FFT curves.

For example, an increase in signal strength detected by the detection operation406may indicate that a dielectric object (e.g., a human) has approached the wireless transmission system to within a detectable proximity. In one implementation, the proximity of the dielectric object is determined based on the magnitude of the change in signal strength. If this proximity is a distance where a radiation risk exists (e.g., as defined by applicable SARs regulations), the detected change in signal strength satisfies a threshold power change condition and the adjustment operation410decreases the power of the transmitted RF carrier wave to reduce the radiation risk. In this situation, the magnitude of the power decrease is based on the particular threshold power change condition satisfied.

Alternatively, a change in the signal strength detected by the detection operation406may indicate that a dielectric object has moved away from the wireless transmission system. If the dielectric object has moved to a distance where the radiation risk is mitigated or eliminated as compared to a prior position, the decrease in signal strength may satisfy a threshold power change condition. In this situation, the adjustment operation410increases the power of the transmitted RF carrier wave by a magnitude that depends on the particular threshold power change condition satisfied.

After the adjustment operation410adjusts the power of the transmitted RF carrier wave, a waiting operation412is assumed until another change in signal strength is detected by the detection operation406.

If the determination operation408determines that the detected increase in signal strength does not satisfy a threshold power change condition, the adjustment operation410is not taken. Rather, the waiting operation412is assumed until another change in signal strength is detected by the detection operation406.

The implementations of the invention described herein are implemented as logical steps in one or more computer systems. The logical operations of the present invention are implemented (1) as a sequence of processor-implemented steps executing in one or more computer systems and (2) as interconnected machine or circuit modules within one or more computer systems. The implementation is a matter of choice, dependent on the performance requirements of the computer system implementing the invention. Accordingly, the logical operations making up the embodiments of the invention described herein are referred to variously as operations, steps, objects, or modules. Furthermore, it should be understood that logical operations may be performed in any order, adding and omitting as desired, unless explicitly claimed otherwise or a specific order is inherently necessitated by the claim language.

The above specification, examples, and data provide a complete description of the structure and use of exemplary embodiments of the invention. Since many implementations of the invention can be made without departing from the spirit and scope of the invention, the invention resides in the claims hereinafter appended. Furthermore, structural features of the different embodiments may be combined in yet another implementation without departing from the recited claims.