| CPC G06F 3/013 (2013.01) [G01S 13/75 (2013.01); G06K 19/07773 (2013.01); H01Q 1/273 (2013.01)] | 19 Claims |

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1. A body-part tracking device, comprising:
a first electronic component configured to receive a first radio-frequency wave;
a first antenna element electrically connected to the first electronic component, and
a second antenna element electrically connected to the first electronic component,
wherein the first electronic component is configured to, in response to the first radio-frequency wave, transmit a second radio-frequency wave through the first antenna element,
wherein the first electronic component is configured to, in response to the first radio-frequency wave, transmit a third radio-frequency wave through the second antenna element,
wherein the second radio-frequency wave has a first frequency, and the third radio-frequency wave has a second frequency different from the first frequency,
wherein a viewing focus or position of a wearer's pupil is calculated by determining differences in amplitude, phase, and or frequency between the first radio-frequency wave and the second radio-frequency.
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