Patent ID: 8258774

Claim:
An apparatus comprising: a housing; a plurality of reflectors that are each secured to the housing, wherein the reflectors are substantially reflective to radiation having a wavelength that is less than 10 mm and greater than 100 μm, and wherein the reflectors are arranged to form a propagation path; and an integrated circuit (IC) that is secured to the housing and located in the propagation path, wherein the IC includes: a first antenna that is coupled to the propagation path; a second antenna that is coupled to the propagation path; a third antenna that is coupled to the propagation path; a fourth antenna that is coupled to the propagation path; an first oscillator that is coupled to the first antenna and applies a first signal to the propagation path traveling in a first direction, wherein the wavelength of the first signal is less than 10 mm and greater than 100 μm; an second oscillator that is coupled to the third antenna and applies a second signal to the propagation path traveling in a second direction, wherein the wavelength of the second signal is less than 10 mm and greater than 100 μm; a first PLL that is coupled to the second antenna and the first oscillator; a second PLL that is coupled to the fourth antenna and the second oscillator; and detection circuitry that is coupled to each of the first and second PLLs, wherein detection circuitry measures the phase difference between the first and second signals to determine physical movement.