Metasurface-Enhanced Micromechanical Photoswitch for Zero Power Human Presence Sensing

This letter reports on zero standby power human presence detectors based on an optimized micromechanical photoswitch (MP) with a metasurface-enhanced long wavelength infrared (LWIR) absorber, increased thermal sensitivity, reduced bias voltage, and a wide field-of-view. The reported device shows the capability of detecting a human body around 2.65 m and human hand around 1 m distance using low bias voltages without using any focal lenses. Existing wireless motion detectors based on pyroelectric IR sensors consume ∼100 μW power on standby continuously and produce frequent false alarms due to nonrelevant objects (such as moving cars and falling leaves), which inevitably drains the battery in a relatively short period of time (typically less than a year). The demonstrated zero-power sensor here exploits the LWIR energy emitted from a human body for true presence detection without consuming any electrical power on standby. The first experimental demonstration of human body detection with vacuum packaged MP at a distance comparable to commercial motion detectors is enabled by the optimization of an MP in terms of thermomechanical performance (thermal sensitivity ∼1.5 nm/nW, stiffness ∼0.2 nN/nm, and threshold ∼10 nW) and IR absorption (η > 60% in λ = 6–14 μm, field-of-view ∼110°). The new broadband LWIR metasurface absorbers improve the structural symmetry of MP by matching the material stacks of reflecting and absorbing heads. This improvement allows the MP to work with lower voltage bias, thus making it compatible with low-power electronics.