Experimental Realization of a Metamaterial Detector Focal Plane Array

We present a metamaterial absorber detector array that enables room-temperature, narrow-band detection of gigahertz (GHz) radiation in the $S$ band (2–4 GHz). The system is implemented in a commercial printed circuit board process and we characterize the detector sensitivity and angular dependence. A modified metamaterial absorber geometry allows for each unit cell to act as an isolated detector pixel and to collectively form a focal plane array . Each pixel can have a dedicated microwave receiver chain and functions together as a hybrid device tuned to maximize the efficiency of detected power. The demonstrated subwavelength pixel shows detected sensitivity of $-77\mathrm{dBm}$, corresponding to a radiation power density of $27\mathrm{nW}/{\mathrm{m}}^2$, with pixel to pixel coupling interference below $-14\mathrm{dB}$ at 2.5 GHz.

Figure 1

System architecture of our metamaterial microwave power detector array. (a) Radiation is incident from port 1 with electric field polarization as depicted. A schematic of the full device is shown (exploded view) and the layers shown from top to bottom are the ELC, Rogers dielectric spacer, patterned ground plane, and microwave power receiver circuit. (b) Photo of an individual pixel, i.e., an ELC unit cell with dimensions of $a=27.3$, $l=24$, $w=3.5$, and $g=4$; all in millimeters. (c) Photo of the circuit layer with vias indicated. The vias transport the received signal (port 3) to the microwave power receiver circuit underneath each unit cell where the different highlighted regions are: (I) balun, (II) impedance matching circuit, (III) low noise amplifier, and IV) microwave power detector.

Figure 2

Numerical simulations of the metamaterial absorber. (a) Simulated results of the free space reflection ($S_{11}$ dashed gray curve, blue), transmission ($S_{31}$ gray curve, green), and reflection coefficient ($S_{33}$ black curve, red). Simulated current densities (b) and electric field magnitude (c) shown directly underneath the ELC (left) and above the ground plane (right) at the simulated design frequency of 2.0 GHz.

Figure 3

Experimental measurements in anechoic chamber for the center pixel on the MMA-FPA. (a) $S$-parameter data shows the reflection coefficient ($S_{33}$ black curve, red) and the transmission ($S_{31}$ gray curve, green) with the dashed gray line at 2.5 GHz the frequency for sensitivity and off-angle measurements. (b) Mutual coupling (MC) between neighboring metamaterial pixels located parallel (light gray curve, gold), perpendicular (black curve, blue), and diagonal (gray curve) with respect to the electric field polarization. (c) Sensitivity characterization with the output of microwave power detector of single pixel as function of incident power, and is sensitive as indicated by dashed red line down to $-77\mathrm{dBm}$ at 2.5 GHz.

Figure 4

Off-angle performance characterization of the MMA-FPA at 2.5 GHz for both the electric field vector perpendicular (TE) and parallel (TM) to the floor of the chamber. The ELC resonators are characterized for the correct polarization ($E$-field perpendicular the split gap), shown for both TE (gray curve, gold) and TM (black curve, blue). The cross polarization (E-field parallel to the gap) are both 20 dB lower than that of the correct polarization, shown for TE (gray curve, green) and TM (black curve, red).