## 3 Hardware  
Figure 5 displays the hardware schematic of our assembled instrument, which consists of three printed circuit boards (PCBs) designed using Fusion 360 electronics design software. The PCBs were fabricated using the ProtoMat S103 PCB milling machine from LPKF Laser & Electronics. Additional files are available in the Supplementary Materials. The main board is equipped with an Arduino Mega 2560, which serves as the primary controller for the instrument. The Arduino Mega 2560 is a microcontroller-based board which has 54 digital input/output pins, 15 of which can be used as PWM outputs, 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power connector, an ICSP connector, and a reset button. The microcontroller features 256 KB of flash memory, 8 KB of which is occupied by the board's bootloader, 8 KB of SRAM memory, and 4 KB of EEPROM memory. The secondary board features an, which is responsible for controlling the \(Z\)-axis translation and angle board rotation of the characterized metasurface in the instrument. The Arduino Uno is a microcontroller-based board with 14 digital input/output pins, 6 of which can be used as PWM outputs, 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power connector, an ICSP connector, and a reset button. The microcontroller has 32 KB of Flash memory, 0.5 KB of which is occupied by the board's bootloader, 2 KB of SRAM memory, and 1 KB of EEPROM memory. The receiver antenna can move on the XY plane, whereas the metasurface can move in the \(Z\) direction and rotate along the \(Z\) axis, as can be seen in Figure 1a. Each of these degrees of freedom is actuated by a Nema 17 HS4401 stepper motor that is driven by a DRV8825 driver. The translation is aided by a threaded shaft. Each stepper motor has a torque of 0.42 N\(\cdot\)m uses up to 1.7 A per phase, and has a resolution of 1.8\({}^{\circ}\) per step, with 200 steps per turn. The motors measure 42 \(\times\) 42 \(\times\) 40 mm and weigh 280 g. The DRV8825 features  
Figure 4: (**a,b**) show the measured return loss of the fabricated helical antenna (a photo can be seen in the inset of (**a**)) at different frequency ranges. The measurement was performed with the VNA. an adjustable SMD potentiometer for current limiting, overcurrent and overtemperature protection, and the ability to operate with up to six microstep resolutions (1, 1/2, 1/4, 1/8, 1/16, and 1/32 step). It operates from 8.2 V to 45 V and can deliver up to approximately 1.5 A per phase, without a heat sink or forced airflow. With proper heat dissipation, this driver can reach up to 2.2 A per coil. The data collected is stored on a SD card using an SD card module HW-203 installed on the main board. The received RF signal is directed to a LTC5596 RMS power detector, which is mounted on a DC2158A evaluation board, from analog devices. The LTC5596 is a high-precision power detector that offers a wide RF input bandwidth from 100 MHz to 40 GHz, with a linear response in dB and a logarithmic slope of 29 mV/dB over a dynamic range of 35 dB, with accuracy typically better than \(\pm\)1 dB. Note that in our setup, the frequency response of the helix antenna (see Figure 4) is sufficient to filter out any other signal that is present in the environment. In the case of a noisy environment or when using broadband antennas, an RF filter stage can be added prior to the LTC5596 to assure that only the frequency of interest is being detected. Figure 6 illustrates the instrument's signal conversion system, which includes a 3D-printed case to shelter the components, connectors, and a power switch (a), a DC2158A evaluation board for LTC5596 IC and a voltage regulator circuit to convert 12 V in 3.3 V (b), and the zoomed-in image of DC2158A showing LTC5596 IC, RF in, and DC out (c). Figure 5: Instrument hardware schematic. Following the DC conversion, the signal is directed to an operational amplifier (OP07) integrated within the main board of the instrument.