Uncrewed Systems Technology 044 l Xer Technolgies X12 and X8 l Lidar sensors l Stan UGV l USVs insight l AUVSI Xponential 2022 l Cobra Aero A99H l Accession Class USV l Connectors I Oceanology International 2022

40 Focus | Lidar sensors the starting sequence of the Lidar as well as the packet generation of the point cloud measurements for data transfer to an external PC via Ethernet. SPAD ToF sensor A stacked sensor using a direct ToF (dToF) method is an industry first for automotive Lidar applications. This uses 10 µm 2 single-photon avalanche diode (SPAD) pixels and distance measuring processing circuit on a single chip, resulting in a 1/2.9-type form factor with a 6.25 mm diagonal. The SPAD pixel structure uses avalanche multiplication to amplify electrons from a single incident photon, causing a cascade. SPAD pixels are used as a type of detector in a dToF sensor, which measures the distance to an object by detecting the ToF (time difference) of light emitted from a source until it returns to the sensor after being reflected by the object. The sensor uses the same stacking and copper-to-copper connections as those for CMOS image sensors to combine a chip with 100,000 SPAD pixels in a 597 x 168 array, with the distance measuring processing circuit on a second chip. The copper pads are included in the pixel array to provide the connection to the processing chip. The sensor also uses a light incidence plane with irregularities on its surface to refract incident light, thereby enhancing the absorption rate. These features result in a 24% photon detection efficiency in the 905 nm wavelength commonly used by automotive Lidar light sources. That makes it possible to detect distant objects with a low reflection rate at high resolution and distance resolution. An active recharge circuit is included on the circuit section, which comes with a connection for each pixel. This allows a response speed of 6 ns at normal operation for each photon. This stacked construction enables a Lidar sensor with a range of 300 m and an accuracy of 15 cm using a 6 x 6 block of pixels, or a resolution of 30 m with a 3 x 3 pixel block. A mechanical scanning Lidar reference design with a rotating polygon mirror has been developed using a 905 nm laser and the SPAD sensor for evaluating the sensor. 3D imaging Researchers have also found a way to use standard image sensors to provide 3D Lidar images with a new type of low- cost modulator Using a technique called acoustic resonance, researchers have built a simple acoustic modulator using a thin wafer of lithium niobate, a piezoelectric material, coated with two transparent electrodes. When electricity is introduced through the electrodes, the crystal lattice of the lithium niobate vibrates at very high, very predictable and very controllable frequencies, rotating the polarity of the light. This can be used to modulate the light, and the geometry of the wafers and the electrodes defines the frequency of light modulation to fine-tune the frequency. A polarising filter is placed after the modulator that converts this rotation into intensity modulation, providing modulation at 3.7 MHz across a 1 cm 2 area. The modulator design is simple, and integrates into a proposed system that uses off-the-shelf cameras to build an integrated Lidar for UAVs and space rovers where power consumption is key. The researchers have cited a voltage of 2 V peak to peak to drive the modulator, and say they have further reduced the energy consumption by at least 10 times, with a reduction of 100 times being possible. June/July 2022 | Uncrewed Systems Technology Measuring the vibration in a Lidar sensor (Courtesy of TU Wien) The point cloud generated by a stacked time-of-flight image sensor (Courtesy of Sony Semiconductor)