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69 channels, which in turn is determined by the number of detectors. The new design approaches vary according to the technology and integration strategy, creating a complex ecosystem of suppliers. This has led to a wide range of ‘solid state’ systems that reduce the size, weight and power of the sensor engines using a range of components from different suppliers. One approach is to use a micro- machined mirror as the central element. Another is to use an array of photo- receivers with a single laser source, known as a flash sensor. A third approach is to use an array of laser diodes to provide the illumination, with an array of detectors for 3D Flash sensing. A fourth, and more solid-state approach is to use a single laser source that can be steered into a beam, with an array of photodiodes as the detector. These different techniques are used to create a Lidar sensor engine that is then integrated into a vehicle and linked to a control unit. The unit might process the data locally or combine the Lidar data with other data from visible light or infrared cameras, say, using data fusion algorithms. They can also be integrated into modules for UAV systems. However, the different approaches require different components and a range of processing techniques. Micro-machined mirrors The driver for the current generation of smaller Lidar systems is to replace the traditional rotating mirror with one that has been micro-machined. These use existing silicon chip technology to create an array of mirrors, each around 10 microns on a side. The mirrors can flex, and an array of transistors underneath are switched on and off to control the position of each individual mirror. This allows a single beam from a laser diode to scan in different patterns to illuminate an area. The reflected signals are received by a photodetector array. There are many different designs of mirror array, using techniques such as torsion beams or individual hinges, each with different switching times and resistance to shock, and each is proprietary to a particular manufacturer. A typical micro-mirror can resist up to 50 g of shock, making it far more robust than a traditional rotating mirror system. The technology has become well- established in computer and TV projectors but it has highlighted Lidar | Focus The control unit might process Lidar data locally or combine it with other data from, say, cameras using data fusion algorithms Unmanned Systems Technology | February/March 2018 A Lidar sensor produces a point cloud of data for mapping or obstacle detection (Courtesy of Quanergy)