Laser sensors for military sonars and monitoring military assets and earthquakes

Rajesh Uppal September 1, 2022 Industry, Photonics Comments Off on Laser sensors for military sonars and monitoring military assets and earthquakes 668 Views

Laser, a device that stimulates atoms or molecules to emit light at particular wavelengths and amplifies that light, typically producing a very narrow beam of radiation. Lasers deliver coherent, monochromatic, well-controlled, and precisely directed light beams. Laser technology has observed a great advancement over the last few decades. This technology is used for a wide range of applications including medical sciences, military, industrial manufacturing, electronics, holography, spectroscopy, astronomy and much more.

Another important area is Laser sensors that can detect, count, trigger, map, profile, scan, and guide as well as verify levels, proximities, and distances to objects. Laser sensors come in several configurations, with some detecting presence and others measuring distance. A proximity type laser sensor, also called a laser photoelectric sensor, is commonly used to detect presence of a part.

Laser sensors generally work well in a dirty environment since the focused light can “burn” through dust. The focused beam also enables long sensing distances, and detection of small objects or targets through small openings.

Principles of measurement used by laser sensors

The method used to measure distance depends on the accuracy and distance capability required of the device. Laser light must be focused, and it must stay narrow over a great distance and at a narrow spectrum (color of light). The emitted light can then be triangulated or pulsed, with each pulse return measured to create distance readings.

Measurement principles include triangulation, time-of-flight measurement, pulse-type time-of-flight systems, and modulated beam systems. For distances of a few inches with high accuracy requirements, “triangulation” sensors measure the location of the spot within the field of view of the detecting element. The laser beam is projected from the instrument and is reflected from a target surface to a collection lens. The lens focuses an image of the spot on a linear array camera (CMOS array). The position of the spot image on the pixels of the camera is then processed to determine the distance to the target. Triangulation devices may be built on any scale, but the accuracy falls off rapidly with increasing range.

Time-of-flight technology is often used in long-range laser distance sensors, also called rangefinder laser sensors. These types of sensors use a transmitter diode to generate a very short pulse of narrow-spectrum red or infrared light which reflects from the target object and back to a sensitive, laser energy detector, also called a receiver diode. The accurate and precise electronics in the sensor can measure the light transit time and use the constant for the speed of light to calculate the object’s distance from the sensor.

One common example of this approach is “phase measurement” in which the laser’s output is typically sinusoidal and the phase of the outgoing signal is compared with that of the reflected light. Phase measurement is limited in accuracy by the frequency of modulation and the ability to resolve the phase difference between the signals. Some modulated beam rangefinders work on a range-to-frequency conversion principle, which offers several advantages over phase measurement.

Time-of-flight laser distance sensors are available in a measurement range from 1 cm to over 100 m and are similar in size, output options and laser sensing capabilities to CMOS sensors. These long-distance sensors have good resolution, from about one mm at close distances, to less than 2.5 cm of error over 100 m. To improve measurement accuracy, multiple measurements are often made, slowing the response time of these devices to several milliseconds.

For very long range distance measurements (up to many miles) “time-of-flight” laser rangefinders using pulsed laser beams are used. Modulated Beam Systems use the time light takes to travel to the target and back, but the time for a single round-trip is not measured directly. Instead, the strength of the laser is rapidly varied to produce a signal that changes over time.

Spectroscopy

Most types of laser are an inherently pure source of light; they emit near-monochromatic light with a very well defined range of wavelengths. By careful design of the laser components, the purity of the laser light (measured as the “linewidth”) can be improved more than the purity of any other light source. This makes the laser a very useful source for spectroscopy.

The high intensity of light that can be achieved in a small, well collimated beam can also be used to induce a nonlinear optical effect in a sample, which makes techniques such as Raman spectroscopy possible. Other spectroscopic techniques based on lasers can be used to make extremely sensitive detectors of various molecules, able to measure molecular concentrations in the parts-per-1012 (ppt) level. Due to the high power densities achievable by lasers, beam-induced atomic emission is possible: this technique is termed Laser induced breakdown spectroscopy (LIBS).

Mobile laser scanning

Accurate three-dimensional (3D) point cloud data have been an important data source for 3D urban models, which are an integral part of urban planning, simulation, mapping and visualization, emergency response training, and so on. Mobile laser scanning (MLS) is an emerging technology for generating highly accurate 3D point clouds and thus have many potential urban applications.

A MLS system consists of 3D laser scanner, GNSS (global navigation satellite system), IMU (inertial measurement unit), and camera. They are usually mounted on moving platforms (e.g., vehicle, boat, backpack, robot), and can collect 3D surface information along the driving paths. Due to the short measure range and flexibility of data acquisition, a MLS system can acquire very accurate (millimeter-level) point clouds of high point density (up to a few thousand points/m2).

Given those advantages, MLS data have been used in recent years in a wide range of urban applications, including urban land cover analysis, digital 3D city modeling, urban environment monitoring, and autonomous vehicle driving. The use of these data has involved techniques such as data fusion and classification (e.g., using machine learning approaches) developed from the remote sensing, computer vision and robotics communities

Applications

Laser sensors are often used in process monitoring and closed-loop feedback control systems. Material handling is a popular application to enable positioning of cranes, gantries and automatic guided vehicles. They are also suitable for automation, chemical industry, medical technology and special machine construction.

Laser distance sensors are excellent for the use in engineering for quality control and process monitoring. Laser sensors are ideal for many specific applications in Plant Management and Automation, Security and Surveillance, Vehicle Guidance and Automation and Traffic Management. They are used in many sectors of industry and research for distance measurement. Particularly in confined spaces non-contacting sensor systems are the best solution.

These laser distance sensors use a focused, coherent light to measure distance to a target object. In factory automation applications, the target is usually a product or a machine element. They detect any solid object and produce an output proportional to the measured distance—independent of material, color and brightness. A few of the many other applications include component alignment, height measurement, robot positioning and weld head location.

Lidars (Light Detection and Ranging) are similar to radars in that they operate by sending light pulses to the targets and calculate distances by measuring the received time. Since they use light pulses that have about 100,000 times smaller wavelength than radio waves used by radar, they have much higher resolution. LIDARs are rapidly gaining maturity as very capable sensors for number of applications such as imaging through clouds, vegetation and camouflage, 3D mapping and terrain visualization, meteorology, navigation and obstacle avoidance for robotics as well as weapon guidance.

Low-cost laser sensors survey earthquake damage

A low-cost, laser-based sensor that can monitor and rapidly assess earthquake damage to a building has been created by scientists in the US. Designed to be installed in multilevel buildings in earthquake-prone regions, the system can determine whether floors in a building have shifted relative to each other. Its inventors say that the device could allow for the rapid assessment of critical buildings like hospitals in the wake of a disaster.

During earthquakes, horizontal ground motions can cause different floors of multilevel buildings to be displaced sideways in relation to each other, a phenomenon that engineers call “interstorey drift”. Assessing this drift plays a vital role in ensuring that a building is safe to use after an earthquake and to identify if structural repair work is needed. Finding a reliable method to do this quickly and cheaply, however, has proven challenging.

A traditional approach uses accelerometers that are installed in key points around a building. These determine the forces exerted on the structure during an earthquake and subsequently calculate the extent of drift. This method, however, is time-consuming, impeded by the frequency limitations of the sensors and sometimes unsuccessful in the event of permanent structural damage. Also, accelerometers are expensive to implement on a wide-spread basis.

“Until now, there’s been no way to accurately and directly measure drift between building stories, which is a key parameter for assessing earthquake demand in a building,” explains David McCallen, of the Lawrence Berkeley National Laboratory and the University of Nevada – who led the research.

“The major earthquakes that struck in southern California this [month] serve as a reminder of the risks associated with seismic activity,” notes McCallen. He adds that it is very important to develop “sensors and data analysis that can rapidly measure infrastructure health and inform the most effective response after the next major quake”.

To achieve this, McCallen and his colleagues have spent four years developing sensors that — when placed within a building — can directly and rapidly measure interstorey drift and potentially relay their findings to a disaster response centre.

Their device is called a discrete diode position sensor (DDPS) and works by shining a laser from the ceiling of a room to a sensor pad on the floor. This autonomous detector contains an array of inexpensive, photo-sensitive diodes that can determine, by measuring the displacement of the laser beam, if, by how much and in what direction the ceiling has drifted relative to the floor after an earthquake. From this, engineers can work-out the effect of the quake on the building’s integrity.

“Previous generations of DDPS were quite a bit larger than the system we are now able to deploy,” says McCallen. “Based on design advancements and lessons learned, the sensor is a quarter of the size of our original sensor design, but features 92 diodes staggered in a rectangular array so that the laser beam is always on one or more diodes.”

So far, the researchers have only tested the drift sensor in the laboratory, putting the device through its paces in three rounds of trials on a shake table. “The rigorous testing the DDPS has undergone indicates how the drift displacements measured on the three testbeds compared to representative drifts that could be achieved on an actual full-scale building undergoing strong shaking from an earthquake,” McCallen says.

Military applications

The Military also uses laser technology for sensors, range-finders and target designators that are used for intelligence, surveillance and reconnaissance. Lasers is capable of providing secure data transfer for military because of its immunity to EMI in the visible and infrared spectrum. The probability of intercepting a laser signal is very low due to its narrow beam divergence and coherent optical beam, making the laser a suitable candidate for secure military tactical operations. Besides the communication aspect, the highly directive nature of a laser beam is also used as a directed energy laser weapon.

Furthermore, laser sensors are deployed in the battlefield or in space for tracking the path of a wide range of military vehicles like missiles, unmanned aerial vehicles, fighter aircraft, warships, submarines, and so on. Advancements in space operations and laser technology have offered synergistic possibilities of using lasers from space-based platforms during military operations.

In the coming months, the team will install sensors in a multistorey building at the Lawrence Berkeley National Laboratory. The structure is located adjacent to California’s Hayward Fault Zone, which is one of the most potentially dangerous earthquake regions in the US. In the future, the devices could be installed in buildings throughout regions that are particularly earthquake prone. Emerging 5G communications systems could be used to link the sensors to central disaster response centres, say the researchers

However, McCallen explains, “we also need to have back-up hardened communications in a post-earthquake environment in case existing network connectivity is down, so we envision back-up communications that could blip data through a satellite so that there would be high certainty in the ability to send building response data to remote locations”.

Looking to the future, McCallen adds “We are excited that this sensor technology is now ready for field trials, at a time when post-earthquake response strategies have evolved to prioritize safe, continued building functionality and re-occupancy in addition to ‘life safety’.”

Laser technology

CMOS technology is often used in short-range, high-precision laser sensors. The basic principle is optical triangulation using a CMOS linear imager. A diffuse triangulating laser distance sensor transmits a laser through a lens and to the target, which reflects the light back to the sensor. A lens focuses this reflected light into a small spot onto the CMOS linear imager. The distance to the target object changes the angle of the reflected light and where the light is received on the linear imager.

These CMOS, diffuse triangulating laser distance sensors are available in measurement ranges from about 1.5-60 cm. They are packaged in small housings, about 50 mm x 50 mm, with either analog or discrete outputs—and generally work well regardless of the material, color or brightness of the target object. These distance sensors have high-resolution, in the low µm range depending on the measurement span, and response times less than a millisecond.

Fiber laser sensors have greatly increased in popularity over the last few decades as they are a low-cost, highly sensitive, electrically passive, and highly reliable alternative to many other solutions such as the dye laser or the semiconductor laser. They are also immune to electromagnetic interference and can be easily incorporated into a multiplex signal or system.

Class 1 lasers are eye-safe under all operating conditions. However, Class 2 lasers are visible lasers safe for quick accidental viewing of less than 0.25 s but may damage the eye if deliberately stared into.

Laser Sensor Market

Apart from this, governments across the globe are also encouraging the deployment of ADAS features worldwide, which will drive the growth of the market. For instance, the US Department of Transportation’s National Highway Traffic Safety Administration (NHTSA) published the Federal Automated Vehicles Policy related to highly-automated vehicles (HAV), which range from vehicles with advanced driver-assistance systems features to autonomous vehicles.

Furthermore, the growing adoption of laser technology for quality checks in various industrial verticals and increasing usage of laser technology for optimal communication are creating potential opportunities for the market to grow in the forecasted period.

On the other hand, high costs associated with the deployment of laser technology, stringent regulatory framework and policies imposed by the government, and lack of skilled personnel and expertise are restricting the market and hampering the growth.

Moreover, technical complexities in high-power lasers and increasing concern related to the environment over the use of rare-earth elements are significant challenges that may negatively affect the market’s growth.

Market Segments

By Application Type, the market is classified into Laser Processing {Macro-Processing [Cutting (Flame Cutting, Fusion Cutting, and Sublimation Cutting), Drilling (Single-pulse Drilling, Helical Drilling, Percussion Drilling, and Trepanning Drilling), Welding, and Marking & Engraving], Micro-Processing, and Advanced Processing}, Optical Communications, and Others.
By Laser Type, the Laser Technology market is classified into Solid Laser and Liquid Laser.
By End-User Industry Type, the Laser Technology market is classified into Automotive, Aerospace & Defence, Commercial, Industrial, Medical, Research, Semiconductor & Electronics, Telecommunications, and Others.

The emerging semiconductor laser technologies are significantly revolutionizing the industrial automation process. IIoT is expected to become a game-changer for the modern factory providing a new trend to the market. The applications of an industrialized inspection need detection of the presence and absence of an object. This can be solved by using a laser sensor to address quality control tasks.

According to Emerson, the projected growth of the global factory automation market is expected to increase from 3% in 2019 to 3.5% by 2021, which significantly holds the market demand. Further, the use of laser sensor technology innovation in the maritime and offshore industry is expected to be a future trend. Primarily a laser-based navigational aid, LADAR (Laser Detection and Ranging), combines long-distance object detection with high-accuracy measurement, giving users a full 2D/ 3D/4 D ( 3 D plus time) perspective for optimal maritime awareness.

End-user industries such as automotive, are greatly benefiting from the advances in laser use, mostly with future sales of the autonomous vehicle. Autonomous cars use other sensors to see, notably radars and cameras, but laser vision is hard to match. Radars are reliable but do not offer the resolution needed to pick out things like arms and legs. Cameras deliver the detail but it requires adopting machine-learning-powered software such that it that can translate 2-D images into 3-D understanding. Lidar on the other hand offers hard, computer-friendly data in the form of exact measurements.

Laser Industry

The well-known players in the Laser Sensor market are Fiso Technologies, Prime Photonics, Banner, Bayspec, Omron, Laser Technology, Keyence, Ifm, Acuity, JENOPTIK, LAP, MTI Instruments.

In April 2020, Xiaomi unveiled the company’s new smart Internet of Things (IoT) home appliance Mi Vacuum -Mop P series in India. The Mi Vacuum is incorporated into twelve different multi-directional sensors and a dedicated Laser Distance Sensor (LDS) navigation system such that it can be used to scan complex environments accurately and avoid obstacles during the cleaning process.