Monthly Archives: March 2019

Metamaterials Improve LIDAR

Light Detection and Ranging or LIDAR is a remote sensing method. The technique uses the time of flight of pulsed laser light to measure variable distances. Airborne systems record additional data, which, when combined with the data from the light pulses are able to generate three-dimensional information about the neighboring environment that offer precise surface characteristics.

In general, a LIDAR comprises a laser, a scanner, and a specialized receiver for Global Positioning System or GPS. Although so far, common platforms for LIDAR used helicopters and airplanes for acquiring data over broad areas, autonomous vehicles are now using Topographic LIDAR extensively for navigation through road traffic using a near-infrared laser to map the nearby area.

Using LIDAR systems help scientists and engineering professionals examine both artificial and natural environments with precision, accuracy, and flexibility. As the market for LIDAR is still in its nascent state and its technologies fragmented, there are only about 70 LIDAR companies worldwide, making it a hotbed of new technology.

For scanning a wide area, conventional LIDAR systems have to rely on electro-mechanical spinners to steer laser light beams. Not only does this method reduce the scan speed, but it also affects measurement accuracy. A Seattle-based, venture-backed startup, Lumotive, is now developing a new technology that will change the way LIDAR systems function.

According to Bill Colleran, co-founder, and CEO of Lumotive, they are developing a LIDAR system that can steer beams but has no moving parts. Rather, their patented technology uses the light-bending properties of metamaterials such as Liquid Crystal Metasurfaces or LCM to steer the laser beams. Bill calls the use of such metamaterials “pivotal technology.”

However, Lumotive is not the only player in the field to offer LIDAR systems that do not rely on mechanical scanning. Other rivals have used optical phased arrays or MEMS mirrors to claim their LIDARs use a lower number or no mechanical components.

According to Bill, Lumotive LIDAR systems use LCM semiconductor chips. The main advantages of LCM are it offers a large optical aperture of about 25 x 25 mm, resulting in a longer range for the LIDAR, along with a 120-degree field of view. The high performance of the LCM comes from its fast-random-access beam steering capability.

When a laser beam shines onto the Lumotive’s liquid crystal metasurface chip, programmed electrical signals can direct the reflected light into any direction within its 120-degree field of view.

Metamaterials are mostly artificially structured materials that allow unprecedented control over their properties, specifically in new ways for controlling the flow of electromagnetic radiation including light. For instance, Kymeta has a flat-panel satellite antenna technology based on metamaterials.

Kymeta’s antenna can move electronically. It does not require the conventional phase shifters, amplifiers, and related components on its surface. This not only cuts down the cost, it also consumes far less power and does not require cooling devices. Compared to conventional antenna systems, Kymeta is able to increase the density of their flat-panel antenna elements dramatically, while controlling the phase and amplitude simply by activating or deactivating individual antenna elements. Lumotive have adapted the Kymeta antenna’s metamaterial architecture to their LIDAR system.

Role of LEDs in Horticulture

While LEDs have revolutionized indoor and exterior lighting methods, they have been revolutionizing operations involving indoor grow facilities. This is mainly because LEDs are highly flexible in their spectral output, while their efficiency is very high. That means they emit much lower heat.

A new standard from ASABE specifies the performance of LED lighting products for horticulture applications. The standard spells out the test methods to measure the optical radiation from LEDs in the range 280-800 nm. Note the visible spectrum covers about 390-700 nm.

According to the Standards and Technical director of ASABE, Scott Cedarquist, in horticultural applications, LED lighting has generated very high levels of interest in their projects in the last 20 years. Therefore, horticultural lighting makes use of several terminologies that are primarily focused on plants. Two of them are PPFD or Photosynthetic Photon Flus Density and PPF or Photosynthetic Photon Flux.

While PPFD measures the number of active photons falling on a surface per unit area per unit of time, PPF is the number of photons created by a lighting system per second.

Horticultural lighting primarily focuses on delivering photons that initiate photosynthesis and other processes in plants. These spur plant development as they excite electrons. Horticultural applications use LED products that are different from those used for general illumination. The difference is primarily that the former has a wider spectral output typical for horticultural applications. This is necessary as different plants respond differently to various wavelengths.

According to academic and industry research, each type of plant has a specific light recipe that helps the plant to yield higher growth in the shortest period. The recipe holds the variation in optical spectra for optimizing the overall growth of the plant, thereby improving desirable plant characteristics. For instance, increasing the potency of cannabis or the flavor of vegetables.

The light output from LEDs has another characteristic. Not only do LEDs provide a precise output spectrum, but this spectrum can also be tuned to optimize the spectrum for different plants and the phases of their life.

LED lighting products are primarily used in horticulture as vertical farms. This is due to the far lower heat output from LEDs as compared to that from other light sources. This allows the LEDs to be interspersed very close to the plants without damaging them. Therefore, facility managers are able to maximize the use of available space. This has made vertical farming very popular in urban areas. Horticulturists are making use of abandoned buildings which they are converting to grow food, thereby making new products available at cheaper rates.

The high efficiency of LEDs also helps considerably in energy savings. However, grow facility managers are more interested in the yield of the crop, and use of LEDs for high-value crops such as cannabis offer revenue increase from higher yield and shorter life cycle, rather than from energy savings. Similarly, more traditional crops such as flowers and leafy vegetables also use LED lighting not for energy savings, but rather for the ability to produce more crops in a shorter period.

Automation Applications of Thermopile Arrays

For a temperature difference occurring between two ends of a thermocouple, it develops an electrical voltage difference. A series of such thermocouples form a thermopile sensor, with each element being a thin wire made from two materials differing in the thermal activity. All the hot junctions of the thermocouples are placed on a thin common absorbing area that forms the sensor face, while the cold junctions are placed on a heat sink with a high thermal mass.

As an instrument, the thermopile sensor can remotely measure the temperature of objects and people. The operation of the thermopile is better understood in terms of heat flow rather than temperature rise. Any object with a temperature higher than the ambient is actually sending out heat in specific spectral characteristics and density. According to primary thermodynamics, heat flows from an object at a higher temperature to another at a lower temperature, causing a change in energy levels of both the objects in the process.

The amount of heat absorbed depends on the field of view and surface area the Thermopile sensor presents to the heat source. Heat reaching the thermocouples inside flows through the membrane structure of the thermopile, finally reaching the heat sink or the housing bottom. This heat flow causes a difference of temperature on the ends of the thermocouples located on the absorber and those on the heat sink, ultimately resulting in a voltage difference between the ends of the thermopile sensor.

Compared to the traditional contact-based temperature sensors, thermopile temperature sensors are of the non-contact type, and hence, they are more popular industrially. Rather than use conduction for heat transfer, thermopile temperature sensors use infrared radiation, allowing better reliability and performance in several constrained applications.

The voltage difference on the ends of the thermopile sensor is analyzed by a Thermopile sensor IC, which provides temperature readout in a convenient digital format. Continuous improvements in this field are resulting in devices that consume reduced power, are smaller and more affordable. This translates into more application opportunities for thermopile temperature sensors in home appliances, office equipment, medical instruments, and consumer devices.

Thermopiles with single-element infrared sensors are popular in the low-end market, as they are good for detecting the presence of stationary warm bodies in a room. However, these simple sensors are unable to provide the direction of movement of a moving object in their field of view. For this additional functionality, engineers use thermopile arrays.

Rather than use a single sensing element as in a thermopile temperature sensor, thermopile arrays use multiple IR sensing elements working together. Integrated signal processing capabilities and coordinated sensing elements of the modern thermopile arrays allow the devices to measure not only absolute temperatures but also temperature gradients. This allows thermopile arrays to sense the direction of movement of the heat source, such as up, down, left, right, and diagonally. Thermopile arrays can detect the presence of multiple objects or people even as they move about in different directions. This allows them to sense the proximity of the heat source and handle control tasks with simple gestures.