FEATURE THE INTERNET of THINGS
BRIDGING TECHNOLOGY GAPS IN IoT
AND INCREASING DESIGN SPEED A leading team of engineers at Murata Japan, offer some design considerations for developing next generation IoT communication networks
D
esigners focus on developing IoT modules that fit the specific needs
of each application in terms of functionality and shape. With hardware integrated into a module, the next step is to assemble software that performs the various sensor functions that the application needs, aiming to minimise power consumption. This involves careful balancing of power- management strategies to ensure that the processor can sleep for as long as possible but be ready to report changes in state over the wireless connection. It is important not to forget the vital
role of cloud services in the overall IoT solution. In contrast to traditional embedded systems, where all the functionality is delivered using software running in the device, the IoT relies on connectivity and remote services to create value. The advanced functions that can be performed by high- performance servers deliver much more effective IoT applications than are possible using software running in discrete nodes. To support wireless connectivity, an
effective RF design is essential. The sensor node may, for example, be embedded in the structure of a bridge. Or it may be inside a smart meter sitting inside a buried pipe. Low-frequency RF can penetrate these structures, and low- power wide-area network (LPWAN) protocols take advantage of these bands to support otherwise hard-to-reach sensor nodes. But to ensure IoT nodes remain in contact, an efficient antenna design is vital. In many cases, the size and shape of
the IoT device is at odds with the needs of the antenna. The low frequencies and long wavelengths desired for LPWAN demand similarly large antenna structures if advanced design techniques are not employed. The antenna needs to provide high gain and a radiation
22 DECEMBER/JANUARY 2019 | ELECTRONICS
pattern that fits the needs of the application, so that nulls are not formed in the desired direction of communications. Furthermore, the antenna should be tuned through the selection of suitable materials and shape to present an impedance to the system that makes it possible to decode weak RF signals. Although PCB materials can provide effective substrates for compact antennas, their design requires extensive experience. For example, the antenna pattern should be printed in such a way that antennas are kept away from other circuitry and ground connections that will distort the electric field around them. Use of components such as inductors can help improve the performance of a small antenna. The inductors compensate for the increase in capacitive reactance that can result from the use of sub- wavelength antennas, and the inductors can be constructed using printed coils. A key concern is to avoid the introduction of unwanted nulls, but that can be achieved through smart antenna design.
DESIGN SPECIFICATIONS For ease of integration, the antenna can be moulded into the package of the SoC module used to provide IoT functionality. In many situations this provides a simple way to integrate wireless connectivity and intelligent sensing into a product. In other cases, it makes sense to make the antenna part of the overall package design. In the case of a patch antenna, for example, it is possible to improve overall performance by placing the PCB carrying the main antenna against a sheet of metal that may form part of the IoT device’s enclosure. To maintain a long operational life, the
energy source needs careful planning. In any large-scale sensor network, the cost of maintenance caused by the need to replace batteries becomes prohibitive. Often, the IoT device and its battery will
be practically inaccessible; consider a sensor node embedded in the structure of a bridge or buried within a water pipe. As a result, the IoT device should be designed so that the energy source will last longer than the expected lifetime of the product. Energy harvesting can help ensure that the energy source remains topped up over many years. A bridge sensor, for example, can harness vibrations from heavy traffic passing overhead. An IoT device in a pipe can harvest energy from passing water or gas. This energy can be harnessed by a secondary battery, working in partnership with a non-rechargeable long-life cell. In any battery, safety is a prime
consideration. This is a particular concern for secondary, rechargeable batteries where the effects of charging need to be taken into account. Lithium- ion batteries, for example, present a fire risk if they are charged too quickly or suffer internal failures that lead to the buildup of lithium metal fibres. A supercapacitor provides a safer alternative but suffers from high leakage, which wastes precious harvested energy. To overcome the problem of delivering
long life in a rechargeable energy source, Murata developed its UMA series based on lithium titanate as the cathode material, in place of traditional lithium- ion materials. One key advantage of the lithium titanate construction is that it does not suffer from dangerous thermal runaway effects and does not require charging to be carefully controlled. The battery chemistry allows constant- current charging, which enables rapid charging that is not possible with lithium-ion chemistries.
Murata
www.murata.com/en-eu T: 01252 811666
/ ELECTRONICS
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