New-Tech Europe Magazine | Feb 2017

Sensors Special Edition

and reducing maintenance. However, a truly contactless connector must be able to transmit both data and power. For power, there are few options. Capacitive power transfer (CPT) has the advantage of being able to penetrate (floating) metal and has low EMI, but it suffers from low power density and short range. Some generalized comparisons of various wireless options, using pros and cons, are shown for easy reference (Figure 1.) For contactless power transfer, an inductively coupled power transfer (ICPT) option proves to have more pros than cons. It is has high power density at reasonable distance, is well known with widely available product and technology solutions, and high efficiency is possible. The downside is that it cannot penetrate metal. For data transmission, there are a number of options. Capacitive coupling’s low EMI is also an advantage for data transfer, but such coupling requires significant surface- plate area, which can be challenging for tiny, rotating couplers. Inductive coupling for data suffers from low bit rates. Other options include RF at 60 GHz, 2.45 or 5 GHz, sub-GHz, and ICPT, as well as optical links. Each has pros and cons, as shown in Figure 1. The 2.45-GHz industrial, scientific, medical (ISM) band is also unlicensed, with global acceptance and wide usage, most notably as “wireless Ethernet” under the moniker of Wi- Fi. In the final analysis, it turns out that a hybrid architecture, RF for data and inductive coupling for power, is the best approach for contactless connectivity. Defining induction Inductive power transfer has been with us for quite some time, but for the sake of clarity a quick run

Figure 2. In inductive coupling, the coupling is determined by the distance (z) and the ratio of D2/D, while the efficiency of power transfer between transmitting coil L1 and receiver coil L2 depends on the coupling (k) between the inductors and their Q factor design criteria that need to be considered for each application. be considered when deciding how to meet the design specification most effectively. These include:

The ability to transmit over “certain distances” as mentioned above is particularly interesting. There are instances where power and data need to be transferred wirelessly across small distances, such as through a wall or other material. Also, more connector freedom may be needed without mechanical wear and tear, or the environment may be too hazardous to introduce any possibility of arcing. It’s at this point that advances in contactless connectivity need to be considered. Contactless connectivity “Contactless connectivity requires both contactless power and contactless data technology which can easily connect over a short distance without physical contact” [TE Connectivity (TE)]. There are many benefits to be accrued from contactless over traditional connectors which should

Improved reliability: Delivers robust power and data without wires or physical contact. Also, the connectors are hermetically sealed ensuring environmental integrity. Greater flexibility: There is an unlimited range of motion, allowing 360° movement, tilt, angle and misalignment. Unlimited mating cycles: There are unlimited mating cycles in wet and dusty environments. This is particularly suitable where slip rings or spring cables reach their limit. Connection through walls or materials: Contactless technology allows connection through walls or materials, which is not possible with traditional connectors. Improved safety: There is no arcing, which is a major plus in hazardous environments such as gas-filled chambers. Cost savings: There is no wear and tear thus improving the uptime

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