By Jordi Miró, Antenna & Product Engineer, Ignion.
In the IoT world, it’s a given that devices will end up deployed in a wide variety of environmental conditions. Some devices live next to materials that only incrementally affect their wireless performance. Other devices must work adjacent to materials that can significantly jeopardize the device’s wireless signal. How can developers make intelligent product decisions – particularly regarding antenna characteristics — that pre-emptively reduce risk before committing to costly manufacturing?
The surest way is to be aware of the deployment conditions during the design stage and adapt the antenna performance to those target conditions. Until recently, this method was better in theory than in practice. Developers needed to produce prototypes using multiple antenna selections, and through trial and error, arrive at the most robust solution. This process was often inconsistent and always time-consuming.
Today, with Virtual Antenna® technology, antenna response can easily be tuned during pre-product testing. This allows IoT designers to optimize the design for the target environmental settings. The end benefits are more cost-effective testing, rapid design optimization, faster time to market, and optimal performance in the field.
This post will allow you to see how several common materials and their proximity to the deployed devices impact antenna performance. The materials assessed are concrete, wood, body phantom, and metal.
We produced a test with a 100 mm x 50 mm evaluation board covering LTE-Cat M in the most used low and high-frequency bands for IoT deployments (699-960 MHz and 1710-2200 MHz). The materials were tested with the device in terms of distance to better determine the performance impact and best decide the deployment location. Five different distances between the PCB of 100 mm x 50 mm and the surrounding material were evaluated: 20 mm, 15 mm, 10 mm, 5 mm, and 0 mm. The matching network used in this analysis remained the same, to evaluate the shifting in frequency, if any, introduced by each material.
The results shown below demonstrate how the aforementioned materials affect the antenna performance in total efficiency percentage (%), depending on the distance between the device and the underlying material.
In IoT asset tracking, wood pallets are often in close proximity to the tracking devices. The impact on antenna performance in proximity to wood is the least problematic. The only noticeable effect is in the high bands, due to material insertion of losses. It’s fair to conclude that the antenna is highly robust to this material.
Proximity to concrete is a different matter, causing a drop in antenna efficiency, especially at high bands. It is seen that the antenna is robust towards detuning from the presence of concrete and the performance is somewhat decreased, thus it is advised to keep some distance from it.
Human/animal body in proximity – such as with wearable devices – has a significant impact on antenna performance. The antenna performance is quite affected by the human body’s capacitive nature, especially when the antenna is almost touching the skin. This effect can be noticed in almost all the antenna parameters such as total efficiency, as can be seen below.
Sometimes, a perfectly tuned antenna behaves totally differently in the nearest area of an organic body becoming non-operative. Nevertheless, the good news is that, in most circumstances, a few millimeters can prevent adverse effects on the human body.
Ignion TIP: We recommend locating the placement with minimum exposure to the body and to leave as much distance as possible. Put the antenna on the surface furthest from skin contact.
As can be seen below, metal is probably the most challenging material when placed close to an antenna. A reconfiguration/retuning of the matching network is required to adjust to the specific distance between the device and the metal. This step allows you to maximize device performance despite the surrounding metals near the antenna.
Many IoT designers struggle with marked antenna performance fall-off due to metal in the vicinity of the device. The tailored capabilities of the Virtual Antenna® technology allow IoT designers to deal with these problems without major impacts but assuming some efficiency losses. For instance, devices implemented in supply containers are perfectly functional even though they are made of metal since the antenna integration considers the presence of metal at the design stage.
While it’s not possible to know all the environmental conditions that can affect device performance, the four materials discussed here will cover a great many use cases. The flexibility of Virtual Antenna® technology allows for proactive design decisions that can mitigate the effects of wireless degradation – in advance of product manufacturing.
By letting you see the performance in advance, you can build in the needed buffer for the degradation that may occur when put in proximity to these environmental factors.
Want to see a more in-depth analysis of how proximity materials affect your IoT device’s antenna performance? Read all about it in our latest design guide here.