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IoT Devices: How Small Is Too Small?

By: Ken Everett

After a year hampered by COVID-19, Internet of Things (IoT) spending is rebounding, with double-digit growth expected in 2021, and a compound annual growth rate (CAGR) of 11.3 percent over the 2020-2024 period, according to analyst firm IDC. As awareness of the Internet of Things market grows, businesses of all sizes and in every industry are continuously thinking about ways they can incorporate IoT into their day-to-day activities to drive down cost and improve efficiencies.

According to a study by analyst firm ABI Research, asset tracking is one of the highest-growth segments in the IoT market. ABI expects 51 percent growth per year through 2024 as the industry moves from tracking only high-value goods into low-value, high-volume markets, which will quickly account for most shipment numbers.

As new business cases emerge for the IoT as device and connectivity costs continue to decrease, businesses are able to broaden the range of assets they track. This often leads to requests for some interesting devices, most of which need to be small. But does hardware size really matter in the IoT, and what are the trade-offs?

Technology is advancing rapidly, and building smaller devices is possible given some of the higher density integrated circuits and smaller components available. However, there are some fundamental technical reasons why smaller is not necessarily better. There often needs to be a compromise between the size of the device and its performance, both in terms of battery life and radio frequency (RF) efficiency.

Battery size

The goal of any battery-powered asset tracking device is to last for the useful life of the asset: deploy once and never have to change the batteries. The logistical cost of having to maintain and service batteries has been a barrier to broader adoption of many IoT devices.

Battery technology as it relates to IoT devices has not advanced much in recent years. The simple fact remains that if you reduce the size of your battery power source, the amount of energy to power your device decreases. This is fine for customers who start with a usage profile in mind and know exactly how much power their device needs to operate over a given period of time. However, what usually happens is when companies see success with small projects, they quickly want to update to more aggressive tracking parameters, which then require more energy usage. These low-power projects can quickly demand more power requirements.

Primary lithium cells are the most suitable for the majority of use cases, and common batteries include LiFeSO2 (for example, Energizer Ultimate Lithium) and LiSOCl2 (lithium thionyl chloride or “LTC”). These provide some of the highest energy densities and are able to deliver the peak currents needed during transmission of data. Both of these chemistry types offer good temperature ranges, with the LTC batteries being the most suitable for harsh temperature environments such as heat, humidity, dust and other conditions. Sticking to “off the shelf” primary cells when determining battery type means batteries are readily available for resellers to purchase directly. The end customer can even buy replacement batteries themselves as needed from their local home-improvement or department store.

Lithium coin cells (for example CR2032) are used in a number of small devices such as Bluetooth tags or beacons due to their small size. These coin cells have relatively low specifications for peak current (typically 30mA max) so cannot be used to power a cellular modem, or even peak LoRaWAN or Sigfox transmissions.

Rechargeable battery packs are useful for scenarios where the device can be regularly plugged in and recharged. One example of this is in bike or scooter tracking—the equipment’s battery is generally charged overnight, and the asset is placed back on the street in the morning. However, in IoT asset location scenarios, most customers want to minimize the amount of interaction required with the device once it has been deployed. It must “just work” with a typical expected battery lifetime of three to five years, or even longer. Think industrial applications where the IoT devices are in hard-to-reach locations, such as in the mining and oil and gas industries.

Advancements are being made in lowering the amount of energy needed to generate a location or sensor data for the asset and in the energy required to transmit that information up to a back-end system that can act on that information. Lower energy needed means benefits including longer battery life, smaller batteries, and more frequent updates.

Antenna and PCB size

To understand antenna and PCB size, some elements of physics should be summarized as they relate to RF signals. A dipole antenna has two radiating elements,



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