The requirements of batteries in RF-connected systems
16 April 2020
According to Forrester research, over 85% of companies were implementing or planning IoT deployments at the end of 2019. New developments and technologies will span the industry but powering these devices will remain a prevalent issue. Here, J.D. DiGiacomandrea, Applications Engineering Manager at Ultralife Corporation, explains how Ultralife Thin Cell technology will help design engineers create the next generation of connected devices.
When the first networked computer system was developed in 1969, it didn’t initially seem like it was particularly successful. The first transmission between nodes on the ARPANET network crashed, with only two of the five letters of the word ‘login’ being successfully sent. But this transmission set in motion a chain of technological advancements and events that would go on to reshape the world.
50 years later, connected systems and the internet are ubiquitous in modern society. Today’s fast connection speeds mean a person can not only transmit the word ‘login’ halfway around the world but can remotely login to a connected computer. Yesterday’s goal of being able to transmit messages between networked nodes successfully is often taken for granted; the modern challenge is improving devices to wirelessly communicate with, control and command one another with minimal human interaction.
The fundamental goal of the Internet of Things (IoT) is to streamline processes and improve efficiency, whether it’s in the running of the home or in cost-driven industrial environments. In both of these areas, power is key. If a node loses power, the system will be unable to communicate properly, and the benefit of that connectivity is lost.
For example, if you are wirelessly networking industrial machinery, motors and robots with a manufacturing execution system (MES) and a sensor loses power, the performance data of the connected system cannot be collected or analysed. If that node happened to be connected to a system that is pivotal in monitoring the ability of a plant to deliver product to schedule, this can have a significant negative effect.
Unfortunately, there is no silver bullet to fixing connectivity challenges. The solution will depend on the type of communication technology that the device uses, such as radio frequency (RF) or Wi-Fi. As an IoT battery manufacturer, Ultralife Corporation has experience of providing power solutions for devices that use a wide range of communications technologies, and it is RF that can present some of the more interesting design challenges.
Slim profile power
Historically, the role of RF in industrial settings has predominately been in asset tracking through RF identification (RFID) tags. These tags transmit their movement and location data and come in two variants: passive and active. Passive tags contain no battery but are powered by the RF energy transmitted by battery-powered RFID readers; whereas active tags contain batteries and continuously broadcast information to be monitored.
Modern sensors that communicate using RF bursts share some common design considerations with RFID tags. Much like the tags, these sensors are often designed to be discrete and compact but require an in-built power supply to ensure consistent transmission. Therefore, these devices need a compact battery with a high energy density, high pulse power capabilities and long performance life – a balancing act that poses a challenge for many battery manufacturers.
It is for this reason that Ultralife Corporation developed its Thin Cell technology. Thin Cell batteries can be manufactured as thin as 0.7mm and as small as 20mm x 20mm, making them the ideal choice for products with a discrete profile. In addition to this, the cells have a high volumetric and gravimetric energy density that performs markedly better than the best lithium coin cells.
The Thin Cell’s typical energy density is around 500Wh/l and 400Wh/Kg, compared to 300Wh/l and 260Wh/kg in lithium coin-cell counterparts. For Design Engineers, this means a product that can be made lightweight and compact without sacrificing performance.
However, what makes designing RF-enabled devices more challenging than some others is not the need to effectively pack high energy into small packages but to ensure the device will be able to transmit the data when required, and that the power required to do so is available.
Pulsed Power in IoT
The wireless spectrum is full of different standards, protocols, and requirements that help to connect the world of IoT. There are a number of different technologies such as Wi-Fi, ZigBee, Bluetooth, BLE and others to meet this connection requirement.
Typically, we are seeing increased demand for long distance and low power wireless communication between IoT nodes. In order to transmit long distances, no matter what protocol or waveform you are using, you will need power to do so. In the past, when an IoT device needed power, it was limited by the low discharge current ratings of coin cells. The Ultralife Thin Cell is designed to provide up to 10x the discharge current from the same capacity cell, in a thinner, lighter form factor.
Take, for example, the ubiquitous CR2025 cell. This is a very common coin cell used in many designs from Vehicle Key FOBs to garage door openers. Although this cell will provide 170mAh of capacity, it is limited to only 6mA of discharge current before the voltage drops below acceptable levels. The Ultralife Thin Cell CP124920 is rated for 165mAh and will discharge up to 30mA or higher under pulse loads, such as when transmitting on a wireless protocol.
This higher power discharge capability is due to a much lower internal resistance of the cell, which is particularly useful in cold applications where batteries don’t perform as well. Furthermore, the lower internal resistance also allows higher pulse currents to be emitted from the battery without the risk of browning out the system.
A lot has changed in the past 50 years and the technological landscape is unrecognisable from the first networked computer. With an ever-growing number of organisations and individuals connecting systems into IoT networks, proper consideration of power is essential.
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