What is the Internet of Things? A Power Perspective

The Internet of Things (IoT) can mean a lot of things. To some, it means Bluetooth^® low energy (BLE) compatible devices, enabling smartphones to communicate and even control any modern, electronic device in sight. To others, the IoT implies ubiquitous sensors deployed on everything from high-value assets for tracking to conditional monitoring on equipment for preventative maintenance (better known as the Industrial IoT or IIoT) to medical wearables/implantables, sending data to the cloud for massive processing and generation of data analytics.

The incredible amount of data analytics and the industries built around them are what is implied by the famous 2006 quote from British mathematician Clive Humby [1], who remarked, “Data is the new oil.” Perhaps, for many, the IoT means just adding "smart" moniker to everything, from toasters to window shades, even if it is not clear exactly what that means for the tech of today and tomorrow.

The IoT means many battery-based and low-power systems along with the aggregation of systems, especially in non-tethered applications such as remote monitoring, electric/autonomous vehicles (EV/AVs), aerospace/MIL applications, and other ground-based large transportation (i.e., railway). From a power point of view, it can mean ubiquitous deployments of wireless sensor networks (WSN) embedded in environments that are inaccessible and/or very costly and/or dangerous to access (i.e., deep oil wells, permanently embedded in structures, wind generator turbine blades).

It also means previously unattainable levels of telemetry, control, and preventative maintenance opportunities. As these varied lists of systems and applications imply, the IoT/IIoT can be integral both in low-power and high-power deployments even if the circuits themselves are relatively low power in nature.

Most of the “things” in the IoT are the low-power systems typically sourced with battery power. These are mostly sourced with primary or non-rechargeable batteries. Given that we are expected to have 100s of billions (if not > 1 T) end devices in the near future, battery power to support this growth means a global tragedy in terms of hazardous waste in landfills if we are throwing away more than 100 M batteries every day.

Aside from these serious environment or sustainability considerations, this is typically bad business in the purely economic sense because, even if all those small primary batteries are very cheap in high volumes, if they must ever be replaced, then the cost may end up being many times more than the entire system (e.g., operating and maintenance expenses can heavily dwarf capital expenses to dominate the total cost of ownership).

This environmental dilemma combined with the very low system power budgets of many of these devices raises the value proposition for the utilization of secondary or rechargeable batteries (or other energy storage devices, such as capacitors) along with scavenging ambient energy, also known as energy harvesting. This convergence of IoT/IIoT, energy harvesting, energy storage, and low-power communications encompasses the majority of what is known as the Power IoT ecosystem.

Maximizing battery life is critical in most IoT/IIoT applications, which ties into the relationship of available power (e.g., the energy source) to the system power budget (e.g., the loads). It seems that most engineering efforts and resources are poured into maximizing available power and pushing power converter efficiency, while much less focus is placed on reducing the system power budget.

This can be a little perplexing because there are more opportunities to minimize system load consumption with the use of intelligent power management (IPM) techniques than there are opportunities to implement a bigger battery or a more efficient power converter. In other words, Moore’s Law will drive the system power budget down much faster than the energy density of batteries increases. Generally, battery capacity only doubles roughly every decade, whereas things like integrated circuits (ICs) and even microelectromechanical systems (MEMS) sensors can halve power consumption nearly every other year, while still increasing functionality.

As shown in the figure below, think of your energy source as a denominator and your system power budget as the numerator. The viability of your system is the inflection point at which these two meet and one can decrease the numerator much faster than one can increase the denominator. In other words, when the ratio becomes <1.
It should also be noted that a lot of consideration and design should be invested in how to NOT power things. There is nothing greener or more efficient (in terms of dissipated power) than something off. So, the best path to optimizing the system power budget comes in figuring out how to keep things off or in the minimal power state to still accomplish the application.

Given radios are typically the biggest consumers in an IoT/IIoT device system power budget, finding the right ratio of transmission versus sleep time can have huge implications on battery life. Even if your temperature sensor is capable of sampling at 1kHz, do you need to know that info with that level of granularity? Even more important, is it necessary to process and transmit that amount of data?

The growing trend of integration of computing, sensors, radios, displays, motor control, energy storage, and power management is increasing typical size, weight, and power (a.k.a. SWaP factors) challenges. Traditionally disaggregated systems are combined in increasing complex integrated components such as System-on-Chip (SoC) or integrated motor drive system loads.

It may seem like the messaging here is a bit in conflict since there is mention of increasing SWaP factor challenges while mentioning the reduction of individual system components concurrently. In reality, this is not quite the paradox it may seem on the surface because the tendency of system designers/integrators is to always pack in as many loads/features as they can fit and afford.

For any power supply designer, it may feel like a cardinal sin to mitigate energy efficiency and the optimization of power commutation as a top priority, but there are applications wherein delivering power to the load at all costs is what matters at the end of the day. For example, in industrial automation, an unplanned power outage can have serious consequences. This point can also be particularly evident in applications requiring very little power in somewhat inaccessible and/or harsh environments. Some examples of this can be medical implantables/devices or WSNs embedded in large structures such as bridges or buildings.

Wireless power transfer (WPT) has been gaining a lot of notoriety in recent years, sometimes for consumer convenience, but sometimes to address the challenges of energy delivery. For one, it is important to distinguish many WPT applications are incorrectly classified as energy harvesting modalities. While this may be more of a semantical argument, WPT typically involves the commutation of power from a directed (typically off-line or wall source), where one of the “wires” just happens to be a wireless link. This is as opposed to true, ambient scavenging of far-field radio frequency (RF) energy.

For most of the consumer applications, WPT means a step backward in time in terms of energy efficiency because the inefficiency of the wireless transfer is equivalent to using a wired, ac-dc adaptor (a.k.a. the infamous wall wart) from 20+ years ago simply because one cannot make the tiny effort to plug in a wire. On the other hand, if one wants to capture/process/read data from an IoT node embedded in a solid piece of concrete or provide energy for an in-situ WSN embedded in living tissue, WPT can make a lot of sense irrespective of the inefficiency of the power commutation.

Even if the system or IoT device is very low power and runs on low voltages, it should not be assumed to be in a separated/safety extra-low voltage (SELV) environment. Particularly, in IIoT applications, the WSN or IoT node may be connected to a large piece of machinery or high-power system that runs off of and/or utilizes three-phase voltages, requiring low-wattage power supplies capable of running from high AC input voltages.

This means power solutions may need to support wide input voltage ranges, provide many kVs of isolation, and contain numerous protection features such as overvoltage protection (OVP), over-current protection (OCP), and over-temperature protection (OTP), among other protection modes. Again, all these design requirements may need to be intrinsic to the power solution even if it sources a relatively low amount of power in the 1s or low 10s of watts. This is also important in applications with direct human exposure such as medical devices and medical-imaging applications.

As alluded to earlier, the IoT/IIoT can provide unprecedented opportunities for minimizing carbon footprint as well as capital/operations expenditures (CAPEX/OPEX) with the use of massive data analytics, optimizing consumption, and preventative maintenance via conditional monitoring, etc. At the same time, the IoT/IIoT can also provide unprecedented waste in terms of hazardous materials like batteries and consume more precious metals, rare earth materials, and finite gases than are available on the planet.

The compatibility of IoT/IIoT technologies with energy harvesting is among the most exciting and promising symbiotic relationships in these markets because the ideal scenario is a sensor system that is perpetually self-powered from the ambient environment. Not only will this mitigate the critical path items for reliability (i.e., primary batteries, connectors, etc.), but also enable “forever” systems that operate in maintenance-free deployments.

Like most convoluted issues in life, a key take-away message is that there are no absolute, simple answers in terms of solutions or the associated business and pay-back calculations. One must consider many second-order factors if trying to maximize performance and sustainability concurrently.

In future publications, we will dig into the concept of “embodied energy” or “cradle-to-grave” lifecycle in which the true footprint of a product (typically measured in carbon emission and water consumption footprints) is assessed over a truly comprehensive lifecycle, which spans from raw material capture and manufacturing through product use life and post-production (i.e., recycling, hazardous material handling, etc.).

[1] Wikipedia contributors, "Clive Humby," Wikipedia, The Free Encyclopedia, https://en.wikipedia.org/w/index.php?title=Clive_Humby&oldid=1067348557 (accessed April 15, 2022).