Industry Article

Designing for the IoT: Microcontroller-Free Smart-Passive-Sensors​ ​(SPS)​

December 05, 2017 by onsemi

Designing for the IoT comes with a unique set of challenges that require unique hardware solutions to overcome. Learn how smart passive sensors (SPSs)—sensors that function without a battery and without a microcontroller—are an example of IoT-specific design.

Designing for the IoT comes with a unique set of challenges that require unique hardware solutions to overcome. Learn how smart passive sensors (SPSs)—sensors that function without a battery and without a microcontroller—are an example of IoT-specific design.

To learn more about IoT-specific design challenges and solutions, check out the accompanying on-demand webinar: Sensors, Power, and the Internet of Things: How Big Data is Influencing How We Design

Sensors and sensor networks are an integral part of the IoT ecosystem. Many markets are already using, or will soon be using IoT devices. You can currently find IoT-connected devices and systems in many industries:

  • Automotive
  • Transportation and marine
  • Home automation and security
  • Logistics
  • Inventory and supply chain
  • Agricultural and livestock
  • Industrial, construction, and power
  • Medical and personal healthcare



In each industry, the needs are different, but the benefits are similar. Among the benefits of utilizing IoT-connectivity are cost savings, process optimization, yield enhancement, analytics, and data storage.

But designing for the IoT can be a challenge because devices need to have reliable connectivity, low-power requirements, and often a small form factor. 

Smart ​Passive ​Sensors ​(SPS)

ON Semiconductor has introduced the world’s first wireless sensor—using standard protocol—that is battery-free and microcontroller-free. Let's take a look at how smart passive sensors are designed to fulfill the needs of IoT design. 


Features ​and ​Capabilities ​of ​Smart ​Passive Sensors

Due to their unique inherent features (e.g., battery-free, wireless, ultra-thin, and low cost to scale) these sensors allow for new sensing capabilities. One of the most important of these capabilities is dynamically sensing data in challenging applications.

For example, an SPS would be suitable for:

  • Hard-to-access applications: SPSs require less maintenance and can be placed in areas such as underground, inside walls, or areas that are toxic or pose health dangers and/or hazards.
  • Space-constrained applications: Smaller-sized sensors are crucial to fit in tighter spaces, such as within doorways, in RFID tags, and in wearables (e.g., bandages)
  • Using multiple sensors for cost-effectiveness: Cost-effective sensors allow for more data-gathering, multiple data points, and scalability.

Practical ​Applications

High-Power ​Switchgear ​Equipment

To prevent catastrophic failures inside high-power switchgear boxes, it’s essential to identify high - resistance points inside the equipment. And because such points can be found through temperature monitoring, the traditional method is to manually monitor these high-resistance points during scheduled maintenance intervals. This manual process involves extensive use of labor and yields limited data points—perhaps only one data point every year. SPSs can wirelessly, and continuously, monitor and analyze temperatures on busbars, circuit breaker contacts, and cable connections.

Smart ​Healthcare

Nurses are experiencing an increase in workload. This, in turn, makes it more challenging for them to effectively monitor each patient's status. SPS devices allow nurses to monitor the status of their patients by sending alerts for:

  • Patient is out of bed
  • Temperature change
  • IV bag is empty
  • Catheter bag is full
  • Bed liner needs changing


An SPS that is continuously monitoring can provide early detection with faster resolution—and, because they are wireless, the sensors will not impede patient comfort.

Server ​Racks

As data centers become larger and larger, the difficulty and cost of monitoring their equipment increases, as well. Some of the major maintenance issues associated with server racks are energy usage and temperature.

A full turnkey solution includes a network of SPSs, as well as reader hardware and software. SPS temperature sensors can monitor—completely wirelessly—the air inlet temperatures inside server racks, helping to optimize cooling efforts. This saves energy and reduces costs. Additionally, these wireless sensors can provide a means for early detection of equipment failure and can also help track assets, thereby lowering labor costs.

Digital ​Farming

Sensors are used in animal husbandry for identifying specific livestock and for monitoring temperatures. Animal identification can be used to regulate feeding schedules and for tracking various factors such as milk production indicators. An animal’s temperature can be used for early detection of illness or for detecting ovulation.

SPS wireless, battery-free, and maintenance-free sensors offer improved accuracy, combine animal identification and temperature sensing into one device, and can be placed either on an animal’s skin or injected beneath it.

Cold ​Chain/Logistics

SPS sensors can be used to monitor the temperatures of food and/or pharmaceuticals during shipment. The continuous temperature monitoring of these goods allows for immediate detection of failures, thus allowing shipments to be rejected before being unloaded—long before any defects can affect customers.


The IoT enables professionals across many industries to get more information extremely quickly. Despite that the applications an IoT device might be used in can be vastly different, the actual device requirements are often similar:

  • Reliable connectivity for continuous monitoring
  • Low maintenance
  • Small size
  • Low power needs

ON Semiconductor’s Smart Passive Sensors (SPS) are the world’s first battery-free and microcontroller-free wireless sensors. Their unique features make them ideal for applications including hard-to-access and space-constrained areas. Full turnkey development solutions are available which include the SPS devices, reader hardware, and software.

Learn more about devices designed for the IoT in ON Semiconductor's free webcast, now available on-demand: Sensors, Power, and the Internet of Things: How Big Data is Influencing How We Design

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