Intelligent passive sensors have brought new choices for ubiquitous sensing, which can monitor pressure, temperature, humidity, or distance, eliminating the issues of volume, power consumption, and cost that traditional smart sensors consider. Device designers can now extend intelligent systems and the Internet of Things to previously inaccessible areas and applications without being limited by size or price.

The increasing reliance on * technology and the Internet of Things (IoT) has driven the demand for sensors that can be easily deployed from small to large quantities, and provide low scalability and maintenance free solutions.

The advancement of technology has made it possible to interconnect many different types of devices. The interconnection that began with smartphones has evolved into the networking of thermostats, home appliances, vehicles, and other devices known as the Internet of Things (IoT). The Internet of Things consists of many devices that transmit data back and forth through various interfaces, with wireless cloud interfaces being a common interface. As the number of interconnected devices continues to grow, the demand for more data also increases.

There are many sources of data generation, and electronic sensors are typically used to collect data from interconnected devices. A sensor is a device that converts physical or environmental characteristics such as temperature and humidity into electrical signals.

The demand for data has driven the growth of different types of sensor markets, such as temperature, humidity, pressure, and distance sensors that provide the necessary data for system operation. Due to the power of the Internet of Things to process data from different channels, electronic sensors will become more popular. According to Markets and Markets research, the sensor market is expected to exceed $38 billion by 2022. The demand for obtaining more sensor data from more locations will drive the development of new types of sensors that are smaller in size, lower in power consumption and cost, and easy to deploy in large quantities and confined spaces.

Electronic sensor structure

Traditional electronic sensors, regardless of their design, contain the same functional modules. The core module of a sensor is the actual sensing element. The sensing element is a part of the sensor that responds to the sensor environment and converts environmental conditions into electrical parameters. In addition to sensing components, sensors also require a power supply for the electronic components and data processing and interconnection circuits inside the sensor. Most electronic sensors include sensing elements, power modules, and data processing modules located at each sensing node. The cost of expanding to multiple sensing nodes has become a barrier for some applications as more sensing data is needed. The physical size of the components required for sensor power and communication modules limits the selection of small-sized sensors, while battery powered sensors involve maintenance and environmental issues, which also limits the deployment of sensors in certain applications. The cost and size of traditional electronic sensors limit the expansion of sensor networks or the deployment of multi-sensor systems or disposable sensors for intelligent sensing, hindering the further development of the Internet of Things.

So an alternative method is needed, ideally without relying on bulky and expensive batteries, microcontrollers (MCUs), and related circuits. Many connected sensors are mostly in standby or sleep mode to extend battery life, and only require power and intelligence during the exchange of small data packets with the host system when awakened. If sensors can be temporarily powered by external sources and most data processing is done externally, it can achieve cost-effective expansion of sensor networks and make innovations such as multi sensor or disposable sensors economically feasible.

There is a technology that can provide a solution: wireless passive sensors can already be loaded from memory, queried or rewritten through wireless readers, and activated by energy in the RF field transmitted by the reader. The traditional RFID communication standard has been validated as stable and reliable, providing a powerful platform for developing new intelligent passive sensors that separate sensing functions from the power and control circuits required by traditional electronic sensors.

Intelligent passive sensors can unleash the potential of RFID technology and standards to support convenient and energy-efficient wireless data exchange. Figure 1 shows the key functional components of an intelligent passive sensor, including an antenna, stimulus detector, and sensor block control IC. The passive sensor tag function is achieved by integrating a printed antenna and stimulus detection circuit, as well as an RF IC.

Intelligent passive sensors communicate using the industry standard UHF Gen 2 protocol and can be read by a suitable RFID reader. Some fixed or handheld commercial readers have passed label and functional verification. Anson Semiconductor's intelligent passive sensor ecosystem provides a battery powered portable reader with built-in antenna, graphical user interface, and IoT connectivity, which can serve as a hub for collecting sensor tag data.

When the reader starts communication, the self regulating sensor IC detects humidity or pressure by measuring impedance changes in the stimulation circuit, and sends these data, as well as digital temperature data from the on-chip temperature sensor, to the reader. Sensors monitor several parameters, including detected distance, received signal strength (RSSI) of motion or presence, as well as temperature and humidity. Each sensor also has a programmable EPC code as an identification identifier for *. The RFID front-end automatically compensates for environmental changes to sense humidity, pressure, and other parameters.

Figure 1: The intelligent passive sensor combines RFID technology with a passive, MCU free sensing block.

Typical Applications

Low cost or disposable passive sensors can benefit a large number of important applications. For example, by monitoring the temperature at multiple locations inside the server rack of a data center or at the connection of high-power circuit breakers in industrial power switches, the trend of temperature changes can be monitored, and abnormal temperature increases can be quickly detected for preventive maintenance or corrective measures. Intelligent passive sensors are directly connected to components such as metal casings, device packaging, or heat sinks, and can respond to periodic queries from readers within the RF range of all sensors.

The monitoring strategy shown in Figure 2 is based on intelligent passive sensors and RFID readers/transceivers connected to the cloud, which can provide a more real-time and cost-effective method of protecting devices than other methods such as manual temperature measurement or thermal imaging.

Figure 2: Multiple intelligent passive sensors can monitor the temperature of several locations with high cost-effectiveness.

Passive intelligent sensor tags are also suitable for digital agriculture applications, such as detecting livestock diseases or verifying livestock ovulation cycles in livestock monitoring applications. Farmers also use RFID tags for animal identification and tracking, and the industry standard for injectable tags has been established. By increasing investment in equipment or systems, intelligent passive sensors can help further improve animal health and increase livestock production.

Similarly, the use of intelligent passive sensors for humidity or pressure detection has been applied in medical, industrial testing, as well as automotive comfort and safety. In the medical field, humidity sensors can be inconspicuously attached to hospital bed sheets to detect patient occupancy rates and bed capacity, while non-invasive temperature sensors can be connected to the patient's skin and wirelessly monitored using nearby readers.

More applications include water leakage testing in the automotive industry: a set of intelligent passive sensors is quickly and accurately installed in the car before the water leakage test begins, eliminating the need for manual detection and simplifying data collection and analysis.

In addition, humidity and pressure sensing for detecting the status of car seat belts, as well as additional distance sensing, can achieve more intelligent car occupancy detection than traditional seat wire or airbag systems. Intelligent passive sensors can distinguish between the human body and objects placed on the seat, and can easily extend sensing to rear passenger seats and movable seats with minimal additional cost.

From home automation and connected cars to industrial control, quality inspection, agriculture, healthcare, construction, supply chain management, and many other applications, intelligent passive sensor tags can also perform many other leak detection, occupancy sensing, and temperature or humidity level monitoring.

summary

Intelligent passive sensors have brought new choices for ubiquitous sensing, which can monitor pressure, temperature, humidity, or distance, eliminating the issues of volume, power consumption, and cost that traditional smart sensors consider. Device designers can now extend intelligent systems and the Internet of Things to previously inaccessible areas and applications without being limited by size or price.