Wireless Sensors and Sensor Networks

An increasing number of sensors are connected in wireless sensor networks. The sensor units are often required to take up little space, have a low cost per unit and operate for a long time without an external power supply. Collected data from the sensors is often sent to a cloud platform that is accessible from a web interface.

LoRaWAN sensor network for measuring soil properties at a vineyard

At RISE, we have experience in designing and building wireless sensor systems based on the specific needs of the customer. We can help with the entire chain from idea to a pilot system through:

measurement method
choice of sensors
wireless communication
ultra-reliable low-latency data transmission, processing, and analysis
wireless propagation channel modeling
design of measurement electronics
transmission and collection of data
data storage
signal processing and analysis
presentation of results in a suitable user interface

Active Sensors

Active wireless sensors have internal batteries to supply energy sensors, readout electronics and radio unit. Active sensors can measure and transmit data continuously, but to save energy it is more common for the sensors to measure at a given time interval and to sleep between measurements. Measured data is sent to a recipient that saves data locally or sends data on via mobile networks/internet to a cloud database. Depending on the requirements of the application, the battery life of a wireless sensor unit can vary from days up to several years.

There are many standards for wireless sensor communication and the technology is rapidly evolving. Usually, small amounts of data need to be transferred after each measurement. Examples of standards for wireless sensor communication that RISE have experience working with are Bluetooth Low Energy (BLE), ANT Wireless, LoRaWAN and NB-IoT.

Passive Sensors

Passive sensors have no internal energy source to perform the measurements and data transmission. Passive sensors are usually simpler, cheaper and take up less space than active sensors. The passive sensor is supplied with energy from an external reader, which means that the sensors cannot log data and only measure while reading.

Below are a few examples of passive wireless sensors that RISE has experience working with:

Magnetoelastic resonance (MER) sensors
- MER sensors are made of a magnetostrictive material that changes its dimension when the sensor is exposed to a magnetic field. With an externally applied magnetic field, the sensor can be made to vibrate like a tuning fork. The vibrations give rise to a magnetic field that can be read at distances up to 30-40 cm. The vibration frequency and attenuation of the sensor gives information about the condition of the sensor and with different coatings the sensor can be made sensitive to, for example, temperature, relative humidity or viscosity.
RFID sensors
- RFID is traditionally used as an electronic label that provides a unique identity as well as information from a small internal memory. RFID sensors have an extended functionality in that they can harvest energy from the reader's field to supply a sensor connected to the RFID chip. An advantage of RFID sensors is that they can use conventional (low power) sensors to perform the measurement. An RFID tag can measure, for example, temperature, relative humidity, brightness, inclination or acceleration. The readout distance for a UHF RFID sensor tag is up to 5-10 meters.