A major challenge of cold chain monitoring is to find a traceability solution that can be used throughout the whole supply chain. A practicable approach is wireless sensors that detect temperature in containers, trucks and refrigerated shelves. But this leaves the question of how to power and network the large number of individual wireless sensors needed to communicate with long-range wireless networks such as GSM or IP. A complex cabling would raise the costs into infinity. The effort needed to change batteries of thousands of sensors would be disproportional to the benefit of tracking. Besides this, batteries are a weak point and can become the Achilles’ heel of the system’s reliability causing down times. But down times are out of the question in the supply chain.

Sensors powered by surrounding environment
Energy-harvesting wireless technology can overcome these challenges, connecting a large number of battery-less and maintenance-free sensors into existing IP, Wi-Fi or mobile networks that process data for uninterrupted monitoring.

The energy-harvesting principle – gaining energy from the surrounding environment – allows wireless modules to work without batteries and cables. There are a variety of sources: an electro-dynamic energy converter uses mechanical motion; a miniaturized solar module generates energy from indoor light. Combining a thermoelectric converter with a DC/DC converter taps temperature differences as an energy source. These small amounts of harvested energy are sufficient to transmit a wireless signal and enable operation of numerous maintenance-free sensor and actuator units.

Energy-saving radio protocol
For optimal RF effectiveness, the modules’ radio protocol uses the 902 MHz frequency band in the U.S., which has an ideal penetration of walls. RF reliability is assured because wireless signals are just 0.7 milliseconds in duration and are transmitted multiple times for redundancy. The range of energy-harvesting wireless sensors is about 900 feet in an open field and up to 90 feet inside buildings.

The 902 MHz modules allow for integration into very small product enclosures. Interference from co-located devices, such as Wi-Fi, is eliminated, ensuring high system reliability. These contribute to enable an effective, robust wireless platform. Each module comes with a unique 32-bit identification number to exclude any possibility of overlap with other wireless sensors. The battery-less wireless devices can be integrated with other communication protocols such as Ethernet/IP, Wi-Fi or GSM via gateway controllers incorporating the energy harvesting wireless standard into a supply chain monitoring system.

Data detection from everywhere
The energy-harvesting wireless technology is particularly suited for small devices, such as sensors that detect data from many different points and make them available to an intelligent controller. The sensors are powered by temperature differences between the environment and the cooling system which delivers an impressive amount of energy: just the cooling of a drop of water by 1 degree Celsius releases energy for about 20,000 energy-harvesting wireless telegrams. The danger of a system failure caused by dying batteries is eliminated, providing higher system reliability.

In a cold chain monitoring system, temperature data from self-powered sensors placed within food containers, trucks or refrigerated shelves, for instance, can be used to alert when temperatures approach thresholds and investigation or maintenance of the cooler is required. The information is sent to a central controller or even as a push notification to the smartphone of the person in charge. This enables the user to react in time before the cold chain was interrupted. In addition, this data, collected at thousands of containers, can be consolidated to find potential gaps in the temperature-controlled supply chain for an optimized logistic process.

Processing in the cloud
Connecting the self-powered sensor system to IP provides ways to reach out and control temperature from virtually anywhere on the globe. It allows centralized, or even outsourced computing resources (cloud-based computing), thus driving down infrastructure cost. Cloud-based computing resources enable the integration of external information; for example, a local weather yielding an optimized cooling environment. This information is provided to the remote controller, enabling precise control. The same system that monitors temperature can also be used to ensure that only the actual needed amount of energy is provided, driving down energy waste and costs. Furthermore, the battery-less and wireless operation also allows legacy systems to be retrofitted with sensor intelligence.

Continuously collected data in the supply chain could improve food quality and significantly reduce the loss at an estimated rate of something between 25 and 50 percent. The use of energy-harvesting wireless sensors allows a dynamic creation of control networks, which can dynamically and flexibly provide data from distributed points in the supply chain for a gapless traceability. That way, battery-less data monitoring could prevent tens of thousands tons of food from going to waste.

Source: EnOcean