Leading self-powered sensors and wearables for sustainable IoT

Discover the innovative world of energy harvesting for IoT sensors and wearables.

Autonomous image logger recorder based on scene activity detection. It is powered by a flexible and adhesive PV-cell.

This cutting-edge technology, including advancements in photovoltaics and wireless power transfer, represents a significant leap toward sustainability. Join us in enhancing efficiency, reducing environmental impact, and delving into the future of sustainable tech solutions.

The Internet of Things (IoT) is about to experience a major surge in active devices. Growing investments in the "Industry 4.0" scenario—which envisions billions of interconnected electronic devices—are driving this expansion even more. Such a massive deployment of wireless remote sensors can only be economically and ecologically limited if it relies on batteries.

Ambient energy harvesting

Comparison of energy density for the different energy sources in our surroundings. Source: CEA-LETI - Comparison of energy density for the different energy sources in our surroundings. (Boisseau Sébastien, et al., Boisseau (2012). Electrostatic Conversion for Vibration Energy Harvesting. Intech.)

Energy harvesting from the environment is already widely used to solve this problem and is particularly relevant for products that have a low energy consumption in the range 0.1–10 mW, as many energy harvesting technologies lie in the energy density of 100 µW/cm.

However, in many cases the harvested energy source isn’t dependable in all locations, which precludes a generalized use for critical/deterministic missions. CSEM's wireless power transfer (WPT) technology addresses this point by securing the critical level of energy for the sensors to function. 

Long-range wireless power transfer (WPT)

Long-range (multiple meters) wireless powering would bring:

  • Suppression of batteries or considerable reduction of battery size.
  • More reliable and deterministic operations when compared to pure power harvesting.
  • Ease of adoption of environmentally safe energy storage components.

We aim to rethink the complete wireless power transfer chain from transmitter to receiver in the 24GHz and 60GHz bands, providing freedom to innovate for both the constitutive elements of the chain and the overall system optimization.

Complete WPT process from a transmitter to a receiver

Complete WPT process from transmitter to receiver through various environments.

Microwave wireless power transmission 

Various devices and vehicles within the warehouse being powered by WTP tech.Wireless transfer of electrical energy: Various devices and vehicles within the warehouse are powered by this technology.

Microwave wireless power transmission is breaking the range limitations of common magnetic coupling (e.g. mobile phone charging devices); this comes at the cost of reduced power levels in order to comply with regulations. The extended range enables the remote powering of many devices, such as remote sensors, remote controls, or trackers within the range of the source. The considered devices are low-power, typically operating with 0.1 – 10mW of supplied power.

Target applications can be found in the markets of smart home, industrial IoT, building infrastructure, or warehouse logistics where such a WPT system would act like a WiFi system, with power transmitters replacing routers.

Overall power transmission scheme

Infographics showing beamforming Tx antennas play a crucial role in focusing the energy toward the devices.Wireless transfer of electrical energy: Beamforming Tx antennas play a crucial role in focusing the energy toward the devices.

A transmitter, typically positioned in the ceiling, sends a beam of electromagnetic waves toward the devices to be powered (receivers), which can be placed randomly within range. To keep emission levels within regulations, the system focuses the energy on a receiver and then aims successively at all receivers in the area. Receivers send information back to the transmitter about the received energy level and optimize the transmission in real time. As the range is limited to a few meters, multiple transmitters are used to cover larger areas.

Challenges of indoor microwave power transmission

Regulations severely constrain power emission levels. Furthermore, while the considered bands (24GHz and 60GHz) will allow further miniaturization of transmitter and receiver devices, losses in the transmission path are greater than in older solutions (UHF RFID sits below 1GHz).

Transmission of energy

  • The transmission of energy can and must be adapted to focus on receivers and operate in time windows to keep compliance. Steerable beam approaches are a tool of choice to solve the problem, but they come with increased complexity. New antenna shapes and configurations are under scrutiny, as well as the electronics driving behind them (phasing).

Reception of energy

  • The reception of energy must deal with very low signals. New architectures are being explored for a fully integrated (IC) energy harvesting unit, not only comprising the antenna front-end, rectifier, and maximum power point tracking (MPPT), but also the energy transformation and storage (PMU) necessary to feed the electronics. All these elements interact and must not be designed separately. The aim is also to avoid as many external components as possible; research is ongoing to achieve power management on-chip.

Optimization of power delivery

  • The overall chain optimization requires a protocol for wireless power delivery. Since the transmission becomes highly directional, the power must be applied sequentially to receivers (or groups of receivers, depending on the beam focus and the number of receivers). A communication channel back to the transmitter will be implemented to provide feedback about the receiver status and deal with power-time allocation and channel optimization. 

The potential of other thermal and radiant energy sources

Energy harvesting devices offer immense potential for self-powered sensors and wearables, particularly within the IoT context. This technology converts ambient energy—especially thermal and solar energy—into electric energy, powering sensors and ensuring long-term sustainable operations. This reduces the need for battery replacements or recharging, making these devices ideal for deployment in hard-to-reach places.

Thermal gradient harvesting

Sensor node with thermo-electrical energy scavengerAssembled wireless sensor node (unpackaged) for aircraft strain measurement

The combination of ultra-low-power wireless communications and energy harvesting enables the building of autonomous wireless sensor networks in extreme environments. For example, such a system can be usefully applied in commercial aircraft, where wireless sensing solutions contribute to weight reduction and increased ease of installation and maintenance.

Light harvesting

Perovskite-silicon tandem solar cellsPerovskite-on-silicon-tandem solar cells exhibit excellent performance both indoors and outdoors.

Power Management Units (PMUs) with light harvesting face several challenges that need to be addressed to optimize their performance and efficiency. From variable light conditions to low efficiency of the energy conversion and low-power operation of the PMU itself, the circuit design needs to be carefully thought through and customized according to the light harvester (silicon, organic, perovskite on silicon…). CSEM's know-how on both photovoltaic cells and PMU make us the ideal partner for achieving state-of-the-art performances. 

Looking for an efficient self-powered solution for your wearable device and sensor?

Pervasive sensing brings considerable advantages to optimize processes, leading to savings in resources and reductions in waste. However, large-scale IoT deployments are hampered by battery-related maintenance costs and environmental footprint. As a result, a highly efficient energy harvester combined with a hybrid approach such as wireless power transfer (WPT) is essential to every solution that cannot rely solely on ambient power harvesting.

To address further miniaturization and efficiency challenges of far-field wireless power transfer, CSEM is investigating the complete WPT chain in collaboration with ETHZ and EPFL to provide solutions for transmitters, receivers, and power transfer protocols.

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