🌐Internet of Things (IoT) Systems Unit 10 – Energy & Power Management in IoT Systems

Key Concepts

• Energy efficiency crucial for IoT devices due to limited power resources and long-term operation requirements
• Power management techniques optimize energy consumption, prolong battery life, and ensure reliable operation
• Energy harvesting harnesses energy from the environment (solar, thermal, kinetic) to supplement or replace batteries
• Low-power communication protocols (Bluetooth Low Energy, Zigbee) reduce energy consumption during data transmission
• Duty cycling alternates between active and sleep modes to conserve energy during idle periods
• Dynamic voltage and frequency scaling (DVFS) adjusts processor performance based on workload to minimize energy consumption
• Battery technologies (lithium-ion, solid-state) provide high energy density and long lifetimes for IoT devices
• Energy-aware software design minimizes resource usage and optimizes algorithms for energy efficiency

Energy Challenges in IoT

• Limited battery capacity constrains the operational lifetime and functionality of IoT devices
• Replacing or recharging batteries in large-scale IoT deployments is impractical and costly
• Miniaturization of IoT devices reduces available space for batteries, limiting energy storage capacity
• Harsh environmental conditions (extreme temperatures, humidity) affect battery performance and lifespan
• Intermittent and unpredictable energy availability from energy harvesting sources requires robust power management
• Balancing energy consumption and performance to meet application requirements while conserving energy
• Ensuring reliable operation and data transmission in energy-constrained scenarios
• Addressing the environmental impact and disposal challenges of batteries in large-scale IoT deployments

Power Sources for IoT Devices

• Batteries most common power source for IoT devices, providing portability and independence from external power
  • Primary batteries (alkaline, lithium) non-rechargeable, suitable for low-power and disposable devices
  • Secondary batteries (lithium-ion, nickel-metal hydride) rechargeable, offer higher energy density and longer lifetimes
• Energy harvesting captures energy from the environment to power IoT devices or recharge batteries
  • Solar energy harvesting uses photovoltaic cells to convert sunlight into electrical energy
  • Thermoelectric energy harvesting generates electricity from temperature gradients using the Seebeck effect
  • Piezoelectric energy harvesting converts mechanical stress or strain into electrical energy
• Wireless power transfer enables charging or powering IoT devices without physical connections
  • Inductive coupling transfers power through electromagnetic induction between coils
  • Resonant coupling achieves longer-range power transfer using resonant circuits
• Supercapacitors store electrical energy in an electric field, providing high power density and fast charging/discharging
• Hybrid power systems combine multiple power sources (batteries, energy harvesting) for improved reliability and efficiency

Energy Harvesting Techniques

• Solar energy harvesting captures energy from sunlight using photovoltaic cells
  • Monocrystalline and polycrystalline silicon solar cells offer high efficiency but are more expensive
  • Thin-film solar cells (amorphous silicon, organic photovoltaics) are flexible and lower cost but have lower efficiency
• Thermoelectric energy harvesting utilizes the Seebeck effect to generate electricity from temperature gradients
  • Thermoelectric generators (TEGs) consist of p-type and n-type semiconductor materials connected in series
  • Suitable for IoT devices exposed to temperature differences (industrial equipment, wearables)
• Piezoelectric energy harvesting converts mechanical stress or strain into electrical energy
  • Piezoelectric materials (lead zirconate titanate, polyvinylidene fluoride) generate electric charge when deformed
  • Applicable to IoT devices subjected to vibrations, pressure, or motion (industrial machinery, infrastructure monitoring)
• Radio frequency (RF) energy harvesting captures electromagnetic energy from ambient RF sources (Wi-Fi, cellular networks)
  • Rectenna (rectifying antenna) converts RF signals into DC power
  • Suitable for low-power IoT devices in urban environments with abundant RF sources
• Hybrid energy harvesting combines multiple energy harvesting techniques to improve energy availability and reliability
  • Complementary energy sources (solar and thermoelectric) can provide continuous power under varying conditions

Power Management Strategies

• Duty cycling alternates between active and sleep modes to reduce energy consumption during idle periods
  • IoT devices enter low-power sleep modes when not performing tasks, conserving energy
  • Wake-up mechanisms (timers, interrupts) trigger the device to enter active mode when necessary
• Dynamic voltage and frequency scaling (DVFS) adjusts processor performance based on workload demands
  • Reduces voltage and frequency during low-workload periods to minimize energy consumption
  • Increases voltage and frequency for computationally intensive tasks to meet performance requirements
• Power gating selectively switches off unused components or subsystems to eliminate leakage power
  • Partitions the IoT device into power domains that can be independently controlled
  • Power management integrated circuits (PMICs) enable fine-grained control over power domains
• Energy-aware task scheduling optimizes the execution order and timing of tasks to minimize energy consumption
  • Prioritizes energy-efficient tasks and schedules them during periods of high energy availability
  • Defers or offloads computationally intensive tasks to more powerful devices or cloud services
• Adaptive sensing adjusts the sampling rate or resolution of sensors based on the application requirements and energy constraints
  • Reduces the amount of data collected and transmitted, saving energy in processing and communication
  • Employs event-driven or context-aware sensing to capture relevant data only when necessary

Energy-Efficient Protocols

• Bluetooth Low Energy (BLE) designed for low-power wireless communication in IoT devices
  • Operates in sleep mode by default and wakes up periodically for short data transmissions
  • Supports multiple power modes (advertising, scanning, initiating) to adapt to different use cases
• Zigbee low-power, short-range wireless protocol for IoT networks
  • Uses a mesh network topology to extend the communication range and improve reliability
  • Supports power-saving features (sleep mode, low duty cycle) to minimize energy consumption
• LoRaWAN long-range, low-power wide-area network (LPWAN) protocol for IoT applications
  • Enables long-distance communication (up to several kilometers) with low energy consumption
  • Employs adaptive data rate (ADR) to optimize transmission power and data rate based on network conditions
• IEEE 802.15.4 standard for low-rate wireless personal area networks (LR-WPANs)
  • Defines the physical and media access control (MAC) layers for low-power, short-range communication
  • Forms the basis for other energy-efficient protocols (Zigbee, 6LoWPAN)
• Energy-efficient routing protocols minimize energy consumption in multi-hop IoT networks
  • Cluster-based routing (LEACH) organizes nodes into clusters and rotates cluster heads to balance energy consumption
  • Opportunistic routing exploits the broadcast nature of wireless communication to dynamically select the best forwarding node

Battery Technologies

• Lithium-ion batteries widely used in IoT devices due to high energy density and long cycle life
  • Cathode materials (lithium cobalt oxide, lithium iron phosphate) determine the battery's performance characteristics
  • Anode materials (graphite, silicon) affect the battery's capacity and charging speed
• Solid-state batteries use solid electrolytes instead of liquid or gel electrolytes, offering improved safety and energy density
  • Eliminate the risk of electrolyte leakage and enable thinner and more flexible battery designs
  • Enable higher operating temperatures and faster charging rates compared to conventional lithium-ion batteries
• Thin-film batteries fabricated using vacuum deposition techniques, resulting in ultra-thin and flexible form factors
  • Suitable for wearable devices, smart cards, and medical implants where size and flexibility are critical
  • Provide high energy density and long shelf life but have limited capacity compared to larger batteries
• Printed batteries manufactured using printing technologies (screen printing, inkjet printing) on various substrates
  • Enable customizable battery shapes and sizes to fit specific IoT device requirements
  • Offer low-cost and scalable production but currently have lower performance compared to conventional batteries
• Battery management systems (BMS) monitor and control the charging and discharging processes of batteries
  • Ensure safe and efficient operation by preventing overcharging, overdischarging, and thermal runaway
  • Provide state of charge (SoC) and state of health (SoH) estimation to optimize battery usage and predict remaining lifetime

Case Studies and Applications

• Smart agriculture IoT sensors and actuators optimize crop growth and resource utilization
  • Soil moisture sensors trigger irrigation systems to water crops only when necessary, conserving water and energy
  • Solar-powered IoT nodes enable autonomous operation in remote agricultural fields
• Industrial IoT predictive maintenance and energy management in manufacturing systems
  • Vibration and temperature sensors powered by thermoelectric generators monitor equipment health
  • Machine learning algorithms analyze sensor data to predict maintenance needs and optimize energy consumption
• Smart buildings IoT-enabled energy management systems reduce energy waste and improve occupant comfort
  • Occupancy sensors and smart thermostats adjust HVAC settings based on real-time building usage patterns
  • Piezoelectric energy harvesting from foot traffic powers low-power IoT devices in high-traffic areas
• Wearable healthcare devices monitor vital signs and track physical activity for personalized healthcare
  • Energy-efficient protocols (BLE) enable long battery life for continuous monitoring
  • Flexible and printable batteries conform to the shape of the human body for comfortable wear
• Environmental monitoring wireless sensor networks track environmental conditions and pollution levels
  • LoRaWAN enables long-range communication for sensors deployed in remote locations
  • Hybrid solar and RF energy harvesting provides sustainable power for sensor nodes in urban and rural environments