The primary obstacle to mass-scale RTLS adoption is operational lifecycle cost. For deployments spanning thousands of assets across remote construction sites, vast logistics yards, or agricultural fields, the expense and logistical effort of battery replacement create a significant barrier.
In the article, we detail the engineering approach to building truly autonomous UWB tags by synergizing aggressive low-power design with ambient energy harvesting.
The Foundation: An Aggressive Power Budget
Energy harvesting is only viable if the device’s power consumption is minimized.
The entire design philosophy must shift from “how long will the battery last?” to “how little energy do we need to operate?”. The goal is to create a power deficit so small that ambient energy sources can regularly replenish it.
Establishing the Power Budget
The first step is defining the application’s required performance. What is the necessary update rate? Is sub-second latency required, or is a location ping every few minutes or hours sufficient?
For many remote assets, like shipping containers or large construction equipment, slower update rates are perfectly acceptable. An asset that pings its location once per hour consumes orders of magnitude less power than one pinging every second. This power budget dictates the entire design.
Strategic Power Optimization with Qorvo QM33/35 SoCs
To meet an ultra-low power budget, the choice of System-on-a-Chip (SoC) is fundamental.
The Qorvo QM33 and QM35 series are engineered specifically for these applications. Their power lies in their exceptionally low-power states.
The core strategy involves maximizing the time the SoC spends in its deepest sleep modes. By utilizing the QM33/35’s lowest power mode, which can have a current draw as low as ~100 nanoamperes (nA) with full RAM retention, the tag is effectively off for 99.9% of its life.
An integrated accelerometer can act as a trigger, waking the device only when motion is detected. This prevents unnecessary transmissions from stationary assets, dramatically reducing the average current consumption into the low microampere (μA) range—a key threshold for making energy harvesting practical.
Sourcing Power from the Environment
With a power budget minimized to tens of microwatts, sourcing this energy from the asset’s immediate environment becomes feasible. The choice of harvesting technology is entirely dependent on the asset’s operational context.
Solar: The Primary Choice for Outdoor Assets
For assets with regular access to light, photovoltaics offer the highest power density. The key is selecting the correct cell technology for the environment.
Comparison: Photovoltaic Cell Technologies
According to a report by MarketsandMarkets, the energy harvesting market is projected to reach USD 0.94 billion by 2030 from USD 0.61 billion in 2025, at a CAGR of 9.1% from 2025 to 2030 (source), driven largely by the need for autonomous sensors in IoT applications. Solar remains a primary driver of this growth due to its reliability and high power output.
Kinetic: Power from Motion and Vibration
For assets in constant motion or subject to mechanical vibration (e.g., industrial machinery, vehicles, shipping containers on trains), kinetic energy harvesting is a powerful alternative.
- Piezoelectric Harvesters: These generate a charge when subjected to mechanical stress or vibration. They are ideal for high-frequency vibrations found on industrial motors or engines. A well-tuned piezoelectric device can generate power in the range of 40-100 µW/cm³.
- Electromagnetic Harvesters: These use the relative motion between a magnet and a coil to induce a current. They are better suited for lower-frequency, higher-amplitude movements, like the swaying of a container or the motion of rolling stock.
Radio Frequency (RF): Harvesting from Radio Waves
In environments with a strong and consistent Radio Frequency (RF) presence, such as warehouses with high-power RFID readers or factories with dedicated power-transmitting infrastructure, RF energy can be captured.
While ambient Wi-Fi or cellular signals yield very low power densities (typically below 1 µW/cm²), a dedicated RF power source operating in the ISM bands (e.g., 915 MHz or 2.4 GHz) can provide a reliable stream of microwatts sufficient to trickle-charge a self-powered tag.
System Integration: The Brains Behind the Power
Harvesting raw energy is only half the battle. This sporadic, low-voltage power must be intelligently managed and stored to operate the UWB SoC reliably.
The Power Management integrated circuit (PMIC)
The Power Management integrated circuit (PMIC) is the unsung hero of any self-powered system.
Specialized ultra-low power PMICs perform several vital functions with minimal energy loss:
- Energy Extraction: They employ techniques like Maximum Power Point Tracking (MPPT) to extract the maximum possible power from the solar cell under varying light conditions.
- Voltage Boosting: They can take the very low voltage from the harvester (often <0.5V) and boost it to a stable voltage (e.g., 1.8V or 3.3V) required by the UWB SoC.
- Energy Storage Management: They manage the charging of the storage element, preventing over-charging and over-discharging. Critically, these PMICs must have an extremely low quiescent current (the power they consume just by being on), often in the sub-microampere range, to avoid consuming a significant portion of the harvested energy.
Energy Storage: Supercapacitors vs. Batteries
The choice of where to store the harvested energy has a massive impact on the tag’s lifespan and reliability.
For most UWB harvesting applications with sporadic energy input and a need for extreme longevity and temperature tolerance, supercapacitors are the superior choice. Their ability to endure hundreds of thousands of charge cycles without degradation is a perfect match for the inconsistent nature of ambient energy.
Deployment Blueprint: Tracking on a Large Construction Site
Let’s apply these principles to a real-world scenario: tracking high-value equipment (e.g., generators, concrete saws) on a multi-acre construction site.
The Problem
Assets are moved frequently, theft is a risk, and manual inventory is time-consuming. Battery replacement across hundreds of tools is not feasible.
The Self-Powered Solution
- Tag Hardware: A QM33-based tag is chosen for its low power consumption. It’s paired with a small (2-4 cm²) monocrystalline solar cell and a specialized PMIC. A supercapacitor is used for energy storage to handle the temperature swings of an outdoor site.
- Firmware Logic: An accelerometer serves as the primary wake-up trigger. If the asset is stationary, the tag remains in deep sleep. When motion is detected, it wakes up and pings its location. To conserve energy, the firmware implements an adaptive blink rate: one ping every 10 minutes when moving, and one ping every 12 hours when stationary.
Outcome
The result is a maintenance-free tag with an essentially indefinite lifespan. The daily energy harvested from sunlight, even on overcast days, exceeds the energy consumed by the infrequent pings. This provides reliable location data, improves asset utilization, and reduces theft, directly impacting the project’s bottom line without adding a future maintenance burden.
Self-powered UWB technology: From Technical Feasibility to Business Advantage (conclusion)
Self-powered UWB technology is no longer a theoretical concept. By pairing ultra-low-power System-on-a-Chip (SoC) like the Qorvo QM33/35 with the appropriate, context-aware energy harvesting and power management systems, it is now possible to build RTLS tags that outlast the assets they are designed to track.
This approach fundamentally changes the economic model of RTLS, eliminating the single largest component of its long-term operational cost.
However, designing these systems requires deep, integrated expertise in UWB protocols, low-power embedded firmware, and power electronics.
Partnering with a UWB RTLS expert like needCode is essential to navigating the complexities and successfully deploying a robust, truly autonomous asset tracking solution that delivers business value for years to come.
