How Ultrasonic Wind Sensors Work:
Time of Flight (ToF) vs Acoustic Resonance
(Acu-Res®)

August 1, 2025

What is an Ultrasonic Wind Sensor?


Ultrasonic wind sensors, also known as ultrasonic anemometers, measure wind speed and direction without moving parts. They are widely recognised for their fast response times and high-precision measurements in varying weather conditions. However, not all ultrasonic wind sensors operate using the same technology. Two primary technologies are used: Time of Flight (ToF) and Acoustic Resonance (Acu-Res®).

FT Acu-Res Wind Sensors
ToF vs FT Acu-Res

How Ultrasonic Wind Sensors Measure Wind

1. Time of Flight (TOF) Technology Explained

In Time of Flight ultrasonic wind sensors, an ultrasonic signal is transmitted between two or more transducers. The sensor measures the time it takes for the signal to travel from one transducer to the other. Any wind flow that interferes with the signal will alter this travel time, providing accurate data on wind speed and direction. TOF sensors typically require a larger distance between transducers to ensure precise readings, and are susceptible to variations in air pressure, temperature and humidity - properties which affect the speed of sound in air.

 

2. Acoustic Resonance (Acu-Res®) Measurement Method

Acoustic Resonance ultrasonic wind sensors work by generating ultrasonic standing or resonant waves within a small resonant cavity. The sensor detects changes in the phase of the signal, which correspond to wind disturbances. This method is independent of the varying properties of the air and allows for a compact sensor, enabling high accuracy in urban installations, smart cities, industrial applications and compact weather stations.

Key Design Considerations for Ultrasonic Wind Sensors

When selecting an ultrasonic wind sensor, it's important to consider several factors beyond measurement principles, especially for applications in marine, industrial, or extreme environmental settings.

Material Selection: Ultrasonic wind sensors are manufactured using materials ranging from corrosion-resistant stainless steel to UV-stabilised plastics. For harsh environments like coastal areas or offshore platforms, selecting sensors made from marine-grade metals ensure durability against saltwater and humidity.

Weight and Mounting: The choice of material and measurement method influences the sensor's weight. Lightweight models are ideal for portable weather stations, UAVs, and buoys, whereas more robust models are suited for permanent outdoor installations.

Sealing and Ingress Protection (IP Ratings): Quality sealing mechanisms, such as O-rings and precision gaskets, protect internal components from moisture, dust, and salt ingress. Look for sensors with IP66 or IP67 ratings for reliable performance in outdoor, maritime, or industrial environments.

Temperature Resistance: Ensure the sensor operates within the expected temperature ranges of your location. Many ultrasonic sensors are designed to handle extreme cold or heat, but it's vital to verify the manufacturer's specifications, especially for desert climates, polar regions, or tropical zones.

Vibration, Shock, and EMI Resistance: In dynamic applications such as mounting on boats, drones, offshore platforms or mobile infrastructure, vibration and shock resistance become mission-critical for accurate wind measurement. Acoustic Resonance (Acu-Res®) ultrasonic wind sensors are specifically engineered to endure continuous mechanical vibrations, resist electromagnetic interference (EMI), and absorb shocks without degradation in data precision.

Environmental Protection Features: Some advanced ultrasonic wind sensors come equipped with self-cleaning systems or hydrophobic coatings to prevent dirt, ice, or water buildup on the sensor surface, ensuring long-term measurement reliability in challenging conditions.

 

Feature Time of Flight (ToF) Acoustic Resonance (Acu-Res®)
Measurement Method Pulse transit time Phase shift in standing waves
Signal Strength Moderate Very high (self-amplifying)
Sensitivity to Contamination High Low
Acoustic Path Exposed (100mm+) Protected (10mm)
Ice Resistance Large surface area = hard to heat Up to 3X heating effectiveness
Environmental Robustness Moderate Very high
Size/Form Factor Medium-large (up to 2kg) Compact and rugged (<500g)
Calibration Stability Regular re-calibration Long-term stability
Typical Use Cases Static, general meteorology Dynamic, critical control systems
Power Consumption Moderate (high for heating) Low (energy-efficient heating)

 

Why Acu-Res® Outperforms

While both Time of Flight (TOF) and Acoustic Resonance ultrasonic wind sensors have their place in wind measurement, Acoustic Resonance technology offers distinct advantages for applications where compact design, precision, and resilience in harsh environments are critical. The ability to achieve high accuracy with a smaller sensor footprint, combined with no moving parts and enhanced durability, makes Acu-Res® an ideal choice.

FAQs About Ultrasonic Wind Sensors

Q1: What is the difference between Time of Flight and Acoustic Resonance in wind sensors?

Time of Flight measures how long ultrasonic signals take to travel between transducers. Wind affects this travel time, allowing the sensor to calculate wind speed and direction. In contrast, Acoustic Resonance sensors detect phase shifts in ultrasonic waves within a resonant cavity. This method enables a more compact design with high accuracy, especially in turbulent or confined spaces like urban installations.

Q2: Which ultrasonic wind sensor is best for harsh environments?

Acoustic Resonance (Acu-Res®) ultrasonic wind sensors are ideal for harsh environments such as marine, offshore platforms, industrial sites, drones, and urban smart cities. They offer superior resistance to vibration, shocks, electromagnetic interference (EMI) and environmental factors like dust, salt, and ice, ensuring reliable performance over time.

Q3: Why are ultrasonic wind sensors more reliable than mechanical anemometers?

Ultrasonic wind sensors are more reliable than mechanical anemometers because they have no moving parts that can wear out or jam. This results in lower maintenance, longer operational life, and consistent accuracy even in extreme weather conditions such as heavy rain, storms, and temperature fluctuations.

Acu-Res® Technology

FT Technologies' Acu-Res® gives a signal to noise ratio more than 40dB stronger than other ultrasonic technologies. This wind measurement method is unique to FT Technologies, making the sensors more robust and reliable compared to alternatives on the market. Watch the video to take a closer look at how it works.

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