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Difference between Ultrasonic and Millimeter Wave Radar Blind Spot Monitoring Systems

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Reduced risk from objects in the blind spot is just one aspect of making turning safer for drivers. It is also critical to provide drivers with the information they require. As a result, in order to act quickly in an urgent situation, some warning strategies keep striving to provide drivers with specific data.

Ultrasonic and Radar Blind Spot Monitoring Systems

Blind spots are areas in the vehicle’s surroundings that are not captured by rear-view mirrors. Plus, no perfect mirror or driver seat position would eliminate this blind spot. What is the most effective solution? An automatic warning sensor to alert the driver about a nearby vehicle. It has become a key necessity to improve safety. These sensors operate in such a way that they cover all spots on the road with no limits.

The ability to detect vehicles reliably greatly benefits site safety and traffic control. Choosing the right technology for your vehicle detection application can be difficult. Therefore, consider a few factors, such as task, target size, sensing range, and sensor mounting. Plus, whether the application is primarily indoor or outdoor.

Moreover, there are various technologies introduced for this purpose. Nowadays, two types of sensors are common; Radar and ultrasonic sensors. So, what’s the difference between ultrasonic and Millimeter Wave radar blind spot monitoring systems? Which one is better? We have discussed all that in the article. So, keep reading to know it all!

Sensors In Blind Spot Monitoring Systems

Blind spot monitor systems detect vehicles in blindspot areas by using radar or ultrasonic sensors. These sensors are located inside the left and right sides of the rear bumpers. The cameras are placed in the side-view mirror housings. The difference between ultrasonic and microwave radar blind spot monitoring systems includes that radar is useful in tunnels. However, the other sensors typically go into standby mode in such cases.

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Radar Sensors

Radar sensors have a variety of applications. It facilitates us in weather forecasting, traffic control, and onboard automobiles. It also has functions such as collision warning and brake assistance. Other functions as driver assistance systems evolve toward active safety systems.

Radar sensor units are linked via cable to an in-cab display, which alerts the driver to approaching hazards via audible tones and a series of LEDs. It can be seamlessly integrated with existing reverse alarms, so the alarm only sounds when a hazard or person is detected.


  • Low energy consumption
  • Low impact design
  • Scalable and cost-effective sensor
  • Fast, resilient, and dependable chirp-sequence modulation for object recognition
  • New generation 4D imaging radar sensor for improved comfort, safety, and automated driving

What Exactly Are Radar Sensors?

Radar sensors are devices that convert microwave echo signals to electrical signals. They detect motion using wireless sensing technology by knowing the object’s position and shape. Radar sensors, unlike other sensors, are not affected by light or darkness. They can detect obstructions such as glass and “see” through walls.

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There are multiple types of radar sensors with different applications. Here are some of the most famous ones:

Millimeter Wave Radar

The millimeter wave radar sensor has an operating frequency of 30 to 300GHz. It means that the emitted electromagnetic wave is on a millimeter scale. Millimeter waves have the characteristics of both infrared and microwave due to their long wavelength. The wave is not affected by the outside, allowing it to adapt to various climate environments. Its measurement methods divide millimeter wave radar into two modes.

Frequency continuous modulated wave and pulsed doppler are the most commonly used technique. It is widely used in industrial and automotive applications. However, pulsed Doppler is common in military applications.

Pulse Mode

The pulse method involves using a pulse signal. This signal changes the frequency of the voltage-controlled oscillator in the radar transmitter. After that, it isolates the reflected wave from the transmitted signal in the receiver. Its structure is more complicated than other radar systems. Plus, it is expensive.

Frequency Modulation (FM) Continuous Wave Mode

FM continuous wave mode ranging is the commonly used method. The distance between two objects is determined by the frequency difference between the received and transmitted signals. The transmitted and received signals are combined to produce an intermediate frequency signal. A Fourier transform of this intermediate frequency signal (yields accurate distance information).

Doppler Radar

Doppler radar is in such a system, which is easily integrated into today’s vehicles. So, they bounce radio waves off surfaces such as buildings and parked cars. The radar signal strikes the surface at an angle, causing its reflection to bounce back. The signal continues to hit objects hidden around the corner. Some of the radar signals reflect back to detectors mounted on the car.

Front Radar Sensors

This sensor enables fast, precise, and resilient object detection and tracking. Due to the following features, it is well suited to complex traffic scenarios.

  • Detection range
  • Wide field of view
  • Excellent angle variation
  • New chirp-sequence modulation feature

Despite the small distance between them, the sensor detects a motorcycle rider overtaking a truck. These sensors reliably identify both objects. When the vehicle approaches a tunnel, the radar can see a motorcycle rider in front. It is due to its horizontal separability, which allows it to detect the space between the motorcycle and the tunnel ceiling. These properties enable direct height measurement, better traffic classification, and potential lane obstacles like tires or pallets.

How Do Radar Sensors Work?

When radio waves hit a surface, they reflect. The waves can readily transmit through the atmosphere. Radar is so frequently employed in a variety of object detecting applications. In cars, millimeter wave radar is typically utilized for blind spot monitoring. Radar-based systems use radio waves to find objects within their operational range and alert the driver. The following components make up a basic radar-based system.

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A radar system, in its most basic form, has the following sub-systems:


A waveform generator generates signals powered by amplifiers.


As the name implies, they aided in the transmission of radar signals.


A device that converts transmitter energy into signals in space.


A device used to detect and capture signals.

Range of radar sensors

Automotive radar is generally categorized as follows:

  • Short range radar – 0.5 to 20 meters
  • Medium range radar – 1 to 60 meters
  • long-range radar- 10 to 250 meters

Cost Of Automotive Radars?

In large quantities, conventional automotive radars cost $50-100 per unit, but there is a demand for a $10-30 radar. Future imaging radars are more expensive, with prices ranging from $150 in mass production for a single unit to $1000 for a 360-degree set.

Advantages Of Radar-Based System

  • Long-range radar systems can see up to 250 meters away.
  • Radio waves make it easier to identify an object in the blind spot accurately.
  • It is capable of distinguishing between stationary and moving objects

Why Is FMCW In The Lead For Modulation Techniques For Automotive Radar Applications?

Modulation techniques are crucial in radar technology. They have a shorter measurement time and a lower peak-to-average power ratio than pulse radars. Individual target range and velocity information must be measured simultaneously. Also, they update quickly in automotive safety applications.

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77GHz Automotive Radar Systems

Radar technology allows us to determine three significant parameters easily. It includes range, relative velocity, and arrival direction.

Velocity and range

A higher bandwidth of 4 GHz is extremely advantageous. It improves range resolution and velocity resolution. For that reason, it allows us to distinguish closely spaced objects, which is very useful in applications such as automated parking.

Another reason why 77 GHz is advantageous is that it reduces the size and form factor of the device—so making it very desirable to automotive companies. Plus, it allows them to mount these sensors under challenging positions.

Difference Between Ultrasonic And millimeter wave Radar Blind Spot Monitoring Systems

Radar Sensors

Radar sensors work with electromagnetic waves. Ultrasonic radars, on the other hand, use sound waves to perform their functions. It is the primary distinction between ultrasonic and Millimeter Wave radar sensors. One of the major differences between ultrasonic and radar blind spot monitoring systems is that radar sensors can detect motion and velocity more precisely.

The ultrasonic sensors’ waves bounce off objects and travel at a known speed. Radar waves, unlike ultrasonic waves, react differently to materials as they reflect back on the surface. A radar sensor can compute an object’s speed and direction by detecting its Doppler effect or change in wave frequency.

Another difference between ultrasonic and Millimeter Wave radar blind spot monitoring systems is that insulators do not impact radar-based devices. The system is not affected by the reflective object’s surface.

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Ultrasonic Sensors

An ultrasonic sensor is a non-contact measurement device that uses ultrasonic waves to measure the distance between two objects. This sensor has a transmitter that sends out ultrasonic waves. When waves strike an object, some of their energy reflects back to the sensor’s receiver as an echo signal.

It is a vehicle assistance device that assists drivers in safely changing lanes while driving. They have high-speed frequency sensors for the vehicle’s left and right rear and right and left side buzzer warning indicators. These warning indicators illuminate to alert you to the presence of an object. It includes blind spot detection as well as reversing assistance. Ultrasonic sensors probe the vehicle’s side/rear for moving objects in the detection zone’s blind spot.

The system consists of a control box, two ultrasonic sensors, and two blind region monitors. In addition, a buzzer and a wire harness that connects the ultrasonic waves and computer.

Ultrasonic Sensor’s Physics

Ultrasonic sensors emit short ultrasonic impulses that are reflected by obstacles. After that, the echo signals are received and processed. The ultrasonic transducer is housed within the plastic case of an ultrasonic sensor. It is made of an aluminum pot with a diaphragm that contains a piezoceramic element.

The ECU sends a digital to transmit a signal to the sensor. It causes the aluminum diaphragm to oscillate with square waves for 300 seconds at a resonant frequency of 48 kHz. It results in the emission of ultrasonic pulses. After about 900 seconds of relaxation, the diaphragm receives the reflected sound from an obstacle and vibrates. The piezoceramic element outputs these vibrations as an analog signal.

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Ultrasonic Ranging

Ultrasonic sensors emit waves with a frequency higher than the audible wave range of human ears through the transmitter. After reflection, the receiver gets the waves. The distance between the car and the object identifies by knowing the time difference between receiving and sending. The most commonly used frequencies are 40kHz, 48kHz, and 58kHz. In general, a higher frequency leads to higher accuracy of the sensor. The sensor features small diffraction and good directivity. It allows the ultrasonic sensor to propagate the signals through rays. It is common in low-speed driving scenarios such as automatic parking systems and reversing radars.

Ultrasonic Sensors On A Car

Two to four ultrasonic sensors mounted on the rear bumper detect an obstacle up to 2 to 2.5m away in the case of the rear sonar. The driver is aware of the distance in real-time by varying buzzer sounds.

Ultrasonic Characteristics

The ultrasonic sensor is available in three mechanically compatible sensor variants:

  1. Detection range: max. 2.5 m, min. 15 cm; object presence 6 cm
  2. Detection range: max. 4.5 m, min. 15 cm; object presence 6 cm
  3. Detection range: max. 5.5 m, min. 15 cm; object presence 3 cm

Use Of Ultrasonic Sensors In Cars

There are three main uses of ultrasonic sensors in cars. Parking apps use aggregate data from linked vehicles, and ultrasonic data is a crucial part of that data. Connected vehicles’ ultrasonic sensors can detect available parking spaces nearby. Millions of vehicles are combined with this parking data to produce a complete and exact picture of parking availability.

Ultrasonic sensors are one of the many sensors used by autonomous vehicle (AV) technology. The vehicle’s internal ultrasonic sensors can detect external conditions. This huge data is necessary for the technology that underpins autonomous vehicles to function. AV algorithms use ultrasonic sensor data from millions of linked automobiles.

By enabling vehicles to detect and broadcast road hazard warnings, technology takes advantage of ultrasonic sensor data. When sight is poor, ultrasonic sensors can tell whether a car is too close to another vehicle or a pedestrian.

Several Drawbacks Of Ultrasonic Sensor

  • The detection range of ultrasonic sensors is insufficient for use in moving vehicles.
  • The accuracy of ultrasonic sensors varies significantly with operating temperature.
  • It isn’t easy to read reflections from curved and smooth surfaces
  • Rain and other harsh weather conditions, such as snow, have an impact on the accuracy
  • The field of view of ultrasonic sensors is quite good, but the detection rate of objects present in those regions is low
  • It isn’t easy to detect diverse entities such as living things and street signs

Which Sensor Is More Sensitive To Atmospheric Interference?

Radar-based systems continue to operate normally regardless of environmental factors. These factors include temperature, humidity, rain, snow, etc. Radar is a weather-proof solution. Nearby working conditions do not affect radar-based systems. One of the primary benefits of radar is that it can operate in various lighting conditions, whether at night or during the day.

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The target material’s dielectric constant is an important consideration for radar sensors. It tends to pass right through materials with low dielectric constants because they do not reflect electromagnetic waves.


Electronic devices are capable of performing a variety of nonstop tasks in place of humans. One common reason an electronic device is preferable to a human being is that it can work faster and more reliably because it does not lose focus.

The same goes for a monitoring system. It is a device used to perform continuous measurements. With the help of sensors, this type of electronic device can measure physical information about an object.

The waves emitted by the radar sensor, like those from ultrasonic sensors, bounce off of objects and travel at a known speed (much faster than ultrasonic waves).

Radar is not only less expensive than other technologies, but it also has a broader range of applications. It is a tried-and-true technology thanks to advancements in customized software algorithms. It is quickly becoming one of the most attractive alternatives for car manufacturers.

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