Difference between Ultrasonic and Infrared (IR) Sensors

Ultrasonic and infrared (IR) sensors are widely used in object detection, distance measurement and automation systems. Ultrasonic sensors operate by emitting sound waves beyond human hearing range, while infrared sensors use infrared light to detect objects or measure heat. Understanding difference between these two sensor types is crucial for choosing the right one based on range, environmental conditions and application requirements.

Both technologies utilize frequencies within the electromagnetic (EM) spectrum for various applications. Ultrasonic frequencies reside above 20 KHz, while infrared frequencies range from 430 THz down to 300 GHz.

Figure 1 and 2 illustrate the ultrasonic and infrared frequency ranges within the electromagnetic spectrum.

Ultrasonic Sensors

Figure-1 : Ultrasonic sensor

• As mentioned, ultrasonic frequencies fall above 20KHz in the EM spectrum. A device using these frequencies is known as an ultrasonic sensor.
• Ultrasonic sensors are used in various applications, including distance measurement, automatic car parking systems, humanoid robots, sonography (medical imaging), and ultrasonic flaw detectors.
• An ultrasonic sensor has two main parts: a transmitter and a receiver. The transmitter converts electrical energy into sound waves, typically at 40 kHz, and emits them into the air. The receiver then detects the echo of the reflected sound waves from an object and converts it back into electrical energy. Based on this, calculations are performed according to the sensor’s specific application.

Infrared (IR) Sensors

Figure-2 : Infrared sensor

• Infrared frequencies range from 430 THz to 300 GHz in the EM spectrum, with wavelengths from 700 nm to 1 mm. A device using these frequencies is known as an infrared sensor.
• Like ultrasonic sensors, infrared sensors also have a transmitter and a receiver. When voltage is applied to the IR LED of the transmitter, it generates infrared waves.
• The infrared transmitter emits these waves over a short distance. The receiver detects any reflected infrared waves and generates a corresponding voltage. If there is no object nearby, there won’t be any reflected waves, and the receiver won’t output any voltage.
• If an object is present, the receiver detects the reflected wave and produces a voltage accordingly. Comparators or microcontrollers then process these voltage levels for further analysis. This is how infrared sensors work.

Ultrasonic vs Infrared Sensors

The following table highlights difference between ultrasonic and IR sensor devices. For comparison, the SHARP GP2Y0A21YKOF is used as an example of an infrared sensor, and the Multicomp HC SR-04 as an ultrasonic sensor.

Table 2 below provides a generic comparison between ultrasonic and infrared sensors.

Conclusion : Ultrasonic sensors excel in measuring distances and detecting objects regardless of color or transparency, while infrared sensors are better suited for detecting heat and close range motion in controlled environments. Selecting between them depends on specific application needs such as range, accuracy, ambient conditions and target characteristics.