Infrared is a part of the electromagnetic spectrum, located between the longer wavelength visible light and the shorter wavelength microwave. The wavelength range of infrared radiation (IR) is between 760 nm and 1 mm, which cannot be seen by the human eye, but its heat can be detected. The infrared band is divided into multiple parts, including the near-infrared (NIR) range from 760 nm to 1400 nm (Figure 1).
Electromagnetic spectrum image, highlighting the infrared region
Figure 1: Highlight the electromagnetic spectrum in the infrared region. The wavelength of near-infrared spectroscopy is between 760 nm and 1400 nm, suitable for various applications. (Image source: Broadcom)
How NIR applications work
NIR is particularly useful because it facilitates wireless communication. In most applications, non-contact detection using NIR involves pairing an IR transmitter with a receiver.
For example, the TV remote control uses NIR radiation technology. When the button on the remote control is pressed, the internal circuit will convert the button action into binary code and forward it to the IR transmitter. Then, the transmitter emits encoded information in the form of NIR light pulses. On the other end, paired sensors on the television receive pulses and convert them back into binary code to execute specific commands.
The usage of transmitter and receiver combinations varies in various applications. Similar to a remote control, the receiver decodes the signal emitted by the transmitter. In other cases, a trigger is triggered when radiation is obstructed. This interrupt based mode can be used to detect people or objects.
To avoid external signal interference, the receiver is designed to only detect specific wavelengths, which requires the light emitted by the transmitter to have a matching precise wavelength and sufficient intensity. For example, Broadcom's HSM8-C120 IR ChipLED emitter (Figure 2) is an IR LED that can be used for various applications including consumer electronics, smart meters, and more.
Broadcom's HSM8-C120 ChipLED IR LED emitter
Figure 2: Broadcom's HSM8-C120 ChipLED IR LED emitter has a peak wavelength of 850 nm and is compact in size, making it ideal for high-density PCB circuits. (Image source: DigiKey)
HSM8-C120 is a side emitting surface mount IR ChipLED with a compact package size of only 1.6 mm x 0.93 mm, suitable for various applications with limited space.
The peak wavelength of this LED is 850 nm, with a viewing angle of 150 °, compatible with industry standard automatic surface mount machines and infrared reflow soldering.
Application of NIR LED
Photoelectric smoke detector - IR LED uses the basic principle of object intrusion to detect smoke, integrating the emitter and photoelectric detector in the same detector. Under normal working conditions, LEDs emit infrared radiation, causing the detector to generate current. However, the presence of smoke disrupts the infrared emission path and causes scattering. Therefore, the net current recorded by the photodetector will decrease and trigger an alarm. IR LED can penetrate smoke and detect smaller and denser particles, making it particularly suitable for this application.
Photoelectric smoke detectors are not the only type of detector in this category, other detectors such as those that measure air ionization levels. However, these are all well-known detectors that can produce false positives (false positives). The problem caused by cooking smoke is particularly serious, so smoke alarms in residential buildings must pass the "hamburger test", which means that cooking smoke will not trigger the alarm. IR LED is not affected by kitchen smoke particles, so the false alarm rate is relatively low. IR LED can also be integrated with other systems such as heat, gas, and airflow detectors to obtain more real-time information about hazardous situations.
Household appliances - In addition to being used for remote control, infrared sensors in washing machines can also detect water level, while robot cleaners use infrared sensors to avoid obstacles on the mapping path. There are also similar sensors in microwave ovens that can detect whether the door is open and issue corresponding alarms. Automatic faucets, soap dispensers, and dryers can all use IR LED obstacle and close range detection functions.
Safety Light Curtain - When using large or hazardous industrial equipment in production workshops, warehouses, construction sites, or other industrial environments, the safety of workers is always a top priority. Physical barriers are bulky and require a lot of effort to set up, while IR LEDs are lighter and more portable than physical barriers, making them an effective alternative. IR LEDs can also be set in different shapes and sizes to cover different areas as needed.