How do Smoke Detectors work?
Hey Explorers, Happy Wednesday!
Let’s look at how Smoke Detectors in your home and office spaces work this week. I aim to write my newsletter issues in a way one can follow them while traveling on a bus, having a coffee, waiting for food, etc. Let's jump in!
How it works: 15-second answer
Ionization smoke detectors, suited for flaming fires, contain radioactive material Americium between two charged plates. This material emits alpha particles, creating a current by ionizing air. But smoke disrupts this, stopping the current and triggering the alarm.
Photoelectric smoke detectors, suited for early smoldering smoke, use a light beam and a light sensor (photodiode). In clear air, the light beam doesn't reach the sensor as they are not in line. Smoke scatters the light onto the sensor, generating current and activating the alarm.
Modern detectors often combine both technologies for enhanced safety.
Figure 1: Smoke detectors sound an alarm when it detects smoke or fire.
How do Smoke Detectors work?
There are two mechanisms used by smoke detectors. Let's explore them one by one.
Photoelectric Smoke Detector:
Setup:
Inside the smoke detector casing, we have an infrared LED beam striking the other end. A photodiode sensor is placed at an angle within the casing away from the light beam.
A photodiode is a sensor that generates current when light falls on it. The higher the intensity of light that falls on the sensor, the higher the current generated by the sensor.
Figure 2: Photodiode sensor generates current triggering the alarm when the presence of smoke particles deflects and scatters the light on the sensor.
How it works:
When there is no smoke, the light does not fall on the photodiode as it’s placed away. Hence, there is no current generated by the sensor.
In cases of smoke, they enter the smoke detector casing through the openings and refract (scatter) the light in different directions.
The light falls on the photodiode sensor, producing current. Once the circuit detects that the current is generated, the buzzer goes off and you have an alarm from the smoke detector.
This type of detection technology is typically suitable for situations where there is slow-burning smoke. What about the case of flaming fires?
Ionization Smoke Detector:
This mechanism of smoke detection is more exotic but not necessarily better than the previous one.
Setup:
Inside the plastic casing of a smoke detector, you can typically find a 9V battery that powers two plates, one with a positive charge and the other with a negative charge as shown in Figure 2. A tiny amount of radioactive material called Americium is placed near one of the plates. Americium constantly emits alpha particles due to its radioactivity.
The air in our environment (consisting of 78% Nitrogen and 21% Oxygen) reaches the space between the parallel plates by going through the openings of the smoke detector casing.
Figure 3: Americium emits alpha particles which produce current after chemically reacting with particles in the air. But smoke blocks alpha particles and current is not generated, thereby triggering the alarm.
How it works:
The alpha particles emitted from Americium kick off the electrons from the Nitrogen and Oxygen atoms and make them positively charged.
The electrons (negatively charged) drift to the positively charged plate due to attraction and the positively charged Nitrogen and Oxygen ions drift to the negatively charged plate.
Current is the flow of electrons. As electrons are flowing across the parallel plates here, we have a current.
But when there is a fire in the house, the carbon monoxide, carbon dioxide, and other particles absorb the alpha particles and block the flow of electrons or ions. Thus there are no charged particles created and there is no current.
The circuit detects that there is no current generated. The buzzer goes off and you have an alarm from the smoke detector.
This is how smoke detectors work!
Gadget of the week
Namocell Single Cell Sorter: A California-based biotech company working on a device that can pick and sort individual cells from a mixture, like sorting different types of tiny beads. It uses special technology to see and identify cells based on their light signals. This machine helps scientists study single cells in detail, which is important for research in areas like genetics, cancer, and personalized medicine.
Thank you for reading!
Have an amazing rest of the week, and take care!
Until next to next Wednesday,
Chendur