Editorial Feature

The Sensors Used in an iPhone®

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Image Credit: Viktoriia Kotliarchuk/Shutterstock.com

The iPhone® is part of a line of smartphones by Apple®. Since its release in 2007, this phone has evolved to become one of the most influential devices in popular demand amongst a range of target markets. This smartphone technology is capable of intuitive applications due to the range of sensors integrated into this device.

With the most common models of the iPhone® including the iPod® and iPod Touch®, the user can benefit from some of the most innovative interface techniques possible within the iPhone®.  

The iPhone® technology dates back to 2004 during which the multi-touch screen technology patent was filed. The material composition of the original iPhone® was aluminum, with the iPhone 3G® and iPhone 3GS® manufactured to have a full plastic back for added strength. The iPhone 4® model has been designed to have an aluminosilicate glass front and back cover.

The capacitive touchscreen of the iPhone® makes the touch and gesture features of this phone an exciting user-friendly option and it is the nature of these sensor-controlled features that is the scope of this article.

The main sensors that help inject intuitive and impressive interface technology in the iPhone® include:

Proximity Sensor

The main purpose of a proximity sensor is to measure how close the sensor device is to a particular target. In relation to the iPhone®, this proximity sensor helps the iPhone® device screen switch off as soon as the user moves the device closer to the ear. This sensor-driven control prevents the accidental activation of a touch button whilst the user talks on the phone and saves power.

There are two types of proximity sensors in use: capacitive and inductive sensors. Most modern-day phones are designed with an integrated capacitive proximity sensor. The following video is a great introduction to capacitive touch sensing.

This sensor produces a varying capacitance that interacts with the oscillator circuit. In the event of a change in capacitance as a result of being touched by a finger (external source), the oscillator frequency also changes. This change in capacitance is measured via a frequency measurement component. The basic functional principle is based on a number of variables that change the capacitance. Distance and area are the most important parameters that impact the change in capacitance – the greater the area, the greater the capacitance. A larger distance between the sensor device and the target results in a fall in capacitance.

Motion Sensor/Accelerometer

Motion sensors allow the iPhone® device to switch from a landscape to a portrait display as a result of the user manipulating the direction of the device. A basic functional principle to a motion sensor involves the transformation of the detection of motion into an electrical current. Detection of motion is achieved by measuring the optical change in the target field of view.

The majority of motion detectors are engineered to accurately access data on optical change up to 15–25 meters in length. There are four main types of motion sensors in the iPhone®: passive infrared sensors, ultrasonic, microwave, and tomographic detectors.

Ambient Light Sensor

A typical ambient light sensor detects the intensity of light surrounding the iPhone® and processes this information to help adapt the phone light accordingly. Adjustment to the brightness of the iPhone® screen is a conventional method to help conserve as much battery life as possible. Ambient light sensors work by blocking or filtering the infrared and ultraviolet wavelengths.

Phone devices that are engineered with an ambient light sensor will have these sensors embedded underneath the protective layer of the cover glass. Using photodiodes (light sensors typically used in mobile phones), these sensors detect ambient light intensity and respond to this sensory input by generating a proportional output voltage.

This output voltage travels to the LED driver mode and thus manipulates the LED output current and light intensity to the phone. The following video animates how the LED system works.

The LED structure is silicon-based and has a negative and positive element, which when bridged together create a positive-negative junction and this junction generates energy in the form of light.

Moisture Sensor

The design and engineering process for the iPhone® range is continuously changing to help create the most intuitive device possible for its user. Moisture sensors have also become an important sensor component for this range of cell phones. This type of sensor works by alerting the user when the phone has contact with water.

Moisture sensors are commonly used to take soil moisture measurements. One method to help prevent a malfunction with the iPhone® following its immersion into the water may be to envelop the moisture sensor in a conductive glue to behave as an insulating layer. The idea here is for the device to detect the speed at which the conductive glue is eroded by water molecules.

Recent developments

With the development of newer generations of the iPhone®, a host of other sensors have been introduced.

Gyroscope

A three-axis gyroscope was introduced starting with the iPhone® 4 models. Along with the accelerometer, this gives the phone a six-axis operation, making it more responsive for applications that require the phone to detect how it is held and moved. The gyroscope in the iPhone® is a tiny microelectromechanical (MEMS) device that captures orientation with great accuracy.

Location Sensor/GPS

A GPS system inside the phone determines the location of the phone using satellites. It connects to different satellites, and the satellite data can also be combined with other phone data, such as signal strength, to provide the location with much greater accuracy. 

Barometer

A barometer senses air pressure and may be used for weather sensing or to determine altitude. 

Compass

iPhone® models now come with a built-in compass that can help show in which direction one is going. Although it does not work in a standalone mode, it works in tandem with location sensors, GPS, and other apps, to help determine the phone’s location.

Fingerprint Sensor

iPhone® models starting with the iPhone 5s have a fingerprint sensor that can be used to unlock the phone and apps. It is embedded in the Home button and allows one to use a fingerprint to unlock the device rather than or in addition to using a passcode. 

Face ID 

Some latest models of the iPhone® come with a facial recognition sensor, replacing the fingerprint sensor or the passcode for unlocking the phone. The sensor works by projecting more than 30 000 dots on a face, which helps build a 3D map of the face. An infrared camera converts these dots into an image, which is compared to the data stored on the phone to unlock the device.

Sources and Further Reading

This article was updated on 14th February, 2020.

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