The screen sensors

Types of Screen Sensors

The screen sensors are critical components that make displays responsive to touch gestures. Various types of screen sensors are available, and they work on different principles to detect and locate a touch. They include:

• Capacitive sensors: A capacitive sensor is the most common in screens. It works by measuring changes in the capacitance, which is the ability to store electrostatic energy. In other words, it detects the electric field disturbance caused by a conductive object. These sensors have a high resolution and can register multi-touch. They are thin, durable, and widely used in smartphones, tablets, and laptops.
• Optical sensors: Optical sensors detect touches using infrared light beams. They work by measuring the disruption of light when a finger or stylus touches the screen. These sensors can register touches on large screens. However, their performance may be affected by environmental factors such as dust or reflections. They are used in outdoor kiosks and large touchscreen displays.
• Surface acoustic wave sensors (SaW): An surface acoustic wave sensor relies on the propagation of acoustic waves on the surface of the touchscreen glass. When a finger or stylus touches the screen, the waves are distorted. The distortion is detected and used to locate the touch. SAW sensors are highly sensitive and have good optical clarity. They are mostly found in industrial and medical applications.
• Infrared sensors: An infrared sensor uses invisible IR light beams. When a finger or object touches the screen, it interrupts the infrared light. The interruption is detected and used to locate the touch. Infrared sensors are highly sensitive and work well with gloved hands or styluses. They are ideal for applications such as ATM machines.
• Resistive sensors: A resistive sensor is made of two flexible, transparent layers. Each layer has a conductive material, and the layers are aligned together with a small gap. When pressure is applied on the screen, the two layers touch, and the change in resistance is measured. Resistive sensors can be used in almost every application and work with any object, including a mechanical pencil, gloved hand, or finger. However, they do not have the same optical clarity as the others.

Functions & Features of the Screen Sensors

Functions

The main functions of the screen sensors are to detect touch and convert it into corresponding electrical signals. Then, these signals are sent to the controller to determine the user's intention for operation. The actual working principle may differ according to the type of sensor.

Features

Different types of screen sensors come with different features inspired by improving usability, performance, and efficiency, among others. This table summarizes some of the screen sensor types, their features, and functions.

• Capacitive Sensors

  They use a sensor's capacitance change produced by the human body's electric charge. These sensors feature high durability due to their ability to withstand rigorous use and excellent multitasking capabilities that enable them to function in wet and dry conditions. Capacitive sensors function by measuring the change in capacitance caused by a human charge-battery change due to a battery dielectric.) They are sensitive, reliable, and ideal for touchscreens. Their features include:

  • Advanced sensitivity
  • User-friendly
  • Works with stylus or gloved hands
  • Requires less maintenance
  • Detects speed and position
  • Small and compact
  • Exhibits quick response time

• Photoelectric Sensors

  They use a light beam to detect touch or movement. When the beam is interrupted, the sensor detects the change. Features include long detection ranges, high-speed response, and resistance to harsh environments. They also provide:

  • Accurate Positioning
  • Versatile Applications
  • Quick Response Time
  • Consistency and Reliability
  • Robustness
  • Improved Safety
  • Multipoint Detection
  • Programmable Sensors

• Inductive Sensors

  They detect changes in inductance caused by an approaching metal target. Their principal features include:

  • Presence and position detection for metal objects
  • Proximity and limit switching
  • Automation, robotics, and machinery applications
  • Exhibiting fast response and high sensitivity
  • Having non-contact operation and low wear
  • Being able to operate in harsh environments

• Ultrasonic Sensors

  They work by emitting ultrasonic waves and analyzing reflected waves. Key features include:

  • Detecting distance, speed, and level of objects
  • Multipoint and simultaneous detection
  • Non-contact sensing
  • Operating in difficult conditions
  • Having long range and high resolution
  • Being highly sensitive to small changes
  • Fully programmable

Applications of screen sensors

Screen sensors have a diverse range of applications across multiple industries:

• Consumer electronics: Screen sensors play a vital role in consumer electronic devices like smartphones, tablets, and laptops, where they maximize user interface/UX.
• Automobiles: Modern cars use screen sensors in infotainment systems, touch-sensitive controls on the steering wheel, and even in seat sensors that detect the presence of the driver or passengers.
• Industrial machinery: Screen sensors in industrial machines enable operators to control functions by touching the machine's screen. This can enhance productivity and efficiency.
• Healthcare devices: Healthcare wearables using screen sensors can monitor heart rate, blood oxygen levels, and other vital signs. Medical equipment like thermometers with touch screens can provide accurate body temperature readings. Screen sensors are essential for good performance in healthcare devices.
• Gaming peripherals: The sensors in gaming controllers, handheld consoles, and virtual reality headsets offer immersive gaming experiences. This is made possible by responsive touch and gesture controls.
• Retail and kiosks: Store kiosks and self-service machines use screen sensors, allowing customers to place orders or obtain information. They are highly responsive, improving the efficiency of service delivery in the retail industry.
• Education: Interactive whiteboards, tablets, and laptops in the classrooms use screen sensors to create engaging learning experiences. They respond well to inputs, making it easy for educators to deliver lessons using digital content.
• Aerospace and defense: Aircraft with touch-enabled displays for navigation and mission-critical information rely on screen sensors for accurate control in challenging environments. They are also used in defense applications like handheld military tablets, where ruggedized touch screens are needed for field operations.

How to choose the screen sensors

When choosing screen sensors for capacitive touch displays, some factors must be considered to ensure the sensor's performance, reliability, and compatibility. Here are some important factors to remember when selecting the right sensor for target applications.

• Sensor type: The first step is to decide between a projected capacitive sensor and a surface capacitive sensor. Projected capacitive sensors are more sensitive and precise, making them popular for portable devices, tablets, and smartphones. Surface capacitive sensors are more commonly used on products like kiosks, ATMs, and industrial machines.
• Environmental conditions: One should consider the environmental conditions where the device will be used. If the device is likely to face moisture, dirt, dust, or other environmental factors, they should use a sensor with good resistance to these conditions. Some sensors are better suited for environmental resistance than others.
• Screen size and shape: Capacitive touch screen sensors come in various shapes and sizes, so they should select a sensor that matches the product's screen size and shape. Ensure the sensor can cover the entire screen area and fit the curvature or design features of the device's exterior.
• Transparency and visibility: Check the sensor's transparency and optical performance to ensure it does not significantly affect the display's brightness, color accuracy, and visibility. The transmittance level of the sensor should be high enough for the display to be seen clearly.
• Tracking and multitouch performance: One should evaluate the sensor's ability to accurately detect and track single-touch and multi-touch gestures. Assess its performance in terms of gesture recognition, touch tracking, and palm rejection capabilities.
• Connector configuration: Consider the sensor's connector configuration and make sure it is compatible with the device's PCB layout and assembly process. Choose a sensor whose connector type and position match the connections on the device without requiring major changes to the design.
• Certification compliance: Identify any relevant certifications and standards required for the device, such as IP ratings, EMC/EMI compliance, rohs, and toxic substances control. Choose a sensor that meets these certifications and ensures its compliance during testing and certification processes.
• Cost-effectiveness and supplier: Finally, examine the sensor's cost-effectiveness and the supplier's ability to provide long-term support. Consider the long-term availability of the sensor, its pricing, and the supplier's reputation, reliability, and willingness to support the design and production. Choosing a sensor that balances cost, performance, and supplier support is crucial for successful product development.

Q&A

Q: Capacitive sensors needs a finger to work?

A: Not really. Some other objects like a stylus or even a gloved hand can work, but only certain types of gloves allow it. If the glove has a really thin layer of material, then the sensor will still work. It is important to know that not all gloves are made the same, so some won't let the capacitive sensors work at all.

Q: Can screen sensors in a phone be replaced?

A: Only to a certain extent. When we talk about screen sensors, we refer to the sensors integrated into the display. If a phone's display is damaged and needs replacement, the sensors will also be replaced since they're usually built into the screen. However, if the sensors refer to external screen sensors, like those on a standalone touch screen or tablet, those can be replaced.

Q: Do screen sensors make the device easier to use?

A: Yes it does. Screen sensors make things like opening apps, playing games, and taking pictures a lot easier. Devices with good sensors respond quickly to touch, so everything feels more fun and moves better. This helps out both regular users and people using screens for work because things become simpler and more efficient.

Q: Do screen sensors put more strain on the battery?

A: No, not really. The sensors are made to work with the touch of a finger chosen, so they don't use up extra battery. The efficiency of the sensors actually helps save battery life by making screens respond quickly. If a screen responds fast to touches and swipes, it means the processor doesn't have to work as hard. This lowers power use and helps a device's battery last longer.

Q: How does the weather affect screen sensors?

A: Extreme weather conditions may affect the performance of some screen sensors. For instance, very high or very low temperatures might sometimes cause screens to act up or not work as well, but many sensors are made to work okay in a wide range of temperatures. Very high humidity or rain won't usually be a problem for most sensors, but extremely dry conditions could cause static electricity that affects touchscreens. It's best to keep devices with touch sensors from extreme weather or very dry environments to be safe.