# What is a Force Sensor : Working Principle and Application

There are many laws of physics that are based on the concept of Force. Force, when applied on an object of mass m, changes the object’s velocity. There are many concepts related to force such as thrust, drag, and Torque. When applied on an object, thrust increases the velocity of the object, whereas Drag decreases the velocity and Torque generates changes in the rotational speed of the object. When there is a balanced distribution of forces in the object, no acceleration can be seen. With the advance in technology, a sensor that can help to monitor force is introduced, known as Force Sensor.

## What is a Force Sensor?

Sir Franklin Eventoff, in the 1970s, found some materials, when subjected to force, can change their resistance values. These materials were known as Force-Sensing Resistors. These materials are used to produce a sensor that can measure the Force. A Force Sensor is a sensor that helps in measuring the amount of force applied to an object. By observing the amount of change in the resistance values of force-sensing resistors, the applied force can be calculated.

### Working Principle

The general working principle of Force Sensors is that they respond to the applied force and convert the value into a measurable quantity. There are various types of Force Sensors available in the market based on various sensing elements. Most of the Force Sensors are designed using Force-Sensing Resistors. These sensors consist of a sensing film and electrodes.

The working principle of a Force-sensing resistor is based on the property of ‘Contact Resistance’. Force-sensing resistors contain a conductive polymer film that changes its resistance in a predictable manner when force is applied on its surface. This film consists of, sub-micrometres sized, electrically conducting and non-conducting particles arranged in a matrix. When force is applied to the surface of this film, the microsized particle touches the sensor electrodes, changing the resistance of the film. The amount of change caused to the resistance values gives the measure of the amount of force applied.

To improve the performance of the Force-Sensing resistors various efforts are being made with multiple different approaches such as, to minimize the drift of polymer various electrode configurations are being tested, testing with sensor by replacing the polymer with new materials such as carbon nanotubes, etc….

### Applications of Force Sensor

The main usage of the Force sensor is to measure the amount of force applied. There are various types and sizes of force sensors available for different types of applications. Some of the applications of Force sensor that uses force-sensing resistors includes pressure-sensing buttons, in musical instruments, as car-occupancy sensors, in artificial limbs, in foot-pronation systems, augmented reality,etc….

### Examples of Force Sensors

There are many types of force sensors available for different types of applications. Some of the examples of force sensors are Load cells, pneumatic load cells, Capacitive Load cells, Strain gauge load cells, hydraulic load cells, etc…

Besides force sensors, there is also a category of Force transducers. The main difference between a force sensor and force transducer is that the transducer converts the amount of force measured or applied into a measurable small electrical voltage output signal. Whereas the output of a Force sensor is not an electrical voltage.

### Advantages of FSR

Strain gauge load cell is a force sensor as well as a force transducer. When compared to all other force sensors, the force sensors with force-sensing resistors provides various advantages such as small size, low cost, and good shock resistance. Due to their small size, they are used in portable electronics and enhanced mobile interaction. The main disadvantage of these sensors is their low precision as their measurements differ by 10%.

Force-sensing resistors based Force sensors are also known as FSR. FSR sensors are used in transportation systems for measuring the amount of stress applied to the goods while transporting them one place to another. The functioning of the FSR can be changed by changing the properties of the Force-sensing resistors.

Force -sensing resistors requires a small interface and can work in moderately hostile environments. Here the small conducting and non-conducting particles are formulated to reduce the temperature dependence of the sensor, increase the sensor surface durability and improve its mechanical properties.

With the advance in technology, today sensors are playing a crucial role in measuring various physical phenomenons. Their small size, high durability helps us to use them in portable electronics. Today, sensors are available for measuring stress, pressure, temperature, color, etc…The force-sensing resistors were patented in 1977. What is the unit of Force in SI?