Thin Film Force Sensor - How It Works

How Does a Thin Force Sensing Resistor (FSR) Work?

Published, thin, and versatile sensors have triggered quite the buzz about the design design community recently. This schedules mostly to the grow of wise, lightweight, and power-efficient technologies, which have become entrenched in our daily lives. Normally, when designing these small but effective devices and items, the embedded elements that make them game-changing developments should also share those same characteristics.

Force sensing resistors (AKA, published force sensors, or force delicate resistors) are a large and expanding team of embedded elements, with many new sensing unit kinds having actually been presented recently. However, force sensing resistors are not a brand-new technology at all. In truth, force sensing resistors have been used as an ingrained element for years.

This article shares the fundamentals of force sensing resistor technology, how they work, and how they can be used to catch force dimensions as an ingrained element within a gadget.

How do Force Sensing Resistors Measure Force?

Figure 11: When force is used to a force sensing resistor, the conductance reaction as a function of force is linear.Most designers have learned that the formula for force is an object's mass increased by its velocity (or, F=M*A), or, used stress increased by the contact location (F=P*Area). There are several design units to stand for "F" in these equations, such as Newtons (N), pound-force (lbf), and others.

By themselves, force sensing resistors are not pre-calibrated to associate a force reading to a recognized design unit. However, the force dimension output caught by a force sensing resistor can be associated to the used force through a calibration treatment.

Force sensing resistors are a piezoresistive sensing technology. This means they are easy aspects that function as a variable resistor in an electric circuit. As displayed in Number 1, when unloaded, the sensing unit has a high resistance (like Megaohms (MΩ)) that drops as force is used (usually like Kiloohms (KΩ)). When you consider the inverse of resistance (conductance), the conductance reaction as a function of force is linear within the sensor's assigned force range.

How do You Calibrate a Force Sensing Resistor?

Because of their resistance/conductance linear connection, force sensing resistors can be calibrated with as low as two-to-three known tons. This article explains the detailed calibration process thoroughly.

Also, if your circuit is designed with flexible elements, the sensor's level of sensitivity can be changed for ideal efficiency in your specific force range. This article provides further information on the worth of flexible level of sensitivity.

How are Force Sensing Resistors Made?

Force sensing resistors consist of a semi-conductive material - or semi-conductive ink - included in between 2 thin substrates. As displayed in Number 2, there are 2 various kinds of force sensing resistor technologies - Shunt Setting, and Thru Setting.

Figure 2: This visual shows the distinctions in between shunt and thru setting force sensing resistor technologies.

Shunt setting force sensing resistors are polymer thick-film devices including 2 membrane layers separated by a thin air space. One membrane layer has 2 sets of interdigitated traces that are digitally separated from each other, while the various other membrane layer is covered with an unique distinctive, resisting ink.

Thru setting force sensing resistors are versatile published circuits that utilize a polyester film as its 2 external substrates. Silver circles with traces are positioned over and listed below a pressure-sensitive layer, complied with by a conductive polymer. An sticky layer is used to laminate both layers of the substratum with each other.

Matrix or Single-Point Force Sensing Resistors

Figure 3: Instances of various force delicate resistor technologies.Force sensing resistors can be designed as single-point force sensors, or in a matrix array form, enabling the user to catch stress circulation over a provided location. Force sensing resistor matrices are commonly referred as stress mapping technology.

FlexiForce™ sensors from Tekscan are a thru setting force sensing resistor variety. The versatility of this technology, combined with their running abilities, and their ability to function on simple wiring, make them a great option for installing right into wise devices with limited space and power restrictions. FlexiForce sensors are also highly adjustable. The form, dimension, level of sensitivity, electric discontinuation, and running temperature level, can all be customized for your application's specific needs.

This article covers several efficiencies distinctions in between shunt and thru setting sensing unit technologies, consisting of how they contrast on linearity, wander, accuracy, and various other key factors.

How are Force Sensing Resistors Used?

While new uses for force sensing resistor technology are being found daily, most applications have the tendency to fall under 4 various use categories:
  • Spotting or measuring a price of change in force
  • Spotting or measuring a family member change in force
  • Spotting contact and/or touch
  • Spotting force thresholds to trigger an activity of some sort (e.g., IoT applications)