Force Sensing
Resistors
Force Sensing Resistors (FSRs) are a cost-effective technology for detecting applied force in a wide range of application areas. Small, light and highly customizable, a Force Sensing Resistor could be the perfect HMI solution in your next product!
Standard Force Sensing Resistors
TPE-500 is Tangio's best-in-class series of high-performance Force Sensing Resistors, available in industry standard footprints and interconnect options. This extensive range includes both single point FSR sensors and 2D force sensing linear potentiometers (FSP).
Tangio's force sensors banish the undesirable characteristics found in legacy competing products. We achieve this through state-of-the-art FSR inks, carefully selected materials, intelligent mechanical design, and tightly controlled printing and curing.
Our TPE-500 range offers excellent environmental stability, part-to-part repeatability and long-term durability, whilst maintaining a wide dynamic range, low drift and reassuringly low activation force. Full data sheets and integration guides are available for download.
Better still, our thirty years manufacturing experience guarantees high yield, high quality, and very attractive pricing. All devices in the TPE-500 range are RoHS compliant. You can purchase our standard force sensing resistors in our webstore.
Sensing Force and Position
Force sensing resistors can be built with varying degrees of functionality to match your requirements. Adding sensing lines and altering the corresponding electronics can allow you to not only sense changes in force, but also changes in position.
A single point sensor is the most basic form of force sensing resistor, only sensing a change in force. Next up, force sensing potentiometers not only sense a change in force but also a change in position in one direction. Force sensing potentiometers can be made in linear or ring configurations.
Force sensing trackpads (aka 4-wire sensors) sense a change in force as well as 2D position, similar to a laptop trackpad but with the added advantage of variable force sensing.
Finally, 3D matrix sensors sense a change in force and will also report 2D position for multiple simultaneous inputs.
Custom Force Sensing Resistors
The largest part of our business is the design and mass production of semi and fully-custom force sensors for our global client base.
Developing a custom resistive force sensor with Tangio starts with a discovery phase where our engineers will discuss the desired user experience and your mechanical and electrical requirements.
We provide expert advice not only on the sensor design but also on the sensor integration into your product, to ensure consistent and repeatable results.
Tangio has full turn-key in-house production facilities for rapid prototyping and high quality offshore production partners for mass production.
Time to prototypes is typically only a few weeks, and costs compare very favourably with other technologies.
How Force Sensing Resistors Work
Shunt Mode
Shunt Mode force sensors are the most frequently used design. They are constructed in two layers of flexible polymer. One layer is printed with Tangio's best-in-class force-sensing ink and the other with printed silver interdigitated electrodes. The two substrates are then positioned facing each other and assembled using an adhesive gasket around the perimeter.
Electrodes can be designed in various configurations depending on the application including, but not limited to: various patterns to influence sensitivity, various materials including silver, copper, carbon and blends, or on a printed circuit board (PCB).
When a force is applied to the device, the shunt or shorting circuit is complete. The more force applied, the more conductive the output.
Thru Mode
Thru Mode force-sensing resistors are constructed in two layers of flexible polymer. Conductive pads, which can be silver, or a silver/ graphite blend ink, are printed on each of the two substrates.
Force-sensing ink is printed on both conductive pads. The two substrates are then positioned facing each other and assembled using an adhesive gasket around the perimeter.
When force is applied, the conductive pads make contact. The more force applied to the Thru Mode device, the more conductive the output.
FSR Characteristics
A typical Force vs. Resistance response (FR curve) is logarithmic and has three principal elements.
1. Break force - This is the force required for the two membrane layers to contact. In this region the resistance is infinite until enough force is applied to make contact.
2. Area Effect - In this region the size of the contact area between the two layers is increasing with increasing force and thereby reducing the resistance.
3. Surface Effect - In this region as the force is increased the contact of the two ink surfaces increases at a microscopic level.
