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Incorporating Capacitive Force Sensors in next generation product designs

Published: 21 January 2016 - Lisa Peake

New breed of capacitive sensor measures even minute levels of force with high repeatability

Design engineers interested in integrating miniature force sensors into product designs now have an option to evaluate and integrate a new breed of capacitive technology-based sensor that can accurately, and with high repeatability, measure forces as low as 1 gram. With this new option in the designer’s toolbox, engineers can now measure applied force at discreet points even at very low levels, opening up a range of possibilities in next generation consumer electronics, medical device, robotics and many other applications.

Although capacitive sensor technology has largely supplanted resistive for touch screens, until recently product designers have been limited to resistive sensors to measure force. This type of sensor measures the resistance of conductive material, such as an elastomer, foam, or conductive ink, to detect pressure. In this approach several layers of circuitry touch each other, changing the circuit’s resistance. Because there is a transition from contact to non-contact, however, there is a dead-space that limits the sensitivity of the sensor at lower levels of pressure.

Capacitive sensors, on the other hand, involve two electrodes separated by a compressible dielectric structure. When pressure is applied, the gap decreases and capacitance rises. Unlike resistive technology, the two electrodes never touch. Consequently, capacitive sensors are less susceptible to wear or failure even if subjected to multiple, repeat loads. Capacitive sensor technology has several advantages over resistive, including greater stability in terms of repeatability and durability, and can measure low levels of pressure with accuracy.

According to Dr. Jae Son, founder of Pressure Profile Systems (PPS), the possible applications for measuring force using capacitive sensors are virtually unlimited. One area that has generated quite a bit of interest is in the testing and development of wearables, which can include clothing, shoes, headphones, wristbands, bras and pressure garments. 

“By integrating capacitive tactile sensors in the testing and development of wearables, for example, manufacturers could capture and quantify the amount of pressure experienced by customers at specific spots to optimize fit and function,” says Dr. Son.  “Comfort, after all, plays a large role in determining whether someone will like a product or not.”

There are also many applications in medical equipment design. According to Dr. Son, PPS sensor technology has contributed to the creation and research of an array of novel medical applications such as advanced catheter system that provides clinicians with more-useful and detailed data to aid in diagnosis of esophageal problems and a Screening Clinical Breast Exam called SureTouch that detects breast lumps and, essentially, quantifies the sense of touch. One manufacturer wanted to use a miniature force sensor to control the amount of force used when injecting insulin using a syringe, but there wasn’t a precise miniature force sensor available. That is about to change with capacitive miniature force sensors.  

PPS has developed a new breed of miniature capacitive force sensors called SingleTact, which are designed to allow engineers to conduct feasibility studies, create prototypes, and even integrate into next generation products. These ultra-thin single-element sensors accurately and reliably quantify force at a discrete point as low as 1 gram. 

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Source: Electronics

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