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June, 2016
Next Generation Product Designs Incorporate Capacitive Force Sensors
By Del Williams D
esign engineers now have an option to eval- uate and integrate into their products 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 tool-
box, engineers can now measure applied force at discrete points even at very low levels, opening up a range of possibilities in next generation con- sumer electronics, medical devices, robotics and many other applications. Although capacitive sensor technology has
largely supplanted resistive for touchscreens, 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 conduc- tive ink, to detect pressure. In this approach sever- al layers of circuitry touch each other, changing the circuit’s resistance. Because there is a transi- tion from contact to non-contact, however, there is a dead space that limits the sensitivity of the sen- sor at lower levels of pressure.
Capacitive Sensors Capacitive sensors, on the other hand,
involve two electrodes separated by a compressible dielectric structure. When pressure is applied, the
A new breed of
capacitive sensor measures even minute levels of force with high repeatability.
gap decreases and capacitance rises. Unlike resis- tive technology, the two electrodes never touch. Consequently, capacitive sensors are less suscepti-
ble to wear or failure even if subjected to multiple, repeated loads. Capacitive sensor technology has several
advantages over resistive, including greater stabil- ity in terms of repeatability and durability, and can measure low levels of pressure with accuracy. According to Dr. Jae Son, founder of Pressure
Development of Wearables Dr. Son says that one area that has generat-
ed quite a bit of interest is in the testing and devel- opment of wearables, which can include clothing, shoes, headphones, wristbands, sport bras and pressure garments. “By integrating capacitive tactile sensors in
the testing and development of wearables, for exam- ple, 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 deter- mining whether someone will like a product or not.” To accomplish this, sensors can be embedded in mannequins or sewn into straps that go between the clothing and a mannequin or human tester dur- ing the development process. There are also many applications in medical
Standard SingleTact; both sizes.
Profile Systems (PPS), the possible applications for measuring force using capacitive sensors are virtu- ally unlimited.
Capacitive Tactile Sensing For the past 19 years, PPS has provided inno-
vative capacitive tactile sensing solutions includ- ing sophisticated array systems to such companies as Apple, Microsoft, Qualcomm, J&J, Google and others. In this capacity, PPS is often approached as
to the feasibility of integrating pressure (using arrays that measure thousands of points of force) and force sensors (that measure discrete points) in consumer electronics, robotic, ergonomic, medical and automotive applications.
Los Angeles Office: 3528 Torrance Blvd., Suite 100
Torrance, CA 90503 Phone: (310) 540-7310 Fax: (310) 540-7930
equipment design. According to Dr. Son, PPS sen- sor technology has contributed to the creation and research of an array of novel medical applications such as an advanced catheter system that provides clinicians with 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 minia- ture force sensor to control the amount of force used when injecting insulin using a syringe, but there wasn’t a precise miniature force sensor avail- able. That is about to change with the introduction of miniature capacitive force sensors.
Monitoring Blood Pressure The technology is also well-suited for moni-
toring blood pressure, where extremely low pres- sure measurements are required, and could be
Continued on next page
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