Flexible Fabric Sensors Are Key Interface Between Rigid Electronics And Humans

Flexible Fabric Sensors Are Key Interface Between Rigid Electronics And Humans

Sensors Insights by Keith McMillen

Flexible fabric sensors have emerged as one of the most sought-after sensors in markets that affect consumers every day, including automotive, augmented reality (AR), virtual reality (VR), wearables, health, sports, and remote sensing. With consumers accustomed to wearing and using comfortable materials (such as fabric and leather) in their everyday lives, these materials are now converging with computers to create wearables and other fabric-based items for use in healthcare to study and treat medical conditions; entertainment to enhance gaming and experience AR simulations; and automotive to protect drivers and prevent danger. These essential flexible fabric sensors are the key interface between rigid electronics and “squishy” humans.

For manufacturers worldwide, demand for smarter fabric sensors is reaching a new high. OEMs now require sensors that report on more than just simple basic data. Precise physical changes that affect users are now required, such as pressure, location, bend, and stretch. These new smarter sensors take wearable devices from entertainment use alone to providing useful medical and other technical data. The major markets of health, sports, automotive, and remote sensing would not even be possible with the previous sensor technology, such as FSRs (Force Sensitive Resistors) that cannot be folded, washed, or maintained stable for periods of time consistent with health and automotive product life cycles.

Foot-pressure sensor.
Foot-pressure sensor.

Unlike these older FSR and other sensors that contained uncomfortable wires and rude interconnects that measure heart rate and other simple functions alone, the new sophisticated smart fabric sensors (from companies such as BeBop Sensors), is the only viable fabric solution that senses precise physical changes and is straightforward to manufacture. This new flexible sensor technology is already a proven technology, with millions of sensors in use in the field today. This patented fabric sensor technology covers a huge dynamic range, is durable, washable, easily deployed, and more affordable – by a wide margin – than other sensor technologies.

Fabric sensors can use multiple base fabrics, such as twill, felt, Kevlar, Lycra Spandex and pongee (an artificial silk). These different fabrics have different characteristics that can be matched to a given application. Kevlar is used for high temperature applications. A non-woven blend of polyester and nylon is preferred for systems that require the largest dynamic range. A stretchable fabric, such as Lycra, is ideal for making a comfortable and accurate data glove. A 24-sensor data glove with support for haptic feedback is made by printing conductive inks on both sides of a TPU (thermoplastic polyurethane) and connecting traces from both the adhesive and barrier side of the TPU film before applying to Spandex sensor fabric.

Forte data glove on hand.
Forte data glove on hand.

Stability is also an essential quality of any sensor. After numerous lab and field tests, the new flexible fabric sensors are proven stable and have been tested to 1,000,000 hits with a 32-kg force over a 645-mm square area with less than a ±3% mean variation.

An additional application ideal for fabric sensors is airbag deployment sensors in car seats. Present systems typically rely on a bladder and pressure sensor that produces a single value related to the weight of the occupant. BeBop’s occupant classification system (OCS) uses a 1mm thick array that can be located under the covering of the car seat above the foam and heater. A pressure map reflecting the shape and force of the occupant provides data to recognize different occupants as well as inanimate objects, such as child seats. BeBop’s sensor fabric used for automotive cabin sensing also performs over a wide temperature range from -50°C to +90°C with a linear temperature coefficient, making it a straightforward compensation.

BeBop Sensors Occupant Classification System for automotive market - computer vision composite view.
BeBop Sensors Occupant Classification System for automotive market - computer vision composite view.

Another automotive application is a smart steering wheel. Autonomous piloting requires knowledge that the driver has his or her hands on the wheel before relinquishing control. Similarly, the driver can take control simply by gripping the wheel. Other side benefits include “double-gripping” to answer or terminate a call and swiping to adjust audio volume or car temperature.

Concussion awareness is also an important issue and has increased over the last five years. A major Hollywood movie has even brought this subject into the mainstream. Solutions on the market generally rely on an accelerometer to capture impact force. While useful, simple impact measurement is not sufficient.

BeBop Sensors smart-helmet sensor system.
BeBop Sensors smart-helmet sensor system.

Some parts of the skull are more fragile than others, so knowing the impact area history can provide a more complete picture of the damage. BeBop has produced an array of sensors that can fit most helmet sizes. For example, a motorcycle helmet could be required to dial an emergency number if the incident merits attention.

BeBop Sensors smart-helmet sensor – side.
BeBop Sensors smart-helmet sensor – side.

With a basic accelerometer sensor, an accidental drop of the helmet could initiate the call. This burgeoning fabric sensor market will soon bring everyone closer to the power of computing hidden within everyday clothing, fabrics, and other objects.

 

About the author

Keith McMillen is the Founder and CEO of BeBop Sensors www.bebopsensors.com, the leader in smart fabric sensor wearable technology. McMillen has started and sold two companies in his 30+ years innovating in the sensor and audio market. Zeta Music revolutionized stringed instruments and was sold to Gibson Guitars in 1992. Octiv, started in 2000, received funding from 3i and Intel Capital and was sold to Plantronics in 2005. McMillen is the inventor on numerous patents; has released hundreds of profitable products; published dozens of scholarly papers, and was winner of a Guthman Award in 2010.