• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer
  • Subscribe
  • Advertise

Sensor Tips

Sensor Product News, Tips, and learning resources for the Design Engineering Professional.

  • Motion Sensing
  • Vision systems
    • Smart cameras
    • Vision software
    • Lighting
    • Optics
  • Pressure
  • Speed
  • Temperature
  • Suppliers
  • Video
    • EE Videos
    • Teardown Videos
  • EE Learning Center
    • Design Guides
    • Tech Toolboxes

Hybrid sensors for connected vehicles

July 26, 2022 By Lee Teschler

The dependence of smart vehicle features on sensing technology has manufacturers thinking about how to field devices that combine functions in economical ways.

Estimates are that today’s vehicles can have between 60 and 100 sensors onboard. And over the next decade the number of sensors is expected to double. No wonder, then, there are efforts afoot to have one sensor to double or triple duty in connected vehicles of the future.

As an example of these efforts, consider the work of engineers at Tohoku Fujikura Ltd. (TFL) in Japan. They devised a combination SBR (seat belt restraint) sensor and seat heater. It is interesting to review the steps TFL went through in devising this device.

Briefly, the SBR occupant detection sensor sends a signal when two electrodes facing each other touch because of pressure applied to the seat surface. The signal goes to an electronic controller unit (ECU) that determines whether or not a passenger is in the seat and, if necessary, tells the passenger to fasten their seatbelt.

seat sensor positions
The two typical positions for a seat belt restraint sensor in a vehicle seat.

There are two types of SBR sensors. One sits on the upper seat just under the top surface leather (A-Surface). The other sits on the seat forming (B-Surface), basically, under the seat cushion. Though SBR sensors have long been required for front seats, a recent amendment to international car safety standards requires the installation of SBR sensors in all passenger seats.

To distinguish between a passenger and luggage, a conventional SBR device has an H shape so it operates only when at least one electrode on the left and right side make contact. This reduces detection errors from factors such as shopping bags on the seat. TFL engineers say the H shape also makes for reliable detection even if the seat occupants change their position or posture.

SBR sensor
A conventional SBR sensor. The switches sit at each end of the “H” shape. SBR sensors use multiple switches as a way to distinguish loads from packages and other debris from a human occupant.

The A-Surface SBR sensor is about 0.3 mm thick and resides under the surface of the seat or back rest so it is relatively close to the passenger or to objects placed on the seat. Its position gives the sensor a relatively large pressure load that is stable. However, TFL says there are issues associated with fixing the sensor precisely between the surface leather and the seat cushion foam. And passengers apparently can feel the sensor when they sit on it.

That brings us to built-in seat heaters designed to warm passengers. Conventional seat heating devices consist of one long electric heating wire about 1.0 mm in diameter arranged on the surface of a 2.0-mm-thick flexible non-woven cloth. The occupant detection sensor turns the heating operation on or off. To expand the heating area, the seat heater requires some thick buffer material between the leather seat covering and the cushion form to expand the heated area and make the heating wire unnoticeable to the passenger sitting on it. The problem is the buffer material also increases the amount of energy necessary to effectively heat the seat.

Ghost view of the TFL prototype SBR sensor/heater. TFL engineers also left space on the surface holding the SBR electrodes for other sensors such as for sensing the physique of the seat occupant. Engineers say these options will be explored in future work.

The combo seat heater/SBR sensor TFL engineers devised is soft and flexible enough to fit the base seat cushion form and puts the sensor electrodes on a printed conductive circuit. To combine the SBR sensor and the seat heater, TFL developed a printed circuit woven (PCW) sheet composed of copper circuit printed on a glass cloth (GC) substrate. (Interestingly, TFL says the PCW sheet was originally developed for wearable application.) The heated area is about 10.25×9 in. The electrode on the GC is 0.1-mm-thick screen-printing copper said to handle temperatures up to 300ºC.

assembly steps
Assembly steps involved in creating the substrates of the hybrid sensor/heater. The “basket holes” refer to vacant areas in the woven substrate due to the weft and warp of the weaving process.

There are electric circuits facing each other on both sides of the GC that connect through holes between the warp and weft of the GC weave. A low-elasticity resin is applied to areas of the GC to form a substrate for printed circuit features making up sensor connections and electrodes. Conductive metal ink is selectively applied next to create the copper circuit traces on the GC comprising the heater conductive elements and to create the conductive electrodes on the resin. A second layer of low-elasticity resin is then applied to serve as a flexible protective coating for the conductive heating elements and the conductive circuit elements. TFL says the physical and mechanical properties, appearance, and environmental resistance of the PCW sheet can be adjusted through resin coating, impregnation, and forming processes.

seat heater sensor combo
The completed sensor/heater hybrid as it appears in a seat, left, and its appearance on a thermal camera when in the process of heating.

Like conventional SBR sensors, the hybrid device has upper and lower electrodes that face each other. The use of a GC substrate instead of conventional double-sided adhesive PET film minimizes the rigid area of the sensor so seat occupants are less likely to notice it.

The seat heater material is less than 0.15-mm-thick and is configured with a copper feeder circuit and a printed high-resistance heating carbon film. The carbon film is formed by printing a high-resistance heating carbon ink on the both sides of the heating substrate fully overlapping copper feeder circuit. The heating device generates about 80ºC and the area around the SBR sensor gets up to around 40ºC.

TFL says a variety of materials are candidates for use as surface protection material including non-woven or needle-punched fabrics. Thus the hybrid SBR/heater device can be used in leather seats as well as in seats with less expensive coverings.

You may also like:


  • What are the types and uses of position sensors? 

  • What sensors are used in AR/VR systems?

  • How can a machine recognize hand gestures?

  • Want to feel better?

  • What sensors do you need to land on the moon?

Filed Under: Electrical sensing, Featured, Frequently Asked Question (FAQ), Position, Proximity Tagged With: FAQ

Primary Sidebar

Featured Contributions

Integrating MEMS technology into next-gen vehicle safety features

Fire prevention through the Internet

Beyond the drivetrain: sensor innovation in automotive

Sensors in American football can help the game

Select and integrate sensors into IoT devices

More Featured Contributions

EE TECH TOOLBOX

“ee
Tech Toolbox: 5G Technology
This Tech Toolbox covers the basics of 5G technology plus a story about how engineers designed and built a prototype DSL router mostly from old cellphone parts. Download this first 5G/wired/wireless communications Tech Toolbox to learn more!

EE LEARNING CENTER

EE Learning Center
“sensor
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for EE professionals.

RSS Current EDABoard.com discussions

  • How to start a startup in VLSI
  • Requests to Deactivate/Delete EDABoard User Account
  • UART Basic Before Writing Code
  • PFAS-Free Die Attach Paste
  • LED driver using PWM

RSS Current Electro-Tech-Online.com Discussions

  • Simple LED Analog Clock Idea
  • Microinverters and storeage batteries?
  • PIC KIT 3 not able to program dsPIC
  • Fun with AI and swordfish basic
  • Is AI making embedded software developers more productive?

EE ENGINEERING TRAINING DAYS

engineering
“bills

RSS Featured White Papers

  • 4D Imaging Radar: Sensor Supremacy For Sustained L2+ Vehicle Enablement
  • Amphenol RF solutions enable the RF & video signal chains in industrial robots
  • Implementing Position Sensors for Hazardous Areas & Safety

DesignFast

Component Selection Made Simple.

Try it Today
design fast globle

Footer

EE WORLD ONLINE NETWORK

  • 5G Technology World
  • EE World Online
  • Engineers Garage
  • Analog IC Tips
  • Battery Power Tips
  • Connector Tips
  • DesignFast
  • EDA Board Forums
  • Electro Tech Online Forums
  • EV Engineering
  • Microcontroller Tips
  • Power Electronic Tips
  • Test and Measurement Tips

SENSOR TIPS

  • Subscribe to our newsletter
  • Advertise with us
  • Contact us
  • About us

Copyright © 2025 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy