The world of electronics is full of clever designs and ICs, but they are mostly non-flexible and rigid implementations of the engineer’s circuit idea. This is typically not very conducive to many of the applications in which the circuit will be used. The circuit may be placed on or inside human body, in clothing, or on some surface that is not straight, flat, and full of sharp angles. Much of the analog world we live in has softer lines, curves, and bends that move and change.
How do we adapt to these needs? Some developers are working with materials like graphene, which is both flexible and conductive. It is a lattice of pure carbon just a single atom thick. Other developers have chosen to pursue silicon sliced extremely thin, to a thickness less than the hair on your head. But silicon is a brittle material, especially at these thicknesses.
John Rogers, a material scientist at the University of Illinois at Urbana-Champaign has numerous patents covering silicon fabrics. These stretchable fabrics retain silicon's electrical performance while allowing flexibility. Rogers' company, MC10, is furthering the cause of biological sensors that can fit the shape of the heart, brain, and other organs of the body.
and rubber that stretches more than 200 percent.
Now the world of innovative electronic solutions can literally fit in the palm of your hand. You can have circuitry on your brain or under your skin. Besides biological applications, circuits (not merely sensors) can be embedded in or along the contours of steel cables. An obvious application is on the cables of a suspension bridge. Stress could be monitored and engineers could be warned of any potential failure.
Wireless, flexible sensors
Some designs have even gone to inkjet-printed circuitry on a paper-based material. One technique like this uses inkjet-printed RFID circuits on flexible paper substrates. This gives the designer the advantages of low-cost and environmentally friendly RFID sensing.
Engineers have used inkjet-printed antenna configurations at frequencies as high as 7 GHz with good results.
paper or other flexible substrate.
(Source: Reference )
This antenna is printed on paper. Additional circuitry is printed for ICs, sensors, passive components, and a power source.
on a paper substrate with support components.
(Source: Reference )
One use for this technology has been implemented in the “smart shoe.” The implementation needs no battery, since it is in an RFID configuration on a paper substrate. This is a remarkable enhancement to autonomous, wearable sensing applications that work over a relatively long range.
This technology has been taken one step further in that an asynchronous wireless link has been created between these flexible RFID imprinted tags and a wireless sensor network (WSN) with only a basic protocol. Connecting a simple RFID reader to the more complex WSN in this way has significant cost-savings ramifications.
One of the biggest areas of focus with potentially the most benefit to mankind is the use of flexible circuits in and on the human body. Second skin, neuroscience, water soluble circuits, and intra-cardiac imaging catheters are only a few of the amazing things that flexible electronic circuitry has brought to the industry.
John Rogers’ team is also involved in electronic skin that can contain temperature sensors, light detectors, and other integrated components in a rubberized sheet. This sheet can be applied as one would a temporary tattoo. It can bend and stretch with no damage to the circuitry. It can also be washed off after it serves its purpose. Less than a micron thick, there is no need for a polymer backing. The electronics are stamped directly onto the skin and sealed with a spray-on bandage.
Doctors can measure electrical conductivity or the spread of heat across the skin. They can identify levels of hydration as well as send small electrical currents to stimulate muscles as part of a physical therapy treatment program.
Neuroscience can also benefit from this technology. It has been demonstrated in the lab that an animal’s behavior can be modified by using a light flash in a technique called optogenetics. This reprograms the brain’s neurons in a specific area to respond to light. Micro-LED devices are small and less invasive than fiber-optic cables implanted into the brain and then connected to a cumbersome helmet linked to a laser.
Each square LED is 5 microns thick and 50 microns square. Four of these are put into a thin, flexible polymer sheet and then layered with other sheets containing sensors that monitor temperature, light, and electrical activity. The entire device is a tongue-depressor-shaped object that measures 10 microns thick — thinner than a spider web!
Intracardiac catheters for electrophysiological interventions in atrial fibrillation cases use intracardiac echocardiography (ICE) as an alternative to a fluoroscope (which has potentially harmful ionizing radiation) for guided imagery in these procedures.
Capacitive micromachined ultrasonic transducers (CMUT) create micro-linear (ML) and ring catheters. The CMUT is in a phased-array configuration running at 10 MHz.
(Source: Reference )
Click on the image for a short slide show of additional portions of the medical device.
Flexible electronic integrated circuitry holds a rich future in many areas of design. The applications are limited only by our imaginations. Please give us examples you know about or for which you would like to see designs.
- “Progress Towards the First Wireless Sensor Networks Consisting of Inkjet-Printed, Paper-Based RFID-Enabled Sensor Tags,” Vasileios Lakafosis, Student Member IEEE; Amin Rida, Student Member IEEE; Rushi Vyas, Student Member IEEE; Li Yang, Member IEEE; Symeon Nikolaou, Member IEEE; and Manos M. Tentzeris, Fellow IEEE.
- “Forward-Looking Intracardiac Imaging Catheters Using Fully Integrated CMUT Arrays,” Amin Nikoozadeh, Ömer Oralkan, Mustafa Gencel, Jung Woo Choe, Douglas N. Stephens, Alan de la Rama, Peter Chen, Feng Lin, Aaron Dentinger, Douglas Wildes, Kai Thomenius, Kalyanam Shivkumar, Aman Mahajan, Chi Hyung Seo, Matthew O’Donnell, Uyen Truong, David J. Sahn and Pierre T. Khuri-Yakub
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