by Wilfried Bair
VP of Engineering, NextFlex
Flexible hybrid electronics (FHE) and sensor technologies are a perfect match for each other. Nearly every current application of FHE technology that either NextFlex or our partners are working on involve sensors, so it’s beneficial for both platforms to grow and thrive alongside each other. Of course, these benefits ultimately carry down to the applications that use both FHE and sensors, such as chemical sensing systems and human health/fitness monitoring devices. When we drill down into this topic, it shows a unique symbiotic relationship that’s critical to the development of next-generation manufacturing.
Sensors Benefit from FHE
When we develop FHE projects, we first look at the applications. Oftentimes we need to create a sensing platform for these FHE applications, so we look for sensors to fit requirements of those specific applications. For example, chemical sensors are in high demand for environmental monitoring devices, where there is a broad range of use cases.
Starting with workplace safety, fabric integrated with body worn sensors will provide warning for dangerous levels of chemicals in a work environment. For public safety, FHE based sensors can be inexpensively and widely installed to monitor environmental pollution levels. For example, schools can monitor local pollution to decide whether it is safe for students to perform athletic activities outside. FHE based chemical sensor can also be used to warn of air or waterborne chemicals caused by an accident or an attack.
In general, there are a few barriers that need to be surmounted with traditional sensors: they’re heavy, need high power to operate and are not easily deployed. However, advancements in FHE technology resolve these legacy problems by allowing sensing systems to become lightweight, low-power and able to be conveniently used.
For IoT uses, FHE offers a low-cost sensor platform to be easily deployed without the need to create bulky and expensive enclosure or housings. The widely used rigid boards are not able to provide the form factor and ease of deployment as FHE-based systems do. For example, in healthcare applications, a rigid and bulky puck-like device worn on the arm can be reduced to a truly wearable band-aid like device, which doesn’t bump out or impact movement.
FHE Benefits from Sensors
FHE creates an ideal sensor platform for any type of sensing applications and in some cases actuation as well. This means the reverse is true: sensors are often an ideal use for FHE. NextFlex has defined four application focus areas: human monitoring, asset monitoring, soft robotics and printed array antennas. Except for antennas, all three application focus areas for FHE are sensor-based, particularly human monitoring devices and infrastructure monitoring systems.
12 projects in NextFlex’s Project Call programs, where we fund active, ongoing FHE developments, directly deploy and utilize sensors. These projects are all within the rapidly advancing fields of human health monitoring or asset monitoring.
For example, in human health monitoring, GE is leading a wearable EKG project that combines stretchable sensor leads and a flexible (but not stretchable) unit. The wearable EKG system houses the core electronics including battery and antennas for wireless communication. Traditional EKG monitors are bulky and have to be disconnected at each stage of the care process, however, a wearable and wireless EKG can travel with the patient through the entire chain of care. In addition, continuous heart rate monitoring is offered by flexible sensors that can adhere comfortably to a patient.
In asset monitoring, Boeing is leading a condition-based monitoring sensor array project that combines multiple flexible and bendable sensors designed for wireless communications, and a flexible battery. The project is looking at the integration of these sensors for a variety of conditions, including temperature, strain, humidity and pressure, with the goal of overcoming cabling, access and size restrictions presented by traditional sensors. This allows the sensor array to be used on a variety of industrial and aeronautics equipment, testing platforms and logistics items that could not have sensors placed on them before.
What is next in sensing on flexible platforms
Typically MEMS sensors are in a rigid package where final calibration is performed after the sensor has been placed in the final package. Contrary to the standard way of utilizing MEMS sensors, we’re evaluating the feasibility of a MEMS bare die, directly placing it on substrates and measuring the performance of MEMS on flex, as opposed to a conventionally packaged MEMS device. These MEMS sensors on flex have many potential applications for wearables and textile integration.
Under an ongoing DARPA project, we’ll perform this type of MEMS on flex evaluation for the first time. Over a nine-month period, we will investigate the feasibility of bare thin MEMS sensor die on flexible substrates. Device testing will indicate the feasibility of using current MEMS inertial sensing designs in a thin and flexible format, with the goal of identifying alternate design approaches or the feasibility of using software to compensate for performance losses due to flexing and bending that naturally occurs in a wearable non-rigid form factor.
These developments can ultimately unlock other applications, especially for body-worn sensing systems. A potential use case could be for body-worn navigation where GPS signals are not available or reception is poor due to weather or dense tree foliage, for example. MEMS sensors on flexible substrates can be body worn and would be able to provide navigation information when GPS signals are not present including altitude detection to determine what floor of buildings you’re on. This is similar to vehicle-based navigation in cities when GPS signals are blocked by high-rise buildings, where the vehicle will use ABS and steering wheel position sensing information to continue navigation until GPS signals are available again.
When examined together, the development of FHE technology and sensor technology are often one and the same, with one benefitting as the other advances. We’ll continue to examine FHE applications for how they might integrate sensors in the future, because when sensors are better, FHE will ultimately be better too.
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This article is a part of MEMS Journal's ongoing market research project in the area of flexible hybrid sensors and electronics. If you would like to receive our comprehensive market research report on this topic, please contact Dr. Mike Pinelis at [email protected] for more information about rates and report contents.
Copyright 2018 MEMS Journal, Inc.
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