Abstract
Force sensors that are thin, low cost, flexible and compatible with commercial microelectronic chips are of great interest for use in biomedical sensing, precision surgery, robotics and in various “smart control” technologies. By leveraging a novel combination of microfluidics and capacitive sensing we have developed a thin, flexible force sensor that is conformable and robust. The sensor consists of a partially filled microfluidic channel made from a deformable material, with the channel overlaying a series of interdigitated electrodes that are coated with a thin polymer layer for insulation. When a force is applied to a fluid reservoir at the base of the channel, the fluid is displaced along the channel, passing over the electrodes and thus inducing a capacitance change, which is proportional to the amount of force applied. The microfluidic molds themselves are made of low-cost sacrificial material inks deposited via aerosol-jet printing, which is also used to print the electrode layer. The sensors exhibit a nearly linear change in capacitance in response to external load, with a sensitivity of up to 3.8 pF/N and a force range of up to 9 N achieved with the present design. We quantify the effects of changing the electrode morphology, liquid permittivity, sensor thickness and geometry, as well as the thickness of the insulation layer over the electrodes, on sensor range and sensitivity, using a combination of experiments and finite element analysis simulations. We further demonstrate how the sensor can be used to remotely control a robotic clamp. The conformable force sensors developed here are thin, flexible and facilitate easy signal processing. The fabrication processes are low-cost, amenable to fast prototyping and mass manufacturing. We envisage a large range of industrial and biomedical applications for this novel force sensor.
Highlights
Force-sensing requirements are ubiquitous across the fields of biomedical engineering, robotic surgery, and health monitoring, among others.[1,2,3,4,5] The ability to provide real-time force monitoring can enhance the outcome of many surgical procedures
Force sensors that are thin, low-cost, flexible, and compatible with commercial microelectronic chips are of great interest for use in biomedical sensing, precision surgery, and robotics
The sensor consists of a partially filled microfluidic channel made from a deformable material, with the channel overlaying a series of interdigitated electrodes coated with a thin, insulating polymer layer
Summary
Force-sensing requirements are ubiquitous across the fields of biomedical engineering, robotic surgery, and health monitoring, among others.[1,2,3,4,5] The ability to provide real-time force monitoring can enhance the outcome of many surgical procedures. The process of AJP involves a programmable, adjustable injection of air-focused aerosols that contain target-material particles, which are generated via pneumatic or ultrasonic approaches onto desired substrates.[30,31,32] More recently, this technology has been tested in making functional microfluidic devices.[33] In the novel sensor design discussed in this article, instead of using parallel-plate electrodes adopted in previous works[10,25], single-plate, interdigitated silver electrodes were directly printed to enhance the sensitivity of capacitance measurements.
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