Characterization of a Commercial Thin Film-based Pressure Sensor

Gait analysis plays an important role in various applications such as health care, clinical rehabilitation, sport training and pedestrian navigation. In order to monitor the human gait, an interesting approach is to analyze the foot plantar pressure distribution between the foot and the ground. In recent years, the emergence of flexible, soft and lightweight sensors facilitates the rapid technological advances in in-shoe foot pressure measurements, thereby especially carbon nanotubes-based sensors provide an outstanding solution for the implementation of flexible, soft pressure sensors in foot pressure distribution analysis. This chapter focuses on the design and implementation of multiwalled carbon nanotubes (CNT)/polydimethylsil-oxane (PDMS) based nanocomposite pressure sensors for the analysis of the foot pressure distribution. The sensor is durable, stable and shows sensitivity of 3.3 k\({\Omega }\)/kPa and hysteresis smaller than 3.64% with maximum detectable pressure up to 217 kPa, which is suitable for the measurement of human foot pressure. The proposed sensor has been implemented in a flexible in-sole, which is designed based on normal arch foot anatomy. A total of 12 sensors are distributed in the heel, lateral back foot, midfoot and front foot. The foot pressure distribution for different persons while walking and standing using nanocomposite sensor based in-sole were investigated by measuring the changing in resistance of the pressure sensors, when pressure applied on it. It shows that foot pressure distribution is higher in the fore foot and the heel while person standing in normal position. While walking, initially the foot pressure is in the heel and then transferred to the entire foot and finally it is concentrated on the fore foot.KeywordsCarbon nanotubesPolydimethylsiloxaneNanocompositesPressure sensorsScreen printingSolution mixingGait analysis

Saline based microfluidic soft pressure sensor utilizing a three-dimensional focused electric field for motion and healthcare monitoring

Textile-based pressure sensor arrays: A novel scalable manufacturing technique

Innovations in soft materials have advanced the development of implantable devices for pressure monitoring, but fabrication and integration challenges remain, such as limited patterning resolution and poor scalability, hindering their miniaturization and wireless sensing capabilities. This study introduces methods and advantageous features of incorporating liquid metal into microfabriated, wireless soft implantable pressure sensors and wearable readout systems for large-area pressure mapping and adaptive implantation with autonomous folding and self-healing capabilities. Eutectic gallium-indium, a type of liquid metal, serves as both the deformable electrode for capacitive sensors and a low-resistance conductor for inductors. It is integrated into a thin-film, battery-free, inductive-capacitive wireless sensing platform. Scalable wireless sensor arrays are created through microfabrication for large-area pressure mapping. The wireless pressure sensor is also integrated with soft ferromagnetic and self-healing layers in cuff-type sensors to allow for autonomous folding in response to external magnets, eliminating the need for suturing. In addition, a miniaturized wearable readout system integrated into medical gloves enables wireless and real-time pressure monitoring. The presented wireless soft pressure-sensing method with large-area mapping and secure implantation capabilities offers alternatives to conventional medical tools for intraoperative monitoring and examinations.

Polyisoprene-nanostructured carbon composite – A soft alternative for pressure sensor application

This paper proposes a low-cost soft pressure sensor. The pressure sensor is fabricated by 3D printing. The material uses soft silicone with ductility and skin-friendly properties, which can better restore the original shape after extrusion. And when it comes into contact with the skin, it will not cause skin allergies because o-f the time. The conductive cotton yarn is used as the main wire inside the sensor (the sensor size is about 17.5mmx13.5mmx4mm). Users feel comforted when using this soft material, increasing measurement accuracy. In addition, to monitor the sensor's resistance range and deformation it needs to be tested by the CNC lathe status after the sensor is completed.

Ionic pressure sensors are made of ionic compounds suspended in a suitable solvent mixture. When external pressure is exerted on them, it is reflected as a change in electrical parameters due to physical deformation and a redistribution of ions within the sensing medium. Variations in the composition and material of the sensing medium result in different pressure sensors with varying operating ranges and sensitivity. This work presents the design and fabrication procedure of a novel soft-pressure sensor for a very low-pressure range (<20 mm Hg) using Aloe vera gel and Glycerin as the solvent for the ionic sensing medium. We also provide a comparative study on the performance of sensor prototypes with varying solvent concentrations and geometric parameters based on a series of characterization experiments. Maximum sensitivity () was observed when using 40% glycerin in the sensing medium, filled in a toroidal geometry with outer and inner channel diameters of 8 mm and 7 mm, respectively. The proposed sensor is entirely soft and can be designed to conform to any desired geometry.

Continuous and long‐term pressure monitoring by devices implanted in the human body promises substantial improvements for diagnosis, health monitoring, surveillance of disease progression, or surveillance of the response to a treatment but also for precision during surgeries. Here, we report on a piezoresistive sensor made entirely of parylene‐C eliminating the need for heterogeneous encapsulation. Material characterization demonstrated that parylene‐C is excellently suited as a construction material. The pressure sensor comprises a parylene‐C membrane, which is functionalized with gold strain sensors for pressure sensitivity. It was bonded to the reference pressure cavity, thereby establishing a long‐time stable hermetic sealing. The presented design and fabrication enable for the first time a monolithic, highly soft and flexible pressure sensor entirely made of biocompatible material. It exhibited high pressure sensitivity of up to 6.2 µV·mmHg −1 with very good repeatability and negligible hysteresis, made possible by thin‐film strain sensors on a parylene‐C membrane with a gauge factor of 7.5. Simulations show how the design can be easily even further miniaturized. Initial in vitro assay confirmed that parylene‐C is biocompatible on cell culture level. Such biocompatible and chronically implantable pressure sensors are opening new possibilities in medical treatments and long‐term supervision.

Around 8 million people in Germany suffer from type 2 diabetes. One of the secondary and accompanying diseases is diabetic foot syndrome, which currently affects 250,000 patients. Therapeutic and preventive measures are designed to reduce the risk of foot wounds (ulcers). These include the detection of increased pressure values in the entire foot area. A pressure-measuring stocking can be used to continuously record pressure loads during activities of daily living. It is important to use skin-friendly, heat- and moisture-regulating textiles with very thin and soft sensors that do not create pressure points and are very comfortable to put on, take off and wear. Machine washing should be possible for daily cleaning. And the manufacturing costs must be low. The solution presented is the use of thin (1 mm) capacitive dielectric elastomer pressure sensors based on skin-compatible silicones, which are bonded at any position on the smart wool sock. The signal cables are knitted in elastically during stocking production and are connected to a removable radio electronics unit at the end of the stocking. The measurement data from up to 16 pressure sensors on the entire foot can thus be sent wirelessly to a mobile receiving device (e.g. smartphone) to warn patients of excessive pressure and inform the doctors treating them.

The measurement of surface pressure in wind tunnel or in flight tests gives very important data for aerodynamics analysis. In fact, the pressure measurement gives valuable information about air flow phenomena such as shock, flow separation and boundary layer transition. In this paper a real-time image processing system for pressure sensitive paint (PSP) measurement and calibration has been designed using a calibrated pressure sensor. In the implementation of the system, TCL paper is used to luminaphore inside a windowed enclosure and a factory-calibrated pressure sensor for validation of measurement. The pressure measurement of PSP is based on the images acquired from a CCD camera sent to the MyRIO processor module in which the real-time image processing has been applied. The results are compared with the calibrated sensor from which the A and B coefficients of the Estern Volmer Equation have been calculated. During the several tests done for the pressure measurement, the accuracy of the PSP measurement has been calculated in this paper. Both normal and real-time image processing analysis have been compared as well.

To audit the reliability of the Camino intracranial pressure (ICP) sensor (Camino Laboratories, San Diego, CA) in our clinical practice as part of a continuing quality assurance program, and to assess its relative usefulness as compared with currently available ICP monitoring technologies that we reviewed. Prospective audit of ICP device reliability and function in 50 patients with head injuries. Zero drift was recorded immediately after the ICP device was removed from the patient. Dynamic frequency response bench testing of each functioning catheter from 0 to 30 Hz and static calibration testing from 0 to 100 mmHg during environmental temperature variation from 22 to 40 degrees C were carried out. Zero drift (range, -13 to 22 mmHg; median, -1 mmHg) was recorded immediately after the devices were removed from patients. Seventeen (50%) of the devices tested for zero drift had absolute drifts of at least 3 mmHg. There was no correlation between recorded zero drift and duration of monitoring (r = 0.154, P = 0.207). Five sensors (10% of those tested) failed during patient monitoring and were replaced. Static and dynamic calibration tests of the functioning sensors were within the manufacturer's specifications. However, the sensitivity of the devices to environmental temperature remains a problem. The Camino ICP sensor remains one of the most popular ICP monitoring devices for use in patients with traumatic brain injuries. However, our recent in-house assessment demonstrated the robustness of the device to be less than adequate during routine practice. In this study, more than 50% exhibited zero drift greater than 3 mmHg, which is unacceptable in a catheter tip ICP monitoring device in which zero drift and calibration cannot be checked in vivo. A review of the literature revealed that other available ICP monitoring devices may prove to be more reliable and thus more appropriate for routine clinical measurement of ICP.

The fabrication and characteristics of a micromachined chromium nitride (Cr-N) thin-film pressure sensor with high overpressure tolerance for high temperature applications are presented. The proposed pressure sensor consists of a Cr-N thin-film, patterned after a Wheatstone bridge configuration, and then sputter-deposited onto thermally oxidised Si membranes with a buried cavity for overpressure tolerance and an Al interconnection layer. This device is very suitable for high temperature integrated pressure sensors.

ABSTRACTHigh‐reliability assembly techniques for miniaturized in‐line pressure sensor with diaphragm using a thin strain sensor have been developed to monitor the hydraulic pressure in the pipetting such as dispensing devices. The pressure sensor with a thin strain sensor as a diaphragm has two problems, (i) water leakage and (ii) sensitivity reduction by adding hydraulic pressure. These problems were clarified to generate tensile stress in the adhesive (Ag paste) by adding hydraulic pressure and peeling a strain sensor from SUS housing. To overcome these problems, the stress in Ag paste was needed to keep compressive stress even when adding pressure. In this paper, a pressing mechanism is newly proposed to make compressive stress in Ag paste and assemble on the pressure sensor. First, to press the strain sensor to the SUS housing, a lid was bonded on the strain sensor with wafer‐level‐packaging (WLP) technique. Next, a pressing mechanism was designed to assemble the miniaturized pressure sensor. The pressing mechanism was composed of a cover, two coil springs, and a spring base with a pressing point. The pressing mechanism generates compressive stress to Ag paste even under high hydraulic pressure. The pressure sensor which implements the pressing mechanism has high‐pressure resistance and high reliability under the repetitive hydraulic pressure of 10 million times, without water leakage and sensitivity decrease.

Currently, self‐healing soft materials are increasingly applied in flexible electronics, such as intelligent responsive electronic skins and various soft pressure sensors. However, there still exist serious bottlenecks such as complex healing process, severe performance loss after healing, and limitations imposed by external environments, resulting in slow healing speed and deficiencies in healing performance. Liquid metal (LM), as an emerging self‐healing material, has been widely adopted in new‐generation electronics due to its unique fluidity at room temperature, high surface tension, excellent metallic conductivity, and resistance to extreme environments. Nevertheless, it also faces challenges including low mechanical strength, surface oxidation, complex packaging processes, etc. Researchers have achieved new breakthroughs after combining LM with self‐healing materials. This review will conduct an in‐depth analysis of the self‐healing capability and mechanisms of various LM‐based composites, and systematically discuss the common methods for inducing self‐healing and reliable characterization techniques. The challenges related to healing speed, efficiency, flexibility and conductivity reliability in electronics are expounded, together with the development opportunities. This provides important guidance for future flexible electronics fields such as self‐healing flexible circuits, neural interfaces, robot soft sensors, radiation‐resistant self‐sealing layers for spacecraft, etc.

Cold silicon piezoresistive strain gauge pressure sensors have several advantages over the conventional pressure measuring devices/systems used in cryogenics. A cryogenic pressure sensor calibration facility has been set up at Pressure Systems, Inc. for calibrating cryogenic pressure sensors in the temperature range 1.5 – 400 K. This paper presents a brief review of this calibration facility together with the low temperature characteristics of the cryogenic piezoresistive pressure sensors. The pressure sensors calibrated so far include 202 k Pa absolute (30 psia), 202 k Pa differential (30 psid) and 1013 k Pa absolute (150 psia) range devices. These calibrations are linear and are repeatable to within +/− 0.1% and +/− 0.5% full scale outputs for 202 k Pa and 1013 k Pa range pressure sensors respectively.