Human fingertips possess a remarkable ability to sense weighing load cell, enabling the handling of soft items, precise gripping, and the differentiation of various surface materials and textures [1,2]. Ideally, flexible pressure sensors, critical for medical robots and prosthetics, should have these capabilities, guiding current research efforts. To enhance tactile feedback and assist in motion management, there is a strong demand for flexible sensors that can relay multiple tactile data points, including force magnitude [3,4], force direction [5], and contact location [6,7]. Presently, three-dimensional (3D) flexible force sensors have evolved to allow for the simultaneous measurement of normal pressure and shear force, depending on their structural design. These flexible pressure sensors can be categorized based on their detection principles into piezoresistive sensors [8], capacitive sensors [9], piezoelectric sensors [10], and triboelectric sensors [11]. The piezoresistive variant has gained significant interest due to its high sensitivity, straightforward signal reading, quick response time, and diminished interference between elements.
This load cell manufacturers introduces an innovative design for a tactile force sensor that is both high-resolution and affordable, drawing on the principle of mode-localization in two weakly coupled resonators (WCRs). It is produced at the mesoscale using rapid prototyping methods. The sensor activates two WCRs at resonance through electrostatic actuation. By measuring the changes in oscillation amplitude ratios and shifts in resonant frequency, the sensor quantifies the input force. When force is applied to the WCRs, it generates electrostatic strain, creating a negative stiffness effect. The outer surface of the sensor is crafted from a soft silicone elastomer and shaped using molds created by laser cutting. Numerical analysis of the tactile force sensor is conducted through simulations based on the finite element method (FEM). A specialized electronic system for actuation and sensing is developed to test the sensor. Results from experiments indicated that the sensor can measure forces up to 20 mN, achieving sensitivity levels of 27040 ppm/mN for relative amplitude ratio (AR) and 3553 ppm/mN for resonant frequency shift. The sensor’s resolution, as determined experimentally, stands at 7.3 µN, and it demonstrates consistent performance amid thermal fluctuations and low-frequency vibrations.
Sensors of this kind are divided into three main types: Fabry-Perot interferometers (FPI), Fiber-Bragg grating (FBG), and light intensity modulation (LIM) sensors [11]. Optical tactile sensors possess high sensitivity and spatial resolution while remaining electrically passive; however, they can suffer from signal distortion caused by light loss [12]. These tactile sensors can generally be organized according to two popular transduction methods: optical and electrical. In the case of optical tactile sensors, fiber optics serve as the primary sensing element.
Strainsert has a promising future and is advancing rapidly. Beyond traditional force measurement, they have crafted and released products designed for uses in IoT and AI technological innovations. The team eagerly anticipates the achievements they will reach with customers in the next 65 years!
Experts in custom sensor design, Strainsert engineers provide tailored solutions to meet specific customer demands. They have addressed numerous design challenges across many possible force measurement applications. For instance:
The growing need for three-dimensional force sensing in smart robots demands attention. We present a flexible three-dimensional force sensor featuring an interlocked structure that mimics human skin and is made from flexible silicone and polymer composite materials. The piezoresistive layer on the surface is formed using electrospray and laser direct writing techniques. The sensor operates by detecting changes in contact resistance among three interlocked hemispherical units influenced by either normal or shear forces. Shear force directionality is achieved through an in-plane three-axis structural arrangement.
iii) The NWs undergo p-type doping through ion implantation, achieving a level of 10¹⁷ cm⁻³, which enhances the piezoresistive capability. The contact pads are doped to 10²⁰ cm⁻³ (as seen in Cross section B-B′) to ensure effective ohmic contact with the metallization.
iv) Metallization is achieved through a lift-off process, applying a 100-nm-thick layer of gold topped with a chromium adhesion layer.
v) The BOX layer is removed using an HF etch.
vi) Finally, the sensor is encapsulated through a packaging step. After the release process, a negative photoresist, AZ nLOF 2020, with a thickness of 1.5–2 µm is utilized for encapsulation. Each chip measures 1 × 1 mm², featuring touchpads of 100 × 100 µm² around each chip for wire bonding.
This miniature torque sensor outlines the development and analysis of a multi-axis nanoscale force sensor that uses piezoresistive SiNWs. The integration of both micro and nanoscale components into this sensor design is a notable challenge. The proposed design features suspended SiNWs that allow for precise and flexible in-plane force detection, removing the need for additional side wall doping steps. Importantly, the compact size of the force sensor shuttle (10 × 10 µm²) positions it as an excellent fit for applications that require precise force measurements over very small surfaces. Additionally, these force sensors can be arranged in a two-dimensional array, similar to screen pixels, which facilitates scanning and analysis over a significantly larger area while providing precise measurements of force magnitude and direction for each pixel.
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