Magnetic sensor and method for making and using same

Abstract

Described herein are magnetic sensors (e.g., force sensors), and methods of making and using same, that can employ soft magnetic composites (e.g., composites including a population of magnetic particles dispersed within an elastomeric resin) paired with magnetometers. These sensors can overcome many of the traditional shortcomings that have hindered the effectiveness of existing compression sensors in certain applications, including large size, lack of three-dimensional sensing capability, the need for the sensor to incorporate rigid components, and / or signal quality issues associated with the orientation or deformation of soft composites under compression.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Application No. 63 / 195,115, filed May 31, 2021, which is incorporated by reference in its entirety.

[0002] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT This disclosure was made with government support under Grant No. DE-NA-0002893 awarded by the Department of Energy. The U.S. Government has certain rights in this disclosure. [Background technology]

[0003] Soft compressive sensors are being pursued in diverse fields including soft robotics (Rosle et al. 2019), healthcare (Biswas et al. 2020), biomechanics (Low et al. 2015), and more. Sensors constructed from silicone rubber or other soft materials create a flexible interface, allowing for event detection while protecting the underlying surface. For example, wearable sensors may utilize soft materials to render the device imperceptible to the wearer. One type of sensor concept utilizes a rigid permanent magnet embedded within silicone or silicone-magnetic powder composites paired with a magnetometer (Wang et al. 2016a; Mirzanejad and Agheli 2019; Hellebrekers et al. 2019; Rosle et al. 2019).

[0004] Although such sensors may provide an inexpensive wireless sensor platform, existing designs are unable to adequately detect dynamic material compression events. Thus, improved sensor designs are needed. Summary of the Invention

[0005] Described herein are magnetic sensors (e.g., force sensors) and methods of making and using the same. The magnetic sensors can use soft magnetic composites (e.g., composites including a population of magnetic particles dispersed within an elastomeric resin) paired with magnetometers. These sensors can overcome many of the traditional shortcomings that have hindered the effectiveness of existing compression sensors in certain applications, including large size, lack of three-dimensional sensing capability, the need for the sensor to incorporate rigid components, and / or signal quality issues associated with the orientation or deformation of soft composites under compression. As a result, the sensors described herein can be utilized in wearable technology applications.

[0006] Provided herein is a force sensor including a magnetic actuator having a proximal end and a distal end, a magnetometer operably positioned proximate the distal end of the magnetic actuator, and a spacer disposed between the magnetometer and the distal end of the magnetic actuator, thereby creating a standoff distance between the magnetometer and the distal end of the magnetic actuator. In some embodiments, the magnetic actuator includes an elastomeric resin and a population of magnetic particles dispersed within the elastomeric resin. In some embodiments, the spacer can be an elastomeric spacer.

[0007] In some embodiments, the force sensor includes a magnetic actuator having a proximal end and a distal end, the magnetic actuator including an elastomeric resin and a population of magnetic particles dispersed within the elastomeric resin; a magnetometer operably positioned proximate the distal end of the magnetic actuator; and a spacer disposed between the magnetometer and the distal end of the magnetic actuator, thereby creating a standoff distance between the magnetometer and the distal end of the magnetic actuator.

[0008] In some embodiments, the force sensor includes a magnetic actuator having a proximal end and a distal end, a magnetometer operably positioned proximate the distal end of the magnetic actuator, and an elastomeric spacer disposed between the magnetometer and the distal end of the magnetic actuator, thereby creating a standoff distance between the magnetometer and the distal end of the magnetic actuator.

[0009] In some embodiments, the force sensor can include a magnetic actuator having a proximal end and a distal end, a magnetometer operably positioned proximate the distal end of the magnetic actuator, and an elastomeric housing surrounding at least a portion of the magnetic actuator and extending beyond the distal end of the magnetic actuator, thereby creating a standoff distance between the magnetometer and the distal end of the magnetic actuator. In some embodiments, the elastomeric housing is not disposed between the magnetometer and the distal end of the magnetic actuator.

[0010] In some embodiments, the magnetic actuator and magnetometer can be sized relative to one another so that a force applied to the magnetic actuator in the xy plane relative to the magnetometer, along the z-axis relative to the magnetometer, or any combination thereof, produces a magnetic field response that is increasing and proportional, or decreasing and proportional, or decreasing and proportional to the applied force.

[0011] In some embodiments, the magnetic actuator and magnetometer can be sized relative to one another so that under a force applied along the z-axis relative to the magnetometer, compression of the magnetic actuator produces a magnetic field response that is increasing and proportional, or decreasing and proportional, or decreasing and proportional to the applied force.

[0012] In some embodiments, the magnetic actuator and magnetometer can be sized relative to each other so that under an applied force in the xy plane relative to the magnetometer, the shear of the magnetic actuator produces a magnetic field response that is increasing and proportional, or decreasing and proportional, or decreasing and proportional to the applied force.

[0013] In some embodiments, the force sensor can include two or more magnetic actuators, each magnetic actuator having a proximal end and a distal end, a magnetometer operably positioned proximate the distal end of the one or more magnetic actuators, and a spacer disposed between the magnetometer and the distal end of the one or more magnetic actuators, thereby creating a standoff distance between the magnetometer and the distal end of the one or more magnetic actuators.

[0014] In some embodiments, the two or more magnetic actuators and the magnetometer are sized relative to each other so that a force applied to the two or more magnetic actuators in the xy plane relative to the magnetometer, along the z-axis relative to the magnetometer, or any combination thereof, generates a magnetic field response that is increasing and proportional, or decreasing and proportional, or decreasing and proportional to the applied force. In some embodiments, each of the magnetic actuators is adjacent to each other. In some embodiments, the magnetometer is operably positioned proximate to a distal end of the magnetic actuator. In some embodiments, the sensor further comprises a rigid spacer disposed between the magnetometer and the distal end of the two or more magnetic actuators, thereby creating a distance between the magnetometer and the distal end of the two or more magnetic actuators, the rigid spacer being formed from a rigid material such as hard plastic, wood, glass, non-magnetic metal, or a material having a Shore A hardness of more than 70 and / or a Shore D hardness of more than 10.

[0015] It will be appreciated that embodiments using a rigid spacer can be used, for example, for remote sensing, or for sensing through a wall or across empty air space. One example is sensing through a protective casing, where the magnetometer is outside the casing and the elastomeric portion of the sensor is inside the casing. In these examples, the wall of the casing can function as the rigid spacer. In this way, the rigid spacer need not be an exclusive part of the sensor. In some embodiments, a portion of the spacer can be void space (e.g., air space) as well.

[0016] In some embodiments, the force sensor can include a magnetic actuator having a proximal end and a distal end, two or more magnetometers operably positioned proximate the distal end of the magnetic actuator, and a spacer disposed between the two or more magnetometers and the distal end of the magnetic actuator, thereby creating a standoff distance between the one or more magnetometers and the distal end of the magnetic actuator.

[0017] In some embodiments, the magnetic actuator and the two or more magnetometers are sized relative to one another so that a force applied to the magnetic actuator in the xy plane for the two or more magnetometers, along the z-axis for the two or more magnetometers, or any combination thereof, produces a magnetic field response that is increasing and proportional, or decreasing and proportional, to the applied force. In some embodiments, each of the magnetometers is adjacent to one another.

[0018] In some embodiments, the magnetic actuator may have a substantially circular horizontal cross-sectional shape, a cylindrical shape, or a substantially conical shape, hi some embodiments, the standoff distance may be greater than 0 mm to 5 mm.

[0019] In some embodiments, the spacer may be formed from an elastomeric resin, a rigid material, or any combination thereof. In some embodiments, when the spacer is formed from an elastomeric resin, the spacer comprises a portion of the housing that partially or completely surrounds the magnetic actuator. In some embodiments, the elastomeric spacer comprises a portion of the housing that partially or completely surrounds the magnetic actuator. In some embodiments, the elastomeric resin further comprises a non-magnetic filler, such as silica particles. In some embodiments, the sensor may further comprise a rigid spacer disposed between the magnetometer and the distal end of the elastomeric spacer, thereby creating a standoff distance between the magnetometer and the distal end of the elastomeric spacer, the rigid spacer being formed from a rigid material, such as hard plastic, wood, glass, a non-magnetic metal, or a material having a Shore A hardness of greater than 70 and / or a Shore D hardness of greater than 10. In some other embodiments, the sensor further comprises a rigid spacer disposed between the magnetometer and the distal end of the elastomeric housing, thereby creating a standoff distance between the magnetometer and the distal end of the elastomeric housing, the rigid spacer being formed from a rigid material such as hard plastic, wood, glass, a non-magnetic metal, or a material having a Shore hardness greater than 70 A or greater than 10 D.

[0020] In some embodiments, the magnetic particles comprise magnetic microparticles. In some embodiments, the magnetic microparticles have an average particle size of 1 micrometer to 150 micrometers (e.g., 1 micrometer to 50 micrometers). In some embodiments, the magnetic particles comprise magnetic nanoparticles. In some embodiments, the magnetic nanoparticles have an average particle size of 50 nm to less than 1 micrometer, such as 50 nm to 500 nm. In some embodiments, the magnetic particles comprise anisotropic magnetic particles.

[0021] In some embodiments, the magnetic particles are present in the elastomeric resin in an amount of 0.1% to 90% by weight based on the total weight of the elastomeric resin, for example, 50% to 90% by weight, 40% to 80% by weight, 30% to 70% by weight, 20% to 60% by weight, 15% to 50% by weight, 0.1% to 50% by weight, 0.1% to 40% by weight, 0.1% to 30% by weight, 0.1% to 20% by weight, 0.1% to 10% by weight, 0.1% to 5% by weight, 0.1% to 2.5% by weight, or 0.1% to 1% by weight based on the total weight of the elastomeric resin.

[0022] In some embodiments, the dipoles of the magnetic particles are aligned and / or oriented within the magnetic actuator, hi some embodiments, the dipoles of the magnetic particles are aligned and / or oriented within the magnetic actuator when the magnetic actuator is compressed 10%-60% under an applied force.

[0023] In some embodiments, the sensor further comprises a microcontroller, a processor, or a combination thereof operably coupled to the magnetometer and configured to calculate the force applied to the magnetometer based on the measurement of the change in magnetic field strength.

[0024] The details of one or more embodiments of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will become apparent from the description and drawings, and from the claims. [Brief description of the drawings]

[0025] [Figure 1]Shown are A) the 3D printed forms used to create the silicone sensor, B) the magnetometer used in the study, and C) an example of several magnetic sensors, including cylindrical and conical magnetic elements of varying diameter and height. Depiction of the magnetization of the sensor between two magnets while D) unstrained and E) distorted by the magnetic attraction. Photographs of the experimental setup for F) compression and G) shear tests. All sensor designs have the magnetic element positioned away from the magnetometer, so that there is a pure rubber gap between the magnetic element and the magnetometer. [Figure 2A] 14 shows the Z-axis magnetic field response plotted against time during compression testing of a 2×4 cylindrical sensor. The graph displays data from tests performed with the sensor magnetized while unstrained and while strained by the attractive force of a magnet. [Figure 2B] 14 shows the Z-axis magnetic field response plotted against time during a compression test of a 2×2 cylinder. The graph displays data from tests performed with the sensor magnetized while unstrained and while strained by the attractive force of the magnet. [Figure 2C] 1 shows the Z-axis magnetic field response plotted against time during a compression test of a 3×3 cylinder. The graph displays data from tests performed with the sensor magnetized while unstrained and while strained by the attractive force of a magnet. [Figure 2D] 14 shows the Z-axis magnetic field response plotted against time during compression testing of a 5×4 cylindrical sensor. The graph displays data from tests performed with the sensor magnetized while unstrained and while strained by the attractive force of a magnet. [Figure 3A] 13 shows the magnetic field response in the X, Y and Z axes plotted against time during shear testing of a sensor with a 2×4 cylindrical sensor. [Figure 3B] 13 shows the magnetic field response in the X, Y and Z axes plotted against time during compression testing of a sensor with a 2×4 cylindrical sensor. [Figure 3C]13 shows the magnetic field response in the X, Y and Z axes plotted against time during shear testing of a sensor with a 2×4 cylindrical sensor. [Figure 3D] 13 shows the magnetic field response in the X, Y and Z axes plotted against time during compression testing of a sensor having a 4×4 cylindrical sensor. [Figure 4A] 1 shows the Z-axis magnetic field response plotted against displacement during increasing compression stages of a compression test for a 2×4 cylindrical sensor, and a 5×4 cylindrical and a 3×3 conical sensor. [Figure 4B] 1 shows the Z-axis magnetic field response plotted against force during increasing compression stages of a compression test for a 2×4 cylindrical sensor, as well as a 5×4 cylindrical and a 3×3 conical sensor. [Figure 4C] 4 is a plot showing the relationship between peak magnitude and volume of a magnetic element of a sensor. [Figure 4D] 1 is a plot showing the relationship between linearity in terms of force and the volume of the magnetic element of the sensor. [Figure 5A] 13 shows the magnetic field response in the Z axis plotted against time during compression testing of 2×4 cylindrical sensors containing 50%, 67%, and 80% magnetic filler. [Figure 5B] 1 shows the magnetic field response in the Z axis plotted against time during compression testing of 2.5×4 cylindrical sensors containing 67% and 80% magnetic filler. [Figure 6A] Shown is the magnetic field response versus strain during a compression test of a 2 x 4 cylindrical sensor (total height 4 mm) with a 0-2 mm silicone spacer between the sensor and magnetometer under test. [Figure 6B] Shown is the magnetic field response versus strain during a compression test of a 3 × 4 cylindrical sensor (total height 4 mm) with a 0–2.5 mm silicone spacer between the sensor and magnetometer under test. [Figure 6C] 13 shows an image of the setup for testing the effect of additional standoff distance between the sensor and magnetometer via a rigid plastic spacer, and an inset graph as an example of data collected during these tests. [Figure 6D]Plot of magnetic field response versus strain during compression testing of a 3 x 4 cylindrical sensor (total height 5 mm) with a 0-2 mm rigid plastic spacer between the sensor and magnetometer under test. [Figure 7] Illustrates the deformation of sensors with magnetic elements of 2 mm diameter (AB) and 3 mm diameter (CD) while compressed on top of a surface mounted MLX90393 magnetometer as in this study. The 2 mm diameter of the magnetic element in the sensor in A is shown to increase to 3.36 mm in B when the sensor is compressed to 50% strain. The 3 mm diameter of the magnetic element in the sensor in C is shown to increase to 4.53 mm in D when the sensor is compressed to 50% strain. [Figure 8] Shown are A) an image where the sensor is integrated into the existing padding of a football helmet, B) an image of the helmet after integration of the sensor and implementation of the microcontroller module, and C) an image of a helmet-force plate impact test performed at a slight rightward angle. D) X and Z axis of the raw force plate data, the force plate data after downsampling, and force (N) plotted against time from the in-helmet sensor data from the helmet-force plate impact shown in C. [Figure 9A] 1 shows force (N) plotted against time from the Z-axis of the in-helmet sensor and force plate during helmet-force plate impacts from primarily straight-on angles. [Figure 9B] 13 shows force (N) plotted against time from the X-axis of the in-helmet sensor and force plate during a helmet-force plate impact from a rightward angle. [Figure 9C] Shown is force (N) plotted against time from a leftward angle. [Figure 10A] 1 shows force (N) and compressive displacement (mm) plotted against time for an exemplary sensor. 2.5 mm×4 mm cylindrical 80% filler sensor performance calibration formula. [Figure 10B] 1 shows force (N) and compressive displacement (mm) plotted against time for an exemplary sensor. 2.5 mm×4 mm cylindrical 80% filler sensor performance data is shown. [Figure 11] Illustrate piston design. [Figure 12] Shows magnetic field strength plotted against time for a magnetized 5x4 normal or z-axis sensing (large volume example) with approximately 40% distortion or distortion. Magnitude increases from 422uT to 766uT (positive direction only). Positive response only for the first approximately 1mm of compression. Large magnetic volumes cause signal quality issues. [Figure 13] 1 shows the magnetic field strength plotted against time for a magnetized 2×4 normal or z-axis sense with or without distortion. The magnitude increases from 1684 uT to 2747 uT. [Figure 14] 13 shows an image of a setup for testing the response of a force sensor to different vertical and horizontal standoff distances when force is applied in a vertical and / or horizontal orientation. [Figure 15A] Magnetic field response plotted against time for a 10x5mm cylindrical cushion with a 2.5x4 cylindrical magnetic element (80% Nd) using different vertical remote distances from 2mm to 10mm. [Figure 15B] 1 shows the magnetic field response plotted against time for a 10×5 mm cylindrical cushion with a 2.5×4 cylindrical magnetic element (80% Nd) using a vertical standoff distance of 10 mm. [Figure 16] Magnetic field response plotted against time for a 2.5 x 4 mm, 80% Nd magnetic element using different horizontal standoff distances for gaps from the rubber cushion to the magnetometer substrate of 2 to 7 mm (true gap is 5.75 to 10.75 mm from the magnetometer to the magnetic element). [Figure 17] Figure 1 shows the magnetic field response plotted against time for a 5 x 4 mm cylindrical, 80% Nd magnetic element using different horizontal standoff distances for a gap of 2 mm to 7 mm from the rubber cushion to the magnetometer substrate (true gap is 5.75 to 10.75 mm from the magnetometer to the magnetic element). Within both graphs, one data plot immediately returns to baseline. This is attributable to failure of the mechanical testing unit, but demonstrates minimal time lag between removal of force from the sensor and the sensor's return to baseline signal. [Figure 18]1 shows the magnetic field response plotted against time for a piston design setup with a 10×5 mm cylindrical cushion and a 2.5×4 mm cylindrical magnetic element (80% Nd) when force is applied in a vertical orientation with no gap. [Figure 19] Figure 1 shows the magnetic field response plotted against time for a piston design setup with a 10 x 5 mm cylindrical cushion and a 2.5 x 4 mm cylindrical magnetic element (80% Nd) when force is applied in a vertical orientation at different vertical standoff distances from 2 mm to 5 mm. [Figure 20] 1 shows the magnetic field response plotted against time for a rubber cushion of 3 mm total height and a cylindrical magnetic element of 2-3 mm height with a diameter of 2 mm. [Figure 21] 1 shows an image of an exemplary 3D printed magnetic sensor. [Figure 22] 1 shows images of exemplary 3D printed magnetic sensors with different dimensions including 4×4 mm, 3×4 mm, and 2.4×4 mm. [Figure 23] FIG. 13 shows the magnetic field response plotted against time for 3D printed magnetic sensors with different dimensions including 4×4 mm, 3×4 mm, and 2.4×4 mm. [Figure 24A]1 illustrates a vertical cross-section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In this embodiment, the magnetic actuator (101) has a substantially cylindrical shape. In some embodiments, the plate (106) may be absent. [Figure 24B]1 illustrates a horizontal cross section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In this embodiment, the magnetic actuator (101) has a substantially cylindrical shape. In some embodiments, the plate (106) may be absent. [Figure 25A]1 illustrates a vertical cross-section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In this embodiment, the magnetic actuator (101) has a substantially rectangular cubic shape. In some embodiments, the plate (106) may be absent. [Figure 25B]1 illustrates a horizontal cross section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In this embodiment, the magnetic actuator (101) has a substantially rectangular cubic shape. In some embodiments, the plate (106) may be absent. [Figure 26A]1 illustrates a vertical cross-section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In this embodiment, the magnetic actuator (101) has a substantially conical shape. In some embodiments, the plate (106) may be absent. [Figure 26B]1 illustrates a horizontal cross section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In this embodiment, the magnetic actuator (101) has a substantially conical shape. In some embodiments, the plate (106) may be absent. [Figure 27A]1 illustrates a vertical cross-section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In this embodiment, the magnetic actuator (101) has a substantially spherical or ovoid shape. In some embodiments, the plate (106) may be absent. [Figure 27B]1 illustrates a horizontal cross section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In this embodiment, the magnetic actuator (101) has a substantially spherical or ovoid shape. In some embodiments, the plate (106) may be absent. [Figure 28]1 illustrates a vertical cross-section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In this embodiment, the maximum cross-sectional dimension of the elastomeric housing (111) is greater than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In some embodiments, plate (106) may be absent. [Figure 29]1 illustrates a vertical cross-section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, the elastomeric housing (104) does not completely surround the magnetic actuator (101). However, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that the portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In some embodiments, the plate (106) may be absent. [Diagram 30]1 illustrates a vertical cross section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, the elastomeric housing (104) does not completely surround the magnetic actuator (101). The elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), thereby creating a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this embodiment, no elastomeric housing is disposed in a region (112) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In Figure 30, the elastomeric housing (104) does not extend beyond and surround the proximal end (107) of the magnetic actuator (101). However, in some embodiments, the elastomeric housing (104) extends beyond and surrounds the proximal end (107) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In some embodiments, the plate (106) may be absent. [Diagram 31]1 shows a vertical cross-sectional view of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, an elastomeric spacer (105) is disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. [Diagram 32]1 illustrates a vertical cross-section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that the portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a first portion (114) of the standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The sensor further includes a rigid spacer (113) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101), such that the rigid spacer (113) creates a second portion (115) of the standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In some embodiments, the plate (106) may be absent. [Diagram 33]1 shows a vertical cross section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, two magnetometers (102A and 102B) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometers (102A and 102B) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometers (102A and 102B) and the distal end (108) of the magnetic actuator (101). In some embodiments, the plate (106) may be absent. In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional distance (117) between the two magnetometers (102A and 102B) when the magnetic actuator (101) is not subjected to an applied force. Using this sensor, rotation can be measured based on the signals detected by the two magnetometers in the xy axis. [Diagram 34]1 illustrates a vertical cross section of an exemplary force sensor (100) including two magnetic actuators (101A and 101B), each having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operatively positioned proximate the distal ends (108) of the two magnetic actuators (101A and 101B), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal ends (108) of the magnetic actuators such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal ends (108) of the two magnetic actuators (101A and 101B). The elastomeric spacer (105) creates a standoff distance (103) between the magnetometer (102) and the distal ends (108) of the two magnetic actuators (101A and 101B). In some embodiments, the plate (106) may be absent. In this example, the maximum cross-sectional dimension of the magnetometer (110) is less than the maximum cross-sectional distance (116) between the two magnetic actuators (101A and 101B) when the magnetic actuators are not subjected to an applied force. This sensor can be used to determine the location of a pinpoint force applied to the top surface of the elastomeric housing. [Diagram 35]1 illustrates a vertical cross-section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that the portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a first portion (114) of the standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The sensor further includes a rigid spacer (113) disposed between the magnetometer (102) and the distal end (108) of the magnetic actuator (101), such that the rigid spacer (113) creates a second portion (115) of the standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The sensor further includes a gap (119) between the magnetometer (102) and the rigid spacer (113), such that the gap (119) creates a third portion (118) of the standoff distance (103) between the magnetometer (102) and the distal end (108) of the magnetic actuator (101). The gap (119) may be an air gap (e.g., space) or may be filled with any other material, such as a fabric. In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In some embodiments, the plate (106) may be absent. [Diagram 36]1 illustrates a vertical cross-section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operatively positioned substantially adjacent to and parallel to the magnetic actuator (101), and a plate (106). In this example, a portion of the elastomeric housing (104) extends beyond the distal end (108) of the magnetic actuator (101), such that a portion of the elastomeric housing forms an elastomeric spacer (105) disposed between the plate (106) and the distal end (108) of the magnetic actuator (101). The elastomeric spacer (105) creates a standoff distance (103) between the plate (106) and the distal end (108) of the magnetic actuator (101). [Figure 37] 1 illustrates a vertical cross-section of an exemplary force sensor (100) including a magnetic actuator (101) having a proximal end (107) and a distal end (108), an elastomeric housing (104) formed from an elastomeric resin, a magnetometer (102) operably positioned proximate the distal end (108) of the magnetic actuator (101), and a plate (106). In this example, the magnetic actuator (101) abuts the magnetometer (102) (i.e., there is no standoff distance between the magnetometer (102) and the distal end (108) of the magnetic actuator (101)). In this example, the maximum cross-sectional dimension of the magnetic actuator (109) is less than the maximum cross-sectional dimension of the magnetometer (110) when the magnetic actuator (101) is not subjected to an applied force. In some embodiments, the plate (106) may be absent. [Figure 38A] An image of a flat flexible magnetometer circuit and controller chip is shown. [Figure 38B] shows an image of a sensor formed by combining a silicone sensor component (magnetic actuator enclosed in an elastomer housing) with a flat flexible magnetometer circuit. [Figure 38C]13 is a plot showing magnetic field response versus time during several repeated stepwise 1 mm compression cycles performed on a sensor using a flat flexible magnetometer circuit. [Figure 39] Includes images of qualitative silicone adhesive bond testing (top left and top right) as well as images of three sensors constructed using three different silicone adhesives (SILPOXY, MED4-4220, and MED3-4013) to bond the silicone sensor component (magnetic actuator enclosed in an elastomer housing) to the magnetometer circuit board. All three of these adhesives were found to have sufficient bond strength to bond the silicone sensor component to the magnetometer circuit board. [Diagram 40] 13 is a plot spreading magnetic field response versus time during 1 mm step compression testing of sensors formed by combining silicone sensor components with a flat flexible magnetometer circuit using various silicone-based adhesives. [Diagram 41] 1 is a three-dimensional rendering of an exemplary flat flexible magnetometer circuit and controller chip.

[0026] Like reference symbols in the various drawings indicate like elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Although several embodiments of the present disclosure have been described, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.

[0028] definition To facilitate understanding of the disclosure set forth herein, several terms are defined below. Unless otherwise defined, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Publications cited herein and the materials for which they are cited are specifically incorporated by reference.

[0029] General definition As used herein, the term "comprising" and variations thereof are used synonymously with the term "including" and variations thereof, and are open and non-limiting terms. Although the terms "comprising" and "including" have been used herein to describe various embodiments, the terms "consisting essentially of" and "consisting of" can be used in place of "comprising" and "including" to provide more specific embodiments of the present invention. Except as noted, all numbers expressing quantities of ingredients, reaction conditions, geometries, dimensions, and the like used in the specification and claims should at least be understood and interpreted in light of the number of large digits and ordinary rounding approaches, but not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims.

[0030] As used herein and in the claims that follow, the terms "comprise" (and forms, derivatives, or variations thereof, such as "comprising" and "comprises") and "include" (and forms, derivatives, or variations thereof, such as "including" and "includes") are inclusive (i.e., open-ended) and do not exclude additional elements or steps. For example, the terms "comprise" and / or "comprising" as used herein specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Thus, these terms not only cover the recited elements or steps, but may also include other elements or steps not expressly recited. Furthermore, as used herein, the use of terms such as "a," "an," and "the," when used in conjunction with elements, can mean "one," but is also consistent with the meanings of "one or more," "at least one," and "one or more." Thus, an element preceded by "a" or "an" does not, without further constraints, preclude the presence of additional identical elements.

[0031] The use of the term "about" applies to all numerical values, whether or not they are explicitly stated. This term generally refers to a range of numbers that one of ordinary skill in the art would consider a reasonable amount of deviation (i.e., having the same function or result) from the recited numerical values. For example, this term can be interpreted to include a deviation of ±10 percent of a given numerical value, as long as such deviation does not alter the end function or result of the value. Thus, a value of about 1% can be interpreted as being in the range of 0.9% to 1.1%. Furthermore, a range can be interpreted to include the start and end of the range. For example, a range of 10% to 20% (i.e., a range of 10% to 20%) can include 10% and can include 20%, and can include percentages of 10% to 20%, unless otherwise expressly stated herein.

[0032] Where combinations, subsets, groups, etc. of elements are disclosed (e.g., combinations of components in a composition or combinations of steps in a method), it is understood that although specific reference to each of the various individual and collective combinations and permutations of those elements may not be expressly disclosed, each is specifically contemplated and described herein.

[0033] Ranges may be expressed herein as from "about" one particular value and / or to "about" another particular value. "About" means within 5% of the value, for example, within 4, 3, 2, or 1% of the value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values ​​are expressed as approximations by use of the antecedent "about," it will be understood that the particular value forms another embodiment. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. It is understood that there are several values ​​disclosed herein, and that each value is also disclosed herein as "about" the particular value in addition to the value itself. For example, if the value "10" is disclosed, then "about 10" is also disclosed.

[0034] As used herein, the terms "may," "optionally," and "may optionally" are used interchangeably and are meant to include cases where a condition occurs as well as cases where a condition does not occur. Thus, for example, a statement that a formulation "may include an excipient" is meant to include cases where the formulation includes the excipient as well as cases where the formulation does not include the excipient.

[0035] By way of non-limiting illustration, examples of certain specific embodiments of the present disclosure are given below.

[0036] Force Sensors Exemplary force sensors are illustrated in FIGS. 24A-37, which are described in the description of the figures above.

[0037] Briefly, disclosed herein is a force sensor including a magnetic actuator having a proximal end and a distal end, a magnetometer operably positioned proximate the distal end of the magnetic actuator, and a spacer disposed between the magnetometer and the distal end of the magnetic actuator, thereby creating a standoff distance between the magnetometer and the distal end of the magnetic actuator. In some embodiments, the magnetic actuator includes an elastomeric resin and a population of magnetic particles dispersed within the elastomeric resin. In some embodiments, the spacer can be an elastomeric spacer.

[0038] In some embodiments, the force sensor includes a magnetic actuator having a proximal end and a distal end, the magnetic actuator including an elastomeric resin and a population of magnetic particles dispersed within the elastomeric resin; a magnetometer operably positioned proximate the distal end of the magnetic actuator; and a spacer disposed between the magnetometer and the distal end of the magnetic actuator, thereby creating a standoff distance between the magnetometer and the distal end of the magnetic actuator.

[0039] In some embodiments, the force sensor includes a magnetic actuator having a proximal end and a distal end, a magnetometer operably positioned proximate the distal end of the magnetic actuator, and an elastomeric spacer disposed between the magnetometer and the distal end of the magnetic actuator, thereby creating a standoff distance between the magnetometer and the distal end of the magnetic actuator.

[0040] In some embodiments, the force sensor can include a magnetic actuator having a proximal end and a distal end, a magnetometer operably positioned proximate the distal end of the magnetic actuator, and an elastomeric housing surrounding at least a portion of the magnetic actuator and extending beyond the distal end of the magnetic actuator, thereby creating a standoff distance between the magnetometer and the distal end of the magnetic actuator. In some embodiments, the elastomeric housing is not disposed between the magnetometer and the distal end of the magnetic actuator.

[0041] In some embodiments, the magnetic actuator and magnetometer can be sized relative to one another so that a force applied to the magnetic actuator in the xy plane relative to the magnetometer, along the z-axis relative to the magnetometer, or any combination thereof, produces a magnetic field response that is increasing and proportional, or decreasing and proportional, to the applied force.

[0042] In some embodiments, the magnetic actuator and magnetometer can be sized relative to one another so that under a force applied along the z-axis relative to the magnetometer, compression of the magnetic actuator produces a magnetic field response that is increasing and proportional, or decreasing and proportional, to the applied force.

[0043] In some embodiments, the force sensor includes two or more magnetic actuators, each magnetic actuator having a proximal end and a distal end, a magnetometer operably positioned proximate the distal end of the one or more magnetic actuators, and a spacer disposed between the magnetometer and the distal end of the one or more magnetic actuators, thereby creating a standoff distance between the magnetometer and the distal end of the one or more magnetic actuators.

[0044] In some embodiments, the two or more magnetic actuators and the magnetometer are sized relative to each other so that a force applied to the two or more magnetic actuators in the xy plane relative to the magnetometer, along the z-axis relative to the magnetometer, or any combination thereof, generates a magnetic field response that is increasing and proportional, or decreasing and proportional to the applied force. In some embodiments, each of the magnetic actuators is adjacent to each other. In some embodiments, the magnetometer is operably positioned proximate to a distal end of the magnetic actuator. In some embodiments, the sensor further comprises a rigid spacer disposed between the magnetometer and the distal end of the two or more magnetic actuators, thereby creating a distance between the magnetometer and the distal end of the two or more magnetic actuators, the rigid spacer being formed from a rigid material such as hard plastic, wood, glass, non-magnetic metal, or a material having a Shore A hardness of more than 70 and / or a Shore D hardness of more than 10.

[0045] In some embodiments, the force sensor can include a magnetic actuator having a proximal end and a distal end, two or more magnetometers operably positioned proximate the distal end of the magnetic actuator, and a spacer disposed between the two or more magnetometers and the distal end of the magnetic actuator, thereby creating a standoff distance between the one or more magnetometers and the distal end of the magnetic actuator.

[0046] In some embodiments, the magnetic actuator and the two or more magnetometers are sized relative to one another so that a force applied to the magnetic actuator in the xy plane for the two or more magnetometers, along the z-axis for the two or more magnetometers, or any combination thereof, produces a magnetic field response that is increasing and proportional, or decreasing and proportional to the applied force. In some embodiments, each of the magnetometers is adjacent to one another.

[0047] In some embodiments, the magnetic field response may increase by 5-20% less than proportional to the applied force.

[0048] In some embodiments, the magnetic actuator can have a maximum cross-sectional dimension that is less than the maximum cross-sectional dimension of the magnetometer when the magnetic actuator is not subjected to an applied force. The maximum cross-sectional dimension of the magnetic actuator can be 5% to 80% of the maximum cross-sectional dimension of the magnetometer when the magnetic actuator is not subjected to an applied force. In some embodiments, the magnetic actuator can have a maximum cross-sectional dimension that is less than the maximum cross-sectional dimension of the magnetometer when the magnetic actuator is compressed 40% under an applied force. In some embodiments, the maximum cross-sectional dimension of the magnetic actuator can be 50% to 90% of the maximum cross-sectional dimension of the magnetometer when the magnetic actuator is compressed 40% under an applied force.

[0049] In some embodiments, the magnetic actuator can have a maximum cross-sectional area that is less than the maximum cross-sectional area of ​​the magnetometer when the magnetic actuator is not subjected to an applied force. The maximum cross-sectional area of ​​the magnetic actuator can be 50%-90% of the maximum cross-sectional area of ​​the magnetometer when the magnetic actuator is not subjected to an applied force. In some embodiments, the magnetic actuator has a maximum cross-sectional area that is less than the maximum cross-sectional area of ​​the magnetometer when the magnetic actuator is compressed 40% under an applied force. In some embodiments, the maximum cross-sectional area of ​​the magnetic actuator is 50%-90% of the maximum cross-sectional area of ​​the magnetometer when the magnetic actuator is compressed 40% under an applied force.

[0050] In some embodiments, the magnetic actuator and magnetometer are sized relative to one another so that compression of the magnetic actuator under a window of applied force ranging from an applied force effective to compress the magnetic actuator by 5% to an applied force effective to compress the magnetic actuator by 40% produces a magnetic field response that increases and is proportional, or decreases and is proportional, to applied force over the window of applied force. In some embodiments, the magnetic actuator and magnetometer are sized relative to one another so that compression of the magnetic actuator under a window of applied force ranging from an applied force effective to compress the magnetic actuator by 3% to an applied force effective to compress the magnetic actuator by 20% produces a magnetic field response that increases and is proportional, or decreases and is proportional, to applied force over the window of applied force.

[0051] In some embodiments, a force applied to a magnetic actuator in an xy plane relative to the magnetometer generates a magnetic field response that is increasing and linear with respect to the applied force. In some embodiments, a force applied to a magnetic actuator along a z-axis relative to the magnetometer generates a magnetic field response that is increasing and linear with respect to the applied force. In some embodiments, a force applied to a magnetic actuator in an xy plane relative to the magnetometer generates a magnetic field response that is increasing and linear with respect to the applied force, and a force applied to a magnetic actuator along a z-axis relative to the magnetometer generates a magnetic field response that is increasing and linear with respect to the applied force.

[0052] In some embodiments, the magnetic actuator and the magnetometer can be sized relative to each other so that under an applied force in the xy plane relative to the magnetometer, the shear of the magnetic actuator produces a magnetic field response that is increasing and proportional, or decreasing and proportional, relative to the applied force. The magnetic actuator can have a maximum cross-sectional dimension that is smaller than the maximum cross-sectional dimension of the magnetometer when the magnetic actuator is not subjected to an applied force. In some embodiments, the maximum cross-sectional dimension of the magnetic actuator can be 5% to 80% of the maximum cross-sectional dimension of the magnetometer when the magnetic actuator is not subjected to an applied force. In some embodiments, the magnetic actuator can have a maximum cross-sectional dimension that is smaller than the maximum cross-sectional dimension of the magnetometer when the magnetic actuator is sheared 40% under an applied force. In some embodiments, the maximum cross-sectional dimension of the magnetic actuator can be 50% to 90% of the maximum cross-sectional dimension of the magnetometer when the magnetic actuator is sheared 40% under an applied force.

[0053] In some embodiments, the magnetic actuator can have a maximum cross-sectional area that is less than the maximum cross-sectional area of ​​the magnetometer when the magnetic actuator is not subjected to an applied force. The maximum cross-sectional area of ​​the magnetic actuator can be 50%-90% of the maximum cross-sectional area of ​​the magnetometer when the magnetic actuator is not subjected to an applied force. In some embodiments, the magnetic actuator has a maximum cross-sectional area that is less than the maximum cross-sectional area of ​​the magnetometer when the magnetic actuator is sheared 40% under an applied force. In some embodiments, the maximum cross-sectional area of ​​the magnetic actuator is 50%-90% of the maximum cross-sectional area of ​​the magnetometer when the magnetic actuator is sheared 40% under an applied force.

[0054] In some embodiments, the magnetic actuator and magnetometer are sized relative to each other so that the magnetic actuator shear under a window of applied force ranging from an applied force effective to induce a 5% magnetic actuator shear strain to an applied force effective to induce a 40% magnetic actuator shear strain produces a magnetic field response that increases and is proportional, or decreases and is proportional, to the applied force over the applied force window. In some embodiments, the magnetic actuator and magnetometer are sized relative to each other so that the magnetic actuator shear under a window of applied force ranging from an applied force effective to induce a 3% magnetic actuator shear strain to an applied force effective to induce a 20% magnetic actuator shear strain produces a magnetic field response that increases and is proportional, or decreases and is proportional, to the applied force over the applied force window.

[0055] In some embodiments, the magnetic actuator can have a maximum cross-sectional dimension between 1 mm and 25 mm, for example between 1 mm and 5 mm, between 1 mm and 10 mm, between 1 mm and 15 mm, between 1 mm and 20 mm, between 5 mm and 20 mm, between 5 mm and 15 mm, between 10 mm and 25 mm, or between 10 mm and 20 mm.

[0056] In some embodiments, the magnetic actuator may be substantially circular in horizontal cross-section, cylindrical in shape, or substantially conical in shape. In some embodiments, the magnetic actuator has a substantially circular horizontal cross-section. In some embodiments, the magnetic actuator has a substantially cylindrical shape. In some embodiments, the magnetic actuator has a substantially conical shape.

[0057] In some embodiments, the standoff distance can be greater than 0 mm to 5 mm, such as greater than 0 mm to 1.5 mm, greater than 0 mm to 3 mm, greater than 1 mm to 5 mm, greater than 1 to 3 mm, or greater than 2 mm to 5 mm. In some embodiments, the standoff distance can be selected to provide a measurable signal, such as a magnetic field response of greater than 100 μT at an applied force. In some embodiments, there may be no standoff distance.

[0058] In some embodiments, the spacer may be formed from an elastomeric resin, a rigid material, or any combination thereof. In some embodiments, the spacer may be formed from an elastomeric resin. In some embodiments, the spacer may be an elastomeric spacer.

[0059] In some embodiments, the elastomeric housing is formed from an elastomeric resin.In some embodiments, the elastomeric spacer can be formed from an elastomeric resin.

[0060] In some embodiments, the spacer can be formed from a rigid material. In some embodiments, when the spacer is formed from an elastomeric resin, the spacer comprises a portion of a housing that partially or completely surrounds the magnetic actuator. In some embodiments, the elastomeric spacer comprises a portion of a housing that partially or completely surrounds the magnetic actuator.

[0061] In some embodiments, the elastomer resin further comprises a non-magnetic filler such as silica particles. In some embodiments, the elastomer resin comprises a crosslinkable composition such as a crosslinkable silicone composition. In some embodiments, the elastomer resin comprises (A) a first organosilicon compound having at least two ethylenically unsaturated moieties per molecule, and optionally (B) one or more additional organosilicon compounds. In some embodiments, the sensor can further comprise a rigid spacer disposed between the magnetometer and the distal end of the elastomer spacer, thereby creating a standoff distance between the magnetometer and the distal end of the elastomer spacer, the rigid spacer being formed of a rigid material such as hard plastic, wood, glass, non-magnetic metal, or a material having a Shore A hardness of more than 70 and / or a Shore D hardness of more than 10. In some other embodiments, the sensor further comprises a rigid spacer disposed between the magnetometer and the distal end of the elastomeric housing, thereby creating a standoff distance between the magnetometer and the distal end of the elastomeric housing, the rigid spacer being formed from a rigid material such as hard plastic, wood, glass, a non-magnetic metal, or a material having a Shore hardness greater than 70 A or greater than 10 D.

[0062] In some embodiments, the sensor further comprises a microcontroller, a processor, or a combination thereof operably coupled to the magnetometer and configured to calculate the force applied to the magnetometer based on the measurement of the change in magnetic field strength.

[0063] Composite materials forming magnetic actuators As discussed above, the magnetic actuator can be formed from a composite material that includes an elastomeric resin and a population of magnetic particles (eg, anisotropic magnetic particles) dispersed within the elastomeric resin.

[0064] magnetic particles The magnetic particles can be any suitable magnetic particles.

[0065] In some embodiments, the magnetic particles include magnetic microparticles. The microparticles can be of any shape and have one or more dimensions ranging from 1 micrometer to 150 micrometers (e.g., 1 micrometer to 100 micrometers, or 1 micrometer to 50 micrometers). In some embodiments, all dimensions can range from 1 micrometer to 150 micrometers (e.g., 1 micrometer to 100 micrometers, or 1 micrometer to 50 micrometers).

[0066] In some embodiments, the magnetic particles can include nanoparticles. As used herein, the term "nanoparticle" generally refers to a particle of any shape having one or more dimensions ranging from 1 nm up to, but not including, 1 micrometer.

[0067] In some embodiments, the population of magnetic particles is a monodisperse population of magnetic particles. In other embodiments, the population of magnetic particles is a polydisperse population of anisotropic magnetic particles. In some cases where the population of magnetic particles is polydisperse, more than 50% of the particle size distribution, more preferably 60% of the particle size distribution, and most preferably 75% of the particle size distribution are within 10% of the median particle size.

[0068] The magnetic particles can include any suitable magnetic material, such as ferromagnetic alloys including Fe, Nd, Co, Ni, or combinations thereof. In certain embodiments, the magnetic particles can include Ni particles. In some embodiments, the magnetic particles can include spherical (or substantially spherical) magnetic particles. In some embodiments, the magnetic particles can include cubic magnetic particles. In other embodiments, the magnetic particles can include anisotropic magnetic particles. Such particles can be formed using methods known in the art, including synthesis driven by suitable shaping ligands, template-assisted synthesis, template-assisted electrodeposition, and magnetically directed assembly. Examples of such materials are described, for example, in Lisjak et al. “Anisotropic Magnetic Nanoparticles: A Review of their Properties, Synthesis, and Potential Applications” Progress in Materials Science, 2018, 95, 286-328, which is incorporated herein by reference in its entirety for its description of anisotropic magnetic particles and is attached to this application.

[0069] The magnetic particles may be essentially uniform throughout, meaning that the composition does not vary throughout the particle cross-section (from the particle surface to the particle center). Alternatively, the magnetic particles may possess a non-uniform structure. For example, the particles may possess a core-shell structure, or a multi-layer structure (e.g., a magnetic core coated with a non-magnetic shell material).

[0070] The magnetic particles may have any desired shape. In certain embodiments, the particles may have a non-spherical shape. As generally used herein, "non-spherical" is used to describe a particle having at least one dimension that differs from another dimension by a ratio of at least 1:1.10. In one embodiment, the non-spherical particle has at least one dimension that differs from another dimension by a ratio of at least 1:1.25. A wide variety of shapes are considered to be "non-spherical" shapes. For example, the non-spherical particles may be in the shape of a rectangular disk, a high aspect ratio rectangular disk, a rod, a high aspect ratio rod, a worm, an oblate ellipsoid, an oblate ellipsoid, an elliptical disk, a UFO, a circular disk, a barrel, a bullet, a pill, a pulley, a biconvex lens, a ribbon, a ravioli, a flat pill, a bicone, a diamond disk, a peeled disk, an elongated hexagonal disk, a taco, a wrinkled prolate ellipsoid, a wrinkled oblate ellipsoid, or a porous elliptical disk. Additional shapes beyond those illustrated in the figures are also within the definition of a "non-spherical" shape.

[0071] In some embodiments, the magnetic particles can include rod-shaped particles. As used herein, "rod-shaped" refers to particles having an elongated spherical or cylindrical shape (e.g., pill shape) or a flat rod shape such as a green bean shape. Rod-shaped particles have an aspect ratio of at least 1.25 (e.g., at least 1.5, at least 2, at least 2.5, or at least 5). As used herein, "aspect ratio" refers to the length divided by the diameter of a particle.

[0072] In certain embodiments, the particles can be rod-shaped. In some embodiments, the rod-shaped particles can have an aspect ratio defined as the length of the rod-shaped particle divided by the diameter of the rod-shaped particle of at least 1.25 (e.g., at least 2.5, at least 5, at least 10, at least 15, at least 25, at least 50, at least 100, at least 150, at least 200, at least 250, or more). In some embodiments, the rod-shaped particles can have an aspect ratio defined as the length of the rod-shaped particle divided by the diameter of the rod-shaped particle of 500 or less (e.g., 250 or less, 200 or less, 150 or less, 100 or less, 50 or less, 25 or less, 15 or less, 10 or less, 5 or less, or 2.5 or less).

[0073] The rod-shaped particles can have an aspect ratio ranging from any of the minimum values ​​described above to any of the maximum values ​​described above, in certain embodiments, the rod-shaped particles can have an aspect ratio of 1.25 to 500 (e.g., 5 to 500, 5 to 250, 5 to 100, 5 to 500, 5 to 250, or 5 to 100).

[0074] In some embodiments, the rod-shaped particles can have an average diameter of at least 5 nm (e.g., at least 25 nm, at least 50 nm, at least 100 nm, at least 200 nm, at least 300 nm, at least 400 nm, at least 500, at least 600 nm, at least 700 nm, at least 800 nm, or at least 900 nm). In some embodiments, the rod-shaped particles can have an average diameter of 950 nm or less (e.g., 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less, 500 nm or less, 400 nm or less, 300 nm or less, 200 nm or less, 100 nm or less, 50 nm or less, or 25 nm or less).

[0075] The rod-shaped particles can have an average diameter ranging from any of the minimum values ​​described above to any of the maximum values ​​described above, in certain embodiments, the rod-shaped particles can have an average diameter of 50 nm to 800 nm (e.g., 50 nm to 500 nm, or 100 nm to 300 nm).

[0076] In some embodiments, the rod-shaped particles can have an average length of at least 500 nm (e.g., at least 1 micrometer, at least 5 micrometers, at least 10 micrometers, at least 15 micrometers, at least 20 micrometers, at least 25 micrometers, at least 50 micrometers, at least 75 micrometers, at least 100 micrometers, at least 150 micrometers, or at least 200 micrometers). In some embodiments, the rod-shaped particles can have an average length of 250 micrometers or less (e.g., 200 micrometers or less, 150 micrometers or less, 100 micrometers or less, 75 micrometers or less, 50 micrometers or less, 25 micrometers or less, 20 micrometers or less, 15 micrometers or less, 10 micrometers or less, 5 micrometers or less, or 1 micrometer or less).

[0077] The rod-shaped particles can have an average length ranging from any of the minimum values ​​described above to any of the maximum values ​​described above, in certain embodiments, the rod-shaped particles can have an average length of 500 nm to 100 micrometers (e.g., 1 micrometer to 25 micrometers).

[0078] In some embodiments, the magnetic particles can include anisotropic magnetic particles. In some embodiments, the dipoles of the magnetic particles are aligned and / or oriented within the magnetic actuator. In some embodiments, the dipoles of the magnetic particles are aligned and / or oriented within the magnetic actuator when the magnetic actuator is compressed 10% to 60% under an applied force.

[0079] The magnetic particles may be present in the composition in an amount of 0.1% to 90% by weight based on the total weight of the elastomeric resin, for example, 50% to 90% by weight, 40% to 80% by weight, 30% to 70% by weight, 20% to 60% by weight, 15% to 50% by weight, 0.1% to 50% by weight, 0.1% to 40% by weight, 0.1% to 30% by weight, 0.1% to 20% by weight, 0.1% to 10% by weight, 0.1% to 5% by weight, 0.1% to 2.5% by weight, or 0.1% to 1% by weight based on the total weight of the elastomeric resin.

[0080] The magnetic particles can be present in the composition in an amount of 0.01% to 20% by volume (e.g., 0.01% to 15% by volume, 0.01% to 10% by volume, 0.01% to 7.5% by volume, 0.01% to 5% by volume, 0.01% to 2.5% by volume, or 0.01% to 1% by volume) based on the total volume of the composition.

[0081] In some embodiments, the magnetic particles can be uniformly dispersed throughout the elastomeric resin. In other embodiments, the magnetic particles can be non-homogeneously dispersed throughout the elastomeric resin. For example, the magnetic particles can be at a varying concentration throughout the elastomeric resin (e.g., a higher concentration in regions close to the magnetometer and a lower concentration in regions further away from the magnetometer). In some embodiments, a gradient of magnetic particles can be dispersed within the elastomeric resin.

[0082] Elastomer Resin The elastomeric resin can include elastomeric resins suitable for use in additive manufacturing processes. Such materials are known in the art. In some examples, the elastomeric resin can include thermoplastic polymers such as acrylonitrile butadiene styrene (ABS), polyphenylene sulfide (PPS), polyphenylsulfone (PPSU), polyetheretherketone (PEEK), polyurethane (PU), polyetherimide (PEI), polyphenylene ether (PPE), polycarbonate (PC), and combinations thereof. In some embodiments, the elastomeric resin can include a crosslinkable composition (e.g., a blend of monomers, oligomers, and / or polymers that can be crosslinked during an additive manufacturing process). Depending on the additive manufacturing process used, the crosslinkable composition can be selected such that crosslinking can be induced thermally and / or by irradiating with electromagnetic radiation (e.g., UV and / or visible light). In certain embodiments, the elastomeric resin can include a crosslinkable silicone composition. For example, the elastomer resin can include (A) a first organosilicon compound having at least two ethylenically unsaturated moieties per molecule, and optionally (B) one or more additional organosilicon compounds.Suitable silicone compositions are known in the art.See, for example, U.S. Patent No. 10,155,884 to Dow Silicones Corp., U.S. Patent Application Publication No. 2017 / 0312981 to Wacker Chemie AG, U.S. Patent Application Publication No. 2018 / 0370141 to Wacker Chemie AG, U.S. Patent Application Publication No. 2018 / 0066115 to Wacker Chemie AG, U.S. Patent Application Publication No. 2018 / 0186076 to Dow Corning Corp., and U.S. Patent Application Publication No. 2019 / 0100626 to Lawrence Livermore National Security LLC, each of which is incorporated herein by reference in its entirety. Other suitable elastomeric resins are described, for example, in U.S. Patent Application Publication No. 2016 / 0319150 to Cornell University.

[0083] Optionally, the composition may further optionally include a non-magnetic filler. The non-magnetic filler may be, for example, an organic filler, an inorganic filler, a ceramic powder, or a combination thereof. The organic filler may be a polymer, such as, but not limited to, polystyrene, polyethylene, polypropylene, polysulfone, polyamide, polyimide, polyetheretherketone, etc. The organic filler may also be a smaller molecule, either amorphous or crystalline in nature, and may be of various shapes and sizes. The inorganic filler or ceramic powder may be any inorganic compound that is compatible with the curing chemistry. Examples include, but are not limited to, silicon dioxide, titanium dioxide, zirconium dioxide, barium titanate, strontium titanate, etc. Mixtures of two or more inorganic or organic and inorganic fillers are also suitable.

[0084] In embodiments including a non-magnetic filler, the non-magnetic filler may be present in any suitable percentage by weight of the composition, for example, from about 0.01% to about 90% by weight, from about 1% to about 80% by weight, from about 5% to about 80% by weight, from about 10% to about 80% by weight, from about 15% to about 80% by weight, from about 25% to about 80% by weight, from about 30% to about 80% by weight, from about 40% to about 80% by weight, or from about 0.01% to about 90% by weight. In some embodiments, the amount of the hydroxypropyl amine may be present in an amount of about 0.1%, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, or about 70% or more by weight.

[0085] The non-magnetic filler can have any suitable particle size, e.g., the longest dimension of the particle, such as the average longest dimension. For example, the non-magnetic filler can have a primary particle size of about 5 to about 100, about 10 to about 90, about 20 to about 80, about 30 to about 70, about 40 to about 60, or about 50 micrometers, alternatively, 5 micrometers or less, alternatively, 100 micrometers or more. As used herein, "primary" particle size refers to the actual particles in a non-agglomerated state, which may optionally be agglomerated to form larger "secondary" particles.

[0086] Any of the compositions may optionally and independently further comprise additional ingredients or components ("additives"). Examples of additional ingredients include, but are not limited to, adhesion promoters, dyes, pigments, antioxidants, initiators for crosslinking, carrier vehicles, heat stabilizers, flame retardants, thixotropic agents, flow control additives, inhibitors, elongation and reinforcing fillers, and crosslinking agents. One or more additives may be present in any suitable weight percent of the composition, such as from about 0.1% to about 15%, from about 0.5% to about 5%, or about 0.1% or less, about 1%, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or about 15% or more by weight of the composition. EXAMPLES

[0087] Example 1: Proof-of-principle sensor overview Detecting the magnitude and velocity of compression or shear events can provide valuable data for assessing the forces experienced by sensitive equipment or even the human body. Compression sensors have traditionally had limited use in areas such as wearable technology due to the large size of the sensor, lack of three-dimensional sensing capability, need for rigid components, or signal quality issues associated with the orientation or deformation of soft composite materials under compression. Specifically, soft magnetic composite materials paired with magnetometers to sense material deformation are hampered by such issues. Here, experiments evaluated soft silicone magnetic powder composites of various shapes, sizes, magnetic filler concentrations, and orientations to magnetometers to optimize sensor performance. Sensors with cylindrically shaped magnetic elements with smaller diameters (≦2.5 mm) exhibited a linear response to compression when paired with a 3 mm×3 mm magnetometer. A soft magnetic element constructed with 80% magnetic powder by weight, the highest concentration tested, had the greatest sensitivity. Using parameters from these studies, we designed a sensor that was integrated into a football helmet and successfully recorded three-dimensional force data from a head impact while worn, demonstrating the potential of such sensors in wearable technology applications.

[0088] Introduction Soft magnetic sensors operate by detecting changes in the magnetic field as embedded magnetic materials move relative to a magnetometer during compression of the soft material. Previous designs of soft magnetic sensors have limitations that prevent them from accurately and reliably detecting forces in sensitive components or wearable technology applications. For example, most previous sensors utilized rigid permanent magnets (Wang et al. 2016b; Rosle et al. 2019), which create durability issues (Wang et al. 2016a). Large solid magnets are not suitable for applications where forceful contact between the sensor and a person would cause discomfort, such as when embedded within a shoe insole, unless the cushioning is made significantly thicker than a typical shoe insole (Johnson and Ozkan; Lam et al. 2017).

[0089] Materials that maintain high magnetic flux while remaining compliant when force is applied are desired. Unfortunately, soft sensors constructed with silicone magnetic powder composites have also experienced signal quality issues (Mirzanejad and Agheli 2019), lacking the sensitivity required to accurately sense high forces (Hellebrekers et al. 2019), and none have displayed the ability to accurately sense shear forces. Previous reports have used sensors that require operation below a certain level of force before compressing further, resulting in reduced signal (Mirzanejad and Agheli 2019). It was hypothesized that misalignment of the magnetic dipoles occurred because the magnetic elements in the sensor deformed under compression. We hypothesized that the geometry of the magnetic elements may also be too large, as the smallest magnetic elements in the study could sense the largest forces.

[0090] Soft magnetic sensors also present the opportunity to detect shear forces in addition to compression. For example, shear can be detected using a three-axis magnetometer paired with a properly designed soft magnetic element, although no such sensor has yet been reported. This is likely due to problems caused by the geometry of the magnetic element or an improper orientation of the sensor and magnetic element. Indeed, a soft three-dimensional force sensor suitable for wearable technology applications has not been realized.

[0091] Therefore, soft magnetic sensors were fabricated with the view to achieving properties suitable for wearable technology while overcoming the signal quality issues presented in previous reports. Multiple geometries of the magnetic element and magnetic filler concentrations were investigated. Methods for aligning the dipoles of the magnetic particles embedded within the magnetic element were also investigated. The relative position of the magnetic element with respect to the magnetometer location was evaluated. Finally, sensor design considerations were compiled and used in wearable technology applications.

[0092] method Sensor design and construction All sensors were cylinders of 10 mm diameter and 5 mm height composed of polydimethylsiloxane (PDMS) silicone rubber elastomer (Sylgard 184, 20:1 base to curing agent ratio, Dow Chemical Company; Pevely, MO, USA) and were separate cylindrical or conical parts of a construct composed of silicone magnetic powder composite. The magnetic powder used in the composite was neodymium iron boron alloy (NdFeB) with an average particle size of <10 μm (American Elements, Los Angeles, CA, USA). The most effective geometry for the magnetic element of the sensor was the main question of the investigation, so the geometry of this magnetic element was variable. Sensors were fabricated with cylindrical magnetic elements of 2, 3, 4, and 5 mm diameter and 2, 3, and 4 mm height, and conical magnetic elements of 3, 4, and 5 mm base diameter and 3 and 4 mm height. Sensors were identified by the geometric shape of their magnetic element following the convention: diameter x height shape, so a sensor with a cylindrically shaped magnetic element with a diameter of 2 mm and a height of 4 mm was labelled as a 2x4 cylindrical sensor.

[0093] Fabrication was accomplished via a two-step molding process. The first step molds were created by 3D printing onto a flat plastic surface (Figure 1A). Each mold contained pegs with dimensions following the geometry of the desired magnetic elements to leave cavities that would be filled by the silicone-magnetic powder composite during step 2 of the process. Liquid silicone precursor was poured into each mold and cured for 48 hours at ambient conditions to avoid distorting the mold. After curing, the silicone was removed from the mold. Unless otherwise indicated, the magnetic powder was mixed with the liquid silicone precursor in a 1:1 ratio (50 wt% magnetic filler concentration) and distributed into the cavities within each silicone structure. These silicone cylinders with the liquid silicone-magnetic powder composite were cured at 60°C for 2 hours to avoid settling of the magnetic powder within the liquid silicone.

[0094] Magnetic dipole alignment When creating silicone magnetic powder composites, it is possible to align the dipoles of the magnetic material while the silicone is curing (Mirzanejad and Agheli 2019; Hellebrekers et al. 2019) or after the silicone is cured (Kim et al. 2018). For this investigation, the dipoles of the magnetic particles were aligned after the silicone was cured to test whether misalignment of the particle dipoles under deformation of the sensor would corrupt the signal. Compression tests were performed on the sensor under two different magnetic dipole alignment schemes. First, the magnetic dipoles were aligned by placing strong permanent magnets (~650 mT) on either side of the sensor, and the sensor was placed within the outer portion of the original 10 mm × 5 mm cylindrical forming mold, so that the sensor maintained its original shape while magnetized (Figure 1D). Using this method, the magnetic particle dipoles would be aligned vertically while the sensor was not compressed. Thus, deformation of the magnetic elements during compression of the sensor would cause misalignment of the particle dipoles. The second magnetic dipole alignment scheme involved placing the sensor between the same strong permanent magnets without the original mold cylinder such that the sensor was distorted by approximately 40% by the force of attracting the two magnets (Figure 1E). This configuration aligned the magnetic dipoles in the vertical direction while the sensor was compressed. Thus, the magnetic dipoles are aligned in the vertical direction upon sensor compression. It is hypothesized that the signal strength would be stronger in the second configuration because the deformation of the sensor should act to align the dipoles in the vertical direction rather than misaligning them.

[0095] Compression and Shear Tests An MLX90393 three-axis magnetometer breakout board (Adafruit Industries, New York City, NY, USA) was wired to an Arduino Uno microcontroller and communicated data to a computer via I2C. The surface of the breakout board was leveled with the magnetometer chip using polyurethane to avoid undesired deformation of the sensor construct around the magnetometer chip (Figure 1B). The magnetometer board was mounted to the bottom geometry of an Electroforce5500 (TA Instruments, Eden Prairie, MN, USA) using double-sided tape. The sensor was then placed on top of the magnetometer and the axial translator of the ElectroForce5500 was lowered until it contacted the top side of the sensor. The sensor was oriented so that the magnetic element was away from the magnetometer, giving at least 1 mm of space between the magnetic element and the magnetometer, as pilot studies showed that leaving no gap between the magnetic element and the magnetometer surface significantly reduced signal strength. Compressive forces were applied by displacing the axial slider in increments of 0.5 mm to 2.5 mm of compression displacement on the specimen (Figure 1F) and returned to 0 displacement in matching decompression steps. Each step was held for 10 s, except for the 2.5 mm displacement step, which was maintained for 20 s (Figure 2).

[0096] Tests for the detection of shear forces were also performed on an Electroforce5500 with adapted settings (Figure 1G). The configuration of the sensor construct to the magnetometer was consistent with the compression test. The top of the sensor was pressed into a 3D printed adapter connected to the axial translator of the Electroforce5500. The axial translator was displaced in 0.5 mm steps for a total displacement of 1 mm in both Y-axis directions. Each step was maintained for 10 seconds (Figure 3A, Figure 3C).

[0097] Magnetometer readings from all three axes, as well as time and axial translator displacement, were collected during each test. A load cell attached to the bottom geometry of the Electroforce5500 collected force data during all compression tests, but was not able to collect force during the shear tests.

[0098] Football helmet integration and verification A 2.5 × 4 cylindrical sensor with 80% magnetic filler by weight was integrated into a football helmet (Riddell; Rosemont, IL) by cutting a 10 mm diameter × 5 mm height cavity in the helmet's forehead pad and fixing the sensor within the cavity. A magnetometer was affixed to the sensor and data was wirelessly communicated to a nearby computer at a sampling rate of 29 Hz using a WIFI-enabled microcontroller module (M5Stick-C, M5Stack, Shenzhen, China). The in-helmet sensor was calibrated against a three-dimensional force plate (4060-08, Bertec, Columbus, Ohio, USA) sampled at a rate of 2 kHz by conducting several helmet-force plate impacts from different angles while mounted vertically and wearing the helmet. Force data (N) from the force plate were downsampled to match data from the in-helmet sensor, and a calibration regression equation was fitted to the force plate readings plotted against the raw magnetic field strength readings (μT) from the in-helmet sensor during the impact. Thirteen experiments were conducted in which the helmet was impacted from different angles against a vertically mounted three-dimensional force plate while being worn.

[0099] statistical analysis The magnetic field strength readings (in μT) from each axis were normalized by subtracting the average signal recorded during the first 5 seconds of each test when the displacement was zero. Several metrics were used when considering the performance of each sensor. The peak magnitude of the sensor during the compression test was taken as the peak observed magnetic field strength reading from the Z-axis of the magnetometer, and the average of the absolute value of the peak observed readings from the Y-axis was used in both directions during the shear test. The correlation coefficient of the relationship between the magnetic field response and the applied compressive force considered linearity in terms of force, and the correlation coefficient of the relationship between the magnetic field response and the displacement of the axial mover considered linearity in terms of displacement.

[0100] The reliability of the in-helmet sensor with respect to the force plate was assessed by the interclass correlation coefficient (ICC) of the peak force measured on the primary axis of the impact (i.e., z-axis for linear impacts and x-axis for angled impacts) from the in-helmet sensor and the force plate. In addition, the percent error of the peak force readings between the in-helmet sensor and the force plate was calculated for each impact.

[0101] result Compression test results Soft magnetic sensors were constructed using different shapes (cylinder, cone) of PDMS weighted with neodymium powder as magnetic elements embedded within larger PDMS cylindrical constructs (Figure 1). These magnetic elements were placed in close proximity to a magnetometer to measure the change in magnetic field strength and direction as the sensor was deformed (Table 1). Prior to testing, a rare earth magnet was used to magnetize the magnetic powder filler when the magnetic element was uncompressed or compressed to a strain of about 40%. All sensors were significantly more sensitive when the magnetic particle dipoles were aligned while the sensor was compressed. The peak magnitude for each sensor design increased by 53% to 217% compared to tests performed with the magnetic particle dipoles oriented perpendicularly while the sensor was uncompressed. Compressing the sensor during magnetic dipole alignment addresses the previously mentioned issue where deformation of the magnetic element causes misalignment of the dipoles with the magnetometer, resulting in a drop in magnetic field strength (Mirzanejad and Agheli 2019). Therefore, all further results are presented only from sensors with the magnetic particle dipoles aligned while the sensor is compressed.

[0102] Exemplary compression test data for several sensors with representative magnetic element geometries are presented in FIG. 2. All sensors were able to detect the speed, duration, and magnitude of compression events to some degree. However, the sensitivity of the response and the linearity of the response with respect to displacement and force varied widely between the different magnetic element geometries (Table 1). Sensors with larger magnetic element volumes generally failed at a certain level of compression, so that further increases in compression did not result in an increase or reversal of the signal, as previously reported (FIG. 4). The peak magnitude of each sensor with respect to force and the linearity of its magnetic response are plotted against the volume of the magnetic element in FIGS. 4C-D. These relationships indicated that a larger magnetic element volume was indeed detrimental to signal quality.

[0103] The 2 × 4 cylindrical sensor was the most sensitive design for sensing compression events, as it displayed the largest peak magnitude of 2,748 μT. This sensor also performed well according to all other metrics, including linearity of response with respect to both displacement and force (Table 1). The sensor designed with the largest magnetic element, the 5 × 4 cylindrical sensor, paradoxically had the smallest peak magnitude (766 μT) of all sensors and performed poorly by all other metrics considered. This sensor was only able to sense compression up to about 1 mm (20% strain) before further compression resulted in a reversal in the signal direction (Figure 2D). [Table 1]

[0104] Shear test results Exemplary shear displacement test data for representative magnetic element geometries are presented in Figures 3A and 3C. Table 1 displays the peak response from the Y-axis averaged over the two directions of shear displacement. All sensors adequately detected the rate, duration, and magnitude of shear displacement events, and no sensor design presented signal quality issues considered for larger magnetic element volumes during sensing of compression events. Linearity of response with respect to shear displacement was greater than r=0.998 for all sensor designs.

[0105] The trend towards poorer performance from larger magnetic element volumetric sensors did not apply to sensing shear forces. The sensor with a 4mm diameter x 4mm height cylindrical magnetic element was the most sensitive design with a peak magnitude of 570μT. In addition, all cylindrical magnetic elements with a height of 4mm had improved sensitivity over all other sensor designs for sensing shear displacement. The 2mmx4mm cylindrical magnetic element performs well in shear and normal compression dimensions. The 4mmx4mm cylindrical magnetic element has slightly greater sensitivity for shear displacement but poorer quality for normal compression sensing.

[0106] Magnet diameter, magnetic filler concentration, magnet location Additional sensors were constructed to investigate the optimal magnetic element geometry at finer resolution, and the effect of increasing magnetic filler concentration on sensor sensitivity. The magnetic elements in each sensor were 4 mm in height and ranged in diameter from 1 to 3 mm (in 0.5 mm increments), with magnetic filler concentrations of 67% and 80% by weight in the magnetic elements. As expected, sensors with magnetic elements with higher magnetic filler concentrations showed a significant increase in signal strength. The 2 × 4 cylindrical sensors with magnetic filler concentrations of 67% and 80% showed a 2.3-fold and 4.8-fold increase in sensitivity, respectively, compared to the same sensor design with a 50% magnetic filler concentration in the magnetic element (Figure 5).

[0107] The 2×4 cylinder sensor outperformed the other magnetic element diameters tested with a sensor having a magnetic filler concentration of 67%, which is consistent with the results of the original study with sensors having a magnetic filler concentration of 50%. The 1×4 and 1.5×4 cylinder sensors were not as sensitive as the 2×4 cylinder sensor, and the 2.5×4 and 3×4 cylinder sensors displayed the typical signal quality issues for sensors with larger magnetic element diameters previously described. For the sensors with a magnetic filler concentration of 80%, the 2.5×4 cylinder sensor displayed the highest peak magnitude and did not have the signal quality issues present in the 2.5×4 cylinder sensor with a magnetic filler concentration of 67%. Thus, increasing the magnetic filler concentration may also increase the maximum diameter of the magnetic element that can be compressed to 50% strain without displaying a blunted or inverse signal response. This may be due to the higher concentration of magnetic filler hardening the material so that less deformation of the magnetic element occurs during compression. In fact, photogrammetry showed that the increase in the diameter of the magnetic elements of the sensors constructed with 80% magnetic filler was less than the increase in diameter of the sensors with 50% magnetic filler concentration. At 50% strain, the diameter of the magnetic elements of the 2×4 cylindrical sensor increased by 70.6% and 55.8% for the magnetic elements constructed with 50% and 80% magnetic filler, respectively. Similarly, the diameter of the magnetic elements of the 3×4 cylindrical sensor increased by 47.6% and 41.7% for the magnetic elements constructed with 50% and 80% magnetic filler, respectively.

[0108] To investigate the optimal sensor height while keeping the magnetic element geometry constant, 2x4 and 3x4 cylindrical sensors with 50% magnetic filler concentration in the magnetic element were constructed with a total sensor height of 4 mm, such that the magnetic element was exposed at the bottom of the sensor and in direct contact with the magnetometer. Pure silicone disks of different heights but of the same material (i.e., same stiffness) and diameter as the sensor were created so that they could be added as spacers between the magnetometer and the sensor to increase the total sensor height. Tests were performed by compressing each sensor configuration to 50% strain in steps of 0.5 and 0.25 mm. For the 2x4 cylindrical sensor, as the total sensor height increases, the signal linearity (with respect to strain) also increases, but the signal sensitivity decreases concomitantly slightly (Figure 6A). For the 3x4 cylindrical, as the sensor height increases, the signal linearity increases significantly and the sensor sensitivity also increases until the total sensor height exceeds 6 mm (Figure 6B). Thus, the optimal sensor height varies with the geometry of the magnetic element, as larger magnetic elements require a taller sensor, which increases the space between the magnetic element and the magnetometer to function properly, however a taller overall sensor may be inadequate for many wearable technology applications that require a low profile sensor.

[0109] Similar tests were performed in experiments to quantify the effect of increasing the remote distance between the silicone magnetic powder sensor construct and the magnetometer. In this experiment, a hard (polylactic acid) plastic disk was 3D printed and used as a spacer between the magnetometer and the sensor to simulate remote sensing at different distances (Figure 6C). All tests for this experiment were performed with a 3x4 cylindrical sensor of the same design as the original study described in the methods (total height 5mm). Increasing the remote distance between the magnetometer and the sensor increased the linearity of the signal, such that when the distance was 1.5mm or greater, the signal continued to show an increase in magnetic field strength up to 50% distortion, but the sensitivity of the signal was reduced (Figure 6D). Increasing the gap (or sensor height) may make the signal more linear for larger sensor geometries.

[0110] Football helmet demonstration American football is associated with more concussions than any other sport currently played in the United States (Daneshvar et al. 2011), and understanding the kinematic characteristics of head impacts may be a key factor in understanding, preventing, and providing appropriate treatment to concussed individuals (McAllister and McCrea 2017). To evaluate the utility of the current sensor design in real-world applications, a 2.5 × 4 cylindrical sensor with 80% magnetic filler concentration was integrated into existing padding within a football helmet. The additional padding within the helmet made this sensor imperceptible to the wearer, thus enabling the study of helmet impacts using traditional forces placed on the impact surface compared to magnetic sensors within the helmet.

[0111] The force vector was clearly observable in all experiments by analyzing the force-time curves for each of the three axes of the in-helmet magnetic sensor (Figures 8A-B). The sensor displayed excellent agreement with the force plate for peak forces (ICC=0.981). In addition, the peak forces of 8 of the 13 impacts exhibited reasonably low errors (1-13%) when compared to the force plate, although some impacts had larger errors (25-51%). The sensor had an overall high agreement with the force plate according to ICC, and most impacts were accurately measured, although a higher sampling rate may be required to consistently and accurately quantify impacts containing high frequency components. Data from all helmet-force plate impacts are presented in Figure 9.

[0112] Consideration Signal Quality for Complex Sensor Designs Many previous researchers who designed sensors using magnets or other soft materials embedded within PDMS have detailed the mechanism of using the displacement of the magnetic element to sense the applied force (Wang et al. 2016b, b; Rosle et al. 2019), including sensors designed with silicone magnetic powder composites (Mirzanejad and Agheli 2019; Hellebrekers et al. 2019). Silicone magnetic powder composites, unlike hard permanent magnets, are prone to deformation, and therefore the magnetic field can deviate during deformation. The implications of this fact for soft sensor applications have been modeled and discussed previously (Mirzanejad and Agheli 2019). The authors showed that the magnetic dipoles of the particles in the composite magnetic element gradually deviate from the vertical orientation under compression, which contributes to the reversal of the direction of the signal observed at a certain level of force (which varies depending on the sensor design), resulting in the sensor being able to operate only below a certain level of force or strain. In this study, a significant increase in signal strength was observed for each sensor design when the magnetic particle dipoles were aligned while the sensor was compressed. Thus, increasing compression aligned the magnetic dipoles with the magnetometer's Z-axis rather than moving the dipoles away from alignment with the magnetometer's Z-axis. This finding supports the notion that shifting the alignment of the magnetic dipoles must be considered in compression sensors using silicone magnetic powder composites.

[0113] Surprisingly, the slowing or reversal of signal direction beyond a certain level of strain was persistent regardless of magnetic dipole alignment, but this phenomenon was limited to larger volume magnetic elements, inviting further consideration of signal quality issues. A second detriment to this signal quality was the lateral displacement of magnetic particles during compression due to deformation of the magnetic element (Figure 7). The MLX90393 magnetometer has a square surface of 3 mm x 3 mm, and thus any reasonable lateral movement of magnetic particles towards or beyond the boundaries of the magnetometer surface could act to reduce the field strength readings. With regard to the cylindrical magnetic elements in this study, magnetic elements with diameters of 2 mm or less (<67% of the magnetometer width) exhibited an increase in signal with increasing deformation up to 50% strain. Photogrammetry showed that the diameter of the magnetic element of the 2 x 4 cylindrical sensor increased to 3.36 mm at 50% strain, slightly more than the magnetometer width, and sensors of this design did not display major signal quality issues. However, the signal of the 3×4 cylindrical sensor reversed at strains >40%, such that further compression caused a reduction in magnetic field strength. Photogrammetry showed that the diameter of the magnetic element of the 3×4 cylindrical sensor increased by more than 4 mm at strains above 40%. Thus, compression displaces the magnetic particles around the magnetic element laterally by more than 1 mm from the z-axis of the magnetometer, with the resulting position being more than 1 mm laterally of the boundary of the magnetometer. Such particles act against the increase in magnetic field strength, resulting in a dominant signal (reversing the overall signal) at higher strains for sensors containing larger magnetic elements. The single exception to this rule was the 2.5 mm diameter sensor with 80% magnetic filler concentration (83% of the magnetometer width), which displayed a linear increase in magnetic field strength up to a strain of 50%. This could be attributed to its stiffer magnetic element, and photogrammetry confirmed the less deformation of the magnetic element with 80% magnetic filler concentration. Overall, the geometry of the magnetic element and its position relative to the magnetometer primarily affect the linearity of the compressed signal, while the amount of magnetic material primarily affects the sensitivity or strength of the signal.

[0114] Shear force sensing ability The ability of soft force sensors to accurately quantify shear forces or displacements would also advance the field and broaden applications for monitoring biomechanics. For example, shear forces acting on the plantar surface are a significant risk factor for the development of foot ulcers in patients with diabetic neuropathy (Wu et al. 2007; Lam et al. 2017), and detection of ground reaction forces in the horizontal plane is desirable for biomechanical analysis of sports movements (Holm et al. 2008). Finally, true three-dimensional force sensors are currently not available for instrumented football helmets (Siegmund et al. 2016; Merrell et al. 2017), but such technology could aid in the proper analysis of head impacts to combat the prevalence of traumatic brain injury.

[0115] Signal quality issues were less evident when sensing shear in the control experiments as all sensors had a very linear response during shear displacement when compared to compression sensing. Also, all sensors possessed specificity in the signal for each axis such that vertical and horizontal forces could be easily distinguished during both shear displacement (Figure 3A, Figure 3C) and normal compression testing (Figure 3B, Figure 3D). It can be seen that the most important sensor design specification for sensitivity in the shear direction was the height of the magnetic element. The 4x4 cylindrical sensor displayed a maximum peak magnitude of 570.7 μT. However, the 2x4 cylindrical sensor displayed the largest peak magnitude (487.4 μT) for shear sensing when comparing only sensors that did not display significant signal quality issues during compression testing.

[0116] Wearable Application Considerations No sensor design was superior in all metrics, therefore, the most effective design may be optimized for a particular application using the parameters investigated here. For example, the 3 × 3 conical sensor displayed the most linear magnetic field response with respect to force (r = 0.980) of all sensor designs and required the second least magnetic material (Table 1). The sensitivity and linearity of larger magnetic elements such as the 3 × 4 cylindrical sensor increased with a higher overall sensor design, however, this increase in height may make the sensor unsuitable for many wearable applications (Figure 6B). The 2.5 × 4 cylindrical sensor with a magnetic filler concentration of 80% displayed the highest sensitivity of the sensor, capable of sensing strains of up to 50% (Figure 5B), but the magnetic element was stiff enough that it could potentially be perceived to touch if firmly compressed. However, for many applications such as the football helmet presented here, this does not adversely affect the effectiveness of the sensor. A few millimeters of additional padding separated the wearer's head and the sensor, making the sensor imperceptible, but forces were still transmitted through the additional padding so that the sensor could function properly.

[0117] conclusion Previous designs of compression sensors using rigid magnets embedded in silicone, or magnetometers to detect the displacement of silicone magnetic powder composites, had limitations in feasibility, functionality, and signal quality that limited their usefulness. Several experiments were conducted to identify design parameters to improve the sensitivity and accuracy of the sensors, and therefore broaden the applications of these sensors to include wearable technology. Sensors constructed with silicone magnetic powder composites provided a platform for designing thin sensors without saturating the magnetometer, while remaining soft enough for potential use in wearable technology. Magnetizing the magnetic elements of the sensor while it is compressed to align the dipoles of the magnetic particles reduces unwanted deviations in the magnetic field during deformation, thereby improving signal fidelity. Finally, the diameter of the magnetic elements was controlled in relation to the width of the magnetometer to ensure that lateral movement of the magnetic particles during deformation of the sensor did not corrupt the signal. Sensors fabricated according to these design specifications were capable of detecting velocity, duration, and magnitude of three-dimensional forces with a highly linear signal, and when integrated into a football helmet, performed successfully in detecting head impacts.

[0118] Additionally, the magnetic element should be as tall as possible (within the constraints of the overall sensor size), but there should be at least a 1 mm gap between the magnetic element and the magnetometer if a 50% strain is required. If lower levels of strain are expected to be maximum, this gap can be reduced to increase sensitivity with a smaller diameter magnetic element.

[0119] References Biswas S, Shao Y, Hachisu T, et al (2020) Integrated Soft Optoelectronics for Wearable Health Monitoring.Adv Mater Technol 5:2000347. Daneshvar DH,Nowinski CJ,McKee AC,Cantu RC(2011)The Epidemiology of Sport-Related Concussion.Clinics in Sports Medicine 30:1-17. Hellebrekers T,Kroemer O,Majidi C(2019)Soft Magnetic Skin for Continuous Deformation Sensing.Advanced Intelligent Systems 1:1900025. Holm DJ,Stalbom M,Keogh JWL,Cronin J(2008)Relationship Between the Kinetics and Kinematics of a Unilateral Horizontal Drop Jump to Sprint Performance:Journal of Strength and Conditioning Research 22:1589-1596. Johnson JG,Ozkan SS Three Dimensional Force Sensing Array with Applications in Robotics and Biomechanics.76 Kim Y,Yuk H,Zhao R,et al(2018)Printing ferromagnetic domains for untethered fast-transforming soft materials.Nature 558:274-279. Lam BL,Stomberg NA,Laovoravit TD(2017)MagneForce: Validation of a Modular Tri-Axial Force Sensor for Gait Analysis.112 Low JH,Khin PM,Yeow CH(2015)A pressure-redistributing insole using soft sensors and actuators.In: 2015 IEEE International Conference on Robotics and Automation(ICRA).IEEE,Seattle,WA,USA,pp 2926-2930. McAllister T,McCrea M(2017)Long-Term Cognitive and Neuropsychiatric Consequences of Repetitive Concussion and Head-Impact Exposure. Journal of Athletic Training 52:309-317. Merrell AJ,Christensen WF,Seeley MK,et al(2017)Nano-Composite Foam Sensor System in Football Helmets.Ann Biomed Eng 45:2742-2749. Mirzanejad H,Agheli M(2019)Soft force sensor made of magnetic powder blended with silicone rubber.Sensors and Actuators A:Physical 293:108-118. Rosle,Wang,Hirai(2019)Geometry Optimisation of a Hall-Effect-Based Soft Fingertip for Estimating Orientation of Thin Rectangular Objects.Sensors 19:4056. Siegmund GP, Guskiewicz KM, Marshall SW, et al (2016) Laboratory Validation of Two Wearable Sensor Systems for Measuring Head Impact Severity in Football Players. Ann Biomed Eng 44:1257-1274. Wang H, de Boer G, Kow J, et al(2016a)Design Methodology for Magnetic Field-Based Soft Tri-Axis Tactile Sensors.Sensors 16:1356.https: / / doi.org / 10.3390 / s16091356 Wang H, de Boer G, Kow J, et al(2016b)A Low-cost Soft Tactile Sensing Array Using 3D Hall Sensors.Procedia Engineering 168:650-653. Wu SC, Driver VR, Wrobel JS, Armstrong DG (2007) Foot ulcers in the diabetic patient, prevention and treatment. Vasc. Health Risk Manag. 3:65-76

[0120] Example 2: Magnetic cushion and remote sensing Different vertical and horizontal standoff distances were tested when the force was applied in vertical and horizontal orientations (see FIG. 14).

[0121] Using a 10x5mm cylindrical cushion with a 2.5x4 cylindrical magnetic element (80% Nd), different vertical standoff distances were tested from 2mm to 10mm. The signal decreases with distance (see Figure 15).

[0122] Using a 2.5x4mm or 5x4mm cylinder, different horizontal standoff distances of the 80% Nd magnetic element were tested with a gap from the rubber cushion to the magnetometer substrate of 2 to 7mm (true gap from magnetometer to magnetic element of 5.75 to 10.75mm) (see Figures 16 and 17). When using a 5x4mm cylinder, 50% strain of the 80% Nd magnetic element was reached using electronic force (reaching the 150N limit).

[0123] A strong signal is measured at a distance of approximately 5 mm, and a measurable signal remains at a distance of approximately 10 mm.

[0124] Example 3: Piston Magnetic Cushion and Remote Sensing Using a piston design setup with a 10x5mm cylindrical cushion and a 2.5x4 cylindrical magnetic element (80% Nd), different vertical standoff distances from 2mm to 10mm were tested when applying force in a vertical orientation (see Figures 18 and 19). The piston design increased the overall sensitivity by approximately 2x compared to the non-piston design. However, using a 2.5x4mm, 80% Nd magnetic element in a 5mm tall sensor would saturate the magnetometer before reaching 40% strain.

[0125] Shorter height sensors were tested, including a sensor with a rubber cushion of 3 mm total height and a cylindrical magnetic element of 2 mm diameter by 2-3 mm height. A compression of 1 mm (33% strain) was applied to each test sample in 0.2 mm steps. The 3 mm total height sensor showed high sensitivity as shown in Figure 20. A 2 x 3 mm cylindrical magnetic element with no gap between the magnetic element and the magnetometer showed sensitivity up to 33% strain. The 2 x 2.25 mm cylinder with a 0.75 mm gap was the most sensitive at 33% strain (see Figure 20).

[0126] Example 4: 3D printed magnetic sensor cushion 10.5×10.5×5 mm constructs with variable size magnetic elements were printed (FIG. 21). Materials used were non-magnetic ink SE1700 and magnetic ink SE1700 with 25% by weight NdFeB particulates. The infill had a strand spacing of 0.5 mm.

[0127] The printing parameters are shown in Table 2 below. [Table 2] The sample can include a 5mm tall cushion with a 4mm magnetic portion printed first, then a 1mm layer of SE1700 printed on top (see FIG. 22).

[0128] For the two dual designs, a 0.65mm offset between was used to allow for perfect integration of the magnetic and non-magnetic parts without any unnecessary overlap that could cause fill and result in magnetic defects located throughout the non-magnetic part. Some key printing parameters include a 2 / 10 bar increase in pressure due to the incorporation of magnetic filler.

[0129] FIG. 22 shows prints of different sizes including 4×4, 3×4, and 2.4×4.

[0130] The performance of the printed magnetic sensor cushion is shown in Figure 23. The 4x4 mm rectangular prism has the higher initial sensitivity. The 2.4x4 mm rectangular prism has the highest linear signal up to 40% strain.

[0131] Example 5: Flat Flex Circuit Sensor In this example, we demonstrate that the sensors described herein can also be achieved using a magnetometer mounted on a flat flexible circuit, as shown in Figures 38A-38C. This strategy allows for the fabrication of the sensor without the use of a rigid circuit board. As a result, the entire sensor can be relatively compliant, making the sensor more suitable for use in wearable technology applications. The signal from the circuit made with the flat flex cable is robust and appears to be similar in quality to the sensor made with a magnetometer mounted on a rigid circuit board.

[0132] Demonstration of sensor units bonded with different adhesives A selection of silicone adhesives were screened for use in bonding the rubber component of the sensor to the magnetometer (FIG. 39). Four silicone adhesives made by NuSil (MED1-4013, MED3-4013, MED2-4220, and MED4-4220) and one adhesive made by Smooth-On (Silpoxy) were qualitatively tested to determine whether they could adequately bond to the silicone and magnetometer substrates with sufficient strength for a functional force sensor. Silpoxy, MED4-4220, and MED3-4013 appeared to have sufficient bonding capabilities with the desired materials and were therefore used in subsequent sensor embodiments.

[0133] Sensor structure The sensor was constructed by bonding the silicone sensor components to the magnetometer circuit board using Silpoxy, NuSil MED3-4013, and NuSil MED4-4220. Each sensor unit was subjected to a stepwise compression cycle to demonstrate that this sensor platform can function properly using several different adhesives. The sensor was compressed in increments of 0.5 mm to a total of 1 mm, which was a 33% strain of the rubber component of the sensor (3 mm height), and the compression was removed in the same stepwise fashion (Figure 40). These data demonstrate that the sensor platform can operate properly when the silicone sensor components are bonded to the magnetometer using several different adhesives, but also provide evidence that the adhesive properties affect the sensitivity of the sensor, as softer adhesives produce stronger signals from compression. The peak magnetic signal magnitudes from 1 mm compression were 10,097 μT, 8,395 μT, and 7,059 μT for MED4-4220 (durometer=17 A), MED3-4013 (20 A), and Silpoxy (40 A), respectively.

[0134] The compositions and methods of the appended claims are not limited in scope by the specific compositions and methods described herein, which are intended as illustrations of some aspects of the claims, and any compositions and methods that are functionally equivalent are intended to fall within the scope of the claims. Various modifications of the compositions and methods in addition to those shown and described herein are intended to be within the scope of the appended claims. Furthermore, only certain representative compositions and method steps disclosed herein are specifically described, but other combinations of compositions and method steps are also intended to be within the scope of the appended claims, even if not specifically recited. Thus, although combinations of steps, elements, components, or ingredients may be explicitly recited herein, other combinations of steps, elements, components, and ingredients are included even if not explicitly recited.

Claims

Claim 1 A force sensor comprising: A magnetic actuator having a proximal end and a distal end, the magnetic actuator comprising an elastomeric resin and a population of magnetic particles dispersed within the elastomeric resin; A magnetometer operably positioned proximate to the distal end of the magnetic actuator; A spacer disposed between the magnetometer and the distal end of the magnetic actuator, thereby creating a standoff distance between the magnetometer and the distal end of the magnetic actuator; The magnetic actuator and the magnetometer are sized relative to one another such that a force applied to the magnetic actuator in the x-y plane relative to the magnetometer, along the z-axis relative to the magnetometer, or any combination thereof, produces a magnetic field response that increases and is proportional, or decreases and is proportional, to the applied force.

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