Prototype Accelerometer Research Articles

Co-design of a walking activity intervention for stroke survivors.

Stroke survivors may not maintain gains made in gait performance after task-oriented circuit training. Behavior change interventions may enhance the long-term adoption of physical activity. This study uses a co-design methodology to develop an intervention and tools to facilitate physical and exercise therapists in supporting an active lifestyle in stroke survivors, which is defined as a lifestyle that integrates daily walking performance with day-to-day activity. (1) To describe the insights generated during the co-design process; and (2) To describe the tools that were developed during the co-design process. A multidisciplinary team consisting of staff members of the Royal Dutch Society for Physical Therapy, exercise and physical therapists specializing in neurorehabilitation and conducting task-oriented circuit class training in primary care settings or day therapy centers within residential care facilities, stroke survivors and their carers, experts in measuring movement behavior in stroke survivors, a company specializing in manufacturing sensors and related software, behavior change specialists, and co-designers all collaborated in a three-stage (define, develop, and deliver) co-design process. In the design process, the team iteratively developed a prototype accelerometer system for measuring walking performance with a feedback function for stroke survivors and their therapists and a prototype toolbox for therapists to support the facilitation of behavior change in their stroke survivors. This study shows how co-design can be applied to develop interventions for stroke survivors. Both the prototype system for measuring walking performance and the toolbox incorporate behavior change techniques to support a more physically active lifestyle in stroke survivors. Further research will investigate the feasibility of the intervention.

Mode-localized accelerometer in the nonlinear Duffing regime with 75\u2009ng bias instability and 95\u2009ng/\u221aHz noise floor

Mode-localized sensors have attracted attention because of their high parametric sensitivity and first-order common-mode rejection to temperature drift. The high-fidelity detection of resonator amplitude is critical to determining the resolution of mode-localized sensors where the measured amplitude ratio in a system of coupled resonators represents the output metric. Operation at specific bifurcation points in a nonlinear regime can potentially improve the amplitude bias stability; however, the amplitude ratio scale factor to the input measurand in a nonlinear regime has not been fully investigated. This paper theoretically and experimentally elucidates the operation of mode-localized sensors with respect to stiffness perturbations (or an external acceleration field) in a nonlinear Duffing regime. The operation of a mode-localized accelerometer is optimized with the benefit of the insights gained from theoretical analysis with operation in the nonlinear regime close to the top critical bifurcation point. The phase portraits of the amplitudes of the two resonators under different drive forces are recorded to support the experimentally observed improvements for velocity random walk. Employing temperature control to suppress the phase and amplitude variations induced by the temperature drift, 1/f noise at the operation frequency is significantly reduced. A prototype accelerometer device demonstrates a noise floor of 95 ng/√Hz and a bias instability of 75 ng, establishing a new benchmark for accelerometers employing vibration mode localization as a sensing paradigm. A mode-localized accelerometer is first employed to record microseismic noise in a university laboratory environment.

Design principles for a single-process 3d-printed accelerometer – theory and experiment

Fused-filament fabrication, one of the most accessible additive manufacturing technology, has already been used to manufacture piezoresistive static/quasistatic strain sensors, force sensors and wind sensors. Recent research showed that fused-filament fabrication could also be used for the manufacturing of dynamic sensors. However, the anisotropic mechanical and piezoresistive behaviour, the heterogeneity, the large number of process parameters and the large number of possible geometrical designs open up numerous design options for manufacturing. Additionally, a small size is difficult to achieve due to the relatively low geometrical tolerances and the resolution of fused-filament fabrication. This paper is focused on the design principles of a single-process, fused-filament fabricated, uni-axial accelerometer with a piezoresistive sensing element. The anisotropic piezoresistive behaviour is researched for the maximum sensitivity in the measured acceleration direction and the minimal cross-axis sensitivity for the perpendicular axes. The analytical accelerometer model is based on a Bernoulli-Euler beam and is used to understand the frequency and the geometrical influences of the piezoresistive accelerometer with a beam-shaped sensing element and an attached intertial mass. Finally, a small-sized (22 × 22 × 15 mm3), single-axis, prototype accelerometer, with an approximately linear response up to-425 Hz and a low cross-axis sensitivity was manufactured. The derived principles can be used for further optimisation of the developed prototype sensor and as a foundation for the derivation of design principles for other types of fused-filament fabricated accelerometers, including 3-axis accelerometers. keyword: accelerometer; piezoresistivity; additive manufacturing; fused filament fabrication; dynamic sensor; 3D printing.

Properties of (Bi,M)ZrO3 (M: alkali metals)-modified (K,Na)NbO3 lead-free piezoceramics

Abstract In this work, the piezoelectric and thermal aging characteristics of 0.955(K,Na)NbO 3 ceramics doped with 0.045(Bi,M)ZrO 3 {M: Na, K, (Na,K), (Na,K,Li), (Na,Li), (K,Li), Li} were investigated. All the ceramics prepared by conventional solid-state process showed a rhombohedral−orthorhombic−tetragonal (R−O−T) or a R−T phase boundary, and the KNN-BNKLZ ceramic exhibited the highest d 33 value of ~300 pC/N ( T C ~337 °C). The effect of Li + on the piezoelectric and thermal aging properties of the KNN-BMZ ceramics was considerably larger than those of Na + and K + . The higher fraction of T phase relative to R phase with increasing Li + content is detrimental to the piezoelectric properties but beneficial to the thermal aging rate. The temperature-dependent behaviors of the charge sensitivity obtained from the prototype accelerometers were consistent with those of d 33 . The results indicate that the structural manipulation of the R−T phase boundary region is required to optimize the piezoelectric properties and thermal aging stability for accelerometer applications.

Piezoelectric and ferroelectric properties of (Bi,Na)TiO3–(Bi,Li)TiO3–(Bi,K)TiO3 ceramics for accelerometer application

AbstractThe piezoelectric and ferroelectric properties of 0.76(Bi0.5Na0.5)TiO3–0.04(Bi0.5Li0.5)TiO3–0.2(Bi0.5K0.5)TiO3 (abbreviated as 0.76BNT–0.04BLT–0.2BKT) ceramics were investigated to clarify the optimal sintering temperature, and the vibration characteristics were examined for a compression‐mode accelerometer assembly in which 0.76BNT–0.04BLT–0.2BKT ceramics sintered at the optimized temperature served as the piezoelectric elements. The increase in the grain size of the 0.76BNT–0.04BLT–0.2BKT ceramics with the sintering temperature provides a beneficial contribution to the piezoelectric coefficient; however, it detrimentally contributes to the depolarization temperature. The charge sensitivity of the prototype accelerometers was evaluated with changes in the seismic mass and the layer number of the piezoceramics. The deviation between the theoretical and measured values of charge sensitivity was less than 10%.

Medium-high frequency FBG accelerometer with integrative matrix structure.

To meet the requirements for medium-high frequency vibration monitoring, a new type fiber Bragg grating (FBG) accelerometer with an integrative matrix structure is proposed. Two symmetrical flexible gemels are used as elastic elements, which drive respective inertial mass moving reversely when exciting vibration exists, leading to doubling the wavelength shift of the FBG. The mechanics model and a numerical method are presented in this paper, by which the influence of the structural parameters on the sensitivity and eigenfrequency is discussed. Sensitivity higher than 200 pm/g and an eigenfrequency larger than 3000Hz can be realized separately, but both cannot be achieved simultaneously. Aiming for a broader measuring frequency range, a prototype accelerometer with an eigenfrequency near 3000Hz is designed, and results from a shake table test are also demonstrated.

Performance of a Sensitive Micromachined Accelerometer With an Electrostatically Suspended Proof Mass

A three-axis micromachined accelerometer with a proof mass suspended electrostatically in six degrees of freedom was designed and tested to evaluate its performance of this sensitive sensor for potential microgravity space applications. The device is based on a glass/silicon/glass bonding structure, fabricated by bulk micromachining process, and operated with force-balance technology. The motion of the proof mass with respect to each side is fully servo-controlled by capacitive position sensing and electrostatic force feedback. The design and simulation of multiaxis suspension control loops are presented based on the stiffness requirements for different full-scale ranges. The ground test of this sensitive accelerometer is facilitated by setting the vertical axis at a relatively high measurement range to counteract the one-g gravity, whereas the range in two lateral axes can be set as low as possible to achieve high sensitivity. Detailed experimental results of electrostatic suspension, threeaxis accelerometer, and its cross-axis sensitivity are presented with the device operated initially in an atmospheric environment. The preliminary test results of a prototype accelerometer show that a sensitivity up to 688.8 V/g and a noise density down to 3 μg/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> can be achieved by setting an extremely low full-scale range of ±2.90 mg. The results also show that much different stiffness levels in the design of three-axis suspension is a major source of cross coupling effects in the prototype accelerometer.

Testing of MEMS capacitive accelerometer structure through electro-static actuation

The present paper discusses a method for testing a MEMS capacitive accelerometer structure through electrical actuation. The response of a standard MEMS capacitive accelerometer structure for different electrical actuation voltages has been analyzed. The accelerometer structure along with a capacitance sensing integrated circuit (IC) MS3110 is modeled and simulated. A set of proto-type accelerometer structures is fabricated and packaged in PGA packages. The packaged MEMS structures and MS3110 IC are integrated on a printed circuit board. The MEMS structure is actuated by applying the electrical signal through the actuation fingers and the change in capacitance is measured by the MS3110 IC. The simulated and measured results show some interesting phenomenon like dipping and frequency doubling which are useful for initial testing and characterization of a MEMS accelerometer structure.

MEMS Capacitive Accelerometer-Based Middle Ear Microphone

The design, implementation, and characterization of a microelectromechanical systems (MEMS) capacitive accelerometer-based middle ear microphone are presented in this paper. The microphone is intended for middle ear hearing aids as well as future fully implantable cochlear prosthesis. Human temporal bones acoustic response characterization results are used to derive the accelerometer design requirements. The prototype accelerometer is fabricated in a commercial silicon-on-insulator (SOI) MEMS process. The sensor occupies a sensing area of 1mm × 1mm with a chip area of 2mm × 2.4mm and is interfaced with a custom-designed low-noise electronic IC chip over a flexible substrate. The packaged sensor unit occupies an area of 2.5mm × 6.2mm with a weight of 25mg. The sensor unit attached to umbo can detect a sound pressure level (SPL) of 60dB at 500Hz, 35dB at 2kHz, and 57dB at 8kHz. An improved sound detection limit of 34-dB SPL at 150Hz and 24-dB SPL at 500Hz can be expected by employing start-of-the-art MEMS fabrication technology, which results in an articulation index of approximately 0.76. Further micro/nanofabrication technology advancement is needed to enhance the microphone sensitivity for improved understanding of normal conversational speech.

Novel optical accelerometer based on Fresnel diffractive micro lens

This paper presents an innovative optical accelerometer based on an integration of a Fresnel diffractive micro lens with a reflecting membrane. The reflecting membrane mounted on an inertial mass is placed parallel behind the diffractive micro lens. The light intensity at the conjugate position of an applied monochromatic point source is highly sensitive to the displacement of the membrane. The working principle is specifically discussed. In addition, this sensor makes use of a quad beam structure to allow the flat displacement of the inertial mass. Mechanical simulations using finite element method show the designed structure has a wide range of operation. A prototype accelerometer has been successfully developed. Dynamic tests indicate that the accelerometer has promising performance. This accelerometer can be fabricated using microelectromechanical systems (MEMS) technology, with relatively few process steps, so it is suitable for batch production. By optimizing structural designs, it can be a competitive candidate for a number of application fields ranging from vibration monitoring to inertial navigation.

Design optimization and implementation of a microgravity capacitive HARPSS accelerometer

This paper reports on the design optimization and implementation of a lateral capacitive accelerometer with high sensitivity and micro-g resolution, fabricated through the high-aspect ratio polysilicon and single-crystal silicon process on regular silicon wafers. A new implementation of vertical corrugation in silicon electrodes is developed to reduce the mechanical noise equivalent acceleration of the sensor. The predicted effect of corrugation on thermomechanical noise and also on static sensitivity is verified using ANSYS steady-state thermal simulation and FEMLAB linear stationary electrostatics analysis, respectively. The number of corrugated electrodes and the sense gap spacing is optimized to minimize the system (sensor + circuit) noise floor, while satisfying process and electronics limits. The open-loop differential sensitivity of a 60-/spl mu/m-thick prototype accelerometer is measured to be 0.25 V/g equivalent to 4.5 pF/g over a 1-g range. The estimated total noise equivalent acceleration of the system (sensor + circuit) is 0.95 /spl mu/g//spl radic/Hz in atmosphere.

A low-noise low-offset capacitive sensing amplifier for a 50-/spl mu/g//spl radic/Hz monolithic CMOS MEMS accelerometer

This paper describes a CMOS capacitive sensing amplifier for a monolithic MEMS accelerometer fabricated by post-CMOS surface micromachining. This chopper stabilized amplifier employs capacitance matching with optimal transistor sizing to minimize sensor noise floor. Offsets due to sensor and circuit are reduced by ac offset calibration and dc offset cancellation based on a differential difference amplifier (DDA). Low-duty-cycle periodic reset is used to establish robust dc bias at the sensing electrodes with low noise. This work shows that continuous-time voltage sensing can achieve lower noise than switched-capacitor charge integration for sensing ultra-small capacitance changes. A prototype accelerometer integrated with this circuit achieves 50-/spl mu/g//spl radic/Hz acceleration noise floor and 0.02-aF//spl radic/Hz capacitance noise floor while chopped at 1 MHz.

Basic Consideration of Trident-Type Tuning Fork Accelerometers Using Coriolis Force Phenomenon

In this paper we deal with a new type of accelerometer using the Coriolis force phenomenon. This accelerometer, which consists of a trident-type tuning fork resonator, is driven and its signal is detected by piezoelectric ceramics. In this study, two kinds of accelerometers are investigated. First, the construction and operating principle of the accelerometers proposed by us are described and, next, the experimental results of prototype accelerometers are presented. The results prove that the prototypes can basically operate as accelerometers.

Polysilicon process development for fully integrated surfacemicromachined accelerometer with CMOS electronics

In this paper we shall discuss the required polysilicon characteristics to produce free-standing mechanical structures such as accelerometers. Protection of the metallization and electronics during the removal of the sacrificial oxide will be discussed along with drying techniques. A process for producing mechanical structures with active CMOS transistors will be presented along with a prototype accelerometer. Tumbletest results for the accelerometer show that even with external, off-chip electronics, these devices can easily distinguish ± 1 g. Capacitancevoltage ( CV) curves for the accelerometers are shown as a quick way of checking these devices using standard integrated-circuit test instruments. Analysis of the current-voltage ( IV) characteristics of both the n-channel and p-channel transistors shows that the additional processing has no effect on the threshold voltage but does significantly increase the channel shortening.

Optically Powered Electrical Accelerometer and Its Field Testing

This paper introduces an optically powered electrical accelerometer recently developed by the author for measuring dynamic response of civil structures and describes a field test using its prototypes installed on a 310-m tall concrete TV tower, together with the results of system identification analysis based on the field measurement. This sensor employs an electric circuit, LC oscillator, in the sensor head. The resonant frequency of the LC oscillator is modulated by the movement of a pendulum installed inside the sensor head, indicating the acceleration of the pendulum support. The oscillatory electric voltage is transformed to an optical signal and transmitted through an optical fiber. The LC circuit is optically powered as well. Therefore, there are no electrical cables involved in this sensor, which brings many advantages to the sensor, such as immunity to an electromagnetic field and significantly less troublesome cabling problems. Prototype accelerometers were fabricated and installed on the TV tower to measure its ambient vibration. Based on the measurements, dynamic characteristics of this tower, including the natural frequencies, damping ratios, and mode shapes, were successfully identified. They are essential for the assessment of the dynamic response of the tower under wind and earthquake loads. This field test has not only provided valuable information of the tower's dynamic characteristics, but also demonstrated the excellent performance and great potential of this optically powered sensor for civil structure applications.

A miniature, high-sensitivity, electron tunneling accelerometer

Prototype low-noise miniature accelerometers have been fabricated with electron-tunneling transducers. The electron-tunneling transducer permits detection of small displacements of the proof mass with high electrical response; such a transducer is essential for a high-performance miniature accelerometer. Prototype accelerometers have shown self-noise of approximately 10 −7 g ( Hz) − 1 2 or less between 10 and 200 Hz, and close to 10 −8 g ( Hz) − 1 2 near the resonance frequency of 100 Hz. Directivity measurements give nulls at least 50 dB below the maximum. A dual-axis prototype designed for underwater acoustic applications is packaged in an 8 cm 3 volume with a mass of 8 g.

Performance limitations of surface-machined accelerometers fabricated in polysilicon gate material

Abstract In this paper we seek to determine the limitations imposed on the sensitivity, dynamic range and bandwidth of surface-micromachined accelerometers by their small masses and spring constants. The dynamic behaviour of a simple sprung mass system is considered to obtain a fundamental model for the accelerometer. The model is then extended to include thermal noise. We describe a prototype accelerometer structure fabricated using CMOS-compatible processing, which exploits the polysilicon gate material for the micromachined device. We apply the model to this simple accelerometer structure to determine the potential performance (range, sensitivity and bandwidth) of surface micromachined accelerometers. We conclude that it should be possible to fabricate an accelerometer with a sensitivity of 0.01 m s−1 using surface-micromachining technology.

Development of a novel electrochemically active membrane and 'smart' material based vibration sensor/damper

Vibration control has been achieved using state-of-the-art 'smart' materials. A 'smart' material has been developed from a metallized ionomer membrane called Nafion. This electroded material can sense mechanical vibrations and generate a voltage response. Electroded Nafion has a unique vibrational damping property. Damping with this material is achieved by dissipating the electrical energy generated as heat. This can be done using an external resistance or optimally by creating an internal conductive path. A prototype accelerometer cell has been developed which shows excellent linear characteristics and high sensitivity. It is found that the most critical element in both of the applications is the sum of the internal and the contact resistances of the electroded Nafion hydrogen pressure cell. Accordingly, a study of the resistance of these Nafion-based cells has been made and the results are included and discussed.

An electron tunneling sensor

New methods have been developed to implement position sensors based on electron tunneling. The electron tunneling methods enable position to be detected with sub-Ångstrom resolution using a compact mechanical structure and simple electronic control elements. A prototype accelerometer is the first sensor based on these principles; it shows reliable operation with a 10 μg/√Hz noise-limited sensitivity and abandwidth of approximately 3 kHz. Based on these results, it is expected that tunnel sensors optimized for many applications will enable an entirely new class of sensors to be developed.

Excess noise measurements in ion-implanted silicon resistors : H. R. Bilger, J. L. Tandon and M.-A. Nicolet. Solid St. Electron.17, 599 (1974)

In this paper we shall discuss the required polysilicon characteristics to produce free-standing mechanical structures such as accelerometers. Protection of the metallization and electronics during the removal of the sacrificial oxide will be discussed along with drying techniques. A process for producing mechanical structures with active CMOS transistors will be presented along with a prototype accelerometer. Tumbletest results for the accelerometer show that even with external, off-chip electronics, these devices can easily distinguish ± 1g. Capacitancevoltage (CV) curves for the accelerometers are shown as a quick way of checking these devices using standard integrated-circuit test instruments. Analysis of the current-voltage (IV) characteristics of both the n-channel and p-channel transistors shows that the additional processing has no effect on the threshold voltage but does significantly increase the channel shortening.