The use of on-body wearable sensors is widespread in several academic and industrial domains. Of great interest are their applications in ambulatory monitoring and pervasive computing systems; here, some quantitative analysis of human motion and its automatic classification are the main computational tasks to be pursued. In this paper, we discuss how human physical activity can be classified using on-body accelerometers, with a major emphasis devoted to the computational algorithms employed for this purpose. In particular, we motivate our current interest for classifiers based on Hidden Markov Models (HMMs). An example is illustrated and discussed by analysing a dataset of accelerometer time series.

/pdf/machine-learning-methods-for-classifying-human-physical-b62qw3cvfj.pdf

Machine Learning Methods for Classifying Human Physical Activity from On-Body Accelerometers

A system and method for filtering and organizing items from computer memories based on common elements. In accordance with one aspect of the invention, filters are provided for manipulating the items. The filters are essentially tools for narrowing down a set of items. In one embodiment, the filters are dynamically generated based on the properties of the separate items. The system utilizes virtual folders. The virtual folders expose regular files and folders to users in different views based on their metadata instead of the actual physical underlying file system structure on the disk. In accordance with another aspect of the invention, quick links are provided. In one embodiment, quick links are a set of predefined links (e.g., located on the left side of the display) that can be clicked on to generate useful views of the sets of items. In accordance with another aspect of the invention, libraries are provided. Libraries consist of large groups of usable types of items that can be associated together.

System and method for filtering and organizing items based on common elements

This review paper focuses on interdigital electrodes-a geometric structure encountered in a wide variety of sensor and transducer designs. Physical and chemical principles behind the operation of these devices vary so much across different fields of science and technology that the common features present in all devices are often overlooked. This paper attempts to bring under one umbrella capacitive, inductive, dielectric, piezoacoustic, chemical, biological, and microelectromechanical interdigital sensors and transducers. The paper also provides historical perspective, discusses fabrication techniques, modeling of sensor parameters, application examples, and directions of future research.

/pdf/interdigital-sensors-and-transducers-540fhwik2c.pdf

Interdigital sensors and transducers

Over the past two decades, several advances have been made in micromachined sensors and actuators. As the field of microelectromechanical systems (MEMS) has advanced, a clear need for the integration of materials other than silicon and its compounds into micromachined transducers has emerged. Piezoelectric materials are high energy density materials that scale very favorably upon miniaturization and that has led to an ever-growing interest in piezoelectric films for MEMS applications. At this time, piezoelectric aluminum-nitride-based film bulk acoustic resonators (FBAR) have already been successfully commercialized. Future innovations and improvements in inertial sensors for navigation, high-frequency crystal oscillators and filters for wireless applications, microactuators for RF applications, chip-scale chemical analysis systems and countless other applications hinge upon the successful miniaturization of components and integration of piezoelectrics and metals into these systems. In this article, a comprehensive review of micromachined piezoelectric transducer technology will be presented. Piezoelectric materials in bulk and thin film forms will be reviewed and fabrication techniques for the integration of these materials for microsensor applications will be presented. Recent advances in various piezoelectric microsensors will be presented through specific examples. This review will conclude with a critical assessment of the future trends and promise of this technology.

https://iopscience.iop.org/article/10.1088/0957-0233/20/9/092001/pdf

Piezoelectric MEMS sensors: state-of-the-art and perspectives

IC-compatible microelectromechanical intermediate frequency filters using integrated resonators with Q's in the thousands to achieve filter Q's in the hundreds have been demonstrated using a polysilicon surface micromachining technology. These filters are composed of two clamped-clamped beam micromechanical resonators coupled by a soft flexural-mode mechanical spring. The center frequency of a given filter is determined by the resonance frequency of the constituent resonators, while the bandwidth is determined by the coupling spring dimensions and its location between the resonators. Quarter-wavelength coupling is required on this microscale to alleviate mass loading effects caused by similar resonator and coupler dimensions. Despite constraints arising from quarter-wavelength design, a range of percent bandwidths is still attainable by taking advantage of low-velocity spring attachment locations. A complete design procedure is presented in which electromechanical analogies are used to model the mechanical device via equivalent electrical circuits. Filter center frequencies around 8 MHz with Q's from 40 to 450 (i.e., percent bandwidths from 0.23 to 2.5%), associated insertion losses less than 2 dB, and spurious-free dynamic ranges around 78 dB are demonstrated using low-velocity designs with input and output termination resistances of the order of 12 k/spl Omega/.

High-Q HF microelectromechanical filters

The emergence of micro sensors and actuators is pushing forward the revolution of intelligent systems technology. Intelligent systems technology allows a dramatic change in the way that machines, tools, and systems serve humans. This paper reviews recent R&D and commercial status of inertial sensors using silicon micromachining technologies and discusses the requirement for commercialization of the research results.

Micromachined inertial sensors

An air-gap type film bulk acoustic resonator (FBAR) is created by securing two substrate parts, one providing a resonance structure and the other providing a separation structure, i.e., a cavity. When the two substrate parts are secured, the resonance structure is over the cavity, forming an air gap isolating the resonant structure from the support substrate. The FBAR may be used to form a duplexer, which includes a plurality of resonance structures, a corresponding plurality of cavities, and an isolation part formed between the cavities. The separate creation of the resonance structures and the cavities both simplifies processing and allows additional elements to be readily integrated in the cavities.

Air gap type FBAR, duplexer using the FBAR, and fabricating methods thereof

In fabricating microelectromechanical systems (MEMS), bulk micromachining using [100] and [110] single crystal silicon and surface micromachining using polycrystalline silicon are used. However, both micromachining methods have drawbacks, and micromachining actuating or sensing MEMS using single crystal silicon has been an active research topic in resent years. This paper presents electrostatic actuation of a resonator fabricated by the SBM (surface/bulk micromachining) process. The SBM process allows fabricating released structures in single crystal silicon. To fabricate electrodes and to electrically isolate them, a junction isolation method using reverse-biased diodes is developed. The breakdown voltage of this isolation method is measured to be larger than 150 volts. A SBM processed microresonator is actuated at 36 kHz. A displacement of several /spl mu/m is achieved in atmosphere with a 20 volts peak-to-peak supply.

Electrostatic actuation of surface/bulk micromachined single-crystal silicon microresonators

A resonator having a membrane formed of a piezoelectric layer sandwiched between first and second electrode is suspended above a cavity formed from the back surface of the support structure. In one embodiment, the cavity walls are substantially perpendicular to the back surface. In another embodiment, the first electrode is formed in the cavity such that it is electrically connected to an electrode on the back surface of the support structure. In yet another embodiment, the cavity is formed via an etch through via holes in the back surface of the support structure, which leads to greater flexibility in designing a method of manufacture while reducing the need for alignment relative to other designs.

Bulk acoustic wave resonator, filter and duplexer and methods of making same

A surface-micromachined silicon accelerometer with a novel concept, which has a stiffness tuning capability to improve the sensor resolution, is developed. Imposing an electrostatic force to the electrodes reduces the stiffness of the sensor structure. By adopting the stiffness tuning, the initially stiff structure guarantees the stability of fabrication, and the reduced stiffness, only along the sensing direction, produces the improved resolution. One of the major improvements in the developed accelerometer is the branched comb-finger type electrode which senses the relative position between the mass and the electrode. Maintaining the same capacitance variation, such electrodes allow a larger initial gap between the mass and the electrode, so that the clash problem can be easily eliminated. The accelerometer was successfully fabricated with the active size of 650×530 μm 2 , the 7-μm thick polysilicon structure, and a proof mass of about 1 μg. Experimental results show that the equivalent noise level of the accelerometer is improved by 30 dB through the stiffness tuning. The accelerometer has the bandwidth of 350 Hz, linearity of 0.3% FS, and sensing range of 50 g.

Byeoung-ju Ha

Papers

Micromachined inertial sensors

Air gap type FBAR, duplexer using the FBAR, and fabricating methods thereof

Electrostatic actuation of surface/bulk micromachined single-crystal silicon microresonators

Bulk acoustic wave resonator, filter and duplexer and methods of making same

Capacitive type surface-micromachined silicon accelerometer with stiffness tuning capability