Junliang Tao

Hair flow sensors: from bio-inspiration to bio-mimicking—a review

A great many living beings, such as aquatics and arthropods, are equipped with highly sensitive flow sensors to help them survive in challenging environments. These sensors are excellent sources of inspiration for developing application-driven artificial flow sensors with high sensitivity and performance. This paper reviews the bio-inspirations on flow sensing in nature and the bio-mimicking efforts to emulate such sensing mechanisms in recent years. The natural flow sensing systems in aquatics and arthropods are reviewed to highlight inspirations at multiple levels such as morphology, sensing mechanism and information processing. Biomimetic hair flow sensors based on different sensing mechanisms and fabrication technologies are also reviewed to capture the recent accomplishments and to point out areas where further progress is necessary. Biomimetic flow sensors are still in their early stages. Further efforts are required to unveil the sensing mechanisms in the natural biological systems and to achieve multi-level bio-mimicking of the natural system to develop their artificial counterparts.

A new time-domain reflectometry bridge scour sensor

Scour is a major threat to bridge safety. Bridge failures cost millions of dollars each year as the result of not only the direct costs of replacing and restoring these bridges but also the indirect costs related to the disruption of transportation network. Instruments for bridge scour monitoring are necessary to study scour process and support bridge management. Lack of robust and economic scour monitoring devices prevents the implementation of bridge scour monitoring program among bridge owners. This study describes the development of a new time-domain reflectometry scour sensor. The geometry of this sensor was designed to allow for easy installation through common geotechnical boreholes. Coating was applied to the sensor, which provided it with a large range of sensing depths compared to an uncoated metallic rod sensor. The coating also provided corrosion protection. The design of this new sensor was studied by numerical simulations with finite element method. From the results, the effective sampling areas of this sensor were determined. Laboratory evaluations showed that this sensor was sensitive to simulated scour process. An algorithm was developed to determine scour depth from sensor signals. The results indicated that the sensor provided accurate scour depth measurement.

Emulating the directional sensitivity of fish hair cell sensor

This article describes the sensor development efforts that are inspired by the unique acoustic source tracking capability of aquatics such as fish. The physiological basis in the natural system has been attributed to the unique directional responses of hair cell sensor in the otolith. To emulate such directional transduction behaviors, a hair sensor based on piezoelectric microfiber is attempted. The sensor employs piezoelectric fiber both as the hair shaft and as the transduction element. A pair of electrodes was deposited on the fiber surface both for sensor signal collection and for polarizing the piezoelectric materials. Both computational modeling analysis and experimental study were conducted to validate the sensor performance. The hair sensor was found to possess directional responses that change in the pattern of a cosine function of the loading direction, resembling that observed in the hair cell sensor in the biological system. Such transduction behaviors pave the technical basis to emulate the unique acoustic tracking strategy by aquatics. PACS 07.07.Df, 07.10.Pz, 77.84.Cg, 87.19.lt

Bio-inspired flow and acoustic sensor

This paper describes the efforts toward the development of bio-inspired flow and acoustic sensor from fish. Anatomy study has indicated a basic transduction element is the hairy structure. This study describes the fabrication of sensing element that emulate the mechano-electrical transduction mechanism. These include the use of advanced lithographic technology for sensor electrode deposition. The sensor was polarized under high voltage gradient. Preliminary experimental evaluation indicates that the hairy structures are responsive to external excitations. Especially, the hairy structure made of the SDW method not only produces transduction component for mechano-electrical coupling, it is also rugged, sensitive and fracture resistant. The hairy structure also features directional sensitivity which could be used for acoustic field direction determination. The hairy structure is being further refined and will ultimately be integrated into develop bio-inspired flow and acoustic sensors.

A bio-inspired flow sensor

Accurate measurement of the turbulent flow is an important step toward understanding the mechanisms of many unknown phenomena. Turbulence generally can not be easily measured without significantly disturbing the original flow conditions. This paper introduces the efforts that aim to develop a bio-inspired sensor for monitoring turbulent flow. The sensor will consist of an array of micro-pillars or nano-pillars. Piezoelectric elements serve as transductors, which provides a key sensing element in the construction of micro-pillar. A prototype design was fabricated for the micropillar. The performance of sensing principle by this micropillar was evaluated and was found to be sensitive. The micropillar will be further refined into sensing arrays for real time sensing of flow turbulence.

A New Method for Soil Water Characteristic Curve Measurement Based on Similarities Between Soil Freezing and Drying

The soil water characteristic curve (SWCC) is the basis to explain a variety of processes in unsaturated soils, ranging from transport phenomena to mechanical behaviors. In this paper, a new method is developed for SWCC estimation based on the similarity between the freezing/thawing process and drying/wetting process in soils. The theoretical basis for this method is first reviewed. The concept of the soil freezing characteristic curve (SFCC) is introduced to describe the relationship between the unfrozen water content and matric suction in frozen soils. SFCC is analogous to SWCC in that both of them describe the energy status of liquid water associated with liquid water content. Relationships between SWCC and SFCC are discussed. To measure the SFCC, a thermo-time domain reflectometry (TDR) sensor was developed which combines both temperature sensors and conventional TDR sensor. The TDR module and algorithm measured the bulk free water content of soils during the freezing/thawing processes, while the built-in thermocouples measured the internal temperature distribution. SFCCs were obtained from the simultaneously measured TDR and temperature data. Experiments were conducted on a few types of soils to validate this new procedure. The SFCC was obtained from thermo-TDR data collected in specimens subjected to a controlled thawing process, while the SWCC was directly measured by ASTM D5298, the filter paper method. Reasonable agreements were found between SWCC and SFCC. The experimental results implied that the SWCC could be estimated from SFCC, which also provided more evidence of the similarity of freezing/thawing processes and desorption/sorption processes.

A non-contact wearable wireless body sensor network for multiple vital signal detection

In this paper, we describe the development of a wearable wireless body sensor network (WBSN) to contactless detect multiple vital signals. The ECG, EEG, respiration rate, eye blinking activities as well as the motion can be detected by different sensor nodes. Instead of traditional galvanic contact, the ECG signals can be detected through cloth and even with an explicit air gap up to 30mm from the chest nodes. From these, the respiration rate, heart rate (HR), and heart rate variability (HRV) can be obtained. The EEG signals can be collected without any preparation from the brain nodes, and the eye blinking activities, such as the blinking frequency, opening time and closure time can be acquired from a simple eye node with a distance up to 15mm. Moreover, the sensor nodes can detect the motion simultaneously with the vital signals by 3D accelerometers. All these nodes collect the data in real time and communicate with a gateway node using a wireless sensor network platform that include iMote2 module following IEEE 802.15.4. The gateway collects data and transfers to computer. The power supply can be provided from both batteries and energy scavenger of a thermal electric module to extend the lifetime of the WBSN.

Thermally Induced Water Flux in Soils

A comprehensive study is presented for the formulation of thermally induced water flux. For conditions without ice lenses, either frozen or unfrozen conditions, a theory is proposed to address the underestimation of water flux by the model of Philip and de Vries. In addition, experiments with a modified capillary rise method are proposed to calculate a gain factor that accounts for this underestimation. For thermally induced flux in frozen soils with ice lenses, a theoretical formulation is derived for the segregation potential, which is the key parameter in the model of Konrad and Morgenstern. This theoretical formulation, which is lacking in previous research, is expressed in a simple mathematical form and can be conveniently used for accurate prediction of segregation potential. The validity of the theory is proved with reported data, and more auxiliary relationships are provided for accurately predicting the segregation potential with the proposed formulation.

Bio-inspired directional sensor with piezoelectric microfiber and helical electrodes:

Inspired by the hair cells of vertebrates and aquatics, we proposed a hair sensor design that mimics the directionality and linearity of hair cells. The sensor promotes a novel use of piezoelectric microfiber with unique helical electrodes. The sensing mechanism was modeled both analytically and numerically. The analytical model explicitly illustrates the effects of the various design parameters on the performance of the sensor; the numerical model took into account the complex geometry of the sensor and elucidated the importance of the orientation of piezoelectric polarization on the piezoelectric effects. Both models provide valuable insight to optimize the sensor performance. Hair sensor prototypes were fabricated and characterized in the laboratory. The sensor output was found to be linearly dependent on the magnitude of applied displacements. Besides, at the same magnitude of deflection, the sensor responses followed a cosine function with the loading direction, which is similar to what is observed on the directionality of biological hair cells. These experimental observations were consistent with the results of model simulations. An algorithm was proposed to determine the magnitude and direction of acoustic stimuli by utilizing just a pair of orthogonally polarized and closely spaced hair cell sensors.

Comparison Study on Computer Simulations for Bridge Scour Estimation

This paper compares the use of 1D and 2D hydraulic models for bridge scour prediction. Two representative computational software developed by Federal Highway Administration (FHWA), HEC-RAS and Flo2dh, are used as the benchmark comparison bases. The procedures for model construction and scour estimation are illustrated by developing simulation examples. The comparison shows that 1D model using HEC-RAS, while is easy to construction, does not account for the effects of flow disturbance due to hydraulic obstructions. These include the spatial variation of the alignment angle, which significantly affects the depth of scour prediction. Higher dimensional mode such as Flo2dh captures the effects of flow field distribution. It is however difficult to use and requires deliberations to run proper simulations. Further development of computational simulation and visualization technologies is necessary and will help place computer aided bridge scour simulations into the hands of practitioners.