Cold Arm Research Articles

Modeling and Design Enhancement of Electrothermal Actuators for Microgripping Applications

Microgrippers are miniature tools that have the capability to handle and manipulate micro- and nano-scale objects. The present work demonstrates the potential impact of the incorporation of perforations on a ‘hot and cold arm’ electrothermal actuation mechanism in order to improve the operation of microgrippers in terms of arm opening and operating temperature. By applying a voltage to one arm and setting the other as a ground, the current passes through the electrothermal actuator and induces its displacement along the in-plane direction. The difference in the geometry of the two arms causes one arm to expand more than the other and this results in transverse bending. A computational model was developed using a finite element analysis tool to simulate the response of the thermal actuators with varying geometries and investigate the impact of incorporating perforations on the arms of the thermal actuators to enhance its performance in terms of deflection and operating temperature. The simulation results were compared to their experimental counterparts reported in the literature. A good agreement between the numerical and experimental data was obtained. A novel design of a microgripper, made of perforated electrothermal actuators, was introduced. Its main characteristics, including the tip opening of the gripper arms, the applied voltage, and the stress and temperature distributions, were analyzed using the developed computational model. Different perforation shape and distribution were investigated. The present study demonstrates the capability of perforations to enhance the operation of microgrippers as manifested by the obtained higher tip displacement and lower tip temperature in comparison to conventional microgripper designs made of non-perforated thermal actuators. Furthermore, the highest stress generated on the microgripper elements was found to be much lower than the yield strength of the constituent material, which indicates proper functioning without any mechanical failure.

The Effects of Cold Arm Width and Metal Deposition on the Performance of a U-Beam Electrothermal MEMS Microgripper for Biomedical Applications.

Microelectromechanical systems (MEMS) have established themselves within various fields dominated by high-precision micromanipulation, with the most distinguished sectors being the microassembly, micromanufacturing and biomedical ones. This paper presents a horizontal electrothermally actuated ‘hot and cold arm’ microgripper design to be used for the deformability study of human red blood cells (RBCs). In this study, the width and layer composition of the cold arm are varied to investigate the effects of dimensional and material variation of the cold arm on the resulting temperature distribution, and ultimately on the achieved lateral displacement at the microgripper arm tips. The cold arm widths investigated are 14 m, 30 m, 55 m, 70 m and 100 m. A gold layer with a thin chromium adhesion promoter layer is deposited on the top surface of each of these cold arms to study its effect on the performance of the microgripper. The resultant ten microgripper design variants are fabricated using a commercially available MEMS fabrication technology known as a silicon-on-insulator multi-user MEMS process (SOIMUMPs)™. This process results in an overhanging 25 m thick single crystal silicon microgripper structure having a low aspect ratio (width:thickness) value compared to surface micromachined structures where structural thicknesses are of the order of 2 m. Finite element analysis was used to numerically model the microgripper structures and coupled electrothermomechanical simulations were implemented in CoventorWare. The numerical simulations took into account the temperature dependency of the coefficient of thermal expansion, the thermal conductivity and the electrical conductivity properties in order to achieve more reliable results. The fabricated microgrippers were actuated under atmospheric pressure and the experimental results achieved through optical microscopy studies conformed with those predicted by the numerical models. The gap opening and the temperature rise at the cell gripping zone were also compared for the different microgripper structures in this work, with the aim of identifying an optimal microgripper design for the deformability characterisation of RBCs.

Essential design and fabrication considerations for the reliable performance of an electrothermal MEMS microgripper

Over the past years, microelectromechanical systems (MEMS) have become a vital component within a wide range of technologies, making the study of their performance and operational reliability a very critical aspect for their correct functionality. Microgrippers are one such type of MEMS devices with one of their key applications being the manipulation of biological tissues and cells. This paper presents a microgripper design based on the ‘hot and cold arm’ electrothermal actuation mechanism that is suitable to study the deformability properties of human red blood cells under healthy and pathological conditions. The main scope of this paper is to highlight a number of failure mechanisms that are typical of surface micromachined MEMS microgrippers. These include out-of-plane buckling of the hot arm, stress concentrations, device stiction, and residual stresses. The studied polysilicon microgripper structures were designed and fabricated in line with the specifications of the commercial fabrication process PolyMUMPsTM. The microgripper design was numerically modelled and electrothermomechanically studied using finite element analysis in CoventorWare $$^{\circledR }$$ . Experimental testing on the fabricated structures was used to demonstrate reliable microgripper performance as well as instances of the considered failure mechanisms. Results for the reliable microgripper performance show that the microgripper arms deflected as expected when actuated, with the obtained simulation and experimental results in good agreement. The investigated failure mechanisms have led to the identification of essential design and fabrication considerations whose thorough investigation, with the aid of appropriate modelling approaches, is essential to define improvement solutions and best practices to mitigate the failure or malfunction of the microgripper during operation.

Numerical Investigation of a MEMS Thermal Actuator Performance by Modifying its Geometric Dimensions

Abstract Mechanical displacement and thermal stress investigation of a two hot arm thermal microactuator (polysilicon type) with different structural and geometrical parameters was investigated in this paper with Comsol Multiphysics software, starting from a validation model based on the real dimensions of a two hot arm thermal microactuator, experimentally tested at different actuation voltages. Variation at different actuation voltages (between 1 and 9 V) for the radiative energy received by the cold arm from the short hot arm and the ratio between the resistive heat energy and radiative energy at different cold arm widths dw with gap between arms g = 2 µm, and respectively at different gap widths g with dw = 15 µm was numerically computed here. Total displacement versus actuation voltages for the actuator models was also evaluated, along with von Mises stress and temperature distributions for identification of maximum bending stress along the inner (short) hot arm of the actuator.

The Effects of Structure Thickness, Air Gap Thickness and Silicon Type on the Performance of a Horizontal Electrothermal MEMS Microgripper

The ongoing development of microelectromechanical systems (MEMS) over the past decades has made possible the achievement of high-precision micromanipulation within the micromanufacturing, microassembly and biomedical fields. This paper presents different design variants of a horizontal electrothermally actuated MEMS microgripper that are developed as microsystems to micromanipulate and study the deformability properties of human red blood cells (RBCs). The presented microgripper design variants are all based on the U-shape ‘hot and cold arm’ actuator configuration, and are fabricated using the commercially available Multi-User MEMS Processes (MUMPs®) that are produced by MEMSCAP, Inc. (Durham, NC, USA) and that include both surface micromachined (PolyMUMPs™) and silicon-on-insulator (SOIMUMPs™) MEMS fabrication technologies. The studied microgripper design variants have the same in-plane geometry, with their main differences arising from the thickness of the fabricated structures, the consequent air gap separation between the structure and the substrate surface, as well as the intrinsic nature of the silicon material used. These factors are all inherent characteristics of the specific fabrication technologies used. PolyMUMPs™ utilises polycrystalline silicon structures that are composed of two free-standing, independently stackable structural layers, enabling the user to achieve structure thicknesses of 1.5 μm, 2 μm and 3.5 μm, respectively, whereas SOIMUMPs™ utilises a 25 μm thick single crystal silicon structure having only one free-standing structural layer. The microgripper design variants are presented and compared in this work to investigate the effect of their differences on the temperature distribution and the achieved end-effector displacement. These design variants were analytically studied, as well as numerically modelled using finite element analysis where coupled electrothermomechanical simulations were carried out in CoventorWare® (Version 10, Coventor, Inc., Cary, NC, USA). Experimental results for the microgrippers’ actuation under atmospheric pressure were obtained via optical microscopy studies for the PolyMUMPs™ structures, and they were found to be conforming with the predictions of the analytical and numerical models. The focus of this work is to identify which one of the studied design variants best optimises the microgripper’s electrothermomechanical performance in terms of a sufficient lateral tip displacement, minimum out-of-plane displacement at the arm tips and good heat transfer to limit the temperature at the cell gripping zone, as required for the deformability study of RBCs.

Analytical, Numerical and Experimental Study of a Horizontal Electrothermal MEMS Microgripper for the Deformability Characterisation of Human Red Blood Cells.

Microgrippers are typical microelectromechanical systems (MEMS) that are widely used for micromanipulation and microassembly in both biological and micromanufacturing fields. This paper presents the design, modelling, fabrication and experimental testing of an electrothermal microgripper based on a ‘hot and cold arm’ actuator design that is suitable for the deformability characterisation of human red blood cells (RBCs). The analysis of the mechanical properties of human RBCs is of great interest in the field of medicine as pathological alterations in the deformability characteristics of RBCs have been linked to a number of diseases. The study of the microgripper’s steady-state performance is initially carried out by the development of a lumped analytical model, followed by a numerical model established in CoventorWare® (Coventor, Inc., Cary, NC, USA) using multiphysics finite element analysis. Both analytical and numerical models are based on an electothermomechanical analysis, and take into account the internal heat generation due to the applied potential, as well as conduction heat losses through both the anchor pads and the air gap to the substrate. The models are used to investigate key factors of the actuator’s performance including temperature distribution, deflection and stresses based on an elastic analysis of structures. Results show that analytical and numerical values for temperature and deflection are in good agreement. The analytical and computational models are then validated experimentally using a polysilicon microgripper fabricated by the standard surface micromachining process, PolyMUMPs™ (Durham, NC, USA). The microgripper’s actuation is characterised at atmospheric pressure by optical microscopy studies. Experimental results for the deflection of the microgripper arm tips are found to be in good agreement with the analytical and numerical results, with process-induced variations and the non-linear temperature dependence of the material properties accounting for the slight discrepancies observed. The microgripper is shown to actuate to a maximum opening displacement of 9 m at an applied voltage of 3 V, thus being in line with the design requirement of an approximate opening of 8 m for securing and characterising a RBC.

Electrothermal MEMS fiber scanner for optical endomicroscopy.

We report a novel MEMS fiber scanner with an electrothermal silicon microactuator and a directly mounted optical fiber. The microactuator comprises double hot arm and cold arm structures with a linking bridge and an optical fiber is aligned along a silicon fiber groove. The unique feature induces separation of resonant scanning frequencies of a single optical fiber in lateral and vertical directions, which realizes Lissajous scanning during the resonant motion. The footprint dimension of microactuator is 1.28 x 7 x 0.44 mm3. The resonant scanning frequencies of a 20 mm long optical fiber are 239.4 Hz and 218.4 Hz in lateral and vertical directions, respectively. The full scanned area indicates 451 μm x 558 μm under a 16 Vpp pulse train. This novel laser scanner can provide many opportunities for laser scanning endomicroscopic applications.

Modelling and experimental verification of heat dissipation mechanisms in an SU-8 electrothermal microgripper

Within this work, a microgripper based on a hot–cold arm principle was tested to give a greater understanding of the associated heat dissipation methods. Experiments were conducted in air at atmospheric and sub-atmospheric pressure, and in helium, argon and helium at sub-atmospheric pressure. The change in deflection, when using gases with different thermal conductivities and at varying pressures showed the significance of conduction through the atmosphere. The experimental results were found to verify a theoretical model created previously by this group, and a further model developed independently; both predicted the deflection that a given current would cause.

An Alternative to the Traditional Cold Pressor Test: The Cold Pressor Arm Wrap

Recently research on the relationship between stress and cognition, emotion, and behavior has greatly increased. These advances have yielded insights into important questions ranging from the nature of stress' influence on addiction1 to the role of stress in neural changes associated with alterations in decision-making2,3. As topics being examined by the field evolve, however, so too must the methodologies involved. In this article a practical and effective alternative to a classic stress induction technique, the cold pressor test (CPT), is presented: the cold pressor arm wrap (CPAW). CPT typically involves immersion of a participant's dominant hand in ice-cold water for a period of time4. The technique is associated with robust activation of the sympatho-adrenomedullary (SAM) axis (and release of catecholamines; e.g. adrenaline and noradrenaline) and mild-to-moderate activation of the hypothalamic-pituitary-adrenal (HPA) axis with associated glucocorticoid (e.g. cortisol) release. While CPT has been used in a wide range of studies, it can be impractical to apply in some research environments. For example use of water during, rather than prior to, magnetic resonance imaging (MRI) has the potential to damage sensitive and expensive equipment or interfere with acquisition of MRI signal. The CPAW is a practical and effective alternative to the traditional CPT. Composed of a versatile list of inexpensive and easily acquired components, CPAW makes use of MRI-safe gelpacs cooled to a temperature similar to CPT rather than actual water. Importantly CPAW is associated with levels of SAM and HPA activation comparable to CPT, and can easily be applied in a variety of research contexts. While it is important to maintain specific safety protocols when using the technique, these are easy to implement if planned for. Creation and use of the CPAW will be discussed.

An Alternative to the Traditional Cold Pressor Test: The Cold Pressor Arm Wrap

Recently research on the relationship between stress and cognition, emotion, and behavior has greatly increased. These advances have yielded insights into important questions ranging from the nature of stress' influence on addiction1 to the role of stress in neural changes associated with alterations in decision-making2,3. As topics being examined by the field evolve, however, so too must the methodologies involved. In this article a practical and effective alternative to a classic stress induction technique, the cold pressor test (CPT), is presented: the cold pressor arm wrap (CPAW). CPT typically involves immersion of a participant's dominant hand in ice-cold water for a period of time4. The technique is associated with robust activation of the sympatho-adrenomedullary (SAM) axis (and release of catecholamines; e.g. adrenaline and noradrenaline) and mild-to-moderate activation of the hypothalamic-pituitary-adrenal (HPA) axis with associated glucocorticoid (e.g. cortisol) release. While CPT has been used in a wide range of studies, it can be impractical to apply in some research environments. For example use of water during, rather than prior to, magnetic resonance imaging (MRI) has the potential to damage sensitive and expensive equipment or interfere with acquisition of MRI signal. The CPAW is a practical and effective alternative to the traditional CPT. Composed of a versatile list of inexpensive and easily acquired components, CPAW makes use of MRI-safe gelpacs cooled to a temperature similar to CPT rather than actual water. Importantly CPAW is associated with levels of SAM and HPA activation comparable to CPT, and can easily be applied in a variety of research contexts. While it is important to maintain specific safety protocols when using the technique, these are easy to implement if planned for. Creation and use of the CPAW will be discussed.

Analysis and simulation of semiconductor thermoelectric power generation process

This paper presents an improved model of thermoelectric power generation, taking into consideration the effect of air heat transfer in a closed cavity between the thermoelectric couples. We have used the ANSYS software, under the condition of different numbers of thermoelectric couples and different models, to simulate numerically and analyze the temperature field and, the voltage field of thermoelectric power generation. Results show that the energy conversion efficiency of 127 pairs of thermoelectric couples increases rapidly as the temperature gradient between the hot and cold ends increases as compared with 1 pair of thermoelectric units; it is enhanced from 0.39% to 5.16% at an average of 3.02% while the temperature gradient varies from 20℃ to 220℃. The output voltage of the chip, power, and energy conversion efficiency would increase as the cross-sectional area increases while the cold junction temperature stays at 305℃, and the cold arm galvanic greater the temperature difference across the greater the increase rate, and thermoelectric power generation chip resistance, along with the cross-sectional area of the galvanic arm decreases. The output power can be up to 28.9W as the temperature difference is 220℃.

Design and Analysis of Electro thermally Actuated Microgripper

Micro-Electro-Mechanical Systems (MEMS) technology offers the opportunity to produce mechanical, electromechanical, and electrochemical devices with the same unprecedented levels of miniaturization, and functionality as modern Very Large Scale Integrated (VLSI). Micro grippers are used for manipulation of biological samples, for assembling of micro parts and for micro assembly. Electro thermal micro grippers are promising tools enabling assembly and manipulation of nano-scale structures. In this paper MEMS based U-shaped thermally actuated micro-gripper is designed using two hot and one cold arm type thermal actuator. Then the effect of coefficient of thermal expansion and poisson’s ratio on stress for thermally actuated micro-gripper is analyzed and the results shows that the stress increases with the increase in coefficient of thermal expansion and the stress decreases with the increase in poisson’s ratio.

Design and Validation of Silicon-on-Insulator Based U Shaped Thermal Microactuator

method compatible with standard microelectronics. The basic two-arm electrothermal actuators design uses the principle of Joule heating for thermal expansion and movement. The thermal actuator can be categorized as in-plane and out of plane actuator (10), (11), where driving mechanism behind the two type of actuator is hot (narrow arm) and cold (wider arms) beam actuation and bimorph actuation. The potential application of electrothermal actuators includes optical switching (12), (13) and microgrippers (14) and micro robotic application (15). Among the different type of thermal actuators, the horizontal U shaped microactuator is more common compared to the V shaped and bimorph actuation mechanism. The horizontal U shape microactuator has a narrow hot cold arm. It operates based on the differential thermal expansion of these arms, when a voltage is applied between its contact pads (16). Two-arm actuators design consists of a thin arm, wide arm and flexure arm connected together at one end and constrained elastically at the anchors, which in turn are rigidly attached to the substrate. Application of a potential difference at the anchors generates a non uniform electrical field. The large current density in the thin arm causes a greater thermal expansion than that in the wide arm. This basic microactuator has been improved in various ways to produce higher deflections. In the present work, a FEM modeling and characterization of fabricated actuator are presented to explain the behavior of thermal actuator. These actuators are typically fabricated by a MUMPS (Multi User MEMS Process) bulk micromachining process that utilizes silicon as a structural layer. Commercial MEMS software's COMSOL 4.2 multiphysics tool is used for FEM simulation. In order to improve the performance of thermal actuator specifically mechanical motion, a better way is to vary the geometrical parameter of the structure rather than change the applied voltage. This works includes the study of geometrical parameters of thermal microactuator for enhanced mechanical motion. The effects of the variation in geometrical parameters on thermal actuator performance are also established. The fabricated actuator was tested and validated experimentally with simulated results.

Performance of silicon-on-insulator multiuser MEMS processes–based electrothermally actuated silicon microgrippers

Recently, microgrippers are finding more importance in the field of tissue engineering and microassembly in semiconductor electronics. Large force and, hence, large displacement, low power, and low temperature are the essential features to be considered during the design of the microgrippers. The electrical and mechanical behaviors of electrothermally actuated silicon microgrippers are presented. The effect of increasing the flexure length and the cold arm area to improve the displacement is discussed. These microgrippers are normally of the open type, in which the arms have an initial open gap of 20 μm, and they move away from each other with the applied voltage. The displacement of each arm is observed to be 24 μm for the applied voltage of 10 V. The response time of the device is less than 5 ms, and the maximum power dissipation is 110 mW. The displacement of the microgrippers can be increased with increased flexure length and cold arm length with short extended arms. This structure also shows lower stress.

Ex-Vivo Perfusion of Human Donor Hearts Reduces Cold Ischemia Time

Purpose Cold ischemia is an obligatory part of solid organ transplantation. Prolonged cold ischemia time (CIT) in heart transplantation can impact early allograft function and may be associated with chronic rejection. CIT beyond 6 hours is associated with increased recipient mortality based on ISHLT/UNOS database. Ex-vivo organ perfusion (Organ Care System (OCS)) maintains the donor hearts in a warm, beating state and reduces CIT. The purpose of this study is to compare CIT of donor hearts preserved on ice vs. on OCS. Methods and Materials PROCEED II is an FDA approved prospective, randomized, international multi-center study that is designed to compare OCS to cold static preservation of the donor hearts during transport. As of 10/01/12, 79 patients had been enrolled into this study. 40 patients were randomized to cold static preservation arm (control group); 39 patients were randomized to OCS (OCS group). Results Table 1 compares the cross clamp time and CIT for the OCS and Control groups.There is a statistically significant increase in possible cross clamp time (p Conclusions Ex vivo perfusion of donor hearts on OCS reduces CIT by nearly 40% when compared to the control group. Reduction in CIT may improve short and long term heart allograft function. Cross Clamp Vs. CIT for the OCS and Control Groups OCS Group - mean ± SD (range) Control Group - mean ± SD (range) Total Cross Clamp Time (min) 329 ± 79 (149-543) 180 ± 66 (36-312) OCS Group Explantation and Instrumentation Time (min) 29 ± 7 (16-50) N/A OCS Group Implantation Time (min) 80 ± 23 (43-142) N/A Total CIT (min) 109 ± 26 (62-169) 180 ± 66 (36-312)

Showering emboli of an atrial mass: a fatal phenomenon.

Dear Editor Left atrial (LA) myxoma, the most common type of primary cardiac tumor is an uncommon disease with an annual incidence of 0.5 per million populations which may be associated with brief isolated ischemic events or may represent a major source of neurological morbidity. Clinically apparent cerebral emboli have been reported in the range of 25%. In most patients with atrial myxoma, embolization of tumor fragments results clinically in isolated nonfatal ischemic strokes, but in others sudden plugging of the mitral valve opening may cause syncope or sudden cardiac death. So although atrial myxomas are rare, failure to recognize them may deprive patients of life-saving tumor resection (1-3). We describe a 73-year-old woman with history of confirmed diagnosis of LA mass (max size = 3x4cm) highly suggestive of LA myxoma by transesophageal echocardiography (TEE) two months ago. It had a gelatinous appearance with villous surface. She refused surgery at that time and presented with a rapidly progressive illness resulting in coma within 24 hours from multiple myxomatous emboli. On arrival to the emergency room, physical examination revealed shallow breathing with a respiratory rate of 29/min, blood pressure of 180/110 mm Hg, and temperature of 37.7°C. She was unresponsive to verbal stimuli and had no spontaneous motor movements. Eyes were deviated to the right. With painful stimuli she grimaced. Pupils were 3 mm in size and minimally reactive to light. No papill-edema was found. Muscle-stretch reflexes were increased in both the upper and lower extremities with bilateral extensor responses. Laboratory examination revealed a respiratory, compensated metabolic acidosis with a lactate level of 7 mmol/L. Creatinine phosphokinase and Troponin I were very high. Levels of urea nitrogen and creatinine were increased most probably due to tumor emboli in kidney artery. The electrocardiogram showed a normal sinus rhythm with acute ST segment elevation inferolateral myocardial infarction due to embolization in coronary artery (3). A radiograph of the chest showed near normal findings. Cranial computed tomographic scan revealed several low attenuation areas within both cerebral hemispheres with multiple hemorrhages scattered throughout both hemispheres and effacement of cerebral-sulci, consistent with massive cerebral infarction. The patient rapidly progressed to unresponsive coma. Also cold and pulseless left arm and both lower extremities were highly suggestive of multiple peripheral artery embolizations (2, 3). Surprisingly TEE showed no any remenant of LA mass, large patent foramen ovale (PFO) and large emboli in proximal portion of right pulmonary artery (simultaneous pulmonary emboli) with moderate both ventricular dysfunction. Previous studies suggest that atrial myxoma is seen in 0.5% of acute stroke patients, with women in the fifth decade at greatest risk. Transthoracic echocardiograms have been repeatedly negative in patients with atrial myxoma, TEE or magnetic resonance imaging may increase the detection of atrial myxoma (4-6). Atrial myxoma may present with many clinical syndromes. Patients are seen primarily by internists or cardiologists with palpitations, exertional dyspnea, fever, fatigue, or weight loss or syncope. In addition, the exceptional friable and spongy mass of atrial myxoma may easily dislodge fragments into the systemic circulation. The central nervous system is one of the most susceptible areas of embolization (1, 5, 6). Our patient arrived at the emergent departement in a moribund condition and demonstrated an unrelenting process of embolization. An overwhelming shower of myxomatous material resulted in occlusion of many arteries even pulmonary artery via PFO. More frequently, patients with atrial myxoma are seen with small and single territory of cerebral infarcts, this much vessels occlusion has not yet been reported, to our knowledge. Our case was unique regarding to its gelatinous appearance and villous surface LA myxoma resulting in fatal multiple organ embolizations. It can be concluded that large gelatinous myxoma with villous surface should be surgically resected as soon as possible specially if associated with PFO.

Axillary artery lesions from humeral neck fracture: A study in relation to repair

Whether axillary artery injuries associated with proximal humeral fractures must be repaired is uncertain. The present study reports three cases treated with various approaches. In case 1, the left humeral surgical neck was broken, the radial pulse disappeared and the arm temperature was significantly reduced. Computerized tomography angiography (CTA) revealed a 3-cm filling deficiency in the axillary artery. The injured artery was reconstructed with a segment of the greater saphenous vein after the fracture was reduced and fixed with a plate. In case 2, the axillary artery was compressed by the broken humeral segment, which caused the right hand to become cool. The fracture was fixed but the axillary artery embolism was not treated. In case 3, the humeral neck was broken with injury to the brachial plexus, although the patient’s hand remained warm. Digital subtraction angiography (DSA) revealed that the axillary artery was injured badly but there was extensive collateral circulation. The proximal humeral fracture was reduced and fixed without artery reconstruction. The three cases all resulted in a good outcome with the bone healed and limb alive. No ischemic necrosis occurred. However, the neurapraxia did not dissappear completely. Axillary artery injury resulting from humeral neck fracture is a rare but disabling traumatic event. Early diagnosis based on signs of acute ischemia of the arm enables early treatment and a favourable outcome. An angiogram is the best way to diagnose the artery injury and evaluate the condition of the collateral circulation. The injured artery in a cold arm should be repaired, while in a warm arm reconstruction is unnecessary due to rich collateral circulation.

A thermal-driven silicon micro xy-stage integrated with piezoresistive sensors for nano-positioning

This paper describes a novel micro xy-stage, driven by double-hot arm horizontal thermal micro-actuators integrated with a piezoresistive sensor (PS) for low-voltage operation and precise control. This micro xy-stage structure is linked with chevron beams and optimized to amplify the displacement generated by the micro-actuators that provide a pull force to the movable platform. The PS employed for in situ displacement detection and feedback control is fabricated at the base of a cold arm, which minimizes the influence of temperature change induced by electro-thermal heating. The micro xy-stage structure is defined through the use of a simple micromachining process, released by backside wet etching with a special tool. For an input power of approximately 44 mW, each chevron actuator provides about 16 µm and the total displacement of the platform is close to 32 µm. The sensitivity of the PS is better than 1 mV µm−1, obtained from the amplified voltage output of the Wheatstone bridge circuit. The potential applications of the proposed micro xy-stage lie in micro- or nano-manipulation, as well as the positioning of ultra-small objects in nanotechnology.

Monolithic micro-electro-thermal actuator integrated with a lateral displacement sensor

This paper presents monolithically fabricated horizontal thermal actuators integrated with piezoresistive sensors for in situ displacement sensing. The great advantage of a hybrid system is the use of closed feedback control for improving the transient response of a thermal actuator and positioning accuracy. It consists of two ‘hot arms’ made of doped silicon for Joule heating-induced thermal expansion when a current flow passes through them. The piezoresistor is embedded in the base of the ‘cold arm’ flexure for monitoring the tip deflection and for performance characterization. This ‘cold arm’ is not a part of the electrical circuit, which further improves the heat power efficiency and the measurement accuracy. Optimization is achieved mainly through modification of the geometry as well as the fabrication process. The fabricated micro-electro-thermal actuator with an integrated sensor is intended for use as a scanning cantilever in atomic force microscope or as a sample holder to drive the moving object through arrays configuration.

Design and Modeling of an Efficiency Horizontal Thermal Micro-Actuator with Integrated Piezoresistors for Precise Control

An integrated system made up of a double-hot arm electro-thermal microactuator and a piezoresistor embedded at the base of the 'cold arm' is proposed. The electro-thermo-mechanical modeling and optimization is developed to elaborate the operation mechanism of the hybrid system through numerical simulations. For given materials, the geometry design mostly influences the performance of the sensor and actuator, which can be considered separately. That is because thermal expansion induced heating energy has less influence on the base area of the 'cold arm,' where is the maximum stress. The piezoresistor is positioned here for large sensitivity to monitor the in-plane movement of the system and characterize the actuator response precisely in real time. Force method is used to analyze the thermal induced mechanical expansion in the redundant structure. On the other hand, the integrated actuating mechanism is designed for high speed imaging. Based on the simulation results, the actuator operates at levels below 5 mA appearing to be very reliable, and the stress sensitivity is about 40 MPa per micron.