ABIOCOR Total Artificial Heart System
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The ABIOCOR Total Artificial Heart System
QIS COLLEGE OF ENGINEERING & TECHNOLOGY
Everyone knows heart is a vital organ. Your heart is the engine inside your body that keeps everything running. Basically, the heart is a muscular pump that maintains oxygen and blood circulation through your lungs and body. Like any engine, if the heart is not well taken care of it can break down and pump less efficiently, a condition called heart failure. There are many people suffering with heart problems and heart failure problems.
Until recently, the only option for many severe heart failure patients has been heart transplants and VAD (Ventricular Assist Device). Heart Patients hoping to have a heart transplant may not be able to realize their hope because the amount of donor hearts in relation to the amount of patients in need of a donor heart is minuscule. Heart patients looking to have a VAD implant may find that the system is not yet so safe or dependable because the materials used for it have, in the past, run the risk of causing a stroke. Due to the lack of reliable options heart patients have, researchers have been trying to come up with a new method to aid these patients. The most recent success has been the AbioCor Total Artificial Heart System.
In this paper we presented an artificial heart system called The ABIOCOR which overcomes the defects in the above two mentioned methods. We also presented its design and the components present in it and the importance of each component and their function. The AbioCor System consists of a set of internal components and external components. All of these components keep the artificial heart pumping blood and keep sending that blood throughout the patientâ„¢s body. The AbioCor System acts as a natural heart and allows the patient to be free of too many restrictions; the patient is allowed to be mobile, and is also allowed to return many of the activities he participated in before undergoing heart failure. The AbioCor is also designed to increase the life expectancy of the heart patient by at least two times.
The AbioCor Total Artificial Heart System is designed to give patients with heart failure an option other than heart transplant and Ventricular Assist Device (VAD). VAD Systems are intended for patients with a failing left ventricle; the VAD is implanted and replaces the ventricle by acting as a pump. Heart Patients hoping to extend their life expectancy by having a heart transplant may not be able to realize their hope because the amount of donor hearts in relation to the amount of patients in need of a donor heart is minuscule. Heart patients looking to have a VAD implant may find that the system is not yet so safe or dependable because the materials used for it have, in the past, run the risk of causing a stroke. Due to the lack of reliable options heart patients have, researchers have been trying to come up with a new method to aid these patients. The most recent success has been the AbioCor Total Artificial Heart System. The AbioCor System acts as a natural heart and allows the patient to be free of too many restrictions; the patient is allowed to be mobile, and is also allowed to return many of the activities he participated in before undergoing heart failure. The AbioCor is also designed to increase the life expectancy of the heart patient by at least two times (Fact monster).
The components of the AbioCor system are simple in design; that is, the components are not decorated, nor are they coated with materials that are not necessary. The thoracic unit has a similar physical appearance to the appearance of a natural heart. This is because it contains inflows and outflows; aside from the similarity in inflows and outflows, the thoracic unit is very different from a natural heart because it is made of plastic and titanium and it is not full of veins as a natural heart is. The external and internal TET s are almost identical in their design, they both have a round top and a long thin end (similar to the shape of a lollipop); however, the external TET is covered with silicone. The rest of the AbioCor Systemâ„¢s components have geometric designs (mostly rectangular) and are not extravagant in their appearance. For example, the implanted controller and the implanted battery appear very similar; they are both cased in titanium, they both are covered in the solid color of titanium, and they both have the same shape. The console and the PCE control module are generally boxes with no artistic designs or variety in color. Internal Components:
1. Thoracic Unit (Artificial Heart):
The thoracic unit weighs slightly more than two pounds (0.9 kg) and is about the same size and shape of a natural heart. It is made of titanium, and Angioflex, a polyurethane plastic. The thoracic unit is implanted in the chest, where a natural heart would be located, and connects to the right and left atria, the aorta, and the pulmonary artery. In order for blood to enter and exit from the unit, grafts must be sewed onto the right and left atria, the aorta, and pulmonary artery of the patient. They must also be sewed onto the thoracic unitâ„¢s four heart valves. These grafts then allow for the two arteries and the two atria to each be snapped onto the graft of one of the heart valves. Conclusively, one valve will be snapped onto the aorta, another valve will be snapped onto the pulmonary artery, another to the left atrium and another to the right atrium.
The thoracic unit contains two hydraulic motors; one keeps the blood pumping from each ventricle (blood pump), and the other operates the motion of the four heart valves. The pumping from these hydraulic motors is caused by an oscillating pusher plate that squeezes sacs that then emit blood to the lungs and to the rest of the body (Total Artificial Hearts (TAH)). Additionally, the unit has a left and a right blood pump. Each blood pump has an inflow opening and an outflow opening. When the blood moves to the right blood pump the blood is pumped out through the outflow opening and is led to the lungs. When the blood moves into the left blood opening it will be led to the rest of the body.
2. Implanted Transcutaneous Energy Transmission (TET):
The implanted TET is an electric coil that provides all of the AbioCor Systemâ„¢s internal devices with electrical energy. It is connected to the thoracic unit, the implanted controller, and the implanted battery. The implanted TET is located on the upper-left area of the chest (opposite of the artificial heart). In order to fit the patientâ„¢s insides properly, it has the capability of adjusting its shape. Because the implanted TET provides the AbioCor System with energy without having to run wires in and out of the patientâ„¢s body, it may also be referred to as a wireless power transfer system. In order to provide internal devices with energy without the use of an external power connection, the implanted TET converts energy from radio waves, sent to it by an external TET, to electrical energy.
3. Implanted Controller:
The implanted controller is a small automatic computer located in the abdomen of the patientâ„¢s body. It is secured in a titanium case and connects to all internal components (the implanted TET, the artificial heart, and the implanted battery), meaning that it also receives energy from the implanted TET. The job of the implanted controller is to oversee the internal components of the AbioCor System, to communicate with the AbioCor Console or the Patient-Carried Electronics (PCE), and to control the blood flow output of the artificial heart. In order to monitor all internal components and communicate with external components, the implanted controller exchanges information with the console or the PCE (whether the implanted controller exchanges information with the console or the PCE depends on which of these two power sources the patient is using), if a problem is detected by either of the two external power sources, the patient is immediately notified. The implanted controller is also able to manage the artificial heartâ„¢s cardiac output rate to make sure that the artificial heat generates the necessary blood flow. The cardiac output rate is the amount of blood that flows through the heart, expressed in liters per minute. Due to monitoring of blood outflow, the incoming blood flow is guaranteed to match the outgoing blood flow. Aside from working automatically, the implanted controller can also be supervised by a clinician.
4. Implanted Battery:
The implanted battery is placed in the abdomen, opposite from the implanted controller, and is implanted when the implanted controller and the artificial heart are placed in the patientâ„¢s body. Just like the implanted controller, the implanted battery is kept in a titanium case, it receives energy from the external TET, and is connected to all other internal components (in the case of the implanted battery, these internal components are be the artificial heart and the implanted controller). The battery is constantly being recharged by an external battery pack that transfers power to the internal components of the Abercorn System through the external and internal TETs. If the patient were to separate himself from the external TET and battery pack (such as to take a shower), the implanted battery would provide the internal system of the AbioCor with energy for 30 - 40 minutes (Leung, Benedict). The battery itself can last for about a year before it would need to bed replaced. In order to replace it, the patient would be required to receive minor surgery. External Components:
1. External Transcutaneous Energy Transmission (TET):
The external TET is placed directly over the location of the internal TET to transfer energy through the skin (the external TET is placed over the skin, while the internal TET is placed under the skin, inside the patientâ„¢s body). It is connected to the console or the Patient-Carried Electronics (PCE) and is in the form of a silicone ring. The external TET provides the internal TET with energy from either the PCE control module or the AbioCor console. Both of these act as power supplies so what determines which will be used is the location of the patient. If the patient is stationary and is near a power outlet, his source for energy may be the console; if the patient is mobile and has no intentions of remaining in the same location for a long period of time, he may use the PCE as a power source. The several Watts of energy received from the external TET are transmitted to the internal TET in the form of radio waves (Shiba, Kenji). The amount of this energy is enough to penetrate the skin and to be received by the internal TET.
The console is a small computer containing a keyboard and screen that is used to provide power to the external TET and the internal TET and is also used to communicate with the implanted controller. To provide power to both TET s, the console is plugged into an electrical outlet. The internal TET is then able to transmit energy by being plugged into the back of the console. In order to communicate with the implanted controller, the console uses wireless technology; it consists of an antenna that sends commands to the implanted controller and then receives information regarding the internal componentsâ„¢ status. If something goes wrong within the internal system, the console immediately notifies the patient by setting off an alarm sound or alarm lights (Abiomed). In case of a power outage, the console also consists of a backup battery that will keep the system powered for 35 â€œ 40 minutes (Abiomed).
3. Patient-Carried Electronics:
The patient using the AbioCor System is not forced to stay in bed hooked up to the systemâ„¢s console; he is also given the option to move around and not have to depend on a power outlet to power the systemâ„¢s components. If the patient chooses to be mobile he may use the Patient-Carried Electronics (PCE) by plugging the external TET into the PCEâ„¢s control module. The PCE serves as a portable power supply, and is placed in a shoulder bag called the PCE Battery Bag. The battery bag stores a control module (this module takes the place of the console when the patient is mobile) and two pairs of batteries.
4.PCE Battery Bag:
The PCE Battery Bag weighs about 10 pounds and may be carried by using an attached shoulder strap (Abiomed). The inside of the bag contains a battery compartment that holds four batteries, and plastic cardholders. The outside of the bag contains pockets used to carry the PCE control module and any extra objects the patient may want to place in them.
Each pair of PCE Batteries supplies the AbioCor internal system with power for about one hour (Abiomed). Since the battery bag can carry two pairs of PCE batteries, the internal system may be supplied with power for about two hours if the patient uses only the two pairs stored in the battery bag. The batteries used for the PCE package differ from common store-bought batteries, the PCE batteries are especially made to power the AbioCor system. Additionally, since the PCE batteries donâ„¢t last very long, they must be changed several times a day and the patient must be aware of the amount of batteries he will be needing so he can take extra batteries (aside from those located in the battery bag) if necessary.
6. PCE Control Module:
The PCE control module is to be placed in one of the pockets, located on the outer part of the PCE battery bag, where it is connected to the batteries by a battery cable and is also connected to the external TET. Instead of being connected to the batteries, the control module may also be connected to any source of Alternating Current (AC) Power by using an AC Power Adapter. Once connected to a power source (batteries or AC Power), the control module converts the energy from the power source into electromagnetic energy in the form of radio waves. By converting the energy from the power source, the external TET is able to transfer energy to the internal TET. The control module, like the console, also monitors the status of all of the AbioCor Systemâ„¢s internal components by communicating with the implanted controller through wireless technology. If a problem occurs within one of the internal devices, the control module immediately notifies the patient.
To maintain operation, the AbioCor System must first have a source of power; depending on whether or not the patient is mobile, this power source will either be the console or the PCE control module. Both power sources cause the AbioCor System to perform the same function and to do so in a similar way. The only difference between the two sources is that the console receives its energy from a power outlet and is stationed in one place and the PCE control module receives its energy from a battery pack carried in the PCE battery bag and is portable. From the power source, energy will travel through the external TET in the form of radio waves. These radio waves will penetrate the patientâ„¢s skin and enter the implanted TET, which will then convert the radio waves into electrical energy. This electrical energy will travel to the implanted battery where it will remain to keep the battery charged. The energy stored in the battery will be used by the implanted controller to monitor the thoracic unitâ„¢s (artificial heart) cardiac output rate. This energy supplied to the artificial heart keeps the blood flowing into the heart and out into the body. The heart will take turns in sending blood to the lungs and to the rest of the body because it cannot send blood to both areas simultaneously as a natural heart would.
Besides controlling the artificial heartâ„¢s cardiac output rate, the implanted controller also oversees the performance of all internal components to make sure that everything is working properly. The information gathered by the controllerâ„¢s supervising is sent to the AbioCor Systemâ„¢s power source (the console or the PCE control module) using wireless technology. If the power source detects a problem, an alarm light or an alarm sound notifies the patient. Otherwise, if no problems are detected the AbioCor System follows a cyclic function and continues to operate.
The AbioCor System consists of a set of internal components and external components. The internal components are those located inside the patientâ„¢s body; they are the thoracic unit (artificial heart), the internal Transcutaneous Energy Transmission (TET), the implanted controller, and the implanted battery. The external components are those located outside of the patientâ„¢s body; these are the external Transcutaneous Energy Transmission (TET), the console, the Patient-Carried Electronics (PCE), the PCE battery bag, the PCE batteries, and the PCE control module. The PCE control module and the console both serve to provide the whole system with energy. The internal and external TETs work together to convert this energy into usable energy for all internal components and to transport that energy from the patientâ„¢s exterior to the patientâ„¢s interior. Once the energy has reached the patientâ„¢s interior, it is used to maintain the implanted battery charged and to provide power for the artificial heart and for the implanted controller. All of these components keep the artificial heart pumping blood and keep sending that blood throughout the patientâ„¢s body.
Abiomed. Product Details.
Bonsor, Kevin. How Artificial Hearts Work.
Brain, Marshall. How Hydraulic Machines Work.
Cho, B.H., Gyu Bum Joun. An energy transmission system for an artificial heart using
leakage inductance compensation of transcutaneous transformer. IEEE. Nov. 1998
Factmonster. heart, artificial. <http://factmonster.com/ce6/sci/A0823119.html>
Institute of Medicine. The Artificial Heart: Prototypes, Policies, and Patients.
Washington, D.C.: National Academy Press, 1991.
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NON-VOLATILE OVONICS UNIFIED MEMORY (OUM)
Nowadays, digital memories are used in each and every fields of day-to-day life. Semiconductors form the fundamental building blocks of the modern electronic world providing the brains and the memory of products all around us from washing machines to super computers. But now we are entering an era of material limited scaling. Continuous scaling has required the introduction of new materials.
Current memory technologies have a lot of limitations. The new memory technologies have got all the good attributes for an ideal memory. Among them Ovonic Unified Memory (OUM) is the most promising one. OUM is a type of non-volatile memory, which uses chalcogenide materials for storage of binary data. The term “chalcogen” refers to the Group VI elements of the periodic table. “Chalcogenide” refers to alloys containing at least one of these elements such as the alloy of germanium, antimony, and tellurium, which is used as the storage element in OUM. Electrical energy (heat) is used to convert the material between crystalline (conductive) and amorphous (resistive) phases and the resistive property of these phases is used to represent 0s and 1s.
To write data into the cell, the chalcogenide is heated past its melting point and then rapidly cooled to make it amorphous. To make it crystalline, it is heated to just below its melting point and held there for approximately 50ns, giving the atoms time to position themselves in their crystal locations. Once programmed, the memory state of the cell is determined by reading its resistance.
The use of phase-change Chalcogenide alloy films to store data electrically and optically was first reported in 1968 and in 1972, respectively. Early phase-change memory devices used tellurium-rich, multi-component Chalcogenide alloys with a typical composition of Te81Ge15Sb2S2. Both the optical and electrical memory devices were programmed by application of an energy pulse of appropriate magnitude and duration. A short pulse of energy was used to melt the material, which was then allowed to cool quickly enough to “freeze in” the glassy, structurally disordered state. To reverse the process, somewhat lower- amplitude, longer-duration pulse was used to heat a previously vitrified region of the alloy to a temperature below the melting point, at which crystallization could occur rapidly. Differences in electrical resistivity and the optical constants between the amorphous and polycrystalline phases were used to store data. During the 1970s and 1980s, significant research efforts by many industrial and academic groups were focused on understanding the fundamental properties of Chalcogenide alloy amorphous semiconductors. Prototype optical memory disks and electronic memory device arrays also were announced, beginning in the early 1970s. Rapidly crystallizing Chalcogenide alloys were later reported by several optical memory research groups. These new material compositions, derived from the Ge-Te-Sb ternary system, did not phase segregate upon crystallization like the earlier Te-rich alloys, but instead exhibited congruent crystallization with no large-scale atomic motion.
In the 1990s, researchers at Energy Conversion Devices Inc. and Ovonyx Inc. Developed new thermally optimized phase-change memory device structures that exploited rapidly crystallizing Chalcogenide alloy materials to achieve increased programming speed and reduced programming current.
These devices could be programmed in 20 ns—about six orders of magnitude faster than the early phase-change memory cells, and their much lower programming current requirements permitted the design of memory arrays using memory bit access devices (transistors or diodes) fabricated at minimum litho-graphic dimensions. Ovonyx is now commercializing its phase-change memory technology called Ovonics Unified Memory (OUM) through a number of license agreements and joint development programs with semiconductor device manufacturers.
The crystalline and amorphous states of chalcogenide glass have dramatically different electrical resistivity, and this forms the basis by which data are stored. The amorphous, high resistance state is used to represent a binary 0, and the crystalline, low resistance state represents a 1. Chalcogenide is the same material used in re-writable optical media (such as CD-RW and DVD-RW). In those instances, the material's optical properties are manipulated, rather than its electrical resistivity, as Chalcogenide’s refractive index also changes with the state of the material.
The term “chalcogen” refers to the Group VI elements of the periodic table. “Chalcogenide” refers to alloys containing at least one Group VI element such as the alloy of germanium, antimony, and tellurium discussed here. Energy Conversion Devices, Inc. has used this particular alloy to develop a phase-change memory technology used in commercially available re-writeable CD and DVD disks. This phase-change technology uses a thermally activated, rapid, reversible change in the structure of the alloy to store data. Since the binary information is represented by two different phases of material it is inherently non-volatile, requiring no energy to keep the material in either of its two stable structural states.
Used in a binary mode, the two structural states of the Chalcogenide alloy, as shown in Figure, are an amorphous state (no long-range order of atoms) and a polycrystalline state (composed of many crystals, each having atoms placed in a repetitive order). Relative to the amorphous state, the polycrystalline state shows a dramatic increase in free electron density (similar to a metal). This difference in free electron density gives rise to a difference in reflectivity and, more importantly, resistivity. In the case of the rewriteable CD and DVD disk technology, this difference in reflectivity is used to read the state of each memory bit by directing a low-power laser at the material and detecting the amount of light reflected.
Glassy materials are produced by rapidly super cooling a liquid below its melting point to a temperature at which the atomic motion necessary for crystallization cannot readily occur. Chalcogenide alloys - materials containing one or more elements from Group VI of the periodic table—are typically good glass formers, in large part because the Group VI elements form pre-dominantly twofold-coordinated covalent chemical bonds that can produce linear, tangled, polymer like clusters in the melt. This increases the viscosity of the liquid, inhibiting the atomic motion necessary for crystallization. Many amorphous Chalcogenide alloys have been reported in the literature. The Ge2Sb2Te5 (GST 225) Chalcogenide alloy currently used in OUM rmemory devices melts at approximately 610C۫ and has a glass-transition temperature of 350C۫. In order to crystallize an amorphous region of GST 225, the material must be heated to a temperature somewhat below the melting point and held at this temperature for a time sufficient to allow the crystallization to occur. The compositional dependence of crystallization kinetics in the GeSbTe ternary system has been extensively studied and reported in the literature. OUM cells based on GST 225 that can be programmed (crystallized) to the “SET” state in <20 ns have been reported
Figure 3. Schematic temperature–time relationship during programming, in a phase-change rewriteable memory device. Tm and Tx are the amorphization and crystallization temperatures, respectively. The SET and RESET states of the memory correspond to a stored binary 1 or binary 0
• For R/W CD’s and DVD’s heat is supplied by use of a laser
• For integrated circuits heat is supplied by resistors
ELECTRONIC PROPERTIES OF CRYSTALLINE AND AMORPHOUS GST ALLOYS
Two special electronic properties of chalcogenide amorphous semiconductor alloys are required for the operation of OUM memory—the strong dependence of electrical resistivity on the structural state of the material and the high-field threshold switching phenomenon. Polycrystalline GST 225 alloy has a resistivity of ~25 mΩcm, while resistivity in the vitreous state is three orders of magnitude higher—sufficient to enable good memory read capability. Both structural states of the alloy are semiconductors with comparable energy band gaps. The band gap Eg is 0.7 eV in the amorphous state and 0.5 eV in the poly-crystalline state. The conductivity activation energy Ea is ~0.3 eV for the amorphous state and 0.02 eV for the polycrystalline state. In addition, the amorphous phase exhibits a very low, trap-limited hole mobility of ~2 ×10-5cm2/V s, while the polycrystalline phase shows band-type mobility of ~10 cm2/ V s. These large differences come about because of disorder-induced localized electronic states as originally described by Mott and by Cohen, Fritzsche, and Ovshinsky (CFO) and later by Kastner, Adler, and Fritzsche.When chalcogenide alloy semiconductors are amorphized, electronic energy levels originating in the valence and conduction bands are pulled into the what was originally the empty energy band gap of the crystalline material. As described by Mott– CFO, these new gap states are localized spatially and do not extend throughout the material. Consequently, carriers move through the amorphous material either by hopping among the localized states or by being successively thermally excited to spatially extended band states and then being trapped into localized states. This gives rise to a mobility gap—a range of energy between the valence and conduction bands in which carriers have small, trap-limited mobility. The later work by Kastner, Adler, and Fritzsche explained the observation that Ea≈ Eg/2 in terms of a large density of special negatively and positively charged traps that also result from structural disorder in amorphous chalcogenide alloys. Kastner argued that charged traps (valence alternation pairs) act like compensating dopant levels in a conventional crystalline semiconductor, effectively forcing the Fermi level to lie near the mid gap between the energy levels of the two types of traps. In the polycrystalline state, crystal vacancies are proposed to give rise to acceptor-like states that move the Fermi level close to the valence-band edge. This Fermi level position, plus the loss of the disorder produced trapping states, gives rise to the nearly degenerate p-type high conductivity of the polycrystalline state. Thus, the phase-change memory cell uses a reversible change in long-range atomic order (the amorphous-to-crystalline phase change) to modulate both the Fermi level position in the Chalcogenide alloy and the carrier mobility to change the cell’s resistance.