Mechatronic for Health Sciences Lecture No. 3 PDF

FACULTY OF APPLIED HEALTH SCIENCES Mechatronic for Health Sciences [MEC 141] Lecture No. 3 Associated Professor Dr. Reda Ahmed Khalf-Allah  Lecture No. 3 Design of Biomedical Instrumentation Biomedical Instrumentation Design › Medical device’ means any instrument...

FACULTY OF APPLIED HEALTH SCIENCES Mechatronic for Health Sciences [MEC 141] Lecture No. 3 Associated Professor Dr. Reda Ahmed Khalf-Allah  Lecture No. 3 Design of Biomedical Instrumentation Biomedical Instrumentation Design › Medical device’ means any instrument, apparatus, machine, appliance, implant, software, material, or other similar or related article, intended by the manufacturer to be used, alone or in combination, for human beings, for one or more of the specific medical purpose(s) investigation, replacement, modification, or support of the anatomy or of a physiological process, supporting or sustaining life, control of conception, disinfection of medical devices, Generalized Medical Instrumentation System › The major difference between this system of medical instrumentation and the conventional instrumentation system is that the source of the signals is living tissue or energy applied to living tissue. The design of the instrument must match: › Measurement needs (environmental conditions, safety, reliability, etc.) › Instrument performance (speed, power, resolution, range, etc.). Measurand: The physical quantity, property, or condition that the system measures. Types of biomedical measurands: ›Internal– Blood pressure. ›Body surface–ECG or EEG potentials. ›Peripheral– Infrared radiation. ›Offline–Extract tissue samples, blood analysis, or biopsy What is a Biomedical Sensor? Any instrumentation system can be described as having three fundamental components: a sensor, a signal processor, storage device. In the case of biomedical instrumentation, a biomedical sensor is the interface between the electronic instrument and the biological system CHARACTERISTICS of sensors 1. Range It is the difference between the maximum and minimum value of the sensed parameter. Temperature range of a thermocouple is 25-225°C. 2- Resolution The smallest change the sensor can differentiate. It is also frequently known as the least count of the sensor. Resolution of an digital sensor is easily determined.  3. Sensitivity It is the ratio of change in output to a unit change of the input. The sensitivity of digital sensors is closely related to the resolution. 4. Error Error is the difference between the result of the measurement and the true value of the quantity being measured.  5. Accuracy It is the difference between measured value and true value. The accuracy defines the closeness between the actual measured value and a true value. 6- Response time Response time is the amount of time required for a sensor to respond completely to a change in input. It describes the speed of change in the output on a step-wise change of the measurand. STANDARD SIGNAL TYPES Most modern equipment works on the following standard signal ranges Electric – 4 to 20 mA Pneumatic – 0.2 to 1.0 bar (or) 3 to 15 psi The advantage of having a standard range is that all equipment is sold readily calibrated. This means that minimum signal (temperature, speed, force, pressure and so on)is represented by 4 mA or 0.2 bar and the maximum signal is represented by 20 mA or 1.0 bar. HYDRAULIC SIGNAL TRANSMISSION SYSTEM The hydraulic systems consists a number of parts which include storage tank, filter, hydraulic pump, pressure regulator, control valve, hydraulic cylinder, piston and leak proof fluid flow pipelines. The output shaft with piston transfers the motion or force however all other parts help to control the system. Schematic of Hydraulic system PNEUMATIC SIGNAL TRANSMISSION SYSTEM Schematic of Pneumatic system COMPARISONS OF ELECTRICAL,HYDRAULIC& PNUEMATIC SYSTEM  Classification of Biomedical Sensors Biomedical sensors can be classified according to how they are used with respect to the biological system: 1. Noninvasive biomedical sensors do not even contact the biological system being measured. Sensors of radiant heat or sound energy coming from an organism are examples of non contacting sensors. Noninvasive sensors can also be placed on the body surface like Skin surface thermometers, bio potential electrodes, and strain gauges placed on the skin. 2. Indwelling sensors (minimally invasive sensors) : are those that can be placed into a natural body cavity that communicates with the outside. Examples: oral– rectal thermometers, intrauterine pressure transducers, and stomach pH sensors. 3. Invasive sensors: are those that need to be surgically placed and that require some tissue damage associated with their installation.  We can also classify sensors in terms of the quantities that they measure: 1. Physical sensors: are used in measuring physical quantities such as displacement, pressure, and flow. 2. Chemical sensors: are used to determine the concentration of chemical substances within the host. A sub-group of the chemical sensors that are concerned with sensing the presence and the concentration of biochemical materials in the host. 3. Bio-analytical sensors or biosensors: used to measure some internal quantities like enzymes.  1. Physical Sensors Physical variables measured include temperature, strain, force, pressure, displacement, position, velocity, acceleration, optical radiation, sound, flow rate, viscosity, and electromagnetic fields. Temperature Sensors; Temperature is an important parameter in many control systems, most familiarly in environmental control systems. Several distinctly different transduction mechanisms have been employed to measure temperature. The mercury thermometer is a temperature sensor which produces a non electronic output signal. The most commonly used electrical signal generating temperature sensors are thermocouples, thermestors, and resistance thermometers.  Thermocouples; Thermocouples employ the Seebeck effect, which occurs at the junction of two dissimilar conductors. A voltage difference is generated between the hot and cold ends of the two conductors due to the differences in the energy distribution of electrons at the two different temperatures. The voltage magnitude generated depends on the properties of the conductor, e.g., conductivity and work function, such that a difference voltage will be measured between the cold ends of two different conductors. The voltage changes fairly linearly with temperature over a given range, depending on the choice of conductors.  Resistance thermometer; The resistance thermometer relies on the increase in resistance of a metal wire with increasing temperature. As the electrons in the metal gain thermal energy, they move about more rapidly and undergo more frequent collisions with each other and the atomic nuclei. These scattering events reduce the mobility of the electrons, and since resistance is inversely proportional to mobility, the resistance increases. Resistance thermometers typically consist of a coil of thin metal wire. Platinum wire gives the largest linear range of operation. The resistance thermometer is a ‘‘modulator’’ or passive transducer. In order to determine the resistance change, a constant current is supplied and the corresponding voltage is measured (or vice versa).  Thermistors; Thermistors are resistive elements made of semiconductor materials and have a negative temperature coefficient of resistance. The mechanism governing the resistance change of a thermistor is the increase in the number of conducting electrons with increasing temperature, due to thermal generation, i.e., the electrons that are the least tightly bound to the nucleus (valence electrons) gain sufficient thermal energy to break away (enter the conduction band) and become influenced by external fields.  Displacement and Force Sensors; Many types of forces can be sensed by the displacements they create. For example, the force due to acceleration of a mass at the end of a spring will cause the spring to stretch and the mass to move. Its displacement from the zero acceleration position is governed by the force generated by the acceleration (F =m · a) and by the restoring force of the spring. Another example is the displacement of the center of a deformable membrane due to a difference in pressure across it. Both of these examples require multiple transduction mechanisms to produce an electronic output: a primary mechanism which converts force to displacement (mechanical to mechanical) and then an intermediate mechanism to convert displacement to an electrical signal (mechanical to electrical).  2.Chemical Sensors There are many biomedical situations where it is necessary to know the concentration or chemical activity of a particular substance in a biological sample. Chemical sensors provide the interface between an instrument and the specimen to allow one to determine these quantities. These sensors can be used on a biological specimen taken from the host and tested in a laboratory, noninvasive or invasive sensors.  The below table indicates the most famous biomedical sensors, the most common three types of the biomedical sensors are electrochemical, optical and thermal biomedical sensors:- Electrochemical Optical Thermal a. Amperometric a. Colorimetric a. Calorimetric b. Potentiometric b. Emmision and b. Thermo absorption conductivity c. Coulometric c. Fluorescence Clark amperometric electrode for sensing oxygen  3. Bio-analytical Sensors: A special class of sensors of biological molecules has evolved in recent years. These bioanalytical sensors take advantage of one of the following biochemical reactions: (1) enzyme–substrate. (2) antigen–antibody. (3) ligand–receptor. The advantage of using these reactions in a sensor is that they are highly specific to a particular biological molecule, and sensors with high sensitivity and selectivity can be developed based upon these reactions. The basic structure of a bio-analytical sensor  There are two principal regions of the sensor. The first contains one component of the biological sensing reaction such as the enzyme or the antibody, and the second region involves a means of detecting weather the biological reaction has taken place. This second portion of a bio analytical sensor is made up of either a physical or chemical sensor that serves as the detector of the biological reaction. This detector can consist of an electrical sensor such as used in electrochemical sensors, a thermal sensor, a sensor of changes in capacitance, a sensor of changes in mass, or a sensor of optical properties.  Example bio-analytical sensor One example of a bioanalytical sensor is a glucose sensor. The first portion of the sensor contains the enzyme glucose oxidase. This enzyme promotes the oxidation of glucose to glucuronic acid and hydrogen peroxide while consuming oxygen in the process. Thus, by placing a hydrogen peroxide or an oxygen sensor along with the glucose oxidase in the bio analytical sensor, one can determine the amount of glucose oxidized by measuring the amount of hydrogen peroxide produced or oxygen consumed. Glucose + 02 ► gluco + H2O2 The H2O2 produced by this chemical reaction is electrolyzed by applying a potential to the platinum electrode, with production of positive hydrogen ions, which will flow toward this electrode. The amount of glucose concentration in the blood sample can thus be measured by measuring the current flow between the electrodes  Applications Of Biomedical Sensors Biomedical research: One of the application fields of the biomedical sensors is using them in continuous biomedical research. So, these sensors can be used to improve the quality of the biomedical product). Patient care applications: Sensors are used as a part of instruments that carry out patient monitoring by making measurements such as blood pressure, oxygen saturation, body temperature and ECG.  Specimen analysis: This can include analyses that can be carried out by the patients themselves in their homes such as it is done with home blood glucose analyzers. Sensors also are a part of large, multi-component, automatic blood analyzers used in the central clinical laboratories of medical centers. Many sensors have: 1.A primary sensing element such as diaphragm, converts pressure to displacement. 2.A variable conversion element, such as a strain gage, then converts displacement to an electrical voltage 3.Sometimes the sensitivity of the sensor can be adjusted over a wide range by altering the primary sensing element. 4.Many variable conversion elements need external electric power to obtain a sensor output. Signal conditioning Preprocessing Usually, the sensor /transducer output had arrange of millivolts, ›The gain of the amplifier on this stage depends strongly on the next stage’ s requirements. ›Often the output is converted to digital form and then processed by specialized digital circuits or a microcomputer as there will be logic and arithmetic units.  Logic and arithmetic control: ›The basic and complicated modes of calculations for the raw amplified data gathered from the patient’s body through the sensor/ transducer are performed. ›signal filtering adjustment, based on operator selection mode, mathematical manipulation between inputs to calculate required parameter and so on.  Postprocessing Final processing is performed. Either based on manipulating the signal to match the requirement of the output elements or to adjust the scale of: time, frequency, and signal level for the real shape mode. Specialized digital circuits or a microcomputer are used to perform several functions like: average repetitive signal, reduce noise, and converting information from the time domain to the frequency domain. Thank you