1/6/2018. Prof. Steven S. Saliterman. Prof. Steven S. Saliterman

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1 Introductory Medical Device Prototyping Department of Biomedical Engineering, University of Minnesota A sensor converts one form of energy to another, and in so doing detects and conveys information about some physical, chemical or biological phenomena. More specifically, a sensor is a transducer that converts the measurand (a quantity or a parameter) into a signal that carries information. For our purposes, we are generally trying to convert the measurand into an electrical signal that can be input into a microcontroller. Something in our environment: Ambient temperature, barometric pressure, humidity, gas, light, dust, air quality, water quality, soil moisture, and radiation. Biomedical: Blood pressure, pulse, body temperature, height, weight, respiratory rate, laboratory (blood, urine, cerebral spinal fluid); respiratory and blood gasses, flow (blood, urine and air), intraocular, intracranial and tympanic membrane pressures; electrocardiogram, electrical activity of muscles and nerves, and internal organ imaging (x-ray, ultrasound, camera, NMR). 1

2 Other physical measurements: Stress, stain, strength, pressure, distances, magnetic fields, sound, light, water levels, motion (acceleration), orientation (gyro), proximity and location (GPS). Images User interactions: Tactile, button presses, flexion, knob turning; hand and other body part motion, and eye movement tracking. Sensors may be classified based on the following: Measurand - temperature, pressure, flow etc. Transduction (physical and chemical effects) - SAW, ion selective FETs, optodes (chemical transducer) etc. Materials - resistive, piezoelectric, magnetic, permeable membranes, etc. Technology MEMS, biomems, plasmon resonance, CMOS imaging, charge coupled devices etc. Energy requirement - active or passive. Applications - industrial, automative, aviation, consumer electronics, biomedical etc. Continuous operation without effecting the measurand. Appropriate sensitivity and selectivity. Fast and predictable response. Reversible behavior. High signal to noise ratio. Compact Immunity to environment. Easy to calibrate. 2

This can be done with a high gain instrumentation amplifier The instrumentation amplifier inputs replace the volt meter in the top circuit. Karki, J.

3 If the bridge resistors have the same value, equal to the strain gauge's resistance at rest, then the voltage is zero. The voltage can be amplified to get a higher sensitivity for the complete circuit. This can be done with a high gain instrumentation amplifier The instrumentation amplifier inputs replace the volt meter in the top circuit. Karki, J. Texas Instruments: Signal Conditioning Wheatstone Resistive Bridge Sensors. Application Report, SLOA034, September Direct transduction from mechanical to electrical domains and vice versa. May be used as sensors or actuators. The reversible and linear piezoelectric effect manifests as the production of a charge (voltage) upon application of stress (direct effect) and/or as the production of strain (stress) upon application of an electric field (converse effect). Three modes of operation depending on how the piezoelectric material is cut: transverse, longitudinal and shear. Amplifiers are needed to detect the small voltage. Tadigadapa, S., and K. Mateti Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technology 20, no. 9: Converse Piezoelectric Effect - Application of an electrical field creates mechanical deformation in the crystal. Polling - Random domains are aligned in a strong electric field at an elevated temperature. Direct Piezoelectric Effect - When a mechanical stress (compressive or tensile) is applied a voltage is generated across the material. Adopted from bme240.eng.uci.edu 3

The piezoelectric effect is a linear phenomenon where deformation is proportional to an electric field: S = de and D = dt Where S is the mechanical strain, d is the piezoelectric coefficient, E is

4 The piezoelectric effect is a linear phenomenon where deformation is proportional to an electric field: S = de and D = dt Where S is the mechanical strain, d is the piezoelectric coefficient, E is the electric field, D is the displacment (or charge density) linearly, and T is the stress. These equations are known as the converse piezoelectric effect and the direct piezoelectric effect respectively. Tadigadapa, S., and K. Mateti Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technology 20, no. 9: Crystals Quart SiO 2 Berlinite AlPO 4 Gallium Orthophosphate GaPO 4 Tourmaline (complex chemical structure) Ceramics Barium titanate BaTiO 3 Lead zirconate titanate PZT, Pb [ZrxTi1-x] O3 ; x = 0,52 Other Materials Zinc oxide ZnO Aluminum nitride AlN Polyvinylidene fluoride PVDF Adopted from Piezomaterials.com 4

V Out Q R C C R T F T P 1 V Out Q C T F Tadigadapa, S., and K. Mateti. 2009. Piezoelectric MEMS sensors: state-of-the-art and perspectives.

com/photos/blafetra/14524883649 Absolute Orientation (Euler Vector, 100Hz) Three axis orientation data based on a 360 sphere.

Acceleration Vector (100Hz) Three axis of acceleration (gravity + linear motion) in m/s^2.

5 V Out Q R C C R T F T P 1 V Out Q C T F Tadigadapa, S., and K. Mateti Piezoelectric MEMS sensors: state-of-the-art and perspectives. Measurement Science & Technology 20, no. 9: Apollo 11 Gyroscope 1969 Apollo Command Module 1973 Gyroscope image courtesy of Absolute Orientation (Euler Vector, 100Hz) Three axis orientation data based on a 360 sphere. Absolute Orientation (Quaterion, 100Hz) Four point quaternion output for more accurate data manipulation. Angular Velocity Vector (100Hz) Three axis of 'rotation speed' in rad/s. Acceleration Vector (100Hz) Three axis of acceleration (gravity + linear motion) in m/s^2. Magnetic Field Strength Vector (20Hz) Three axis of magnetic field sensing in micro Tesla (ut). Linear Acceleration Vector (100Hz) Three axis of linear acceleration data (acceleration minus gravity) in m/s^2. Gravity Vector (100Hz) Three axis of gravitational acceleration (minus any movement) in m/s^2. Temperature (1Hz) Ambient temperature in degrees celsius. Courtesy of Adafruit 5

6 Platinum resistor: Linear, stable, reproducible. Material property dependency on temperature, Thermocouples (e.g. Type K) Thermistor: a semiconductor device made of materials whose resistance varies as a function of temperature. Thermodiode and Thermotransistor. Potentiometric devices fabricated by the joining of two different metals forming a sensing junction: Based on the thermoelectric Seebeck effect in which a temperature difference in a conductor or semiconductor creates an electric voltage: D V = a sdt Where D V is the electrical voltage, a is the Seebeck coefficient expressed in volts/k, and s D T is the temperature difference ( T - T ). S ref Gardner, JW, VK Varadan and OO Awadelkarim, Microsensors, MEMS and Smart Devices. John Wiley & Sons, Ltd. W. Sussex (2001). When a p-n diode is operated in a constant current (I O ) circuit, the forward voltage (V out )isdirectly proportional to the absolute temperature (PTAT). kbt I V out = ln æ 1 ö q + ç I çè S ø Where k b is the Bolzman constant, T is temperature, q is the charge on an electron, I is the operating current and I is the saturation current. S Gardner, JW, VK Varadan and OO Awadelkarim, Microsensors, MEMS and Smart Devices. John Wiley & Sons, Ltd. W. Sussex (2001). 6

7 Hot wire or hot element anemometers. Based on convective heat exchange taking place when the fluid flow passes over the sensing element (hot body). Operate in constant temperature mode or in constant current mode. Calorimetric sensors. Based on the monitoring of the asymmetry of temperature profile around the hot body which is modulated by the fluid flow. The heat transferred per unit time from a resistive wire heater to a moving liquid is monitored with a thermocouple: Gardner, JW, VK Varadan and OO Awadelkarim, Microsensors, MEMS and Smart Devices. John Wiley & Sons, Ltd. W. Sussex (2001). In a steady state, the mass flow rate can be determined: The volumetric flow rate is calculated as follows: dm P Q = = (T T) h m 2 - dt c 1 m Where Q m is the mass flow rate, P h is the heat transferred per unit time, c m is the specific heat capacity of the fluid and T 1,T 2 are temperature. Q dv = Q m V = dt ρm Where Q V is the volumetric flow rate, Q m is the mass flow rate and ρ m is the density. 7

8 Cantilever type flow sensors Measuring the drag-force on a cantilever beam. Differential pressure-based flow sensors When a fluid flow passes through a duct, or over a surface, it produces a pressure drop depending on the mean velocity of the fluid. Electromagnetic Laser Doppler flowmeter The phenomenon is due to the interaction between an electromagnetic or acoustic wave and a moving object: the wave is reflected back showing a frequency different from the incident one. Lift-force and drag flow sensors Based on the force acting on a body located in a fluid flow. Microrotor Rotating turbine Resonating flow sensors Temperature effects resonance frequency of a vibrating membrane. Silvestri, S. and E. Schena Micromachined Flow Sensors in Biomedical Applications. Micromachines 2012, 3, Potentiometric Sensors Ion selective electrodes (ISE) into the nanodimension range New ion recognition chemistries New ion selective membranes Importance of the reference electrode Voltametric Sensors Carbon paste electrodes (CPE) for organic molecule detection Micro and Ultramicro electrodes Environmental monitoring Carbon nanotubules Stripping voltammetry Privett, Benjamin J., Jae H. Shin, and Mark H. Schoenfisch Electrochemical Sensors. Analytical Chemistry 82, no. 12: Electrochemical Biosensors Selective and sensitive biological binding Aptamer-based biosensors Glucose, creatinine, pathologic bacteria, DNA Enzyme biosensors Immunosensors Bacteria, virus and cancer biomarkers Ion Selective Field Effect Transistors Based on the electrochemical phenomena occurring within the chemically sensitive membrane placed on top of the transistor gate and on electrical transduction of the signal by this semiconductor device. Privett, Benjamin J., Jae H. Shin, and Mark H. Schoenfisch Electrochemical Sensors. Analytical Chemistry 82, no. 12:

9 Photocurable polymers have been used for encapsulation of ion selective field effect transistors (ISFET) and for membrane formation in chemical sensitive field effect transistors (ChemFET). G D G D Charge Carriers In Charge Carriers Out S P- Channel S N- Channel Shown: Insulated Gate Field-Effect Transistor (IGFET). MOSFET (metal oxide is common). Abramova, Natalia, and Andrei Bratov Photocurable Polymers for Ion Selective Field Effect Transistors. 20 Years of Applications. Sensors 9, no. 9: Silicon (semiconductor) substrate A B S G D A small signal on the plate above (gate) brings electrons to the surface, allowing current to flow and amplifying the original signal. Optical chemical sensors are usually configured as transducers, with transductions steps of electricaloptical-chemical-optical-electrical conversion: Boisde, G. and A. Harmer, Chemical and Biochemical Sensing with Optical Fibers and Waveguides, Artech House, Boston (1996) 9

$An optical fiber consists of a solid cylindrical core of transparent material surrounded by a cladding of similar material but of lower refractive$ $index than the core: The refractive index is the ratio of the speed of light in a vacuum to the speed of light in the medium: c vacuum n = ³1 c$

10 Esashi, Masayoshi Revolution of Sensors in Micro-Electromechanical Systems. Japanese Journal of Applied Physics 51, no. 8: An optical fiber consists of a solid cylindrical core of transparent material surrounded by a cladding of similar material but of lower refractive index than the core: The refractive index is the ratio of the speed of light in a vacuum to the speed of light in the medium: c vacuum n = ³1 c material Snell s law defines the relationship between incident and refracted light, measured as an angle from a perpendicular to the surface: n sin I = n sin R i r 10

Glucose and anticoagulation monitoring: Images courtesy of

Technomic Pub. Co., Lancaster, PA (2000) Pressure: Fraden, J.

11 Glucose and anticoagulation monitoring: Images courtesy of LifeScan, Inc. and HemoSense, Inc. Temperature: Image courtesy of Braun Harsanyi, G., Sensors in Biomedical Applications, Technology and Applications. Technomic Pub. Co., Lancaster, PA (2000) Pressure: Fraden, J. Noncontact temperature measurement in medicine. Bioinstrumentation and Biosensors, D.L. Wise, Ed, Marcel Dekker (1991). 11

intraocular pressure sensors. Senors and Actuators 41:42, pp.

12 Intraocular pressure: Bergveld, A.P., The merit of using silicon for the development of hearing aid microphones and intraocular pressure sensors. Senors and Actuators 41:42, pp (1994) Pulse oximetry: Parker, D. Sensors for monitoring blood gasses in intensive care. J Phys. E. Sci. Instrum. 20, pp (1987). 12

13 Respiratory spirometry and CO 2 : Implanted pacemaker and rhythm monitor: What are sensors and what do we sense? Sensor Classification and ideal sensor. Piezoelectric Sensors Thermo and thermo flow sensors Electrochemical sensors Ion Selective Field Effect Transistors Optical sensors Clinical applications 13

Prof. Steven S. Saliterman Introductory Medical Device Prototyping

Prof. Steven S. Saliterman Introductory Medical Device Prototyping Introductory Medical Device Prototyping Department of Biomedical Engineering, University of Minnesota http://saliterman.umn.edu/ A sensor converts one form of energy to another, and in so doing detects