Transducers for Medical Devices

Transducers for Medical Devices

Sensor Technology Pressure Force / Load Cell Vibration / Acceleration Humidity Temperature / Thermofile Optical / SpO2 Position (LVDT, Encoders) Tilt Magneto Resistive (MR) Piezo Film

Blood Pressure Monitoring Piezoresistive MEMS pressure sensor Surgical procedure, ICU Replace 1-3 days Low cost, high volume capability Value add capability AAMI compliant Tape and Reel ETO, E-beam, Gamma Piezoresistive MEMS pressure sensor Low cost, high volume

Angioplasty Inflation Pump MEMS pressure sensor and digital display in a pump Pump is used to inflate and deflate the angioplasty balloon Cryogenic Balloon Angioplasty Microfused strain gage pressure sensor measures pressure levels of cryogenic gases used in novel angioplasty procedures

Blood Pressure Sensors Arterial Tonometry Low cost gel filled MEMS sensor Complex MEMS array Piezoresistive MEMS pressure sensor measures air flow in breathing aid devices Also measures the altitude levels Working on multi sensor module to measure humidity, flow, temperature and pressure

Body and Skin Temperature Thermopile Sensor Distance-Ring 5-25 mm Optic Tympanum Generation 1 Generation 2 Generation 3

Spirometer T amb -Sensor 2 Heaters Air Flow MAFS-Chip LMM-02 is sensitive & fast Designed for bidirectional measurement

Infusion and Syringe Pump Sensors Multiple technologies: MEMS pressure sensor, Microfused load cells, cantilever beams, encoders Capabilities: Occlusion detection Bubble, level and flow detection Empty syringe detection Flow rate measurements Piezoceramic diaphragm pump drives fluid at very slow rates

Parkinson s Study Miniature sensors for Parkinson s tremor study

Premature Newborn Cabinet Humidity control of airflow for optimized, safe ambiance

SpO2 Sensors Disposables and non disposables Measures pulse rate and oxygen levels in the blood

Piezoelectric Piezoelectric Polymer Characteristics Transmitter or receiver Wide dynamic range (nano strain 10 9 Newtons) Broad frequency response (0.1 Hz 100 MHz) Die cut into any shape Spun into cable Patterned metallizations (electrodes, sputtering) Flexible, robust, inert, biocompatible Piezo converts mechanical strain to voltage and changes dimension with applied voltage PCMCIA Anti-tamper Panel

Numerical Classification of Axes g 31 -- stretch axis g 32 -- transverse to stretch axis g 33 -- thickness and polarization axis Dynamic transducer material - generates charge or voltage in response to change in stress or temperature Excellent linearity - charge/voltage is proportional to applied stress over very wide range Dynamic range : over 14 orders of magnitude (>280 db) - from fc to mc, nv to kv High voltage sensitivity (20 x piezoceramic PZT) Very broad bandwidth : from mhz to GHz Low Q factor : can be < 1 in water, < 12 in air High dielectric strength : up to 100 V/micron flexible material, conforms to curved surfaces

Frequency Response of Piezofilm 12 decade freq response of piezo film cryogenic tests particle sizing probe ink level switch u/s flowmeter limit of air u/s microscope small digitizers large-area digitizers ultra-high-speed vibration fence-mounted cable buried cable upper limit typical imbalance signals LLF of ACH-01 accelerometer LLF of ACH-04-08-05 accelerometer prototype accelerometer 1E-4 1E-2 1E0 1E2 1E4 1E6 1E8 1E10 Frequency (Hz)

Applications of Piezofilm Accelerometers Actuators Contact microphones Flexible switches Hydrophones Dual-axis Tilt Sensor Impact/shock sensors Motion sensors PIR, pyroelectric or thermal sensors Piezo cable Traffic sensors Ultrasonic transducers Traffic

Applications (Accelerometer) Calorie tracker Fence security sensor Gun recoil High-speed pump monitor Energy Expenditure Imbalance detection Leak detection (water transmission) Loudspeaker motional feedback Ultracentrifuge bearing monitor Vehicle motion detector Vibration

Hospital Beds Vital Sign Monitoring Breathing patterns and heart rate Patient weight Patient leaving bed Bed tilt Body temperature Blood oxygen levels

Bone Density Piezoelectric film - used as an ultrasound transducer to detect bone density Non-invasive and highly accurate

Pacemaker Miniature Piezoelectric film sensor measures patient activity level and adjusts Pacemaker function Highly sensitive and reliable Cantilever beam sensor (6.35mm in length) Biologically inert material Pacemaker

Defibrillator Safety Piezoelectric film sensor detects the heart rhythm Can save all the events in memory Data can be hand carried to the doctor Can be designed to activate cell phone for medical emergency

Sleep Apnea Patch Piezoelectric film used to detect Obstructive Sleep Apnea (brief Interruption in breathing during sleep) Multiple sensing methods: Dynamic strain gage sensing chest movement Contact microphone sensing snoring Pyroelectric sensor monitoring exhalation

Electrodes Surface electrode Subintegumental electrode Intracellular electrode (microelectrode)

Electrodes

Electrodes

Electrode Equivalent Circuits Detects charge distribution (movement of ion) Electrode (metal) electrolyte (chemical) skin (ion) Depends on the reactions between electrode and electrolyte

d d C j R 1, Impedance Low frequency : C d open k R R Z s d 4 25. 0 (from graph when f = 0) High frequency : C d short, R d is relatively high 400 Z H R s k R d 25 F C R f C C R f d d c d d d 0.04 2 1 2 1 Electrode Equivalent Circuits

Electrode Equivalent Circuits

Thermal Transducers Liquid Expansion Thermometer : mercury thermometer Cheap and easy to use Not good for skin temperature discrete measurement Electrical thermometer : thermistor, thermocouple small Possible for remote transmission ± 0.1 accuracy continuous measurement Liquid Crystal : Uses optical characteristics of liquid crystal 온도, 압력, 전기, 자기장, 화학적요인에민감 ( 분자상호간의연결력이약하므로 - 평행조직 ) 열이가해지면색깔을나타냄 (violet, blue, green, yellow, red) skin temperature

Thermal Transducers 반도체물질의저항값 R t 온도계수에따라 thermistor 저항값의변화가차이남 R t 가비선형성을보인다 Linearizing resistor thermistor 의비선형성을제거하기위해 thermistor 와병렬로연결하는저항 Wheatstone bridge Bridge의한변에합성저항 R tp 를삽입 Voltage Division Sensitivity of a Wheatstone Bridge

Straingage 역학적변화 ( 길이의변화 ) 에따른저항값의변화를감지 (Gage Factor) Hooke's Law : 선형압력-뒤틀림곡선에대한압력및뒤틀림사이의관계식 감도 : 길이의변화에따른출력전압의변화율 (Wheatstone bridge) 종류 - Bonded : 탄력성있는물질의표면에부착 - Unbonded : gage의양끝부분만을연결

Straingage

Capacitive Transducers 평행판콘덴서의용량 극판간격의변화가콘덴서의용량을변화시키는원리를이용 차동용량성변환기의구조 - equilibrium position이변화 감도 : x 의변화에따른 V out 의변화분 (x에대하여미분 )

Inductive Transducers Advantages : High output power Disadvantages - Limited frequency response characteristics - Possible to be affected by environmental electromagnetic force