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
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Surgical procedure, ICU
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Replace 1-3 days
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Low cost, high volume capability
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Value add capability
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AAMI compliant
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Tape and Reel
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ETO, E-beam, Gamma
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Piezoresistive MEMS pressure sensor
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Low cost , high volume
Angioplasty Inflation Pump •
MEMS pressure sensor and digital display in a pump
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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
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Low cost gel filled MEMS sensor
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Complex MEMS array
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Piezoresistive MEMS pressure sensor measures air flow in breathing aid devices
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Also measures the altitude levels
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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
Tamb-Sensor
2 Heaters
Air Flow
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MAFS-Chip LMM-02 is sensitive & fast Designed for bidirectional measurement
Infusion and Syringe Pump Sensors
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Multiple technologies: MEMS pressure sensor, Microfused™ load cells, cantilever beams, encoders
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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
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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 – 109 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
g31 -- stretch axis g32 -- transverse to stretch axis g33 -- 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 Frequency (Hz)
1E6
1E8
1E10
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
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Patient weight
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Patient leaving bed
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Bed tilt
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Body temperature
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Blood oxygen levels
Bone Density •
Piezoelectric film - used as an ultrasound transducer to detect bone density
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Non-invasive and highly accurate
Pacemaker •
Miniature Piezoelectric film sensor measures patient activity level and adjusts Pacemaker function
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Highly sensitive and reliable
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Biologically inert material
Cantilever beam sensor (6.35mm in length)
Pacemaker
Defibrillator Safety •
Piezoelectric film sensor detects the heart rhythm
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Can save all the events in memory
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Data can be hand carried to the doctor
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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)
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Multiple sensing methods: – Dynamic strain gage sensing chest movement – Contact microphone sensing snoring – Pyroelectric sensor monitoring exhalation
Electrodes
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Surface electrode
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Subintegumental electrode
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Intracellular electrode (microelectrode)
Electrodes
Electrodes
Electrode Equivalent Circuits •
Detects charge distribution (movement of ion)
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Electrode (metal) – electrolyte (chemical) – skin (ion)
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Depends on the reactions between electrode and electrolyte
Electrode Equivalent Circuits
Impedance
Rd ,
1 jCd
Low frequency : Cd open
Z 0 Rd Rs 25.4k (from graph when f = 0)
High frequency : Cd short, Rd is relatively high
Z H Rs 400
Rd 25k f
1 1 Cd Cd 0.04 F 2Rd Cd 2f c Rd
Electrode Equivalent Circuits
Thermal Transducers •
Liquid Expansion Thermometer : mercury thermometer – Cheap and easy to use – Not good for skin temperature – discrete measurement
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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, 화학적 요인에 민감 (분자 상호간의 연결력이 약하므로 - 평행조직) – 열이 가해지면 색깔을 나타냄 (violet, blue, green, yellow, red) – skin temperature
Thermal Transducers •
반도체물질의 저항값 Rt – 온도 계수에 따라 thermistor 저항 값의 변화가 차이남 – Rt가 비선형성을 보인다
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Linearizing resistor – thermistor의 비선형성을 제거하기 위해 thermistor와 병렬로 연결하는 저항
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Wheatstone bridge – Bridge의 한 변에 합성저항 Rtp 를 삽입 – Voltage Division – Sensitivity of a Wheatstone Bridge
Straingage 역학적 변화(길이의 변화)에 따른 저항 값의 변화를 감지 (Gage Factor) • Hooke's Law : 선형 압력-뒤틀림 곡선에 대한 압력 및 뒤틀림 사이의 관계식 • 감도 : 길이의 변화에 따른 출력전압의 변화율 (Wheatstone bridge) • 종류
- Bonded : 탄력성 있는 물질의 표면에 부착 - Unbonded : gage의 양 끝부분만을 연결
Straingage
Capacitive Transducers •
평행판 콘덴서의 용량
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극판 간격의 변화가 콘덴서의 용량을 변화시키는 원리를 이용
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차동 용량성 변환기의 구조 - equilibrium position이 변화
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감도 : x 의 변화에 따른 Vout 의 변화분 (x에 대하여 미분)
Inductive Transducers
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Advantages : High output power
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Disadvantages - Limited frequency response characteristics - Possible to be affected by environmental electromagnetic force
