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Transducers for Medical Devices
• Pressure
• Force / Load Cell
• Vibration / Acceleration
• Humidity
• Temperature / Thermofile
• Optical / SpO2
• Position (LVDT, Encoders)
• Tilt
• Magneto Resistive (MR)
• Piezo Film
Sensor Technology
• 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
Blood Pressure Monitoring
• Piezoresistive MEMS pressure sensor
• Low cost , high volume
Inflation Pump
• MEMS pressure sensor and digital display in a pump
• Pump is used to inflate and deflate the angioplasty balloon
Angioplasty
Cryogenic Balloon Angioplasty
• Microfused™ strain gage pressure sensor measures pressure levels of cryogenic gases used in novel angioplasty procedures
• Arterial Tonometry
• Low cost gel filled MEMS sensor
• Complex MEMS array
Blood Pressure Sensors
• 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
Tympanum
Distance-Ring
Thermopile Sensor
5-25 mm
Optic
Generation 1 Generation 2 Generation 3
Body and Skin Temperature
• MAFS-Chip LMM-02 is sensitive & fast
• Designed for bidirectional measurement
Air Flow
2 Heaters
Tamb-Sensor
Spirometer
• 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
Infusion and Syringe Pump Sensors
• Miniature sensors for Parkinson’s tremor study
Parkinson’s Study
• Humidity control of airflow for optimized, safe ambiance
Premature Newborn Cabinet
– Disposables and non disposables
– Measures pulse rate and oxygen levels in the blood
SpO2 Sensors
• 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
Piezoelectric
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
Numerical Classification of Axes
1E-4 1E-2 1E0 1E2 1E4 1E6 1E8 1E10Frequency (Hz)
prototype accelerometer
LLF of ACH-04-08-05 accelerometer
LLF of ACH-01 accelerometer
typical imbalance signals
buried cable upper limit
fence-mounted cable
ultra-high-speed vibration
large-area digitizers
small digitizers
limit of air u/s microscope
u/s flowmeter
ink level switch
particle sizing probe
cryogenic tests
12 decade freq response of piezo film
Frequency Response of Piezofilm
Accelerometers
Actuators
Contact microphones
Flexible switches
Hydrophones
Impact/shock sensors
Motion sensors
PIR, pyroelectric or thermal sensors
Piezo cable
Traffic sensors
Ultrasonic transducers
Applications of Piezofilm
Traffic
Dual-axis Tilt Sensor
Calorie tracker
Fence security sensor
Gun recoil
High-speed pump monitor
Imbalance detection
Leak detection (water transmission)
Loudspeaker motional feedback
Ultracentrifuge bearing monitor
Vehicle motion detector
Applications (Accelerometer)
Vibration
Energy Expenditure
• Breathing patterns and heart rate
• Patient weight
• Patient leaving bed
• Bed tilt
• Body temperature
• Blood oxygen levels
Hospital Beds Vital Sign Monitoring
• Piezoelectric film
- used as an ultrasound transducer to detect bone density
• Non-invasive and highly accurate
Bone Density
• Miniature Piezoelectric film sensor
measures patient activity level and
adjusts Pacemaker function
• Highly sensitive and reliable
• Biologically inert material
Cantilever beam sensor
(6.35mm in length)
Pacemaker
Pacemaker
• 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
Defibrillator Safety
• 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
Sleep Apnea Patch
• Surface electrode
• Subintegumental electrode
• Intracellular electrode (microelectrode)
Electrodes
Electrodes
Electrodes
• Detects charge distribution (movement of ion)
• Electrode (metal) – electrolyte (chemical) – skin (ion)
• Depends on the reactions between electrode and electrolyte
Electrode Equivalent Circuits
d
dCj
R
1,Impedance
Low frequency : Cd open kRRZ sd 4.250(from graph when f = 0)
High frequency : Cd short, Rd is relatively high 400sH RZ
kRd 25
FCRf
CCR
f d
dc
d
dd
04.02
1
2
1
Electrode Equivalent Circuits
Electrode Equivalent Circuits
• 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, 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
• Linearizing resistor
– thermistor의 비선형성을 제거하기 위해
thermistor와 병렬로 연결하는 저항
• Wheatstone bridge
– Bridge의 한 변에 합성저항 Rtp 를 삽입
– Voltage Division
– Sensitivity of a Wheatstone Bridge
Thermal Transducers
• 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
역학적 변화(길이의 변화)에 따른 저항 값의 변화를 감지 (Gage Factor)
Straingage
Straingage
• 평행판 콘덴서의 용량
• 극판 간격의 변화가 콘덴서의 용량을 변화시키는 원리를 이용
• 차동 용량성 변환기의 구조 - equilibrium position이 변화
• 감도 : x 의 변화에 따른 Vout 의 변화분 (x에 대하여 미분)
Capacitive Transducers
• Advantages : High output power
• Disadvantages
- Limited frequency response characteristics
- Possible to be affected by environmental electromagnetic force
Inductive Transducers