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