Transducers for Medical Devices

• Low cost gel filled MEMS sensor • Complex MEMS array Blood Pressure Sensors ... Dual-axis Tilt Sensor . Calorie tracker Fence security sensor Gun re...

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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


5-25 mm

Optic Tympanum

Generation 1

Generation 2

Generation 3



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 – 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




1E2 1E4 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


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


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

Biologically inert material

Cantilever beam sensor (6.35mm in length)


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


Surface electrode

Subintegumental electrode

Intracellular electrode (microelectrode)



Electrode Equivalent Circuits •

Detects charge distribution (movement of ion)

Electrode (metal) – electrolyte (chemical) – skin (ion)

Depends on the reactions between electrode and electrolyte

Electrode Equivalent Circuits


Rd ,

1 jCd

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 2Rd Cd 2f c Rd

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, 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

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


Capacitive Transducers •

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)

Inductive Transducers

Advantages : High output power

Disadvantages - Limited frequency response characteristics - Possible to be affected by environmental electromagnetic force