a microbubble pressure transducer with bubble nucleation

15
A MICROBUBBLE PRESSURE TRANSDUCER WITH BUBBLE NUCLEATION CORE Author: Lawrence Yu, Ellis Meng Reporter: 朱朱朱 Date: 2015/6/15

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Page 1: A microbubble pressure transducer with bubble nucleation

A MICROBUBBLE PRESSURE TRANSDUCER WITH BUBBLE NUCLEATION CORE

Author: Lawrence Yu, Ellis Meng

Reporter: 朱家君Date: 2015/6/15

Page 2: A microbubble pressure transducer with bubble nucleation

Outline• Introduction• MEMS pressure transducer• Design and operation• Measurement results• Conclusions

Page 3: A microbubble pressure transducer with bubble nucleation

Introduction• Purpose: μBPT + μBNC

→ achieve low power operation in wet environments.• Operation: electrochemical impedance measurement

→ hydrostatic pressure change

→ μB size instantaneous response

Page 4: A microbubble pressure transducer with bubble nucleation

MEMS pressure transducer• Capacitive, piezoresistive, piezoelectric transduction:

• μBPT: no need of hermetic packaging

→ in vivo monitoring

→ reduce overall sensor footprint

Page 5: A microbubble pressure transducer with bubble nucleation

Design• Previous work: silicon microfluidic channels

→ poor control

(> 6% size variation)

Page 6: A microbubble pressure transducer with bubble nucleation

This work• Circular Parylene chamber and flexible substrate:

→ short EI measurement path

→ limited sensitivity

• Trade-off:

Optimal electrolytic nucleation EI measurement

Spacing between electrodes ↓ Spacing between electrodes ↑

localized bubble formation measurement range ↑

Page 7: A microbubble pressure transducer with bubble nucleation

Improvement

• μB formation:

1) generated within a nucleation core

2) coalesce into a single bubble

3) growing bubble extends outwards

4) fill measurement region of the channel

5) electrolysis current is terminated

6) μB detaches from μBNC

7) remains in the measurement channel

(respond to local pressure changes

transmitted via the liquid interface ports)

↑External pressure

Page 8: A microbubble pressure transducer with bubble nucleation

Model

• Iac applied across the EI measurement electrodes:

→ monitor the volumetric conductive path (Rs)

• Rs:

Page 9: A microbubble pressure transducer with bubble nucleation

Operation • a) Nucleation via electrolysis

in μB nucleation core.• b) μB enters measurement

channel.• c) Continued growth fills

microchannel• d) Detachment of μB from

μBNC and localization in

the measurement channel.

Page 10: A microbubble pressure transducer with bubble nucleation

Fabrication • a) Deposit 1st Parylene and perform Pt lift-off.• b) Pattern sacrificial photoresist, deposit 2nd Parylene

layer, and etch interface ports.• c) Release device from silicon substrate and soak in

electrolyte to fill channel.

Page 11: A microbubble pressure transducer with bubble nucleation

Measurement

Current pulse v.s impedance Magnitude and phase

To eliminate capacitive effects, measurement frequency was selected where phase ~0° (10 kHz)

Page 12: A microbubble pressure transducer with bubble nucleation

Current injection v.s. impedance

Impedance-pressure correlation (Type III)

Page 13: A microbubble pressure transducer with bubble nucleation

Real-time pressure tracking (type III)

Page 14: A microbubble pressure transducer with bubble nucleation

Conclusion • μB nucleation by electrolysis and real-time pressure

tracking (-93 Ω/mmHg over 0-350mmHg). • Repeatable, efficient electrolytic generation of stable

microbubbles (< 1.5 nL with < 2% size variation) was achieved using a μBNC structure attached centrally to the microchannel.

• Biocompatible construction (only Parylene and Pt)• Small footprint• Low power consumption (< 60 μW)• Liquid-based operation of μBPTs are ideal for in vivo

pressure monitoring applications.

Page 15: A microbubble pressure transducer with bubble nucleation

The End