a microbubble pressure transducer with bubble nucleation
TRANSCRIPT
A MICROBUBBLE PRESSURE TRANSDUCER WITH BUBBLE NUCLEATION CORE
Author: Lawrence Yu, Ellis Meng
Reporter: 朱家君Date: 2015/6/15
Outline• Introduction• MEMS pressure transducer• Design and operation• Measurement results• Conclusions
Introduction• Purpose: μBPT + μBNC
→ achieve low power operation in wet environments.• Operation: electrochemical impedance measurement
→ hydrostatic pressure change
→ μB size instantaneous response
MEMS pressure transducer• Capacitive, piezoresistive, piezoelectric transduction:
• μBPT: no need of hermetic packaging
→ in vivo monitoring
→ reduce overall sensor footprint
Design• Previous work: silicon microfluidic channels
→ poor control
(> 6% size variation)
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 ↑
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
Model
• Iac applied across the EI measurement electrodes:
→ monitor the volumetric conductive path (Rs)
• Rs:
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.
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.
Measurement
Current pulse v.s impedance Magnitude and phase
To eliminate capacitive effects, measurement frequency was selected where phase ~0° (10 kHz)
Current injection v.s. impedance
Impedance-pressure correlation (Type III)
Real-time pressure tracking (type III)
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.
The End