The precise temperature control of ball SAW sensors for trace moisture

measurement at ppb level of concentration

Yusuke Tsukahara, Kazushi Yamanaka, Nobuo Takeda, Shingo Akao, Toru Oizumi, Hideyuki Fukushi, ToshihiroTsuji

Ball Wave Inc.

2017/6/20 Ball Wave Confidential 1

Process Industry : A 10

The ball SAW sensor

• What is the ball SAW sensor?

• How does it measure the trace moisture?

• We had a difficulty caused by temperature variation.

• How did we solve it?

• Our detection limit is about 1ppbV trace moisture in N2 gas.

• We detect the trace moisture in hydrocarbon gases with a same calibration curve.

• We detect a-few-seconds spikes of trace moisture.

2017/6/20 Ball Wave Confidential 2

What is the ball SAW sensor?

Piezoelectric

Sphere

Sensitive

Film

Interdigital

Transducer

SAW

Long propagation

⇒High sensitivity

Molecules

2017/6/20 Ball Wave Confidential 3

(Surface Acoustic Wave)

SAW goes around and around and around the sphere.

What is the ball SAW sensor?

2017/6/20 Ball Wave Confidential 4

Piezoelectric

Sphere

Sensitive

Film

Interdigital

Transducer

SAW

Long propagation

⇒ High sensitivity

Molecules

Time of

1 turn

Without Gas

With Gas

Without Gas

With Gas

Time

Time of

100 turns

Amorphous silica film

stiffens when it absorbs

water molecules.wet

dry

wet

dry

water

Amorphous silica

Quartz crystal 1~3mm in diameter.

How does it measure the trace moisture?

2017/6/20 Ball Wave Confidential 5

TCXO

ADC1

FDIV

SwitchTxRx

Ball SAW sensor

BPF 2+

BPF1

Synthesizer

A

BPF1

BPF2 ADC2 C

FDIV

BPF3

BPF4 D B

Amp Amp

FDIV

How does it measure the trace moisture?

2017/6/20 Ball Wave Confidential 6

We measure

(1) the decay rate and

(2) delay-time of pulses.

Difficulty caused by temperature variation.

• We have to measure the ppm level of change in the delay-time of pulses.

• But the delay-time strongly depends on temperature.

• We need to compensate it for the trace moisture detection at ppbV level.

2017/6/20 Ball Wave Confidential 7

How did we solve it?

2017/6/20 Ball Wave Confidential 8

13 13.1 13.2 13.3

−500

0

500

−200

0

200

13 13.1 13.2 13.3

−20

0

20

Am

plit

ude

(mV

)Time (μs)

Am

plit

ude

(mV

)

80 MHz

240 MHz

Wavelet transform

Waveform at 4th turn

We use two frequencies to

compensate for the temperature

variation.

How did we solve it?

2017/6/20 Ball Wave Confidential 9

)()()( REF111 TTAwGfTBt -+=D

)()()( REF222 TTAwGfTBt -+=D

)()()( 1212 wGTBCfftCttW -=D-D=D

Cff

ttffTTAtT

-

D-D=-=D

)/(

)/()(

12

2112REF1

[ ])273(/exp)()( B12 +D=- TkaTBCff e

From these equations, we obtain

Relative delay time changes at frequencies 1f and 2f , are given by

where w and T are moisture

concentration and temperature,

respectively.

where

and C=A2/A1.

Ref: Proceedings of Symposium on Ultrasonic Electronics, Vol. 37 (2016) 16-18 November, 2016

6/20/2017 Ball Wave Confidential 10

Falcon Trace (code name)

We implemented the method

in a prototype.

Our calibration curves for high end and low end

2017/6/20 Ball Wave Confidential 11

Decay rate due to moisture dB Delay time ratio of two frequencies

Our detection limit is about 1ppbV.

2017/6/20 Ball Wave Confidential 12

Trace moisture measurement

in the nitrogen gas

Trace moisture in hydrocarbon gases.

• It works in hydrocarbon gases with the same calibration curve.

2017/6/20 Ball Wave Confidential 13

-20%

0%

20%

40%

60%

80%

100%

120%

0 60 120 180 240 300 360 420 480 540 600

TIME (sec)

PH

AS

E S

HIF

T

N2 100sccm

H2 100sccmCH4 75sccm

C2H6 51sccm

Transient Characteristics @ 1,800ppm H2O Injection

Trace moisture in hydrocarbon gases.

2017/6/20 Ball Wave Confidential 14

MFC

MFC

Ball SAW

N2

H2

CH4

C2H6

･･･

Exhaust

0.07 to 0.998 L/min

0.002 to 0.03 L/min

1 L/min

Rotary

Valve

Dry Gas line

Wet Gas line

~3 m

~0.3 m

Bubbler

0 ℃

Saturated vapor pressure

@0 ℃ = 611 Pa

40 to 2000 nmol･mol-1 H2O

MFC

0.1 L/min

H2O Vapor Generation Case 1: Bubbler Method

Trace moisture in hydrocarbon gases.

2017/6/20 Ball Wave Confidential 15

-20%

0%

20%

40%

60%

80%

100%

120%

0 60 120 180 240 300

TIME (sec)

PH

AS

E S

HIF

T

N2 100sccm

H2 100sccmCH4 75sccm

C2H6 51sccm

Transient Characteristics @ 1ppm H2O Injection

Trace moisture in hydrocarbon gases.

2017/6/20 Ball Wave Confidential 16

MFC

MFC

Ball SAW

Exhaust

0.1 L/min

0.1 L/min

1L/min

Rotary

Valve Dry Gas line

Wet Gas line

~3 m

H2O

nW

Diffusion Tube

nW = DWSe / LRT

L

e

~0.3 m

N2

H2

CH4

C2H6

･･･

1 nmol･mol-1 H2O

H2O Vapor Generation Case 2: Diffusion Tube Method

A-few-seconds spikes in the trace moisture.

2017/6/20 Ball Wave Confidential 17

• Injected dry N2 gas and 10ppmv wet N2 gas alternatively in 5 seconds into the sensor cell.

dry N2

wet N2

sensor cell

90mm

PC

A-few-seconds spikes in the trace moisture.

2017/6/20 Ball Wave Confidential 18

Background is not an artifact but is due

to the adsorption of moisture on the

inner surface of piping.

-65℃ FP

-90℃ FP

2017/6/20

A-few-seconds spikes in the trace moisture.

Ball Wave Confidential 19

90mm

PC A dry chamber

The ball SAW sensor works with 0 flow rate.

The open-face sensor

A-few-seconds spikes in the trace moisture.

2017/6/20 Ball Wave Confidential 20

90mm

PC

We can monitor a leakage in a moment.

leak

A dry chamber

The open-face sensor

Thank you for listening.

• We offer a unique solution for the trace moisture measurement with

versatile capabilities.

• A prototype for commercial model is available now for early access.

2017/6/20 Ball Wave Confidential 21