DESIGN BY RULE

Designing the IDT

Wavelength ~240 µm

Transducer size 3 cm long × 1 cm wide

Finger length / aperture 25 mm / 20 mm overlap

Electrode width / spacing 40 µm / 80 µm

Fingers 168 total, in 42 groups of 4

Two opposing IDT sets face each other across the channel, each launching a wave toward the center.

DESIGN BY RULE

Designing the channel

The microfluidic channel uses 3 inlets, each 40 µm in diameter, feeding into a channel with mirrored outlets. The whole layout — channel and IDTs alike — is kept symmetric about a centerline.

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Symmetry isn't cosmetic here — it's what keeps the standing wave centered and the particle sorting balanced.

DESIGN BY ANALYSIS

Simulate before you fabricate

Before cutting any wafers, the design is modeled in finite-element software, combining solid mechanics and electrostatics physics.

Substrate Lithium niobate, 128° Y-cut, X-propagating, on a 4-inch wafer

SAW region 2.5 cm × 500 µm, with 50 µm of air above

Electrodes Gold, 250 nm thick

DESIGN BY ANALYSIS

Setting the boundary conditions

Solid mechanics

Fixed constraint, free surface, piezoelectric material, and a periodic boundary condition

Electrostatics

+10V drive electrode, a ground, and a zero-charge boundary elsewhere

Every simulation is only as good as its boundary conditions — get these wrong, and the results mean nothing.

DESIGN BY ANALYSIS

What the simulation found

Modal frequency 16.473 MHz

Displacement field Shows the acoustic wave propagating

Electrostatics Confirms a 5V voltage peak

A virtual probe then measures the SSAW's displacement field with the microfluidic channel positioned right at the center of the device.

The simulation confirms the design works before a single wafer is touched.

UNIT 27 STUDY COMPLETE

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