Transducer Design Flashcards by Brianne Selin

Another name for ultrasound probe and it’s function

Transducer

Converts energy from electrical energy to acoustic energy and than acoustic energy back to electrical energy

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Transducer

Piezoelectric crystal or element

Signal conversion device

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Crystal

Piezoelectric material

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Element

Another name for the piezoelectric crystal

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Scan-head

Another name for transducer

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Probe

Another name for transducer

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Transducer assembly

Another name for transducer including the housing and internal circuitry

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Housing

Contains all probe components

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Backing material

A mixture of metal, plastic, or epoxy bonded to the back of the crystal

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Crystal - in the probe

Ceramic element that piezoelectric properties

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Matching layer

Used to reduce sound refraction from the skin

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When and who discovered the piezoelectric principle

Jacque and Pierre curie in the 1880’s

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What does the piezoelectric principle explain

Why some material can convert electrical energy to mechanical energy and vice versa

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What are some of the natural materials that have piezoelectric properties that were used in early machines

Quartz
Lithium sulphate
Rochelle salt
Tourmaline

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What are some of the man-made synthetic crystals that are used in modern day equipment

Lead zirconate 
Lead titanate
Barium titanate 
Lead zirconate titanate (PZT)
Polyvinylidene Fluoride (PVFD)

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What are the man-made ceramic synthetic crystals

PZT Barium Metaniobate

Barium Titanate

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What are the man-made composite synthetic crystals

Epoxy with PZT inserts

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What are the man-made polymer synthetic crystals

PVFD

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How does the piezoelectric effect (direct) occur when a mechanical pressure is applied

The mechanical pressure deforms the crystal
This changes the orientation of the electric dipoles
This change produces a small electrical voltage

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How does the reverse piezoelectric effect occur when a electrical voltage is applied

The electrical voltage changes the orientation of the dipoles causing the crystal to expand and contract

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What are electric dipoles

The molecules with the crystal with a positive charge at one end and a negative charge at the other

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How can any dipolar material be influenced

By a electrical or magnetic field

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Can a random alignment of dipoles cause sufficient vibration when a electrical current is applied

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Why is proper alignment of dipoles needed

It allows for a better vibration of the crystal

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What must be considered when the crystal vibrates

That different modes of vibration may occur

What was the shape of the crystal in early probes

Disc

What were the two modes that the crystal could the vibrate in early probes

Thickness mode | Radial mode

Are the crystals in modern day probes shaped differently than early probes

Yes

What are the three modes of vibrations that crystals can vibrate in today’s probes

Thickness Length Width

What is the most desirable vibration in today’s probes

Thickness

Why are synthetic materials used in the production of crystals

Allows a more pure product to be developed because there are less imperfections

How are substance aligned so that they can enhance the piezoelectric properties for ultrasound production

A substance is heated beyond its Currie temp which forces the bonds between the molecules to weaken and when subjected to a electrical field the dipoles align accordingly and when the substance is cooled the bonds strengthen

What is the Currie temperature for PZT

350° Celsius

What does reheating do to synthetic crystals and why are probes not put into autoclaves

Reheating can potentially cause depolarization, which why probes are not put into an autoclave. Also the plastic would melt

What kind of bath are the substance subjected to that will cause the bonds to weaken

Oil bath

What determines what frequencies a probe can emit

The crystal

What are the different frequencies

Resonate Driving Operating Harmonic

What is resonant frequency

The frequency that the crystal likes to ring at

What determines resonant frequency

Crystal material | Crystal thickness

What is another name for resonant frequency

Fundamental frequency

What is driving frequency determined

By the Alternating current (AC) voltage that is sent to the crystal

What is driving frequency

The different frequency that a crystal can be forced to ring at because of the voltage being altered

What is the operating frequency

The frequency that is being used to scan

What is the Harmonic frequency

Two times the resonant frequency

How are lower frequencies and higher frequencies of a crystal determined

By crystal thickness

What produces lower frequencies

Thicker crystals

What produces higher frequencies

Thinner crystals

Thickness of the crystal which determine resonance frequency is equal to what

1/2 wavelength

What is the relationship of crystal thickness to frequency

Proportional | Ex: doubled thickness = 1/2 f

What is important when calculating crystal thickness

Speed of sound in the crystal as the constant

What is a crucial part of transducer design

Backing material

What is the backing material typically

Epoxy resin with metal powder (tungsten)

Where is the backing material located on the crystal

On the back

What’s another name for backing material

Damping block

What is the purpose of the backing material

To reduce the SPL which will improve axial resolution

What does the backing material do the amplitude of the wave

It reduces it, which reduces sensitivity

Anything that improves the spl also

Improves the axial resolution

What would happen if the amount of damping material increased

The length of the pulse will shorten

What is another function of the damping material

Absorbing sound so that reflections don’t occur behind the crystal

How does the damping material absorb sound

The Z value of the damping must be comparable to the element

Typically how many cycles per pulse are produced as a result of the damping material

2-3

What length of a pulse is ideal to improve resolution

Short

What is dynamic damping

Is an electronic means to suppress the ringing of the crystal

When is dynamic damping used

In Doppler

What is the matching layer

Prevent sound from returning to probe before entering the patient

Why is the matching layer important

The z value that the matching layer has between the crystal and the skin helps reduce the amount of reflection

What is the potential problem of adding a matching layer

The reflections that can occur between them and the crystal

What is the key to solving the problem of the matching layer

Cut the thickness of the matching layer in 1/4 of the wavelength

What does 1/4 of the wavelength do

It helps create destructive interference of waves that reverberate between the matching layers

Are there multiple matching layers used for the multiple frequencies that come out of the probe

Yes

The many matching layers will accommodate multiple frequencies which will improve what

Improves the transmission and reception of a wide bandwidth of frequencies

What is the gel considered as

A matching layer as it helps the sound transmit into the patient

Does the gel have a z value between the last matching layer of the probe and the skin

Yes

What method did older technology use for driving voltage

Spike voltage

What method did newer technology use for driving frequency

Burst voltage

What kind of current does spike voltage use to vibrate the crystal

Direct

Direct current

Current from the pulse hits the crystal where one spike is equal to one pulse

Another name for dc current

Saw-tooth voltage

What type of current does burst voltage use

Alternating current

Current from the pulser hits the crystal where one voltage burst is equal to one pulse

Burst voltage

Looks like a sine wave | Frequency of the voltage determines the frequency of the probe

In ac mode what determines the resonating frequency

Driving frequency of the voltage

In dc mode what determines the resonant frequency

The driving frequency and the resonant frequency are always equal to each other

Bandwidth

The range of frequencies that are produced by a pulse

When a crystal rings at its resonant frequency what normally happens

A very small range of frequencies are produced

What happens when the crystal is dampened

The pulse length shortens and a greater range of frequencies are emitted from the probe

What does crystal thickness and material determine

The most efficient frequency to ring at

Shorter the pulse

Wider the bandwidth

What does a wider bandwidth mean

More options of what driving frequency can be chosen

What does the size of the bandwidth and attenuation limit

The frequencies that the probe can be driven at

Frequencies that have an amplitude of less than half of the resonant frequency are

Too weak to be used by the system

6dB bandwidth

The useable bandwidth | Is equal to one half amplitude or 1/4 the intensity of the resonant frequency

Fraction bandwidth

The common way to express the bandwidth of the probe FB= bandwidth/ frequency

Broadband design

A probe with a FB over 80%

Quality factor

Another term for describing the band width of the probe Q= frequency/bandwidth The reciprocal of fraction bandwidth

Low Q

Desirable for 2D scanning

High Q

Colour Doppler Pulsed Doppler CW Doppler

To optimize the 2D image

Use more damping to shorten the pulse

An increased bandwidth means

A lower Q factor

Modes requiring more sensitivity will benefit from

A narrower bandwidth or higher Q

Reducing SPL

Increase in bandwidth