Transducer Architecture

How many components make up the basic transducer?

7

What is the case’s function?

Protects the internal components of transducer and protects the patient from electrical shock

What is the case normally made out of?

Plastic or metal covering

What is the electrical shield’s function?

Prevents outside electrical signals (static) from entering the transducer. Shield helps prevent electrical noise from contaminating US signals

What is the electrical shield normally made out of?

A thin metallic lining, just inside of the case

What is the acoustic insulator’s function?

Prevents vibrations within the case that could induce an electrical voltage to PZT

What is the acoustic insulator normally made out of?

Cork or rubber inner lining

What is the wires function?

It is the electrical connection between PZT and US system for transmission and reception

What is important about the wire in a transducer?

Each crystal has a wire hookup

What does PZT look like in a simple probe

Coin shaped

What is related to the crystals dimenstions?

The characteristics of the sound beam

The active element is __________ of the wavelength

½

Where does the matching layer lie?

Between the crystal and skin

What is the matching layer’s function?

Increases efficiency of transmitting sound between the crystal and skin

What is the matching layers main function?

Protect the active element

The crystal’s impedance is _______ the skins

Greater

Acoustic gel “Z” is between __________ and ________ to optimize sound transmission

Matching layer and skin

The matching layer is __________ of the wavelength

¼

What is another name for the backing material?

Damping element

What is the backing material normally made with?

Epoxy resin impregnated with tungsten filaments

Where is the backing material located on the basic transducer?

Bonded to the back side of the crystal

What is the function of the backing material?

Reduces ringing, restricts PZT deformation —> creating shorter pulses

What is absorbed into the backing material?

Sound energy

_______ impedance and backing material impedance are similar

PZT

In which direction does the sound energy move?

Away from the patient

The backing material has a high degree of __________________.

Sound absorption

How many consequences of backing material are there?

3

What are the consequences of backing material?

Decreased sensitivity, wide bandwidth, and low-quality factor

What does decreased sensitivity mean?

During reception, transducers with damping material are less able to convert low-level sound reflections into meaningful electrical signals

The backing material not only reduces the active element vibration during ____________ and also during _________.

Transmission and reception

What is another name for wide bandwidth?

Broadband

Vibrates for a long time at one frequency.

Resonant frequency (main)

What does the backing material prevent the PZT from doing?

Ringing freely

The PZT is restricted, and in return the

Pulse emitted is a short duration and increases the bandwidth

What is bandwidth mean?

Range of frequencies in the pulse (difference between highest and lowest frequencies)

Which type of transducer has a greater bandwidth: continuous wave or imaging?

Imaging

What type of transducer has more backing material: therapeutic or imaging?

Imaging

How do we find the bandwidth ?

Highest freq. - lowest freq.

Quality Factor is a _________ number

Unitless

What relationship does quality factor and bandwidth have?

Inverse

What is the formula to find quality factor?

QF = Main frequency (MHz) / bandwidth (MHz)

Because imaging probes use backing material and have a wide bandwidth,

They often have a low-Q

Because therapeutic ultrasound and continuous waves do not contain backing material,

They have a narrow bandwidth and a high-Q

What is the relationship between quality factor and resonant frequency?

Direct

What does quality factor describe?

The transducer’s ability to emit a clean pulse with a narrow bandwidth