Ultrasound References

Overview

This page includes ultrasound basic knowledge, ultrasound transducer parameters, working theory, design procedures, and basic circuits to drive an ultrasound transducer.

Ultrasound Basics

Vibration and Wave

A vibration source in a mechanical medium will cause wave propagation.
Ultrasound is a mechanical wave, which cannot exist in the vacuum.
Ultrasound transfers energy within the medium, but does not transfer mass.

Longitudinal wave: particle movement in the same direction of the wave propagation.

Compression: Ultrasound propagation causes local medium density and pressure varying with time. The density or pressure will increase when it is compressed.
Rarefaction: When low pressure pass through, the local density will decrease.
Transverse wave: particle movement in the direction perpendicular to the wave propagation.

Ultrasound Parameters

Frequency: The number of times a vibrating particle goes through its original position within one second. The unit is “Hertz” or simplified as “Hz”. For ultrasound, the frequency is around mega hertz, or “MHz”.
Propagation speed: The distance that the wave peak pass within one second. It is determined by elasticity and density property of the acoustic medium.
Wavelength: The distance between the two adjacent wave peaks
Amplitude: For vibration, the amplitude is maximal distance a particle moves away from its original position.
Pressure: Wave propagation can be understood as the particles vibration abound their balance position, also can be thought as pressure variation in the acoustic medium alternatively. Pressure, especially from the surface, cause particle to move. Take a small volume inside the acoustic medium, when more neighbor particles move in, a high pressure is introduced, and on the contrary, when the particle move out, a low pressure in generated.
Power: Since the particles are vibrating, it possesses kinetic velocity and energy. An ultrasound source will generate energy, and this energy divided by time is power. When frequency is fixed, the power is proportional to the density and second power of particle vibration amplitude. When particles have the same vibration amplitude, the power will be proportional to the fourth power of the frequency.
Intensity: it is the power on unit area.

Medium Acoustic Property

Air: Only low frequency ultrasound can propagate in air at a speed of 300m/s with a very high attenuation. The acoustic impedance of air near zeros.
Water: Sound velocity in water is around 1500m/s at room temperature. Water has very little attenuation to ultrasound. The acoustic impedance of water is about 1.5MRayl.
Soft tissue: Sound velocity in soft tissue is around 1540m/s. The attenuation of soft tissue is around 0.3 dB/cm/MHz. The acoustic impedance of soft tissue is around 1.5MRayl.
Bone: Sound velocity in bone is much fast that in soft tissue. Bone also has a higher attenuation. Normally, ultrasound beam cannot penetrate bone. Back to Top

Ultrasound Reflection

Big surface: The surface must be big compared to the ultrasound wavelength when reflection happens.
Impedance mismatch: The acoustic impedance on both side of the surface must be different.
Wavefront pattern: The reflected wave from a spherical wave emitted from a point has the same shape as that emitted from its mirrored counterpart.
Dependence on angle: For plane wave, the reflected wave has the same angle to the surface as that of incident wave.

Plane wave reflected by a tilt plane surface

Ultrasound Refraction

Big surface: Ultrasound refraction only happen at big surface compared to its wavelength.
Velocity mismatch: The acoustic medium at both sides of the surface must have different sound velocity.
Dependence on angle: The refracted wave obey Snell’s Law.

Plane wave refracted by acoustic medium with slower sound velocity

Plane wave refracted by acoustic medium with faster sound velocity

Spherical wave refracted by acoustic medium with slower sound velocity

Spherical wave refracted by acoustic medium with faster sound velocity

Ultrasound Scattering

Small particle size: Ultrasound will be scattered when encounters a small particle compared to its wavelength.
Impedance mismatch: The particle must have a different acoustic impedance from its background.
Independence of angle: The scattered wave will spherical when the particle size is very small.

Spherical wave scattered by a small object

Ultrasound Attenuation

Causes of ultrasound attenuation:
- Scattering
- Absorption
- Reflection
Ultrasound attenuation values in type of tissue: Water has minimal attenuation to ultrasound. Blood has an attenuation of 0.03dB/cm/MHz. Soft tissue has a value of 0.3dB/cm/MHz. Air, bone, stone, and metal will normally attenuate all the imaging ultrasound beam energy they encountered.
Ultrasound attenuation values increase with frequency.
Effects on image: Far field image will look darker without compensation. Resolution in far field is lower than near field due to the downshift of the center frequency of the echo. Back to Top

Ultrasound Application

HIFU: Depends on application, low than half of the diagnostic frequency.
Abdominal imaging: 3.5 ~ 5 MHz.
Cardiovascular imaging: 2.5 ~ 3.5MHz.
Ophthalmology, eye application: 15 ~ 50MHz.
Dermatology, skin application: 15 ~ 50 MHz.
Small organ: 5 ~ 12MHz.
Peripheral vascular: 5 ~ 10 MHz.
Intravascular (IVUS): 10 ~ 50 MHz.
Frequency, Penetration, and spatial resolution: Higher frequency gives better resolution, and less penetration. The transmitted power of ultrasound pulse for imaging is regulated by FDA. The highest energy within FDA regulation is always used for the best signal to noise ratio. As long as the signal from the farthest depth has enough SNR, the highest frequency is always the first choice. Back to Top

Beamforming

Ultrasound Beamforming

Interference phenomena: Sound is an acoustic wave, following the superposition principle. Acoustic wave cause pressure at each location of the medium vary with time, and thus the particles to vibrate with time. If the pressure or the displacement of the particle is recorded, in most cases, it is a sinusoidal function: y = A sin (2π f t + Ф ), A is the amplitude, f is frequency and Ф is the initial phase. Inside the acoustic medium, or the acoustic field, Ф varied with location, and amplitude and frequency are the same if we don’t consider the wave spread and attenuation. If two pressure waves propagate to a single point, the final pressure at the point will be arithmetic summation of these two: y = A₁ sin (2π f₁ t + Ф₁ ) + A₂ sin (2π f₂ t + Ф₂ ). Depends on frequency and initial phase, the combination can be stronger or weak compared to the incident waves, and can even become zero if the two have the same amplitude and frequency, but opposite initial phase. If the wave sources and acoustic field are fixed, the initial phase for each location will be fixed too, and thus vibration at some points will be enhanced while other points may be weakened consistently.
Huygen’s principle: This principle of wave analysis, proposed by the physicist Christiaan Huygens (1629-1695), basically states that: Every point of a wave front may be considered the source of secondary wavelets that spread out in all directions with a speed equal to the speed of propagation of the waves.
Aperture size and wavelength: The aperture is the active area that transmits or receives acoustic wave at certain moment. For a single-element transducer, the aperture size is the transducer element size. For array transducer, the aperture are all the elements that works together simultaneously. To achieve a confined beam, the aperture size need to be much larger compared to the sound wave length. At 5MHz, the ultrasound wavelength is about 0.3mm in water, and a 5mm diameter transducer will give a decent beam. However, at normal sound frequency such as 1kHz, the wavelength is about 0.3m, it need a 5m diameter speaker to give a sound beam that propagate forward. Since most speakers are small compared to the sound wavelength, and they behave like a point source, with sound spread all the directions.
Beam field from a piston aperture: The most simple transducer shape is a piston transducer. The beam from a piston transducer is similar to a flash light beam.
- Acoustic pressure along central axis have many maximums and minimums and from the last peak, it goes down monotonously.
- Cross section view of the beam at different depth vary with depth.
- Longitudinal section view view
- Main lobe and side lobes
Near field and farfield:
- At each sound field point location, the acoustic pressure is the summation of contributions from each point at transducer surface. When aperture size is much bigger than the wavelength, the points locations within the transducer area and close to the center see an unlimited aperture, at same depth, will receive the same amount of acoustic contribution from the nearly unlimited transducer surface, and thus ultrasound wave behaves like plane wave. However, the locations close to the edge still see the limited aperture, and thus the plane wave area is smaller than the aperture area. Moving away from transducer, this plane wave zone decreases quickly.
- For a point at the central axis of the aperture surface, the biggest time difference for sound to travel from different points on aperture surface to it is from aperture center point compared from aperture edge point. This time difference vary lot at distance close to aperture surface, and acoustic pressure will become maximum minimum alternatively. At certain depth it became one wavelength, and from there it slowly decrease to infinitesimal when depth goes to infinity, and accordingly the acoustic pressure will decrease monotoneuosly.
- The acoustic field before this depth is called near field, and beyond this depth is called farfield. Since acoustic intensity is unpredictable in near field, and strictly speaking, it should be avoid to use it for echo information. However, for imaging ultrasound, since it is wide bandwidth, the acoustic intensity is also uniform in near field, and thus near field is not so serious.
Beamwidth: Beam width is usually calculated from the cross-sectional or longitudinal section acoustic field view, and it is a parameter related with dB level. On cross-section view, draw a line through the center, or on longitudinal section view, draw a line at certain depth perpendicular to the central axis, a 1-D acoustic profile is obtained. On this profile, -xdB level bean width is the distance between the two points that have this dB level intensity. Beam width can also be represented in angle. At certain distance, normally the focal or natural focal depth, draw a half circle center at the aperture center, and along this half circle, a 1D acoustic profile can be obtained. One this 1-D profile, the horizontal axis is angle from -90 to +90 degree, the beam width will be the angle difference between the two dB level points.
Natural focus: ultrasound beam from a flat aperture will get narrow and then spread out within and angle range. The depth where beam is most narrow is the natural focus of the aperture. Back to Top

Ultrasound Focus

Method: When aperture is concave, the uniform excitation on the aperture will generate a concave wave front, and it will converge to a point when propagating. As shown in the following figure: The concave wave front that is necessary to achieve the focused beam can be obtained by mechanically shape the aperture into concave, or the using an array transducer and control the transmit delay of each element. Theoretically, the round concave surface gives the best focus effect. The focal effect from of transducer can be improved with more element, smaller element size, and high resolution delay control.

F number: is the ratio of focal depth over aperture equivalent diameter, it is the diameter for round aperture, and the total aperture element length for array transducer. Focus effect is greatly related with frequency, focal depth and aperture size. When focal depth and aperture size are combined into f number, and so the focus effect will be determined by f number and frequency.
Focal zone characteristics
- Beam width: The beam width is narrowest at focal point, and it is governed by the f number and center frequency:
- Focal distance (length): For a focused beam, it is narrowest at focal depth, and spread on both sides away from the focal depth.
- Maximal Intensity: Beam also get maximal intensity at focal point. Back to Top

Ultrasound Transducer

Piezoelectric Effect

Piezoelectricity is the ability of some materials (notably crystals and certain ceramics) to generate an electric potential in response to applied mechanical stress. The material that shows piezoelectricity is called piezoelectric material. Applied electrical charge on both sides of a piece of piezoelectric material, it will cause stress inside and thus generate deform. If the electrical charge is alternative, the piece of material will oscillate and generate mechanical wave. The piezoelectric material has a special structure that will cause positive and negative charge center mismatch when an external stress is introduced from certain direction. Piezoelectric ceramic have many small regions inside it, called “domain”, and each domain has its own piezoelectric direction. When an external stress is introduced, some domains give positive charge if they are lined up according to the stress direction; some domains may give very minimal charge if its own direction is perpendicular to the stress direction; and some domains will give negative charge if it is against the stress direction. The domains are very small at level of a few microns to hundreds microns, and normally they are randomly distributed, without special processing to line up all the domains, the material will not show piezoelectric as a whole piece. The processing is called poling, use a high DC voltage applied on both sides of the piece of material for a short duration of time, such as 1 to 10 seconds. Different material needs different voltage to reverse the domains, and this voltage is called coercive voltage. Pure piezoelectric crystal may be a single domain and doesn’t need poling.
Curie temperature: When temperature is high enough, the piezoelectric domains inside ceramic will have such a high kinetic energy and it will break away from the poling direction and resume to its original random direction. This temperature is called Curie temperature. Piezoelectric ceramic will lose its piezoelectricity when its temperature is above its Curie temperature.
Kt: It is thickness mode mechanical-electrical coupling efficient, the key indicator of piezoelectricity performance of the material in thickness mode. By definition, it is the ratio of energy send out to the energy stored by the material. Without piezoelectricity, a ceramic plate with two sides coated with electrodes will behave as a capacitor, the impedance will only have imaginary part, no real part. The current go through it and the voltage applied on it will be always 90 degree to each other and thus no energy is emit out but all stored and released. With piezoelectricity effect, at resonant frequency, the impedance will have real part and imaginary part, the real part will consume electrical energy, convert it into acoustic.
Common piezoelectric materials: commonly used piezoelectric materials are ceramics, crystals and polymers. Crystal usually has lower Kt, and it not good for thickness mode, but good in bar mode. Ceramic has a better Kt, good in thickness mode. Both of crystal and ceramic have high acoustic impedance, usually above 30Mryls. Matching layers are required to transmit acoustic. Back to Top

Transducer construction

Thickness resonance mode: The positive and negative charge center will mismatch and form a dipole when external force is applied. The dipole direction maybe parallel or perpendicular to the external force direction. For most ultrasound application, the transducer is a plate of piezoelectric material with two sides coated with electrodes. With this structure, the dipole direction will be parallel to the external force, called 3-3 mode or thickness mode. There are also transducers in the other way, the stress and electrical field perpendicular, called 1-3 mode, are common in low frequency application range.
Bandwidth and Q: When it says the transducer has a center frequency of 5MHz, it doesn’t mean the transducer only works at exactly 5.0MHz, and it won’t work at 5.1MHz or 4.9MHz. It always has a range, and it is called spectrum if it drawn with vertical axis as magnitude and horizontal axis as frequency. Most good transducer will have bell or Gaussian shape spectrum curve. It has best response to the input excitation at center frequency, and the response will become weak as the excitation frequency moves away from the center frequency. On the spectrum, with the maximum point marked as 0dB, two points can be found at both sides with magnitude of -3dB, -6dB, or any other number you can name. The frequency range between these two data points is called Bandwidth. It is obvious that bandwidth is always linked with a dB level, such -3dB bandwidth or -6dB bandwidth. On the voltage spectrum, -6dB is often used, and on the power spectrum, -3dB is more commonly used. Q is a simple name of “Quality factor”, is the ratio of center frequency over the bandwidth. The lower the Q, the wider the bandwidth, and the pulse will be short. For ultrasound imaging, the transducer need transmit a very short pulse to achieve sharp resolution, and thus a low Q is required for the whole system, or we can say, the imaging system is a wide band width system. High Q system is for resonant, for example, a crystal watch has a very high Q.
Damping: Damping is to decrease the system Q. For ultrasound transducer, it normally means the backing layer. Heavy damping results in wide bandwidth, short pulse length, but lower sensitivity. Doppler transducer usually has lower damping, and thus a higher sensitivity can be achieved since the Doppler signal is normally weak because it is generated from blood scattering.
Matching layer: Most medical ultrasound transducer is based on piezoelectric ceramic or crystal, having a very high acoustic impedance (about 30MRyl), and human acoustic impedance is only about 1.5MRyls. Without matching layer, the vibration of the ceramics will be bounce back and forth inside itself and gradually die out, only a small port of energy can be released to the tissue with each time of bouncing. The final pulse enter the tissue will be long with a lower amplitude. With a proper matching layer, the pulse will enter the tissue with minimal lengthened. Back to Top

Array Transducer

Linear array: In a linear array transducer, all the elements form a line. The element usually as a rectangle shape with width in the array direction or lateral direction, and height in elevation direction. The center to center distance of the two adjacent elements is defined as pitch size and gap between them is called kerf. Normally the pitch size is required to be smaller than 1 wavelength, but some cases it can be 1.25 wavelength. The kerf is normally around 50 microns depends on the blade thickness to cut the elements. Linear array is widely used when acoustic window is big enough, such as abdominal or limb vessel scan. In a linear array, each time only a group of elements work together to transmit or receive, i.e. the aperture size is smaller than he transducer active surface. The ultrasound beam is perpendicular to the transducer surface, and scan a rectangle area.

Phased Linear Array: it is exactly the same as linear array in term of element arrangement. For phased linear array, the element pitch size is required to be smaller than half of the wavelength. In a phased array, all the elements work together, i. e. the aperture are all the elements, and the aperture size is the whole transducer active surface. Phase array steer the beam by apply different delay on each element, and it requires small acoustic window. It is widely used in cardiovascular scan where the rib gap is the small acoustic window.
Curved array: Curved array is very similar to the linear array. All the elements form a line, but it is curved and most likely is convex. Compared to the linear array, it gives a bigger scan area when acoustic window is limited.

Annular array: An annular array consists concentric rings elements with the center one having a round shape. Annular array elements work together and normally have time delay to achieve focused beam. Due to its special geometry shape, annular give best focused beam with focal depth adjustable electronically. Most annular array have equal area elements to keep impedance of each the same.

Circular array: a circular array has all the elements form a circle, facing one side.
1.25D 1.5D 1.75D array: in linear array, either linear scan or phased scan, there is only one element in elevation direction, i.e. the direction perpendicular to the scan direction and depth. The focal depth cannot be changed in this direction also it can be dynamically changed in lateral direction. To improve this capability, the element is divided into several pieces in elevation direction, with the first one, or the primary one is bigger in size. Depends on the number of pieces and the size, it is called 1.25D. 1.5D, or 1.75D. It partially improves the elevation focus property.
2D array: in 2D array, the element forms a M X N matrix. Beam can be steered in all the directions and thus the transducer is capable of scanning a volume, generating echo information for a 3D image. A 64 x 64 element array will require more than 3600 channels for beamforming, and it increase the cost of the imaging system greatly. Back to Top

Transducer

Signal and Circuits

Unipolar Transmitter

How it works:
This circuit transmits a short pulse at a low duty factor level, mainly for diagnostic applications. When there is no transmit signal, the MOSFET M1 is off and the capacitor C1 is charged through R1 by HV. When a transmit trigger signal arrives at the gate of M1, it will cause M1 to turn on and C1 will discharge to the load transducer (RL). A negative pulse will be applied on the transducer. The pulse width is determined by the time constant: Τ = RC.

If the trigger pulse width is narrower compared to 5RC, the transmitted pulse width will be determined by the trigger pulse as shown in the above right figure.

R1: provides a charging current to C1 through HV. Its value is determined by the period of the pulse repetition. It has to be small enough to let C1 fully charged before the next transmit. If it is too small, big current will go through it when M1 is turned on, causing C1 not discharge properly to the load, or even the damage of M1.
M1: Three parameters for M1 are important.
- Vds: how much voltage it can handle. This parameter has to be at least 1.2 times higher than your pulse amplitude. For example, if you want to transmit a 100v negative pulse on the transducer, the Vds for M1 should be 120 – 150 v.
- Cgs, tr, tf: Switch speed. These parameters determine how fast M1 can turn on/off. Tr, tf, is determined by Cgs, and testing circuit. With a special designed driving circuit, a faster switch speed can be achieved. Normally, tr/tf should be less than a quarter of your center period. If you excite the circuit at 10MHz, the center period is 100ns, and tr+tf should be less than 50ns.
- RDS(on): the on resistance. It should be less than five percent of the transducer impedance.
C1:
- Voltage tolerance: should be at least 1.5 times higher than HV.
- Capacitance: determined by the pulse width and transducer impedance. The time constant, RC, should be less than 20 percent of the pulse width.

Bipolar Transmitter

How it works:
This circuit transmits a bipolar burst and the number of cycles depends on the trigger signal. A single bipolar pulse is usually used in diagnostic applications. The circuit requires two high voltage (HV) supplies with one positive and one negative. The trigger signal has to be well controlled with one positive and one negative, having 180° phase difference. The negative trigger signal turns on MOSFET M1 sending a positive pulse on the load RL through D1. The followed positive trigger signal turns on M2 and sends a negative pulse on RL via D2.

Guideline for the Component Value Selection:M1: Three parameters for M1 are important. Vds: how much voltage it can handle. This parameter has to be at least 1.2 times higher than your pulse amplitude. For example, if you want to transmit a 100v peak-to-peak bipolar pulse on the transducer, the Vds for M1 & M2 should be 120 – 150 v.Cgs, tr, tf: Switch speed. These parameters determine how fast M1 &M2 can turn on/off. Tr, tf, is determined by Cgs, and testing circuit. With a special designed driving circuit, a faster switch speed can be achieved. Normally, tr/tf should be less than a quarter of your center period. If you excite the circuit at 10MHz, the center period is 100ns, and tr+tf should be less than 50ns.RDS(on): the on resistance. It should be less than five percent of the transducer impedance. Diode: current rating, make sure it can handle the peak current.

Additional circuits are required to make above transmitter work properly including trigger signal coupling and MOSFET drivers. The complementary dual pulse signal can be generated from an edge signal (a single pulse with uncontrolled width).

With some modifications of the above circuit, only one positive HV is required and cost will be reduced. However, for each transmit, only one cycle bipolar pulse is transmitted and it satisfies most diagnostic applications. Transformer coupling is required to transmit a burst.

The following modules includes combinations of above functions. Back to Top

Transceiver

Time Gain Control (TGC)

Ultrasound imaging is based on pulse-echo method. The transmitted acoustic pulse will lose its energy due to two main factors: beam spread and attenuation. As shown in Fig. 1, along the axial axis through the center of a piston transducer, the beam will reach its maximum at certain depth and then decrease monotonously. How fast it decreases is determined by the geometry and bandwidth of the transducer, and frequency and bandwidth of the excitation pulse.

The echo signal will decrease in the same way even if the tissue structure is the same. The gain for the echo has to increase with depth to maintain a uniform brightness of the image from near field to far field. Soft tissue has an attenuation of about 0.3dB/MHz/cm to the acoustic pulse. The Time-Gain-Compensation (TGC) has to compensate the lose from both of beam spread and attenuation.

The TGC amplifier usually is a variable gain amplifier with gain controlled by a TGC voltage curve. The curve can be generated by an analog oscillation circuit or a digital curve through DAC, triggered by the pulse transmit signal.

The most simple TGC curve is a saw-tooth curve with adjustable slope. For most imaging system, TGC curve is adjustable independently for each depth segments such as 1cm at 5MHz.

Signal Conditioning

Echo signal needs go through a series of processing before enters ADC or brightness modulation to construct image, including filter, amplification, and dynamic range control.

An about four-order LC filter should provide enough sharp cutoff for the required bandwidth. It is important to have a band-pass filter before the main amplification.

Echo signal needs about 60-90dB gain in total and a 60dB fixed gain with a 30dB adjustable gain should be enough for most applications.

Dynamic range control can be achieved by logarithmic amplification in analog domain or a look-up-table in digital domain which is more flexible. The echo signal from bone or air may be 100dB stronger than the scattering from soft tissue. Dynamic range has to be compressed since the display usually only have about 30dB (256 grayscale).

Echo signal is mainly amplitude modulated, and it needs go through envelop detection before brightness modulation. Envelop can be conducted in analog domain with a simple rectifier and low pass filter or using Hilbert transform in digital domain. The Hilbert transform method has better performance since it detects the true amplitude of the analytic signal. However, the analog circuit will reduce the required ADC clock dramatically since the carrier frequency is removed.

Ultrasound Transducer Design Procedure

Center Frequency

The center frequency of an ultrasound transducer is determined by the application. A higher frequency generates an ultrasound beam with energy that is more confined, and attenuates faster. For imaging, it means better resolution and reduced imaging depth.

Bandwidth

The bandwidth of ultrasound transducer is an important factor for imaging. When imaging is based on the ultrasound pulse-echo method, the bandwidth of the ultrasound transducer determines the pulse length, and thus, the axial resolution. The best axial resolution can be achieved is half of the pulse length. Normally, a transducer with a 50% bandwidth is an acceptable lower limit for B-mode imaging. Higher bandwidths correspond to heavier damping, causing a lower sensitivity.

Aperture Dimensions

Geometry size is determined by the target lateral resolution. For a round or square transducer shape, the lateral resolution can be calculated using our “Ultrasound Calculator”. For a given depth, a focused transducer will provide a narrower beam with an increase in aperture size. If the application requires steering the beam or dynamically changing the focal depth, an array type of ultrasound transducer is necessary. Our “Beam Profile Simulation” can accurately predict the ultrasound beam from common ultrasound transducer shapes.

Active Material

If the ultrasound transducer equivalent diameter is bigger than 3~5 times of the active material thickness, the material will work in thickness mode. In thickness mode, the primary parameter to consider is a high kt. Otherwise, the parameter of interest should be k33. The second parameter to consider is the dielectric constant. Since most electronic cables and pulsers have an impedance of 50?, it is important to design a transducer that can match that same impedance to prevent loss. For a small area transducer, an active material with a higher dielectric constant is preferred. Our “Ultrasound Calculator”, can quickly calculate the impedance.

Matching Layer

Most piezoelectric material has a high Q-factor, which is the inverse of percentage bandwidth. Backing materials can provide damping to achieve a desired bandwidth. Matching layers can also be added to improve the energy coupling between the impedance of PZT (33MRyl) and target impedance (1.5MRyl for soft tissue). Our “Transducer KLM Model Simulation” can predict the electrical impedance and transmitted or received pulse of the transducer.

Backing Layer

Impedance Matching

The ultrasound transducer structure has a capacitive component at the center frequency. Simple tuning is to remove this capacitive element using a series, or shunt inductor. Our “Ultrasound Calculator” provides a quick value if the impedance of the transducer at center frequency is known. To match the cable and achieve best pulse shape, our “Transducer KLM Model Simulation” provides solutions.