Analyzing vibration and acoustics of natural processes

Vibration measurement for animal communication research

For every living species on our planet, there are corresponding biological applications of laser vibrometry. One of the most well-known ones is insect communication. Certain insects, such as the cicada, communicate by “singing” in the audible frequency range, while other sounds produced are ultrasonic and imperceptible to humans. Some insects are so small that their signals are, in actual fact, only vibrations that are transmitted through plants.

Entomologists can detect these audible and inaudible sounds using laser vibrometers. Non-contact measuring technology allows them to “listen in” on animals without disturbing them, and thereby examine their natural communication behaviour. Imagine the honeycomb vibrations in beehives. Signals such as these can only be measured with highly sophisticated measuring technology. Other biological applications include studying communication between elephants, fruit ripeness, spiderweb motion and the hearing mechanism in crickets, frogs or fruit flies.

Another benefit of laser vibrometers lies in the fact that the measuring technology is portable and has its own self-sufficient power supply, allowing you to carry out measurements right in the field too.

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A practical example:

Ears are complex micromechanical machines that amplify tiny acoustic vibrations and convert them into electrical signals. What kind of structures and processes are responsible for signal processing inside the ear? Measurements performed on fruit flies with the laser Doppler vibrometer offer insights into the sophisticated mechanisms of hearing of these insects.

“I love working with the laser because it gives me an insight into the exciting world of vibrational communication in insects, plus it’s really easy to operate too.”

Dr. Biol. Taina Conrad, Institute of Evolutionary Ecology and Conservation Genomics, University of Ulm

Biomechanics have never been so realistic

The finite element method (FEM) is used in biomechanics to solve key medical issues – in bone surgery, for example, to generate realistic bone models from computer tomography data. These models are verified using their dynamic properties. The 3D laser vibrometer was used for the first time to determine the modal parameters of a pelvic bone and enabled measurement of spatial deflection shapes with unprecedented accuracy and resolution.

Accurately verified models help us to understand biomechanics better and ultimately lead to improved treatment methods, safer use of implants and a better quality of life.

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Contactlessly recording physiological data

While laser vibrometers are already widely used in industry and mechanical engineering where zero influence on the sample is required, their use for recording physiological data is fairly recent by comparison. In such situations, non-contact measurement isn’t just more pleasant for the patient; it offers decisive hygienic benefits too. The applications are based on the realization that many of the body’s physiological activities have mechanical components too. Some of the energy – however small – is transported to the skin and creates skin movement. Accordingly, a wide range of internal body sounds, pulses and vibrations can be recorded simply by directing a laser beam at the body.

Various cardiovascular activities can be recorded with laser vibrometers:

• Ballistocardiac Movements
• The heart walls’ local signals in the individual phases of the cardiac cycle
• The Blood Vessels’ Pressure Signals
  
  

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A Practical Example:

Sound from speech, for example, is radiated not only from the mouth and nostril openings, but also from the surfaces of the head and neck. Scientists can use Polytec Scanning Vibrometers to measure vibrations caused during phonation. The method is suitable for evaluating the speech of patients with cleft palate or velopharyngeal insufficiency in the throat area. Vibration patterns may be helpful as visual feedback on speaking exercises for such patients.

Developing ultrasonic devices with maximum reliability

Safety is the top priority in medical technology. Consequently, complete documentation of the development stages is indispensable for producing good products and providing legal certainty. Laser vibrometers are therefore extremely important in the development and quality assessment of medical instruments, such as dental or surgical ultrasonic devices and imaging methods. The efficiency and safety of health care products, such as inhalators, respirators and toothbrushes, can all be improved by carrying out measurements with Polytec vibrometers. Laser vibrometers have also become indispensable for the development, inspection, calibration and certification of middle ear implants and implantable hearing aids.

Ultrasonic energy has to get to where it’s needed in medical devices. Polytec’s PSV Scanning Vibrometer quickly and clearly illustrates how energy is distributed by ultrasonic actuators and thus speeds up the development process. Localization of a particular operating frequency’s vibration nodes allows you to optimize the design and thereby reduce energy dissipation. Thanks to the high spatial resolution and measurement accuracy in the picometer range, high-frequency deflection shapes are quickly and reliably visualized too.

Laser vibrometry is the decisive key technology in the design and development of medical ultrasonic instruments. It is the ideal tool for verifying FE simulations – both for invasive and diagnostic medical ultrasonic instruments. Thanks to its linearity well into the high MHz range and the complete lack of feedback effects, coupled with high lateral resolution, this technology is suitable for nearly all structural dynamic tasks. Calculation methods derived from the basic technology for sound field visualization and for durability (strain / stress) open up further applications. Consequently, laser Doppler vibrometry is a tool suited to the development of efficient, reliable and effective instruments for the doctor and the researcher.

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Understanding the auditory mechanism and sound conduction

The human ear is one of the most sophisticated sound and vibration amplification systems. Offering ease of operation and unsurpassed accuracy, state-of-the-art laser vibrometers help to determine vibrational characteristics and dynamic properties. They are therefore opening up completely new possibilities for researchers to understand exactly how hearing works. Scientists are using highly sensitive and non-intrusive laser vibrometers to examine not only sound conduction from the eardrum to the stapes footplate in the middle ear, but also the details of electromechanical signal transduction occurring in the cochlea of the inner ear.

The eardrum’s vibration behaviour gives direct insight into the causes of hearing loss, due to stapes fixation or sclerotic changes in the ossicular chain. In medical research, laser tympanometry with laser vibrometers allows the audiologist to quickly measure the eardrum’s frequency response.

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A practical example:

Laser vibrometers are also indispensable for the development, inspection, calibration and certification of middle ear implants. In research, laser vibrometers are used during operations to check that middle ear implants and prostheses (TORP, PORP) are securely connected. They therefore help to ensure that operations are successful and to document the same in an audit-proof way.