Electromechanical film

Last updated

Electromechanical Film (EMFI, EMFIT, trademarks of Emfit Ltd) is a thin, flexible film that can function as a sensor or actuator. It is composed of a charged polymer coated with two conductive layers, making it an electret. It was invented and first made by Finnish inventor Kari Kirjavainen. Its voided internal structure and high resistivity allow it to hold a high electric charge and make the film very sensitive to force. Changes in the film's thickness create an electric charge and make it operate as a sensor, or when an electric voltage is applied, it can function as an actuator. This gives the film applications in different fields of technology, including, but not limited to, mechanical vibration and ultrasound sensors, microphones, loudspeaker panels, keyboards, and physiological touch sensors. [1] Other than being cheap, its main advantage is its versatility; it can be cut, reshaped, and resized depending on its surface of application. [2]

Contents

Manufacturing and structure

The base film is first made from bi-axially orienting a polypropylene film. It is created through a "film-blowing" process, in which the plastic is extruded using a film blowing machine in the shape of a tube. Through the process of foaming, gaseous bubbles can be formed at a fixed density in the tube, which would give rise to EMFi's "voided internal structure". It is then expanded into two different directions depending on the desired thickness and orientation (bi-axial orientation). The tube is then coated with some electrically conductive material and then cut open into a film. This film is then charged using the Corona Treatment, and the electrically conductive layers create electrodes.

EMFiT sensor has three layers, two of which that are homogeneous and act as electrodes as mentioned above, and a middle layer that is filled with flat, disk-shaped voids. Upon receiving charge from the Corona method, electrical breakdowns occur and the surfaces of the voids are permanently charged. There is one basic type of EMFFIT sensor film manufactured currently, the thicknesses being 70 μm respectively. [3] [4] [2]

Operation

Sensor

The film can be used as a sensor. As the film is charged, it creates an electric field. When pressure is applied to the film, the film's thickness is reduced and changes in the shapes of the individual voids in its structure occur. Any electric charges residing in these voids will move and create mirror charges at the electrode surfaces of the film. These charges are proportional to the force applied to the film, which is given by the equation:

Δq = kΔF

where ΔF is the dynamic force, Δq is the charge generated, and k is the sensitivity factor. [1]

Actuator

The same sensor film can also be used as an actuator. Changes in thickness can be induced by applying a voltage on the film; compression and expansion of the film depends on the polarity of the voltage, and it occurs when both the outer surfaces of the film either attract or repel from each other. [4] The attractive force between the surfaces while the film is uncharged is given by the equation:

F = 12CU2x

where C is the capacitance of the film and x is the film's thickness. [1]

Applications

EMFIT sensor film has a diverse range of applications due to it being flexible, durable, and sensitive to a wide range of frequencies. These properties are attributed to its base material: cellular voided Ferro-electret film. Due to these properties, in conjunction with the two modes of operation, it has already seen use in vandalism-proof keyboards, guitar pickups, flat speakers, and vital signs ballistocardiography sensors. esmicrophones.

Limits

Due to the thermal constraints faced by using polypropylene as base material, applications where high sensitivity is needed, long-term temperatures should be below 70 °C, which limits its scope in terms of some potential applications such as the automotive industry.

The air voids present in the structure become smaller and higher in pressure as force is applied to the film. This means that the film becomes harder to compress as it goes under more load, meaning that in the sensor mode, the charge output is non-linear, which can make calibrating the sensor difficult. [6]

Related Research Articles

In physics, the term dielectric strength has the following meanings:

Electrowetting is the modification of the wetting properties of a surface with an applied electric field.

<span class="mw-page-title-main">Electret</span> Object with trapped electrical charge

An electret is a dielectric material that has a quasi-permanent electrical polarisation. An electret has internal and external electric fields, and is the electrostatic equivalent of a permanent magnet.

<span class="mw-page-title-main">Quartz crystal microbalance</span>

A quartz crystal microbalance (QCM) measures a mass variation per unit area by measuring the change in frequency of a quartz crystal resonator. The resonance is disturbed by the addition or removal of a small mass due to oxide growth/decay or film deposition at the surface of the acoustic resonator. The QCM can be used under vacuum, in gas phase and more recently in liquid environments. It is useful for monitoring the rate of deposition in thin-film deposition systems under vacuum. In liquid, it is highly effective at determining the affinity of molecules to surfaces functionalized with recognition sites. Larger entities such as viruses or polymers are investigated as well. QCM has also been used to investigate interactions between biomolecules. Frequency measurements are easily made to high precision ; hence, it is easy to measure mass densities down to a level of below 1 μg/cm2. In addition to measuring the frequency, the dissipation factor is often measured to help analysis. The dissipation factor is the inverse quality factor of the resonance, Q−1 = w/fr ; it quantifies the damping in the system and is related to the sample's viscoelastic properties.

<span class="mw-page-title-main">Electrophoretic deposition</span>

Electrophoretic deposition (EPD), is a term for a broad range of industrial processes which includes electrocoating, cathodic electrodeposition, anodic electrodeposition, and electrophoretic coating, or electrophoretic painting. A characteristic feature of this process is that colloidal particles suspended in a liquid medium migrate under the influence of an electric field (electrophoresis) and are deposited onto an electrode. All colloidal particles that can be used to form stable suspensions and that can carry a charge can be used in electrophoretic deposition. This includes materials such as polymers, pigments, dyes, ceramics and metals.

<span class="mw-page-title-main">Electroactive polymer</span>

An electroactive polymer (EAP) is a polymer that exhibits a change in size or shape when stimulated by an electric field. The most common applications of this type of material are in actuators and sensors. A typical characteristic property of an EAP is that they will undergo a large amount of deformation while sustaining large forces.

An atomic battery, nuclear battery, radioisotope battery or radioisotope generator is a device which uses energy from the decay of a radioactive isotope to generate electricity. Like nuclear reactors, they generate electricity from nuclear energy, but differ in that they do not use a chain reaction. Although commonly called batteries, they are technically not electrochemical and cannot be charged or recharged. They are very costly, but have an extremely long life and high energy density, and so they are typically used as power sources for equipment that must operate unattended for long periods of time, such as spacecraft, pacemakers, underwater systems and automated scientific stations in remote parts of the world.

<span class="mw-page-title-main">Electrostatic precipitator</span> Filtration device

An electrostatic precipitator (ESP) is a filterless device that removes fine particles, such as dust and smoke, from a flowing gas using the force of an induced electrostatic charge minimally impeding the flow of gases through the unit.

<span class="mw-page-title-main">Capacitor types</span> Manufacturing styles of an electronic device

Capacitors are manufactured in many styles, forms, dimensions, and from a large variety of materials. They all contain at least two electrical conductors, called plates, separated by an insulating layer (dielectric). Capacitors are widely used as parts of electrical circuits in many common electrical devices.

<span class="mw-page-title-main">Electric spark</span> Abrupt electrical discharge through an ionised channel

An electric spark is an abrupt electrical discharge that occurs when a sufficiently high electric field creates an ionized, electrically conductive channel through a normally-insulating medium, often air or other gases or gas mixtures. Michael Faraday described this phenomenon as "the beautiful flash of light attending the discharge of common electricity".

A ferroelectret, also known as a piezoelectret, is a thin film of polymer foams, exhibiting piezoelectric and pyroelectric properties after electric charging. Ferroelectret foams usually consist of a cellular polymer structure filled with air. Polymer-air composites are elastically soft due to their high air content as well as due to the size and shape of the polymer walls. Their elastically soft composite structure is one essential key for the working principle of ferroelectrets, besides the permanent trapping of electric charges inside the polymer voids. The elastic properties allow large deformations of the electrically charged voids. However, the composite structure can also possibly limit the stability and consequently the range of applications.

<span class="mw-page-title-main">Dielectric elastomers</span>

Dielectric elastomers (DEs) are smart material systems that produce large strains and are promising for Soft robotics, Artificial muscle, etc. They belong to the group of electroactive polymers (EAP). DE actuators (DEA) transform electric energy into mechanical work and vice versa. Thus, they can be used as both actuators, sensors, and energy-harvesting devices. They have high elastic energy density and fast response due to being lightweight, highly stretchable, and operating under the electrostatic principle. They have been investigated since the late 1990s. Many prototype applications exist. Every year, conferences are held in the US and Europe.

Adhesive bonding describes a wafer bonding technique with applying an intermediate layer to connect substrates of different types of materials. Those connections produced can be soluble or insoluble. The commercially available adhesive can be organic or inorganic and is deposited on one or both substrate surfaces. Adhesives, especially the well-established SU-8, and benzocyclobutene (BCB), are specialized for MEMS or electronic component production.

In electrical engineering, capacitive sensing is a technology, based on capacitive coupling, that can detect and measure anything that is conductive or has a dielectric constant different from air. Many types of sensors use capacitive sensing, including sensors to detect and measure proximity, pressure, position and displacement, force, humidity, fluid level, and acceleration. Human interface devices based on capacitive sensing, such as touchpads, can replace the computer mouse. Digital audio players, mobile phones, and tablet computers will sometimes use capacitive sensing touchscreens as input devices. Capacitive sensors can also replace mechanical buttons.

<span class="mw-page-title-main">Ferroelectric polymer</span> Group of crystalline polar polymers that are also ferroelectric

Ferroelectric polymers are a group of crystalline polar polymers that are also ferroelectric, meaning that they maintain a permanent electric polarization that can be reversed, or switched, in an external electric field.

A biotransducer is the recognition-transduction component of a biosensor system. It consists of two intimately coupled parts; a bio-recognition layer and a physicochemical transducer, which acting together converts a biochemical signal to an electronic or optical signal. The bio-recognition layer typically contains an enzyme or another binding protein such as antibody. However, oligonucleotide sequences, sub-cellular fragments such as organelles and receptor carrying fragments, single whole cells, small numbers of cells on synthetic scaffolds, or thin slices of animal or plant tissues, may also comprise the bio-recognition layer. It gives the biosensor selectivity and specificity. The physicochemical transducer is typically in intimate and controlled contact with the recognition layer. As a result of the presence and biochemical action of the analyte, a physico-chemical change is produced within the biorecognition layer that is measured by the physicochemical transducer producing a signal that is proportionate to the concentration of the analyte. The physicochemical transducer may be electrochemical, optical, electronic, gravimetric, pyroelectric or piezoelectric. Based on the type of biotransducer, biosensors can be classified as shown to the right.

<span class="mw-page-title-main">Surface chemistry of neural implants</span>

As with any material implanted in the body, it is important to minimize or eliminate foreign body response and maximize effectual integration. Neural implants have the potential to increase the quality of life for patients with such disabilities as Alzheimer's, Parkinson's, epilepsy, depression, and migraines. With the complexity of interfaces between a neural implant and brain tissue, adverse reactions such as fibrous tissue encapsulation that hinder the functionality, occur. Surface modifications to these implants can help improve the tissue-implant interface, increasing the lifetime and effectiveness of the implant.

Double-layer capacitance is the important characteristic of the electrical double layer which appears at the interface between a surface and a fluid. At this boundary two layers of electric charge with opposing polarity form, one at the surface of the electrode, and one in the electrolyte. These two layers, electrons on the electrode and ions in the electrolyte, are typically separated by a single layer of solvent molecules that adhere to the surface of the electrode and act like a dielectric in a conventional capacitor. The amount of charge stored in double-layer capacitor depends on the applied voltage.

Optoelectrowetting (OEW) is a method of liquid droplet manipulation used in microfluidics applications. This technique builds on the principle of electrowetting, which has proven useful in liquid actuation due to fast switching response times and low power consumption. Where traditional electrowetting runs into challenges, however, such as in the simultaneous manipulation of multiple droplets, OEW presents a lucrative alternative that is both simpler and cheaper to produce. OEW surfaces are easy to fabricate, since they require no lithography, and have real-time, reconfigurable, large-scale manipulation control, due to its reaction to light intensity.

A piezoelectric microelectromechanical system (piezoMEMS) is a miniature or microscopic device that uses piezoelectricity to generate motion and carry out its tasks. It is a microelectromechanical system that takes advantage of an electrical potential that appears under mechanical stress. PiezoMEMS can be found in a variety of applications, such as switches, inkjet printer heads, sensors, micropumps, and energy harvesters.

References

  1. 1 2 3 4 Paajanen, Mika; Lekkala, Jukka; Kirjavainen, Kari (2000-08-01). "ElectroMechanical Film (EMFi) — a new multipurpose electret material". Sensors and Actuators A: Physical. 84 (1): 95–102. doi:10.1016/S0924-4247(99)00269-1. ISSN   0924-4247.
  2. 1 2 US 4654546,Kirjavainen, Kari,"Electromechanical film and procedure for manufacturing same",published 1987-03-31
  3. ↑ Savolainen, A.; Kirjavainen, K. (1989-02-01). "Electrothermomechanical Film. Part I. Design and Characteristics". Journal of Macromolecular Science, Part A. 26 (2–3): 583–591. doi:10.1080/00222338908051994. ISSN   0022-233X.
  4. 1 2 Paajanen, Mika; Välimäki, Hannu; Lekkala, Jukka (2000-03-01). "Modelling the electromechanical film (EMFi)". Journal of Electrostatics. 48 (3): 193–204. doi:10.1016/S0304-3886(99)00065-0. ISSN   0304-3886.
  5. ↑ Albert Manninen, Johan Sand, Jaakko Saarela, Tapio Sorvajärvi, Juha Toivonen, and Rolf Hernberg, "Electromechanical film as a photoacoustic transducer," Opt. Express 17, 16994-16999 (2009)
  6. 1 2 Junnila, Sakari; Akhbardeh, Alireza; Värri, Alpo (2009-12-01). "An Electromechanical Film Sensor Based Wireless Ballistocardiographic Chair: Implementation and Performance". Journal of Signal Processing Systems. 57 (3): 305–320. doi:10.1007/s11265-008-0307-2. ISSN   1939-8115.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.