Murata’s solution “Ionizer”
Ionizer contributes to improve amenity of vehicle
Murata Manufacturing Co., Ltd. established the unique technology to simultaneously control ion and ozone

Enhancing in-vehicle amenity through electronic technology has become a popular subject among automobile-related manufacturers. One of the electronic devices that Murata has intensively developed for those auto-related manufacturers is an Ionizer, or ion generator. Having a unique structure, Murata’s Ionizer provides vehicles with added values, such as air cleaning and electrostatic discharge countermeasure. Murata is also working on the development of its application in cooperation with automobile manufacturers.

Fig-1. Murata’s Ionizer: “MHM series”

Ionizer is a device that ionizes molecules in the air by charging it either positively or negatively (See Fig-1). Air ion provides various effects such as de-smoking, air-cleaning, oxidation suppression, charging or discharging. When ozone is added to ionizer, it also exerts such effects as deodorizing, sterilizing and mite control. Therefore, ionizer and ionizer-related device are utilized in various fields such as consumer electronics, industrial machinery, and OA equipment. In consumer electronics field, ionizers are used in air cleaners, dust collection system of air conditioners, sterilizing and deodorizing system of vacuum cleaners and freezers. Also in industrial machinery and OA equipment that tend to be charged easily, ionizers are utilized frequently.

In addition to these fields, the need for ionizer has become higher in the automobile field. For example, it is possible to clean air in a vehicle by installing ionizer in the air conditioner and by letting negative ion be emitted. It is also possible to prevent mold from growing as well as to remove bacteria and smell from air conditioner by letting negative ion containing ozone into it at the same time. In other words, the environment in the car can be more comfortable by maintaining in-vehicle air clean and by preventing foul smell when you turn on the air-conditioner.

In fact, the air conditioner with such function is already installed in some cars in the market. As customers who place great importance on amenity are on the rise, automobiles with an air conditioner having such function will surely increase more and more. Moreover, the electrostatic charge elimination effect can remove static electricity which is a cause of pain or discomfort to a driver and passengers, and fire accident at the time of fueling. Currently, Murata is developing an electrostatic charge elimination system to be installed in a vehicle and an ionizer to be installed into this system in cooperation with Nissan Motor Co.,Ltd.

Unique feature not seen in competitive products has been realized

Fig-2. Principle of ionizer (click to enlarge)

Murata’s ionizer is a needle-electrode type (See Fig-2), the most popular one in the market. When a high voltage as high as some kilo-Volts is applied to a needle-type electrode, the electric field concentrates around the tip of the needle. The highly-concentrated electric field generates corona discharge, thus exciting and ionizing air molecules. The ionizer made on this principle has been offered by various manufacturers. However, Murata’s ionizer has a distinct feature. “We started developing our ionizer, on the premise that it must be different from those already out in the market.” (Mr. Shinji Kato, Chief of the 2nd device design section, HV module products group, Power module products division, Module business division, Murata Manufacturing Co., Ltd.)

Mr. Shinji Kato
Chief of the 2nd device design section, HV module products group, Power module products division, Module business division, Murata Manufacturing Co., Ltd.

There are three main features in Murata’s Ionizer. The first feature is that driving voltage is low. The driving voltage of other suppliers’ products adopting the same type of ionizer is as high as -4.0kV to -7.0kV. However, with Murata’s Ionizer, it is as low as -2.5kV to -4.0kV. The second feature is that it is very compact. While the size of other company’s Ionizer is more than 8cm3, Murata’s Ionizer (standard type) is as small as 4cm3. The third feature is that it can control ozone that is generated simultaneously with ion. As described above, various effects can be obtained by using ozone and ion at the same time. On the other hand, since ozone has a nature to oxidize other material, if it is generated more than necessary, it may damage environment. “Conventional needle electrode type ionizers cannot avoid generating ozone more than 0.1ppm due to the leakage current between the needle electrode and the earth electrode, and the amount of produced ion cannot be controlled. However, Murata’s Ionizer generates less than 0.1ppm ozone, and can be designed to produce a desired amount of ion.” (Mr. Yasuhiko Shimanaka, Section head of the 2nd device design section, HV module products group, Power module products division, Module business division, Murata Manufacturing Co., Ltd.) These particular characteristics, namely, driving voltage reduction and ozone control, were focal points at the development stage, in order to make Murata’s product different from other competitive products.

Fig-3. Structure of Ionizer

Unique structure utilizing a technology for high-voltage use resistors

The key to realize these features is in its unique structure (See Fig-3). Murata’s Ionizer has a GND electrode and a high-voltage electrode on Alumina substrate, part of which is cut out in U-shape. On the bottom part of U-shape, an edge of thin wire electrode (Φ70µm) is fixed, and from here, line type high-voltage electrode is extended along the center axis of U-shape, a unique feature of Murata’s Ionizer. On the periphery of substrate, the GND circuit pattern consisted of resistor is printed surrounding the high-voltage electrode, and both sides of tip of high-voltage electrode, which are the ends of U-shape, the GND electrode pattern is allocated. The surface of substrate is covered with resin. “It is possible to lower driving voltage or to adjust amount of generated ion by optimizing material characteristics and pattern of GND electrode or area to be covered with resin overcoat. In developing this technology, the material technology accumulated through a long time development of high-voltage use resistor has had a great contribution.” (Mr. Shimanaka)

Mr. Yasuhiko Shimanaka
Section head of the 2nd device design section, HV module products group, Power module products division, Module business division, Murata Manufacturing Co., Ltd.

Currently, Murata offers “MHM Series” ionizer as a standard product, a negative ion generating ionizer in a resin case. Adding to this, Murata intends to actively develop customized ionizers to meet users’ needs (See Fig-4). “Using the same structure, we can also provide users with an ionizer that generates not only negative ion but also plus ion. We can also make an ionizer that can both generate an appropriate amount of ozone and stop as necessary, while emitting ion.” (Mr. Kato) Customized ionizers have already been installed into cleaners and home-use air conditioners in the market. Besides, Murata currently develop an ionizer unit for use in an electrostatic charge removing system in automobiles. No less important is a fact that Murata offers not only several types of ionizers but also power supply units to go with each of them, and the kit containing both. “Following the kits, we are planning to produce modules containing an ionizer and a power supply unit” (Mr. Kato) (See Fig-5) These kits or modules will enable effective development of systems using an ionizer.

Fig-4. Example of custom ionizers
Two ionizers are integrated in a single unit in order to generate ample ion

Fig-5. Power supply module for ionizer use

Murata foresees the rise of needs for ionizers, as the momentum to place importance on automotive amenity is picking up, and the company is actively promoting their products to in-vehicle equipment manufacturers in Europe and North America. “Actually, we are receiving several specific business inquiries in Europe. We anticipate that the ionizer market will expand in Asia as well. We are conducting a market research.” (Mr. Shimanaka)

Release pain or uncomfortable feeling resulted from electrostatic charge with ionizer

Fig-A. Ionizer developed for an in-vehicle electrostatic charge removal system (prototype)

Murata and Nissan are jointly developing an electrostatic charge removal system that eliminates static electricity from human body by an ionizer. When an electrostatically-charged driver or passengers get on or off the vehicle, discharge often occurs and causes pain and discomfort. The goal of this system is to eliminate such discomfort. The neutralizing system also helps to reduce the risk of fire by electrostatic discharge at the time of fueling. Especially with the recent spread of self-service stations, neutralization systems are called for in order to prevent fire accidents. Currently, Murata and Nissan are jointly researching how static electricity gets charged in human body to figure out the specifications of ionizers for neutralization, and where to install it in the car in order to get the optimum effect. Murata is developing an ionizer for this system as well (See Fig-A).

Fig-B Electrostatic potential in human body when getting off the vehicle (click to enlarge)

Static electricity gets charged in human body by the friction between the seat material and the clothing when a person is seated. The electrostatic potential changes according to the body movement at the time of getting on or off the vehicle. When a person gets off, it reaches to 3kV – 20kV (See Fig-B). Generally speaking, people feel pain of discharge when the electrostatic potential becomes higher than 2kV. In other words, in order to avoid discomfort, it has to be kept under 2kV. Since the polarity of potential changes depending on the combination of the seat material and clothing, it could be either positive or negative.

Given the generation mechanism of static electricity, Murata developed an ionizer that emits both plus and negative ion at the same time. “A prototype unit is equipped with a front cover to prevent a person from touching the electrode. Various creative ideas are applied so that ion can be emitted effectively from the unit.” (Mr. Shimanaka) Further, Murata currently searches an optimum position to install the unit in the car based on their study results about the distance at which enough neutralization effect can be brought about. So far, the research shows that the significant effect can be observed when ion is delivered to a hand grabbing a handle inside of the car door.