EMATs are the devices that essentially consist of a stack of wires and magnets to excite and receive ultrasonic waves in an electrically conductive material, be it magnetic or non-magnetic. When a wire, placed near to the surface of an electrically conducting object, is driven by an A.C at a desired ultrasonic frequency, eddy currents will be induced in the object by electromagnetic induction. Their penetration in the object is given by the classical electromagnetic skin effect. In the presence of a static magnetic field (B0), these induced eddy currents (J) will experience Lorenz forces (f) given by

f = J X B0

Through a variety of interactions, these Lorentz forces are transmitted into the lattice and serve as a source of ultrasonic waves. EMATs are reciprocal devices i.e. they can be used as transmitters or as receivers of ultrasound. When an EMAT transmitter is placed near a electrically conducting material, not necessarily in contact with, ultrasonic waves are launched in the material through the reaction of induced eddy currents and static magnetic fields (Lorentz forces). This eliminates the problems associated with acoustic coupling to the metal part under examination as the electro-mechanical conversion takes place directly within the electromagnetic skin depth of the material surface. Thus, EMATs allow non-contact operation and enable inspection at elevated temperatures, on moving objects, in vacuum or oily or rough surfaces and also in remote and hazardous locations.

EMATs can launch a variety of ultrasonic wave modes with relatively well controlled polarization, intensity and angular distribution. Unlike piezoelectric transducers, it is possible to perform inspection at any angle of incidence with one stationary EMAT. This is achieved by varying the excitation frequency and/or the delay times between the array elements of a phased array transducer system. Typical EMAT probes, wave modes and their applications are as follows:

Practical Applications of EMATs

EMAT Type

Angle Beam Probes
SV – Waves
SH – Waves
Application for UT of pipes, Control of liquid level, ISI of Coarse Grained welds

Angle Beam Probes
Lamb modes
Application for UT of sheets and plates
Rayleigh waves
Application for UT of the tread of railway wheels

Angle Beam Probes
SH modes Application for Thickness measurement of high alloyed sheets

Normal Beam Probes
Linearly polarised shear waves
Radially polarised shear waves
Application for Stress and texture analysis, wall thickness measurement

Shear Horizontal (SH) Waves

It is possible to generate shear horizontal (SH) waves using EMATs while the same is very difficult with PZTs. SH wave mode has provided solution to many non-destructive inspection situations, primarily due to the following attractive features of SH waves over L or SV waves:

Reflection, refraction and diffraction without mode conversion

Complete corner reflection independent of angle of incidence

Propagation in thick-walled components (thickness >> wavelength) as a bulk wave even along the surface

Propagation in thin walled components (thickness <>

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The introduction of the farm tractor revolutionized the way in which agriculture was done. With the replacement of human effort, and animal inputs, production was increased exponentially, with more being done in less time.
The first machines which could be considered "tractors" were massive steam driven machines developed in the 1870's. These machines had tremendous power at its advantage, however versatility was definitely not an advantage.

The invention of the internal combustion engine gave a boost to farm tractor production. Companies like International Harvester, Case, Rumley, and Hart-Parr adopted their steam driven tractors to use the smaller internal combustion (IC)engines, however the steel tracks for wheels were still used. The diesel engine was later developed by the German Engineer Rudolph Diesel, from Germany's Dresden's University of Technology. This enabled a better tractor to be manufactured with the more reliable, less problematic diesel engine.

Popular tractors today include Agco, Allis Chalmers, Case-IH, David Brown, Deutz, Fiat, Ford, New Holland, Massey Ferguson, McCormick, and combines Gleaner, and New Idea.

Maintenance parts for all of these tractors are provided by the respective companies. Dealers for all of these tractors are found throughout North American and most parts of the world.

However, a least expensive method of maintenance parts are from replacement manufactures (aftermarket supplies), and good used or rebuilt parts from salvaged yards. Popular aftermarket suppliers are:

Vapormatic. Vapormatic is a British based manufacturer of replacement parts for most agriculture equipment. This company was started in 1949 when two engineers experimented trying to operate tractors with vaporizing tractor oil. Several major mergers and sales were made during the coming years. The major merger was the sale of the entire Vapormatic company to John Deere in 2001. The Bepco brand of replacement parts for ag equipment is another famous British tractor parts company providing parts for David Brown, Deutz-KHD, Fendt, Fiat, Ford, New Holland, Case-IH, John Deere, Steyr, Renault, Same-Laborghini-Hurliman, Perkins, Massey Ferguson, Landini, Zetor, Valmet, Merlo, Kubota, Manitou, JCB and McCormick.

The major development with Bepco is its merger with the other British company, Tract-Pieces. Today, the combined companies is known as Bepco-Tracpieces Group. TISCO, an American brand of tractor parts, begain its humble beginning after Ben Calmenson began working out of his car's truck, selling parts for ag equipment in 1937. Soon after, he began manufacturing parts for the machines. Today, TISCO is owned by the Woods Equipment Company, and provides more than 37,000 parts for ag equipment

Male Clevite. Male Clevite is most known in the parts world as Clevite. This is a US based company that manufactures for both OEM companies, and sells parts as aftermarket to the non OEM companies.. The advantage of using Clevite is that the aftermarket parts are offered the same warranty as the OEM, since they are both the one and same parts Federal Mogul is known for its many sub-variations of names. Names like FP Diesel, Diesel Guard, Moog chassis parts, champion spark plugs, National and Payen gaskets, Sealed Power o rings and sealing parts, and Wager parts. These are all popular parts that are used for both heavy duty applications, ag equipment, and automotive sector.

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Wide tires and serious off-road driving place tremendous demands on all of the steering components. Not the least of these is the power steering pump. Sherm's Bronco is running 36"X14.5 Super Swampers that required very high performance power steering. On a Rubicon trip in 1997, his power steeringpump boiled over and blew the dipstick and fluid out of the pump.

I looked at the Saginaw conversion and found that the pressures, particularly at low RPM, were not as great as the current Ford power steering pumps. It is more compact than the Saginaw unit, is readily available, and bolts directly up to the serpentine bracket.

To combat the heat developed in heavy off-road applications, I felt that more cooling was required than to simply install a pump, I used the inner automatic transmission cooler found in all automatic radiators. I also located a 1990 Ford Taurus 24-finned transmission cooler. I also used braided line to connect all of the power steering pump components. I used a 1992 Ford F-150 high pressure hose that fit perfectly in the Bronco.

After the Ford power steering pump was installed, I routed the return line from the power steering pump into the inner automatic transmission cooler with braided line, from that point I used braided line to connect to the finned cooler. The finned cooler was then connected to the power steering box with more braided line. A single cooler might not operate under the extreme off-road conditions where I wanted it to perform.





The Ford pump has a very large opening to the reservoir and can be easily filled on the trail. It also has a bleed hole in the cap. The cap is secured by locking with a quarter turn of the cap. These pumps are used on everything from Lincoln Continental, the Escort, to the F-250 pickup. This pump and coolers hold a quart and a half of ATF. When driving the Bronco off-road, the finned cooler was lukewarm.

Before using this, or any other high pressure power steering pump, reseal used power steering box, to prevent leakage from the sector shaft and worm gear shaft.

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