EP2920798A1

EP2920798A1 - Planar transformer

Info

Publication number: EP2920798A1
Application number: EP13791791.0A
Authority: EP
Inventors: Jörg BLANKE
Original assignee: Phoenix Contact GmbH and Co KG
Current assignee: Phoenix Contact GmbH and Co KG
Priority date: 2012-11-16
Filing date: 2013-11-12
Publication date: 2015-09-23
Anticipated expiration: 2033-11-12
Also published as: EP2920798B1; CN104838458A; DE102012111069A1; WO2014076067A1; CN104838458B; US9711271B2; US20150332838A1

Abstract

Planar transformer, produced from a plate-like conductor substrate (6) with an integrated primary winding (1), secondary winding (2) and coupling winding (3). The conductor substrate (6) has pairs (61, 62; 63, 64) of cutouts through which in each case a two-part ferromagnetic core (4; 5) which is provided with yoke limbs is inserted. A limb of each core (4; 5) is surrounded by the primary winding (1) or the secondary winding (2), while the coupling winding (3) loops around the remaining limbs of the cores. At least one minimum total isolation separation distance (L), which is made up of partial isolation separation distances between the coupling winding (3) and adjacent yoke limbs or adjacent windings, is maintained for electrical isolation between the primary winding (1) and the secondary winding (2).

Description

planar transformers

description

The invention relates to a planar transformer having a primary winding, with a secondary winding, with a coupling winding and with a conductor substrate, the carrier of one or more magnetic core rings.

US 8,022,802 B2 relates to a sensor for measuring electrical parameters in a high voltage environment and includes isolation transformers in various embodiments, including an embodiment having a single main circuit board for a plurality of juxtaposed ones

Windings magnetically linked by magnetic core rings, and another embodiment comprising a main circuit board, a sub-circuit board, and two magnetic core rings passing through openings of the main and sub-circuit boards. In and on the main circuit board are the primary winding and the secondary winding, while on the sub-circuit board, the coupling winding for coupling the two magnetic core rings is arranged. There is some gap between the two circuit boards, and the coupling winding on the slave circuit board also has one

Distance to the respective edge of the openings in the

Magnetic core rings on. In this way, relatively large toroidal openings in the magnetic core rings are needed.

In another transformer (DE 10 2005 041 131 AI) are the ferromagnetic cores to form coils

wound, with the windings of the coils on various ferromagnetic cores are attached to comply with required isolation distances. The

Ferromagnetic cores are magnetically coupled to one another via an additional winding embedded in a printed circuit board. Because of the necessary winding of the

Ferromagnetic cores is a so-built transformer to manufacture only at high cost.

From US 2011/0140824 AI a transformer is known, are mounted in the potential to be separated windings asymmetrically on different circuit boards, the

stacked on top of each other with a two-piece

ferromagnetic core are connected to the transformer.

In US 2011/0095620 AI a Planarübertrager for miniaturized applications is described, the

Coil turns on opposite sides of a

insulating substrate are arranged. The device works due to induction, without ferromagnetic cores.

EP 0 715 322 A1 discloses a transformer manufactured in planar technology, in which conductor tracks are accommodated in layer layers in a printed circuit board and so on

Forming transformer windings. A ferromagnetic core surrounds the transformer windings with annular

Thighs outside, and with a cylindrical thigh inside.

From DE 20 2009 002 383 Ul a planar transformer is known which contains a multilayer board, the high

Dielectric strength of the PCB layers between each other, between the primary to the secondary windings, guaranteed. The transformer can be controlled potential-free with opposing signals. One too

transmitting signal in positive magnetic

Flow direction of a common primary winding, or a single primary winding directly generates a positive control signal in a first secondary winding in the same coupling direction. A signal in the negative magnetic flux direction of a second or the same winding generates directly in a second secondary winding in the opposite coupling direction to the first secondary winding also a positive control signal or in the first secondary winding a negative

Control signal, and if no further signal is to be transmitted, takes place by circuit elements

automatic or digitally controlled degaussing of the transformer by one or two as a short circuit

controlled windings immediately at the end of a previously transmitted signal. DE 10 2009 037 340 A1 shows a transformer in which wound, annular cores are connected via a short-circuit winding. The short-circuit winding is, for example, connected by soldering with corresponding contacts of a printed circuit board.

The invention is based on the object, a

Planarübertrager specify that is easy to manufacture and in the smallest space allows potential separation for two or more potential groups.

The new Planarübertrager has at least two

Yoke legs provided ferromagnetic cores and a single, plate-shaped conductor substrate for forming a primary winding and at least one secondary winding, which are coupled together by at least one coupling winding. The conductor substrate forms a

plate - shaped carrier for the ferromagnetic cores, which are divided to form assemblable yoke core halves and thereby have at least two cross - through yoke legs, which are formed by recesses in the

Conductor substrate can be inserted to form by closing the yoke core halves each having a magnetic core ring.

In the smallest space a potential separation between

To achieve primary winding and secondary winding, one must accept that the magnetic core rings only small

Separation distances to the plate-shaped conductor substrate

comply, in the region of a first ring core opening parts of the primary winding and in the region of a second

Ring core opening Parts of the secondary winding near the

Surface of the conductor substrate receives. Thus, the relevant magnetic core ring in terms of potential of the adjacent primary winding or secondary winding

slammed, although of course, an insulating layer, referred to as functional insulation, covers the respective winding of the ferromagnetic material of at least two

Magnetic core rings separated, which are spaced apart electromagnetically linked to each other via the coupling winding, but at different potentials (the

Primary winding or the secondary winding) are. Thus, the coupling winding must have a sufficient isolation separation distance to adjacent inner sides of the toroidal core openings and to adjacent turns of

Primary winding and secondary winding comply, so that the Potentials can be separated from each other by a total insulation separation distance. This total insulation separation distance can be adjusted to the respective

Separation intervals between the coupling winding and toroidal core opening or adjacent winding of the primary winding or secondary winding are divided, but a respective minimum of separation distance must be maintained. In a first construction, the one leg of the

Magnetkernringes the primary winding, while the other leg is looped by a first portion of the coupling winding, which also wraps around the leg of an adjacent ring core with a second portion, the other leg receives the secondary winding. There may be several provided with secondary windings

Secondary magnetic core rings with a single

Primary magnetic core ring are coupled. In a second construction, in each case a first leg of the two magnetic core rings of two windings in

entwined different layer planes of the conductor substrate, wherein the coupling winding, the two

Magnetic core rings connects and the primary winding is assigned to a magnetic core ring, while the secondary winding is associated with the other magnetic core ring. As far as a respective second leg of the two magnetic core rings in one of the different layer planes of the

Conductor substrate is free of the mentioned windings, there may be an auxiliary winding, such as for control purposes, are arranged. But it is also possible that Primary winding or the secondary winding with a

Continue section on the free thigh.

In that the magnetic core rings as split yoke cores and the windings including the coupling winding as integral parts of the plate-shaped conductor substrate

be formed, is the production of the

Planarübertragers simplified as the legs of the

Jochkerne need only inserted through recesses in the plate-shaped conductor substrate and need to be completed in each case a magnetic core ring. At the same time, this design allows a good space utilization of the toroidal core opening while potential separation between adjacent magnetic core rings.

Embodiments of the invention will be described with reference to FIGS

Drawings described. Showing:

Fig. 1 shows a first type of transformer in

Planar design in a schematic plan view,

2 shows the transformer of FIG. 1 according to section A-B, FIG. 3 shows a second design of a transformer in FIG

Top view and

4 according to section C-D,

Fig. 5 a transformer with two secondary windings in

Top view and

6 according to section E-F,

Fig. 7 shows a further transformer with two

Secondary windings in plan view,

Fig. 8 shows a further transformer in a schematic

Top view and

9 according to section GH, a variant of the further transformer of Figure 8, 9 in a schematic plan view,

another transformer with coupling winding near the surface in a schematic plan view and section I-J,

another transformer with E-shaped core halves in a schematic plan view and section K-L. The main parts of the transformer are a primary winding 1, a secondary winding 2, a coupling winding 3, a first two-part magnetic core ring 4, a second two-part magnetic core ring 5 and a single plate-shaped

Conductor substrate 6. The magnetic core rings 4, 5 each comprise two Jochkernhälften 41, 51 and 42, 52, which close to the ring 4 with the first ring core opening 43 and the ring 5 with the second ring core opening 53. The magnetic core rings 4, 5 each have passage legs 44, 45 and 54, 55 and connecting legs between the pass-through legs. The leg 44 or 54 may belong to the one or the other core half 41, 42 or 51, 52, or may also be divided, as in FIG. 9

shown. The plate-shaped conductor substrate 6 has two pairs of recesses 61, 62 and 63, 64, the

Openings for the Durchgriffsschenkel 44, 45 and 54, 55 of the magnetic core rings 4, 5 form. The pairs 61, 62 and 63, 64 of the recesses are separated from one another via an insulating path and receive the passage legs 44, 45 and 54, 55 of the magnetic core rings 4, 5. The

Primary winding 1 surrounds the recess 61 in several Layer layers of the conductor substrate 6, of which four layer planes 11, 12, 13, 14 are indicated here and on the surface of the conductor substrate, or

near the surface, and in the conductor substrate interior

extend. The conductor substrate 6 fills the

Toroidal openings 43 and 53 almost out.

As indicated in FIG. 1, the primary winding 1 assumes a spiral course in each layer plane. The four spiral shapes are interconnected to give the primary winding 1. In a similar way

Spiral shapes of the secondary winding in four layer planes 21, 22, 23, 24 present and surround the recess 64. The coupling winding 3 wraps around with its portion 34 the Durchgriffsschenkel 45 and with its portion 35 the Durchgriffsschenkel 55 and is in the sense of

Short circuit winding closed, d. H. forms a pipe ring. The coupling winding may be arranged in two layer planes 31, 32 and is surrounded on all sides by an insulating layer having a thickness giving a partial insulation separation distance of L / 2. Here, "L" means the total insulation separation distance resulting from the

Plate thickness of the conductor substrate 6 minus the distance of the layer planes 31, 32 calculated from each other. The

Layer planes 12, 13 and 22, 33 are by a

Insulating layer separated, which as

Through the mediation of the magnetic core rings 4, 5 and the

Coupling winding 3 are the primary winding 1 and the Secondary winding 2 with galvanic isolation in the total isolation separation distance L coupled together.

The magnetic core rings 4 and 5 with their core halves 41, 42 and 51, 52 surround the respective annular opening 43, and 53, respectively. The core halves may be the same or different and may be of different geometric shapes

be composed. The cross sections can be rectangular, rounded, round or oval. Air gaps may be provided between the core halves, but it is

possible to close the air gaps largely when the core halves by gluing or stapling

be assembled together. In detail, the

Core halves assume U, I and E shapes.

As shown in Fig. 1, take the layers of

Primary winding 1 in about half of the cross-sectional area of the annular opening 43, while the layers 31, 32 of the

Coupling winding 3, the other cross-sectional area half of the ring opening 43 occupy. In doing so, partial insulation separation distances of L / 2 become both the

Yoke legs, as well as to the primary winding 1

complied with. The same situation applies to the

Secondary side again. Again, take the layers of

Secondary winding 2 in about half of

Cross-sectional area of the ring opening and the

Coupling winding 3 has partial insulation separation distances of L / 2 to the opening edge or to the layers of the secondary winding. In this way there is a potential separation

between the primary winding 1 and the secondary winding 2 with a total insulation separation distance 2-L / 2 = L chosen to be at least as large as required by EN 60079-11, ie the minimum total insulation separation distance, or more.

The coupling winding 3 is constructed isolated to all other potentials. Thereby, the isolation separation distance L can be established in two partial isolation separation distances. The distribution of the total insulation separation distance L may deviate from the distribution L / 2 + L / 2 in other

Done way. To meet the requirements of EN 60079-11, the smaller partial insulation separation distance must be greater than L / 3. As well as from the graphic

Representations can be seen, need not be followed by the primary winding 1 and secondary winding 2 to the associated magnetic core ring 4 and 5, no large isolation distances. It often suffices the mentioned functional isolation, so that the individual turns of the windings are not bridged by the adjacent connecting legs. It is therefore possible to assign the magnetic core rings the same electrical potential as the windings.

The isolation separation distance between the adjacent ones

Magnetic core rings 4 and 5 are chosen to be large enough for the magnetic core rings to hold their respective different potentials during operation of the transformer. If the primary and secondary windings to the associated

Magnetic core rings do not comply with large insulation distances, this means that a lot of the cross-sectional area of the ring opening 43 or 53 can be used for the turns of the windings 1 and 2 and this space gain

means a larger number of turns on the same surface and thus achieving a higher inductance,

compared with the case where the windings are not allowed to reach at the edge of the ring openings. The new

Planarübertrager is therefore suitable for miniaturization.

Figs. 3, 4 show a variant of the transformer according to Fig. 1, 2, wherein the inner layer of the plate-shaped

Conductor substrate 6 is used only for the coupling winding 3, which also here with each half

Isolation separation distance L / 2 is separated from all other potentials. The primary winding 1 and the secondary winding 2 are located on the top and bottom of the conductor substrate 6, or near the surface in overlap with the subregions 34 and 35 of the coupling winding 3. Opposite the

Embodiment of Fig. 1, 2, the ring opening 43, 53 smaller compared to the embodiment of FIG. 1, 2 are executed, but at the expense of the number of turns of primary and secondary winding. FIGS. 5 and 6 show a variant of the transformer with two secondary windings. Accordingly, there are two

Secondary magnetic core rings 5a, 5b and two secondary windings 2a and 2b and a coupling winding 3 with two "ears" or branches 36, 37. The legs of the magnetic core rings

penetrate the conductor substrate 6 at the openings 61, 62, 63a, 63b, 64a, 64b. Otherwise, the details correspond to those of the transformer of FIGS. 1 and 2. However, the details as described with reference to FIGS. 3 and 4,

be applied. In the structure of the transformer of Fig. 5, 6, the outputs of the secondary windings 2a, 2b are independent of each other. The respective output voltage depends on the transmission ratio of the primary winding respective secondary winding, ie the outputs are connected in parallel. If one output is not used, a current can still be taken from the other output. Fig. 7 shows a further variant of the transformer with two secondary windings 2a, 2b. For this variant, three magnetic core rings 4, 5 a, 5 b and a coupling winding. 3

used, all three magnetic core rings 4, 5a, 5b

chained together. The legs of the magnetic core rings penetrate the conductor substrate 6 at the openings 61, 62, 63a, 63b, 64a, 64b. The outputs of the two

Secondary windings are not functionally independent of each other because they are in series in the equivalent circuit diagram. This means that ideally only one current can flow at the same time at both outputs at the same time.

8 and 9 show a construction of the transformer in which each of the magnetic core rings 4, 5 has a leg 44 or 54 looped around by two windings. The leg 44 is looped around by the primary winding 1 and by the partial region 34 of the coupling winding 3, while the leg 54 is looped around by the secondary winding 2 and by the partial region 35 of the coupling winding 3. The leg 45 parallel to the leg 45 and the leg 54 parallel leg 55 are thus free and can, for example, carry an auxiliary winding, which is usable for control purposes. As can be seen from FIG. 9, the primary winding 1 and the secondary winding 2 lie on the top and bottom of the conductor substrate 6, or close to the surface and in partial overlap with the subregions 34, 35 of the coupling winding 3, which are arranged in two layer layers 31, 32 can. Fig. 10 shows a variant of the embodiment of Fig. 8, 9. The legs 44, 45 and 54, 55, the two

Magnetic core rings 4 and 5 are each covered with spiral winding sections 15, 16, 17, 18 and 25, 26, 27, 28, respectively. The winding section 15 forms left-handed spiral windings on the upper side of the

Conductor substrate 6 and pierces the conductor substrate in a via to form again left-handed spiral windings on the underside of the conductor substrate 6, which are largely covered in the drawing of the winding section 15 and therefore can be seen in the drawing only in tracks. The winding section 16 is conductively connected on the underside to the winding section 17, with the outer lead winding of the

Winding section 17. From there, right-handed spiral-shaped windings are run through, which in turn are partially covered by the winding section 18. Via a via, the pipe is placed on top of the

Conductor substrate 6 out where the clockwise spiral windings continue to the line terminal on the outer edge of the conductor substrate 6. The shapes of the secondary winding 2 are mirror images of the shape of the primary winding 1. The coupling winding 3 extends in a layer plane in the interior of the conductor substrate 6 corresponding to the representation in FIG. 9.

FIGS. 11 and 12 show an embodiment of the invention

Übertragers, in which the coupling winding 3 is located on the top and bottom of the conductor substrate 6 and thus the same potential as the magnetic core rings 4, 5 has. An insulation separation distance between the magnetic core rings is not required. The primary winding 1 and the Secondary winding 2 extends in the inner layers of

Conductor substrates each with a half insulation separation distance to the magnetic core rings 4, 5 and the coupling winding 3. The core halves 41, 42 and 51, 52 are designed for example U-shaped. Here, as in the other embodiments, the magnetic core rings may be assembled in a manner different from that illustrated, the halves may each consist of more than one part. So you can, for example, four leg bars to a

Join magnetic core ring together.

FIGS. 13, 14 show an embodiment of the transmitter with E-shaped core halves 41, 42, which form a central web corresponding to the leg 44 during the merger, which extends through the opening 61 in the conductor substrate 6. The other magnetic core ring 6 has such a central web to form the leg 54. The leg 44 is surrounded by the primary winding 1 and the legs 54 of the secondary winding 2 spirally in two layer planes 11, 14, similar to that shown in Fig. 9. The coupling winding 3 with their

Subareas 34, 35 forms a closed loop around the two central webs of the magnetic core rings. It can do this in two layer planes 31, 32 within the

Conductor substrates 6 done.

Because of the E-shape of the core halves 41, 42 and 51, 52, three openings 61, 62a, 62b and 64, 63a, 63b are respectively required in the conductor substrate 6. Each two of these openings are considered as pairs in the sense of the following claims. The embodiment of Fig. 13, 14 corresponds functionally to the embodiment of Fig. 8, 9. It can but also a construction according to FIG. 10 are used, wherein the third leg 46 or 56 still for a

Auxiliary winding is available. Also, one could for the yoke legs 44, 45 and 54, 55, the construction of FIG. 1, 2 with free legs 46, 56 apply for replacement purposes.

Finally, you could also two or three primary windings and corresponding secondary windings with each other, for. B. for the purpose of failure replacement, combine. The plate-shaped conductor substrate 6 in all

Embodiments are preferably made as an electronic circuit board. However, production as a sprayed substrate is also possible. The transformer can be produced both as a single component with a separate circuit board, in which case this component on a

Main board must be fitted, as well as directly into a main PCB integrate.

Other variants may be added to the variants described. For example, it is possible the

Primary winding and / or the secondary winding to be provided with one or more center taps.

The transformer is manufactured as follows:

There are two-part, yoke legs having

ferromagnetic cores as described and illustrated. The ferromagnetic cores contain two halves 41, 42, and 51, 52, respectively, which can be assembled into a closed ring structure, the magnetic core rings 4, 4a, 4b, 5, 5a, 5b, and do not necessarily consist of only two parts. In addition, a conductor substrate 6 provided with at least two pairs of recesses 61, 62, 63, 64 as yoke leg openings, for each magnetic core ring own, separate from other pairs of recesses. At least one of the two recesses of the first pair, namely the

Opening 61, has been made surrounded by the primary winding 1, as well as the second recess 64 of the second pair with respect to the secondary winding 2. The other recess 62 of the first pair is over the

Coupling winding 3 linked to the recess 63 of the adjacent pair of recesses.

The yoke core halves 41, 42 and 51, 52 are thereby mounted to the magnetic core rings 4, 5, that the yoke legs are pushed through the associated recesses of the conductor substrate 6 and the yoke core halves are closed to form a respective magnetic circuit. As a result, the primary winding 1 with the coupling winding 3 and via this with the secondary winding 2 is electromagnetic

concatenated.

From the above it can be seen that the transformer according to the invention is easy to manufacture. Between the

Primary side and the secondary side can be one

Potential separation can be achieved, as required, for example, for potentially explosive areas according to the standard EN 60079-11. In this case, only small spaces within the ring structure of the magnetic core rings are required, since a relatively large packing density of the windings on the primary side and the secondary side is possible without having to resort to the conventional winding of the yoke legs. Therefore, the economic production of the new Transformers possible, even with miniaturized design of the transformer.

Claims

claims

Planar transformer, comprising:

a primary winding (1),

at least one secondary winding (2),

at least one coupling winding (3),

a first, with yoke legs (44, 45) provided, consisting of a ferromagnetic core

A magnetic core ring (4) including two yoke core halves (41, 42) surrounding a first toroidal core opening (43) and a second yoke limb (54, 55) made of a ferromagnetic core

Magnetic core ring (5) containing two yoke core halves (51, 52) surrounding a second ring core opening (53), and

a single plate-shaped conductor substrate (6) with at least two pairs of recesses (61, 62, 63, 64), the openings for receiving the yoke legs

(44, 45, 54, 55) of the ferromagnetic cores, wherein at least one (61) of the two recesses of the first pair is surrounded by the primary winding (1) and this recess (61) or the other recess

(62) of the first pair of a first portion

(34) of the coupling winding (3) is looped,

further comprising at least one (64) of the two

Recesses of the second pair of the

Secondary winding (2) is surrounded and this recess

(64) or the other recess (63) is looped around by a second portion (35) of the coupling winding (3), wherein the primary winding (1), the secondary winding (2) and the coupling winding (3) are formed as integral parts of the single plate-shaped conductor substrate in order to make good use of the space

Ring core openings (43, 53) to achieve

wherein the potential separation between the

Primary winding (1) and the secondary winding (2) at least a minimum total insulation separation distance (L) is maintained,

wherein the primary winding (1) takes a helical course in two or more layer planes (11, 12, 13, 14) of the single plate-shaped conductor substrate (6),

wherein at least one secondary winding (2) has a spiral shape in two or more

Layer planes (21, 22, 23, 24) of the single

plate-shaped conductor substrate (6) occupies, and wherein the coupling winding (3) extends in layer planes (31, 32) of the plate-shaped conductor substrate (6) and the minimum total isolation separation distance (L) is the sum of minimum part isolation separation distances of these

Layer planes (31, 32) from the top and bottom of the conductor substrate (6) or to adjacent layers of primary winding (1) and secondary winding (2) results, of which a minimum partial isolation separation distance L / 3 to L / 2 while the other minimum partial insulation separation distance is 2L / 3 to L / 2.

Planar transformer according to claim 1, wherein in the case of several layers of the coupling winding (3) these layers with each other by one

Isolation layer are separated from each other, which is relatively thin compared to the insulation to form the insulation separation distance.

Planar transformer according to claim 1 or 2,

wherein the primary winding (1) and the secondary winding (2) also on the surface of the conductor substrate, or near the surface, extend and thus outer layers of layer planes (11, 14, 21, 24) of the

Occupy conductor substrate (6), so that the first magnetic core ring (4) in terms of potential to the primary winding

(1) and the second magnetic core ring (5) in terms of potential to the secondary winding (2) count.

Planar transformer according to claim 1 or 2,

wherein the primary winding (1) and the secondary winding

(2) extend in the interior of the conductor substrate and thus are limited to inner layers of layer planes (12, 13, 22, 23) of the conductor substrate (6) and wherein the coupling winding (3) extends on the surface of the conductor substrate, or near the surface and thus is on outer layers of the layer planes (31, 32) of the conductor substrate (6), so that

adjacent magnetic core rings (4, 5) in terms of potential to the coupling winding (3) count.

Transformer according to one of claims 1 to 4,

where in the case of two or more

Secondary windings (2 a, 2 b), the coupling winding (3) has a plurality of branches (36, 37). Planar transformer according to one of claims 1 to 5, wherein the primary winding (1) and / or the

Secondary winding (2) extends in a plurality of layer planes (11, 12, 13, 14; 21, 22, 23, 24) of the plate-shaped conductor substrate (6) and has a minimum partial insulation separation distance of at least L / 3 to the coupling winding (3) occupies.

Planar transformer according to one of claims 1 to 5, wherein the primary winding (1) and / or the

Secondary winding (2) on the surface of the plate-shaped conductor substrate (6), or

extends close to the surface and close to the

Ring core openings (43, 53) of the associated

Magnetic core rings (4; 5) is arranged, while the coupling winding (3) has a central portion of the

Ring core openings (43, 53) of the associated

Magnetic core rings (4; 5) occupies.

Planarübertrager according to one of claims 1 to 7, wherein the plate-shaped conductor substrate (6) the

Printed circuit board of a transformer, in which the coupling winding (3) is located completely inside the circuit board and the primary and

Secondary windings (1, 2) are arranged in and on the circuit board.

Planar transformer according to one of claims 1 to 7, wherein the primary winding (1) and / or the

Secondary winding (2) located inside the

plate-shaped conductor substrate (6) and the Coupling winding (3) on the conductor substrate, or near the surface, are located.